Effect of verapamil and phenoxybenzamine on nickel-induced coronary vasoconstriction in the anaesthetized dog.

Ni-induced coronary vasoconstriction has been studied in the dog heart in situ in the presence of the selective Ca-antagonist verapamil, and after blocking the alpha-receptors with phenoxybenzamine (PBZ). Verapamil totally abolished the coronary blood flow (CBF) and basal conductance (BC) decreasing effect of low doses of Ni2+ (0.02-0.2 mg/kg-1). The effect of higher doses of Ni2+ (2.0-20.0 mg/kg-1) was reversed by verapamil, i.e. high doses of exogenous NiCl2 increased CBF and BC in the presence of verapamil. The CBF decreasing effect of nickel was not significantly influenced by PBZ pretreatment. The results indicate that trace amounts of exogenous NiCl2 induce coronary vasoconstriction in the dog heart in situ by enhancing Ca2+-influx into vascular smooth muscle cells, which is not mediated by alpha-receptors.