Effects of Estradiol on Serum and Pituitary Gonadotropin Concentrations during Selective Elevations of Follicle Stimulating Hormone1

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Abstract
Release of follicle stimulating hormone (FSH) without a concomitant elevation in peripheral luteinizing hormone (LH) concentration occurs in estrous and acutely ovariectomized (ovx) proestrous hamsters. In both cases, a rapid decline in circulating estradiol-17.beta. (E2) levels is observed before the elevation in serum FSH concentration. Artificially maintained E2 levels in both estrous and ovx proestrous hamsters prevented the elevation in pituitary FSH concentration and depressed the rise in serum FSH that normally would have occurred. Pituitary LH concentrations increased in estrous hamsters given E2, but did not increase in untreated estrous controls. Serum LH concentrations remained low in both groups. Administration of E2 to ovx proestrous hamsters had little effect on pituitary or serum LH concentrations. These observations suggest that in both estrous and ovx proestrous hamsters, selective elevations in pituitary and serum FSH concentrations are dependent on the decline of peripheral E2 concentrations.