Actions of dimethylphenylpiperazinium.

The actions of 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP) have been studied to discover under what conditions a blocking action could be seen. Dimethylphenylpiperazinium has a stimulant action on autonomic ganglia, stimulating the superior cervical ganglion and causing contraction of the nictitating membrane. It caused slowing followed by acceleration of the rate of beat of isolated rabbit atria. The denervated gastrocnemius muscle contracted if dimethylphenylpiperazinium was injected intra-arterially. Under other circumstances a blocking action was seen. It blocked peristalsis in the isolated guinea-pig ileum stimulated by raising intraluminal pressure and inhibited the response of the rat diaphragm and of the cat gastrocnemius stimulated through the motor nerve. It is suggested that dimethylphenylpiperazinium acts by depolarization, causing stimulation of resting muscle but inhibition by prolonging depolarization.