In vivo production of steroids with central depressant actions by the ovary of the rat.

1. In addition to progesterone and 20-dihydroprogesterone, the following unconjugated steroids were isolated from ovarian tissue and ovarian venous blood of mature, non-pregnant rats: pregnenolone, 3betaOH-5alpha-pregnan-20-one, 3alphaOH-5alpha-pregnan-20-one, 20alphaOH-5alpha-pregnan-3-one and 5alpha-pregnane-3alpha, 20alpha-diol.2. Their concentration in the ovarian tissue and their secretion rates into the ovarian venous blood was of the same order of magnitude as that of progesterone.3. In the evening of the day of pro-oestrus significant increases in the ovarian contents of the following steroids were observed: progesterone, +140%; 3alphaOH-5alpha-pregnan-20-one, +320%; 20alphaOH-5alpha-pregnan-3-one, +195%; sum of pregnenolone and 3betaOH-5alpha-pregnan-20-one, +275%.4. At the same time the ovarian progeterone secretion rate was increased by 365%, that of 3alphaOH-5alpha-pregnan-20-one by 190%.5. A possible physiological role of the ovarian allopregnane derivatives as central depressant agents is discussed.