Regulation of the pulsatile releases of luteinizing and follicle- stimulating hormones in ovariectomized hamsters

Abstract

Four modifications of common radioimmunoassay (RIA) techniques were combined to increase the sensitivity of the gonadotropin assays by an order of magnitude compared with those generated according to the instructions provided by the National Pituitary Agency. The 4 modifications are enzymatic radioiodination; purification of radiolabeled hormones by Sephadex and concanavalin A chromatography; reduced 1st antibody concentration; and a prolonged incubation time. These methods increase the sensitivities of the RIA and allow for the quantitation of luteinizing hormone (LH) and FSH levels in small volumes of plasma. These methods were used to measure the changes in pulse frequency and amplitude of LH and FSH in ovariectomized hamsters after a variety of neuroendocrine manipulations. Alterations in catecholaminergic neurotransmission affect the frequency and amplitude of LH but not FSH release, and suggest that the hypothalamic mechanisms responsible for LHRH-mediated LH release are distinct from those that regulate FSH secretion. Alterations in LHRH-pituitary interactions (elicited by injections of LHRH antisera or a potent LRHR agonist), suggest the existence of separate control mechanisms responsible for LH an FSH release at the level of the adenohypophysis. The complex and separate neuroendocrine regulatory control over the secretion of each gonadotropin is evidenced.