Differential regulation of progestin receptor immunoreactivity in the rabbit oviduct

Cellular distribution of progestin receptor immunoreactivity (PR-IR) in paraffin-embedded rabbit oviduct tissue was determined using a monoclonal antibody and the indirect immunoperoxidase method. Ampullar and isthmic tissue from ovariectomized animals primed with 17 beta-estradiol or vehicle alone was examined. As expected, in the absence of estradiol, PR-IR was rarely observed in the ampulla. Estradiol treatment increased PR-IR in cell nuclei of the stroma and muscularis of the ampulla, but not of the epithelium. In contrast, PR-IR was seen in epithelial cell nuclei of the isthmus in the absence of estradiol. Surprisingly, while estradiol treatment increased PR-IR in cell nuclei of the stroma and muscularis of the isthmus, it decreased PR-IR in the epithelium. These results suggest for the first time a differential regulation of progestin receptors in the ampulla and isthmus of the oviduct. In particular, while estradiol treatment increased PR-IR in the stroma and muscularis and was without effect on PR-IR in the epithelium of the ampulla, it decreased PR-IR in the epithelium of the isthmus.