Fsh Pleomorphism in the Rat-Regulation by Gonadal Steroids

Abstract

Molecular distribution profiles for follicle-stimulating hormone (FSH), luteinizirig hormone (LH), and thyroid-stimulating hormone (TSH) in anterior pituitary extracts from intact and gonadectomized rats of both sexes, androgen-treated orchidectomized rats, and estrogen-treated ovariectomized rats were obtained by exclusion chromatography. Hormonal activities of the extracts and of the eluted fractions were determined by radioimmunoassay. Two internal “markers”, serum albumin (SA) and ovalbumin (OA), were added to each aliquot of pituitary extract before it was applied to the column. The locations of the FSH, LH and TSH peaks were plotted in relation to those of these two standard proteins. The elution position of TSH was relatively constant; it invariably peaked just ahead of the OA marker, behind FSH and LH. Generally, LH also varied little in location, although the LH from female rats did tend to be retarded slightly. By contrast, there were distinct differences among the FSH peaks. FSH from males and androgen-treated male castrates was eluted close to the SA peak, ahead of FSH from untreated male or female castrates. FSH from intact females was eluted last, behind that from castrates. The effect of orchidectomy appears to reflect the loss of endogenous androgen, since it was completely reversed by treatment with exogenous androgen. Brief treatment with exogenous estrogen failed to reverse the effect of ovariectomy, but the possibility remains that more prolonged estrogen treatment would do so. Although gonadectomy increases the rate of FSH secretion similarly in rats of both sexes, orchidectomy and ovariectomy shifted the elution position of FSH in opposite directions. Consequently, the qualitative influences of endogenous gonadal steroids on the synthesis of FSH by the rat pituitary appear to be independent of their quantitative influences.