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We studied the effects of removal of the superior cervical sympathetic ganglion on cerebral blood flow and vascular reactivity to adrenergic agonists and antagonists in 11 unanesthetized goats. Cerebral blood flow was measured by an electromagnetic flow transducer previously implanted on the internal maxillary artery. Ganglionectomy produced an increase of 66 ± 8.26% (SEM) in cerebral blood flow; this increment decreased gradually, and 1525 days later values for cerebral blood flow were similar to those obtained before ganglionectomy. The administration of norepinephrine (0.03-9 /ng) and tyramine (50-500 /*g) into the internal maxillary artery in normal goats produced dose-dependent reductions in .cerebral blood flow. At 6-8 days after ganglionectomy the reduction of cerebral blood flow produced by norepinephrine was markedly increased, whereas the effects of tyramine were diminished. Before ganglionectomy the administration of phentolamine (1 mg) into the internal maxillary artery produced a 31% increase in cerebral blood flow, whereas the injections of propranolol (1 mg) into the same site reduced cerebral blood flow by 14%. After removal of the superior cervical ganglion the effects of the same doses of the adrenergic blocking drugs were considerably lessened. These results support the view that the perivascular sympathetic nerve endings play an active role in the overall regulation of cerebrovascular resistance in the goat and indicate that both aand /3-receptors display a tonic adrenergic activity in the cerebral blood vessels.

Cerebral blood flow and vascular reactivity after removal of the superior cervical sympathetic ganglion in the goat.