Follicular dynamics and secretion of inhibin and oestradiol-17 beta during the oestrous cycle of the hamster.

Plasma and ovarian levels of inhibin were determined by a radioimmunoassay (RIA) at 3-h intervals throughout the 4-day oestrous cycle of hamsters. Plasma concentrations of FSH, LH, progesterone, testosterone and oestradiol-17 beta were also determined by RIAs. In addition, hamsters were injected at various times with human chorionic gonadotrophin (hCG) to determine the follicular development. The changes in plasma concentrations of FSH after injection of antisera to oestradiol-17 beta (oestradiol-AS) and inhibin (inhibin-AS) on the morning of day 2 (day 1 = day of ovulation) were also determined. Plasma concentrations of inhibin showed a marked increase on the afternoon of day 1, remained at plateau levels until the morning of day 4, then increased abruptly on the afternoon of day 4 when preovulatory LH and FSH surges were initiated. A marked decrease in plasma concentrations of inhibin occurred during the process of ovulation after the preovulatory gonadotrophin surges. An inverse relationship between plasma levels of FSH and inhibin was observed when the secondary surge of FSH was in progress during the periovulatory period. Plasma concentrations of oestradiol-17 beta showed three increase phases and these changes differed from those of inhibin. Changes in plasma concentrations of oestradiol-17 beta correlated well with the maturation and regression of large antral follicles. Follicles capable of ovulating following hCG administration were first noted at 2300 h on day 1. The number of follicles capable of ovulating reached a maximum on the morning of day 3 (24.8 +/- 0.6), and decreased by 0500 h on day 4 (15.0 +/- 1.1), corresponding to the number of normal spontaneous ovulations.(ABSTRACT TRUNCATED AT 250 WORDS)