A Study of the in Vivo Release of Luteinizing Hormone-Releasing Hormone as Estimated With the Push-Pull Perfusion Technique

171 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.The in vivo release of luteinizing hormone-releasing hormone (LHRH) from the mediobasal hypothalami (MBH) of unanesthetized rats and sheep was estimated by means of a push-pull perfusion (PPP) system. Ovariectomized (OVx) rats received 5 (mu)g estradiol benzoate at 1000 h, followed 48 h later by 1.5mg progesterone (P) or oil. Rats in which P was administered showed a significant (p < 0.01) 40-min elevation of LHRH secretion at approximately 6 h following P. Basal LHRH release in all rats was pulsatile, with pulse magnitude ranging between 0.2-lpg/10 min. The detection of LHRH was correlated with placement of the cannula tip approximately 0.5 mm from the rostral median eminence. A PPP system was also used to carry out the first examination of LHRH release during stages of the estrous cycle and following Ovx. It was found that (i) a biphasic LHRH surge occurs on proestrus which may prime and then stimulate pituitary gonadotrophes, (ii) increases in LHRH pulse amplitude occur between 1500-1900 h in diestrus I and II rats, but not in Ovx or estrus rats, and (iii) LH but not LHRH release is increased in Ovx rats, suggesting that the negative feedback effect of estrogen operates at the level of the pituitary gland. Our data are also consistent with the hypothesis that a circadian oscillator directs LHRH release during the estrous cycle, and that varying levels of circulating estrogen can modify the amplitude of the signal generated by this oscillator. The circhoral rhythm of LHRH release and its momentary relationship to pulsatile LH release was also studied in Ovx sheep using a PPP and bleeding procedure. It was demonstrated that (i) hypothalamic LHRH release in the Ovx ewe occurs in rhythmic pulses, (ii) LH pulses invariably are preceded or accompanied by LHRH pulses, and (iii) LH pulse amplitude is highly correlated with LHRH pulse amplitude. Furthermore, this study establishes the PPP technique as a direct method by which the output of LHRH can be measured and correlated on a momentary basis with circulating pituitary hormone levels.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD