EFFECTS OF VISNADINE ON RAT ISOLATED VASCULAR SMOOTH MUSCLES

Visnadine, an active principle extracted from the fruit of Ammi visnag a, exhibits peripheral and coronary vasodilator activities and has bee n used for the treatment of angina pectoris. The present study was und ertaken to further characterize the inhibitory effects of visnadine on the contractile responses in rat isolated aortic rings and portal vei n segments. Visnadine (< 10(-5) M) selectively inhibited the contracti ons induced by depolarization with 80 mM KCI or by CaCl2 in KCI-depola rized aorta and the spontaneous activity of the portal vein. Its inhib itory effects were not increased as the time of depolarization was pro longed and were similar in aorta incubated in 5 or 40 mM KCI. At conce ntrations higher than 10(-5) MI visnadine also inhibited the contracti le responses induced by noradrenaline and phorbol 12-myristate 13-acet ate (PMA), being equipotent to inhibit noradrenaline-induced contracti ons in either Ca2+-containing or Ca2+-free medium and PMA-induced cont ractions. In conclusion, the present results suggest that visnadine pr eferentially inhibited the contractile responses mediated by Ca2+ entr y through L-type Ca2+ channels, whereas at high concentrations it may also interfere with other sites involved in vascular smooth muscle con traction.