Blocking of Adrenergic-cholinergic Interaction by Phenoxybenzamine

Abstract

The selective administration of any naturally occurring catecholamine (dopamine, norepinephrine and epinephrine) into the sinus node artery induced suddenly deceleration of sinus rhythm in the course of its acceleration response, indicating depression of P wave or shift to A-V nodal rhythm. Atropine blocked the negative chronotropic effect. Phenoxyhenzamine and hemicholinium also blocked this effect, while acetylcholine (ACh) acted ordinarily even after treat-ments with these compounds. These observations suggest catecholamine-ACh interaction in which either phenoxybenzamine or hemicholinium blocks ACh release at the cholinergic nerve terminals.