Testosterone enhances GABA and taurine but not N-methyl-D,L-aspartate stimulation of gonadotropin secretion in the goldfish: possible sex steroid feedback mechanisms.
The effects of gonadal steroids on GABA-, taurine (TAU)- and N-methyl-D,L-aspartate (NMA)-induced gonadotropin-II (GTH-II) release were investigated in male and female goldfish in vivo. In sexually regressed goldfish (both sexes mixed), intraperitoneal implantation for 5 to 10 days with solid Silastic pellets containing testosterone (100 micrograms/g), oestradiol (100 micrograms/g) or progesterone (100 micrograms/g) was previously shown to elevate serum sex steroid levels to values comparable to those in sexually mature animals, and to potentiate gonadotropin-releasing hormone-stimulated GTH-II release. In the present study, testosterone but not oestradiol or progesterone enhanced the stimulatory effects of exogenous GABA (100 micrograms/g) on GTH-II release in vivo. TAU (1 mg/g) stimulated GTH-II release in sexually regressed mixed sex and sexually recrudescent male goldfish, and both testosterone and oestradiol implantation enhanced GTH-II release induced by TAU. The glutamate agonist NMA (25 to 50 micrograms/g) was also found to stimulate GTH-II release; however it was relatively less effective in elevating serum GTH-II levels than GABA and TAU, and its effects were not modulated by sex steroid treatments. Pretreatment of goldfish with alpha-methyl-p-tyrosine to deplete brain and pituitary catecholamines did not affect NMA action on GTH-II release. Our results indicate that GABA, TAU and NMA are involved in the neuroendocrine regulation of GTH-II release in goldfish, and support the idea that testosterone participates in the positive feedback regulation of pituitary gonadotropin release in a non-mammalian vertebrate by enhancing GABA- and TAU-stimulated GTH release in vivo.
Trudeau
V L
VL
Department of Zoology, University of Alberta, Edmonton, Canada.
Sloley
B D
BD
Peter
R E
RE
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D004343:Drug Implants; D004958:Estradiol / Q000494:pharmacology; D005246:Feedback / Q000502:physiology; D005260:Female; D006054:Goldfish / Q000502:physiology*; D006062:Gonadotropins / Q000378:metabolism*; D008297:Male; D008781:Methyltyrosines / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology*; D011374:Progesterone / Q000494:pharmacology; D011863:Radioimmunoassay; D013654:Taurine / Q000494:pharmacology*; D013739:Testosterone / Q000008:administration & dosage / Q000494:pharmacology*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D019805:alpha-Methyltyrosine; D005680:gamma-Aminobutyric Acid / Q000008:administration & dosage / Q000494:pharmacology*
D004343:Drug Implants; D006062:Gonadotropins; D008781:Methyltyrosines; D013654:Taurine; D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D005680:gamma-Aminobutyric Acid; D016202:N-Methylaspartate; D019805:alpha-Methyltyrosine; D014446:Tyrosine 3-Monooxygenase