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

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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.