Inhibition by ketanserin of serotonin induced cerebral arteriolar constriction.

We studied the effects of serotonin on pial arterioles in anesthetized cats equipped with acutely implanted cranial window for the observation of the pial microcirculation. Serotonin topically applied caused cerebral arteriolar constriction. Ketanserin, a specific 5-HT2 inhibitor, completely blocked the vascular response of serotonin. Aggregated platelet supernatant was topically applied and caused generalized cerebral arteriolar constriction that could be blocked with ketanserin. We conclude that serotonin causes generalized cerebral arteriolar constriction that is due to the stimulation of 5-HT2 receptor. Aggregating platelets release serotonin, which mediates the vasoconstrictive action of the supernatant solution.