In vitro metabolism of progesterone, 17-hydroxyprogesterone, and 17,20 beta-dihydroxy-4-pregnen-3-one by ovaries of the common carp Cyprinus carpio: production rates of polar metabolites.

[14C]Progesterone, 17-[3H]hydroxyprogesterone, and 17,20 beta-[3H]dihydroxy-4-pregnen-3-one (17,20 beta P) were incubated for 1, 3, 6 or 24 hr with ovaries from carp which had received injections of either carp pituitary extract or saline. All three substrates were very rapidly metabolized to polar products, but 17,20 beta P was not detected as a metabolite of either progesterone or 17-hydroxyprogesterone. The major metabolite in all incubations was very similar, but not identical, in chemical and chromatographic properties to 5 beta-pregnane-3 alpha, 6 alpha, 17,20 beta-tetrol. A compound isopolar with 5 beta-pregnane-3 alpha, 6 alpha, 17,20 alpha-tetrol was isolated only in incubations of progesterone and 17-hydroxyprogesterone. It is suggested that hydroxylation and reduction may be a deactivation mechanism allowing 17,20 beta P to build up as an intermediate, and active maturation inducing steroid, only in response to the ovulatory gonadotrophin surge, thus assisting in synchrony of oocyte maturation.