Leptin correlates with measures of body fat stores. Growth hormone (GH) treatment may affect leptin levels either directly or indirectly by influencing body composition and circulating insulin level. Here, the effects of GH treatment on the leptin axis and body composition of six severely obese, but otherwise healthy, prepubertal boys were studied. Fasting serum leptin was significantly reduced after only 3 wk of GH treatment. Body fat percentage, but not BMI, decreased significantly (p < 0.05) after 3 mo. The serum leptin concentration per unit fat mass decreased significantly during GH treatment (p < 0.05), suggesting that such treatment might have a direct effect on serum leptin independently of the effects on body composition. Leptin RNA expression in abdominal subcutaneous tissue was not significantly changed by treatment.
Conclusions: The data indicate that GH has an early downregulatory effect on the circulating leptin level independently of the concomitant changes in body composition. Whether GH affects leptin production or metabolism needs further study.