A Hypothalamic Follicle Stimulating Hormone-Releasing Factor

Abstract

FSH activity in 1.5 ml of rat plasma was evaluated by a new sensitive mouse uterine weight method devised by the authors. No FSH activity was found in 1.5 ml of plasma from normal females, but it was readily determined in 1.5 ml plasma from chronically ovariectomized female rats. Treatment of ovariectomized females with single, subcutaneous doses of 50 ∧g estradiol benzoate and 25 mg progesterone significantly lowered plasma FSH activity on measurement 3 days later. Ten min after the intravenous injection of a crude acidic extract of 2 rat stalk-median eminences, a significant elevation in plasma FSH occurred in the ovariectomized, estrogen, progesterone-blocked rats, whereas cerebral cortical extract was without effect on plasma FSH in these animals. Furthermore, stalkmedian eminence extract failed to alter plasma FSH in hypophysectomized rats. The extract was also ineffective when injected directly into the immature test mice for 3 days. These results indicate that contamination of the extracts with FSH cannot account for the FSHreleasing action observed. Stalk-median eminence extract also increased FSH activity in plasma of ovariectomized rats in which release of FSH had been blocked by electrolytic lesions in the median eminence, whereas cortical extract was ineffective under these conditions. It is concluded that an FSH-releasing factor resides in stalk-median eminence tissue. (Endocrinology74: 446, 1964)