Propranolol ameliorates exercise-induced regional myocardial dysfunction in dogs

Effect of exercise on propranolol pharmacokinetics

The effect of submaximal exercise on the pharmacokinetics of low dose intravenous propranolol was studied in 15 healthy human subjects. There was a wide individual variation in the results for each subject and a large difference in the degree of changes with exercise. The effect of exercise on the pharmacokinetics of propranolol, a flow limited drug, is marked but variable. This phenomenon may have profound effects on patients taking the drug regularly who exercise intermittently and drug doses may have to be adjusted.

The effects of nitroglycerin on regional myocardial contractile dysfunction produced by treadmill exercise or isoprenaline stimulation in dogs

1. To compare different methods of cardiac stress testing that are clinically applied in the management of coronary heart disease, 2 groups of dogs each were chronically instrumented and subjected to treadmill exercise or isoprenaline infusion in the presence of coronary stenosis. 2. It was of interest to determine differences in haemodynamic and regional myocardial contractile parameters, the response to antianginal therapy (nitroglycerin 15 micrograms kg-1 15 min-1, i.v.), and, in particular, whether this response differed according to the mode of cardiac stimulation, i.e. treadmill exercise or isoprenaline infusion. 3. After stenosis of the circumflex branch of the left coronary artery which affected resting myocardial function only minimally, treadmill exercise or isoprenaline infusion induced transient regional contractile dysfunction. Heart rate, arterial blood pressure, left ventricular end-diastolic pressure and left ventricular dp/dtmax were registered and myocardial oxygen demand was calculated. Regional contractile performance was assessed by ultrasonic distance measurement in the underperfused and in a normally perfused area. 4. Treadmill exercise led to an increase in systolic arterial and left ventricular end-diastolic pressure. In contrast, isoprenaline-induced stimulation led to a decrease in diastolic arterial and left ventricular end-diastolic pressure. Regional contractile function in the critically underperfused area showed a deterioration during both modes of stress. Nitroglycerin completely abolished stress-induced contractile dysfunction only in the group where treadmill exercise was employed for stimulation. 5. The inability of nitroglycerin to prevent myocardial dysfunction in the isoprenaline group may be due to exhaustion of the arterial and/or venous vasodilator potency of nitroglycerin in the presence of adrenoceptor vasodilatation induced by isoprenaline. 6. These findings indicate that clinical antianginal drug testing and the evaluation of the course of disease in patients with coronary heart disease may be highly dependent on the test method chosen.

Comparison of the haemodynamic effects of the selective bradycardic agent UL-FS 49, with those of propranolol during treadmill exercise in dogs

1. To clarify whether the bradycardic agent UL-FS 49 exhibits a positive inotropic effect even in the absence of improvement in regional myocardial function of an underperfused myocardial area, this study was undertaken in dogs with unimpaired coronary flow. 2. We also investigated the haemodynamic and functional effects of the negative chronotropic and inotropic beta-adrenoceptor blocker propranolol. 3. UL-FS 49 did not depress total or regional myocardial performance. Moreover, an increase in positive left ventricular dp/dt max at rest suggests a positive inotropic effect of UL-FS 49. 4. Propranolol, in contrast to UL-FS 49, led to a marked reduction in positive dp/dt max, stroke volume and systolic wall thickening at rest and during exercise. Additionally, propranolol decreased the exercise values of cardiac output, left ventricular work and left ventricular power to a far greater extent than UL-FS 49. 5. In contrast to propranolol, the selective bradycardic agent UL-FS 49 did not decrease total or regional ventricular performance and caused less reduction in cardiodynamic parameters during exercise. 6. These results suggest that patients with moderate coronary insufficiency or patients with coronary vessel disease and mild left ventricular failure may attain a higher exercise limit under selective bradycardia with UL-FS 49 in comparison to that possible with a beta-adrenoceptor antagonist, such as propranolol.