Localization and regulation of estrogen and progestin receptors in the Macaque oviduct

In non-human primates, the oviduct undergoes dramatic, hormonally regulated changes in morphological structure. In spayed animals, the epithelium is undifferentiated, and estro­ gen treatment can stimulate differentiation to a fully ciliated and secretory state. This state can be maintained indefinitely by estrogen, but if progestin treatment is initiated the epithelium will atrophy, dedifferentiate, and remain so as long as combined progestinestrogen treatment is continued. Oviductal estrogen receptors increase in number during estrogen treatment and decrease during combined progestin-estrogen treatment. Consequently we have concluded that progestins act as estrogen antagonists by suppressing estrogen re­ ceptors below physiologically effective levels. However, our immunocytochemical studies show that in estrogen-treated animals, estrogen and progestin receptors are present only in secretory cells, stromal cells and smooth muscle cells, not in ciliated cells. This suggests that the effects of estrogens and progestins on ciliogenesis must be mediated indirectly, through other cell types that contain both receptors. We suggest that the cell type directly involved in mediating these effects is the stromal cell, because after combined progestinestrogen treatment, only stromal cells retain progestin receptors. Consequently only stromal cells can directly mediate the sustained antagonistic effects of progestin treatment. We propose a model of steroid hormone action in the oviduct in which estrogens and progestins act directly on oviductal stromal cells to regulate the secretion of various growth factors or other mediators which are the proximal agents that regulate epithelial cell differentiation in the primate oviduct.