In vitro vasorelaxing activity of suloctidil

The vasorelaxing effect of suloctidil was evaluated in isolated rat and rabbit aorta and in isolated rabbit mesenteric and saphenous artery. Suloctidil inhibited contractions induced by increasing extracellular calcium in depolarized arteries, mainly in a competitive way. In the rat aorta, the pA2 value was 7.50 for suloctidil, while pA2 values of 9.96, 7.90 and 8.10 were obtained for nifedipine, cinnarizine and verapamil, respectively. Suloctidil more potently inhibited calcium-induced contractions in small arteries (mesenteric and saphenous artery), than in the aorta. Suloctidil also reduced the tonic component of the responses to norepinephrine. In contrast to the effects on calcium-induced contractions, the effects of suloctidil on norepinephrine-induced responses was mainly noncompetitive. In addition, and unlike cinnarizine and verapamil, high concentration of suloctidil also reduced the phasic component of contractile responses to norepinephrine. Furthermore, unlike nifedipine, verapamil, diltiazem and cinnarizine, suloctidil was devoid of a negative inotropic effect in spontaneously beating guinea-pig atria. In conclusion, suloctidil behaves as a Ca2+-channel blocker in arteries and displays an additional mode of action that could include receptor-operated Ca2+-channels or an intracellular site of action. In addition, suloctidil was found to affect small arteries more than the aorta, and not to affect the atria.