Earlier studies established that stroke-prone spontaneously hypertensive rats (SHRSP) invariably infarct after middle cerebral artery (MCA) occlusion. Normotensive rats are usually protected from infarction after the occlusion. Objectives of this study were to characterize the anastomosing collaterals that may determine the different outcomes to MCA occlusion in SHRSP and Wistar Kyoto rats (WKY). Young (5-10 week) and old (40-69 week) rats of each sex were anesthetized, then administered papaverine to produce maximal vasodilatation of the cerebrovascular bed. Under control conditions latex was injected into the arterial tree to measure the internal diameter of branches of the anterior cerebral artery (ACA), the MCA, and the ACA-MCA anastomosing collaterals. Large diameter ACA and MCA rami in old, but not young, SHRSP were significantly smaller in diameter than the respective ACA and MCA branches in old WKY. The number of ACA-MCA anastomoses was the same for SHRSP and WKY. Mean internal diameter of the ACA-MCA anastomoses was significantly (p < 0.0001) smaller in SHRSP than WKY in both age groups. There were significant negative correlations between age and 1) the internal diameter of the ACA-MCA anastomoses in WKY but not SHRSP, and 2) the largest diameter ACA and MCA rami in SHRSP but not WKY. The findings suggest that vascular resistance of fully relaxed collaterals is greater in SHRSP than WKY, thereby compromising the dorsal collateral circulation before large diameter vessel changes occur that accompany the established form of hypertension.
Sudden occlusion of the middle cerebral artery (MCA) doidal suture was thinned with a dental burr to permit just above the rhinal fissure reduces blood flow to the microscopic observation of the collaterals through a territory of the occluded MCA and invariably results in closed cranial window. The observation permitted asinfarction in the stroke-prone spontaneously hyperten-sessment of vessel filling during latex injection. Details sive rat (SHRSP) ; Coyle and of the procedure are given elsewhere (Coyle and Jokelai-