Abstract: Compositions and methods for relaxing smooth muscle in a warm-blooded animal are provided, comprising the step of administering to the animal a transition-metal nitrosyl complex. In one aspect, the transition-metal nitrosyl complex is represented by the formula L.sub.3 M(NO).sub.y X.sub.3-y where L is a two-electron Lewis base or L.sub.3 is a six-electron Lewis base, M is a Group 6 or 8 transition-metal, and when y is 1, X is carbon monoxide, and when y is 2, X is a halide or pseudohalide. In another aspect, the transition-metal nitrosyl complex is represented by the formula ?M(NO).sub.2 X.sub.y !.sub.2 where X is a halide or pseudohalide, and when M is a Group 6 transition-metal, y is 2, and when M is a Group 8 transition-metal, y is 1. Methods are also described for treating hypertension, angina pectoris, congestive heart disease, and impotence utilizing pharmaceutical compositions comprising the above-described transition-metal nitrosyl complexes.

Abstract: Compositions and methods for relaxing smooth muscle in a warm-blooded animal are provided, comprising the step of administering to the animal a transition-metal nitrosyl complex. In one aspect, the transition-metal nitrosyl complex is represented by the formula L.sub.3 M(NO).sub.y X.sub.3-y where L is a two-electron Lewis base or L.sub.3 is a six-electron Lewis base, M is a Group 6 or 8 transition-metal, and when y is 1, X is carbon monoxide, and when y is 2, X is a halide or pseudohalide. In another aspect, the transition-metal nitrosyl complex is represented by the formula [M(NO).sub.2 X.sub.y ].sub.2 where X is a halide or pseudohalide, and when M is a Group 6 transition-metal, y is 2, and when M is a Group 8 transition-metal, y is 1. Methods are also described for treating hypertension, angina pectoris, congestive heart disease, and impotence utilizing pharmaceutical compositions comprising the above-described transition-metal nitrosyl complexes.