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 17β-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 17α-hydroxyprogesterone (17α-OHP) standards. A smaller peak that co-eluted with 11β-hydroxyandrostenedione (11β-OHA4) and very small peaks co-eluting with 20α-dihydroprogesterone (20α-DHP) and E2 were also seen. MV and PV stage follicles produced predominantly E2, together with a small combined A4 + 17α-DHP peak, traces of 11β-OHA4 and two peaks that did not co-elute with any of the reference standards. The PO stage follicles produced only 17, 20β-dihydroxy-4-pregnene-3-one (17,20β-P).
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