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

Abstract

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 microU/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.

Age-Dependent Regulation of Lipogenesis in Human and Rat Adipocytes

“…This indicates that the observed difference in insulin-induced lipogenesis probably is a postbinding effect because an increased number of insulin receptors or increased insulin receptor binding should result in greater sensitivity. In accordance with these results, we previously demonstrated that the insulin receptor RNA expression as well as the sensitivity to the antilipolytic effect of insulin was similar in adipocytes from different age groups (22).…”

“…The activation of lipogenesis is mediated by stimulation of glucose transport through recruitment of GLUT4 from intracellular compartments to the plasma membrane (18) and by intracellular events increasing the activity of acetyl-coenzyme A carboxylase, fatty acid synthetase, and glycerol-3-phosphate dehydrogenase (20,21). We previously reported that neither the insulin-induced inhibition of lipolysis nor insulin receptor expression in isolated adipocytes differ among various age groups (22), but we are not aware of any studies on insulininduced lipogenesis during development.…”

In vitro Effects of Leptin on Human Adipocyte Metabolism

“…This concentration induces approximately half-maximal stimulation of lipolysis [26]. Insulin was added to a final concentration of 0.1–1,000 µU/ml.…”

“…This study was designed to investigate the in vitro effect of leptin on lipolysis, the insulin-induced inhibition of lipolysis, and lipogenesis in human adipocytes. Since others and we have previously reported that there are marked differences in adipose tissue metabolism between children and adults [22, 23, 24, 25, 26, 27], the studies were performed with adipocytes obtained from both children and adults.…”

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

“…Insulin has potent antilipolytic effects in both children and adults,6 and the absence of lipolysis products and ketone bodies during episodes of spontaneous hypoglycaemia indicates a hyperinsulinaemic pathogenesis 7. Catecholamines are the only hormones with acute and pronounced lipolytic effects after the neonatal period 8.…”