Role of adrenergic nerves in blood-induced cerebral vasospasm.

Abstract

Cerebral arteries have an abundant supply of adrenergic nerve fibers which are believed to release vasoactive substances responsible for the induction of cerebral vasospasm. To assess the importance of adrenergic nerves in this phenomenon, high doses (600 microgram/ml) of 6-hydroxydopamine (6-OHDA) were used to produce in vitro chemical sympathectomy in bovine middle cerebral artery. 6-OHDA reduced catecholamine fluorescence to undectable limits. H3-norepinephrine re-uptake was reduced to 1.5% of intact controls. Arterial norepinephrine content was reduced by 92%. Contractile responses to norepinephrine, serotonin, and fresh human whole blood were modestly reduced after denervation. This reduction was probably due to alpha receptor inactivation by 6-OHDA, because after protection of the alpha receptors with phentolamine the vessel response was the same as in untreated controls. Contractions in response to aged human whole blood were not affected by denervation. The results suggest that the endogenous release of catecholamines does not play a major role in the initiation or spread of blood-induced vasospasm in large cerebral arteries.

The Pharmacology of Cerebral Vasospasm

“…On the other hand, Simeone et al [1979] induced denervation with 6-hydroxydopamine and found that there was little differ ence in the reactivity of the vessels to cate cholamines, 5-HT or whole blood. Toda et al [1977] examined the contractility of blood vessels in spasm obtained from dogs, and found that the vessel in spasm did not differ significantly from control preparations in re sponse to 5-HT, noradrenaline, histamine, or high potassium.…”

The Nature of Cerebral Vasospasm

“…(c) Neurogenic effects may certainly be in volved in any kind of CBF regulation [29][30][31][32][33][34][35][36] and in the development of cerebral vaso spasm as well [44][45][46][47][48][49][50][51]. Neurogenic stimuli may exert their effects upon any cerebral arteries, especially the larger ones which pos sess an abundant vasoconstrictor adrenergic nerve supply [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], Under normal condi tions, neurogenic regulation of CBF is pre cisely adjusted, and thus should not cause vasospasms disturbing normal blood supply to the brain.…”