Negative dromotropic response to phenylephrine blocked by phenoxybenzamine.

Abstract

In most canine excised and cross-circulated A-V node preparations phenylephrine induced a monophasic long-lasting positive dromotropic effect, and in some a triphasic response, i.e., positive-negativepositive dromotropic one. The negative dromotropic response was abolished by phenoxybenzamine and also blocked by l-hyoscyamine. Then, the triphasic response was converted to a monophasic positive one which was blocked by 1-alprenolol.