Resistance of the histamine H2 receptor in guinea-pig heart to blockade by phenoxybenzamine.

Phenoxybenzamine is a potent irreversible H1 receptor antagonist in a variety of tissues. In order to assess the ability of this agent to antagonise the H2-receptor, we have examined the effects of phenoxybenzamine on the histamine-induced positive inotropic effect in electrically driven strips of guinea-pig right ventricle. Even at concentrations as high as 10(-4)M no significant change in the responses to histamine was observed. It is concluded that the histamine H2 receptor is unexpectedly resistant to antagonism by 2-haloalkylamines.