Serum leptin levels during recombinant human GH therapy in adults with GH deficiency.

OBJECTIVE Recent studies suggest an involvement of the obese (OB) gene and its product leptin in the regulation of body fat. Since adults with growth hormone deficiency (GHD) have a high body fat mass which can be normalized with recombinant human (rh) GH therapy, we investigated whether GH influences serum leptin directly or indirectly via its lipolytic effect. DESIGN Fourteen adults with GHD were treated with subcutaneous injections of rhGH given every evening for 52 weeks. Serum leptin, fat mass and body fat percentage were measured at baseline and after 4 and 52 weeks of treatment. METHODS Serum leptin was measured with a commercially available RIA. Total body water was determined by dilution of deuterium. Fat free mass was estimated by assuming a hydration of 73%. Fat mass was estimated by subtracting fat free mass from weight. RESULTS At baseline, serum leptin levels were exponentially related to body fat percentage (r = 0.88; P < 0.0005). rhGH treatment for 4 weeks did not significantly influence serum leptin levels, whereas treatment for 52 weeks significantly decreased serum leptin levels (15.6 +/- 2.9 to 10.8 +/- 2.1 micrograms/l; P = 0.020). Fat percentage was significantly decreased after 52 weeks of treatment (37.6 +/- 2.1 to 33.8 +/- 2.5%; P < 0.0005). The decrease in serum leptin could largely be explained by the decrease in body fat percentage, whereas the relation between leptin and body fat percentage did not change. CONCLUSIONS The influence of GH on serum leptin in indirect, via its effect on body fat percentage.