Randomised clinical trial: Design of the SYNERGY-NASH phase 2b trial to evaluate tirzepatide as a treatment for metabolic dysfunction-associated steatohepatitis and modification of screening strategy to reduce screen failures

BACKGROUND

The use of histological inclusion criteria for clinical trials of at-risk metabolic dysfunction-associated steatohepatitis (MASH) is often associated with high screen failure rates.

AIMS

To describe the design of a trial investigating tirzepatide treatment of MASH and to examine the effect of new inclusion criteria incorporating the use of the FibroScan-AST (FAST) score on the proportion of patients meeting histological criteria.

METHODS

SYNERGY-NASH is a Phase 2b, multicentre, randomised, double-blinded, placebo-controlled trial in patients with biopsy-confirmed MASH, F2-F3 fibrosis and NAFLD Activity Score ≥4. New inclusion criteria (FAST score >0.35 and an increase in AST inclusion criterion from >20 to >23 U/L) were adopted during the trial, allowing us to examine its impact on the qualification rate.

RESULTS

1583 participants were screened, 651 participants proceeded to liver biopsy and 190 participants were randomised with an overall screen fail rate of 87%. Following the protocol amendment, the overall qualification rate for per-protocol biopsies was minimally changed from 27.5% to 28.9% with considerable variation among different investigator medical speciality types: endocrinology: from 37.5% to 39.3%; gastroenterology/hepatology: from 26.0% to 23.3%; other specialities: from 21.3% to 29.7%. At 29 sites that performed per-protocol biopsies before and after the amendment, qualification rates changed as follows: all: 26.1% to 29.1%; endocrinology: from 35.0% to 40.9%; gastroenterology/hepatology: 25.6% to 20.0%; other specialities: from 16.1% to 27.8%.

CONCLUSIONS

For at-risk MASH trials based on liver histology, the implementation of inclusion criteria with the proposed FAST score and AST cut-offs in this trial was most effective at non-specialist sites.

Incretin-based investigational therapies for the treatment of MASLD/MASH

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), is the most common form of chronic liver disease. It exists as either simple steatosis or its more progressive form, metabolic dysfunction-associated steatohepatitis (MASH), formerly, non-alcoholic steatohepatitis (NASH). The global prevalence of MASLD is estimated to be 32% among adults and is projected to continue to rise with increasing rates of obesity, type 2 diabetes, and metabolic syndrome. While simple steatosis is often considered benign and reversible, MASH is progressive, potentially leading to the development of cirrhosis, liver failure, and hepatocellular carcinoma. Treatment of MASH is therefore directed at slowing, stopping, or reversing the progression of disease. Evidence points to improved liver histology with therapies that result in sustained body weight reduction. Incretin-based molecules, such as glucagon-like peptide-1 receptor agonists (GLP-1 RAs), alone or in combination with glucose-dependent insulinotropic polypeptide (GIP) and/or glucagon receptor agonists, have shown benefit here, and several are under investigation for MASLD/MASH treatment. In this review, we discuss current published data on GLP-1, GIP/GLP-1, GLP-1/glucagon, and GLP-1/GIP/glucagon RAs in MASLD/MASH, focusing on their efficacy on liver histology, liver fat, and MASH biomarkers.

Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA

BACKGROUND

According to current consensus guidelines for type 2 diabetes management, bodyweight management is as important as attaining glycaemic targets. Retatrutide, a single peptide with agonist activity at the glucose-dependent insulinotropic polypeptide (GIP), GLP-1, and glucagon receptors, showed clinically meaningful glucose-lowering and bodyweight-lowering efficacy in a phase 1 study. We aimed to examine the efficacy and safety of retatrutide in people with type 2 diabetes across a range of doses.

METHODS

In this randomised, double-blind, double-dummy, placebo-controlled and active comparator-controlled, parallel-group, phase 2 trial, participants were recruited from 42 research and health-care centres in the USA. Adults aged 18-75 years with type 2 diabetes, glycated haemoglobin (HbA1c) of 7·0-10·5% (53·0-91·3 mmol/mol), and BMI of 25-50 kg/m2 were eligible for enrolment. Eligible participants were treated with diet and exercise alone or with a stable dose of metformin (≥1000 mg once daily) for at least 3 months before the screening visit. Participants were randomly assigned (2:2:2:1:1:1:1:2) using an interactive web-response system, with stratification for baseline HbA1c and BMI, to receive once-weekly injections of placebo, 1·5 mg dulaglutide, or retatrutide maintenance doses of 0·5 mg, 4 mg (starting dose 2 mg), 4 mg (no escalation), 8 mg (starting dose 2 mg), 8 mg (starting dose 4 mg), or 12 mg (starting dose 2 mg). Participants, study site personnel, and investigators were masked to treatment allocation until after study end. The primary endpoint was change in HbA1c from baseline to 24 weeks, and secondary endpoints included change in HbA1c and bodyweight at 36 weeks. Efficacy was analysed in all randomly assigned, except inadvertently enrolled, participants, and safety was assessed in all participants who received at least one dose of study treatment. The study is registered at ClinicalTrials.gov, NCT04867785.

FINDINGS

Between May 13, 2021, and June 13, 2022, 281 participants (mean age 56·2 years [SD 9·7], mean duration of diabetes 8·1 years [7·0], 156 [56%] female, and 235 [84%] White) were randomly assigned and included in the safety analysis (45 in the placebo group, 46 in the 1·5 mg dulaglutide group, and 47 in the retatrutide 0·5 mg group, 23 in the 4 mg escalation group, 24 in the 4 mg group, 26 in the 8 mg slow escalation group, 24 in the 8 mg fast escalation group, and 46 in the 12 mg escalation group). 275 participants were included in the efficacy analyses (one each in the retatrutide 0·5 mg group, 4 mg escalation group, and 8 mg slow escalation group, and three in the 12 mg escalation group were inadvertently enrolled). 237 (84%) participants completed the study and 222 (79%) completed study treatment. At 24 weeks, least-squares mean changes from baseline in HbA1c with retatrutide were -0·43% (SE 0·20; -4·68 mmol/mol [2·15]) for the 0·5 mg group, -1·39% (0·14; -15·24 mmol/mol [1·56]) for the 4 mg escalation group, -1·30% (0·22; -14·20 mmol/mol [2·44]) for the 4 mg group, -1·99% (0·15; -21·78 mmol/mol [1·60]) for the 8 mg slow escalation group, -1·88% (0·21; -20·52 mmol/mol [2·34]) for the 8 mg fast escalation group, and -2·02% (0·11; -22·07 mmol/mol [1·21]) for the 12 mg escalation group, versus -0·01% (0·21; -0·12 mmol/mol [2·27]) for the placebo group and -1·41% (0·12; -15·40 mmol/mol [1·29]) for the 1·5 mg dulaglutide group. HbA1c reductions with retatrutide were significantly greater (p<0·0001) than placebo in all but the 0·5 mg group and greater than 1·5 mg dulaglutide in the 8 mg slow escalation group (p=0·0019) and 12 mg escalation group (p=0·0002). Findings were consistent at 36 weeks. Bodyweight decreased dose dependently with retatrutide at 36 weeks by 3·19% (SE 0·61) for the 0·5 mg group, 7·92% (1·28) for the 4 mg escalation group, 10·37% (1·56) for the 4 mg group, 16·81% (1·59) for the 8 mg slow escalation group, 16·34% (1·65) for the 8 mg fast escalation group, and 16·94% (1·30) for the 12 mg escalation group, versus 3·00% (0·86) with placebo and 2·02% (0·72) with 1·5 mg dulaglutide. For retatrutide doses of 4 mg and greater, decreases in weight were significantly greater than with placebo (p=0·0017 for the 4 mg escalation group and p<0·0001 for others) and 1·5 mg dulaglutide (all p<0·0001). Mild-to-moderate gastrointestinal adverse events, including nausea, diarrhoea, vomiting, and constipation, were reported in 67 (35%) of 190 participants in the retatrutide groups (from six [13%] of 47 in the 0·5 mg group to 12 [50%] of 24 in the 8 mg fast escalation group), six (13%) of 45 participants in the placebo group, and 16 (35%) of 46 participants in the 1·5 mg dulaglutide group. There were no reports of severe hypoglycaemia and no deaths during the study.

INTERPRETATION

In people with type 2 diabetes, retatrutide showed clinically meaningful improvements in glycaemic control and robust reductions in bodyweight, with a safety profile consistent with GLP-1 receptor agonists and GIP and GLP-1 receptor agonists. These phase 2 data also informed dose selection for the phase 3 programme.

FUNDING

Eli Lilly and Company.

Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial

BACKGROUND

Retatrutide (LY3437943) is an agonist of the glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1, and glucagon receptors. Its dose-response relationships with respect to side effects, safety, and efficacy for the treatment of obesity are not known.

METHODS

We conducted a phase 2, double-blind, randomized, placebo-controlled trial involving adults who had a body-mass index (BMI, the weight in kilograms divided by the square of the height in meters) of 30 or higher or who had a BMI of 27 to less than 30 plus at least one weight-related condition. Participants were randomly assigned in a 2:1:1:1:1:2:2 ratio to receive subcutaneous retatrutide (1 mg, 4 mg [initial dose, 2 mg], 4 mg [initial dose, 4 mg], 8 mg [initial dose, 2 mg], 8 mg [initial dose, 4 mg], or 12 mg [initial dose, 2 mg]) or placebo once weekly for 48 weeks. The primary end point was the percentage change in body weight from baseline to 24 weeks. Secondary end points included the percentage change in body weight from baseline to 48 weeks and a weight reduction of 5% or more, 10% or more, or 15% or more. Safety was also assessed.

RESULTS

We enrolled 338 adults, 51.8% of whom were men. The least-squares mean percentage change in body weight at 24 weeks in the retatrutide groups was -7.2% in the 1-mg group, -12.9% in the combined 4-mg group, -17.3% in the combined 8-mg group, and -17.5% in the 12-mg group, as compared with -1.6% in the placebo group. At 48 weeks, the least-squares mean percentage change in the retatrutide groups was -8.7% in the 1-mg group, -17.1% in the combined 4-mg group, -22.8% in the combined 8-mg group, and -24.2% in the 12-mg group, as compared with -2.1% in the placebo group. At 48 weeks, a weight reduction of 5% or more, 10% or more, and 15% or more had occurred in 92%, 75%, and 60%, respectively, of the participants who received 4 mg of retatrutide; 100%, 91%, and 75% of those who received 8 mg; 100%, 93%, and 83% of those who received 12 mg; and 27%, 9%, and 2% of those who received placebo. The most common adverse events in the retatrutide groups were gastrointestinal; these events were dose-related, were mostly mild to moderate in severity, and were partially mitigated with a lower starting dose (2 mg vs. 4 mg). Dose-dependent increases in heart rate peaked at 24 weeks and declined thereafter.

CONCLUSIONS

In adults with obesity, retatrutide treatment for 48 weeks resulted in substantial reductions in body weight. (Funded by Eli Lilly; ClinicalTrials.gov number, NCT04881760.).

Effects of Novel Dual GIP and GLP-1 Receptor Agonist Tirzepatide on Biomarkers of Nonalcoholic Steatohepatitis in Patients With Type 2 Diabetes

OBJECTIVE

To determine the effect of tirzepatide, a dual agonist of glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1 receptors, on biomarkers of nonalcoholic steatohepatitis (NASH) and fibrosis in patients with type 2 diabetes mellitus (T2DM).

RESEARCH DESIGN AND METHODS

Patients with T2DM received either once weekly tirzepatide (1, 5, 10, or 15 mg), dulaglutide (1.5 mg), or placebo for 26 weeks. Changes from baseline in alanine aminotransferase (ALT), aspartate aminotransferase (AST), keratin-18 (K-18), procollagen III (Pro-C3), and adiponectin were analyzed in a modified intention-to-treat population.

RESULTS

Significant (P < 0.05) reductions from baseline in ALT (all groups), AST (all groups except tirzepatide 10 mg), K-18 (tirzepatide 5, 10, 15 mg), and Pro-C3 (tirzepatide 15 mg) were observed at 26 weeks. Decreases with tirzepatide were significant compared with placebo for K-18 (10 mg) and Pro-C3 (15 mg) and with dulaglutide for ALT (10, 15 mg). Adiponectin significantly increased from baseline with tirzepatide compared with placebo (10, 15 mg).

CONCLUSIONS

In post hoc analyses, higher tirzepatide doses significantly decreased NASH-related biomarkers and increased adiponectin in patients with T2DM.

Cytokeratin-18 and enhanced liver fibrosis scores in type 1 and type 2 diabetes and effects of two different insulins

Data on cytokeratin-18 (K-18) and enhanced liver fibrosis (ELF) score in insulin-treated diabetes patients with non-alcoholic fatty liver disease (NAFLD) are limited. This study analyzed phase III data comparing basal insulin peglispro (BIL) and insulin glargine in type 1 (T1D), and type 2 diabetes (T2D) (insulin-naïve and insulin-treated). Alanine aminotransferase (ALT), K-18, ELF scores and liver fat content (LFC), measured by MRI, were obtained longitudinally. Baseline K-18 (U/L) was higher in T2D (range: 207‒247) than T1D (range: 148‒183), correlated with ALT in all populations (r (range) 0.264‒0.637, p<0.05), but with LFC only in T2D (r (range) 0.474‒0.586, p<0.05). K-18 increased significantly from baseline in BIL-treated, but not glargine-treated patients. Change from baseline (CFB) K-18 was significantly correlated with CFB in ALT in BIL-treated T2D populations. Baseline ELF scores were higher in T2D (range: 9.12‒9.20) than T1D (range: 8.24‒8.36), correlated with ALT in T1D only (0.209, p<0.05), and not correlated with LFC in any population. ELF scores increased significantly from baseline in BIL-treated but not glargine-treated patients. There were no correlations between CFB in LFC and ELF score at week 52 in any treatment group/population. In all BIL-treated populations, CFB in ALT and CFB in ELF score at week 52 were positively correlated. These data characterize associations of K-18 and ELF score with ALT and LFC in insulin-treated patients with T1D and T2D. Hepatopreferential insulins may be associated with increased K-18 and ELF scores but mechanisms and clinical significance are unknown. ClinicalTrials.gov identifiers are NCT01481779, NCT01435616, NCT01454284 and NCT01582451.

Non-alcoholic fatty liver disease (NAFLD) prevalence and its metabolic associations in patients with type 1 diabetes and type 2 diabetes

We investigated non-alcoholic fatty liver disease (NAFLD) prevalence and its metabolic associations in patients with type 1 diabetes (T1D), and in insulin-naïve and insulin-treated patients with type 2 diabetes (T2D). Baseline data from patients who had liver fat content (LFC) evaluated by magnetic resonance imaging in four phase 3 studies of basal insulin peglispro (BIL) were analysed. Associations of NAFLD with clinical characteristics, glycaemic control and diabetes therapy were evaluated. The prevalence of NAFLD (defined as LFC ≥ 6%) was low in T1D (8.8%) but high in T2D, with greater prevalence in insulin-naïve (75.6%) vs insulin-treated (61.7%) T2D patients. LFC (mean ± SD) was higher in T2D patients (insulin-naïve, 13.0% ± 8.4%; insulin-treated, 10.2% ± 7.8%) than in T1D patients (3.2% ± 3.2%). In T2D, NAFLD was associated with several markers of insulin resistance. In all three populations, there was an absence of association of HbA1c with LFC, but insulin doses were higher in patients with NAFLD.

Basal insulin peglispro versus insulin glargine in insulin-naïve type 2 diabetes: IMAGINE 2 randomized trial

AIMS

To compare, in a double-blind, randomized, multi-national study, 52- or 78-week treatment with basal insulin peglispro or insulin glargine, added to pre-study oral antihyperglycaemic medications, in insulin-naïve adults with type 2 diabetes.

MATERIAL AND METHODS

The primary outcome was non-inferiority of peglispro to glargine with regard to glycated haemoglobin (HbA1c) reduction (margin = 0.4%). Six gated secondary objectives with statistical multiplicity adjustments focused on other measures of glycaemic control and safety. Liver fat content was measured using MRI, in a subset of patients.

RESULTS

Peglispro was non-inferior to glargine in HbA1c reduction [least-squares (LS) mean difference: -0.29%, 95% confidence interval (CI) -0.40, -0.19], and had a lower nocturnal hypoglycaemia rate [relative rate 0.74 (95% CI 0.60, 0.91); p = .005), more patients achieving HbA1c <7.0% without nocturnal hypoglycaemia [odds ratio (OR) 2.15 (95% CI 1.60, 2.89); p < .001], greater HbA1c reduction (p < .001), and more patients achieving HbA1c<7.0% [OR 1.97 (95% CI 1.57, 2.47); p < .001]. Total hypoglycaemia rate and fasting serum glucose did not achieve statistical superiority. At 52 weeks, peglispro-treated patients had higher triglyceride (1.9 vs 1.7 mmol/L). alanine transaminase (34 vs 27 IU/L), and aspartate transaminase levels (27 vs 24 IU/L). LS mean liver fat content was unchanged with peglispro at 52 weeks but decreased 3.1% with glargine [difference: 2.6% (0.9, 4.2); p = .002]. More peglispro-treated patients experienced adverse injection site reactions (3.5% vs 0.6%, p < .001).

CONCLUSIONS

Compared with glargine at 52 weeks, peglispro resulted in a statistically superior reduction in HbA1c, more patients achieving HbA1c targets, less nocturnal hypoglycaemia, no improvement in total hypoglycaemia, higher triglyceride levels, higher aminotransferase levels, and more injection site reactions.

Randomized, double-blind clinical trial comparing basal insulin peglispro and insulin glargine, in combination with prandial insulin lispro, in patients with type 1 diabetes: IMAGINE 3

AIMS

To compare the efficacy and safety of basal insulin peglispro (BIL), which has a flat pharmacokinetic and pharmacodynamic profile and a long duration of action, with insulin glargine (GL) in patients with type 1 diabetes.

MATERIALS AND METHODS

In this phase III, 52-week, blinded study, we randomized 1114 adults with type 1 diabetes in a 3 : 2 distribution to receive either BIL (n = 664) or GL (n = 450) at bedtime, with preprandial insulin lispro, using intensive insulin management. The primary objective was to compare glycated haemoglobin (HbA1c) in the groups at 52 weeks, with a non-inferiority margin of 0.4%.

RESULTS

At 52 weeks, mean (standard error) HbA1c was 7.38 (0.03)% with BIL and 7.61 (0.04)% with GL {difference -0.22% [95% confidence interval (CI) -0.32, -0.12]; p < 0.001}. At 52 weeks more BIL-treated patients reached HbA1c <7% (35% vs 26%; p < 0.001), the nocturnal hypoglycaemia rate was 47% lower (p < 0.001) and the total hypoglycaemia rate was 11% higher (p = 0.002) than in GL-treated patients, and there was no difference in severe hypoglycaemia rate. Patients receiving BIL lost weight, while those receiving GL gained weight [difference -1.8 kg (95% CI -2.3, -1.3); p < 0.001]. Treatment with BIL compared with GL at 52 weeks was associated with greater increases from baseline in levels of serum triglyceride [difference 0.19 mmol/l (95% CI 0.11, 0.26); p < 0.001] and alanine aminotransferase (ALT) levels [difference 6.5 IU/l (95% CI 4.1, 8.9), p < 0.001], and more frequent injection site reactions.

CONCLUSIONS

In patients with type 1 diabetes, treatment with BIL compared with GL for 52 weeks resulted in a lower HbA1c, more patients with HbA1c levels <7%, and reduced nocturnal hypoglycaemia, but more total hypoglycaemia and injection site reactions and higher triglyceride and ALT levels.

Basal insulin peglispro: Overview of a novel long-acting insulin with reduced peripheral effect resulting in a hepato-preferential action

Basal insulin peglispro (BIL) is a novel basal insulin with a flat, prolonged activity profile. BIL has been demonstrated in a dog model, in healthy men and in patients with type 1 diabetes (T1D) to have significant hepato-preferential action resulting from reduced peripheral activity. In the IMAGINE-Phase 3 clinical trial program, more than 6000 patients were included, of whom ~3900 received BIL. Of the 7 pivotal IMAGINE trials, 3 studies were double-blinded and 3 were in T1D patients. BIL consistently demonstrated a greater HbA1c reduction, less glycaemic variability and a clinically relevant reduction in the rates of nocturnal hypoglycaemia across comparator [glargine and isophane insulin (NPH)] studies. Trials using basal/bolus regimens had higher rates of total hypoglycaemia with BIL due to higher rates of daytime hypoglycaemia. Severe hypoglycaemia rates were similar to comparator among both patients with T1D or type 2 diabetes (T2D). T1D patients lost weight compared with glargine (GL). Patients with T2D tended to gain less weight with BIL than with glargine. Compared to glargine, BIL was associated with higher liver fat, triglycerides and alanine aminotransferase (ALT) levels, including a higher frequency of elevation of ALT ≥3 times the upper limit of normal, but without severe, acute drug-induced liver injury. Injection site reactions, primarily lipohypertrophy, were more frequent with BIL. In conclusion, BIL demonstrated better glycaemic control with reduced glucose variability and nocturnal hypoglycaemia but higher triglycerides, ALT and liver fat relative to conventional comparator insulin. The hepato-preferential action of BIL with reduced peripheral activity may account for these findings.

Different effects of basal insulin peglispro and insulin glargine on liver enzymes and liver fat content in patients with type 1 and type 2 diabetes

AIMS

To compare effects of basal insulin peglispro (BIL), a hepatopreferential insulin, to insulin glargine (glargine) on aminotransferases and liver fat content (LFC) in patients with type 1 and type 2 diabetes (T1D, T2D).

MATERIALS AND METHODS

Data from two Phase 2 and five Phase 3 randomized trials comparing BIL and glargine in 1709 T1D and 3662 T2D patients were integrated for analysis of liver laboratory tests. LFC, measured by magnetic resonance imaging (MRI) at baseline, 26 and 52 weeks, was analyzed in 182 T1D patients, 176 insulin-naïve T2D patients and 163 T2D patients previously treated with basal insulin.

RESULTS

Alanine aminotransferase (ALT) increased in patients treated with BIL, was higher than in glargine-treated patients at 4-78 weeks (difference at 52 weeks in both T1D and T2D: 7 international units/litre (IU/L), P < .001), and decreased after discontinuation of BIL. More BIL patients had ALT ≥3× upper limit of normal (ULN) than glargine. No patient had ALT ≥3× ULN with bilirubin ≥2× ULN that was considered causally related to BIL. In insulin-naїve T2D patients, LFC decreased with glargine but was unchanged with BIL. In T1D and T2D patients previously treated with basal insulin, LFC was unchanged with glargine but increased with BIL. In all three populations, LFC was higher after treatment with BIL vs glargine (difference at 52 weeks: 2.2% to 5.3%, all P < .01).

CONCLUSIONS

Compared to glargine, patients treated with BIL had higher ALT and LFC at 52-78 weeks. No severe drug-induced liver injury was apparent with BIL treatment for up to 78 weeks.

A randomized clinical trial comparing basal insulin peglispro and insulin glargine, in combination with prandial insulin lispro, in patients with type 1 diabetes: IMAGINE 1

AIMS

The primary objective was to demonstrate that basal insulin peglispro (BIL) was non-inferior compared with insulin glargine (GL) for haemoglobin A1c (HbA1c) at 26 weeks with a non-inferiority margin of 0.4%.

MATERIALS AND METHODS

IMAGINE 1 was a Phase 3, open-label, parallel-arm study conducted in nine countries. Adults with type 1 diabetes (n = 455) were randomized (2:1) to bedtime BIL or GL in combination with prandial insulin lispro for 78 weeks, with a primary endpoint of 26 weeks. An electronic diary facilitated data capture and insulin dosing calculations for intensive insulin management.

RESULTS

At 26 weeks, mean HbA1c was 7.06% ± 0.04% and 7.43% ± 0.06% for patients assigned to BIL (N = 295) and GL (N = 160), respectively (difference -0.37% [95% CI: -0.50 to -0.23], P < .001); more patients on BIL achieved HbA1c <7% (44.9% vs 27.5%, P < .001). Compared with GL, patients using BIL lost weight, with lower fasting serum glucose and between-day fasting blood glucose variability, and 36% less nocturnal hypoglycemia, 29% more total hypoglycemia and more severe hypoglycemia. Total and prandial insulin doses were lower with BIL; basal insulin doses were higher. Alanine aminotransferase increased with BIL, with more patients having elevations ≥3 × ULN. BIL treatment was associated with more frequent injection site reactions and an increase from baseline in serum triglycerides.

CONCLUSIONS

In patients with type 1 diabetes, treatment with BIL compared to GL for 26 weeks was associated with lower HbA1c, less nocturnal hypoglycemia, lower glucose variability and weight loss. Increases in total and severe hypoglycemia, triglycerides, aminotransferases and injection site reactions were also noted.

Randomized Clinical Trial Comparing Basal Insulin Peglispro and Insulin Glargine in Patients With Type 2 Diabetes Previously Treated With Basal Insulin: IMAGINE 5

OBJECTIVE

To evaluate the efficacy and safety of basal insulin peglispro (BIL) versus insulin glargine in patients with type 2 diabetes (hemoglobin A1c [HbA1c] ≤9% [75 mmol/mol]) treated with basal insulin alone or with three or fewer oral antihyperglycemic medications.

RESEARCH DESIGN AND METHODS

This 52-week, open-label, treat-to-target study randomized patients (mean HbA1c 7.42% [57.6 mmol/mol]) to BIL (n = 307) or glargine (n = 159). The primary end point was change from baseline HbA1c to 26 weeks (0.4% [4.4 mmol/mol] noninferiority margin).

RESULTS

At 26 weeks, reduction in HbA1c was superior with BIL versus glargine (-0.82% [-8.9 mmol/mol] vs. -0.29% [-3.2 mmol/mol]; least squares mean difference -0.52%, 95% CI -0.67 to -0.38 [-5.7 mmol/mol, 95% CI -7.3 to -4.2; P < 0.001); greater reduction in HbA1c with BIL was maintained at 52 weeks. More BIL patients achieved HbA1c <7% (53 mmol/mol) at weeks 26 and 52 (P < 0.001). With BIL versus glargine, nocturnal hypoglycemia rate was 60% lower, more patients achieved HbA1c <7% (53 mmol/mol) without nocturnal hypoglycemia at 26 and 52 weeks (P < 0.001), and total hypoglycemia rates were lower at 52 weeks (P = 0.03). At weeks 26 and 52, glucose variability was lower (P < 0.01), basal insulin dose was higher (P < 0.001), and triglycerides and aminotransferases were higher with BIL versus glargine (P < 0.05). Liver fat content (LFC), assessed in a subset of patients (n = 162), increased from baseline with BIL versus glargine (P < 0.001), with stable levels between 26 and 52 weeks.

CONCLUSIONS

BIL provided superior glycemic control versus glargine, with reduced nocturnal and total hypoglycemia, lower glucose variability, and increased triglycerides, aminotransferases, and LFC.

Prospective safety surveillance of GH-deficient adults: comparison of GH-treated vs untreated patients

CONTEXT

In clinical practice, the safety profile of GH replacement therapy for GH-deficient adults compared with no replacement therapy is unknown.

OBJECTIVE

The objective of this study was to compare adverse events (AEs) in GH-deficient adults who were GH-treated with those in GH-deficient adults who did not receive GH replacement.

DESIGN AND SETTING

This was a prospective observational study in the setting of US clinical practices.

PATIENTS AND OUTCOME MEASURES

AEs were compared between GH-treated (n = 1988) and untreated (n = 442) GH-deficient adults after adjusting for baseline group differences and controlling the false discovery rate. The standardized mortality ratio was calculated using US mortality rates.

RESULTS

After a mean follow-up of 2.3 years, there was no significant difference in rates of death, cancer, intracranial tumor growth or recurrence, diabetes, or cardiovascular events in GH-treated compared with untreated patients. The standardized mortality ratio was not increased in either group. Unexpected AEs (GH-treated vs untreated, P ≤ .05) included insomnia (6.4% vs 2.7%), dyspnea (4.2% vs 2.0%), anxiety (3.4% vs 0.9%), sleep apnea (3.3% vs 0.9%), and decreased libido (2.1% vs 0.2%). Some of these AEs were related to baseline risk factors (including obesity and cardiopulmonary disease), higher GH dose, or concomitant GH side effects.

CONCLUSIONS

In GH-deficient adults, there was no evidence for a GH treatment effect on death, cancer, intracranial tumor recurrence, diabetes, or cardiovascular events, although the follow-up period was of insufficient duration to be conclusive for these long-term events. The identification of unexpected GH-related AEs reinforces the fact that patient selection and GH dose titration are important to ensure safety of adult GH replacement.

Occurrence of impaired fasting glucose in GH-deficient adults receiving GH replacement compared with untreated subjects

OBJECTIVE

The effects of GH replacement on glucose metabolism in GH-deficient (GHD) adults in clinical practice are not well defined. Therefore, we assessed GH treatment effects on fasting plasma glucose (FPG) and haemoglobin A1c (A1c) concentrations in GHD adults in a clinical setting.

DESIGN

Post-hoc analysis of the observational Hypopituitary Control and Complications Study conducted at 157 US centres (1997-2002).

PATIENTS

GH-deficient adults who were GH-naïve at study entry and had at least two FPG measurements.

MEASUREMENTS

Effect of GH treatment on the frequency and time course of abnormal FPG (> or =5.6 mmol/l) development, FPG normalization, progression of increased FPG and abnormal follow-up A1c (>6%) values in GHD patients treated with GH (n = 403) or untreated (n = 169) at their physician's discretion.

RESULTS

In subjects without pre-existing diabetes mellitus, development of an abnormal FPG tended to occur in a greater percentage of GH-treated than untreated subjects (35.3% versus 24.5, P = 0.06). Additionally, GH treatment was associated with a mild, transient increase in FPG and shorter time to development of an abnormal FPG in these subjects (P < 0.01). Most ( approximately 80%) abnormal FPG values were below 7 mmol/l and normalized in 69% of GH-treated subjects without diabetes. Treatment with GH had no effect on the rate of FPG normalization, progression of increased FPG or abnormal follow-up A1c values.

CONCLUSIONS

Initiation of GH replacement in GHD adults was associated with a mild increase in FPG that often normalized spontaneously. Nevertheless, clinicians should monitor FPG in patients receiving GH treatment.

Changing patterns of the adult growth hormone deficiency diagnosis documented in a decade-long global surveillance database

BACKGROUND

GH therapy in adult patients with GH deficiency (GHD) was approved over 10 yr ago, and the indication has subsequently gained broad acceptance. The HypoCCS surveillance database is a suitable means to examine the evolution of diagnostic patterns since 1996.

METHODS

Baseline demographics, reported cause of GHD, and diagnostic tests were available from 5893 GH-treated patients. Trends for change over time in diagnosis, GH stimulation test data, and IGF-I measurements were analyzed at 2-yr intervals by linear regression models, with entry year as the predictive variable.

RESULTS

Over the decade, there was a decrease in patients enrolled with diagnoses of pituitary adenoma (50.2 to 38.6%; P < 0.001), craniopharyngioma (13.3 to 8.4%; P = 0.005) and pituitary hemorrhage (5.8 to 2.8%; P = 0.001); increases in idiopathic GHD (13.9 to 19.3%; P < 0.001), less common diagnoses (7.4 to 15.8%; P < 0.001), and undefined/unknown diagnoses (1.3 to 8.6%; P < 0.001) were observed. Use of arginine, clonidine, and L-dopa tests declined, whereas use of the GHRH-arginine test increased. Median values for peak GH from all tests except GHRH-arginine and for IGF-I SD scores increased significantly (P < 0.001). Over the decade (1996--2005), idiopathic GHD was reported for 16.7% of patients, and more than half of these had adult onset GHD. In the idiopathic adult onset group, 40.2% had isolated GHD; 18.3 and 4.4% had a stimulation test GH peak of at least 3.0 and 5.0 microg/liter, respectively.

CONCLUSIONS

Significant shifts in diagnostic patterns have occurred since approval of the adult GHD indication, with a trend to less severe forms of GHD.

Growth hormone replacement therapy in adults with growth hormone deficiency improves maximal oxygen consumption independently of dosing regimen or physical activity

CONTEXT

Several studies have demonstrated an improvement in aerobic exercise capacity with 6 months of GH replacement in adults with GH deficiency (GHD).

OBJECTIVE

The objective of the study was to determine whether improvements in aerobic exercise capacity with GH treatment in adults with GHD are related to changes in physical activity or affected by the GH dosing regimen.

DESIGN

This was a randomized, two-arm, parallel, open-label study.

SETTING

The study was conducted at five academic medical centers with exercise physiology laboratories.

SUBJECTS

Study subjects were adults (n = 29) with GHD due to hypothalamic-pituitary disease.

INTERVENTIONS

The intervention was GH replacement therapy, administered either as a fixed body weight-based dosing regimen as an individualized dose titration regimen for 32 wk.

MAIN OUTCOME MEASURES

Maximal oxygen consumption (VO2 max) and oxygen consumption (VO2) at the lactate threshold, ventilatory threshold using a cycle ergometry protocol, and weekly energy expenditure (physical activity questionnaire), assessed at baseline and end point, were measured.

RESULTS

In the group as a whole, VO2 max increased significantly (by 9%) from baseline (19.1+/- 0.89 ml/kg.min) to end point (21.6 +/- 1.23 ml/kg.min, P = 0.010). Compared with baseline, VO2 max also changed significantly within the individualized dose titration regimen group (+2.5 +/- 0.98 ml/kg.min, P =0.034) but not within the fixed body weight-based dosing regimen group (+1.2 +/- 0.78 ml/kg.min, P = 0.15), although these changes from baseline were not significantly different between the two groups. VO2 at lactate threshold, VO2 at ventilatory threshold, and weekly energy expenditure also did not change.

CONCLUSIONS

GH replacement therapy in GH-deficient adults improved VO2 max similarly with both dosing regimens, without any influence of physical activity. There was no effect on submaximal exercise performance.

Effect of growth hormone replacement on BMD in adult-onset growth hormone deficiency

To determine if replacement of GH improves BMD in adult-onset GHD, we administered GH in physiologic amounts to men and women with GHD. GH replacement significantly increased spine BMD in the men by 3.8%.

INTRODUCTION

Growth hormone (GH) deficiency (GHD) acquired in adulthood results in diminished BMD; the evidence that replacement of GH improves BMD is not conclusive. We therefore performed a randomized, placebo-controlled trial to determine whether GH replacement would increase lumbar spine BMD in a combined group of men and women with adult-onset GHD.

MATERIALS AND METHODS

We randomized 67 men and women to receive GH (n=33) or placebo (n=34) for 2 yr. The GH dose was initially 2 microg/kg body weight/d, increased gradually to a maximum of 12 microg/kg/d and adjusted to maintain a normal IGF-I concentration for age and sex. BMD was assessed before treatment and at 6, 12, 18, and 24 mo of treatment. Fifty-four subjects completed the protocol.

RESULTS

BMD of the lumbar spine in the entire group increased by 2.9 +/- 3.9% above baseline in the GH-treated subjects, which was significantly (p=0.037) greater than the 1.4 +/- 4.5% increase in the placebo-treated subjects. In a secondary analysis, spine BMD in GH-treated men increased 3.8 +/- 4.3% above baseline, which was significantly (p=0.001) greater than that in placebo-treated men (0.4 +/- 4.7%), but the change in GH-treated women was not significantly different from that in placebo-treated women. Treatment with GH did not increase total hip BMD more than placebo treatment after 2 yr.

CONCLUSIONS

We conclude that GH replacement in men who have adult-onset GHD improves their spine BMD, but we cannot draw any conclusions about the effect of GH replacement on spine BMD in women with adult-onset GHD.

IGF-I measurements in the diagnosis of adult growth hormone deficiency

Although serum insulin-like growth factor I (IGF-I) concentrations have utility as a screening test for growth hormone (GH) deficiency in children and young adults, they are less accurate for screening in adults over 40 years of age. There are two main limitations in the clinical use of IGF-I levels as a marker of GH secretion. First, IGF-I synthesis is not only regulated by GH but also by nutrient supply and by other hormones; second, low IGF-I levels in the presence of normal or increased GH secretion may reflect a peripheral resistance to GH action. Although serum IGF-I cannot be used as a stand-alone test for the diagnosis of adult GH deficiency, very low IGF-I levels in the context of documented hypothalamic or pituitary disease may be helpful in identifying patients with a high probability of GH deficiency. In the presence of two or more additional pituitary hormone deficiencies, an IGF-I level <84 microg/l (assayed by Esoterix Endocrinology, Inc. Calabasas Hills, CA, USA) indicates a 99% probability of GH deficiency. As this cut-off value has not been validated for other IGF-I assays, an IGF-I standard deviation score (SDS) of <-3 may be considered in adults over age 28; an even lower IGF-I SDS is needed for diagnosis in younger adults. In clinical practice, other causes of low serum IGF-I such as malnutrition, diabetes, hypothyroidism, liver disease, etc., should be excluded before applying these diagnostic criteria.

Efficacy and tolerability of an individualized dosing regimen for adult growth hormone replacement therapy in comparison with fixed body weight-based dosing

To determine whether an individualized dose titration regimen (ID) for adult GH replacement therapy would have similar efficacy and better tolerability than a fixed body weight-based dosing regimen (FD), 387 adults with GH deficiency were randomized to FD (n = 200) or ID (n = 187) for 32 wk. In FD, subjects received sequentially 4, 8, and 12 microg/kg.d GH. ID was started at 0.2 mg/d and increased by 0.2-mg/d increments, based on clinical and serum IGF-I responses, to a maximum of 0.8 mg/d. Increases (mean +/- sd) in serum IGF-I were similar in both groups (FD, 110.2 +/- 87.8 vs. ID, 99.6 +/- 77.7 microg/liter, P = 0.20) despite higher final GH doses in FD (0.70 +/- 0.32 vs. 0.54 +/- 0.22 mg/d, P < 0.001). Favorable changes in several efficacy measures were observed with no significant differences between the FD and ID groups: lean body mass increased; health-related quality of life improved; and abdominal fat mass, hip circumference, sum of skinfolds, and total and low-density lipoprotein cholesterol decreased. The decrease in fat mass was greater with FD than ID for men (-2.7 +/- 2.7 kg vs. -1.8 +/- 2.5 kg, P = 0.04) but not for women (-2.1 +/- 2.4 vs. -2.0 +/- 3.8 kg). The change in waist circumference was greater with FD than ID for women but not for men. There was a significant reduction of systolic blood pressure in ID but not in FD. The adverse event profile was similar between FD and ID except that ID had a lower occurrence of peripheral edema (9.1% vs. 16.5%, P = 0.03) and rash (1.1% vs. 5.5%, P = 0.02) than FD. In summary, the use of ID resulted in improved tolerability and similar efficacy compared with FD. We conclude that GH replacement therapy should be initiated at a low dose and titrated to a dose producing maximal benefits without adverse side effects and an IGF-I level within the age- and sex-adjusted normal range.

Decreased quality of life in adult patients with growth hormone deficiency compared with general populations using the new, validated, self-weighted questionnaire, questions on life satisfaction hypopituitarism module

To develop reference ranges for the Questions on Life Satisfaction Hypopituitarism Module (QLS-H), a new quality of life questionnaire for patients with hypopituitarism, data from 8177 adults were collected in France, Germany, Italy, The Netherlands, Spain, the United Kingdom, and the United States QLS-H scores declined with age, were lower in females than males, and differed significantly among countries. From these reference ranges we derived equations for z-scores, which adjust for age, gender, and country. QLS-H results from 957 adults with GH deficiency (GHD) participating in clinical trials were analyzed. At baseline, QLS-H scores were lower in females and differed significantly among countries. QLS-H scores significantly increased after GH treatment (6-8 months), but differences by country persisted. Calculating z-scores for patients eliminated all gender and most country differences. Pooled z-scores (mean +/- SD) from all patients increased from -0.99 +/- 1.39 at baseline to -0.14 +/- 1.30 after GH treatment. Quality of life assessment in adults with GHD requires the use of z-scores to correct for age, gender, and country differences. This approach allows pooling of data from different cohorts and comparison with general populations. QLS-H scores in adults with GHD were significantly decreased at baseline and were almost normalized after 6-8 months of GH therapy.

Growth hormone release during acute and chronic aerobic and resistance exercise: recent findings

Exercise is a potent physiological stimulus for growth hormone (GH) secretion, and both aerobic and resistance exercise result in significant, acute increases in GH secretion. Contrary to previous suggestions that exercise-induced GH release requires that a "threshold" intensity be attained, recent research from our laboratory has shown that regardless of age or gender, there is a linear relationship between the magnitude of the acute increase in GH release and exercise intensity. The magnitude of GH release is greater in young women than in young men and is reduced by 4-7-fold in older individuals compared with younger individuals. Following the increase in GH secretion associated with a bout of aerobic exercise, GH release transiently decreases. As a result, 24-hour integrated GH concentrations are not usually elevated by a single bout of exercise. However, repeated bouts of aerobic exercise within a 24-hour period result in increased 24-hour integrated GH concentrations. Because the GH response to acute resistance exercise is dependent on the work-rest interval and the load and frequency of the resistance exercise used, the ability to equate intensity across different resistance exercise protocols is desirable. This has proved to be a difficult task. Problems with maintaining patent intravenous catheters have resulted in a lack of studies investigating alterations in acute and 24-hour GH pulsatile secretion in response to resistance exercise. However, research using varied resistance protocols and sampling techniques has reported acute increases in GH release similar to those observed with aerobic exercise. In young women, chronic aerobic training at an intensity greater than the lactate threshold resulted in a 2-fold increase in 24-hour GH release. The time line of adaptation and the mechanism(s) by which this training effect occurs are still elusive. Unfortunately, there are few studies investigating the effects of chronic resistance training on 24-hour GH release. The decrease in GH secretion observed in individuals who are older or have obesity is associated with many deleterious health effects, although a cause and effect relationship has not been established. While exercise interventions may not restore GH secretion to levels observed in young, healthy individuals, exercise is a robust stimulus of GH secretion. The combination of exercise and administration of oral GH secretagogues may result in greater GH secretion than exercise alone in individuals who are older or have obesity. Whether such interventions would result in favourable clinical outcomes remains to be established.

Impact of abdominal visceral fat, growth hormone, fitness, and insulin on lipids and lipoproteins in older adults

We examined the relationship between abdominal visceral fat (AVF) and plasma concentrations of lipids and lipoproteins in 19 females (F) (not on estrogen) and 31 males (M) over the age of 60 (age = 66.8 years). In addition, the effects of growth hormone (GH) release, fitness (Vo(2) peak), insulin, and glucose concentrations (both fasting and in response to an oral glucose tolerance test) on lipids were examined. Subjects were categorized by low (L) and high (H) AVF (L < 130 cm(2), H > 130 cm(2)), fat mass (FM) (above or below median value), and AVF corrected for fat mass. Factorial analysis of variance (ANOVA) showed that when subjects were divided by AVF and FM, similar results were observed with H > L (P <.05) for very-low-density lipoprotein-cholesterol (VLDL-C), triglycerides (TG), VLDL-TG, apolipoprotein (apo)-B, apo-B VLDL, cholesterol (Chol)/high-density lipoprotein (HDL), LDL/HDL, apoB/A1 and L > H for HDL, HDL(2), HDL(3), apo A1, and LDL/apo-B LDL. Gender differences were also observed with F > M for Chol, LDL, HDL, and HDL(2). When AVF was corrected for FM, these gender differences were still present. After correcting for FM, differences remained between H and L AVF groups for VLDL, TG, VLDL-TG, apo-B, apo-B LDL, apo-B VLDL, apoB/A1 (P <.05). Twenty-four hour integrated GH concentration (IGHC) was inversely related to VLDL, TG, VLDL TG, LDL TG, apoB, apoB VLDL, apoB LDL, Chol/HDL, LDL/HDL, and apoB/A1 in F, but not M (P <.05). Vo(2) peak was directly related to Chol, LDL, HDL(3), and apoB LDL with stronger relationships observed in F. Fasting insulin was related to lipids and lipoproteins in both men and women. These data suggest that, in older adults, elevated levels of AVF, FM, and AVF corrected for FM are associated with unfavorable lipid-lipoprotein profiles and extend similar findings reported in younger males and females with elevated AVF. These data also support previous findings indicating that AVF is a primary determinant of GH release.

IGF-I does not affect the net increase in GH release in response to arginine

Arginine stimulates growth hormone (GH) secretion, possibly by inhibiting hypothalamic somatostatin (SS) release. Insulin-like growth factor I (IGF-I) inhibits GH secretion via effects at the pituitary and/or hypothalamus. We hypothesized that if the dominant action of IGF-I is to suppress GH release at the level of the pituitary, then the arginine-induced net increase in GH concentration would be unaffected by an IGF-I infusion. Eight healthy young adults (3 women, 5 men) were studied on day 2 of a 47-h fast for 12 h (35th-47th h) on four occasions. Saline (Sal) or 10 microg. kg(-1). h(-1) recombinant human IGF-I was infused intravenously for 5 h from 37 to 42 h of the 47-h fast. Arginine (Arg) (30 g iv) or Sal was infused over 30 min during the IGF-I or Sal infusion from 40 to 40.5 h of the fast. Subjects received the following combinations of treatments in random order: 1) Sal + Sal; 2) Sal + Arg; 3) IGF-I + Sal; 4) IGF-I + Arg. Peak GH concentration on the IGF-I + Arg day was ~45% of that on the Sal + Arg day. The effect of arginine on net GH release was calculated as [(Sal + Arg) - (Sal + Sal)] - [(IGF-I + Arg) - (IGF-I + Sal)]. There was no significant effect of IGF-I on net arginine-induced GH release over control conditions. These findings suggest that the negative feedback effect of IGF-I on GH secretion is primarily mediated at the pituitary level and/or at the hypothalamus through a mechanism different from the stimulatory effect of arginine.

Gender governs the relationship between exercise intensity and growth hormone release in young adults

We previously reported that in young adult males growth hormone (GH) release is related to exercise intensity in a linear dose-response manner (Pritzlaff et al. J Appl Physiol 87: 498-504, 1999). To investigate the effects of gender and exercise intensity on GH release, eight women (24.3 +/- 1.3 yr, 171 +/- 3.2 cm height, 63.6 +/- 8.7 kg weight) were each tested on six randomly ordered occasions [1 control condition (C), 5 exercise conditions (Ex)]. Serum GH concentrations were measured in samples obtained at 10-min intervals between 0700 and 0900 (baseline) and 0900 and 1300 (Ex + recovery or C). Integrated GH concentrations (IGHC) were calculated by trapezoidal reconstruction. During Ex, subjects exercised for 30 min (0900-0930) at one of the following intensities [normalized to the lactate threshold (LT)]: 25 and 75% of the difference between LT and rest, at LT, and at 25 and 75% of the difference between LT and peak O2 uptake. No differences were observed among conditions for baseline IGHC. To determine whether total (Ex + recovery) IGHC changed with increasing exercise intensity, slopes associated with individual linear regression models were subjected to a Wilcoxon signed-rank test. To test for gender differences, data in women were compared with the previously published data in men. A Wilcoxon ranked-sums two-tailed test was used to analyze the slopes and intercepts from the regression models. Total IGHC increased linearly with increasing exercise intensity. The slope and intercept values for the relationship between total IGHC and exercise intensity were greater in women than in men. Deconvolution analysis (0700-1300 h) revealed that, regardless of gender, increasing exercise intensity resulted in a linear increase in the mass of GH secreted per pulse and summed GH production rate, with no changes in GH secretory pulse frequency or apparent half-life of elimination. Exercise reduced the half-duration of GH secretory burst in men but not in women. Gender comparisons revealed that women had greater basal (nonpulsatile) GH secretion across all conditions, more frequent GH secretory pulses, a greater GH secretory pulse amplitude, a greater production rate, and a trend for a greater mass of GH secreted per pulse than men. We conclude that, in young adults, the GH secretory response to exercise is related to exercise intensity in a linear dose-response pattern. For each incremental increase in exercise intensity, the fractional stimulation of GH secretion is greater in women than in men.

Sensitivity and specificity of six tests for the diagnosis of adult GH deficiency

Although the use of the insulin tolerance test (ITT) for the diagnosis of adult GH deficiency is well established, diagnostic peak GH cut-points for other commonly used GH stimulation tests are less clearly established. Despite that fact, the majority of patients in the United States who are evaluated for GH deficiency do not undergo insulin tolerance testing. The aim of this study was to evaluate the relative utility of six different methods of testing for adult GH deficiency currently used in practice in the United States and to develop diagnostic cut-points for each of these tests. Thirty-nine patients (26 male, 13 female) with adult-onset hypothalamic-pituitary disease and multiple pituitary hormone deficiencies were studied in comparison with age-, sex-, estrogen status-, and body mass index-matched control subjects (n = 34; 20 male, 14 female). A third group of patients (n = 21) with adult-onset hypothalamic-pituitary disease and no more than one additional pituitary hormone deficiency was also studied. The primary end-point was peak serum GH response to five GH stimulation tests administered in random order at five separate visits: ITT, arginine (ARG), levodopa (L-DOPA), ARG plus L-DOPA, and ARG plus GHRH. Serum IGF-I concentrations were also measured on two occasions. For purposes of analysis, patients with multiple pituitary hormone deficiencies were assumed to be GH deficient. Three diagnostic cut-points were calculated for each test to provide optimal separation of multiple pituitary hormone deficient and control subjects according to three criteria: 1) to minimize misclassification of control subjects and deficient patients (balance between high sensitivity and high specificity); 2) to provide 95% sensitivity for GH deficiency; and 3) to provide 95% specificity for GH deficiency. The greatest diagnostic accuracy occurred with the ITT and the ARG plus GHRH test, although patients preferred the latter (P = 0.001). Using peak serum GH cut-points of 5.1 microg/liter for the ITT and 4.1 microg/liter for the ARG plus GHRH test, high sensitivity (96 and 95%, respectively) and specificity (92 and 91%, respectively) for GH deficiency were achieved. To obtain 95% specificity, the peak serum GH cut-points were lower at 3.3 microg/liter and 1.5 microg/liter for the ITT and ARG plus GHRH test, respectively. There was substantial overlap between patients and control subjects for the ARG plus L-DOPA, ARG, and L-DOPA tests, but test-specific cut-points could be defined for all three tests to provide 95% sensitivity for GH deficiency (peak GH cut-points: 1.5, 1.4 and 0.64 microg/liter, respectively). However, 95% specificity could be achieved with the ARG plus L-DOPA and ARG tests only with very low peak GH cut-points (0.25 and 0.21 microg/liter, respectively) and not at all with the L-DOPA test. Although serum IGF-I levels provided less diagnostic discrimination than all five GH stimulation tests, a value below 77.2 microg/liter was 95% specific for GH deficiency. In conclusion, the diagnosis of adult GH deficiency can be made without performing an ITT, provided that test-specific cut-points are used. The ARG plus GHRH test represents an excellent alternative to the ITT for the diagnosis of GH deficiency in adults.

Which patients do not require a GH stimulation test for the diagnosis of adult GH deficiency?

Adult GH deficiency (GHD) is currently diagnosed in patients with either a history of childhood-onset GHD or acquired hypothalamic-pituitary disease by GH stimulation testing. However, GH stimulation tests are invasive, time consuming, and associated with side effects. Based on preliminary analyses of patients enrolled in the U.S. Hypopituitary Control and Complications Study (HypoCCS), we proposed the presence of adult GHD could be predicted with 95% accuracy by the presence of three or more pituitary hormone deficiencies (PHDs) or a serum IGF-I concentration less than 84 microg/liter (11 nmol/liter). To validate the diagnostic utility of these criteria, we studied results obtained in 817 adult patients (mean [SD] age: 46.4 [15.7] yr, body mass index: 30.1 [7.2] kg/m(2)) enrolled in HypoCCS who had serum GH concentrations from stimulation tests (11 different tests used, excluding clonidine) and serum IGF-I (competitive binding RIA) measured at the central laboratory (Esoterix Endocrinology, Calabasas Hills, CA). When patients were stratified into subgroups on the basis of the presence of zero, one, two, three, and four additional PHDs, median (25th, 75th percentile) peak GH levels (micrograms per liter) were 3.5 (0.85, 7.1), 0.73 (0.18, 4.2), 0.29 (0.05, 1.4), 0.06 (0.025, 0.295), and 0.025 (0.025, 0.07), respectively. The mean log (peak GH) concentration was significantly different among the subgroups (P < 0.05). The proportion of patients in each group with severe GHD diagnosed by stimulation testing (peak GH < 2.5 microg/liter) was 41%, 67%, 83%, 96%, and 99% for patients with zero, one, two, three, and four PHDs, respectively. The positive predictive values (PPVs) for GHD of three PHDs, four PHDs, and serum IGF-I less than 84 microg/liter were 96%, 99%, and 96%, respectively. The PPV of these three diagnostic criteria was also 95% or more after excluding the data originally used to identify these potential predictors. Taken together, the presence of either three or four additional PHDs or IGF-I less than 84 microg/liter (55% of the patients met at least one of these criteria) reliably predicted GHD with a high PPV (95%), high specificity (89%), and moderate sensitivity (69%). We concluded that patients with an appropriate clinical history and either the presence of three or four additional PHDs or serum IGF-I less than 84 microg/liter (measured in the Esoterix assay) do not require GH stimulation testing for the diagnosis of adult GHD. In clinical practice, we suggest that other causes of low serum IGF-I should be excluded before applying these diagnostic criteria.

Body composition, physical exercise, growth hormone and obesity

In summary, available literature indicates that GH secretion is blunted profoundly in individuals with relative or absolute obesity. Accumulation of AVF particularly represses GH release. Administration of GH to obese adults decreases total body fat and especially AVF. Furthermore, GH supplementation combined with dietary restriction and/or exercise appears to enhance favorable changes in body composition. Although exercise is a powerful stimulus to GH release, the GH response to exercise is blunted in older and obese individuals. This suggests that higher relative exercise intensities may be necessary for exercise alone to stimulate adequate GH release in obese subjects. In as much as exercise in combination with a second stimulus of GH release (e.g. GHRP-2, L-arginine) drives GH release synergistically, we propose that combining exercise and a GH secretagogue may have utility in restoring GH release in obese adults. Taken as a whole, available data suggest that GH repletion regimens in combination with regular exercise and relevant dietary intervention may provide a tripartite strategy for the management of significant obesity.

Abdominal visceral fat and fasting insulin are important predictors of 24-hour GH release independent of age, gender, and other physiological factors

Numerous physiological factors modulate GH secretion, but these variables are not independent of one another. We studied 40 younger (20-29 yr.; 21 men and 19 women) and 62 older (57-80 yr.; 35 men and 27 women) adults to determine the contributions of several demographic and physiological factors to the variability in integrated 24-h GH concentrations. Serum GH was measured every 10 min for 24 h in an enhanced sensitivity chemiluminescence assay. The predictor variables included: age group (young or old), gender, abdominal visceral fat (by computed tomography), total body fat mass and percentage body fat by dual-energy x-ray absorptiometry, serum IGF-I, fasting serum insulin, 24-h mean estradiol and testosterone, and peak oxygen uptake by graded exercise (treadmill) testing. Multiple ordinary least squares regression analysis was used to quantitatively assess the individual contribution that each predictive measure made to explain the variability among values of integrated 24-h GH concentrations while in the presence of the remaining predictors. The model explained 65% of the variance in integrated 24-h GH concentrations. Abdominal visceral fat (P < 0.002) and fasting insulin (P < 0.008) were consistently important predictors of integrated 24-h GH concentrations independent of age group, gender, and all other predictor variables. Although serum IGF-I was an important overall predictor of integrated 24-h GH concentrations (P = 0.002), this relationship was present only in the young subjects and was modulated by gender. The remaining variables failed to contribute significantly to the model. We conclude that abdominal visceral fat and fasting insulin are important predictors of integrated 24-h GH concentrations in healthy adults, independent of age and gender. Serum IGF-I is an important predictor of integrated 24-h GH concentrations in young but not older subjects. Bidirectional feedback between each of these three factors and GH secretion may account for the strong relationships observed.

Cortisol and growth hormone responses to exercise at different times of day

Exercise of appropriate intensity is a potent stimulus for GH and cortisol secretion. Circadian and diurnal rhythms may modulate the GH and cortisol responses to exercise, but nutrition, sleep, prior exercise patterns, and body composition are potentially confounding factors. To determine the influence of the time of day on the GH and cortisol response to acute exercise, we studied 10 moderately trained young men (24.1 +/- 1.1 yr old; maximal oxygen consumption, 47.9 +/- 1.4 mL/kg.min; percent body fat, 13.2 +/- 0.6%). After a supervised night of sleep and a standard meal 12 h before exercise, subjects exercised at a constant velocity (to elicit an initial blood lactate concentration of approximately 2.5 mmol/L) on a treadmill for 30 min on 3 separate occasions, starting at 0700, 1900, and 2400 h. Blood samples were obtained at 5-min intervals for 1 h before and 5 h after the start of exercise; subjects were not allowed to sleep during this period. Subjects were also studied on 3 control days under identical conditions without exercise. There were no significant differences with time of day in the mean blood lactate and submaximal oxygen consumption values during exercise. The differences over time in serum GH and cortisol concentrations between the exercise day and the control day were determined with 95% confidence limits for each time of day. Exercise stimulated a significant increase in serum GH concentrations over control day values for approximately 105--145 min (P < 0.05) with no significant difference in the magnitude of this response by time of day. The increase in serum GH concentrations with exercise was followed by a transient suppression of GH release (for approximately 55--90 min; P < 0.05) after exercise at 0700 and 1900 h, but not at 2400 h. Although the duration of the increase in serum cortisol concentrations after exercise was similar (approximately 150--155 min; P < 0.05) at 0700, 1900, and 2400 h, the magnitude of this increase over control day levels was greatest at 2400 h. This difference was significant for approximately 130 min and approximately 40 min compared to exercise at 1900 and 0700 h, respectively (P < 0.05). The cortisol response to exercise at 0700 h was significantly greater than that at 1900 h for about 55 min (P < 0.05). A rebound suppression of cortisol release for about 50 min (P < 0.05) was observed after exercise at 2400 h, but not 0700 or 1900 h. Both baseline (before exercise) and peak cortisol concentrations were significantly higher at 0700 h than at 1900 or 2400 h (P < 0.01). We conclude that time of day does not alter the GH response to exercise; however, the exercise-induced cortisol response is modulated by time of day.

Intensity of acute exercise does not affect serum leptin concentrations in young men

PURPOSE

We examined the effects of exercise intensity on serum leptin levels.

METHODS

Seven men (age = 27.0 yr; height = 178.3 cm; weight = 82.2 kg) were tested on a control (C) day and on 5 exercise days (EX). Subjects exercised (30 min) at the following intensities: 25% and 75% of the difference between the lactate threshold (LT) and rest (0.25 LT, 0.75 LT), at LT, and at 25% and 75% of the difference between LT and VO2peak (1.25 LT, 1.75 LT).

RESULTS

Kcal expended during the exercise bouts ranged from 150 +/- 11 kcal (0.25 LT) to 529 +/- 45 kcal (1.75 LT), whereas exercise + 3.5 h recovery kcal ranged from 310 +/- 14 kcal (0.25 LT) to 722 +/- 51 kcal (1.75 LT). Leptin area under the curve (AUC) (Q 10-min samples) for all six conditions (C + 5 Ex) was calculated for baseline (0700-0900 h) and for exercise + recovery (0900-1300 h). Leptin AUC for baseline ranged from 243 +/- 33 to 291 +/- 56 ng x mL(-1) x min; for exercise + recovery results ranged from 424 +/- 56 to 542 +/- 99 ng x mL(-1) x min. No differences were observed among conditions within either the baseline or exercise + recovery time frames. Regression analysis confirmed positive relationships between serum leptin concentrations and percentage body fat (r = 0.94) and fat mass (r = 0.93, P < 0.01).

CONCLUSION

We conclude that 30 min of acute exercise, at varying intensity of exercise and caloric expenditure, does not affect serum leptin concentrations during exercise or for the first 3.5 hours of recovery in healthy young men.

Exercise-dependent growth hormone release is linked to markers of heightened central adrenergic outflow

To test the hypothesis that heightened sympathetic outflow precedes and predicts the magnitude of the growth hormone (GH) response to acute exercise (Ex), we studied 10 men [age 26.1 +/- 1.7 (SE) yr] six times in randomly assigned order (control and 5 Ex intensities). During exercise, subjects exercised for 30 min (0900-0930) on each occasion at a single intensity: 25 and 75% of the difference between lactate threshold (LT) and rest (0.25LT, 0.75LT), at LT, and at 25 and 75% of the difference between LT and peak (1.25LT, 1.75LT). Mean values for peak plasma epinephrine (Epi), plasma norepinephrine (NE), and serum GH concentrations were determined [Epi: 328 +/- 93 (SE), 513 +/- 76, 584 +/- 109, 660 +/- 72, and 2,614 +/- 579 pmol/l; NE: 2. 3 +/- 0.2, 3.9 +/- 0.4, 6.9 +/- 1.0, 10.7 +/- 1.6, and 23.9 +/- 3.9 nmol/l; GH: 3.6 +/- 1.5, 6.6 +/- 2.0, 7.0 +/- 2.0, 10.7 +/- 2.4, and 13.7 +/- 2.2 microg/l for 0.25, 0.75, 1.0, 1.25, and 1.75LT, respectively]. In all instances, the time of peak plasma Epi and NE preceded peak GH release. Plasma concentrations of Epi and NE always peaked at 20 min after the onset of Ex, whereas times to peak for GH were 54 +/- 6 (SE), 44 +/- 5, 38 +/- 4, 38 +/- 4, and 37 +/- 2 min after the onset of Ex for 0.25-1.75LT, respectively. ANOVA revealed that intensity of exercise did not affect the foregoing time delay between peak NE or Epi and peak GH (range 17-24 min), with the exception of 0.25LT (P < 0.05). Within-subject linear regression analysis disclosed that, with increasing exercise intensity, change in (Delta) GH was proportionate to both DeltaNE (P = 0.002) and DeltaEpi (P = 0.014). Furthermore, within-subject multiple-regression analysis indicated that the significant GH increment associated with an antecedent rise in NE (P = 0.02) could not be explained by changes in Epi alone (P = 0.77). Our results suggest that exercise intensity and GH release in the human may be coupled mechanistically by central adrenergic activation.

Hormone pulsatility discrimination via coarse and short time sampling

Pulsatile hormonal secretion is a ubiquitous finding in endocrinology. However, typical protocols employed to generate data sets suitable for "pulsatility analysis" have required 60-300 samples, rendering such studies largely research methodologies, due primarily to considerable assay expense. One successful mathematical strategy in calibrating changes in pulsatility modalities is approximate entropy (ApEn), a quantification of sequential irregularity. Given the degree of differences between ApEn values in pathophysiological subjects vs. healthy controls reported in several recent studies, we queried to what extent coarser (less frequent) and shorter duration time sampling would still retain significant ApEn differences between clinically distinct cohorts. Accordingly, we reanalyzed data from two studies of 24-h profiles of healthy vs. tumoral hormone secretion: 1) growth hormone comparisons of normal subjects vs. acromegalics, originally sampled every 5 min; and 2) ACTH and cortisol comparisons of normal subjects vs. Cushing's disease patients, originally sampled every 10 min. By multiple statistical analyses, we consistently and highly significantly (P < 0.0001) established that serum concentration patterns in tumor patients are more irregular than those of controls, with high sensitivity and specificity, even at very coarse (e.g., 60 min) sampling regimens and over relatively short (2-4 h) time intervals. The consistency of these findings suggests a broadly based utility of such shorter and/or coarser sampling methodologies. Substantial reduction in sampling requirements holds the potential to move analysis of pulsatile hormone release from a primarily research tool to a clinically applicable protocol, in appropriate diagnostic and therapeutic contexts.

Obesity attenuates the growth hormone response to exercise

Resting serum GH concentrations are decreased in obesity. In nonobese (NonOb) individuals, acute exercise of sufficient intensity increases GH levels; however, conflicting data exist concerning the GH response to exercise in obese individuals. To examine the exercise-induced GH response in obese individuals, we studied 8 NonOb, 11 lower body obese (LBO), and 12 upper body obese (UBO) women before, during, and after 30 min (0800-0830 h) of treadmill exercise at 70% oxygen consumption peak. Blood samples were taken every 5 min (0700-1300 h) and were analyzed for GH concentrations with a sensitive (0.002 microg/L) chemiluminescence assay. The impact of 16 weeks of aerobic exercise training on the GH response to exercise was also examined in the obese women. In response to exercise, the 6-h integrated GH concentration was significantly greater (P < 0.05) in the NonOb women (1006 +/- 220 min/microg x L) than in either of the obese groups (LBO, 435 +/- 136; UBO, 189 +/- 26 min/microg x L). No differences were found between the LBO and UBO women. The increased integrated GH concentrations could be accounted for by a greater 6-h GH production rate [micrograms per L distribution volume (Lv)] in the NonOb women than in either of the obese groups (NonOb, 45.6 +/- 12.3; LBO, 16.9 +/- 1.2; UBO, 8.7 +/- 0.64 microg/Lv; P < 0.05). This increase was attributed to a greater mass of GH secreted per pulse in the NonOb women (NonOb, 10.8 +/- 2.5; LBO, 4.9 +/- 0.8; UBO, 4.0 +/- 0.5 microg/Lv; P < 0.05, NonOb vs. both obese groups). After 16 weeks of aerobic training, maximal oxygen consumption increased from 44.7 +/- 2.2 to 48.5 +/- 1.9 mL/kg fat-free mass x min; P < 0.05), but no significant change in body composition occurred in the 10 obese women who completed the training. No change was observed in the GH response to exercise after training (n = 10; pre, 379 +/- 144; post, 350 +/- 55 min/microg x L). In conclusion, the GH response to exercise was attenuated in the obese women compared to NonOb women. Short term aerobic training improved fitness, but did not increase the GH response to exercise.

Impact of acute exercise intensity on pulsatile growth hormone release in men

To investigate the effects of exercise intensity on growth hormone (GH) release, 10 male subjects were tested on 6 randomly ordered occasions [1 control condition (C), 5 exercise conditions (Ex)]. Serum GH concentrations were measured in samples obtained at 10-min intervals between 0700 and 0900 (baseline) and 0900 and 1300 (exercise+ recovery). Integrated GH concentrations (IGHC) were calculated by trapezoidal reconstruction. During Ex subjects exercised for 30 min (0900-0930) at one of the following intensities [normalized to the lactate threshold (LT)]: 25 and 75% of the difference between LT and rest (0.25LT and 0.75LT, respectively), at LT, and at 25 and 75% of the difference between LT and peak (1.25LT and 1.75LT, respectively). No differences were observed among conditions for baseline IGHC. Exercise+recovery IGHC (mean +/- SE: C = 250 +/- 60; 0.25LT = 203 +/- 69; 0.75LT = 448 +/- 125; LT = 452 +/- 119; 1.25LT = 512 +/- 121; 1.75LT = 713 +/- 115 microg x l(-1) x min(-1)) increased linearly with increasing exercise intensity (P < 0.05). Deconvolution analysis revealed that increasing exercise intensity resulted in a linear increase in the mass of GH secreted per pulse and GH production rate [production rate increased from 16. 5 +/- 4.5 (C) to 32.1 +/- 5.2 microg x distribution volume(-1) x min(-1) (1.75LT), P < 0.05], with no changes in GH pulse frequency or half-life of elimination. We conclude that the GH secretory response to exercise is related to exercise intensity in a linear dose-response pattern in young men.

Validity of methods of body composition assessment in young and older men and women

We examined the validity of percent body fat (%Fat) estimation by two-compartment (2-Comp) hydrostatic weighing (Siri 2-Comp), 3-Comp dual-energy X-ray absorptiometry (DEXA 3-Comp), 3-Comp hydrostatic weighing corrected for the total body water (Siri 3-Comp), and anthropometric methods in young and older individuals (n = 78). A 4-Comp model of body composition served as the criterion measure of %Fat (Heymsfield 4-Comp; S. B. Heymsfield, S. Lichtman, R. N. Baumgartner, J. Wang, Y. Kamen, A. Aliprantis, and R. N. Pierson Jr., Am. J. Clin. Nutr. 52: 52-58, 1990.). Comparison of the Siri 3-Comp with the Heymsfield 4-Comp model revealed mean differences of </=0.4 %Fat, r values >/= r = 0.997, total error values </= 0.85 %Fat, and 95% confidence intervals (Bland-Altman analysis) of </=1.7 %Fat. Comparison of Siri 2-Comp, DEXA, and anthropometric models with the Heymsfield 4-Comp revealed that total error scores ranged from +/-4. 0 to +/-10.7 %Fat, and 95% confidence intervals associated with the Bland-Altman analysis ranged from +/-5.1 to +/-15.0 %Fat. We conclude that the Siri 3-Comp model provides valid and accurate body composition data when compared with a 4-Comp criterion model. However, the individual variability associated with the Siri 2-Comp, DEXA 3-Comp, and anthropometric models may limit their use in research settings. The use of anthropometric estimation methods resulted in large mean differences and a considerable amount of interindividual variability. These data suggest that the use of these techniques should be viewed with caution.

The use of anthropometric and dual-energy X-ray absorptiometry (DXA) measures to estimate total abdominal and abdominal visceral fat in men and women

OBJECTIVE

A single-slice computed tomography (CT) scan provides a criterion measure of total abdominal fat (TAF) and abdominal visceral fat (AVF), but this procedure is often prohibitive due to radiation exposure, cost, and accessibility. In the present study, the utility of anthropometric measures and estimates of trunk and abdominal fat mass by dual-energy X-ray absorptiometry (DXA) to predict CT measures of TAF and AVF (cross-sectional area, cm2) was assessed.

RESEARCH METHODS AND PROCEDURES

CT measures of abdominal fat (at the level of the L4-L5 inter-vertebral space), DXA scans, and anthropometric measures were obtained in 76 Caucasian adults ages 20-80 years.

RESULTS

Results demonstrated that abdominal sagittal diameter measured by anthropometry is an excellent predictor of sagittal diameter measured from a CT image (r=0.88 and 0.94; Total Error [TE]=4.1 and 3.1 cm, for men and women, respectively). In both men and women, waist circumference and abdominal sagittal diameter were the anthropometric measures most strongly associated with TAF (r=0.87 to 0.93; Standard Error of Estimate (SEE)=60.7 to 75.4 cm2) and AVF (r=0.84 to 0.93; SEE=0.7 to 30.0 cm2). The least predictive anthropometric measure of TAF or AVF was the commonly used waist-to-hip ratio (WHR). DXA estimates of trunk and abdominal fat mass were strongly associated with TAF (r=.94 to 0.97; SEE=36.9 to 50.9 cm2) and AVF (r=0.86 to 0.90; SEE=4.9 to 27.7 cm2).

DISCUSSION

The present results suggest that waist circumference and/or abdominal sagittal diameter are better predictors of TAF and AVF than the more commonly used WHR. DXA trunk fat and abdominal fat appear to be slightly better predictors of TAF but not AVF compared to these anthropometric measures. Thus DXA does not offer a significant advantage over anthropometry for estimation of AVF.

Recovery of growth hormone release from suppression by exogenous insulin-like growth factor I (IGF-I): evidence for a suppressive action of free rather than bound IGF-I

To determine the time course of recovery of GH release from insulin-like growth factor I (IGF-I) suppression, 11 healthy adults (18-29 yr) received, in randomized order, 4-h i.v. infusions of recombinant human IGF-I (rhIGF-I; 3 microg/kg-h) or saline (control) from 25.5-29.5 h of a 47.5-h fast. Serum GH was maximally suppressed within 2 h and remained suppressed for 2 h after the rhIGF-I infusion; during this 4-h period, GH concentrations were approximately 25% of control day levels [median (interquartile range), 1.2 (0.4-4.0) vs. 4.8 (2.8-7.9) microg/L; P < 0.05]. A rebound increase in GH concentrations occurred 5-7 h after the end of rhIGF-I infusion [7.6 (4.6 -11.7) vs. 4.3 (2.5-6.0) microg/L; P < 0.05]. Thereafter, serum GH concentrations were similar on both days. Total IGF-I concentrations peaked at the end of the rhIGF-I infusion (432 +/- 43 vs. 263 +/- 44 microg/L; P < 0.0001) and remained elevated 18 h after the rhIGF-I infusion (360 +/- 36 vs. 202 +/- 23 microg/L; P = 0.001). Free IGF-I concentrations were approximately 140% above control day values at the end of the infusion (2.1 +/- 0.4 vs. 0.88 +/- 0.3 microg/L; P = 0.001), but declined to baseline within 2 h after the infusion. The close temporal association between the resolution of GH suppression and the fall of free IGF-I concentrations, and the lack of any association with total IGF-I concentrations suggest that unbound (free), not protein-bound, IGF-I is the major IGF-I component responsible for this suppression. The rebound increase in GH concentrations after the end of rhIGF-I infusion is consistent with cessation of an inhibitory effect of free IGF-I on GH release.

The Growth Hormone Research Society consensus guidelines for the diagnosis and treatment of adult GH deficiency

The Growth Hormone Research Society (GRS) convened a workshop in Port Stephens, Australia in April 1997 to establish consensus guidelines for the diagnosis and treatment of adults with GH deficiency (GHD). Scientists with expertise in the field, representatives from industry involved in the manufacture of GH and representatives from health authorities from a number of countries participated in the workshop. The workshop considered the following questions: (1) How should adult GHD be defined? (2) Who should be tested for adult GHD? (3) How should the diagnosis of adult GHD be established? (4) How should GH and insulin-like growth factor-I (IGF-I) assays be standardized? (5) Who should be treated for adult GHD? (6) What dose of GH should be used for treatment of adult GHD? (7) How should treatment of adult GHD be monitored? (8) What are the contraindications to treatment of adult GHD? (9) What safety issues need to be considered? (10) How long should treatment of adult GHD be continued? The consensus guidelines developed at this workshop and the rationale for some of these recommendations will be reviewed in this paper.

Human growth hormone response to repeated bouts of aerobic exercise

We examined whether repeated bouts of exercise could override growth hormone (GH) auto-negative feedback. Seven moderately trained men were studied on three occasions: a control day (C), a sequential exercise day (SEB; at 1000, 1130, and 1300), and a delayed exercise day (DEB; at 1000, 1400, and 1800). The duration of each exercise bout was 30 min at 70% maximal O2 consumption (VO2max) on a cycle ergometer. Standard meals were provided at 0600 and 2200. GH was measured every 5-10 min for 24 h (0800-0800). Daytime (0800-2200) integrated GH concentrations were approximately 150-160% greater during SEB and DEB than during C: 1,282 +/- 345, 3,192 +/- 669, and 3,389 +/- 991 min.microgram.l-1 for C, SEB, and DEB, respectively [SEB > C (P < 0.06), DEB > C (P < 0.03)]. There were no differences in GH release during sleep (2300-0700). Deconvolution analysis revealed that the increase in 14-h integrated GH concentration on DEB was accounted for by an increase in the mass of GH secreted per pulse (per liter of distribution volume, lv): 7.0 +/- 2.9 and 15.9 +/- 2.6 micrograms/lv for C and DEB, respectively (P < 0.01). Comparison of 1.5-h integrated GH concentrations on the SEB and DEB days (30 min exercise + 60 min recovery) revealed that, with each subsequent exercise bout, GH release apparently increased progressively, with a slightly greater increase on the DEB day [SEB vs. DEB: 497 +/- 162 vs. 407 +/- 166 (bout 1), 566 +/- 152 vs. 854 +/- 184 (bout 2), and 633 +/- 149 vs. 1,030 +/- 352 min.microgram.l-1 (bout 3), P < 0.05]. We conclude that the GH response to acute aerobic exercise is augmented with repeated bouts of exercise.

The influence of anatomical boundaries, age, and sex on the assessment of abdominal visceral fat

Single-slice abdominal computed tomography (CT) scanning has been used extensively for the measurement of abdominal visceral fat (AVF). Optimal anatomical scan location and pixel density ranges have been proposed and are specifically reported to allow for the replication and standardization of AVF measurements. Standardization of the anatomical boundaries for CT measurement of AVF and the influence of age and gender on results obtained with different boundary locations have received much less attention. To determine the influence of three boundary analysis methods (AVF-1, AVF-2, and AVF-3) on the measurement of AVF by CT, 54 older (60 years to 79 years) and 37 younger (20 years to 29 years) healthy men and women were examined. The measurement boundary for AVF-1 was the internal most aspect of the abdominal and oblique muscle walls, and the posterior aspect of the vertebral body. AVF-2 used fat measurements enclosed in a boundary formed by the midpoint of the abdominal and oblique muscle walls, and the most posterior aspect of the spinous process. AVF-3 used fat measurements enclosed in a boundary formed by the external border of the abdominal and oblique muscle walls, and the external border of the erector spinae. Greater AVF measures were obtained with AVF-2 and AVF-3 compared with AVF-1 (p < 0.0001). These differences were greater in older compared with younger subjects (p < 0.0001) and greater in women compared with men (p < 0.02). The significantly greater AVF measurements obtained with AVF-2 and AVF-3 resulted from the inclusion of larger amounts of fat that are not drained by the portal circulation. This included retroperitoneal, intermuscular, and intramuscular lipid droplets, which increase with aging. On the basis of these results, we recommend the AVF-1 anatomical boundaries for the measurement of AVF in clinical investigations, particularly with older subjects. These data demonstrate the importance of precise and reproducible anatomical boundaries for the measurement of AVF, particularly in longitudinal studies.

Effect of aging on the sensitivity of growth hormone secretion to insulin-like growth factor-I negative feedback

To determine the effect of aging on the suppression of GH secretion by insulin-like growth factor (IGF)-I, we studied 11 healthy young adults (6 men, 5 women, mean +/- SD: 25.2 +/- 4.6 yr old; body mass index 23.7 +/- 1.8 kg/m2) and 11 older adults (6 men, 5 women, 69.5 +/- 5.8 yr old; body mass index 24.2 +/- 2.5 kg/m2). Saline (control) or recombinant human IGF-I (rhIGF-I) (2 h baseline then, in sequence, 2.5 h each of 1, 3, and 10 micrograms/kg.h) was infused iv during the last 9.5 h of a 40.5-h fast; serum glucose was clamped within 15% of baseline. Baseline serum GH concentrations (mean +/- SE: 3.3 +/- 0.7 vs. 1.9 +/- 0.5 micrograms/L, P = 0.02) and total IGF-I concentrations (219 +/- 15 vs. 103 +/- 19 micrograms/L, P < 0.01) were higher in the younger subjects. In both age groups, GH concentrations were significantly decreased by 3 and 10 micrograms/kg.h, but not by 1 microgram/kg.h rhIGF-I. The absolute decrease in GH concentrations was greater in young than in older subjects during the 3 and 10 micrograms/kg.h rhIGF-I infusion periods, but both young and older subjects suppressed to a similar GH level during the last hour of the rhIGF-I infusion (0.78 +/- 0.24 microgram/L and 0.61 +/- 0.16 microgram/L, respectively). The older subjects had a greater increase above baseline in serum concentrations of both total (306 +/- 24 vs. 244 +/- 14 micrograms/L, P = 0.04) and free IGF-I (8.5 +/- 1.4 vs. 4.2 +/- 0.6 micrograms/L, P = 0.01) than the young subjects during rhIGF-I infusion, and their GH suppression expressed in relation to increases in both total and free serum IGF-I concentrations was significantly less than in the young subjects. We conclude that the ability of exogenous rhIGF-I to suppress serum GH concentrations declines with increasing age. This suggests that increased sensitivity to endogenous IGF-I negative feedback is not a cause of the decline in GH secretion that occurs with aging.

Exercise training decreases the growth hormone (GH) response to acute constant-load exercise

To assess the influence of exercise training on the growth hormone (GH) response to acute exercise, six untrained males completed a 20-min, high-intensity, constant-load exercise test prior to and after 3 and 6 wk of training (the absolute power output (PO) during each test remained constant x PO = 182.5 +/- 29.5 W). Training increased (pre- vs post-training) oxygen uptake (VO2) at lactate threshold (1.57 +/- 0.33 L.min-1 vs 1.97 +/- 0.24 L.min-1 P < or = 0.05). VO2 at 2.5 mM blood lactate concentration ([HLa]) (1.83 +/- 0.38 L.min-1 vs 2.33 +/- 0.38 L.min-1, P < or = 0.05), and VO2peak (3.15 +/- 0.54 L.min-1 vs 3.41 +/- 0.47 L.min-1, P < or = 0.05). Power output at the lactate threshold (PO-LT) increased with training from 103 +/- 28 to 132 +/- 23W (P < or = 0.05). Integrated GH concentration (20 min exercise + 45 min recovery) (microgram.L-1 x min) after 3 wk (138 +/- 106) and 6 wk (130 +/- 145) were significantly lower (P < or = 0.05) than pre-training (238 +/- 145). Plasma epinephrine and norepinephrine responses to training were similar to the GH response (EPI-pre-training = 2447 +/- 1110; week 3 = 1046 +/- 144; week 6 = 955 +/- 322 pmol.L-1; P < or = 0.05; NE pre-training = 23.0 +/- 5.2; week 3 = 13.4 +/- 4.8; week 6 = 12.1 +/- 6.8 nmol.L-1; P < or = 0.05). These data indicate that the GH and catecholamine response to a constant-load exercise stimulus are reduced within the first 3 wk of exercise training and support the hypothesis that a critical threshold of exercise intensity must be reached to stimulate GH release.

Body composition by DEXA in older adults: accuracy and influence of scan mode

Dual energy x-ray absorptiometry (DEXA) measures bone mineral content (BMC), bone mineral density (BMD), fat-free mass (FFM), and provides estimates of percent body fat. Changes in scan mode geometry (pencil beam vs array) may impact these measures and body composition estimates using multi-compartment models. Forty-one adults, ages 59-79 yr, were scanned in each mode and also underwent hydrostatic weighing and measurement of total body water (tritiated water dilution). The effect of scan mode on measurement of DEXA BMC, BMD, FFM, and percent body fat (DEXA %Fat) was examined. The effect of scan mode on percentage body fat determined by a 4-compartment body composition model (4 Comp %Fat) and comparison of DEXA %Fat and 4 Comp %Fat were also examined. BMC and DEXA %Fat were greater (1.3% and 3.9%, respectively, P < 0.01), and BMD and FFM were lower (1.1% and 1.9%, respectively, P < 0.01) with the array scan mode. The 4 Comp %Fat was significantly greater (0.2%) when the array scan mode measurements of total body bone mineral were used; however, these differences were physiologically inconsequential. Comparison between DEXA %Fat and 4 Comp %Fat measures revealed a total error of +/-5.0% in the older adults examined. These results indicate significant scan mode differences in total body BMC, BMD, FFM, and DEXA %Fat measurements and demonstrate the importance of using a single DEXA scan mode for clinical investigation, particularly with longitudinal studies. For all investigations with DEXA, the scan mode should be reported. Furthermore, the error associated with using DEXA alone to estimate percent fat in an older population suggests that this technique is unacceptable in a research setting.

Effect of obesity and feeding on the growth hormone (GH) response to the GH secretagogue L-692,429 in young men

GH secretion and the response to GH secretagogues are significantly diminished in obese individuals. Previous studies have shown that L-692,429 (L), a nonpeptide mimetic of GH-releasing peptide, selectively stimulates GH release in normal young men and in the elderly, who also have diminished GH secretion. A paired, two-site study examined the effects of L on GH release in 12 healthy obese (part A; mean +/- SD: age, 26.1 +/- 3.3 yr; body mass index, 35.0 +/- 3.1 kg/m2) and 10 nonobese (part B; age, 22.2 +/- 2.3 yr; body mass index, < or = 27.0) young men. In part A, placebo, low dose L (0.2 mg/kg), or high dose L (0.75 mg/kg) was administered iv over 15 min on 3 separate occasions after an overnight fast. Samples for GH, PRL, and cortisol determinations were obtained every 15 min. GH release (mean +/- SE) was significantly increased by both doses of L compared to the effect of placebo: 12.6 +/- 1.8 micrograms/L (low dose), 18.5 +/- 2.7 micrograms/L (high dose), and 0.84 +/- 0.1 microgram/L (placebo), respectively (P < 0.05). In a subset of 6 obese men, in samples collected every 5 min, the GH response to both doses of L was significantly greater than that to 1 microgram/kg GHRH. To compare the response to low dose L in the obese and to determine the effects of feeding on this response, 0.2 mg/kg L was administered as described in part A to nonobese young men after an overnight fast (fasted) or a standardized breakfast (fed; part B). Low dose L was an effective GH secretagogue in nonobese young men; however, this effect was attenuated with feeding [43.6 +/- 7.9 (fasted) vs. 17.7 +/- 4.8 (fed) micrograms/L]. Of note, the response to low dose L in fasted obese individuals was similar to that in fed nonobese individuals. The administration of L was well tolerated in both groups. We conclude that L is an effective GH secretagogue in obese and nonobese young men and may have therapeutic benefits when administered to relative (obese or elderly) or absolute GH-deficient individuals.

A kindred with a variant of multiple endocrine neoplasia type 1 demonstrating frequent expression of pituitary tumors but not linked to the multiple endocrine neoplasia type 1 locus at chromosome region 11q13

Acromegaly is uncommon in kindreds with multiple endocrine neoplasia type 1 (MEN1), whereas primary hyperparathyroidism (PHP) has the highest penetrance of any endocrinopathy. We report an unusual MEN1 kindred with frequent expression of pituitary tumors and a low penetrance of PHP. Four members were found to have disease: PHP in generation I, acromegaly (2 cases) in generation II, and hyperprolactinemia associated with a pituitary tumor in generation III. There was no evidence for PHP in 1 patient with acromegaly (age 60 yr), the patient with hyperprolactinemia and the pituitary tumor (age 22 yr), and 1 asymptomatic obligate carrier (age 50 yr). Screening of 26 members revealed the possible diagnosis of PHP in 1 family member in generation II and possible early acromegaly in 2 members of generation III with elevated serum concentrations of insulin-like growth factor I and insulin-like growth factor-binding protein-3 but normal patterns of pulsatile GH release. Although the predisposing genetic defect in typical MEN1 families has previously been mapped to chromosome location 11q13 without evidence of heterogeneity among the 87 families analyzed, linkage of disease in this family to the MEN1 region is unlikely based on haplotype analysis. Localization of the gene(s) responsible for disease in such atypical families may aid in the understanding of the pathogenesis of MEN1. In addition, further study of the earliest changes in patterns of pulsatile GH release in familial acromegaly may allow more insight into the pathogenesis and natural history of this disease.

Growth hormone-releasing hormone and growth hormone-releasing peptide as therapeutic agents to enhance growth hormone secretion in disease and aging

Growth hormone (GH) secretion is pulsatile and is tightly regulated. In this chapter the effects of aging, nutrition, the feedback effects of IGF-I, and the role of body composition in the decline of GH secretion will be discussed. In GH-deficient adults there is an increase in the amount of intra-abdominal (visceral) fat. Similarly, with increasing age, there is an increase in visceral fat and there is a tight correlation between 24-hour GH release and visceral fat in the elderly. This may have serious metabolic consequences, including insulin resistance and increased cardiovascular risk. There are at least four potential mechanisms for the age-related decline in GH secretion: 1) decreased release of growth hormone releasing-hormone (GHRH); 2) increased release of somatostatin; 3) enhanced sensitivity to IGF-I feedback; and 4) decreased somatotroph mass. The latter two potential mechanisms are discussed. There is little evidence that there is any change in sensitivity to IGF-I feedback with aging and the somatotroph cell mass appears to be preserved in older subjects. The GH axis may be stimulated by either GHRH or by growth hormone-releasing peptide (GHRP) and related compounds. Chronic therapy with GHRH in GH-deficient children restores GH secretion and accelerates linear growth. Mutations of the GHRH receptor lead to GH deficiency and short stature. This indicates the essential role of GHRH in regulation of GH secretion. Growth hormone releasing peptide was discovered in 1981. Recently, the GHRP/GH secretagogue receptor has been cloned and orally active GHRP mimetics have been developed. One such compound, MK-677, stimulates pulsatile GH secretion and its effects persist for 24 hours. Oral administration of MK-677 for a month in the elderly demonstrates that this route stimulates a physiologic pattern of GH secretion. The amplitude of the GH pulses was increased but the number of GH pulses was unchanged. Thus, in older individuals, the amount of GH secreted in 24 hours is restored toward that seen in young adults. This compound also enhances GH secretion in GH-deficient adults who had been GH-deficient during childhood. The development of stable, orally active molecules to stimulate the GHRP/GH secretagogue receptor is a practical reality. These GH secretagogues may have a therapeutic role in short stature and adult GH deficiency. In addition, the use of GH secretagogues in normal aging merits investigation, as growth hormone may regulate body composition in older adults.

Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects

Aging is associated with declining activity of the GH axis, possibly contributing to adverse body composition changes and increased incidence of cardiovascular disease. The stimulatory effects on the GH-insulin-like growth factor I (IGF-I) axis of orally administered MK-677, a GH-releasing peptide mimetic, were investigated. Thirty-two healthy subjects (15 women and 17 men, aged 64-81 yr) were enrolled in a randomized, double blind, placebo-controlled trial. They received placebo or 2, 10, or 25 mg MK-677, orally, once daily for 2 separate study periods of 14 and 28 days. At baseline and on day 14 of each study period, blood was collected every 20 min for 24 h to measure GH, PRL, and cortisol. Attributes of pulsatile GH release were assessed by 3 independent algorithms. MK-677 administration for 2 weeks increased GH concentrations in a dose-dependent manner, with 25 mg/day increasing mean 24-h GH concentration 97 +/- 23% (mean +/- SE; P < 0.05 vs. baseline). This increase was due to an enhancement of preexisting pulsatile GH secretion. GH pulse height and interpulse nadir concentrations increased significantly without significant changes in the number of pulses. With 25 mg/day MK-677 treatment, mean serum IGF-I concentrations increased into the normal range for young adults (141 +/- 21 microgram/L at baseline, 219 +/- 21 micrograms/L at 2 weeks, and 265 +/- 29 micrograms/L at 4 weeks; P < 0.05). MK-677 produced significant increases in fasting glucose (5.4 +/- 0.3 to 6.8 +/- 0.4 mmol/L at 4 weeks; P < 0.01 vs. baseline) and IGF-binding protein-3. Circulating cortisol concentrations did not change, and PRL concentrations increased 23%, but remained within the normal range. Once daily treatment of older people with oral MK-677 for up to 4 weeks enhanced pulsatile GH release, significantly increased serum GH and IGF-I concentrations, and, at a dose of 25 mg/day, restored serum IGF-I concentrations to those of young adults.