Effect of sympathetic nerve stimulation and adrenoceptor blockade on pial arterial and venous calibre and on intracranial pressure in the cat

Abstract

Pial arterial and venous caliber were continuously recorded through a closed cranial window preparation during cervical sympathetic nerve stimulation in 10 cats before and after .alpha.- and .beta.-adrenoceptor blockade. In addition, the intracranial pressure (ICP) was simultaneously recorded in 4 of the cats. Under resting conditions 33 arteries (mean diameter 130 .mu.m) constricted by 11.7 .+-. 0.8% and 80 venous portions (mean diameter 152 .mu.m) constricted by 13.7 .+-. 0.7% during sympathetic nerve stimulation. ICP decreased simultaneously by 16.5 .+-. 6.2%. Administration of the .alpha.-adrenoceptor antagonist phenoxybenzamine i.v. (1.5 mg .cntdot. kg-1) abolished the reduction of ICP and markedly reduced, but did not completely abolish, the constrictor response of arteries and veins. The .beta.-adrenoceptor antagonist propranolol (1.5 mg .cntdot. kg-1) did not significantly alter the reduction of ICP or the response of pial veins and small arteries, whereas the response of arteries with a diameter > 150 .mu.m was attenuated. Evidently, the constriction of pial veins and arteries during sympathetic stimulation is mediated predominantly via .alpha.-adrenoceptors. The sympathetic nerves of cerebral blood vessels may have stronger influence on the cerebral capacitance than resistance vessels under normotensive and normocapnic conditions.