Effect of isosorbide dinitrate infusion on the canine left ventricular force-length relationship

Recently, the slope (Ec) of the left ventricular (LV) end-systolic force-diameter (Fes-Des) relationship has been proposed as a new index for assessing myocardial contractility. Using this relationship, the effects of ISDN on LV myocardial contractility were evaluated in 10 healthy adult mongrel dogs. After the intravenous infusion of propranolol and atropine to produce autonomic blockade, the inferior vena cava was gradually occluded for 20 sec to decrease preload while the dogs were kept apneic. The LV diameter was measured by ultrasonic crystals and LV pressure was measured by a micromanometer. After the control measurements, the dogs received intravenous ISDN (1, 5, 10, or 50 micrograms/kg/min), and inferior vena caval occlusion was repeated. Ec and the extrapolated diameter intercept (D0) of the LV Fes-Des relationship were determined for each dog from the end-systolic data. The differences in heart rate between the control state and ISDN infusion at any dose were not statistically significant. The Ec and D0 values also showed no significant changes with ISDN infusion (Ec: 80 +/- 19, 83 +/- 20, 84 +/- 17, 82 +/- 24, and 87 +/- 24 g/cm for 0, 1, 5, 10, and 50 micrograms/kg/min, respectively. D0: 1.38 +/- 0.42, 1.38 +/- 0.40, 1.38 +/- 0.38, 1.34 +/- 0.40, and 1.36 +/- 0.40 cm for 0, 1, 5, 10, and 50 micrograms/kg/min, respectively). These findings suggested that intravenous ISDN did not affect myocardial contractility in the normal in situ canine left ventricle.