SMOOTH-MUSCLE RELAXANT ACTIVITIES OF COMPOUNDS ISOLATED FROM MALAYSIAN MEDICINAL-PLANTS ON RAT AORTA AND GUINEA-PIG ILEUM

Muscle relaxant activities of six compounds isolated from Malaysian me dicinal plants were investigated an the smooth muscles of the rat aort a and longitudinal muscle of the guinea-pig ileum. Except for goniotha lamin, the other five compounds exhibited varying degrees of muscle re laxant activities on the two smooth muscles. Dicentrine, isocorydine, altholactone and usnic acid reduced the contractions to KCI and phenyl ephrine in the rat aorta, whilst atranorin slightly reduced the contra ctions to phenylephrine but not KCI. In addition, dicentrine and isoco rydine markedly reduced the contractile response to phenylephrine in C a2+-free Krebs solution. In the longitudinal muscle of the guinea-pig ileum, altholactone, atranorin, dicentrine and isocorydine inhibited t o a greater extent the phasic than the tonic responses to KCI. All fou r compounds similarly inhibited the contractions induced by ACh. The r esults suggest that the relaxant activities of the compounds are attri buted mainly to inhibition of Ca2+ influx via the calcium channels in the membrane of the smooth muscles. Furthermore, the greater sensitivi ty of dicentrine, isocorydine and altholactone against phenylephrine-i nduced contractions or KCI-induced phasic contractions are due to thei r abilities to inhibit intracellular Ca2+ release in these muscles.