Interactions between sex steroid hormones and leptin in women. Studies in vivo and in vitro

OBJECTIVE: To investigate the associations between sex hormones and leptin. In addition, to investigate the direct effect of sex hormones by incubatio ns of human subcutaneous adipose tissue explants, in vitro. DESIGN: Cross-sectional study and an experimental in vitro study. SUBJECTS: 36 women (age, 23 - 65 y; body mass index, BMI, 19 - 65 kg/m(2)) participated in the cross-sectional study. Subcutaneous abdominal biopsies were taken from nine women (age, 28 - 46 y; BMI, 25.5 - 36.0 kg/m2) for the in vitro study. MEASUREMENTS: Fat distribution parameters (by dual-energy X-ray absorptiome try and anthropometry), sex hormones, leptin and insulin. RESULTS: Leptin correlated significantly with most estimates of adipose tis sue mass (r = 0.5 - 0.9, P < 0.05). However, when the study group was divid ed in three equal groups (non-obese, obese, and very-obese) it revealed tha t the correlation predominantly was found in non-obese. In simple correlati on analysis leptin was significantly associated with estimates of adipose t issue, insulin and several sex hormones. However, in multiple regression an alysis only insulin (partial correlation coefficient = 0.55, P < 0.004) and percentage fat mass (partial correlation coefficient = 0.72, P < 0.001) we re significantly and independently correlated with leptin without any indep endent effect of sex hormones. These findings were in agreement with the in vitro studies where neither estrogen nor androgens (testosterone or DHT) a ffected subcutaneous adipose tissue leptin production. Dexamethasone (10 nM ) stimulated adipose tissue leptin production 3-fold (P < 0.001). CONCLUSION: In regression analysis, where both insulin and measurements of fat mass were taken into account, androgens or estrogens did not independen tly contribute to the variation in leptin levels. Estrogens and androgens h ad no direct effects on adipose tissue leptin production in vitro. Thus, th e sexual dimorphism evident in serum leptin is not likely to be due to a di rect influence of sex hormones on leptin production in females.