EFFECTS OF GENDER, BODY-COMPOSITION, AND MENOPAUSE ON PLASMA-CONCENTRATIONS OF LEPTIN

Circulating concentrations of leptin ([leptin]) vary directly with bod y mass index and percentage body fat, and may thus constitute an affer ent limb of a system regulating body fatness. We tested the hypotheses that: 1). Plasma [leptin] vary more directly with absolute fat mass t han with fractional body fatness per se; and 2). The relationship betw een fat mass and [leptin] is significantly affected by gender and by m enopausal status. [leptin] in the post-absorptive state was examined i n 67 subjects (26 male, 20 premenopausal female, 21 post-menopausal fe males; 43 never-obese, 24 obese) at usual body weight. Body compositio n was determined by hydrodensitometry, and [leptin] wase determined by a double antibody ELISA assay. In male and pre-menopausal female subj ects, subcutaneous adipose tissue aspirations were performed for deter mination of adipocyte volume by the osmium fixation method, and a 3 ho ur oral glucose tolerance tests was performed. At usual body weight, ( [leptin] was better correlated with absolute fat mass than with body m ass index (BMI) or percentage body fat. BMI and % body fat did not acc ount for any of the variance in [leptin] beyond that attributable to F M, per se. The regression equations relating FM to [leptin] did not di ffer significantly between obese and never-obese subjects. [leptin] an d fasting serum insulin concentrations were significantly correlated i n males only. [Leptin] was significantly higher in pre- and post-menop ausal females compared to males, even when [leptin] was corrected for [leptin], corrected for FM, declines significantly in women post-menop ause, this decline is not sufficient to account for the striking sexua l dimorphism in the relationship of leptin to fat mass. This sexual di morphism is apparently also due, in part, to a suppressive effect of c irculating androgens on [leptin].