Characteristics of histamine receptors in the isolated and perfused canine coronary arteries.

The vascular responses of isolated and perfused canine epicardial coronary arteries to histamine, 2-pyridylethylamine (2-PEA, a selective histamine H1-receptor agonist) and dimaprit (a selective histamine H2-receptor agonist) were studied. Histamine produced only a vasodilatation at small doses (less than 0.3 microgram) and a biphasic response, i.e., vasoconstriction followed by vasodilatation at large doses. 2-PEA produced only a vasoconstriction at small doses and at large doses a slight vasodilatation following vasoconstriction. Dimaprit usually induced only a vasodilatation. The selective histamine H1-receptor antagonist chlorpheniramine shifted the dose-response curves of histamine and 2-PEA for inducing vasoconstriction to the right. Cimetidine (a selective histamine H2-receptor antagonist) caused dose-dependent shifts of the dose-response curves of histamine and dimaprit for vasodilatations to the right. Chlorpheniramine did not attenuate the vasodilatations by 2-PEA and histamine. The removal of endothelial cells by an intraluminal injection of saponin (1 mg) did not affect the vascular responses to histamine, 2-PEA and dimaprit. These results indicate that there are 2 types of histamine receptors in canine epicardial coronary arteries: (i) a H1-receptor mediating vasoconstriction and (ii) a H2-receptor, which is not endothelium-dependent, mediating vasodilatation.