HIGH LEPTIN CONCENTRATIONS IN SERUM OF VERY OBESE CHILDREN ARE FURTHER STIMULATED BY DEXAMETHASONE

Serum leptin concentrations and the levels of ob mRNA in adipocytes in obese humans are elevated. Hyperphagia and obesity are characteristic s of hypercortisolism. We have therefore asked whether or not leptin l evels were elevated in very obese children, and whether or not dexamet hasone would increase leptin levels in obese children. A single dose d examethasone suppression test was performed in ten obese chldren (5 gi rls, 5 boys; age 6 to 16 yrs, mean 12 +/- 1, median 12 yrs) to rule ou t hypercortisolism. Body mass index (BMI) in the ten children was calc ulated to be 27-45 kg/m(2). Venous blood was sampled before dexamethas one was given in the evening and at 9.00 a.m. the following morning. E ndogenous cortisol production was suppressed in all patients. Leptin l evels, as measured by a newly developed specific radioimmunoassay, wer e 31.6 +/- 12.9 ug/l, range 19.2-59.9 ug/l before dexamethasone and 39 .9 +/- 16.5 ug/l, range 26.3-80.3 ug/l after dexamethasone in the obes e children (ANOVA, p = 0.01). Simple regression analysis revealed that serum levels correlated significantly with body mass index (r = 0.82, p < 0.001). Non-obese children (BMI < 27 kg/m(2)) had leptin levels b etween 0.1 and 33.3 ug/l, median 2.2 ug/l (N = 713). Girls (5.5 +/- 4. 6 ug/l) (N = 401) had significantly higher leptin levels than boys (1. 7 +/- 2.1 ug/l) (N = 312) (p < 0.0001). We conclude that 1) high serum leptin concentrations are present in obese children. 2) A single dose of dexamethasone significantly increases the high leptin serum levels in these children. We hypothesize that glucocorticosteroids up-regula te leptin levels in the human.