Mechanisms of augmented vascular responses to histamine in atherosclerotic rabbit common carotid arteries.

The vascular responsiveness to histamine, 2-pyridylethylamine and dimaprit was investigated in isolated and perfused atherosclerotic rabbit common carotid arteries enclosed by a hollow silastic collar. The constrictor effects of histamine were significantly enhanced in atherosclerotic arteries, although those of 2-pyridylethylamine were not changed. The dilator effects of histamine and dimaprit, which were completely inhibited after pretreatment with cimetidine, were not influenced by removal of the endothelium but significantly depressed in atherosclerotic arteries. The dose-response curves for histamine in the control group pretreated with cimetidine were shifted to the left and responses reached almost the same level as those of the atherosclerotic group. From these results, it is concluded that histamine-induced vasoconstrictions are enhanced in atherosclerotic arteries, and that the mechanism of the hyperreactivity to histamine might be an attenuation of the vasodilatations mediated via histamine H2 receptors in vascular smooth muscle.