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Approaches to the mechanism of relaxing effect of vitamin K3 on smooth muscle.

Smooth muscle relaxing effect of vitamin K3 was tested by using isolated rat Vas deferens, normal and K+-depolarized rat duodenum. The contractions of the rat Vas deferens elicited by noradrenaline and phenylephrine were inhibited by vitamin K3, noncompetitively. Vitamin K3 inhibited the Ca2+-induced contractions of the K+-depolarized rat duodenum in a noncompetitive manner. The inhibitory effect of vitamin K3 on the K+-depolarized rat duodenum was evaluated by comparing it with that of verapamil, a well-known Ca2+-channel blocker and of trifluoperazine, a calmodulin inhibitor. Further, it was observed that vitamin K3 exerts a dose-dependent relaxing effect on the normal rat duodenum. The effect of vitamin K3 was compared with that of adrenaline, isoprenaline and papaverine. In addition, propranolol, a beta-adrenergic blocking agent, and nicotinic acid, an adenylate cyclase inhibitor, were used as tools in order to investigate the mechanism of the relaxing action of vitamin K3 on smooth muscle.