Effects of Estrogen and Progestogen Treatment on the Response of the Aorta of Male Rats to Hypertension: MORPHOLOGICAL AND CHEMICAL STUDIES

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Abstract
The effects of estrogen and progestogen treatment on the response of the thoracic aortic wall of male rats to hypertension were studied. Hypertension levels induced by clipping the renal artery were similar in untreated (H), estrogen-treated (E), and progestogen-treated (P) hypertensive groups. Hypertension of 8 weeks' duration caused increased wall thickness, increased calculated tangential tension, and increased medial area in groups H and P compared to normotensive controls (C), but wall thickness and medial area in groups E and C were similar despite the striking elevation in calculated tension and wall stress in group E. Chemical studies also showed that the absolute amounts of aortic collagen and elastin in groups H and P were similarly increased over group C values, but absolute amounts of both these fibrous proteins in vessels from group E were no different from those of group C. Noncollagenous alkali-soluble proteins in these vessels were present in absolute and relative amounts corresponding to the following rank: P > H > E > C. Thus, it appears that estrogen-treatment has a distinctly inhibitory effect and progestogen-treatment a slightly stimulatory effect on the aortic wall response to hypertension. Since hypertension-induced morphological and chemical changes have many similarities to features of arteriosclerotic plaque growth, recognition of these differences in hormonal effects on the response of the vessel wall to hypertension may have implications beyond their physiological role as sex hormones.