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

We have combined for modifications of common radioimmunoassay (RIA) techniques 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 four modifications are: a) enzymatic radioiodination, b) purification of radiolabeled hormones by Sephadex and concanavalin A chromatography, c) reduced first antibody concentration, and d) a prolonged incubation time. These methods increase the sensitivities of the RIAs and allow for the quantitation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels in small volumes of plasma. We have used these methods 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 LH releasing hormone (LHRH)-mediated LH release are distinct from those that regulate FSH secretion. Further, alterations in LHRH-pituitary interactions (elicited by injections of LHRH antisera or a potent LHRH agonist), suggest the existence of separate control mechanisms responsible for LH and FSH release at the level of the adenohypophysis. Combined, these studies provide further evidence for complex and separate neuroendocrine regulatory control over the secretion of each gonadotropin.