PHYTOTHERAPY RESEARCH, VOL. zyxwvuts 9, 555-558 zyxwvut (1995) Smooth Muscle Relaxant Activities of Compounds Isolated from Malaysian Medicinal Plants on Rat Aorta and Guinea-pig Ileum zy Mohd. Rais Mustafa* and Rohaini Mohamad Laily Dint and Shamsuddin WahidS t Faculty of Resource Science Technology, University of Sarawak, 94300 Kota Samarahan, Sarawak and zyxw $ Department of Chemistry, Faculty of Applied Sciences, National University of Malaysia, 43600 Bangi, Selangor, Malaysia Department of Pharmacology, Faculty of Medicine, University of Malaya, 59100 Kuala Lumpur, Malaysia Muscle relaxant activities of six compounds isolated from Malaysian medicinal plants were investigated on the smooth muscles of the rat aorta and longitudinal muscle of the guinea-pig ileum. Except for goniothalamin, the other five compounds exhibited varying degrees of muscle relaxant activities on the two smooth muscles. Dicentrine, isocorydine, altholactone and usnic acid reduced the contractions to KCI and phenylephrine in the rat aorta, whilst atranorin slightly reduced the contractions to phenylephrine but not KCI. In addition, dicentrine and isocorydine markedly reduced the contractile response to phenylephrine in Ca2+-free Krebs solution. In the longitudinal muscle of the guinea-pig ileum, altholactone, atranorin, dicentrine and isocorydine inhibited to a greater extent the phasic than the tonic responses to KCI. All four compounds similarly inhibited the contractions induced by ACh. The results suggest that the relaxant activities of the compounds are attributed mainly to inhibition of Ca2+ influx via the calcium channels in the membrane of the smooth muscles. Furthermore, the greater sensitivity of dicentrine, isocorydine and altholactone against phenylephrine-induced contractions or KCI-induced phasic contractions are due to their abilities to inhibit intracellular Ca2+release in these muscles. Keywords: plant products; calcium; calcium-free; rat aorta; guinea-pig ileum. such as prazosin and calcium antagonists are widely used as antihypertensives; organic nitrates and nitrites INTRODUCTION as anti-anginals; xanthine derivatives as bronchodila- Smooth muscle activity is affected by many endogenous tors in the treatment of asthma; papaverine in the substances. A wide range of drugs, synthetic or isolated treatment of colic. The aim of the present study is to from natural resources have relaxant activities on investigate the relaxant effects of major compounds smooth muscles of various types. Thus, vasodilators isolated from Malavsian medicinal dants on smooth Author to whom correspondence should be addressed. zyxwvut gn 0 muscles of the rat aorta and guinea-pig ileum (Fig. 1). About 6000 species of flowering plants are found in the dicentrire (ktimdrpme sesqiped3lis) isaorydine (Alphaaeo curtissi) Figure 1. Chemical structures and sources of medicinal plants of the various compounds. CCC 0951-418X/95/08055S-04 zyxwvutsr 0 1995 by John Wiley & Sons, Ltd. zyxwvutsrqp Accepted (revised) 1.5 December 1994