Lack of involvement of arachidonic acid metabolism in chicken gonadotropin-releasing hormone II (cGnRH-II) stimulation of gonadotropin secretion in dispersed pituitary cells of goldfish, Carassius auratus. Identification of a major difference in salmon GnRH and chicken GnRH-II mechanisms of action.
Gonadotropin (GTH) release in static incubations of dispersed goldfish pituitary cells was stimulated by chicken GTH-releasing hormone II (cGnRH-II), salmon (s)GnRH, phospholipase A2, phospholipase C, phospholipase D, and arachidonic acid (AA). Coincubations with nordihydroguaiaretic acid (NDGA), 5,8,11,14-eicosatetraenoic acid, and indomethacin did not alter the GTH responses to cGnRH-II. In contrast, NDGA reduced sGnRH-stimulated GTH release. Incubation with Ca(2+)-deficient medium abolished the GTH responses to cGnRH-II, reduced sGnRH-stimulated GTH release, but did not alter AA actions on GTH secretion. Apomorphine, a dopamine agonists that had been shown to partially inhibit the GTH responses to sGnRH and to abolish those induced by cGnRH-II, did not affect the hormone response to AA. However, the partial inhibitory actions of NDGA and apomorphine on sGnRH-induced GTH release were additive. These findings suggest the existence of a major difference in cGnRH-II and sGnRH stimulation of GTH release--AA metabolism is not involved in cGnRH-II, as opposed to sGnRH actions. This difference in second messenger activation may also explain the differential sensitivity of the two GnRH peptides to dopamine inhibition and manipulations of extracellular Ca2+ availability. The results further suggest that dopamine and AA affect GTH release via non-overlapping signal transduction pathways.
Department of Zoology, University of Alberta, Edmonton, Canada.
J P
JP
Chang
B
B
Wildman
F
F
Van Goor
D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D002645:Chickens; D006054:Goldfish; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006062:Gonadotropins / Q000378:metabolism*; D007700:Kinetics; D009637:Masoprocol / Q000494:pharmacology; D010740:Phospholipases / Q000494:pharmacology; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D012474:Salmon
D001095:Arachidonic Acids; D006062:Gonadotropins; D007987:Gonadotropin-Releasing Hormone; D009637:Masoprocol; D010740:Phospholipases; D002118:Calcium