Progestin receptors in ovaries of 4-day cycling rats. An autoradiographic study

Using an autoradiographic technique we investigated in vitro the localization of cell constituents with concentrations of a radioactive synthetic progestin (P), 3H-R5020 (17 alpha, 21-dimethyl-19-nor-pregna-4, 9-diene-3, 20-dione) and its metabolites in the ovaries of 4-day cycling adult rats. After incubation of the ovarian tissue sections with radioactive R5020 in the presence or absence of various non-radioactive steroids, specific labeling was found in the tissue sections in each phase of the estrous cycle. The intensity of labeling in the ovary during the estrous cycle was highest in proestrus, followed by that in diestrus, metestrus and estrus. The intensity of labeling in cell constituents was as follows: granulosa cells greater than luteal cells greater than thecal cells greater than stromal cells. These results indicate that the rat ovaries contain cell constituents that specifically bind P and that the intensity of binding fluctuates during the estrous cycle.