Control of the secretory cell cycle in cat oviduct by estradiol and progesterone

The control of the secretory cell cycle by estradiol and progesterone in the oviduct of the cat was studied using light and electron microscopy. The epithelium in ovariectomized animals was cuboidal with no evidence of secretory activity. Estradiol treatment induced hypertrophy, hyperplasia, and the differentiation of both secretory and ciliated cells. Differentiation of the secretory cell included the development of an extensive area of basal rough endoplasmic reticulum and a large supranuclear Golgi region. Apical secretory granules were already present after 3 days of estradiol treatment, and after 4 to 5 days maximum hypertrophy and differentiation had occurred. Most cells contained several apical electron-dense granules; however, no large accumulation of granules in any one cell was ever observed. Occasional release of secretory product by exocytosis occurred during chronic treatment with estradiol. Rapid elevation of the serum levels of estradiol or progesterone by means of IV injection did not enhance exocytosis or result in any ultrastructural alterations. The chronic administration of progesterone to estradiol-primed animals resulted in rapid cell atrophy, dedifferentiation, and death (apoptosis) within the epithelium of the oviduct. Secretory granules were no longer observed after 2 days of estradiol and progesterone treatment, and after 7 days the epithelium was approximately the same height as that measured in ovariectomized animals. These data illustrate that estradiol induces the differentiation and maintains the mature state of the secretory cell within the oviductal epithelium of the cat, and that progesterone has an immediate antiestrogenic effect on these cells. This study also suggests that the secretory product is released gradually, as the granules form and mature during chronic estradiol administration.