Cerebral circulatory and metabolic effects of 5‐hydroxytryptamine in anesthetized baboons.

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Abstract
The cerebral circulatory effects of the intracarotid administration of 5-hydroxytryptamine [5-HT] were examined in anesthetized baboons. Cerebral blood flow was measured by the intracarotid 133Xe technique, cerebral O2 consumption and glucose uptake were measured as indices of brain metabolism and electrocortical activity was continuously monitored. Despite a marked reduction in the caliber of the internal carotid artery (assessed angiographically), the intracarotid infusion of 5-HT 0.1 .mu.g/kg .cntdot. min did not effect any significant changes in cerebral blood flow, O2 consumption or glucose uptake. Following transient osmotic disruption of the blood-brain barrier with the intracarotid infusion of hypertonic urea, the same dose of 5-HT effected a marked reduction in cerebral blood flow from 51 .+-. 2 to 36 .+-. 2 ml/100 g .cntdot. min (mean .+-. SE; P. < 0.01). Both indices of cerebral metabolism were reduced significantly and the EEG showed a more pronounced suppression-burst pattern. Probably, cerebral circulatory responses to 5-HT are dependent upon the integrity of the blood-brain barrier and the predominant effect of the intravascular administration of 5-HT is on cortical activity or metabolism, rather than on cerebrovascular smooth muscle.