Responsiveness of Isolated Cerebral and Peripheral Arteries to Serotonin, Norepinephrine, and Transmural Electrical Stimulation

Abstract

Spirally cut strips of cerebral and peripheral arteries from dogs were used for comparing the vasoconstricting effect of serotonin, norepinephrine, K⁺, and transmural electrical stimulation. Sensitivity of cerebral (basilar, posterior cerebral, and middle cerebral) arterial strips to serotonin was markedly greater than that to norepinephrine with respect to the median effective concentration (ED₅₀) and the maximum response. Contractile responses of isolated human cerebral arteries to serotonin and norepinephrine were similar to those observed in the dog arteries. In contrast, proximal and distal strips from superior mesenteric arteries and strips from renal arteries were more sensitive to norepinephrine than they were to serotonin. Mean values of contractions caused by 5 x 10^-6M serotonin relative to those caused by 30 mM K⁺ in cerebral, internal carotid, external carotid, common carotid, and superior mesenteric arteries were in a descending order, whereas those for norepinephrine were in an ascending order. These studies demonstrate that a gradual transition occurs from characteristic responses seen in mesenteric arteries (high sensitivity to norepinephrine, low sensitivity to serotonin) to those seen in cerebral arteries (high sensitivity to serotonin, low sensitivity to norepinephrine). Transmural stimulation did not produce contractions of cerebral and internal carotid arteries, but contractions were produced in external carotid, common carotid, and superior mesenteric arteries. It appears that sympathetic nerves cannot play an important role in the regulation of vascular tone in large cerebral arteries.