Effect of a teleost GnRH analog on steroidogenesis by the follicle-enclosed goldfish oocytes, in vitro.
The influence of an agonist analog of teleost GnRH [(D-Arg6, Trp7, Leu8, Pro9-NEt)-GnRH; tGnRH-A] on steroidogenesis was studied in prophase-I arrested, follicle-enclosed, goldfish oocytes in vitro. Incubation of the follicles with carp gonadotropin (GtH) significantly increased production of 17 alpha-hydroxyprogesterone (HP) and testosterone following 24 hr of incubation in vitro. Concomitant incubation with tGnRH-A (10(-7) M) significantly attenuated the dose-related increase in GtH-induced testosterone production, but was without effect on the GtH-induced HP level. Time course studies indicated that tGnRH-A exerted its maximum inhibitory action on the GtH-induced testosterone production during the initial 8 hr of incubation in vitro. The inhibition of GtH-induced testosterone production by tGnRH-A was dose dependent with an ED50 of 1.39 +/- 2.88 nM. A significantly higher testosterone level was obtained in the incubation media containing HP as substrate; concomitant treatment with tGnRH-A reduced the conversion of HP to testosterone. The incubation media also contained low, but measurable levels of 17 alpha-hydroxy-20 beta-dihydroprogesterone (DHP), which increased in the presence of 3-isobutyl-methyl-xanthine; lower levels of DHP were obtained in the groups incubated with tGnRH-A. In view of our present findings and previous observations concerning inhibitory effects of tGnRH-A on the progestogen and GtH-induced reinitiation of meiosis in the follicle-enclosed goldfish oocytes (H. R. Habibi, G. Van Der Kraak, E. Bulanski, and R. E. Peter, Amer. J. Physiol. 255, R268-R273 (1988] the influence of testosterone on the GtH- and DHP-induced meiosis in vitro was also studied. Testosterone (1 micrograms/ml) enhanced both GtH- and DHP-induced oocyte meiosis in the goldfish oocytes. Testosterone alone was also found to significantly increase oocyte meiosis in the goldfish oocytes in a dose-related fashion. The present findings demonstrate an inhibitory effect of a GnRH agonist on GtH-induced testosterone production in goldfish oocytes and suggest that tGnRH-A might influence oocyte meiosis in part by influencing steroidogenesis.
Habibi
H R
HR
Department of Zoology, University of Alberta, Edmonton, Canada.
Van Der Kraak
G
G
Fraser
R
R
Peter
R E
RE
D000818:Animals; D003530:Cyprinidae / Q000378:metabolism*; D005260:Female; D006054:Goldfish / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D008540:Meiosis / Q000187:drug effects; D009865:Oocytes / Q000378:metabolism*; D011374:Progesterone / Q000378:metabolism*; D013739:Testosterone / Q000378:metabolism* / Q000494:pharmacology
D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D011374:Progesterone; C058987:5-oxo-pro-his-trp-ser-tyr-gly-trp-leu-pro-glynh2