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

Abstract

ABSTRACT 17α-Hydroxyprogesterone acetate (AP) and 17α-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 oestrone or testosterone propionate (TP) were concomitantly administered. The addition of TP to a regimen of concomitant AP and oestrone did not result in further improvement in the quality of pregnancy maintenance. TP and oestrone 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 oestrone, and oestrone 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.