Gender differences in plasma leptin concentration are not influenced by menopause or hormone replacement therapy

The physiological mechanisms which regulate the production and biological activity of the hormone leptin are unclear. The purpose of this investigation was to determine whether variations in plasma estrogen related to menopause or hormone replacement therapy influence the gender difference in plasma leptin. To this end, 24 post-menopausal women were recruited [no hormone replacement therapy (-HRT n = 12) and hormone replacement therapy (+HRT, n = 12)]. A group of age and adiposity matched male (M) subjects was also studied. Subjects did not differ in age, % fat or aerobic capacity. In contrast, fat mass, waist circumference, and plasma insulin were all significantly (P < 0.05) higher in M vs both -HRT and +HRT. Plasma estrogen was significantly higher in +HRT vs = HRT (164.1 +/- 40.2 vs 37.7 +/- 17.3 pM/l, P < 0.05). Despite this four-fold variation in plasma estradiol, the plasma leptin concentration was not significantly different in the women (17.2 +/- 0.7 vs 16.9 +/- 1.1 ng/ml, -HRT vs +HRT), but remained significantly higher than in M (8.2 + 1.0 ng/ml). These data show that exogenous estrogen replacement does not affect systemic leptin levels in post-menopausal women, and that, despite four-fold variations in plasma estradiol, the gender dichotomy in plasma leptin was unaffected. The data strongly suggest that factors other than estrogen are responsible for the gender dichotomy. (C) 1998 Lippincott-Raven Publishers.