Abstract
Antispasmodic activity of onitin has been assessed and it was found to be an active principle in the herb of Onychium siliculosum (Desv.) C. Chr (Pteridaceae). To compare the effects of onitin and papaverine, the isolated ileum and vas deferens of the guinea pig as well as the stomach strip and uterine muscle of the rat were used. Onitin inhibited contractile responses of the ileum to agonists inculding ACh, K+ and Ba2+ in normal Tyrode solution and to exogenous Ca2+ in high K+ (80 mM), Ca2+-free Tyrode solution. In addition, the contractile responses of stomach strip, vas deferens and uterine muscle to agonists tested, were also inhibited by onitin. Thus, onitin is a non-specific smooth muscle relaxant similar to papaverine, but to a lesser extent. Onitin could non-selectively reduce both the phasic contraction (PC) and the tonic contraction (TC) of the polarized ileum to ACh and the depolarized ileum to exogenous Ca2+. While papaverine could only selectively reduce the TC of polarized and depolarized ileum. It can be concluded that onitin acts a non-specific antispasmodic action like papaverine, but the mechanism of action is different from that of papaverine.
