Reduction in pulse wave velocity and improvement of aortic distensibility accompanying regression of atherosclerosis in the rhesus monkey.

Abstract

Subclavian-to-femoral artery pulse wave velocity, as a measure of aortic stiffiness, was determined in 31 rhesus monkeys (Macaca mulatta) which were divided into 3 groups on atherogenic progression or regression diets: 9 monkeys (IIA) were fed a high cholesterol diet for 38 mo., resulting in an average plasma cholesterol concentration of 638 mg/dl; and 10 (IIB1) and 12 (IIC1) monkeys were fed the same progression diet followed by 24 mo. regression diets, which were manipulated to maintain plasma cholesterol concentrations as close as possible to 300 and 200 mg/dl, respectively. Average pulse wave velocity at a diastolic blood pressure of 70 mm Hg was significantly greater (9.4 .+-. 1.0 (mean .+-. standard error the mean) m/s) in the IIA group than in the IIB1 (6.3 .+-. 0.3) or IIC1 (6.6 .+-. 0.3) groups, although 4 of the IIA monkeys had pulse wave velocities that were not significantly higher than the regression monkeys. Total thoracic plus abdominal aortic cholesterol concentration was significantly reduced from 10.2 .+-. 1.4 mg/g wet wt in the IIA group to 5.7 .+-. 0.6 (IIB1) and 4.6 .+-. 0.6 mg/g wet wt (IIC2). The total percentage of thoracic plus abdominal aortic intimal surface covered with fibrous plus fatty plaque averaged 56.9 .+-. 9.2% (IIA) vs. 33.5 .+-. 6.7(IIB1) and 35.0 .+-. 7.4% (IIC1). Collagen content beneath a given intimal square surface significantly increased from 4.59 .+-. 0.31 mg/cm2 (IIA) to 6.46 .+-. 0.33 (IIB1) and 6.49 .+-. 0.48 mg/cm2 (IIC1); elastin content decreased from 9.47 .+-. 1.56 (IIA) to 6.58 .+-. 0.73 (IIB1) and 6.01 .+-. 0.39 mg/cm2 (IIC1). There was no significant difference in any parameter between the 2 regression groups. A functional improvement of aortic elastic properties with regression of atherosclerosis is suggested. When comparing groups, the improvment appears to follow the reductions in total aortic cholesterol concentrations and in the extent of total atherosclerotic plaque rather than alterations in the collagen: elastin ratio which increased when arterial stiffness decreased with regression.