The effect of 5alpha-androstane-3alpha, 17 beta-diol, its 3 beta epimer and oestradiol benzoate on suppression of LH release after ovariectomy was studied in immature rats. At doses of 50 and 100 mug/100 g body weight/day the 3alpha compound suppressed LH release after ovariectomy to the same extent as 0-1 mug oestradiol benzoate/100 g/day. 3alpha-Androstanediol at a dose of 25 mug/100 g/day suppressed LH release only up to day 45 of life, while the same dose of the 3beta epimer had no effect on LH suppression. The effect of 3beta-androstanediol on inducing precocious vaginal opening was found to be mediated by the ovaries, since it was eliminated by ovariectomy. These results confirm our previous findings on the participation of androstanediol in the normal regulation of LH and in the mechanism of onset of puberty in the rat.

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, 5alpha-pregnane-3alpha, 20alpha-diol was identified as the main metabolite, together with small quantities of 3alpha-hydroxy-kalpha-pregnan-20-one and 5alpha-androstane-3alpha, 17beta-diol. Similar incubations of untreated rat ovaries at the same age did not produce 5alpha-pregnane-3alpha, 20alpha-diol. The quantities of 3alpha-hydroxy-5alpha-pregnan-20-one and 5alpha-androstane-3alpha, 1mbeta-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 LH surge but still before ovulation, 75% of the substrate was converted to 5alpha-pregnane-3alpha, 20alpha-diol, while 3alpha-hydroxy-5alpha-pregnan-20-one as well as 5alpha-androstane-3alpha, 17beta-diol could not be detected.