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 characteristics of hypercortisolism. We have therefore asked whether or not leptin levels were elevated in very obese children, and whether or not dexamethasone would increase leptin levels in obese children. A single dose dexamethasone suppression test was performed in ten obese children (5 girls, 5 boys; age 6 to 16 yrs, mean 12 +/- 1, median 12 yrs) to rule out hypercortisolism. Body mass index (BMI) in the ten children was calculated to be 27-45 kg/m2. Venous blood was sampled before dexamethasone was given in the evening and at 9.00 a.m. the following morning. Endogenous cortisol production was suppressed in all patients. Leptin levels, as measured by a newly developed specific radioimmunoassay, were 31.6 +/- 12.9 microg/l, range 19.2-59.9 microg/l before dexamethasone and 39.9 +/- 16.5 microg/l, range 26.3-80.3 microg/l after dexamethasone in the obese 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/m2) had leptin levels between 0.1 and 33.3 microg/l, median 2.2 microg/l (N = 713). Girls (5.5 +/- 4.6 microg/l) (N = 401) had significantly higher leptin levels than boys (1.7 +/- 2.1 microg/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-regulate leptin levels in the human.