ESTROGEN SYNTHESIS, ESTROGEN METABOLISM, AND FUNCTIONAL ESTROGEN-RECEPTORS IN RAT ARTERIAL SMOOTH-MUSCLE CELLS IN CULTURE

To investigate the mechanisms by which estrogen hormones influence the vascular system, the metabolism of these hormones and the functionali ty of estrogen receptors were characterized in rat aortic smooth muscl e cells from secondary cultures, a widely studied model of vascular bi ology. Aromatase, estradiol-(17)beta-hydroxysteroid dehydrogenase and 17-ketoreductase enzyme activities were demonstrated in these cells. T he presence of functional estrogen receptor could also be demonstrated by estrogen-induced transactivating ability in transfection experimen ts using the luciferase gene reporter and an estrogen responsive eleme nt as transcriptional enhancer although the amplitude of the response was only in the range of 140 to 150%. Immunocytochemical analyses, usi ng monoclonal antibodies that recognize epitopes in the A/B domain of the molecule, showed a predominant cytoplasmic localization of these e strogen receptors, even after estrogen addition to the culture medium. Western blot analysis using antibodies that recognize epitopes in the A/B or F domain gave a mol wt of 67,000. Analysis of the estrogen rec eptor messenger RNA showed that there was no deletion of the proto-sig nals for nuclear accumulation. The aromatase and dehydrogenase activit y results, coupled with the estrogen receptor immunological, RNA analy sis, and transfection data strongly support the contention that rat ao rtic smooth muscle cells are estrogen target cells. This in vitro mode l is convenient for studying the mechanisms of action of estrogen horm ones that seem very peculiar in this cell population.