Leptin, cortisol, and GH secretion interactions in short normal prepubertal children

The hormonal regulation of the ob gene and leptin secretion in humans is st ill unclear. To investigate the interactions among leptin, cortisol, and GH , we analyzed and time-cross-correlated their spontaneous 24-h secretion in 12 short normal prepubertal children of both sexes (6 females and 6 males) . Time-cross-correlation analyses demonstrated that leptin and cortisol wer e correlated in both a negative and positive fashion. The negative correlat ion, with cortisol leading leptin by 4 and 3 h for boys and girls, respecti vely, might reflect the stimulatory effect of CRH on the sympathetic system , which inhibits leptin secretion; the positive correlation, with leptin le ading cortisol by 6 and 5 h for boys and girls, respectively, might reflect a direct effect of leptin on CRH secretion in the hypophyseal portal syste m. Time-cross-correlation analyses also showed a strong positive correlatio n between GH and leptin concentrations, with GH leading leptin by 5 and 2 h for boys and girls, respectively, suggesting a possible direct leptin-rele asing effect of GH on adipocytes. We conclude that cross-correlation analys es of 24-h hormone secretions under baseline physiological conditions sugge st that the hypothalamic-pituitary-adrenal axis might have a prevailing inh ibitory effect on leptin secretion, whereas leptin might exert a positive e ffect on the hypothalamic-pituitary-adrenal axis. The relation between GH a nd leptin could be a direct one and characterized prevalently by a positive effect of GH on leptin secretion. Further investigations using different e xperimental systems are needed to ascertain the validity of these mathemati cally educed conclusions.