In vitro application of testosterone potentiates gonadotropin-releasing hormone-stimulated gonadotropin-II secretion from cultured goldfish pituitary cells.
The in vitro effects of overnight treatment with testosterone (T) on gonadotropin (GTH)-II secretion from primary cultures of dispersed female goldfish pituitary cells were examined. T (100 nM) did not affect basal GTH-II release, but increased GTH-II responses to initial applications of 0.5-h pulses of sGnRH or cGnRH-II in cells from females at sexually regressed, recrudescing, or mature (prespawning) stages. Pretreatment with 10 nM T was also effective, except in experiments with cells from sexually regressed females. Analysis of GTH-II response profiles to the first GnRH pulse revealed that T increased the size of the initial (first 15 min) and sustained (rest of response) release phases, and the duration of the total response to both GnRHs. These results indicate that direct positive influence of T on GnRH-stimulated GTH-II release is demonstrable in cells from female goldfish at all ovarian maturational stages; in addition, T affects both the initial and the sustained response phases. However, compared to the initial GnRH challenge, responses to a second 0.5-h GnRH pulse were decreased in T-treated but not in control cells, suggesting that T also enhanced desensitization. Ovarian maturational conditions modulated the effects of T on the GTH-II response kinetics. In cells prepared from sexually regressed females, T treatment changed the "monophasic" (initial phase only) GTH-II response to sGnRH to a "biphasic" one characteristic of cells prepared from fish at later stages of gonadal recrudescence. Advancing gonadal maturity increased the magnitude of both initial and sustained phases of the T-enhanced GTH-II response to sGnRH, but only elevated the initial phase of T-potentiated cGnRH-II-induced release. Direct actions of T on pituitary cells may play a role in ovarian steroid feedback regulation of GTH-II secretion during the seasonal reproductive cycle in goldfish.
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
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D000818:Animals; D001481:Basal Metabolism; D002478:Cells, Cultured; D005260:Female; D006054:Goldfish / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D012636:Secretory Rate / Q000187:drug effects; D013268:Stimulation, Chemical; D013739:Testosterone / Q000494:pharmacology*
D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; C047717:LHRH, His(5)-Trp(7)-Tyr(8)-