Effect of intracarotid hyperosmolar mannitol on cerebral cortical arterioles--a morphometric study.

The morphometric response of cerebral cortical arterioles to intracarotid hyperosmolar mannitol was assessed utilizing a technique of rapid freezing of rat brain tissue in vivo. A significant decrease in the wall to lumen (W/L) ratio was noted in the small parenchymal arterioles (20-49 mu) (p less than .0001) ipsilateral to the mannitol infusion. Larger arterioles showed a decreased W/L ratio but this change was not significant. Control infusion of 0.9% NaCl resulted in no change in arteriolar caliber. These results indicate that intracarotid hyperosmolar mannitol causes a direct vasodilatory response in small cerebral cortical arterioles.