EFFECTS OF SEROTONIN ON CEREBRAL-CIRCULATION AFTER MIDDLE CEREBRAL-ARTERY OCCLUSION

Serotonin (5-HT) produces constriction of peripheral collateral blood vessels. Using an animal model, the authors tested the hypothesis that 5-HT constricts collateral vessels in the cerebrum. A branch of the m iddle cerebral artery (MCA) was occluded proximally and cannulated dis tally in anesthetized dogs. Blood flow to the area at risk for infarct ion was detected by perfusing the cannulated MCA branch with microsphe re-free blood during systemic injection of radioactive microspheres (s hadow flow technique). Blood flow to collateral-dependent and normal c erebrum was measured during intravenous infusion of 5-HT (10 and 40 mg /kg/minute). Serotonin produced a dose-related reduction of blood flow to collateral-dependent cerebrum, increased collateral Vessel resista nce in large cerebral arteries and collateral vessels, and decreased c erebral artery perfusion pressure. In contrast, blood flow to normal c erebrum was not altered because a decrease in small vessel resistance effectively compensated for a decrease in MCA perfusion pressure. Thes e findings indicate that 5-HT produces constriction of collateral vess els in the cerebrum. This response is clearly different from normal sm all cerebral vessels, which dilate during 5-HT infusion.