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

Pial arterial and venous calibre 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 micron) constricted by 11.7 +/- 0.8% and 80 venous portions (mean diameter 152 micron) 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 X 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 X 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 greater than 150 micron was attenuated. It is concluded that 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 on resistance vessels under normotensive and normocapnic conditions.