Possible involvement of inhibin in the interrelationship between numbers of antral follicles and peripheral FSH concentrations in female rats

Abstract

The possible dependence of peripheral concentrations of FSH on a non-steroidal, ovarian factor, was studied in adult female rats. Increases in FSH levels during the periovulatory period were not correlated with decreases of steroid concentrations, and administration of steroids did not result in a reduction of FSH levels to basal values. However, a negative correlation between FSH levels and numbers of large follicles (volume greater than or equal to 200 x 10(5) micron 3) was demonstrated, and injection of steroid-free bovine follicular fluid, which contains inhibin-like activity, suppressed FSH levels to basal values. These results suggest that an ovarian, inhibin-like factor is involved in the fast regulation of FSH concentrations in the periovulatory period, and that this inhibin-mediated control of FSH might play a role in the regulation of the number of follicles maturing in female rats.