Psychosocial predictors and moderators of weight management programme outcomes in ethnically diverse obese youth

BACKGROUND

An important area of research in childhood obesity is the identification of factors that predict or moderate the responses to obesity intervention programmes, yet few studies have examined the impact of self-esteem and family functioning on obesity treatment outcomes.

OBJECTIVES

We sought to determine whether baseline self-esteem and family functioning predicted or moderated childhood obesity intervention outcomes at 6 months.

METHODS

From 2009 to 2011, seventy-five 10-16 year old, racially/ethnically diverse obese youths with abnormal glucose tolerance were randomized to 6 months of an intensive family-based obesity lifestyle intervention (Bright Bodies) or routine outpatient Clinic Care. We examined youth self-concept, parent-rated family functioning and 6-month outcomes (youths' glucose tolerance, weight, body mass index and percent fat). We set the significance threshold as P ≤ 0.05 for moderator and predictor analyzes.

RESULTS

Having poor family functioning and self-concept scores indicating high anxiety and low self-esteem at baseline predicted poor 6-month outcomes overall (Bright Bodies and Clinic Care groups combined). Additionally, baseline self-esteem and family functioning moderated treatment effects such that Bright Bodies outperformed Clinic Care in youths with low self-esteem and poorly functioning families, whereas youths with high self-esteem and high-functioning families did similarly well with either intervention.

DISCUSSION

Our findings suggest intensive family-based lifestyle programmes are particularly beneficial for youth with low self-esteem and poorly functioning families.

1-Hour plasma glucose in obese youth

Adults with normal glucose tolerance (NGT) but exaggerated plasma glucose excursion at 1 h (1HPG) following the oral glucose tolerance test (OGTT) have significantly higher risk of developing impaired glucose tolerance (IGT) or diabetes. Aim of the study will be to characterize the metabolic phenotype of NGT obese youth according to values of 1HPG. To accomplish this aim, obese patients (N = 1,454; 761 men; 79 IGT; BMI z-score 2.56 ± 0.16 SDS; age 11 ± 0.7 years) from two data sets were analyzed. In all patients, empirical parameters of insulin metabolism were calculated in fasting condition and following an OGTT (1.75 mg of glucose per kilogram/body weight). Receiver-operating characteristic (ROC) analysis was performed in the first group (training set, N = 920) to establish the cutoff value of 1HPG best identifying IGT. The second set (validation set, N = 534) served to verify the goodness of the model and the identified cutoff values. 1HPG ≥ 132.5 mg/dl identified IGT with 80.8% sensitivity and 74.3% specificity in the training set (AUC 0.855, 95% CI 0.808-0.902, p < 0.0001), and 70.3% sensitivity and 80% specificity in the validation set (AUC 0.81, 95% CI 0.713-0.907, p < 0.0001), respectively. NGT patients with 1HPG ≥ 132.5 mg/dl had a metabolic phenotype (triglycerides, insulin action, and secretion) that was in between those of NGT patients with 1HPG below the threshold and IGT patients (p < 0.0001 for all the comparisons). 1HPG ≥ 132.5 mg/dl seems to be associated with increased metabolic risk in obese youth, identifying patients with lower insulin sensitivity, early secretion, and higher total insulin secretion than in obese mates with lower 1HPG.

Islet function in obese adolescents

Concurrent with the epidemic of childhood obesity, an unprecedented increase in the prevalence of several adiposity-related complications in this age group has emerged. In particular, type 2 diabetes (T2D), once considered an illness restricted to adulthood, is progressively affecting more and more adolescents, and represents now roughly 20-45% of new-onset cases in this age group. To unravel the pathogenesis of diabetes development during adolescence, many studies have focused on defining early defects in both insulin sensitivity and secretion that might be implicated in the natural history of the disease. Although a lot still need to be clarified, studies have shown that the progression from normal glucose tolerance to T2D involves intermediate stages of impaired fasting glucose and/or impaired glucose tolerance, also known as prediabetes. Insulin resistance and β-cell dysfunction represent the two major key pathogenetic defects underlying the progression to diabetes in obese youth. In this review, we have sought to mainly describe the role of β-cell function in relation to the ambient insulin resistance in the development of T2D in obese adolescents.

High prevalence of diabetes and pre-diabetes in adults with Williams syndrome

A standard oral glucose tolerance test (OGTT) was administered to 28 adults with Williams syndrome (WS). Three quarters of the WS subjects showed abnormal glucose curves, meeting diagnostic criteria for either diabetes or the pre-diabetic state of impaired glucose tolerance. Fasting mean glucose and median insulin levels did not differ significantly in the total WS cohort versus age-gender-BMI matched controls, though the glucose area under the curve was greater in the WS subjects. HbA1c levels were not as reliable as the OGTT in diagnosing the presence of diabetes. Given the high prevalence of impaired glucose regulation, adults with WS should be screened for diabetes, and when present should be treated in accordance with standard medical practice. Hemizygosity for a gene mapping to the Williams syndrome chromosome region (WSCR) is likely the major factor responsible for the high frequency of diabetes in WS. Syntaxin-1A is a prime candidate gene based on its location in the WSCR, its role in insulin release, and the presence of abnormal glucose metabolism in mouse models with aberrantly expressed Stx-1a.

High normal fasting glucose level in obese youth: a marker for insulin resistance and beta cell dysregulation

AIMS/HYPOTHESIS

A high but normal fasting plasma glucose level in adults is a risk factor for future development of type 2 diabetes mellitus and cardiovascular disease. We investigated whether normal fasting plasma glucose levels (<5.60 mmol/l) are associated with decreases in insulin sensitivity and beta cell function, as well as an adverse cardiovascular profile in obese youth.

METHODS

We performed a cross-sectional analysis in a multiethnic sample of 1,020 obese youth (614 girls and 406 boys; mean age 12.9 years [CI 95% 12.7-13.1], BMI z score 2.34 [CI 95% 2.31-2.38]) with normal fasting plasma glucose. All participants had a standard OGTT, with calculation of indices of insulin sensitivity and beta cell function. For the analysis, prepubertal and pubertal participants were stratified into quartiles of normal fasting plasma glucose.

RESULTS

We observed a significant increase in fasting insulin and AUC 2 h glucose across quartiles. Pronounced changes were observed in insulin sensitivity and secretion, particularly in the pubertal group. Moreover, the odds of presenting with impaired glucose tolerance increased by 4.5% with each 0.06 mmol/l increase in fasting plasma glucose. No significant differences in cardiovascular indices were seen across quartiles.

CONCLUSIONS/INTERPRETATION

These data suggest that in obese youth, independent of age, BMI z score, sex, family history and ethnicity, insulin sensitivity and secretion decline when moving from low to high normal fasting plasma glucose. The simple measure of fasting plasma glucose could assist clinicians in identifying children for targeted diabetes screening and subsequent lifestyle management.

Change in leptin, body composition and other hormones around menarche--a visual representation

AIM

To present a visual representation of changes in body composition, leptin, insulin, estradiol and follicular stimulating hormone (FSH) levels in relation to menarche in girls.

METHODS

Participants were a subset of healthy girls (n = 108) enrolled in a longitudinal study of growth and development conducted at the General Clinical Research Center at the Massachusetts Institute of Technology (MIT). Participants were seen annually from before menarche until 4 years postmenarche for measures of body composition and serum levels of leptin, insulin, estradiol and FSH. Body composition was determined by bioelectrical impedance. Standardized body composition and hormone levels were smoothed and plotted relative to menarche to visualize patterns of change.

RESULTS

At menarche, the mean percentage body fat (%BF) of girls was 24.6% (SD = 4.1%) after menarche %BF was approximately 27%. Leptin levels averaged 8.4 ng/mL (SD = 4.6) at menarche and were approximately 12 ng/mL after menarche. Changes in leptin levels closely paralleled changes in %BF. Insulin, estradiol and FSH levels followed expected patterns relative to menarche. Leptin began rising closer to menarche than did insulin or the other sex hormones.

CONCLUSION

We provide a visual presentation of hormonal and body composition changes occurring throughout the pubertal period in girls which may be useful in generating new hypotheses related to the timing of menarche.

Microalbuminuria in pediatric obesity: prevalence and relation to other cardiovascular risk factors

BACKGROUND

Microalbuminuria (MA) has emerged as a strong predictor of cardiovascular (CV) events, even in nondiabetic adults. While the mechanisms behind this association remain to be established, most studies suggest that MA is the result of increased vascular leakage denoting endothelial dysfunction associated with early vasculopathy.

OBJECTIVE

To examine if a urine albumin creatinine ratio (UACR) in the microalbuminuric range is related to metabolic markers of CV risk in obese and pre-diabetic youth recruited from an obesity clinic.

METHODS

MA was defined as a UACR between 2.0 and 20 mg/mmol. Subjects with gross proteinuria (UACR>20 mg/mmol) were excluded from the study. Analyses were performed to assess the relationship of MA and markers of CV risk, including body mass index (BMI), % body fat, blood pressure (BP), lipid profile, inflammatory markers, insulin sensitivity indexes and degrees of oral glucose tolerance. MA was also correlated with risk factor constellations unique to the metabolic syndrome, a distinct CV risk entity.

RESULTS

Postchallenge alterations in glucose metabolism and overall loss in insulin sensitivity were strongly and positively correlated with the presence of MA (P = 0.002 and 0.01, respectively). Neither the metabolic syndrome nor any of the individual CV risk factors examined were associated with MA.

CONCLUSIONS

These data suggest that early glucose toxicity, as reflected by postchallenge elevations in plasma glucose even below the diagnostic cutoff for diabetes mellitus may contribute to the presence of MA. Whether MA is equally as predictive of CV disease in youth, as in adulthood, remains to be investigated.

Autoantibodies from Sjögren's syndrome induce activation of both the intrinsic and extrinsic apoptotic pathways in human salivary gland cell line A-253

Sjögren's syndrome (SS) is an autoimmune rheumatic disease that targets salivary and lachrymal glands, characterized by a high concentration of serum autoantibodies directed against nuclear and cytoplasmic antigens. It is known that autoantibodies can enter viable cells and this phenomenon has functional consequences including activation of apoptotic process. The objective of this work was to explore whether autoantibodies contained in IgG purified from Sjögren sera trigger apoptotic process in an experimental model represented by the human salivary gland cell line A-253. To define if the intrinsic or extrinsic pathways are activated, we examined which caspases are critical for inducing cell death. The results have demonstrated that morphological changes and DNA laddering, consistent with apoptotic cell death, occurred in A-253 cells treated with IgG from Sjögren sera. Sjögren IgG induced cleavage and activation of the effector caspase-3 and degradation of the caspase-3 substrate poly(ADP-ribose)polymerase. Both the intrinsic and extrinsic apoptotic pathways were activated, since both caspase-8 and caspase-9 cleavages occurred. In conclusion, autoantibodies contained in IgG purified from Sjögren sera mediate apoptosis of the A-253 cell line in a caspase-dependent manner.

Development of type 2 diabetes in children and adolescents

Altered glucose metabolism in obese youth is an emerging phenomenon of the last 2 decades, strongly associated with the increase in the prevalence of childhood obesity. Peripheral insulin resistance, tightly coupled with obesity in this age group, seems to be the major driving force of deteriorating glucose metabolism. Patterns of lipid partitioning, mainly an increased deposition of fat in the intramyocellular and visceral compartments are strongly associated with insulin resistance in this population. Impaired glucose tolerance in this age group is characterized by a decline in first phase sensitivity of the beta cell while a combined decline of first and second phase sensitivity is the hallmark of type 2 diabetes. The dynamics of impaired glucose metabolism in childhood seem to be faster than in adults, representing a limited window of opportunity for successful preventive intervention.

Ethnic differences in beta cell adaptation to insulin resistance in obese children and adolescents

AIMS/HYPOTHESIS

The prevalence of altered glucose metabolism in obese children and adolescents is growing at a significant rate, especially in ethnic minorities. It is not clear whether young people of different ethnic backgrounds differ in their adaptive mechanisms to obesity-related insulin resistance. The aim of this study was to evaluate the early insulin response and insulin clearance in response to an oral glucose load in obese children and adolescents.

METHODS

Seven hundred and nine obese children and adolescents underwent an OGTT. Indices of the early insulin response and insulin clearance were compared in participants of White European, African American and Hispanic origin.

RESULTS

Participants of the three ethnic groups demonstrated similar mechanisms of adaptation to increasing insulin resistance, but with different magnitudes. African American subjects had a greater early insulin response and decreased insulin clearance than their White European and Hispanic counterparts. This happened regardless of whether the cohort was divided by glucose tolerance level or by level of insulin sensitivity. IGT across ethnic groups was characterised by a marked decline in the acute insulin response in the context of severe insulin resistance and very low insulin clearance.

CONCLUSIONS/INTERPRETATION

In obese children and adolescents, mechanisms of adaptation to obesity related to insulin resistance are similar across ethnic groups. The greater early insulin response needed to maintain glucose tolerance in young people of ethnic minorities may partially explain their greater tendency to develop type 2 diabetes.

[The strange case of a patient affected by acromegaly with osteoporomalacia without hypogonadism]

Acromegaly is a rare disease that, in the majority of cases, is due to the presence of a benign growth hormone (GH)-producing tumor of the pituitary. Growth hormone has profound effects on linear bone growth, bone metabolism, and bone mass. In acromegaly, the skeletal effects of chronic GH excess have been mainly addressed by evaluating bone mineral density (BMD). Most data were obtained in patients with active acromegaly, and apparently high or normal BMD was observed in the absence of hypogonadism. The Autors describe a case of patient affected by acromegaly without hypogonadism with serious osteoporosis and biological signs of osteomalacia.

[Prosthetic rehabilitation of edentulous patients after stroke]

AIM

Stroke is actually the 3rd cause of death in the world after cardiovascular diseases and cancer. In Italy, every year there are 100000 new cases; 2/3 of them die or become heavily disabled. The greatest part of patients which survive is old-aged and 70% of patients that survive is a removable denture wearer.

METHODS

At the Neurological Clinic of the Polyclinic Hospital of Bari we have studied 14 removable denture wearers that had had a stroke.

RESULTS

We observed that 85.7 % of removable dentures were inefficient, in 50% there will need a new removable prosthesis; 50% of persons had a bad dental hygiene; 93% of denture wearers with stroke didn't make an odontoiatric control after stroke.

CONCLUSIONS

Although the analysis of the orodental status has been carried out on a limited number of patients, the need of a greater motivation and solicitation in dental check-up is underlined. The role of the dentist in oral rehabilitation and in rehabilitation of post stroke dysphagia in stroke survivors is also examined.

Importance of plasma leptin in predicting future weight gain in obese children: a two-and-a-half-year longitudinal study

OBJECTIVE

To determine whether relatively low leptin levels predict changes in adiposity in prepubertal and pubertal obese children.

RESEARCH METHODS AND PROCEDURES

In a biracial cohort of 68 obese children (33 male and 35 female; 46 Caucasians and 22 African-Americans, age range 7-18 y), we measured at baseline fasting insulin and leptin levels, height and weight and calculated body mass index (kg/m(2)) and expressed body mass index as (BMI) Z-score. After a 2.5-y follow-up, anthropometric measurements were repeated and changes in weight gain were calculated as changes in BMI Z-score.

RESULTS

At baseline obese preadolescent boys and girls had similar age and BMI Z-score, fasting insulin and leptin levels. After an average follow-up of 2.5 y, mean weight change calculated by changes in BMI Z-score from baseline was similar in both groups. In obese adolescent boys and girls at baseline, no significant gender differences were observed for BMI Z-score and insulin levels. In contrast, plasma leptin levels were significantly higher in obese girls compared with obese adolescent boys. At follow-up, there was no significant difference in change in BMI Z-score between obese boys and girls. Multiple linear regression analysis revealed that high basal leptin levels were positively associated with greater changes in BMI Z-score only in girls (r(2)=0.18, P<0.02), after adjusting for basal BMI Z-score, Tanner stage, years of follow-up and basal insulin. High basal leptin levels in girls explained 18% of the weight gain.

CONCLUSION

High leptin levels are associated with excessive future weight gain only in girls.

Temporal patterns of circulating leptin levels in lean and obese adolescents: relationships to insulin, growth hormone, and free fatty acids rhythmicity

Alterations in nutritional status, such as obesity, markedly influence insulin, leptin, GH secretion, and free fatty acid (FFA) levels. We measured every hour for 24 h circulating leptin, insulin, GH, and FFA levels in lean and obese adolescents to determine: 1) the impact of adolescent obesity on the diurnal changes in leptin concentrations; and 2) the temporal relationships between the diurnal patterns of circulating leptin levels and insulin, GH, and FFA levels. During puberty, we found that the 24-h profile of circulating plasma leptin levels follows a bimodal pattern with minimal concentrations occurring early in the afternoon and a nocturnal elevation starting after midnight and culminating early morning. The time course of the diurnal variation in leptin levels in the obese adolescents was not different from that in lean controls. Of note, however, in obese girls leptin 24-h excursion and leptin night to day ratio were lower than those found in lean girls. In obese adolescents, mean GH levels varied significantly less during the day and night than lean controls. During the day, there were distinct preprandial increases and postprandial decreases in FFA levels, whereas after midnight FFA levels rose in both lean and obese adolescents. A significant positive correlation was found between mean plasma insulin levels between 0800 h and 2000 h and peak in leptin in lean and obese girls and boys (r = 0.63, P: < 0.001). Peak leptin was inversely correlated with the area under the nocturnal GH levels in all groups (r = -0.31, P: < 0.0003), whereas it was positively correlated with the nocturnal peak in FFA levels (r = 0.45, P: < 0.004). In summary, we report in obese adolescent girls a blunted relative diurnal excursion in leptin levels. This abnormal rhythmicity may, in part, explain their leptin resistance state. The nocturnal rise in leptin was paralleled by a nocturnal rise in GH and FFA levels. Additional studies are needed to test the potential link between the adipose-derived peptide and GH axis in humans.

Impaired in vivo stimulation of lipolysis in adipose tissue by selective beta2-adrenergic agonist in obese adolescent girls

Studies performed in adults with long-standing obesity suggest a reduced lipolytic sensitivity to catecholamines in subcutaneous abdominal adipose tissue (AT). We used microdialysis to study the in situ lipolytic effects of dobutamine (selective beta1-agonist) and terbutaline (selective beta2-agonist) on glycerol release (lipolytic index) in abdominal subcutaneous AT in 10 obese girls aged 13-17 years, BMI 38 +/- 2.1 kg/m2, and in 7 lean girls aged 11-17 years, BMI 21 +/- 1.1 kg/m2, and compared them with 10 obese women aged 21-39 years, BMI 36 +/- 1.6 kg/m2, and 10 lean women aged 18-42 years, BMI 21 +/- 0.4 kg/m2. Terbutaline at 10(-6) mol/l stimulated glycerol release more efficiently in lean girls than in obese girls (peak response approximately 350 vs. 150% of control, P < 0.01). At the lower concentration of agonist, no significant difference was seen. In women, terbutaline was more effective in lean than in obese women in stimulating glycerol release at both 10(-8) mol/l (peak response lean approximately 175% vs. obese 125% of control) and 10(-6) mol/l (approximately 300 vs. 150% of control, P < 0.05). No significant difference in glycerol release between obese and lean girls or women was detected with selective beta1-stimulation. Our data demonstrate a specific impairment in the capacity of beta2-adrenergic agonists to promote lipolysis in subcutaneous abdominal adipose tissue of obese adolescent girls and women. Thus, decreased mobilization of fat during activation of the adrenergic system might be present early in the development of adolescent obesity.

Changes in body composition after a 12-wk aerobic exercise program in obese boys

Previous studies have shown that vigorous aerobic training programs for obese children result in minimal weight changes, and concluded that they may not be beneficial. Weight change alone may not detect important beneficial changes in body composition associated with vigorous training in these children. Fifteen obese boys (aged 9-12 yr, body mass index (BMI) 31.8+/-6.5, average percent body fat (%BF) 41+/-4.2) underwent a supervised aerobic and resistance training program (12 wk, 2 days/wk for 30 min/session), to investigate the effects on weight and body composition. After the 3-month training period, weight loss averaged only 1.5+/-1.0 kg (not significant), but total body fat decreased by 4.1+/-1.8 kg (p<0.05) and fat-free mass (FFM) increased by 2.6+/-1.1 kg (p<0.05) based on hydrostatic weighing. As a result, %BF fell by 10% (p<0.01). There was a 5.8+/-2.8 mL/kg/min (p<0.05) increase in peak volume of oxygen uptake (VO(2)), along with a 248+/-120 kcal/d (p<0.05) increase in resting energy expenditure (REE). Activity questionnaires showed a significant increase in high intensity recreational activities (6.5+/-1.5 vs 3.5+/-0.5 h physical activity/wk; p<0.01) in the home and a significant decrease in low intensity activities (7+/-2.0 vs 12+/-3.5 h TV viewing/wk; p<0.01).

CONCLUSIONS

Vigorous supervised aerobic training in obese boys has beneficial effects on body composition, fitness and leisure time activities that are not apparent by measurement of changes in body weight alone.

Augmentation of alimentary insulin secretion despite similar gastric inhibitory peptide (GIP) responses in juvenile obesity

Insulin secretion rates are greater after oral glucose than after parenteral administration of an equivalent glucose load. This augmented beta-cell secretory response to an oral glucose load results from the release of mainly two gut hormones: gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1, which potentiate glucose-induced insulin secretion. Because of their insulinotropic action, their abnormal secretion may be involved in the pathogenesis of the hyperinsulinemia of childhood obesity. In this study, we used the hyperglycemic clamp with a small oral glucose load to assess the effect of childhood obesity on GIP response in seven prepubertal lean and 11 prepubertal obese children and in 14 lean adolescents and 10 obese adolescents. Plasma glucose was acutely raised to 11 mM by infusing i.v. glucose and kept at this concentration for 180 min. Each subject ingested oral glucose (30 g) at 120 min, and the glucose infusion was adjusted to maintain the plasma glucose plateau. Basal insulin and C-peptide concentrations and insulin secretion rates (calculated by the deconvolution method) were significantly greater in obese children compared with lean children (p < 0.001). Similarly, during the first 120 min of the clamp, insulin secretion rates were higher in obese than lean children. After oral glucose, plasma insulin, C-peptide, and insulin secretion rates further increased in all four groups. This incretin effect was 2-fold greater in obese versus lean adolescents (p < 0.001). Circulating plasma GIP concentrations were similar at baseline in all four groups and remained unchanged during the first 120 min of the clamp. After oral glucose, plasma GIP concentrations rose sharply in all groups (p < 0.002). Of note, the rise in GIP was similar in both lean and obese children. In conclusion, under conditions of stable hyperglycemia, the ingestion of a small amount of glucose elicited equivalent GIP responses in both lean and obese children. However, despite similar GIP responses, insulin secretion was markedly augmented in obese adolescents. Thus, in juvenile obesity, excessive alimentary beta-cell stimulation may be independent of the increased release of GIP.

Insulin: the other anabolic hormone of puberty

To determine the effect of puberty on insulin action, we used the euglycaemic-hyperinsulinaemic clamp technique in combination with stable isotopes and indirect calorimetry in lean pre-adolescents, adolescents and adults. These studies indicated that the insulin resistance induced by normal puberty alters glucose metabolism but is insufficient to adversely affect insulin-stimulated protein metabolism or to inhibit lipolysis. Using the hyperglycaemic clamp technique, we evaluated the impact of the insulin resistance on insulin secretion in pre-adolescents, adolescents and young adults. These studies revealed that the insulin and C-peptide responses to a standardized intravenous hyperglycaemic stimulus were two- to threefold greater in adolescents than in pre-adolescent children and adults. As growth hormone (GH), insulin-like growth factor I (IGF-I) and insulin levels normally peak during puberty, we examined the influence of insulin on IGF-I regulation by measuring basal GH, total and free IGF-I, and IGF binding protein (IGFBP) levels in lean adolescents and young adults. During the clamp studies, the adolescents exhibited low levels of IGFBP-1 and -2 as well as a reduced insulin-induced suppression of IGFBP-1, compared with lean adults. Thus, we postulate that the insulin resistance of puberty induces compensatory hyperinsulinaemia, which in turn suppresses circulating levels of IGFBP-1, which in turn leads to increased levels of free IGF-1.

Metabolic impact of obesity in childhood

Childhood and adolescent obesity have become the most prevalent nutritional diseases in the United States. The results of a number of studies demonstrate that the metabolic alterations caused by excess body fat are expressed early in the natural history of obesity. Such alterations seem clinically important even in children, as evidenced by the recent increase in type 2 diabetes in obese adolescents. These observations underscore the need for research efforts directed at the development of effective interventions to stem the tide of the childhood obesity epidemic.

Genetic and physiologic analysis of the role of uncoupling protein 3 in human energy homeostasis

By virtue of its potential effects on rates of energy expenditure, uncoupling protein 3 (UCP3) is an obesity candidate gene. We identified nine sequence variants in UCP3, including Val9Met, Val102Ile, Arg282Cys, and a splice site mutation in the intron between exons 6 and 7. The splice mutation results in an inability to synthesize mRNA for the long isoform (UCP3L) of UCP3. Linkage (sib pair), association, and transmission disequilibrium testing studies on 942 African-Americans did not suggest a significant effect of UCP3 on body composition in this group. In vastus lateralis skeletal muscle of individuals homozygous for the splice mutation, no UCP3L mRNA was detectable; the short isoform (UCP3S) was present in an increased amount. In this muscle, we detected no alterations of in vitro mitochondrial coupling activity, mitochondrial respiratory enzyme activity, or systemic oxygen consumption or respiratory quotient at rest or during exercise. These genetic and physiologic data suggest the following possibilities: UCP3S has uncoupling capabilities equivalent to UCP3L; other UCPs may compensate for a deficiency of bioactive UCP3L; UCP3L does not function primarily as a mitochondrial uncoupling protein.

Changes in free insulin-like growth factor-1 and leptin concentrations during acute metabolic decompensation in insulin withdrawn patients with type 1 diabetes

To determine the effect of acute insulin withdrawal and its subsequent replacement on components of the insulin-like growth factor (IGF)-1 binding protein system and on circulating leptin levels in patients with type 1 diabetes. Seventeen patients (age 31 yr +/-10) with type 1 diabetes treated with continuous subcutaneous insulin infusion (HbA1c 7.6% +/-1.0) were studied. The protocol consisted of two phases: acute insulin withdrawal of up to 8 h followed by a further 2-h period of insulin replacement. For the first phase the basal insulin infusion was stopped (at 0300 h), and for the second a single dose of either regular human or insulin lispro was given subcutaneously (0.2 U/kg). Plasma insulin, glucose, growth hormone, glucagon, IGF-1, free IGF-1, IGFBP-1, -2, -3 and leptin were measured.

RESULTS

After interruption of the basal insulin infusion, plasma free insulin levels fell from 60+/-12.0 pmol/L to 10.8+/-4.2 pmol/L, and plasma glucose rose from 5.6+/-0.4 mmol/L to 14.8+/-1.2 mmol/L (P< 0.01). During insulin withdrawal, IGFBP-1 increased by more than 6-fold (from 32+/-8 to 205+/-17 ng/mL, P<0.001), IGFBP-3 increased significantly (from 2631+/-118 to 3053+/-101 ng/mL, P<0.001), and total IGF-1 levels declined modestly (from 226+/-33 to 182+/-26 ng/mL, P<0.001). In contrast, free IGF-1 concentrations (0.72+/-0.22 ng/mL at baseline) were markedly suppressed during insulin withdrawal to values below the detection limit of the assay (0.08 ng/mL) in 15 of the 17 patients (P<0.001). Circulating plasma leptin declined markedly in females from 20+/-3 ng/mL to 11+/-2 ng/mL (P<0.0001) and in males from 10+/-2 ng/mL to 7+/-2 ng/mL (P<0.02). Within 2 h of insulin replacement, the changes in circulating concentrations of IGFBP-1 and IGFBP-3 were partially reversed, and free IGF-1 levels rebounded to 0.54+/-0.22 ng/mL (P<0.1 vs. insulin withdrawal). Growth hormone, glucagon, and IGFBP-2 levels did not change significantly throughout the study. Despite the rapid restoration of plasma insulin and substrate levels, circulating leptin levels continued to fall in the 2-h period after insulin replacement in both females and males. The marked reduction in circulating free IGF-1 after insulin withdrawal and its increase after insulin administration suggest that acute changes in IGFBP concentrations induced by insulin are important regulators of IGF-1 bioavailability in patients with type 1 diabetes. In both males and females, the rapid induction of severe insulin deficiency is associated with a consistent fall in plasma leptin levels.

The long isoform uncoupling protein-3 (UCP3L) in human energy homeostasis

The biological role(s) proposed for UCP3 in energy homeostasis have been based primarily upon amino acid sequence homology to UCP1. Spontaneous mutations of UCP3> have been described in humans, but not in rodents. The functional consequences-or lack thereof-of these mutations in humans will be of great importance in elucidating the biology of this protein. The results of two such studies are summarized here.

Intracoronary shunt prevents left ventricular function impairment during beating heart coronary revascularization

OBJECTIVE

Beating heart coronary revascularization is becoming increasingly popular world-wide. Temporary occlusion of the coronary artery is often required in order to perform the anastomosis. An alternative method to maintain perfusion is to use an intracoronary shunt. In this study, we monitored global left ventricular function and regional wall motion in the presence or absence of a shunt using transesophageal echocardiography (TEE).

METHOD

Left ventricular wall motion score index (WMSI), wall motion score (WMS) in the left anterior descending (LAD) coronary artery territory, and ejection fraction (EF%) were measured by multiplane TEE during construction of the left internal mammary artery (LIMA)-LAD coronary artery anastomosis in 40 patients undergoing revascularization with or without the use of a shunt. WMSI was assessed preoperatively, 1, 3 and 6 min during the construction of the anastomosis and after 5 min of reperfusion. WMS was assessed at 6 min during anastomosis and after 5 min of reperfusion. EF% was calculated preoperatively, 5 min into the construction of the anastomosis, and 5 min after reperfusion.

RESULTS

During construction of the anastomosis, when the shunt was used, there were no changes in WMSI, WMS in the LAD territory or EF%. A significant decline in these parameters was seen in the group in which the shunt was not used, although on reperfusion all the values returned to baseline control.

CONCLUSION

(i) occlusion of the LAD to perform the anastomosis results in temporary impairment in left ventricular function with complete recovery on reperfusion; (ii) the use of an intracoronary shunt presumably by maintaining myocardial perfusion prevents deterioration in ventricular function; (iii) from this data it seems therefore advisable to use an intracoronary shunt in patients with unstable angina, poor left ventricular function, or in cases in which a longer time to perform the anastomosis is anticipated.

The metabolic syndrome and insulin-like growth factor I regulation in adolescent obesity

Although low GH levels are commonly seen in obese adults and children, the effects of obesity on the insulin-like growth factor (IGF)/IGF-binding protein (IGFBP) system have not been established. As GH and IGF-I normally increase during adolescence, we investigated the effects of obesity on circulating total and free IGF-I levels and IGFBP-1, -2, and -3 in 19 obese adolescents [14 +/- 1 yr old; body mass index (BMI), 34 +/- 3], 20 lean adolescents (14 +/- 1 yr old; BMI, 23 +/- 0.5), and 10 lean adults (22 +/- 0.7 yr; BMI, 22 +/- 0.7). Fasting plasma insulin levels were significantly greater in obese adolescents than in either lean group, whereas circulating IGFBP-1 levels were suppressed in an inverse relationship to basal insulin (r = -0.49; P < 0.01). Low IGFBP-1 levels were associated with normal to increased free IGF-I levels in obese adolescents, even though total IGF-I values were lower than those in lean adolescents. Basal GH and IGFBP-3 levels were also lower in obese vs. lean adolescents. Basal IGFBP-1 levels were markedly reduced in obese adolescents (14 +/- 3 ng/mL) vs. those in adolescents and adults. No further suppression of IGFBP-1 levels was observed in the obese group during a two-step 8 and 40 mU/m2 insulin clamp. In contrast, IGFBP-1 levels were promptly lowered in lean adults. Basal IGFBP-2 levels were significantly lower in both groups of adolescents vs. lean adults (P < 0.05), and IGFBP-2 levels did not change during euglycemic hyperinsulinemia. These data suggest that the compensatory hyperinsulinemia that characterizes adolescent obesity chronically suppresses levels of IGFBP-1, and low IGFBP-1 concentrations may serve to increase the bioavailability of free IGF-I, which may, in turn, contribute to lower circulating GH, total IGF-I, and IGFBP-3 concentrations.

Effect of insulin on glycerol production in obese adolescents

Impaired stimulation of glucose metabolism and reduced suppression of lipolytic activity have both been suggested as important defects related to the insulin resistance of adolescent obesity. To further explore the relationship between these abnormalities, we studied seven obese [body mass index (BMI) 35 +/- 2 kg/m2] and seven lean (BMI 21 +/- 1 kg/m2) adolescents aged 13-15 yr and compared them with nine lean adults (aged 21-27 yr, BMI 23 +/- 1 kg/m2) during a two-step euglycemic-hyperinsulinemic clamp in combination with 1) a constant [2H5]glycerol (1.2 mg.m-2.min-1) infusion to quantify glycerol turnover and 2) indirect calorimetry to estimate glucose and net lipid oxidation rates. In absolute terms, basal glycerol turnover was increased and suppression by insulin was impaired in obese adolescents compared with both groups of lean subjects (P < 0.01). However, when the rates of glycerol turnover were adjusted for differences in body fat mass, the rates were similar in all three groups. Basal plasma free fatty acid (FFA) concentrations were significantly elevated, and the suppression by physiological increments in plasma insulin was impaired in obese adolescents compared with lean adults (P < 0.05). In parallel with the high circulating FFA levels, net lipid oxidation in the basal state and during the clamp was also elevated in the obese group compared with lean adults. Net lipid oxidation was inversely correlated with glucose oxidation (r = -0.50, P < 0.01). In conclusion, these data suggest that lipolysis is increased in obese adolescents (vs. lean adolescents and adults) as a consequence of an enlarged adipose mass rather than altered sensitivity of adipocytes to the suppressing action of insulin.

Decreased insulin sensitivity and compensatory hyperinsulinemia after hormone treatment in children with short stature

To assess the effects of GH treatment on carbohydrate and protein metabolism, we studied eight patients with short stature before and after the commencement of GH treatment. The hyperglycemic clamp procedure was employed to produce a hyperglycemic stimulus of 50 mg/dL above fasting levels for 120 min. These patients were then treated with 0.3 mg/kg. week GH for 6 months, after which they were restudied. Patients were compared to eight healthy control children matched for age, sex, and Tanner stage. Fasting plasma glucose did not change significantly, but fasting plasma insulin levels were higher after GH therapy (P < 0.005). Despite identical glucose increments during the glucose clamp procedure, both first, and second phase insulin responses were markedly greater after instituting GH treatment. Even in the face of higher mean plasma insulin levels after GH treatment, the rate of insulin-stimulated glucose metabolism did not differ during the last 60 min of both studies. Hence, the rate of insulin-stimulated glucose metabolism/mean plasma insulin ratio (an index of insulin sensitivity) was sharply reduced after GH treatment (P < 0.01). During the clamp, the fall in circulating branched chain amino acid levels was significantly greater after GH therapy (P < 0.02). We conclude that glucose-stimulated insulin responses are increased in short children treated with GH and that such hyperinsulinemic responses compensate for reductions in insulin sensitivity. The compensatory hyperinsulinemic responses induced by GH therapy may serve a beneficial role by augmenting insulin's anabolic effects on protein metabolism.

Acute incretin response to oral glucose is associated with stimulation of gastric inhibitory polypeptide, not glucagon-like peptide in young subjects

Oral glucose induces a greater insulin response than i.v. glucose, a difference apparently due to the secretion of gut factors ("incretins"). Studies examining the mechanisms of this finding in human subjects are limited, however, because of differences in glucose profiles. To overcome this obstacle, we studied eight young nonobese subjects using the hyperglycemic clamp with and without superimposed ingestion of oral glucose. In both studies, glucose was acutely raised by 12.5 mg/dL above fasting values by the infusion of i.v. glucose and maintained at this level for 180 min. During the experimental study, but not the control, each subject ingested oral glucose (30 g) at 120 min, and the glucose infusion was adjusted to maintain the plasma glucose plateau. Plasma insulin responses were nearly identical during both studies until oral glucose was added. After oral glucose, both plasma insulin and C-peptide levels sharply increased by 45-55% above control values (p < 0.001), indicating a potentiation of insulin secretion rather than decreased hepatic extraction of insulin. Plasma gastric inhibitory polypeptide (GIP) levels increased significantly in response to oral glucose, whereas plasma levels of glucagon-like peptide-1 (7-37) were not affected. The time course of the rise in plasma GIP and insulin was nearly identical. We conclude that the GIP response to a modest oral glucose load may play an important physiologic role in glucose-stimulated insulin secretion in healthy young subjects.

The effect of leptin is enhanced by microinjection into the ventromedial hypothalamus

To determine whether changes in food intake produced by leptin involve targeting the hormone to distinct central nervous system regions, guide cannulas were positioned stereotaxically into three brain regions--the ventromedial hypothalamus (VMH) (bilaterally, n = 6), the dorsal raphe nucleus (n = 3), and the lateral ventricle (n = 3)--of nonobese male rats (400-500 g). Daily food intake and body weight changes were measured during twice-daily injections of saline (0.1 microl) followed by recombinant human leptin (0.05 microg) for 3 days via the brain cannulas. VMH-injected rats also were followed during a postleptin saline recovery interval. This small dose of leptin did not change food intake or body weight from that during the preceding saline injection period in ventricle-injected or dorsal raphe-injected rats. In sharp contrast, VMH-injected rats ate much less food (56 +/- 8% basal) and lost 9 +/- 3 g/day or 5% of their body weight during 3 days of leptin administration. VMH-injected animals fully recovered from leptin-induced effects within 3 days. We conclude that small doses of leptin that do not effect eating behavior when delivered to the ventricle or the dorsal raphe (another brain region believed to regulate feeding), suppress food intake when injected into the VMH. These data suggest that the VMH or a brain region in close proximity to it is a key target for the biological actions of leptin.

Counterregulation in peripheral tissues: effect of systemic hypoglycemia on levels of substrates and catecholamines in human skeletal muscle and adipose tissue

We used microdialysis to distinguish the effects of hyperinsulinemia and hypoglycemia on glucose, gluconeogenic substrate, and catecholamine levels in adipose and muscle extracellular fluid (ECF). Ten lean humans (six males and four females) were studied during baseline and hyperinsulinemic (3 mU x kg-1 x min-1 for 3 h) euglycemia (5.0 mmol/l) and hypoglycemia (2.8 mmol/l). In muscle and adipose, basal ECF glucose was lower (muscle, 3.5 +/- 0.2 mmol/l; adipose tissue, 3.3 +/- 0.2 mmol/l) and lactate was higher (muscle, 2.2 +/- 0.2 mmol/l; adipose, 1.5 +/- 0.3 mmol/l) than respective plasma values (glucose, 4.9 +/- 0.1 mmol/l; lactate, 0.7 +/- 0.1 mmol/l), whereas alanine was higher in muscle ECF (379 +/- 22 micromol/l) than adipose tissue (306 +/- 22 micromol/l) and plasma (273 +/- 33 micromol/l). Plasma catecholamines (unchanged during euglycemia) rose during hypoglycemia with epinephrine, increasing approximately fivefold more than norepinephrine. In contrast, the hypoglycemia-induced increments in muscle dialysate norepinephrine and epinephrine were similar, suggesting local generation of norepinephrine. Compared with euglycemia, hypoglycemia produced a greater increase in lactate and a smaller reduction in alanine in muscle ECF, whereas hypoglycemia caused a greater relative fall in ECF glucose concentrations in muscle (72 +/- 16%) and adipose tissue (69 +/- 9%) than in plasma (42 +/- 3%) (P < 0.05). We conclude that hypoglycemia increases the generation of norepinephrine and gluconeogenic substrates in key target tissues, while increasing the plasma-tissue concentration gradient for glucose. These changes suggest the stimulation of glucose extraction by peripheral tissues, despite systemic counterregulatory hormone release and local sympathetic activation.

Co-existence of severe insulin resistance and hyperinsulinaemia in pre-adolescent obese children

To determine the time course of changes in insulin action and secretion that occur early during the development of obesity, we studied children before the onset of puberty. The reason for choosing the prepubertal stage of development is that it is metabolically characterized by both a high sensitivity to insulin and low glucose stimulated insulin responses. Fifteen obese preadolescents (8 male/7 female, age 10 +/- 0.4 years, body mass index (BMI) 31 +/- 1.2 kg/m2 Tanner Stage I) with a duration of obesity of less than 5 years and 10 non-obese preadolescents (6 male/4 female, age 10 +/- 0.4 years, BMI 18 +/- 0.9 kg/m2) matched for gender were studied. In a cross-sectional analysis, we compared responses in obese preadolescents, with those in obese adolescents and obese adults with a longer duration of obesity. The euglycaemic hyperinsulinaemic clamp with 1-13C-glucose (Hot Ginf) and indirect calorimetry were used to quantitate insulin action and the hyperglycaemic clamp used to assess beta-cell function. Insulin-stimulated glucose uptake measured at two physiological levels of hyperinsulinaemia (approximately 180 and 480 pmol) was reduced by 20 and 45% in all three groups of obese compared to non-obese subjects (p < 0.01). Defects in oxidative and non-oxidative glucose metabolism were observed in all three groups of obese subjects at the higher insulin infusion rate. The ability of insulin to inhibit lipid oxidation was impaired in all three obese groups at both levels of hyperinsulinaemia. Increases in basal and glucose-stimulated insulin levels during the hyperglycaemic clamp mirrored the reductions in glucose uptake during the insulin clamp in all obese groups. These results indicate that insulin resistance and hyperinsulinaemia co-exist in preadolescent children with moderate to severe obesity.

Hyperleptinemia: an early sign of juvenile obesity. Relations to body fat depots and insulin concentrations

Leptin, the OB gene product, is an adipocyte-derived circulating protein. In several rodent models of obesity, such as the db/db mice, fa/fa rats, and ventromedial hypothalamus-lesioned mice, as well as adult obese subjects, leptin mRNA expression and the circulating levels are elevated, suggesting resistance to its action. However, it is unknown whether the rise in leptin concentration occurs early in the natural evolution of human obesity or is a chronic adaptation to the obese state. Moreover, whether the distribution of body fat (i.e., visceral vs. subcutaneous abdominal fat) influences circulating leptin levels has not been assessed. We have determined in a group of obese and nonobese children and young adults whether leptin levels 1) are increased early in the development of obesity, 2) are related to a specific fat depot measured by magnetic resonance imaging, 3) vary during hyperinsulinemic, euglycemic, and hyperglycemic clamp studies, and 4) are different in males vs. females. In the basal state, leptin levels were elevated in obese children. Children and adults demonstrated a strong positive correlation between leptin concentrations and the subcutaneous fat depot (r = 0.84, P < 0.001). Surprisingly, a weaker correlation was found with visceral fat mass (r = 0.59, P = 0.001). Leptin levels remained unchanged under both euglycemic and hyperglycemic hyperinsulinemic conditions in both obese and nonobese subjects. A pronounced effect of gender on leptin levels was also observed. We conclude that, early in the development of juvenile obesity, leptin concentrations are elevated and are more closely linked to subcutaneous than visceral fat mass. Acute increases in insulin concentrations do not affect circulating leptin levels.

Fat distribution and cardiovascular risk factors in obese adolescent girls: importance of the intraabdominal fat depot

The regional distribution of body fat has repeatedly been found to be a significant and independent risk factor for cardiovascular disease in both obese men and women. To determine whether abnormalities in the lipid-lipoprotein profile and systolic and diastolic blood pressure are related to specific fat depots early in the course of obesity, we used magnetic resonance imaging to measure accurately intraabdominal and subcutaneous fat masses in 14 obese [body mass index (BMI; in kg/m2) 30 +/- 1.3] and 10 nonobese (BMI: 21 +/- 0.5) adolescent girls matched for age and Tanner stage of development. Intraabdominal and subcutaneous fat depots were two- to threefold greater in obese than in nonobese girls (P < 0.01). Total cholesterol, triacylglycerol, low-density-lipoprotein (LDL) cholesterol, basal insulin, and systolic and diastolic blood pressure were significantly higher in obese adolescent girls than in control subjects. In obese girls, intraabdominal fat but not BMI or waist-to-hip ratio was highly correlated with basal insulin (r = 0.55, P < 0.04), triacylglycerols (r = 0.53, P < 0.03), and high-density-lipoprotein (HDL) cholesterol (r = -0.54, P < 0.04). Femoral adipose tissue was inversely related to triacylglycerol (r = -0.51) and LDL cholesterol (r = -0.56, P < 0.05) concentrations in obese girls. The study indicates that early in the natural history of obese adolescent girls, cardiovascular risk factors are related to the amount of intraabdominal fat.

Central adiposity and its metabolic correlates in obese adolescent girls

To establish whether alterations in insulin action and secretion and their relationship to body fat distribution occur early in the course of developing obesity, we studied 14 obese adolescent girls [13.2 +/- 0.7 yr, body mass index (BMI) 32 +/- 1.4], 16 nonobese young women (24.0 +/- 0.6 yr, BMI 21.0 +/- 0.9). Insulin action was assessed by a sequential two-step (8 and 40 mU,m-2.min-1) euglycemic insulin clamp in combination with [1-13C]glucose and indirect calorimetry. Insulin secretion was determined by the hyperglycemic clamp technique (6.9 mmol/l). Magnetic resonance imaging was used to quantify visceral and subcutaneous abdominal fat depots. In obese girls, an impairment in glucose disposal was present with both insulin doses; at the higher dose, rates of glucose uptake were reduced by 30% in nonobese girls (240 +/- 30 vs. 340 +/- 19 mg.m-2.min-1, P < 0.05) and by an additional 29% (170 +/- 17 mg.m-2.min-1, P < 0.05) in obese girls. Insulin infusion failed to stimulate glucose oxidation and to suppress lipid oxidation only in obese girls. Suppression of free fatty acid levels, but not hepatic glucose production, was decreased in obese girls compared with controls. Fasting and glucose-stimulated insulin responses were greater in obese than in nonobese adolescents, who, in turn, had greater responses than lean women. In obese girls, visceral fat, but neither waist-to-hip circumference ratio nor subcutaneous fat, was highly correlated with basal insulin secretion (r = 0.89, P < 0.001), stimulated insulin secretion (r = 0.61, P < 0.05), and insulin resistance (r = -0.87, P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of puberty and diabetes on metabolism of insulin-sensitive fuels

Insulin's ability to stimulate glucose metabolism is reduced during normal puberty; these changes are exaggerated in adolescents with insulin-dependent diabetes mellitus (IDDM). Because the effects of puberty and IDDM on the other actions of insulin have not been established, we studied leucine kinetics (using [1-13C]leucine) and fat metabolism during euglycemic hyperinsulinemia (20 mU.m2.min-1) for 3 h in eight healthy and nine IDDM (HbA1 14 +/- 2%) adolescents and six healthy young adult controls. IDDM subjects received overnight low-dose insulin infusion to normalize fasting glucose. Basal and steady-state insulin values (approximately 240 pM) during the study were similar in all three groups. Insulin-stimulated glucose metabolism was reduced by 40% in healthy adolescents vs. adults (P < 0.05) and by an additional 40% in poorly controlled IDDM (P < 0.05 vs, normal adolescents). Although basal glucose and lipid oxidation rates (measured by indirect calorimetry) were similar in all three groups, when insulin was infused, glucose oxidation increased and lipid oxidation decreased only in the two nondiabetic groups. Similarly, insulin significantly reduced plasma free fatty acid levels only in the nondiabetics. Basal leucine flux (an index of protein degradation) was similar in healthy controls but was markedly increased in IDDM adolescents. Despite similar increments in plasma insulin during the clamp, leucine flux remained higher in IDDM adolescents than in healthy controls. Basal leucine oxidation rates were also increased in IDDM subjects compared with nondiabetic groups and declined to a lesser extent during insulin infusion. We conclude that insulin resistance of puberty is selective for glucose metabolism, sparing amino acid/protein metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Gender influences counterregulatory hormone responses to hypoglycemia

It has been generally assumed that counterregulatory hormone responses to hypoglycemia are not influenced by gender. To test this assumption, we analyzed three separate hypoglycemic insulin clamp studies in age-matched, healthy, non-obese females (n = 33) and males (n = 37). In one study (12 females, 17 males), plasma glucose level was rapidly decreased to about 57 mg/dL for 100 minutes with a 0.65-mU/kg/min insulin infusion. Despite an identical decrease in glucose level, the increase in epinephrine (361 +/- 64 v 188 +/- 38 pg/mL, P < .05), norepinephrine (132 +/- 28 v 47 +/- 19 pg/mL, P < .01), and growth hormone ([GH] 16.0 +/- 3.8 v 4.9 +/- 1.9 ng/mL, P < .05) levels, but not glucagon or cortisol levels, were significantly greater in males than in females, respectively. In the second study (10 females, eight males), a 5.0-mU/kg/min insulin infusion was used to decrease glucose levels to 55 mg/dL for 180 minutes. Epinephrine (P < .05) and GH (P < .01) responses were greater in males than in females. In a third study (11 females, 12 males), plasma glucose level was gradually decreased to about 50 mg/dL over 240 minutes. Again epinephrine (P < .01), norepinephrine (P < .01), GH (P < .05), and cortisol (P < .01) responses were nearly twofold greater in males (P < .01). Multivariate analysis of all 70 subjects identified gender as the most significant factor contributing to the epinephrine (P < .001) and norepinephrine (P < .005) responses, and also as a significant contributor to the GH response (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Correction of hyperinsulinemia by glyburide treatment in nondiabetic patients with thalassemia major

Hyperinsulinemia and insulin resistance precede the development of diabetes in patients with thalassemia major on hypertransfusion/desferoxamine therapy. To examine whether these early metabolic defects could be reversed, seven nondiabetic patients with thalassemia (17 +/- 4 y) were studied for 12 mo before and during 12 mo of low-dose treatment with glyburide (1.25 to 3.75 mg/d), a second-generation oral hypoglycemic agent. Plasma glucose responses to oral glucose (1.75 g/kg body weight) were normal before and after glyburide. Plasma insulin responses were markedly increased before glyburide therapy (area under insulin response curve 86 +/- 15 and 96 +/- 15 versus 40 +/- 5 nmol/min/L in normal controls, p < 0.001). However, insulin responses to glucose fell significantly after 3 mo of glyburide (to 52 +/- 7 nmol/min/L, p < 0.05 versus pretreatment) and were normalized after 12 mo (42 +/- 7 nmol/min/L, p = NS versus controls). The rate of insulin-stimulated glucose metabolism during euglycemic insulin clamps (40 mU/m2/min) was low in the patients before treatment (163 +/- 10 versus 215 +/- 17 mg/m2/min in controls, p < 0.05) and increased to 205 +/- 30 mg/m2/min after 3 mo of glyburide. The treatment was well tolerated. In conclusion, in nondiabetic, hyperinsulinemic, thalassemic patients, chronic glyburide therapy normalizes insulin responses to oral glucose. To the extent that insulin hypersecretion contributes to the development of diabetes in thalassemia, glyburide therapy may provide a means of postponing this complication of the disease.

Loss of potentiating effect of hypoglycemia on the glucagon response to hyperaminoacidemia in IDDM

IDDM subjects lose the ability to release glucagon during hypoglycemia. Because replacement of basal levels of amino acids enhances the glucagon response to hypoglycemia in healthy subjects, we tested whether raising amino acid levels during hypoglycemia could reverse the defective alpha-cell response in IDDM patients. For this purpose, 11 IDDM patients (HbA1 9.4 +/- 0.6%) and 8 healthy, nondiabetic subjects received two hypoglycemic insulin clamp studies (0.8 mU.kg-1 x min-1) in which plasma glucose was clamped at 55 mg/dl (3.08 mM) for 180 min. During one of the studies, an infusion of amino acids was superimposed between 120 and 180 min (0.3 g.kg-1 x h-1). This dose of amino acids had a small effect on plasma glucagon levels during euglycemic hyperinsulinemia that was comparable in normal and IDDM subjects. In healthy control subjects, plasma glucagon rose by 80% during the initial hypoglycemic phase of the study. The addition of amino acids produced a further sharp (200-250 ng/L, P < 0.02) rise in plasma glucagon, such a change did not occur in the absence of amino acids. In contrast, plasma glucagon in IDDM patients failed to increase during hypoglycemia alone and rose by only 40-50 ng/L (P < 0.05 vs. controls) when amino acid infusion was superimposed, even though plasma amino acid levels rose to the same extent in IDDM and control subjects. More importantly, the rise in glucagon produced by amino acids was comparable during hypoglycemic and euglycemic hyperinsulinemia in the IDDM patients, results strikingly different from those observed in nondiabetic control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor I inhibits glucose-stimulated insulin secretion but does not impair glucose metabolism in normal humans

The effect of human recombinant insulin-like growth factor I (rhIGF-1) on glucose stimulated insulin secretion was studied in 14 healthy human volunteers. Each subject received a primed-continuous infusion of rhIGF-1 (20 micrograms kg prime, 0.4 micrograms kg-1 min-1) or saline while plasma glucose was raised +2.8 mmol/l (+50 mg/dl) (n = 6) or +7.0 mmol/l (+125 mg/dl) (n = 8) above baseline for 2 h using the hyperglycemic clamp technique. Total IGF-1 levels during the IGF-1 studies increased from 196 +/- 37 to 449 +/- 71 ng/ml. At the +2.8 mmol/l (+50 mg/dl) stimulus, first and second phase C-peptide levels were suppressed during IGF-1 infusion vs control (885 +/- 157 vs 544 +/- 99 pmol/l, p < 0.05 and 1379 +/- 246 vs 832 +/- 130 pmol/l, p < 0.05, respectively), whereas insulin levels were suppressed during the second phase only (215 +/- 43 vs 151 +/- 28 pmol/l, p < 0.05). Despite this, the rate of glucose metabolism was two-fold higher in the IGF-1 infused group (8.0 +/- 0.5 vs 3.5 +/- 0.1 mg kg-1 min-1, p < 0.01). At the higher glucose stimulus +7.0 mmol/l (+125 mg/dl) only second phase C-peptide levels were significantly reduced (1922 +/- 251 vs 1466 +/- 74 pmol/l, p < 0.05). Again, rates of glucose metabolism were higher during IGF-1 infusion (11.8 +/- 1.2 vs 8.9 +/- 0.8 mg kg-1 min-1, p < 0.01). These data suggest that rhIGF-1 inhibits glucose-stimulated insulin secretion in humans, but that this inhibitory effect is partially overcome by increasing the hyperglycemic stimulus. Moreover, despite the decrease in insulin secretion, glucose disposal is accelerated by rhIGF-1.

Insulin-resistant syndromes in children

Puberty is normally associated with a decline in tissue sensitivity to insulin. However, normal glucose homoeostasis is maintained by compensatory increases in glucose-stimulated insulin secretion. Here we describe studies performed in healthy children which have determined the site of insulin resistance (hepatic vs. peripheral) and whether this resistance extends to other substrates such as amino acid and free fatty acid metabolism. The changes in insulin action and secretion that are normally seen during puberty lead us to question the role of insulin resistance in other childhood conditions that are complicated by the later development of type I or type II diabetes, namely thalassaemia major and Turner's syndrome. These studies showed that in patients with thalassaemia and Turner's syndrome, insulin resistance and increased insulin secretion are very early metabolic defects that appear before the development of diabetes.

Impaired stimulation of gluconeogenesis during prolonged hypoglycemia in intensively treated insulin-dependent diabetic subjects

Defective glucose counterregulation commonly seen in intensively treated insulin-dependent diabetes (IDDM) is mediated in part by a failure of compensatory stimulation of hepatic glucose production. Since the response of the liver to insulin-induced hypoglycemia normally involves activation of gluconeogenesis, we measured [14C]alanine conversion to [14C]glucose (a qualitative index of gluconeogenesis) and glucose production (using [3-3H]glucose) in seven intensively treated type I diabetic subjects (hemoglobin-A1, 7.1 +/- 0.4%) during low dose infusion of insulin (0.3 mU/kg.min for 210 min). IDDM patients received insulin overnight to maintain euglycemia before study. Although insulin levels rose to a similar extent as those in normal control subjects (n = 6), the fall in plasma glucose was markedly greater in IDDM (2.5 +/- 0.2 vs. 3.64 +/- 0.2 mM in controls; P < 0.01). The glucagon response was totally lost in IDDM, and epinephrine release was delayed and slightly reduced compared to that in control subjects. In contrast to that in normal subjects, hepatic glucose production in the IDDM subjects remained persistently suppressed by about 60% throughout the study. The conversion of alanine and lactate to glucose remained virtually unchanged in the IDDM, whereas in controls it increased 2-fold above baseline during the last hour of the study. Our data suggest that the failure of gluconeogenesis to increase during hypoglycemia is an important factor contributing to the defective hepatic response observed in the intensively treated type I diabetic subjects.

Effect of growth hormone treatment on hyperinsulinemia associated with Turner syndrome

To determine whether the insulin resistance in patients with Turner syndrome, which may be exaggerated by treatment with human growth hormone, leads to excessive insulin secretion, we applied the hyperglycemic glucose-clamp technique to produce a standard hyperglycemic stimulus (6.9 mmol/L, or 125 mg/dl, greater than fasting plasma glucose level for 120 minutes) in seven patients with Turner syndrome and in seven healthy children. These studies were repeated in the patients after 6 to 12 months of therapy with growth hormone. Fasting plasma levels of insulin were comparable in control subjects and patients before therapy but increased significantly in the patients after 6 to 12 months of treatment with growth hormone. Despite identical glucose increments in the two groups during the glucose-clamp procedure, both first- and second-phase insulin responses were significantly greater in the patients than in the control subjects. Moreover, the hyperinsulinemic responses to glucose were markedly exaggerated in the patients after their treatment with growth hormone, reaching values (first phase 474 +/- 100 pmol and second phase 826 +/- 100 pmol; p less than 0.02 vs pretreatment values) that were almost threefold greater than those in control subjects (p less than 0.001). Nevertheless, the rate of insulin-stimulated glucose metabolism during the last 60 minutes of the clamp procedure was similar in all three groups of studies. Glycosylated hemoglobin, total cholesterol level, and blood pressure remained normal in patients after therapy with growth hormone. We conclude that glucose-stimulated insulin response is increased in patients with Turner syndrome and that these alterations are further exaggerated by treatment with growth hormone. These hyperinsulinemic responses appear to compensate for reductions in insulin sensitivity.

Impairment of counterregulatory hormone responses to hypoglycemia in pregnant women with insulin-dependent diabetes mellitus

Intensive insulin therapy directed at elimination of hyperglycemia is advocated during pregnancy in women with insulin-dependent diabetes mellitus. Because such treatment is complicated by frequent hypoglycemic episodes, we evaluated maternal and fetal responses in nine intensively treated pregnant women with insulin-dependent diabetes mellitus during an insulin-induced, gradual, controlled fall in plasma glucose levels. In contrast to values in nonpregnant control women, reductions in glucose to 44 +/- 2 mg/dl in pregnant diabetic patients failed to elicit an increase in glucagon levels. Epinephrine release during hypoglycemia was also markedly suppressed in the pregnant diabetic subjects (106 +/- 32 vs 327 +/- 52 pg/ml in controls, p less than 0.001). Furthermore, the plasma glucose level at which epinephrine and growth hormone were released was 5 to 10 mg/dl lower in the pregnant women with insulin-dependent diabetes mellitus (p less than 0.05). The basal fetal heart rate remained unchanged and continued to manifest accelerations during the hypoglycemic state. We conclude that the high frequency of hypoglycemia in intensively treated pregnant women with insulin-dependent diabetes mellitus may be due in part to impaired counterregulatory hormonal responses.

Growth hormone and insulin interactions

Insulin and glucose clamp techniques were used to investigate insulin action and insulin secretion during childhood. Preliminary results suggest that growth hormone (GH) therapy leads to changes in glucose, amino acid and insulin responses that are qualitatively similar to those observed during puberty. Furthermore, the insulin resistance normally seen during puberty may be restricted to peripheral glucose metabolism. In patients with Turner's syndrome, data indicate that there is an increase in the glucose-stimulated insulin response which is exaggerated by GH treatment.

Pituitary response to growth hormone-releasing hormone in IDDM. Abnormal responses to insulin and hyperglycemia

In poorly controlled insulin-dependent diabetes mellitus (IDDM), hyperglycemia fails to inhibit the pituitary response to growth hormone-releasing factor (GRF). To evaluate whether this derangement is reversed by a simultaneous elevation of circulating insulin, 0.3 micrograms/kg i.v. GRF 1-40 was administered to nine poorly controlled IDDM subjects (HbA1 greater than 11.1%) with and without concomitant infusion of insulin. In the absence of insulin, the poorly controlled IDDM subjects demonstrated a growth hormone response to GRF similar to that of nondiabetic subjects, despite marked hyperglycemia (approximately 16.8 mM). When insulin was infused into these same patients (insulin clamp) to produce combined hyperinsulinemia (528 +/- 90 pM) and hyperglycemia (16.5 +/- 1.98 mM), the GRF-induced growth hormone rise was markedly exaggerated (65 +/- 11 vs. 20 +/- 4 micrograms/L without insulin infusion, P less than 0.001). This enhancement of GRF-stimulated growth hormone release by insulin was strikingly attenuated (22 +/- 7 micrograms/L) in five well-controlled diabetic subjects studied under conditions of similar hyperinsulinemia (486 +/- 84 pM) and hyperglycemia (16.41 +/- 0.95 mM). In contrast, in nondiabetic subjects, acute hyperinsulinemia reduced the growth hormone response to GRF. We conclude that the failure of hyperglycemia to block the pituitary response to GRF in poorly controlled diabetes is not attributable to the lack of a coincident increase in circulating insulin. The paradoxical stimulatory effect of insulin on GRF-induced growth hormone release may contribute to the high spontaneous growth hormone levels characteristically seen in poorly controlled insulin-treated patients, and its attenuation after intensive insulin therapy may contribute to the reversal of growth hormone hypersecretion in well-controlled diabetic patients.

Does insulin species modify counterregulatory hormone response to hypoglycemia?

OBJECTIVE

To examine whether pork and human insulin induce different counterregulatory responses to hypoglycemia.

RESEARCH DESIGN AND METHODS

The responses to a mild hypoglycemic stimulus were determined in 35 healthy young adults with the glucose-clamp technique to ensure standardization of glucose and insulin levels. Either pork (n = 15) or human (n = 20) regular insulin was infused (0.8 mU.kg-1.min-1) to lower plasma glucose from 4.7 +/- 0.07 to 3.3 +/- 0.04 mM (both groups) over approximately 40 min. Plasma glucose was maintained at that level (with variable rate glucose infusion) for an additional 60 min.

RESULTS

Steady-state insulin levels were similar in both groups (316 +/- 50 vs. 280 +/- 29 pM, pork vs. human). Before insulin administration, basal counterregulatory hormone levels were indistinguishable. Most importantly, after plasma glucose was lowered, hormonal responses were nearly identical. No significant differences in peak values of epinephrine (1769 +/- 404 vs. 1775 +/- 311 pM, pork vs. human), norepinephrine (1.64 +/- 0.23 vs. 1.87 +/- 0.20 nM, pork vs. human), glucagon (163 +/- 29 vs. 175 +/- 20 ng/L, pork vs. human), growth hormone (14 +/- 3 vs. 17 +/- 3 micrograms/L, pork vs. human), or cortisol (543 +/- 83 vs. 458 +/- 28 nM, pork vs. human) occurred.

CONCLUSIONS

Our data suggest that pork and human insulin produce a comparable and robust hormonal response in healthy adults under conditions of controlled hypoglycemia.