Effects of propranolol and pindolol on cardiac output during extended periods of low-intensity physical activity.

The effects of a nonselective beta-adrenergic blocking agent with (pindolol) and without (propranolol) intrinsic sympathomimetic activity properties, compared with placebo-controlled conditions, on metabolic and cardiorespiratory function during long-duration (2 hours) physical activity were examined. After initial cardiorespiratory testing, subjects performed 2-hour walks at 25 and 45% of maximal oxygen consumption (VO2max) under each of the following 3 treatments: pindolol, propranolol and placebo. Medication distribution was randomized and double-blinded. A supine resting blood pressure and electrocardiogram were obtained before each exercise trial. Oxygen consumption, heart rate, stroke volume, cardiac output and blood pressure were determined after 5 minutes of quiet sitting and every 30 minutes during each 2-hour exercise trial. Cardiac output was not significantly different at rest or during exercise, comparing pindolol and propranolol with placebo conditions. Cardiac output tended to decrease over time earlier during propranolol treatment for the 25% VO2max trials in trained normotensive subjects than for the other treatments. Cardiac output decreased at approximately the same time across treatments during the 45% VO2max trials in trained normotensive and untrained hypertensive groups. Finally, owing to the observation that a reduction in cardiac output was delayed or prevented in trained normotensive subjects when compared with that in untrained hypertensives while exercising at 25% VO2max, developing a subject's cardiovascular fitness level may be important in the maintenance of cardiac output during extended periods of low-to-moderate physical activities while under the influence of beta-adrenergic blockade.

Changes in plasma free fatty acids and glycerols during prolonged exercise in trained and hypertensive persons taking propranolol and pindolol.

The extent to which lipolysis is attenuated during prolonged submaximal exercise during beta blockade was determined in 12 normotensive endurance-trained and 12 hypertensive sedentary men using nonselective drugs with and without intrinsic sympathomimetic activity (ISA). Initially, subjects performed a graded treadmill test to determine maximal oxygen uptake (VO2max). This was followed by 2-hour walks at 25 and 45% of the subject's VO2max under each of 3 treatments: pindolol (ISA), propranolol (non-ISA) and placebo. The distribution of medication was randomized and double blinded. Blood samples taken at rest and every 30 minutes during the 2-hour walks were analyzed to determine the concentrations of free fatty acids (FFA) and glycerol. On the basis of the respective changes in FFA, glycerols and the respiratory exchange ratio, beta-adrenergic blockade did not attenuate lipolysis in the untrained hypertensive subjects when compared with the placebo administration. However, beta blockade did demonstrate a tendency to attenuate lipolysis in the trained, normotensive subjects when compared with results after placebo administration. This was particularly evident at 30 minutes of exercise, when both glycerol and FFA concentrations were not increased above resting values under both conditions of beta blockade. No differences between pindolol and propranolol were observed. Therefore, a beta-blocking agent with ISA properties appears to have no clear benefit with respect to lipid metabolism during low and moderate intensity exercise. Furthermore, these data demonstrate that beta blockade does not inhibit exercise-induced lipolysis at low and moderate intensities of exercise as formerly believed, and is unlikely to be the cause of fatigue normally observed during work in patient populations taking beta-blocking medication.

Comparison of the effects of pindolol and propranolol on exercise performance in young men with systemic hypertension.

To determine the effect of intrinsic sympathomimetic activity (ISA) on exercise performance during beta blockade, 12 hypertensive men were studied. The subjects underwent graded treadmill testing while taking pindolol (a beta blocker with ISA), propranolol (a beta blocker without ISA) and placebo, in a double-blind, crossover fashion. Blood pressure, heart rate, oxygen consumption (VO2), cardiac output and stroke volume were determined at 25, 45, 60 and 75% of each subject's VO2 max. Heart rate was significantly lower with pindolol compared with placebo at all stages of exercise, but significantly higher compared with propranolol at all stages of exercise except at 75% of VO2 max and at VO2 max (no significant differences between the 2 beta blockers were recorded at these stages). Mean arterial pressure was statistically equivalent with pindolol and propranolol at all stages of exercise and significantly lower while beta-blocked compared with placebo conditions at 45, 60 and 75% of VO2 max. Cardiac output and VO2 were statistically equivalent across all 3 treatments at all submaximal levels of exercise. It was concluded that, although heart rate was significantly higher with pindolol compared with propranolol at the 3 lower rates of work, cardiac output and VO2 were not different between the drugs, thus making little impact on exercise performance.