The objective of this proposal is to test the hypothesis that important mechanisms by which GnRH and gonadal secretions induce and maintain sexual maturation involve changes in the biopotency as well as the quantity and pattern of the secreted gonadotropins. In this regard, the relative roles of GnRH and gonadal secretions will be separated by the use of the nutritionally restricted castrate lamb model in which endogenous GnRH secretion can be altered by nutritional modification or increased by administration of GnRH of varying frequencies and amplitudes. Comparative information will be obtained from spontaneously maturing lambs. In each of the experimental protocols we will examine the secretory profiles of gonadotropins (bioactive and immunoreactive) and correlate the changes in the B/I ratios with the relative distributions of gonadotropin isoforms following chromatofocusing. The emphasis will be on oFSH. The oFSH isohormones will be characterized for their in vitro biopotency, immunoassayability, receptor binding ability, plasma disappearance rates, and carbohydrate content. The physiological relevance of the oFSH biopotency changes will be further examined by the extraction of oFSH from various serum pools and reconstitution of oFSH free sera derived from different experimental protocols. These reconstituted sera will be tested for their ability to induce maturational indices such as induction of LH receptors in immature granulosa cells, 3H-thymidine incorporation and, if feasible, ovarian follicle growth by means of in vivo assays. Similar physiologic studies will be used to test various oFSH isoforms (of varying degees of glycosylation) derived from oFSH pituitary standards. To complement the above studies the neuroendocrine regulation of oFSH secretion will be further studied in in vitro ovine pituitary culture systems. Therefore, taken together, the proposed studies will provide an unique opportunity to dissect the mechanisms of the neuroendocrine regulation of oFSH heterogeneity at the pituitary level (post- translational modifications) and in the serum (post-secretion alterations). It will be possible to examine whether the various oFSH isoforms in the circulation during pubertal development in the lamb influence physiologic events such as organ growth and function and which FSH isohormones play key roles in target cells responsiveness.
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