Localization of adiponectin and its receptor and its possible roles in the ovary of a vespertilionid bat, Scotophilus heathi

Abstract

The aim of this study was to evaluate the seasonal variation in serum adiponectin levels and ovarian expression of adiponectin and its receptor in the Scotophilus heathi bat and their relationship to the changes in the body fat mass, serum insulin and luteinizing hormone (LH) levels, and ovarian activity. A very high level of circulating adiponectin was found during recrudescence, whereas a very low level of circulating adiponectin was observed during pre-ovulatory period. The increased circulating adiponectin level coincided with fat deposition, insulin resistance and hyperinsulinemia (HI) in S. heathi. Immunocytochemical study in the ovary of bat showed localization of adiponectin mainly in thecal-interstitial cells (TICs), and adiponectin receptor 1 (AdipoR1) in the granulosa cells of growing follicles, but showed no staining in atretic follicle. Seasonal changes in ovarian adiponectin and AdipoR1 levels showed two peaks (during recrudescence and ovulatory phases) coinciding with two periods of follicular development. Adiponectin in the absence of LH, as occur during recrudescence, stimulates androstenedione (A4) synthesis in vitro by up-regulating the insulin receptor (IR). Adiponectin in presence of LH, as occur during pre-ovulatory phase, inhibits A4 synthesis in vitro by down-regulating androgen receptor (AR). Further, the in vitro study showed that adiponectin, in presence of LH, also promotes luteinizing hormone receptor (LH-R) and steroidogenic acute regulatory protein (StAR) level in the ovary, which might help in development of ovulatory follicles. In brief, adiponectin in the absence of LH induces increased A4 synthesis and consequently the condition of delayed ovulation, whereas in the presence LH suppresses both synthesis and action of A4 and thus induces preovulatory condition in the ovary of S. heathi.