Absence of Blocking Effect of Burimamide and Metiamide on Positive Chronotropic and Inotropic Responses to Histamine in Isolated Dog Atrium

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Abstract
When histamine was injected into the sinus node artery of isolated dog atrium perfused with arterial blood led from a carotid artery of the heparinized support dog, positive chronotropic and inotropic effects were induced in a dose-related manner in a range of 0.1-100 .mu.g. The threshold dose for inducing these positive effects was approximately 0.3 .mu.g. These positive responses to histamine were not blocked by tetrodotoxin, desmethylimipramine and alprenolol. These positive effects of histamine were also not significantly influenced by treatment with a histamine H2 receptor antagonist, burimamide or metiamide. However, these histamine-induced positive chronotropic and inotropic effects were significantly suppressed by an adequate dose of histamine H1 receptor antagonist, tripelennamine or diphenhydramine, which enhanced the actions of norepinephrine. In the dog atrium, histamine appears to cause positive chronotropic and inotropic effects via histamine H1 receptors.