EFFECTS OF AGING ON MECHANICS AND COMPOSITION OF CEREBRAL ARTERIOLES IN RATS

The purpose of this study was to examine effects of aging on the mechanics and composition of cerebral arterioles. We measured pressure (servo-null) and diameter in pial arterioles in anesthetized adult (9-12 months old) and aged (24-27 months old) Fischer 344 rats. After deactivation of smooth muscle with EDTA, diameter of pial arterioles at 70 mm Hg pial arteriolar pressure was less in aged than in adult rats (67 ± 4 vs. 81 ± 4 μm [mean ± SEM], p < 0.05). The stress-strain relation and the slope of tangential elastic modulus versus stress (6.8 ± 0.6 vs. 5.3 ± 0.3, p < 0.05) indicated that distensibility of pial arterioles was reduced in aged rats. Cross-sectional area of the vessel wall, measured histologically, was less in aged than adult rats (1,239 ± 91 vs. 1,832 ± 180 μm2, p < 0.05). Point counting stereology was used to quantitate smooth muscle, elastin, collagen, and basement membrane in the arteriolar wall. Cross-sectional areas of smooth muscle and elastin were significantly less in aged than adult rats (744 ± 57 vs. 1,291 ± 119 μm2 for smooth muscle, 52 ± 6 vs. 113 ± 15 μm2 for elastin; p < 0.05), whereas cross-sectional areas of collagen and basement membrane were not significantly different in aged and adult rats (4 ± 1 vs. 3 ± 1 μm2 for collagen, 236 ± 17 vs. 258 ± 31 μm2 for basement membrane). The ratio of nondistensible (collagen and basement membrane) to distensible (smooth muscle and elastin) components was greater in aged than adult rats (0.30 ± 0.01 vs. 0.18 ± 0.01, p < 0.05). Thus, we conclude that, during aging, cerebral arterioles undergo atrophy, distensibility of cerebral arterioles is reduced, and the relative proportion of distensible elements, elastin and smooth muscle, is reduced in the arteriolar wall.