THE EFFECT OF PHENOXYBENZAMINE AND OF TOLAZOLINE ON THE RESPONSE TO SYMPATHETIC STIMULATION.

The effect of phenoxybenzamine has been determined on the physiological response to sympathetic stimulation in two preparations, the rabbit isolated ileum and the guinea-pig isolated vas deferens. In both preparations phenoxybenzamine increased the response to stimulation of low frequency, the response being inhibitory in the one and motor in the other. This increase was large. As the stimulus frequency was raised, phenoxybenzamine caused a progressively smaller increase in the response, and at high frequencies phenoxybenzamine decreased the response. These observations agree with those of earlier workers who showed that antiadrenaline substances have more than one property. They not only block the motor effects of adrenaline and noradrenaline, but at the same time they may increase the response to sympathetic stimulation. The observations which have been made are not consistent with the interpretation which has been placed by others on the effect of phenoxybenzamine on the amount of noradrenaline appearing in the splenic vein following sympathetic stimulation; this interpretation assumes that phenoxybenzamine will decrease the response to sympathetic stimulation at low frequency. The mode of action of phenoxybenzamine is discussed, and fresh evidence that it has an anticholinesterase action is given.