Long-Term Effects of Hypertension on the Rat Aortic Wall and Their Relation to Concurrent Aging Changes: MORPHOLOGICAL AND CHEMICAL STUDIES

Abstract

The effects of long-term (16 months) hypertension on the thoracic aorta of male rats were compared to previously reported short-term (2.5 months) changes and to concurrent aging changes. Hypertension was produced by clipping a renal artery. Although short-term hypertension was characterized by a disproportionate increase in noncollagenous alkali-soluble proteins, which have been attributed primarily to vascular smooth muscle, with long-term hypertension there was no further increase in these proteins but instead there were striking increases in mural accumulations of elastin and collagen. Chronically elevated wall tension in hypertensive vessels was associated with a progressive increase in wall thickness which resulted in a value for wall stress no different from that of control vessels. Concurrent aging changes were qualitatively similar to, but much less pronounced than, those seen with hypertension and were attributed to an increase in wall tension in controls resulting from a combination of significant increases in diameter and systolic blood pressure with age. This study of the interaction of vessel structure and function has revealed common features of what appears to be a diverse group of vascular alterations. KEY WORDSaortic wall tension vessel structure and function elastin collagen aortic wall stress vascular disease• Hypertension results in a strikingly increased thickness and stiffness of the entire vascular tree (1, 2); similar changes are seen to a lesser degree in the vessel wall during growth and aging (3, 4). Morphological and chemical studies of hypertensive vessels have shown that the changes in vessel dimensions and properties are due to smooth muscle hypertrophy (1) and hyperplasia (5) and increased amounts of mural mucopolysaccharides (6), elastin, and collagen (7). Elastin and collagen also accumulate in vessels during aging (4), though the relative degree of increase in each of the fibrous proteins is controversial (4,(8)(9)(10). These similarities and others have led some to suggest that hypertension is an accelerated form of aging (3).Although the changes in vascular morphology associated with hypertension have been well described (1) and no qualitative morphological differences between vessels exposed to acute hypertension and chronic hypertension were found (11), a detailed comparison of short-term and long-term effects of hypertension on the dimensions and chemical composition of the vessel wall has not been done. This would be of considerable interest for several reasons. First, the lack of significant effects of treatment on mortality from coronary artery disease in hypertensive patients has been postulated to be due to

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