Response of the Rat Aortic Media to Hypertension

Clinical and experimental studies indicate that hypertension accelerates the development of arteriosclerosis. Morphological and chemical studies of the distended rat thoracic aorta were undertaken to define the structural and compositional alterations of the media which accompany hypertension and to relate these changes to increases in calculated medial stress. An 8-week period of hypertension was associated with significantly greater diameter, medial thickness, and cross-sectional area of the media of the thoracic aorta than in normotensive animals. Calculated wall tension was significantly higher in hypertensive animals, but the number of medial lamellar units was not greater than that usual in normotensive animals; this resulted in a strikingly elevated value for calculated tension per medial lamellar unit for the aortas of hypertensive animals. A highly significant linear relation was found between total tension and cross-sectional area of the media of the same segment. In addition, the absolute amounts of both medial elastin and collagen were increased in hypertensive animals; however, the percent of these elements remained essentially constant, indicating little change in the composition of aortic tissue. Increments in both fibrous proteins were linearly related to increases in calculated mural stress, and medial accumulations of elastin and collagen proceeded at similar rates. These findings demonstrate a linear relation among vessel dimensions and amounts of medial elastin and collagen and calculated wall tension.