Comparative vasoactive effects of amrinone on systemic and pulmonary arteries in rabbits

Amrinone has been increasingly used in management of low cardiac output syndrome during anesthesia, particularly when associated with right heart failure and pulmonary hypertension. This in vitro study was performed to determine and compare the direct vasoactive effects of amrinone on isolated rabbit systemic and pulmonary arteries. Responses of aortic and pulmonary artery rings from New Zealand white rabbits were assessed in the presence and absence of intact endothelium and with or without precontraction by norepinephrine (NE, 3 x 10(-6)M) or potassium chloride (KCl, 3 x 10(-2)M). Using a tissue bath preparation, cumulative concentration response curves of amrinone were obtained at different concentrations after a period of stabilization. Amrinone caused a dose-related vasodilation of NE-precontracted aortic and pulmonary arteries. It elicited about 65% and 90% relaxation, respectively, at a concentration of 300 mumol/L. Amrinone also induced a dose-related vasodilation of KCl-precontracted aortic and pulmonary arteries but to a lesser degree. All these effects were endothelium independent. By comparison, amrinone caused more relaxation in both NE- and KCl-precontracted pulmonary artery than aortic rings. In conclusion, amrinone has significant endothelium-independent, direct vasodilatory effects on isolated rabbit systemic and pulmonary arteries, more pronounced in the latter, particularly NE-precontracted vessels. Amrinone may have some calcium channel-blocking effect.