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

Abstract

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 were studied. 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 [standard error of the mean]) in cerebral blood flow; this increment decreased gradually, and 15-25 days later values for cerebral blood flow were similar to those obtained before ganglionectomy. Administration of norepinephrine (0.03-9 .mu.g) and tyramine (50-500 .mu.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 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 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. Perivascular sympathetic nerve endings may play an active role in overall regulation of cerebrovascular resistance in the goat, and .alpha.- and .beta.-receptors display a tonic adrenergic activity in cerebral blood vessels.