Submitted to: Journal of Clinical Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/1996
Publication Date: N/A
Citation: Interpretive Summary: Fat cells secrete a hormone called leptin, a product of the ob gene. We know that leptin levels in the blood are increased in obesity. Also, one study showed that treating a certain strain of infertile female mice with injections of this protein caused these mice to regain fertility, eat less and lose body weight and fat mass. We wanted to know how leptin affects the ereproductive function in women. Is it only fat mass that regulates blood leptin levels in pregnant women, or might there be other factors? We studied leptin levels in the blood of pregnant and lactating women. Our results showed that factors other than fat mass alone regulate the level of leptin in the blood of reproductive women. The women's blood leptin level rose in pregnancy; after they gave birth, the level fell along with changes not only in body weight and fat mass, but also in blood insulin. In lactating women, leptin may have affected milk production indirectly by negatively affecting blood levels of a hormone called prolactin. Reproductive hormones probably are involved in the regulation of leptin.
Technical Abstract: Experiments in ob/ob female mice demonstrated that leptin injections not only reduced body weight and fat mass, but also restored fertility. To explore factors regulating ob gene expression in reproductive women, we measured fasting serum leptin levels in pregnant and lactating women. Serum leptin per unit body fat mass was significantly higher at 36 wk of pregnancy than at 3 and 6 mo postpartum (1.25 vs. 0.75, 0.73 ng/ml-1/kg). Postpartum normalization of elevated leptin levels of pregnancy was associated with changes not only in body weight and fat mass, but also serum insulin. In lactating women, leptin may have affected milk production indirectly through its negative effect on serum prolactin levels. Our results provide evidence that factors other than fat mass alone modulate serum leptin in reproductive women.