[Effect of vesnarinone on the myocardial force-length relationship in the in situ canine left ventricle].

The left ventricular (LV) end-systolic force-diameter (Fes-Des) relationship was used to examine the effect of a new positive inotropic agent (vesnarinone) on the contractility of the beta-blocked canine left ventricle. Seven adult mongrel dogs were implanted with ultrasonic crystals to measure the LV diameter and a micromanometer to measure LV pressure. Beta-adrenergic and vagal blockades were induced with intravenous propranolol (2 mg/kg) and atropine (0.2 mg/kg), respectively, and preload was decreased by inferior vena caval occlusion. The slope (Ec) and extrapolated diameter intercept (Do) of the LV Fes-Des relationship were derived from the end-systolic data obtained in the control, beta-blocked state, after sulfolane infusion, and after infusion of vesnarinone (3 mg/kg) dissolved in sulfolane. Ec was used as a new index of LV myocardial contractility. After vesarinone infusion, the LV Fes-Des relationship seemed to be nearly linear, and its Ec value was significantly increased by 18% (68.4 +/- 15.4 vs 80.4 +/- 21.8 g/cm, p < 0.05) without changes in heart rate, whereas Do did not change (1.74 +/- 0.44 vs. 1.70 +/- 0.42 cm). These results indicate that vesnarinone significantly enhances myocardial contractility in the beta-blocked canine left ventricle.