It was demonstrated recently that, in contrast to large cerebral arteries, distensibility of cerebral arterioles is increased in stroke-prone spontaneously hypertensive rats (SHRSP). The goals of this study were to examine composition of normal cerebral arterioles, and to determine whether chronic hypertension alters relative composition of the arteriolar wall. Pial arterioles in normotensive Wistar Kyoto rats contain large amounts of smooth muscle, small amounts of elastin and basement membrane, and very little collagen. Hypertrophy of pial arterioles in SHRSP is characterized by increases in the elastic components, smooth muscle and elastin. The stiffer components, collagen and basement membrane either did not change or decreased. It is concluded that cerebral arterioles contain proportionately more smooth muscle and less collagen than large arteries, and that hypertrophy of cerebral arterioles in SHRSP is accompanied by a relative increase in the more elastic components of the arteriolar wall, which probably contributes to the increase in arteriolar distensibility.
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