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.
Broeder
C E
CE
Department of Kinesiology and Health Education, University of Texas at Austin 78712.
Thomas
E L
EL
Martin
N B
NB
Hofman
Z
Z
Jesek
J K
JK
Scruggs
K D
KD
Wambsgans
K C
KC
Wilmore
J H
JH
D000293:Adolescent; D000328:Adult; D002302:Cardiac Output / Q000187:drug effects*; D004311:Double-Blind Method; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D005082:Physical Exertion / Q000187:drug effects* / Q000502:physiology; D010869:Pindolol / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology*; D013318:Stroke Volume / Q000187:drug effects; D013997:Time Factors
D011433:Propranolol; D010869:Pindolol