Changes in the plasma concentrations of inhibin, estradiol and progesterone during the estrous cycle of the female guinea pig

Plasma inhibin and estradiol started to increase a few days before ovulation (Day 0), decreased after ovulation and remained low during the luteal phase. A significant positive correlationship was observed between inhibin and estradiol. Plasma follicle-stimulating hormone (FSH) was low before ovulation when inhibin and estradiol were high, and high after ovulation, when both inhibin and estradiol were low. Injection of anti-inhibin serum in progesterone capsule implanted guinea pigs induced elevation of plasma FSH in a does dependent manner. These results show the first sequential changes in plasma inhibin and estradiol during the estrous cycle of guinea pigs. These results also suggest inhibin is an important factor for the regulation of FSH secretion during the estrous cycle in guinea pigs.