Mechanoelastic properties of the aorta in chronically hypertensive conscious rats.

The relationship between aortic caliber (AC) and aortic pressure (AP) was studied in eleven normotensive (NCR) and 17 one-kidney, one clip chronic renal hypertensive conscious Wistar rats (RHR) at rest and when transient changes in blood pressure were produced. The mean values for AC, AP, and tangential stress were 20%, 75%, and 73% higher in RHR than NCR. Similarly, the aorta thickness was 21% greater but radius/thickness was unchanged. Pulse pressure increased by 51%, and aortic pulsation was twice that of NCR. At control pressure, dynamic as well as mean distensibility of the aorta tended to be greater in RHR, but not statistically different. During transient changes in pressure, —40 to +40 mm Hg from control levels, dynamic distensibility was the same for both groups, but, at hypotensive levels, mean distensibility decreased significantly in NCR. Mean distensibility was related to distending pressure; an overlap of NCR and RHR values occurred between 130 and 160 mm Hg. At the pressures studied, the dynamic strain of RHR was markedly elevated because aortic pulsation (142%) increased more than caliber (20%). In spite of this, mean strain was similar for both groups. Therefore, RHR responded to a pressure change with a greater change in mean caliber which was proportional to their larger control caliber. Alterations in pressure caused greater changes in the absolute values of diastolic caliber than pulsation for both groups. These properties of the aortic wall appear to be important for baroreceptor resetting in hypertension. (Hypertension 3 (suppl II): II-177-II-182, 1981)