REGULATION OF IN-VIVO GROWTH-HORMONE SECRETION BY LEPTIN

Leptin, the product of the ob gene, is a recently discovered hormone s ecreted by adipocytes that regulates food intake and energy expenditur e. Growth hormone (GH) secretion is markedly influence by body weight being markedly suppressed in obesity and underweight. The aim of the p resent study was to study whether leptin can act as a metabolic signal connecting the adipose tissue with the growth hormone axis. We admini stered leptin antiserum (10 ul, ic.v.) or normal rabitt serum (NRS; 10 ul, i.c.v.) to freely moving fed rats. Furthermore we assessed the ef fect of leptin administration (10 ug, i.c.v.) on fed and fasted rats. Spontaneous GH secretion was assessed over 6 hours with blood samples taken every 15 min. Administration of leptin antiserum led to a decrea se in spontaneous GH secretion as assessed by the area under the curve (AUC) (168+/-72 ng/ml/6h) in comparison to NRS-treated rats (813+/-17 9 ng/ml/6h,p<0.01). While leptin administration (10 ug/rat; i.c.v.) to normal fed rats did not modify spontaneous GH secretion, leptin admin istration to fasted rats led to a reversal of the inhibitory effect ex erted by fasting on GH secretion (AUC, 1650+/-351 ng/ml/6h vs 77+/-32 ng/ml/6h,p<0.01). This data suggests that leptin is a metabolic signal that regulates GH secretion.