Ashraf Kamel

Growth Hormone Treatment Downregulates Serum Leptin Levels in Children Independent of Changes in Body Mass Index

The changes in serum leptin levels during growth hormone (GH) treatment were studied in 27 children, 17 with GH deficiency (GHD), 10 with idiopathic short stature (ISS), and 9 with Prader-Willi syndrome (PWS). Within 1 month of GH treatment, serum leptin levels decreased by 40% in the GHD children (p < 0.01). There was no significant change in serum leptin level in the children with ISS. In children with PWS, the mean serum leptin level decreased by almost 60% after 3 months of treatment (p < 0.001). Thereafter, no further decline was observed in any of the 3 groups. Changes in body composition became evident first after the 3 months of treatment. In the GHD children, the BMI was unchanged while the mean body fat percentage was 2.7% lower after 1 year of GH treatment (p < 0.05). In the ISS children, neither BMI nor body fat percentage were significantly changed during treatment. The PWS children exhibited a significant decrease in BMI after 6 months of GH treatment without any further change during the remaining period of treatment. In this group, the mean body fat percentage decreased from 42 ± 2.4 to 28 ± 2.2% after treatment (p < 0.001). The finding that the fall in leptin occurs before changes in body composition become detectable suggests a direct effect of GH on leptin production, metabolism, or clearance.

In vitro effects of leptin on human adipocyte metabolism.

Objective: Leptin receptors are expressed in adipocytes, suggesting potential autocrine/paracrine effects. Studies on the direct effects of leptin on adipose tissue metabolism in different species have yielded controversial data. To assess the in vitro effects of leptin on human adipocyte metabolism: lipolysis, the insulin-induced inhibition of lipolysis and lipogenesis were studied in adipocytes obtained from infants and adults. Methods: Lipolysis was studied by incubating adipocytes with increasing concentrations of leptin or isoprenaline. Glycerol in the incubation medium was measured as an indicator of lipolysis. For the lipogenesis and insulin-induced inhibition of lipolysis experiments, the cells were preincubated with 0, 25, or 250 ng/ml of leptin for 2 h. Results: Leptin did not stimulate lipolysis in human adipocytes, either in children or adults. Preincubation with leptin did not affect the insulin-induced inhibition of lipolysis, but decreased the insulin-induced lipogenesis (p < 0.05). Conclusions: This study shows that leptin has no direct lipolytic effect in human adipocytes. The lack of effect on the insulin-induced inhibition of lipolysis and the negative effect on lipogenesis indicates that the effect of leptin is not at the proximal insulin-signalling pathway but further downstream.

Insulin induced hypoglycaemia: comparison of glucose and glycerol concentrations in plasma and microdialysate from subcutaneous adipose tissue

AIMS To investigate the dynamics between plasma and dialysate glucose during hypoglycaemia in children. STUDY DESIGN Six children in prepuberty or early puberty were investigated by multiple blood sampling and microdialysis of subcutaneous adipose tissue during a standard arginine–insulin tolerance test. Glucose and glycerol, as an index of lipolysis, were measured in samples from both compartments. Plasma concentrations of insulin and the main counterregulatory hormones were also measured. RESULTS Plasma and dialysate glucose concentrations were very similar at baseline and increased in concert after infusion of arginine, probably in response to glucagon release. After insulin injection, glucose in both plasma and dialysate fell in parallel. The subsequent hypoglycaemic stress response induced a rapid rebound in the plasma concentration with a mean (SD) delay in the dialysate of 16 (3) minutes. Plasma glycerol was approximately fivefold lower than in the dialysate and did not fluctuate significantly. Dialysate glycerol decreased with arginine infusion and reached a nadir immediately following insulin administration. Subsequently, the antilipolytic effect of insulin was overcome by the hypoglycaemic stress response, and lipolysis prevailed in spite of hyperinsulinaemia. CONCLUSION After rapidly induced hypoglycaemia, rebound of interstitial glucose concentrations is significantly delayed compared with plasma concentrations, and the antilipolytic effect of hyperinsulinaemia is opposed possibly by the hypoglycaemic stress response.

Growth Hormone (GH) Treatment Up-Regulates GH Receptor mRNA Levels in Adipocytes from Patients with GH Deficiency and Prader-Willi Syndrome

ABSTRACT: We have investigated the effect of growth hormone (GH) treatment on GH receptor mRNA expression in five prepubertal children with Prader-Willi syndrome and in eight patients with GH deficiency. An adipose tissue needle biopsy was taken before and after 2–4 mo of GH treatment, and RNA was isolated from adipose tissue and from adipocytes. GH receptor mRNA levels were determined by an RNase protection/solution hybridization assay. To further assess the specificity of the assay for GH receptor mRNAs, RNA extracted from human adipose tissue was subjected to Northern blot analysis. GH treatment significantly increased GH receptor mRNA levels in adipose tissue and isolated adipocytes. Our results indicate that GH may have an important role in regulating the GH receptor in humans.

Effects of growth hormone on lipolysis in humans

The ability to change the rate of lipolysis rapidly is one of the key functions of adipocytes. It is well established that adipose tissue is a target for growth hormone (GH), and many studies have been performed to determine the role of GH in the regulation of lipolysis since it was shown that growth-promoting extracts given to rats reduced the fat mass (1) and that plasma fatty acids were affected by GH (2). The results of these studies, however, are conflicting, and GH apparently has very complex effects on lipolysis. In this review, several aspects of the effects of GH on lipolysis in humans are discussed.

Antilipolytic Effect of Insulin and Insulin Receptor Messenger RNA Expression in Adipocytes of Infants, Children, and Adults

Human adipose tissue exhibits marked age-dependent differences in morphology and regulation of lipolysis. The mechanism behind this phenomenon is poorly characterized. The aim of the present investigation was to evaluate the antilipolytic effect of insulin and the expression of insulin receptor mRNA in human adipose tissue during development. To study the antilipolytic effect of insulin, lipolysis was induced with submaximal effective concentrations of isoprenaline or forskolin in adipocytes from five infants below 2 mo of age, five infants above 2 mo of age, six children, and five adults. Isoprenaline was equally effective in stimulating lipolysis in all age groups, whereas forskolin was significantly more effective in adipocytes isolated from adults than from infants and children. Increasing the concentration of insulin during the incubation allowed construction of dose-response curves of insulin inhibition of lipolysis. Maximal inhibition was observed with 30 μU/mL of insulin in the presence of either isoprenaline or forskolin. No differences in the maximal antilipolytic effect of insulin or in the insulin sensitivity expressed as ED50 were observed. Furthermore, the expression of insulin receptor mRNA in adipocytes did not differ from six infants, five children, and six adults as determined with a solution hybridization RNase protection assay. Thus, age-dependent variations in the regulation of lipolysis do not appear to be accompanied by variations in insulin action and insulin receptor gene expression in isolated adipocytes.

EFFECTS OF ARGININ-INSULIN TOLERANCE TEST ON GLUCOSE AND GLYCEROL LEVELS IN PLASMA AND IN MICRODIALYSATE FROM THE SUBCUTANEOUS ADIPOSE TISSUE

We have compared the changes in glucose concentration in dialysate and plasma and studied the effects on lipolysis in the subcutaneous adipose tissue with microdialysis during first the insulin and glucagon surge induced by arginin and thereafter under the insulin in fusion in 6 children. Before the test, the mean plasma and dialysate glucose levels were identical. During the arginin infusion, plasma glucose levels increased whereas the dialysate levels decreased. After insulin, the dialysate and plasma glucose decreased similarily; there was no delay in the dialysate. The stress induced a rapid increase in blood glucose levels but the increase in the dialysate was significantly delayed. The dialysate glycerol decreased during the arginin infusion. After insulin, no further decerease was found. Instead, all subjects showed an increased lipolysis. In conclusion, differences between interstitial and plasma glucose levels were due to a local insulin effect combined with a slow diffusion rate between blood and interstitium. The catecholamine surge induced by the hypoglycemia partly overcomes the antilipolytic effect of insulin.