Effect of hexamethonium on the vascular response to noradrenaline in man.

Intra-arterial infusion of hexamethonium into the brachial artery had no potentiating effect on the constrictor response of the vessels of the forearm or hand to noradrenaline given by the same route. The response of the hand vessels to intravenous infusion of noradrenaline was enhanced after intra-arterial hexamethonium, but this was attributed to entry of the blocking agent into the general circulation resulting in blockade of baroreceptor reflexes since the potentiation was seen to an equal degree on both sides. It is concluded that if increased sensitivity to noradrenaline plays a part in the phenomenon of tolerance to hexamethonium this must be a slowly developing effect.