GENDER DIFFERENCES IN SERUM LEPTIN IN OBESE PEOPLE - RELATIONSHIPS WITH TESTOSTERONE, BODY-FAT DISTRIBUTION AND INSULIN SENSITIVITY

Testosterone levels are decreased in obese men but increased in obese women. The interplay between gonadal steroids and leptin is, at presen t, far from being elucidated. This study was carried out to investigat e the relationship between serum leptin. plasma insulin, insulin sensi tivity and free testosterone in 46 men (29 obese and 17 lean) and 65 p remenopausal women (42 obese and 23 lean). In all subjects, anthropome tric parameters and serum levels of insulin, leptin, free testosterone (T), dehydroepiandrosterone sulphate and sex hormone-binding globulin were measured. An oral glucose tolerance test (OGTT) and an insulin t olerance test were also performed to determine the insulin sensitivity index. Our results show a significant difference in serum leptin betw een lean and obese men (3.19 +/- 0.71 vs. 20.28 +/- 0.26 ng mL(-1); P < 0.0005) as well as between lean and obese women (10.78 +/- 2.14 vs. 34.79 +/- 2.26 ng mL(-1); P<0.00001), Basal T concentration in the obe se men was significantly lower than in the control group (18.6 +/- 1.3 vs. 23.3 +/- 1.4 ng L-1; P<0.01). whereas in the obese women it was s ignificantly higher than in the control group (2.0 +/- 0.2 vs. 1.3 +/- 0.1 ng L-1; P<0.05). When multiple linear regression was performed wi thout body mass index (BMI) in the statistical model, leptin was corre lated with basal insulin (P<0.0001), insulin sensitivity (P<0.0001) an d T (P<0.0001) in both men and women. When BMI was included in the mod el as an independent variable, leptin was significantly correlated onl y with BMI (P<0.0001), the degree of insulin resistance (P<0.05) and T (only in men, P<0.05). This study confirms that serum leptin is stron gly correlated with the degree of obesity and female sex. The negative correlation between leptin and T in men, independent of BMI, is consi stent with the hypothesis that T may possess an inhibitory effect on a dipocyte ob gene transcription.