Abstract
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-17β (E<sub>2</sub>)-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 E<sub>2</sub>-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. E<sub>2</sub> 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.
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