Estrogen synthesis, estrogen metabolism, and functional estrogen receptors in rat arterial smooth muscle cells in culture.

Abstract

To investigate the mechanisms by which estrogen hormones influence the vascular system, the metabolism of these hormones and the functionality of estrogen receptors were characterized in rat aortic smooth muscle cells from secondary cultures, a widely studied model of vascular biology. Aromatase, estradiol-17 beta-hydroxysteroid dehydrogenase and 17-ketoreductase enzyme activities were demonstrated in these cells. The presence of functional estrogen receptor could also be demonstrated by estrogen-induced transactivating ability in transfection experiments using the luciferase gene reporter and an estrogen responsive element as transcriptional enhancer although the amplitude of the response was only in the range of 140 to 150%. Immunocytochemical analyses, using monoclonal antibodies that recognize epitopes in the A/B domain of the molecule, showed a predominant cytoplasmic localization of these estrogen 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 receptor messenger RNA showed that there was no deletion of the proto-signals for nuclear accumulation. The aromatase and dehydrogenase activity results, coupled with the estrogen receptor immunological, RNA analysis, and transfection data strongly support the contention that rat aortic smooth muscle cells are estrogen target cells. This in vitro model is convenient for studying the mechanisms of action of estrogen hormones that seem very peculiar in this cell population.

Gender Differences in Ca 2+ Entry Mechanisms of Vasoconstriction in Wistar-Kyoto and Spontaneously Hypertensive Rats

“…Since the expression of sex hormone receptors in arterial smooth muscle may vary depending on the gender and the status of the gonads, 20 the observed gender differences in the vascular reactivity to estrogen may well be related to the relative abundance of estrogen receptors. This is supported by reports that estrogen receptors have been identified in the rat aorta [21][22][23] and that females have higher levels of estrogen receptors in their arteries than males. 24 However, the gender differences may also be related to differences in the signaling mechanisms downstream from receptor activation.…”

Androgen Increases AT1a Receptor Expression in Abdominal Aortas to Promote Angiotensin II–Induced AAAs in Apolipoprotein E–Deficient Mice

“…Several cell types in male mice express aromatase, including vascular smooth muscle cells, 21,22 a pivotal cell type implicated in Ang II-induced AAAs. 20 To avoid potential confounding effects from conversion of testosterone to estradiol, we administered DHT, the 5-␣ reductase metabolite of testosterone.…”

Estrogen inhibits the response-to-injury in a mouse carotid artery model.

“…Although the mechanism(s) by which estrogen suppresses the vascular response-to-injury is not addressed by the present experiments, systemic effects on lipoproteins and coagulation pathway proteins in the present study were likely minimal due to the short duration of the study, the maintenance of a normal diet (27), and the absence of any effect of the estrogen regimen on lipid levels, which was confirmed by measuring total cholesterol and triglyceride levels. Direct estrogen effects on the vasculature of two general types have been reported (reviewed in reference 8): rapid, nongenomic effects on vascular tone, and genomic effects mediated by altered gene expression via the estrogen receptor, an estrogen-activated transcription factor that is present (16,(37)(38)(39) and functional (17a, 38) in human and rat (40) vascular smooth muscle cells. Based on current models of atherosclerosis and restenosis after vascular injury (41,42), the known effects of estrogen, and the data presented here, a number of mechanisms might contribute to the estrogen effects on the response-to-injury observed in the present study.…”