Heterogeneity of histamine H2-receptor mediated responses in the rabbit aorta

Distribution and properties of histamine H2-receptor mediated responses in segments of rabbit aorta was studied with histamine and H2-receptor stimulating drugs, dimaprit and impromidine. All agonists produced concentration-dependent tonus decreased in precontracted vascular strips, which were antagonised by selective H2-receptor antagonists, cimetidine and oxmetidine. Activities of the agonists were segment-dependent, and increased caudally along the aorta. A nonspecific smooth muscle relaxant, papaverine had homogeneous activity along the vessel, suggesting receptor specific nature of the observed heterogeneity.