Elastic properties and composition of the aortic wall in old spontaneouslyhypertensive rats

We hypothesized that age-linked changes in the composition and elastic prop erties of the arterial wall occur earlier in hypertensive than in normotens ive rats. We evaluated the consequences of hypertension and aging on aortic mechanics, geometry, and composition in 3-, 9-, and 15-month-old awake Wis tar-Kyoto rats (WKY) (normotensive) and spontaneously hypertensive rats (SH R) (hypertensive). The elastic modulus of the thoracic aorta, calculated fr om aortic pulse wave velocity and geometry, was higher in young and adult S HR than in age-matched WKY, as was wall stress; however, isobaric pulse wav e velocity and pulse wave velocity-pressure curves were similar. Elastic mo dulus, isobaric pulse wave velocity, and the slope of the pulse wave veloci ty-pressure curve dramatically increased in old SHR compared with age-match ed WKY; there was no further elevation of blood pressure or wall thickness. Fibrosis did not develop with age in SHR, and the ratio of elastin to coll agen decreased in a similar fashion with aging in both strains. In conclusi on, although elastic properties of the aortic wall are not intrinsically mo dified in young and adult SHR in comparison to age-matched WKY, aging is as sociated with a dramatic stiffening of the aortic wall in old SHR but not i n WKY. Changes in blood pressure, aortic wall geometry, or scleroprotein co mposition do not appear to explain this age-linked aortic stiffening in SHR , suggesting that other mechanisms of disorganization of the media may be i nvolved.