A phenoxazine compound, 2-amino-4,4alpha-dihydro-4alpha-7-dimethyl-3H-phenoxazine-3-one reverses the phenylephrine or high-K+ induced contraction of smooth muscles in rat aorta and guinea pig tenia cecum.

2-Amino-4,4alpha-dihydro-4alpha-7-dimethyl-3H-phenoxazine-3-one (Phx-1) reversed concentration dependently the contraction of both rat aorta and guinea pig tenia cecum induced by phenylephrine or high-K(+). Since Phx-1 suppresses the responses of human mononuclear cells to phytohemagglutinin, (Akazawa et al. Tohoku J. Exp. Med., 196, 185-192, 2002), Phx-1 may be useful for developing new vasorelaxing agents with immunosuppressive action.