Mechanics and composition of arterioles in brain stem and cerebrum.

The goal of this study was to compare mechanics and composition of arterioles in brain stem and cerebrum. We calculated stress and strain of pial arterioles in anesthetized rats from measurements of pial arteriolar pressure (servo-null), diameter, and cross-sectional area of the vessel wall. Composition of pial arterioles was quantitated using point-counting stereology. Before deactivation of smooth muscle with ethylenediaminetetraacetic acid (EDTA), pial arteriolar pressure and diameter were 28 and 30% greater (P less than 0.05) in brain stem than cerebrum. After EDTA, diameter of arterioles was similar in brain stem and cerebrum. Cross-sectional area of the arteriolar wall was 32% greater (P less than 0.05) in brain stem than cerebrum. Stress-strain curves indicated that distensibility of pial arterioles is greater in brain stem than cerebrum. The proportion of nondistensible (collagen and basement membrane) to distensible (elastin, smooth muscle, and endothelium) components was 20% less (P less than 0.05) in brain stem than cerebral arterioles. We conclude that 1) cross-sectional area of the vessel wall in arterioles of comparable size is greater in brain stem than cerebrum, 2) distensibility of arterioles is greater in brain stem than cerebrum, despite greater cross-sectional area of the arteriolar wall in brain stem, and 3) the proportion of elastic components is greater in brain stem than cerebral arterioles, which may contribute to greater arteriolar distensibility in brain stem.