Maintenance of Pregnancy in Ovariectomized Rats with Some Newer Progestins

Abstract

Progestins found capable of maintaining pregnancy in rats castrated on the 8th day after insemination included progesterone, 17α-hydroxyprogesterone acetate, 17α-ethyl-19-nortestosterone, desoxycorticosterone acetate, 9α-bromo-11-ketoprogesterone and 6α-methyl-17α-hydroxyprogesterone acetate. The most potent compound in this respect was 6α-methyl-17α-hydroxyprogesterone acetate. Compounds which failed to maintain pregnancy include 17α-ethinyltestosterone, 17α-ethinyl-19-nortestosterone, 17α-ethinyl-17-hydroxy-5(10)-estren-3-one, and 17α-methyltestosterone. With the exception of 17α-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 6α-methyl-17α-hydroxyprogesterone acetate, 9α-bromo-11-ketoprogesterone and desoxycorticosterone acetate.