Blocking effect of tripelennamine on histamine--induced positive chronotropic and inotropic responses of the dog atrium.

The effects of histamine on inotropic and chronotropic activity were investigated in isolated canine atrium preparations which were suspended in a bath and perfused with arterial blood from a carotid artery of heparinized support dog. Histamine administered into the cannulated sinus node artery in a dose range of 0.3-100 mug produced dose-related positive chronotropic and inotropic effects. The positive responses to histamine were not suppressed by treatment with propranolol in doses which blocked responses to norepinephrine, but these were significantly suppressed by a histamine H1 receptor blocking agent, tripelennamine. On the other hand, these histamine-induced effects were not modified by a histamine H2 receptor blocking agent, burimamide. From these results, it is assumed that positive chronotropic and inotropic effect of histamine may be mediated by histamine H1 receptors in the dog heart.