Effects of cortisol and triiodo-L-thyronine on the steroidogenic capacity of rainbow trout ovarian follicles at two stages of oocyte maturation |
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| Authors: | PK Reddy R Renaud JF Leatherland |
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| Institution: | (1) Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario, N1G 2W1, Canada |
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| Abstract: | The in vitro basal and salmon gonadotropin (sGTH)-stimulated steroidogenic capacity of rainbow trout follicles was examined at four stages early (EV)-, mid (MV)- and peak-vitellogenic (PV), and pre-ovulatory, post-vitellogenic (PO)] of gonadal recrudescence using radioimmunoassays (RIAs) to measure 17 -estradiol (E2) and testosterone (T) production. In addition, follicles were incubated in the presence of 3H]pregnenolone (3H]P5) and the radiolabelled steroid metabolites produced were separated using high performance liquid chromatography (HPLC). Peak basal and sGTH-stimulated E2 and T production was found in PV stage follicles and lowest in PO stage follicles, and there were marked differences in the HPLC profiles of steroid metabolites. For EV stage follicles the major metabolite eluted as a peak that co-eluted with the androstenedione (A4) and 17 -hydroxyprogesterone (17-OHP) standards. A smaller peak that co-eluted with 11-hydroxyandrostenedione (11-OHA4) and very small peaks co-eluting with 20-dihydroprogesterone (20-DHP) and E2 were also seen. MV and PV stage follicles produced predominantly E2, together with a small combined A4 + 17-DHP peak, traces of 11-OHA4 and two peaks that did not co-elute with any of the reference standards. The PO stage follicles produced only 17, 20-dihydroxy-4-pregnene-3-one (17,20-P).In addition, the effects of cortisol and triiodothyronine (T3) on steroidogeneis were investigated in PV and PO stage ovarian follicles. For PV stage follicles, cortisol at 100 ng ml–1 in the incubation medium significantly suppressed both basal and sGtH- stimulated T and E2 production relative to control treatments. T3 at 10 ng ml–1 in the medium had no significant effect on either basal or sGtH-stimulated T or E2 production compared to the controls, nor did it have any beneficial effect over the suppressive effect of cortisol. PO phase follicles taken 1 to 2 weeks prior to anticipated spawning had very low E2 and T production, and there was no effect of cortisol or T3, alone or in combination, on E2 or T production. For PV stage follicles incubated in the presence of 3H]P5, cortisol suppressed T and E2 production, but did not block the steroid pathway at any specific level; T3 had no apparent affect on the metabolism of 3H]P5. The PO stage follicles produced little or no E2; the major metabolite was 17,20-P. Cortisol and T3 had no apparent effect on either basal or sGtH-stimulated 17,20-P production by the follicles at this stage of maturation. |
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| Keywords: | corticosteroids granulosal cells ovulation 17 -estradiol" target="_blank">gif" alt="beta" align="MIDDLE" BORDER="0">-estradiol steroidogenesis teleostean fish testosterone thecal cells |
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