Beta 1-selective and non-selective beta-adrenoceptor blockade, anaerobic threshold and respiratory gas exchange during exercise.
The effect of oral doses of the beta 1-selective adrenoceptor antagonist atenolol (50 mg), the non-selective antagonist propranolol (40 mg) and placebo was investigated during exercise in a crossover comparison in six healthy but untrained subjects. Descriptors of ventilation, respiratory gas exchange, and arterialized blood lactate and glucose were obtained during steady state bicycle ergometric exercise at 20% and 60% of the subjects' previously determined maximal oxygen uptake (VO2 max). At these work intensities, the previously reported increase of respiratory exchange ratio (RER) during non-selective beta-adrenoceptor blockade was found to be trivial (placebo = 0.96 +/- 0.03 s.e. mean; propranolol = 0.97 +/- 0.01; atenolol = 0.97 +/- 0.04; 60% VO2 max, 10 min exercise) and only present during the early minutes of effort. Oxygen uptake and carbon dioxide production did not differ between treatments. Both drugs produced highly significant falls in peak expiratory flow (PEF) rates and tidal volume (VT) which were compensated by an increase in respiratory rate. PEF, 60% VO2 max: placebo = 3.8 +/- 0.3 l/s; propranolol 3.6 +/- 0.3 l/s (P less than 0.03); atenolol 3.1 +/- 0.3 l/s (P less than 0.01). VT, 60% VO2 max: placebo 2.0 +/- 0.1 l; propranolol 1.8 +/- 0.21 (P less than 0.05); atenolol 1.7 +/- 0.1 1 (P less than 0.01). Arterialized lactate was significantly elevated during work at 20% and 60% VO2 max, but rose progressively at the 60% VO2 max load. Ventilation, oxygen uptake and ventilatory equivalent for carbon dioxide also rose progressively at this workload. Ventilatory equivalent for oxygen showed no significant rise.(ABSTRACT TRUNCATED AT 250 WORDS)
McLeod, AA; Knopes, KD; Shand, DG; Williams, RS
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