[Effect of amrinone and vagotomy on airway constriction in dogs: analysis by respiratory system impedance method]

Amrinone, a selective phosphodiesterase III inhibitor, is a positive inotropic agent with vasodilating effect which is attributable to an increase in cyclic AMP in vascular smooth muscle. Little is known about the effect of amrinone on airway mechanics. The purpose of this study was to clarify the bronchodilating effect of amrinone in dogs, when bronchoconstriction was induced by methacholine infusion. We also evaluated the effect of amrinone on bronchoconstriction in vagotomized dogs. To evaluate the effect of amrinone on respiratory function, the total respiratory system impedance was measured using forced oscillation method by imposing a random noise. The analysis was performed by dynamic models and a second-order system curve fitting. From the study, we conclude that amrinone 0.5 mg.kg-1.1.0 mg.kg-1 or 2.0 mg.kg-1 attenuates methacholine-induced bronchoconstriction in a dose-related manner. In vagotomized dogs, amrinone also had the same effect on methacholine induced bronchoconstriction.