PROGESTERONE INTERFERES WITH THE ACTIONS OF PROSTAGLANDIN (PG) E1 BUT NOT THOSE OF PGE2 OR PGF2ALPHA IN A RAT VASCULAR PREPARATION

In the mammary gland some actions of prolactin seem mediated by PGs. Progesterone blocks several of the mammary effects of prolactin. We therefore investigated the effects of 100 ng/ml progesterone (within the normal human plasma concentration in pregnancy) on the vascular effects of PGE2, PGF2α and PGEI. Progesterone had no effects on the responses to PGE2 and PGF2α but significantly (p < 0.01) attenuated the actions of low concentrations of PGEI. It may have enhanced the actions of high PGEI concentrations. Progesterone appears able to block some effects of PGEI and to imitate others. © 1979.