DMPP-induced relaxation of the guinea pig urinary bladder.

Dimethylphenylpiperazinium (DMPP) caused a relaxation of a guinea pig urinary bladder in vitro when a intraluminal pressure of bladder had been increased by physostigmine or histamine. The relaxing effect of DMPP was also observed in the contractions elicited by electrical stimulations. It was not blocked by hexamethonium, phenoxybenzamine, phentolamine, propranolol or tetrodotoxin. ATP and amines (such as glutamic acid, glycine, GABA, 5-HT and histamine) caused no relaxing effect on the physostigmine-induced contraction. The results indicate that the DMPP-induced relaxation appears to be a direct action of DMPP on the smooth muscle of the bladder and to differ from its adrenergic transmitter releasing or atropine-like action.