The hypothalamic-hypophysial-gonadal axis in the freely behaving male rat
Pickle, Robert Lynn
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Permalink
https://hdl.handle.net/2142/23460
Description
Title
The hypothalamic-hypophysial-gonadal axis in the freely behaving male rat
Author(s)
Pickle, Robert Lynn
Issue Date
1991
Doctoral Committee Chair(s)
Ramirez, Victor D.
Department of Study
Physiology
Discipline
Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Language
eng
Abstract
It is a generally accepted finding that pulsatile luteinizing hormone (LH) secretion in the male rat is orchestrated by hypothalamic release of luteinizing hormone releasing-hormone (LHRH). A consequence of both its anatomical predicament and its rapid half-life, is that LHRH is largely undetectable in the systemic circulation and necessarily must be monitored within the vicinity of the hypothalamic-hypophysial axis. The essence of this thesis revolves around technical and methodological advances to the technique of push-pull perfusion, and their application to the hypothalamic-pituitary axis of a model that is uncomplicated by cyclic hormonal variations--the male laboratory rat.
The results presented in this thesis permit the elaboration of a model of testicular feedback regulation of the hypothalamic-pituitary axis. Foremost in this model is the orchestration of pulsatile LH release by pulsatile secretion of LHRH by a hypothalamic pulse generator that is set at a constant frequency of approximately 1 pulse every 40 min. The amount of LHRH released per pulse (its amplitude) is determined by the relative amount of testicular inhibition being exerted on a releasable LHRH pool. Secondly, pituitary LH secretion causes an episode of testosterone (T) secretion from the Leydig cells of the testis. T in turn, exerts an inhibitory effect at the level of the pituitary by decreasing the sensitivity of the gonadotrope to LHRH, and simultaneously, reduces the amplitude of the LHRH pulse. Such dual control insures that when plasma T levels eventually fall to levels no longer capable of restraining the gonadotrope, sufficient LHRH will be available to stimulate the release of LH, and thus reestablish the impetus for another volley of episodic T secretion. As such, the LHRH neurosecretory apparatus is intermittently stimulated to release LHRH commensurate with the episodic secretion of T and availability of pituitary responsiveness. Thus, LHRH levels are maintained in a state of homeostatic balance under actual physiologic conditions.
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