Structural and functional changes in cerebral arteries from spontaneously hypertensive rats.

Segments of basilar arteries from both spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were studied in vitro utilizing a microvessel apparatus. At similar levels of passive force, basilar arteries from SHR developed less force in response to depolarizing solution (130 mM K+) compared to basilar arteries from WKY. Arterial segments from the hypertensive animals required less stretch to achieve each level of passive force. Basilar arteries from SHR but not WKY typically displayed both phasic and tonic spontaneous activity which was inhibited in a reversible manner by washing the tissues in physiological salt solution without added Ca++ (EGTA, 1 mM). There was a significant shift to the left in the EC50 of serotonin and a greater maximal response to this agonist in basilar arteries from SHR compared to those from WKY (p less than 0.01). The EC50 to Ca++ (added to a depolarizing solution) was shifted to the right in the arteries from SHR compared to the normotensive controls (p less than 0.05). There was no difference between the arteries from the two groups of animals in the relaxation response produced by isoproterenol. However, contracted basilar arteries from SHR were less sensitive to the relaxant effects of elevated Ca++ than contracted basilar arteries from WKY (p less than 0.05). These results demonstrate the existence of both structural and functional difference between cerebral vessels of SHR and WKY. Our findings also demonstrate the complex nature of the changes in calcium dynamics in blood vessels from hypertensive animals.