EFFECT OF 1,1-DIMETHYL-4-PHENYL-PIPERAZINIUM ON RESPONSE OF MESENTERIC ARTERIES TO SYMPATHETIC NERVE STIMULATION

The effect of 1,1‐dimethyl‐4‐phenylpiperazinium (dmpp) on the response to sympathetic nerve stimulation of rat mesenteric arteries perfused with Tyrode solution at a constant flow has been studied. dmpp (0·3 μg/ml) infused for 3 min enhanced the vasoconstriction caused by stimulation. Infusion of the same concentration for 16–40 min greatly reduced the response to nerve stimulation but did not affect the vasoconstrictor response to injected noradrenaline. The blockade of the response to nerve stimulation produced by dmpp was overcome either by adding (+)‐amphetamine to the perfusion fluid or by raising the calcium concentration. Neither effect of dmpp was altered by the infusion of atropine. These effects of dmpp were similar to those seen when acetylcholine was added to the perfusion fluid except that the effects of acetylcholine were diminished or abolished by a concentration of atropine much higher than that of acetylcholine. It is concluded that the receptors at the adrenergic nerve terminals are partly muscarinic and partly nicotinic. 1969 Royal Pharmaceutical Society of Great Britain