Effects of estrogen on serum leptin levels and leptin mRNA expression in adipose tissue in rats.

OBJECTIVE In this study, we examined changes in serum leptin levels during the estrus cycle and the role of estrogen in these changes. METHODS We measured serum leptin levels during normal estrus cycles in intact rats and estradiol-17beta (E2)-induced artificial estrus cycles in ovariectomized rats. RESULTS Serum leptin levels increased 1.6-fold from 4.2 +/- 0.2 ng/ml during diestrus stage 2 to 6.7 +/- 0.9 ng/ml during proestrus stage during the 4-day estrus cycle. During the E2-induced estrus cycle, serum leptin levels increased 2.3-fold from 2.3 +/- 0.1 ng/ml at estrus to 5.4 +/- 1.2 ng/ml at proestrus. E2 also increased serum leptin concentrations and leptin mRNA expression in adipose tissue of immature rats. DISCUSSION These findings suggest that increased serum leptin induced by estrogen during proestrus may trigger the preovulatory release of luteinizing hormone. Furthermore, our findings indicate that estrogen has a positive effect on leptin production in adipose tissue.