Characterization of Luteinizing Hormone - Releasing Hormone (Lhrh) Release From Rat Hypothalamus Using an in Vitro System

128 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.The effect of a variety of experimental compounds on the release of immunoreactive luteinizing hormone-releasing hormone (LHRH) from rat hypothalamus was examined using an in vitro superfusion system and sensitive assays for LHRH measurement. High extracellular (60 mM) K('+) ion repeatedly stimulated in vitro LHRH release, an effect attributed to nerve membrane depolarization triggering influx of Na('+) and Ca('++) ions and resulting in exocytosis of LHRH. K('+)-evoked LHRH release was strongly Ca('++)-dependent; however, Na('+) influx was not obligatory in depolarization-induced release. In support of calcium's role in LHRH release, agents permitting influx of Ca('++) (inophore A23187) or increased Ca('++) leakage from intracellular Ca('++) stores (2,4-dinitrophenol) stimulated LHRH release. K('+)-evoked release of LHRH is also thought to involve a microtubular transport mechanism, since colchicine (10('-6) or 10('-5) M) inhibited K('+)-stimulated LHRH output. However, 10('-4) M colchicine dramatically increased LHRH release as well as hypothalamic LHRH content by an unknown mechanism.The release of LHRH is possibly mediated through adenyl cyclase/cyclic AMP, supported by the finding that adenyl cyclase activators (prostaglandin E, and elevated Mg('++) concentration) and cyclic AMP derivatives stimulated in vitro LHRH release. Employing intermittent delivery of dibutyryl cyclic AMP, mean LHRH release was repeatedly triggered, as assessed by specific assay employing Root anti-LHRH serum. This synchronous LHRH release was Ca('++)-dependent. Intriguingly, cyclic AMP-synchronized LHRH release was not observed when NETT or Chen-Ramirez anti-LHRH sera were used in LHRH measurement, in spite of the fact that spontaneous LHRH release and post-superfusion tissue LHRH content did not differ among the three LHRH assays. These results suggest the existence of immunologically distinct hypothalamic LHRH molecules, a fraction of which are released in response to intermittent cyclic AMP administration and recognized as immunogenic by Root anti-LHRH but to a lesser degree by Nett and Chen-Ramirez LHRH antibodies.Taken together, these results suggest that Ca('++) ion plays a crucial role in K('+)-stimulated LHRH release from rat hypothalamic fragments superfused in vitro. In addition, it can be postulated that a microtubular transport mechanism is an important component of the LHRH neurosecretory process. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMIU of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD