Diameter and length changes in cerebral collaterals after middle cerebral artery occlusion in the young rat.

Rapid occlusion of the middle cerebral artery (MCA) in the 36-day-old normal Wistar rat results in change of the dorsal collaterals joining branches of the anterior and middle cerebral arteries. As compared to similarly positioned vessels on the opposite hemisphere and arterioles in unoperated rats of 56 days of age, there were significantly (P less than 0.001) more large (60-120 microM) diameter collaterals on the occluded side 20 days after MCA occlusion. There were fewer small (0-59 microm) diameter collaterals on the occluded side as compared to unoperated rats. The data suggest small diameter arterioles existing at occlusion became large diameter collaterals. The mean number of collaterals per hemisphere was not significantly different (P greater than 0.05) between occluded and unoperated rats. There was no evidence that new vessels were added during the 20-day ligation period. The mean collateral tortuosity value was significantly (P less than 0.01) greater for large diameter vessels on the right occluded side as compared to vessels on the left hemisphere or vessels in unoperated age-matched control rats. The greater tortuosity values of vessels on the occluded side were evidence that collateral vessel length was increased by 24-29% after MCA occlusion. Speculation was made about possible mechanisms responsible for these vascular changes.