Effect of chronic hypertension and sympathetic denervation on wall/lumen ratio of cerebral vessels.

The purposes of this study were to determine whether 1) cerebral vessels undergo hypertrophy during chronic hypertension and 2) sympathetic nerves contribute to cerebral vascular changes in chronic hypertension. Morphometric studies were undertaken in stroke-prone spontaneously hypertensive rats (SP-SHR) and normotensive Wistar-Kyoto (WKY) rats. Unilateral superior cervical ganglionectomy was performed in the SP-SHR at 8 weeks of age. When the rats were approximately 13 months old, they were killed and the brain was fixed with formalin at a perfusion pressure of 80% of the rat's systolic pressure. Wall/lumen ratio was measured in approximately 1200 arteries and arterioles. In parenchymal, but not pial, cerebral vessels there was pronounced vascular hypertrophy in SP-SHR: wall/lumen ratio was 0.08 in WKY and 0.14 in SP-SHR (p < 0.05). Sympathetic denervation attenuated the development of vascular hypertrophy in SP-SHR: wall/lumen ratio was 0.14 in the innervated parenchymal vessels, and 0.10 in denervated vessels (p < 0.05). We conclude that cerebral vessels undergo hypertrophy in stroke-prone SHR and speculate that vascular hypertrophy may protect cerebral vessels by reducing wall stress in chronic hypertension. Sympathetic nerves appear to exert a trophic effect on cerebral vascular muscle in chronic hypertension.