Abstract 246: Thoracic versus Abdominal Aortic Stiffness in Young and Old Non-Human Primates

Abstract

We demonstrated that thoracic aortic stiffness is increased in aging monkeys, with the mechanism involving increased vascular smooth muscle cell (VSMC) stiffness. In view of the importance of increased abdominal aortic stiffness to greater incidence of abdominal aortic aneurysms, the goal of this investigation was to determine differences in thoracic vs. abdominal aortic stiffness in young and old monkeys (fascicularis and rhesus). Most prior studies on aortic stiffness have been conducted in vitro or in anesthetized animals with indirect measurements of stiffness. A novel feature of the current investigation was to measure aortic diameter and pressure instantaneously and continuously in chronically instrumented, conscious young (n=25, 5-12yrs) and old male (n=21, >24yrs) monkeys, instrumented with aortic pressure gauges and ultrasonic aortic diameter crystals on the thoracic and abdominal aorta. The aortic stiffness index, β[[Unable to Display Character: ]][[Unable to Display Character: ]]calculated as a ratio of systolic and diastolic aortic pressures and diameters, was markedly greater, p<0.05, in abdominal, compared with thoracic, aorta in both young (33±5.0 in abdominal vs. 14±2.2 in thoracic) and old monkeys (57±6.3 in abdominal vs. 34±0.4 in thoracic). Although both thoracic and abdominal aortic stiffness were greater in old monkeys, p<0.05, surprisingly, abdominal aortic stiffness in young monkeys (33±5.0) was equal to thoracic aortic stiffness in old monkeys (34±0.4). Using atomic force microscopy, aortic VSMC stiffness was 2 fold greater, p<0.05, in old monkeys vs. young monkeys, but there were no differences in abdominal vs. thoracic aortic VSMC stiffness in either young or old monkeys. In summary, as expected, aging increased aortic stiffness, with the mechanism, in part, due to increased VSMC stiffness. However, aortic stiffness was increased more in the abdominal than thoracic aorta both in young and old monkeys, with the magnitude of the increase in the abdominal aorta of the young monkeys, similar to that which occurs with aging in the thoracic aorta. These findings point out the major differences in stiffness along the aorta and have relevance to the greater frequency of abdominal aortic aneurysms.