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 stiffness, was determined in 31 rhesus monkeys (Macaca mulatta) which were divided into three groups on atherogenic progression or regression diets: nine monkeys (IIA) were fed a high cholesterol diet for 38 months, 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-month 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 ± SEM) m/sec) in the IIA group than in the IIB1 (6.3 ± 0.3) or IIC1 (6.6 ± 0.3) groups, although four 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 weight in the IIA group to 5.7 ± 0.6 (IIB1) and 4.6 ± 0.6 mg/g wet weight (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), whereas 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 two regression groups. These studies suggest a functional improvement of aortic elastic properties with regression of atherosclerosis. When comparing groups, the improvement appears to follow the reductions in total aortic cholesteral concentrations and in the extent of total atherosclerotic plaque rather than alterations in the collagen:elastin ratio which, in fact, increased when arterial stiffness decreased with regression.