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

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Abstract
The possible dependence of FSH [follicle-stimulating hormone, follitropin] peripheral concentrations on a non-steroidal, ovarian factor, was studied in adult female rats. FSH level increases during the periovulatory period were not correlated with steroid concentration decreases, and steroid [estradiol, progesterone, testosterone] administration did not result in a FSH level reduction to basal values. A negative correlation between FSH levels and large follicle (volume .gtoreq. 200 .times. 105 .mu.m3) numbers was demonstrated, and injection of steroid-free bovine follicular fluid, which contains inhibin-like activity, suppressed FSH levels to basal values. Apparently an ovarian, inhibin-like factor is involved in the fast FSH concentration regulation in the periovulatory period, and this inhibin-mediated control of FSH might play a role in the regulation of the number of follicles maturing in female rats.