A radioimmunoassay (RIA) has been developed to detect a range of C21 (pregnane) steroids with a 17,20beta-dihydroxyl (17,20beta) configuration. In conjunction with reverse-phase high-performance liquid chromatography (HPLC), it identifies and quantifies the metabolites of 17,20beta-dihydroxy-4-pregnen-3-one, the putative "maturation-inducing steroid" in female plaice Pleuronectes platessa. Total levels of 17,20beta metabolites which can be extracted from plasma or urine with diethyl ether (i.e., free steroids) are very low (<3 ng/ml). However, total levels of 17,20beta metabolites which can be released by solvolysis (i.e., sulphated steroids) are very high (up to 1 microg/ml in plasma and 10 microg/ml in urine). On HPLC, these sulphated metabolites have been identified (in order of abundance in plasma) as: 5beta-pregnane-3alpha,17,20beta-triol, 5beta-pregnane-3beta,17,20beta-triol, 17, 20beta-dihydroxy-4-pregnen-3-one, and 17, 20beta-dihydroxy-5beta-pregnan-3-one. These steroids are absent from plasmas of fish which have not yet begun final oocyte maturation. The results support the hypothesis that 17, 20beta-dihydroxy-4-pregnen-3-one is the maturation-inducing steroid in plaice but that it is rapidly metabolised to render it inactive. The results also show that the '17,20beta'-RIA, in combination with an overnight acid solvolysis procedure, is a useful procedure for monitoring the effects of exogenous factors (such as gonadotrophin injections) on final oocyte maturation in female plaice.
The relative effectiveness of estradiol-17β, androgens, corticosteroids, progesterone and other pregnene derivatives on germinal vesicle breakdown (GVBD) was investigatedin vitro using folliculated oocytes of three carps,Labeo rohita, Cirrhinus mrigala, andCatla catla. In all three species progesterone and 17α-hydroxyprogesterone could induce GVBD but relatively 17α,20β-dihydroxyprogesterone was consistently found to be the most potent maturation-inducing steroid. Both estradiol-17β and testosterone were ineffective in inducing GVBD. Androsterone and dehydroepiandrosterone were found to be effective inC. catla at all the concentrations used. Deoxycorticosterone (DOC), hydrocortisone (HC) and cortisone were effective inducer of GVBD inC. catla whereas inL. rohita andC. mrigala only cortisone was found to be effective. All 5β-reduced pregnenes were effective in inducing GVBD inL. rohita but inC. catla, only 5β-pregnane-17α-01-3,20-dione and 5β-pregnane-3α,17α,20β-triol and inC. mrigala, 5β-pregnane-3α-ol-20- one could induce oocyte maturation.
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