BACKGROUND: Amrinone is a noncatecholamine, nonglycoside compound, which is known to possess both cardiac inotropic and vasodilatory actions. This drugs has been increasingly used in clinical practice for the management of low cardiac output syndrome during anesthesia, particularly for patients associated with right heart failure and pulmonary hypertension. The aim of this study was to explore the direct vasoactive effect of amrinone and its action mechanisms in the isolated rabbit pulmonary artery. METHODS: The rabbits' pulmonary arteries were dissected free and cut into rings (3 4 mm) and mounted for isometric tension in a tissue chamber. The effects of amrinone (5 10 6 5 10 4 M) on the vascular tension were assessed in the by KCl (40 mM)- or norepinephrine (NE, 10 6 M)- precontracted pulmonary arterial rings with or without endothelium. Also effects of K channel blockers (tetraethyl ammonium 20 mM, glybenclamide 2.5 10 5 M, 4-aminopyridine (4-AP) 5 10 4 M), protein kinase A