PREGNANCY MAINTENANCE AND THE INHIBITION OF PARTURITION IN RATS WITH 17α-HYDROXYPROGESTERONE ESTERS: THE ROLE OF OESTROGENIC AND ANDROGENIC ACTIVITY

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Abstract
17[alpha]-Hydroxyprogesterone acetate (AP) and 17[alpha]-hydroxyprogesterone caproate (HPC) were found to be incapable of maintaining pregnancy in ovariectomized rats when administered alone, even if administration of the drugs was started several days prior to surgery. Further studies with AP demonstrated that it could maintain pregnancy in the castrate rat when estrone or testosterone propionate (TP) were concomitantly administered. Addition of TP to a regimen of concomitant AP and estrone did not result in further improvement in the quality of pregnancy maintenance. TP and estrone alone or together were incapable of maintaining pregnancy. Parturition could be delayed or prevented in intact rats with either progesterone or TP when administration of the steroids was started 3 days before the date of expected delivery. HPC and AP alone or with estrone, and estrone alone did not delay parturition when administration was begun late in pregnancy. Parturition was prevented when administration of AP was begun at least 11 days before expected delivery.