Prolactin Receptor and Uterine Milk Protein Expression in the Ovine Endometrium During the Estrous Cycle and Pregnancy1

Lactogenic hormones regulate epithelial proliferation, differ-entiation, and function in a variety of epitheliomesenchymal or-gans. During pregnancy, the ovine uterus is a potential site for endocrine and paracrine actions of lactogenic hormones in the form of pituitary prolactin (PRL) and placental lactogen (PL). These studies determined temporal and spatial alterations in PRL receptor (PRL-R) and expression of uterine milk proteins (UTMP), a marker of endometrial secretory activity, in the ovine endometrium during the estrous cycle and pregnancy. Slot-blot hybridization analysis indicated that steady-state levels of en-dometrial PRL-R mRNA increased during pregnancy. In situ hy-bridization and immunohistochemical analyses indicated that PRL-R mRNA and protein were exclusively expressed in the en-dometrial glandular epithelium (GE). No PRL-R mRNA expres