[Effect of histamine on the isolated aorta of the rabbit. Study of cyproheptadine].

The vascular effects induced by histamine and their inhibition by cyproheptadine have been studied on rabbit aortic strips. On arteries pre-contracted with phenylephrine, histamine provokes a dose-dependent relaxation only when mepyramine is present in the bath. This effect is independent of the integrity of endothelium. Cyproheptadine (10(-9) M) required the presence of cimetidine to give a parallel antagonism of the histamine curve (Kb: 0.32 nM). At higher concentrations of cyproheptadine (3 X 10(-9) and 10(-8) M) the effect was non-competitive. Cyproheptadine displaced to the right in a parallel manner the dose response curve of noradrenaline (pA2 = 6.6) and of serotonin (pA2 = 8.9) and reduced the contracting effects of KCl (IC50 = 7.3 10(-7) M) and of angiotensin II (IC50 = 4 X 10(5) M).