Inhibin-A and estradiol content of sheep follicles and their association with follicular diameter

Abstract

This study was conducted to investigate dimeric inhibin-A and estradiol content of sheep antral follicles and their association with follicular size. Follicular content of inhibin-A and estradiol in small, medium and large antral follicles were determined by enzyme immunosorbent assay. The results showed that both estradiol and inhibin-A content of follicular fluid increased as the follicular size increased from small to medium and large-sized antral follicles. Although estradiol and inhibin-A content were significantly higher, in large antral follicles compared to small and medium-sized follicles, no significant increase was observed between medium and small follicles. These results indicated that estrogenic active follicles are capable of producing parallel quantities of inhibin-A. To investigate a possible local role for inhibin-A on estrogenic capacity of sheep granulosa cells, cells obtained from antral follicles were cultured in a chemically defined (RPMI-1640) in the presence or absence of 100 ng/ml inhibin for 24, 48 and 72 h. The results showed that granulosa cells acquire an enhanced ability for estradiol production in the absence of inhibin as the time progresses. Inhibin treatment showed no effect on estradiol production of granulosa cells. As inhibin-A is associated with follicular size and their estradiol content, it exerts no effect on estrogenic capacity of granulosa cells. Probably, inhibin-A exerts its effect on sheep follicular development through endocrine and/or paracrine routes rather than an autocrine route.