Maintenance of Pregnancy in Ovariectomized Rats with Some Newer Progestins

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Abstract
Progestins found capable of maintaining pregnancy in rats castrated on the 8th day after insemination included progesterone, 17[alpha]-hydroxy-progesterone acetate, 17[alpha]-ethyl-19-nortestosterone, desoxycorticos-terone acetate, 9[alpha]-bromo-ll-ketoprogesterone and 6[alpha]-methyl-17[alpha]-hydroxyprogesterone acetate. The most potent compound in this respect was 6[alpha]-methyl-17[alpha]-hydroxyprogesterone acetate. Compounds which failed to maintain pregnancy include 17[alpha]-ethinyltestosterone, 17[alpha]-ethinyl-19-nortestosterone, 17[alpha]-ethinyl-17-hydroxy-5(10)-estren-3-one, and 17[alpha]-methyltestosterone. With the exception of 17[alpha]-hydroxyprogesterone acetate, all compounds which maintained pregnancy when administered concomitantly with estrone also maintained pregnancy when administered alone. Higher doses were required, however, for comparable results. Fair correlation between reported potency in the McPhail or Clauberg rabbit endometrium assays and pregnancy maintenance potency existed only for 6[alpha]-methyl-17[alpha]-hydroxyprogesterone acetate, 9[alpha]-bromo-11-ketoprogesterone and desoxycorticosterone acetate.