Suppression of Serum Follicle-Stimulating Hormone by Follicular Fluid in the Maximally Estrogenized,Ovariectomized Mouse*

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Abstract
Serum levels of FSH [follicle-stimulating hormone] in ovariectomized female mice are only partially suppressed by estradiol regardless of the dosage administered. Within the detection limits, serum FSH in intact females is totally suppressed by estradiol. The maximally estrogenized, ovariectomized female was used as a test system for evaluating other nonestrogenic factors which could depress serum FSH. A transplanted ovary lowered serum FSH dramatically under such conditions. Of the large number of steroid and pituitary hormones tested, only large doses of testosterone propionate yielded any further suppression of serum FSH (24%). Charcoal-extracted follicular fluid (porcine) markedly lowered serum FSH concentrations (50% suppression), while a charcoal-extracted saline homogenate of PMS[pregnant mares serum]-treated mouse ovaries was also active in this regard (26% suppression). Charcoal-extracted porcine follicular fluid was administered to nonestrogenized, ovariectomized females, where it depressed serum FSH and markedly elevated serum LH [lutropin] concentrations. Follicular fluid may contain a nonsteroidal factor capable of acting additively with estradiol to regulate FSH secretion. The question of whether this factor also regulates LH secretion in a reciprocal fashion in the mouse requires further work.