title: In vitro effects of thyroid hormones on gonadotropin-induced estradiol-17 beta secretion by ovarian follicles of rainbow trout, Salmo gairdneri.
abstract: Ovarian follicles isolated from rainbow trout during early exogenous vitellogenesis were used to study the in vitro effects of thyroid hormones on salmon gonadotropin (GtH)-induced estradiol-17 beta (E2) secretion. Triiodothyronine (T3) alone did not alter E2 secretion but T3 in the presence of GtH (0.5 micrograms/ml) modified E2 secretion according to a biphasic dose-response curve. Maximum E2 secretion occurred at 1.9 x 10(-8) M T3; a concentration of 3.0 x 10(-7) M was inhibitory. T3 was more potent in stimulating GtH-induced E2 secretion than thyroxine. The stimulatory and inhibitory effects of T3 were consistent over a range of GtH concentrations (0.1-1.0 micrograms/ml). Cycloheximide (0.1-10 microM) decreased E2 secretion by GtH-treated follicles in a dose-dependent manner, but failed to overcome all the stimulatory effects of T3. Time course studies with follicles incubated with GtH, GtH + T3, GtH + cycloheximide, or GtH + T3 + cycloheximide indicated that T3 stimulation of GtH-induced E2 secretion occurs within 6 hr. It is concluded that thyroid hormones amplify the effects of GtH on E2 secretion by isolated ovarian follicles; at least a part of this effect does not require de novo protein synthesis.
authors: Department of Zoology, University of Manitoba, Winnipeg, Canada.
authors: D G
authors: DG
authors: Cyr
authors: J G
authors: JG
authors: Eales
mesh_terms: D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism*; D005260:Female; D006062:Gonadotropins / Q000502:physiology*; D066298:In Vitro Techniques; D006080:Ovarian Follicle / Q000187:drug effects / Q000378:metabolism*; D011863:Radioimmunoassay; D012487:Salmonidae / Q000378:metabolism*; D012621:Seasons; D013963:Thyroid Hormones / Q000494:pharmacology*; D014337:Trout / Q000378:metabolism*
chemical_list: D006062:Gonadotropins; D013963:Thyroid Hormones; D004958:Estradiol; D003513:Cycloheximide