AORTIC-WALL PROPERTIES IN NORMOTENSIVE AND HYPERTENSIVE RATS OF VARIOUS AGES IN-VIVO

The distensibility of the arterial system, which is partly determined by arterial wall structure, smooth muscle tone, and actual pressure le vel, decreases with aging and hypertension. Our aim was to compare aor tic wall properties in 3- and 6-month-old normotensive Wistar-Kyoto ra ts (WKY) and spontaneously hypertensive rats (SHR) at comparable blood pressures in vivo. During ketamine/xylazine anesthesia in rats we per formed ultrasound arterial wall tracking and invasive pressure measure ments to determine, at the level of the thoracic aorta, diastolic pres sure, diastolic lumen area, changes in pressure and lumen area during the cardiac cycle, and indexes of compliance and distensibility. These observations were combined with histological measurements for determi nation of media cross-sectional area and thickness and the incremental elastic modulus under conditions as expected in situ. Anesthesia abol ished the difference in diastolic pressure between SHR and WKY. Betwee n 3 and 6 months of age in WKY, diastolic area and incremental elastic modulus increased significantly, distensibility decreased, and all ot her recorded variables were not modified. Between 3 and 6 months of ag e in SHR, diastolic area and incremental elastic modulus increased, di stensibility of the aortic wall decreased, and all other me chanical a nd structural properties did not change significantly. At both ages, d iastolic area and compliance were significantly smaller in SHR than WK Y. The other mechanical and structural properties measured or calculat ed at comparable pressure did not differ between strains. Differences between the aorta of 3- and 6-month-old rats and between strains obser ved in vivo at comparable pressures can largely be attributed to diffe rences in lumen caliber. These may represent the first findings concer ning remodeling of the aorta in intact rats.