The Uterine Endometrium and Isthmic Oviduct of the Ewe: Does Progesterone Act as an Antiestrogen?

Abstract

The action of progesterone (P) on the estrogen stimulated uterine endometrium and isthmic oviduct of the ewe was studied. Changes in protein:DNA and RNA:DNA ratios, rate of in vitro protein synthesis, alkaline phosphatase and peroxidase activity and the level of cytoplasmic receptors for estradiol (E₂) and P were measured in the endometrium. Only receptor effects were measured in the oviduct. Progesterone decreased the level of both receptors in each tissue but did not decrease protein:DNA and RNA:DNA ratios or protein synthesis; P had little effect on alkaline phosphatase activity and there was no detectable peroxidase activity.