Regional Difference of Increased Stiffness and Extra Cellular Matrix in Aging Monkey Aorta

Abstract

Aortic aneurysm is a vascular disease found most commonly in the elderly population and more frequently in the abdominal aorta (AA) compared to thoracic aorta (TA). However, the physiological basis underlying such regional differences is still under debate. Accordingly, we compared the mechanical and structural differences between TA and AA in aging (20‐25 years old, n=5) male monkeys by both physiological and histological measurements. Thoracic and abdominal aortic diameters were recorded directly from implanted miniature ultrasound crystals. Aortic stiffness was calculated from the pulse aortic pressure and diameter as the elastic modulus (K). TA and AA tissue sections were stained with picric acid sirius red for collagen and Verhoeff Van Gieson for elastin. Stiffness was significantly (p<0.05) higher in AA (K=2596±258) compared to TA (K=1870±195). Collagen density was also higher (40±1%) in AA vs TA (23±1%, p<0.05), whereas elastin density was lower in AA compared to TA (11.2±0.8% vs 21.8±0.7%, p<0.05). Therefore, in a non‐human primate aging model, the abdominal aorta, as compared with the thoracic aorta, demonstrates marked increases in stiffness which can be attributed to a greater increase in collagen and decreased in elastin. These differences in aortic architecture with aging may predispose the abdominal aorta to aneurysm formation.