PRE-OVULATORY CHANGES IN STEROIDOGENESIS IN OVARIES FROM IMMATURE RATS TREATED WITH PREGNANT MARE SERUM GONADOTROPHIN

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Abstract
SUMMARY: The metabolism of progesterone in the 1000 g supernatant fraction of homogenates of ovaries from PMSG-treated immature rats was determined. As early as 52 h after a single injection of 50 i.u. PMSG, still before the LH surge, 5α-pregnane-3α,20α-diol was identified as the main metabolite, together with smaller quantities of 3α-hydroxy-5α-pregnan-20-one and 5α-androstane-3α,17β-diol. Similar incubations of untreated rat ovaries at the same age did not produce 5α-pregnane-3α,20α-diol. The quantities of 3α-hydroxy-5α-pregnan-20-one and 5α-androstane-3α,17β-diol were reduced in PMSG-treated rat ovaries as compared with control ovaries. When progesterone metabolism was examined 64 h after PMSG administration, 5–7 h after the peak of the LH surge but still before ovulation, 75% of the substrate was converted to 5α-pregnane-3α,20α-diol, while 3α-hydroxy-5α-pregnan-20-one as well as 5α-androstane-3α,17β-diol could not be detected.