Regulatory Role of Gonadotropins and Local Factors Produced by Ovarian Follicles on In Vitro Resistin Expression and Action on Porcine Follicular Steroidogenesis

Resistin, a hormone secreted by adipocytes, is thought to be important in reproduction. Our previous study demonstrated resistin expression in porcine ovarian follicles and its direct effect on steroidogenesis. The aim of the current study was to evaluate the effect of gonadotropins and the local ovarian factors, such as insulin-like growth factor type 1 (IGF1) and steroids (progesterone, testosterone, and 17 beta-estradiol), on the expression and secretion of resistin, as well as its steroidogenic action. Porcine ovarian follicles were exposed to follicle-stimulating hormone (FSH) and luteinizing hormone (LH) at 50-150 ng/ml, IGF1 (10-100 ng/ml), and steroids at 10(-8) to 10(-6) M for 24 h. Then, mRNA, protein expression, and medium concentration of resistin were determined using real-time PCR, Western blot analysis, and ELISA, respectively. In the subsequent experiments, ovarian follicles were exposed to resistin and/or FSH, LH, IGF1, and steroids, and ovarian steroidogenesis was analyzed. Additionally, we examined the direct effect of resistin on the protein expression of receptors for gonadotropins and investigated local factors. The results showed that gonadotropins and steroids have stimulatory effects but that IGF1 has an inhibitory effect on resistin expression and secretion. Resistin decreased gonadotropins and local hormone-induced steroid secretion and inhibited 3beta-hydroxysteroid dehydrogenase, 17beta-hydroxysteroid dehydrogenase, and cytochrome P450 aromatase protein expression. Additionally, we demonstrated that resistin increased the expression of receptors for progesterone and testosterone. These findings all show that the expression and function of resistin are regulated by gonadotropins and local factors produced by ovarian follicles.