On the Function of 20α-Hydroxypregn-4-en-3-one During Parturition in the Rat

Subcutaneous administration of 20α-hydroxypregn-4-en-3-one (20α-OH-P) in oil to pregnant rats raised the peripheral plasma concentration of this steroid to levels (18–30 μg/100 ml) approximately double those normally found just prior to delivery. Maintenance of such levels during the 16th to 22nd days of gestation was without effect on the normal termination of pregnancy and failed to influence ovarian weight, ovarian 20α-hydroxysteroid dehydrogenase activity, fetal weight, or plasma concentrations. Thus, no manifestation of a biological influence of 20α-OH-P was detected on either the ovaries, uteri, or pituitaries of pregnant rats. It is concluded, therefore, that normal parturition is not initiated by increasing plasma levels of 20α-OH-P characteristic of terminal pregnancy but is more probably associated with the related decremental changes in progesterone concentration. (Endocrinology83: 1181, 1968)