Abstract
The cardiac effects of DM9278 were studied in isolated and blood-perfused atrial and ventricular preparations from mongrel dogs. In spontaneously beating isolated right atria, DM9278 caused positive chronotropic and inotropic responses in a dose-related manner (1-100μg). DM9278 produced relatively larger positive inotropic than positive chronotropic effects as compared with effects of aminophylline or papaverine. DM9278 increased the developed tension in left ventricles electrically driven at 1.5 -2.0Hz. Positive inotropic and chronotropic responses to DM9278 in both atrial and ventricular preparations were suppressed slightly but not significantly by 1-3μg of propranolol, which completely blocked the positive chronotropic and inotropic effects of norepinephrine (0.01-0.1μg). From these results, it is concluded that DM9278 has direct cardiotonic properties in isolated dog heart tissues, showing relatively selective positive inotropic activity.
