Effects of beta blockade and atropinisation on plasma catecholamine concentration during exercise

The changes in plasma catecholamine concentration (deltaC) following beta-blockade (practolol, 15 mg) and atropinisation (Atropine, 1.8 mg) have been studied on 5 healthy male subjects during exercise on a motor driven treadmill. The results showed that for a given V-2 and % VO2 max, beta blockade was without effect on delta C (except in one athletic subject, but atropine produced a rise in deltaC. In relation to Q, both drugs produced an increase in deltaC, but for a given cardiac frequency (fH) deltaC was higher with beta blockade, and lower with atropinisation than found in control experiments. The intra- and inter-subject variability of delta C in relation of fH was resolved by considering the change in cardiac frequency calculated from baseline value obtained during walking at 6.44 km/h on the level, and expressed as a percentage of the maximal fH attainable for given individuals under the different drug and control conditions (%deltafH). It was concluded that during short term exercise, the rise of deltaC in relation to %deltafH reflects both the myocardial sensitivity to vagal and beta blockade, and the circulatory vasoconstrictor control of blood vessels which is required to sustain increases in systemic and muscle blood flow.