Effect of histamine on aorta preparations of different species.

The effect of histamine (10(-8) to 10(-3)M) on aorta preparations of 5 different species was studied. In aortic ring segments, precontracted by norepinephrine, three types of dose-response curves were found: relaxation (rat), contraction (guinea-pig, cat, mouse) and relaxation followed by contraction at higher doses (rabbit). In relaxed preparations, histamine either had no effect (rat) or elicited a contraction (rabbit, guinea-pig). All the contraction effects proved to be H1-mediated as they were antagonized by mepyramine. These contraction effects were maintained or even increased after rubbing the endothelial surface of the vessel, which suggests a direct action on muscular structures. The differences between the species in the dose-response curves to histamine appeared to be determined by the role of the endothelial structures, which can induce an H1-mediated (rat) or an H2-mediated (rabbit) relaxation or may have no influence (guinea-pig).