Adult growth hormone deficiency

Several reports have focused on the clinical features of the untreated GH-deficient adult and the effect of GH therapy. The results reported are strikingly unanimous. Untreated GH-deficient adults have been shown to have increased cardiovascular mortality, reduced exercise capacity, reduced muscle strength, subnormal glomerular filtration rate and renal plasma flow, defective sweat secretion and defective thermoregulation, reduced energy expenditure and basal metabolic rate, abnormal thyroid hormone metabolism, reduced myocardial function and clinical signs of premature atherosclerosis. Body composition has been found abnormal with increased fat mass, decreased lean body mass, decreased muscle fat ratio, visceral obesity, reduced extracellular fluid volume and reduced bone mineral content. Furthermore, two independent groups have reported impaired psychological wellbeing as compared to normal subjects. Apart from the observation on total mortality, all the above-reported abnormalities improve during GH substitution. The only recognisable side effects so far has been fluid retention, which is usually transient and dose-dependent. It is concluded that GH deficiency has distinct clinical consequences all of which can be totally or partially alleviated by GH replacement therapy.

Marked effects of sustained low growth hormone (GH) levels on day-to-day fuel metabolism: studies in GH-deficient patients and healthy untreated subjects

The metabolic effects of circadian GH levels in the very low physiological range are unknown. Therefore, we studied 1) GH-deficient patients on receiving GH replacement therapy in whom the last GH injection was replaced with a constant iv infusion starting at 24 h of either GH (35 micrograms/h) or saline (SAL), and 2) an untreated healthy control group. Glucose turnover, indirect calorimetry, and forearm exchange of metabolites were investigated the following day in the basal state (8-11 h) and during a euglycemic (11-13 H) and a hypoglycemic (13-14 h) glucose clamp. During infusion, steady state GH levels increased by 1.9 micrograms/L. Basal and insulin-stimulated energy expenditures (EE) were lower in the patients during SAL than during GH infusion, and the basal respiratory exchange ratio was also lower during GH treatment. Protein EE was elevated during SAL compared to GH infusion (P < 0.05). During the clamp, forearm glucose uptake decreased in the GH study compared to that in the SAL study ((P < 0.05). The patients in the SAL study were more sensitive to insulin during the clamp in terms of suppression of endogenous glucose production (EGP; P < 0.05) and infusion rate of glucose necessary to maintain euglycemia (M value; P < 0.01). Lipid oxidation, in particular in the basal state, was decreased during SAL compared to GH infusion (P < 0.01). The SAL-treated compared with the control group was characterized by decreased basal and insulin-stimulated EE (P < 0.01), increased protein EE (P < 0.01), and hypersensitivity to insulin in terms of suppression of EGP (P < 0.05) and M value (P < 0.01). During the hypoglycemic clamp, the patients in the SAL study were hypersensitive to the hypoglycemic actions of insulin in terms of increased M-value and suppression of EGP, and lipolysis was impaired, as judged by the inhibition of net forearm uptake of FFA. In conclusion, very low GH levels exert powerful actions on day-to-day metabolism, resulting in protein and glucose sparing at the expense of lipids.

Effect of growth hormone administration on circulating levels of luteinizing hormone, follicle stimulating hormone and testosterone in normal healthy men

A new area of growth hormone (GH) therapy in adults is the treatment of infertility. The aim of this study was to evaluate the effects of pharmacological GH administration on the secretion of pituitary and gonadal hormones in normal men. Eight healthy men, 23-32 years of age (mean 28.1 years), with a normal body mass index were studied in a double-blind, placebo-controlled crossover design. All participants had a normal semen analysis before entering the study. Each participant was treated with placebo and GH (12/IU/day, Norditropin; Novo Nordisk, Denmark) during two different 14-day periods, separated by a 6 week washout period. Administration of GH for 14 days resulted in a significant increase in serum insulin-like growth factor I (IGF-I; P < 0.01) but no changes occurred in IGF-I values during placebo treatment. The concentrations of follicle stimulating hormone and luteinizing hormone displayed no change during the two periods and did not differ between the GH treatment period and the placebo period. The concentration of testosterone was unchanged during the placebo/GH periods and there was no difference between the GH treatment period and the placebo period. We conclude that GH treatment for 14 days in normal healthy men does not affect gonadotrophin or testosterone patterns.

Impact of 2 weeks high dose growth hormone treatment on basal and insulin stimulated substrate metabolism in humans

OBJECTIVE

Short-term, high dose growth hormone (GH) treatment has been advocated in many catabolic disease states. It is likely that some of the anabolic effects of GH are mediated through activation of lipolysis, but the metabolic impact of therapeutically relevant GH exposure is not known in detail. The present study was accordingly designed to assess the effects of such GH exposure on basal and insulin stimulated intermediary metabolism.

DESIGN, PATIENTS AND MEASUREMENTS

Six healthy young females were examined following daily injections of GH (12 IU/day) or saline for 2 weeks in a placebo controlled design. Each study consisted of a 3 hour basal period and a 2 hour hyperinsulinaemic euglycaemic clamp.

RESULTS

GH treatment caused (1) increased levels of IGF-I (382 +/- 46 vs 294 +/- 22 micrograms/l, P < 0.05) and (2) increased basal values of free fatty acids (714 +/- 40 (GH) vs 634 +/- 64 (placebo) mumol/l, P < 0.05), 3-hydroxybutyrate (118.3 +/- 42.8 (GH) vs 57.7 +/- 21.6 (placebo) mumol/l, P < 0.05), glycerol (54.3 +/- 8.2 (GH) vs 41.4 +/- 8.4 (placebo) mumol/l, P < 0.05) and forearm uptake of 3-hydroxybutyrate, together with increments of plasma glucose (5.28 +/- 0.11 (GH) vs 4.87 +/- 0.16 (placebo) mmol/l, P < 0.05). Basal forearm uptake of glucose, isotopically determined glucose turnover and serum levels of GH, insulin and C-peptide were unaltered. During the clamp GH treatment was associated with (1) a 40% decrease in the administered amount of glucose (M-value) (P < 0.05) and (2) a 70% decrease in forearm glucose uptake (P < 0.05). Indirect calorimetry revealed a 15% increase in resting energy expenditure (P < 0.05) and a decreased basal respiratory exchange ratio (0.75 (GH) vs 0.80 (placebo), P < 0.05), presumably reflecting increased lipid oxidation.

CONCLUSIONS

Administration of GH in a therapeutic dose for 2 weeks, despite apparently normal daytime levels of major metabolic hormones, induces significant increases in circulating lipid fuel substrates, increased energy expenditure and lipid oxidation, together with insulin resistance. Such effects should be considered when applying GH treatment schedules clinically.

Effects of octreotide on insulin-like growth factor I and metabolic indices in growth hormone-treated growth hormone-deficient patients

Animals studies have demonstrated that in addition to inhibiting growth hormone (GH) secretion octreotide inhibits in a direct manner hepatic or peripheral insulin-like growth factor I (IGF-I) generation. To test this hypothesis in humans we studied ten GH-deficient patients with frequent blood sampling during 38 h on two occasions. Regular GH therapy was discontinued 72 h prior to each study period. At the start of each study a subcutaneous (sc) injection of GH (3 IU/m2) was given (at 18.00 h). In a single-blinded crossover design, patients received a continuous sc infusion of either octreotide (200 micrograms/24 h) or placebo (saline). The pharmacokinetics of GH were similar on the two occasions. The area under the curve +/- SEM of serum GH was 142.5 +/- 53.6 micrograms.l-1 x h-1 (octreotide) and 144.8 +/- 41.8 micrograms.l-1 x h-1 (placebo), (p = 0.73); Cmax (microgram/l) was 12.5 +/- 1.47 (octreotide) and 12.8 +/- 1.42 (placebo) (p = 0.83), and Tmax (h) was 6.1 +/- 0.97 (octreotide) and 5.2 +/- 0.65 (placebo) (p = 0.49). Growth hormone administration was associated with an increase in serum IGF-I (microgram/l), which was identical during the two studies, from 85.3 +/- 19.4 to 174.25 +/- 30.3 for octreotide and from 97.0 +/- 26.4 to 158.8 +/- 28.2 for placebo. Mean IGF-I levels (microgram/l) were 138.2 +/- 25.1 (octreotide) and 134.5 +/- 28.6 (placebo) (p = 0.78). Similarly, the increase in IGF binding protein 3 (IGFBP-3) levels was identical. Mean IGFBP-3 levels (microgram/l) were 2303 +/- 323 (octreotide) and 2200 +/- 361 (placebo) (p = 0.25).(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone dose regimens in adult GH deficiency: effects on biochemical growth markers and metabolic parameters

OBJECTIVE

We examined the effects of different doses of GH on insulin-like growth factor I (IGF-I), IGF binding protein 3 (IGFBP-3), body composition, energy expenditure, and various metabolites in GH deficient adults, in order to approach a metabolically appropriate GH dosage in young GH deficient adults.

DESIGN

Ten GH deficient patients (age 21-43) were studied after 4 weeks without GH followed by three consecutive 4-week periods, where the patients received in a fixed order GH 1, 2 and 4 IU/m2 s.c. per day. At the end of each period the patients were hospitalized for a 24-hour examination.

RESULTS

Mean 24-hour levels of GH (mIU/l) were 2.7 +/- 0.3 (0 GH), 7.2 +/- 0.9 (1), 10.8 +/- 1.5 (2) and 18.9 +/- 2.7 (4 IU/m2) (mean +/- SEM) (P < 0.01). Likewise, IGF-I levels increased dose dependently from 61 +/- 21 to 206 +/- 65, 260 +/- 70 and 468 +/- 171 micrograms/l (P < 0.05); serum IGF-I in an age and sex matched control group was 248 +/- 25 micrograms/l. Corresponding serum IGFBP-3 levels also increased from 1860 +/- 239 to 3261 +/- 379, 3762 +/- 434 and 4384 +/- 652 micrograms/l (P = 0.01) respectively. Significant increases in diurnal serum insulin levels after 4 IU/m2 were recorded, whereas plasma glucose levels remained unchanged. Lipid intermediates increased dose independently during GH administration. GH caused a significant increase in resting energy expenditure, whereas the respiratory exchange ratio was unaltered. Fat mass was increased without GH therapy and decreased during the study. Four patients made complaints during 4 IU/m2 GH administration, probably related to GH induced fluid retention.

CONCLUSION

Based primarily on IGF-I and IGFBP-3 levels our data suggest that a GH replacement dose in young GH deficient adults in the order of 1-2 IU/m2 per day is adequate. This is a relatively low dose as compared to dose regimens in children and adolescents.

The effect of low-dose supplementation with n-3 polyunsaturated fatty acids on some risk markers of coronary heart disease

Epidemiological data have suggested that a low dose of dietary n-3 polyunsaturated fatty acids from seafood may protect against coronary heart disease. We studied the effect of supplementation with a low dose of very long-chain n-3 fatty acids (0.65 g day-1) on plasma lipids, haemostasis, and neutrophil aggregation. Twenty-four healthy subjects were randomized to supplementation with very long-chain n-3 fatty acids or a control oil for 8 weeks. Laboratory analyses were done twice before and twice at the end of the supplementation period. The supplement with n-3 polyunsaturated fatty acid did not significantly affect plasma lipids or plasma levels of fibrinogen, factor VII, plasminogen activator inhibitor, whole blood aggregation or aggregability of neutrophil leukocytes. Therefore, the potential beneficial effect of very long-chain n-3 fatty acids in coronary heart disease is likely to be mediated through other mechanisms.

[Influence of various therapeutic models on survival after prehospital cardiac arrest]

We analyzed the outcome after prehospital cardiac arrest in a part of greater Copenhagen. Four different emergency medical systems were acting: a system providing basic life support only (group 1), a system providing basic life support and early defibrillation (group 2), a system providing basic life support followed by advanced cardiac life support (group 3), and a system providing basic life support and early defibrillation followed by advanced cardiac life support (group 4). Over a 2-year period 624 cases of cardiac arrest were reported, 34 were discharged from hospital. The survival to discharge from hospital and the one-year survival were significantly better in group 4. Our data reconfirm that early advanced cardiac life support improves survival rates for prehospital cardiac arrest.

Insulin-like growth factors (IGF) I and II and IGF binding proteins 1, 2 and 3 during low-dose growth hormone (GH) infusion and sequential euglycemic and hypoglycemic glucose clamps: studies in GH-deficient patients

To evaluate the short-term effects of growth hormone (GH), insulin and different levels of glycemia on insulin-like growth factors (IGF) I and II and IGF binding proteins (IGFBP) 1, 2 and 3, we studied six GH-deficient adolescents during a night and the following day in the postabsorptive (basal) state followed by sequential euglycemic (5 mmol/l) and hypoglycemic (3 mmol/l) glucose clamps concomitant with an intravenous infusion (starting at 24.00 h) of GH (35 micrograms/h) or saline. Current GH therapy was withdrawn 24 h prior to each study. Nocturnal levels of IGF-I, IGF-II, IGFBP-2 and IGFBP-3 remained stable during both studies. Nocturnal serum IGFBP-1 increased and correlated inversely with insulin in both studies. Regression analysis revealed a significant inverse correlation between mean nocturnal IGFBP-2 and IGFBP-3 levels. During the daytime, serum IGF-I declined slowly during saline infusion, whereas serum IGF-II remained stable in both studies. Serum IGFBP-1 displayed a gradual significant decline during the basal state and the euglycemic and hypoglycemic clamps seemed to be unaffected by GH levels. By contrast, serum IGFBP-2 remained stable during the same period in both the GH and the saline study. Serum IGFBP-3 declined insignificantly during the daytime in the saline study.(ABSTRACT TRUNCATED AT 250 WORDS)

Defective T-cell stimulatory pathways in patients after allogeneic bone marrow transplantation (BMT) in man

Immunological reconstitution after allogeneic bone marrow transplantation in man is characterized by a decreased lymphocyte transformation response to various mitogens and antigens during a period of from months to years. One reason for the decreased proliferative capability could be an inverted CD4/CD8 ratio; however, the present investigation demonstrates that this is not the only explanation for the immunodeficiency, since the CD4 as well as the CD8 subset, when studied in isolation, have qualitative defects, as evidenced by a reduced response of both subsets to stimulation with PHA, anti-CD2 and anti-CD3 MABs. The reason for the qualitative defect is unknown but a distorted composition of the CD4+ as well as the CD8+ T-cell subsets is suggested by the present investigations. We also observed that the PHA response was almost completely reconstituted one year after BMT, while the PWM response was still severely affected. The present study suggests that T-cell subsets which differ in their capacity to respond to PHA and PWM have different kinetics of reconstitution after BMT.

Subcutaneous absorption kinetics of two highly concentrated preparations of recombinant human growth hormone

OBJECTIVE

The relative bioavailability of two highly concentrated (12 IU/ml) formulations of biosynthetic human growth hormone (GH) administered subcutaneously was compared.

DESIGN

A randomized, crossover study. Conventional GH therapy was withdrawn 72 hours before each study period. There was a washout period of at least four weeks between the study periods.

SETTING

Participants were recruited from an outpatient clinic and were hospitalized during the two study periods.

PATIENTS

Fourteen GH-deficient patients (mean age 25.2 y, range 14-54). One patient was excluded from data analysis because of signs of endogenous GH secretion.

INTERVENTIONS

At the start of each study period, GH 3 IU/m2 was injected subcutaneously. The two formulations, PenFill and PenSet, differ in the buffers used and in the relative content of mannitol and glycine. Serum profiles of GH were monitored frequently for 24 hours. Samples were taken every 30 minutes for 6 hours and then hourly.

MAIN OUTCOME MEASURES

Bioavailability (F) and absorption dynamics of human GH were measured. The relative absorption fractions estimated from the areas under the individual serum concentration curves from 0 to 24 hours, and the observed time (Tmax) to reach the maximum concentration (Cmax) were determined. Short-term metabolic effects of GH on insulin-like growth factor (IGF-I), glucose, and insulin were determined.

RESULTS

The geometric mean (SD) of F was 0.910 (1,236). The 90 percent confidence interval was 0.819-1.010. Mean (+/- SD) of Cmax was 12.65 +/- 5.89 and 12.58 +/- 4.40 ng/mL for PenFill and PenSet, respectively. Corresponding values for Tmax were 5.49 +/- 1.55 and 5.89 +/- 1.79 hours for PenFill and PenSet, respectively. There was a considerable interindividual variation, but the relative absorption fraction did not significantly differ from 1 (p = 0.13). Neither Cmax (p = 0.74) nor Tmax (p = 0.58) of the two formulations was significantly different. Injection of the two formulations induced similar increments in serum IFG-I (p = 0.48). Serum insulin and blood glucose concentrations were not significantly different.

CONCLUSIONS

There is no significant difference between the absorption kinetics and short-term metabolic effects of these two highly concentrated formulations of biosynthetic GH. The two formulations are bioequivalent.

Effect of oral calcium supplementation on blood pressure in patients with previously untreated hypertension: a randomised, double-blind, placebo-controlled, crossover study

It has been claimed that calcium lowers BP. The present randomised, double-blind, placebo-controlled crossover study is the first to investigate the effect on BP of a high oral dose of calcium given for a long period to patients with previously untreated hypertension. Elemental calcium (2 g) was administered for 12 weeks interchanging with a period of 12 weeks of placebo. Twenty patients completed the protocol. There was no significant difference in change of BP during the period of additional calcium intake when compared with placebo (P = 0.33). The risk of not detecting a real BP-lowering effect of calcium of at least 3 mmHg was < 5%. No evidence for the existence of a subgroup of 'responders' was found. It is concluded that a high daily dose of calcium supplementation given for 12 weeks does not decrease BP in previously untreated patients with mild to moderate hypertension.

Lack of impact of pharmacological growth hormone administration on circulating levels of reproductive hormones during the menstrual cycle in normal women

OBJECTIVE

To evaluate the effects of pharmacological growth hormone (GH) administration on the secretion of pituitary and gonadal hormones during the menstrual cycle in normal women.

DESIGN

Randomized, double-blind, placebo-controlled crossover design.

PATIENTS, PARTICIPANTS

Six normally menstruating, healthy women, 22 to 24 years of age and with a normal body mass index.

INTERVENTIONS

Each participant was treated with placebo and growth hormone (12 IU/d) during two different 14-day periods, separated by a 6-week washout period.

MAIN OUTCOME MEASURES

Serum insulin-like growth factor I (IGF-I), estradiol, progesterone, follicle-stimulating hormone, and luteinizing hormone.

RESULTS

Administration of GH for 14 days resulted in a significant increase in serum IGF-I, whereas no changes occurred in gonadotropin or sex steroid response.

CONCLUSIONS

Growth hormone treatment during the first 14 days of menstrual cycle in normal women does not affect gonadotropin or sex steroid patterns.

Assessment of glucose turnover rates in euglycaemic clamp studies using primed-constant [3-3H]-glucose infusion and labelled or unlabelled glucose infusates

Underestimation of glucose turnover rates has been a problem in clamp studies using primed-constant [3-3H]-glucose infusion technique. Due to slow mixing in interstitial compartments concealed specific activity gradients may arise between plasma and interstitial compartments during intravenous unlabelled glucose infusion. Such specific activity gradients, however, can be prevented if plasma specific activity is maintained constant. Two euglycaemic clamp studies (insulin infusion 40 mU m-2 min-1) were performed in six lean normal subjects. Using conventional unlabelled glucose infusates plasma specific activity declined by 74%, tracer determined glucose appearance was smaller than actual glucose infusion rates (317 +/- 11 vs 366 +/- 15 mg m-2 min-1, p < 0.001), and erroneous negative values were calculated for glucose production (- 49 +/- 7 mg m-2 min-1). Average underestimation during the first 2 h correlated with glucose infusion rates (r = 0.88, p < 0.02). In contrast, when plasma specific activity was maintained constant, using appropriately labelled glucose infusates, tracer determined glucose appearance and glucose infusion rates were similar (385 +/- 16 vs 385 +/- 17 mg m-2 min-1), and negative errors for glucose production were avoided. In conclusion, using unlabelled glucose infusates, as in previous studies, suppression of glucose production is overestimated and stimulation of glucose utilization is underestimated. As errors were greater with larger glucose infusions, the mistakes may have been greatest in insulin sensitive control subjects, and smaller in insulin resistant subjects. Therefore, re-evaluation of hepatic insulin sensitivity seems appropriate in diabetes, obesity, and other insulin resistant states.

[Hepatocellular adenoma after oral contraception]

Raised serum basic phosphatase was found incidentally in a woman aged 43 years. Investigation with biopsy revealed a hepatocellular adenoma. The tumour regressed after withdrawal of Neogentrol oral contraception which the patient had consumed for 17 years. The patient did not desire invasive treatment. Employment of oral contraceptive steroids for more than two years is associated with increased occurrence of hepatocellular adenomata. The hepatocellular adenoma is a clearly delimited, most frequently solitary, benign tumour with limited malignant potential but with a considerable risk of rupture with haemorrhage even after withdrawal of oral contraception. The hepatocellular adenoma has no malignant tumour vessels (in contrast to hepatocellular carcinoma) and it appears as a cold region on scintigraphy (in contrast to focal nodular hyperplasia), but the diagnosis can only be established with certainty by histological examination. The hepatocellular adenoma consists most frequently of large pale hepatocytes in trabeculae surrounded by a net of reticulin and separated by sinusoids. Biliary passage and portal spaces do not occur. The best treatment consists of excision of the tumour or embolisation. If invasive treatment is postponed, regular scanning should be performed to observe regression or progression of the tumour and oral contraception and pregnancy should be advised against on account of the risk of growth of the tumour.

[A hypersensitive reaction after radiography of the colon]

A case of systemic allergic reaction following barium enema is described. The reaction was most probably provoked by a latex balloon on the rectal catheter.

Effect of piroxicam in addition to continuous thoracic epidural bupivacaine and morphine on postoperative pain and lung function after thoracotomy

Twenty-eight patients scheduled for lung resection with lateral thoracotomy and postoperative chest drains during combined thoracic epidural bupivacaine plus morphine and general anaesthesia were studied. Postoperative pain treatment was continuous epidural infusion of bupivacaine 0.25% 5 ml h-1 plus morphine 0.2 mg h-1 for 48 h and, in addition, the patients received rectal piroxicam 40 mg randomly and double-blind 12 h and 1 h before surgery and 20 mg 24 h-1 postoperatively or placebo. Pain was evaluated at rest, during cough and mobilisation, together with pulmonary function (FEV1, FVC, PEFR) and sensory level of analgesia repeatedly for 48 h. The results showed efficient pain relief, but without differences in pain scores or need for supplementary analgesics between the two groups. Pulmonary function decreased similarly in the two groups. Thus we were unable to show enhanced analgesia by supplementing an otherwise effective low-dose epidural bupivacaine and morphine treatment with piroxicam after thoracic surgery with chest drains.

Lack of effects of hypoglycemia on glucose absorption in healthy men

OBJECTIVE

To assess the effects of hypoglycemia on glucose absorption by examining the systemic appearance of 3-OMG (a glucose analogue that is transported by the same mechanism as glucose) after oral administration.

RESEARCH DESIGN AND METHODS

Six healthy males 22-31 yr of age were studied during a hypoglycemic (50 mg [2.7 mM]/100 ml) and a euglycemic (90 mg [5.0 mM]/100 ml) glucose clamp. At 50 min after exposure to insulin, an oral glucose load containing 20 g of glucose and 4.5 g of 3-OMG dissolved in 300 ml of tap water was administered. Insulin administration was interrupted 30 min after oral glucose administration.

RESULTS

Plasma glucose was clamped at 88 +/- 1.3 mg (4.9 +/- 0.1 mM)/100 ml during euglycemia and at 50 +/- 1.9 mg (2.7 +/- 0.1 mM)/100 ml during hypoglycemia. Concentrations of glucagon, growth hormone, cortisol, and epinephrine were significantly elevated during hypoglycemia. After 60 min, circulating 3-OMG concentrations increased to zeniths of 11.4 +/- 0.2 mg (585 +/- 10.0 mM)/100 ml (hypoglycemia) and 11.6 +/- 1.1 mg (585 +/- 56.0 microM)/100 ml (euglycemia; P = 0.95). Absorption of 3-OMG was evident between 15 and 20 min after administrations in both situations. Serum insulin was significantly lower during hypoglycemia compared with the control situation (345 +/- 50 microM [hypoglycemia], 445 +/- 50 microM [euglycemia], P = 0.03).

CONCLUSIONS

We conclude that hypoglycemia does not seem to affect intestinal absorption of glucose as judged by systemic appearance of 3-OMG.

Effects of a physiological growth hormone pulse on substrate metabolism in insulin-dependent (type 1) diabetic subjects

When present in inappropriate amounts GH induces substantial insulin resistance and it has furthermore been suggested that modest nocturnal surges of GH may precipitate the emergence of the dawn phenomenon. To characterize the metabolic effects of physiologically relevant, small-scale GH exposure, six type 1 diabetic subjects were studied for 5 h in the postabsorptive state after an iv pulse of either 210 micrograms GH or saline. Identical amounts of insulin were infused on both occasions to maintain a prevailing blood glucose concentration of 125 +/- 12 mg/100 ml. The GH bolus caused an increase in serum GH levels to a peak value of 22 +/- 2 micrograms/L after 10 min, a 70% increase in serum FFA (from 570 +/- 80 to 980 +/- 60 mumol/L) and a 400% increase in blood 3-hydroxybutyrate (3-OHB) (from 100 +/- 15 to 420 +/- 35 mumol/l) concentrations after 180 and 240 min respectively (P less than 0.05). Blood glycerol and forearm uptake of 3-OHB rose in parallel (P less than 0.01). Plasma glucose, isotopically measured glucose turnover and forearm glucose uptake was not affected by GH. Blood lactate concentrations increased (P less than 0.05) and nonoxidative glucose use and lipid oxidation tended to increase with GH. Energy expenditure remained unaffected. These results suggest that under everyday conditions GH acts as an important regulator of fuel fluxes in type 1 diabetic subjects, the main effect being a transient stimulation of lipolysis. Since no significant effect on glucose metabolism was recorded, we do not presently find evidence to support a primary role for small surges of GH in the pathogenesis of the dawn phenomenon.

Effects of growth hormone administration on fuel oxidation and thyroid function in normal man

In a randomized, double-blind, placebo-controlled, cross-over study, we examined the effects of 14 days of growth hormone (GH) administration (12 IU/d subcutaneously) on energy expenditure (EE), respiratory exchange ratio (RER), and thyroid function in 14 normal adults of normal weight (eight men and six women). EE (kcal/24 h) was significantly elevated after GH administration (2,073 +/- 392, [GH], 1,900 +/- 310, [placebo], P = .01). RER was significantly lowered during GH administration (0.73 +/- 0.04 v 0.78 +/- 0.06, P = .02), reflecting increased oxidation of lipids. Total triiodothyronine (TT3) (nmol/L) and free T3 (FT3) (pmol/L) increased significantly during GH (TT3: 1.73 +/- 0.06 [GH], 1.48 +/- 0.08 [placebo], P = .01; FT3: 6.19 +/- 0.56 [GH], 5.49 +/- 0.56 [placebo], P = .01). Concomitantly, an insignificant decrease in reverse T3 (rT3) (nmol/L) was observed (0.07 +/- 0.01 [GH], 0.15 +/- 0.01 [placebo], P = .08). GH caused a highly significant increase in T3/thyroxine (T4) (x 100) ratio (1.84 +/- 0.12 [GH], 1.37 +/- 0.06 [placebo]). Serum thyrotropin (TSH) was not significantly changed by GH. No changes in total thyroxine (TT4) (nmol/L) (98 +/- 6 [GH], 111 +/- 8 [placebo], P = .40) and free thyroxine (FT4) (pmol/L) (17.4 +/- 1.3 [GH], 18.6 +/- 1.1 [placebo], P = .37) after 14 days of GH administration were observed. In conclusion, 2 weeks of GH administration increases EE and lipidoxidation. This finding may partly be mediated by an increase in peripheral T4 to T3 conversion.

Dose-response studies on the metabolic effects of a growth hormone pulse in humans

Whereas the lipolytic and diabetogenic consequences of sustained growth hormone (GH) exposure are well described, the metabolic effects of a short-lived physiological GH pulse have only recently been reported. To assess the possible dose-response of such short-term bolus administration of GH, six healthy, male subjects were each studied thrice for 4 1/2 hours after an intravenous (IV) bolus of either 70, 140, or 350 micrograms GH, resulting in peak GH concentrations of 10, 15, and 34 micrograms/L. Observed results include: (1) Time- (but not dose-) dependent changes (P less than .05) in plasma glucose and an acute (from 10 minutes onward), persistent, 40% decrease in forearm glucose uptake. Total glucose turnover decreased steadily with time on all occasions. (2) Time- and dose-dependent increases (P less than .05) in the concentrations of circulating lipid intermediates, with an increase of 3-hydroxybutyrate (3-OHB) from a basal of 35 mumol/L to peak values of 108 +/- 34 (70 micrograms), 176 +/- 46 (140 micrograms), and 232 +/- 51 mumol/L (350 micrograms), forearm uptake of 3-OHB changed in parallel. (3) Respiratory exchange ratio decreased (P less than .05) with increasing GH doses (indicating increased lipid and decreased glucose oxidation), and energy expenditure remained unaffected. (4) Concentrations of insulin, C-peptide, and glucagon were unchanged throughout all studies. We conclude that the stimulating effects of a modest GH bolus on circulating lipid intermediates and lipid oxidation are dose-dependent. This finding underlines the potential role of GH as a principal physiological regulator of fuel consumption in the maintenance of metabolic homeostasis.

Thyroid function during growth hormone therapy

Administration of growth hormone (GH) in GH-deficient patients has been reported to cause a variety of perturbations in thyroid function. Reports range from decreased sensitivity of thyrotropin (TSH) to thyrotropin-releasing hormone (TRH) stimulation and induction of hypothyroidism to increased energy expenditure and enhanced peripheral thyroxine (T4) to triiodothyronine (T3) conversion. Some of the diversities may relate to the fact that earlier studies were uncontrolled case reports, which furthermore employed pituitary GH preparations, which may have been contaminated with TSH. A confounding variable in terms of incipient TSH insufficiency in some patients may also have been present. Data from a placebo-controlled crossover study of 4-months GH therapy in GH-deficient adults, some of whom were on ongoing T4 substitution, revealed that the most prominent effect on thyroid function was increased peripheral T4 to T3 conversion without significantly affecting TSH levels or secretion from the thyroid gland. It was furthermore observed that T3 levels during placebo were significantly decreased compared to an untreated healthy control group. Comparable findings have been made in a controlled study of 6-months GH therapy in adult-onset GH-deficient patients. More recent data suggest that these effects prevail after long-term (16 months) therapy. Similar findings have also been reported in healthy subjects receiving pharmacological GH doses. It is likely that this effect is not caused by GH per se inasmuch as reduced T4 to T3 conversion is a common observation in catabolic states with concomitant GH hypersecretion. It remains to be shown whether insulin-like growth factor I (IGF-I) stimulates peripheral deiodination.