Comparative effect of amrinone, aminophylline and diltiazem on rat airway smooth muscle.

We investigated the effect of amrinone, a phosphodiesterase III inhibitor, on rat airway smooth muscle, and thereafter, compared its activity with aminophylline and diltiazem. Amrinone produced relaxation of the acetylcholine-induced airway contraction in a dose-related manner. This bronchodilatory activity of amrinone was similar to that of aminophylline, but smaller than that of diltiazem. The 50% relaxant effect (ED50) of amrinone, aminophylline and diltiazem were 3.6 x 10(-4) M, 1.4 x 10(-4) M and 1.4 x 10(-5) M, respectively. Diltiazem was the most potent airway relaxant, and amrinone was less potent in these experiments. Taken together in its positive inotropic and chronotropic effects and anti-inflammatory activity, however, amrinone could be beneficial for treatment of patients suffering from asthma or heart failure with cardiac asthma.