Uterine progesterone levels and intrauterine pressure in ovariectomized post partum rats

Porter and Challis reported that the intrauterine pressure (IUP) of ovariectomized post partum rats was not suppressed by progesterone (P) treatment which increased uterine P levels. This experiment was repeated under rigorously controlled conditions. The exogenously induced increase in uterine P levels from 36 +/- 3 ng/g to 135 +/- 9 ng/g (p less than 0.001) reduced IUP from 61 +/- 3 mm Hg (p less than 0.001). When after 96 hours the P levels returned to pretreatment value, IUP also recovered from suppression.