Abstract

Objectives: We investigated histamine-induced responses in isolated rat aorta preparations and the role of vascular endothelium in these responses.

Study Design: Thoracic aorta segments obtained from 30 male Wistar rats were suspended in organ baths containing Krebs solution and isometric contractions and relaxations were recorded. The contractile and the relaxant effects of histamine and compound 48/80 in resting and phenylephrine-precontracted aortic strips were recorded both in endothelium-intact and –denuded preparations. The antagonistic effects of H1 receptor antagonist, pheniramine, and H2 receptor antagonist, cimetidine on these responses were investigated.

Results: Histamine per se produced contractile responses in all samples. While pheniramine, histamine H1-receptor antagonist, prevented histamine-induced contractile responses, cimetidine, H2-receptor antagonist, had no effect. Histamine produced relaxation in the submaximally contracted endothelial samples by phenylephrine, but no relaxation was observed in preparations without endothelium. Pheniramine prevented the relaxation of preparations with intact endothelium, whereas cimetidine had no effect. Compound 48/80, which releases histamine from mast cells, had no effect on either contraction or relaxation.

Conclusion: Histamine have both a contractile and endothelium-dependent relaxation effect on isolated rat aorta, mediated by H1-receptors.