Role of Contractile Agonists in Growth Regulation of Vascular Smooth Muscle Cells

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Abstract
Accelerated smooth muscle growth is a characteristic feature in arteries of hypertensive patients and animals (1,15,26,27,36,40). In resistance vessels, this accelerated growth of smooth muscle contributes to development of medial thickening or hypertrophy and is thought to play an important role in the etiology of hypertension (1,13). It is hypothesized that medial hypertrophy confers a mechanical advantage such that at any given level of smooth muscle activation vascular resistance is greater in hypertensives than in controls (12,25). It should be noted, however, that medial hypertrophy does not appear to occur in very small arteries (< 100 gm internal diameter) and arterioles, but rather appears confined to large and intermediate sized resistance arteries (i.e. 150–300 gm internal diameter) (8,19,26,40). Extensive medial hypertrophy occurs in large conduit vessels, such as the aorta (33). In these vessels, medial hypertrophy is thought to be an adaptive process to minimize changes in wall stress that occur as a consequence of increases in blood pressure (34).