Calcium antagonism of enpiperate on isolated rabbit aorta strips and guinea pig ileum

Enpiperate, 4-(3, 5)-exocydopropyl-N-methylpiperidyl diphenyl hydroxy acetate, was synthesized in China. It has been shown to have no effect on the normal tension of rabbit aorta strips or contractions induced by NE. It inhibited the contraction of high K+-depolarized rabbit aorta strips at concentrations of 3.8 and 10.9 mumol/L. The same effect was seen on isolated guinea pig ileum, at a concentration of 10.9 mumol/L, which was depolarized by Ca2+ free high K+ Locke-Ringer's solution and the contraction was extragenous Ca2+ dependent. The inhibition was overcome by increasing the extracellular Ca2+ concentration. In the presence of EDTA (0.1 mmol/L), the NE induced intracellular Ca2+ dependent contraction was inhibited by enpiperate (3.8, 10.9 mumol/L), although no significant difference was found between enpiperate and papaverine. It is suggested that enpiperate is a calcium antagonist and that the antagonism is carried out by blocking the potential dependent calcium channel (PDC) in the membrane of vascular smooth muscles. A intracellular calcium antagonistic action may also be involved.