title: Interactions of estradiol with gonadotropin-releasing hormone and thyrotropin-releasing hormone in the control of growth hormone secretion in the goldfish.
abstract: The effects of testosterone (T) and estradiol (E2) on serum growth hormone (GH) concentrations were investigated throughout the seasonal reproductive cycle of the female goldfish. Gonad-intact female goldfish were implanted intraperitoneally for 5 days with silastic pellets containing no steroid (blank), T(100 micrograms/g) or E2 (25-100 micrograms/g). In blank-implanted females, seasonal variations in serum GH were evident; maximal serum GH levels were found in spring while minimal GH levels were found in summer and early autumn. Implantation of E2-containing silastic capsules stimulated increases (2-4 times control) in serum GH levels throughout the reproductive cycle. Implantation of T did not affect serum GH at any time of the year. One possible mechanism by which E2 could exert its effects may be through alteration of pituitary sensitivity to GH-releasing factors. The decapeptide salmon gonadotropin-releasing hormone (sGnRH) is found in the brain and pituitary of goldfish and stimulates gonadotropin (GTH) and GH secretion. In contrast, thyrotropin-releasing hormone (TRH) stimulates GH, but not GTH, release from pars distalis fragments obtained from sexually regressed (ED50 = 5.7 +/- 3.8 nM; August) or sexually mature (ED50 = 0.53 +/- 0.28 nM; March) fish; in vivo E2 treatment resulted in a 3-fold increase in the in vitro GH response to TRH. Furthermore, E2 treatment increased sGnRH-stimulated GH release by approximately 4-fold. These results demonstrate that E2 but not T stimulates GH secretion throughout the reproductive cycle of female goldfish. Furthermore, sGnRH and TRH stimulate GH release in a teleost, and these stimulatory responses are enhanced by physiological levels of E2.
authors: Department of Zoology, University of Alberta, Edmonton, Canada.
authors: V L
authors: VL
authors: Trudeau
authors: G M
authors: GM
authors: Somoza
authors: C S
authors: CS
authors: Nahorniak
authors: R E
authors: RE
authors: Peter
mesh_terms: D000818:Animals; D004343:Drug Implants; D004347:Drug Interactions; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D006054:Goldfish / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D013006:Growth Hormone / Q000097:blood* / Q000378:metabolism; D066298:In Vitro Techniques; D011863:Radioimmunoassay; D012098:Reproduction / Q000187:drug effects / Q000502:physiology; D012636:Secretory Rate / Q000187:drug effects; D013739:Testosterone / Q000494:pharmacology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
chemical_list: D004343:Drug Implants; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D004958:Estradiol; D013973:Thyrotropin-Releasing Hormone; D013006:Growth Hormone