Arrhythmogenic effects of histamine on ischemia hearts of guinea pigs

The arrhythmogenic effects of histamine on guinea pig Langendorff heart prepared 20 min after coronary ligation were studied. The arrhythmias induced by histamine 0.4 and 0.6μmol in the ischemic hearts were much more serious than that in the sham-operated hearts. The arrhythmoenic effects of histamine were antagonized by drugs capable of blocking either H2 receptors (cimetidine 1 and 10μmol/L) or H1 receptors (chlorpheniramine and mepyramine 5 and 10μmol/L). The results suggested that the ischemic and nonischemic hearts differed much in their sensitivities to the arrhythmogenic effects of histamine, which were the resultant of two components: H1 and H2, and mediated mainly by H2 receptors.