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

The changes in plasma catecholamine concentration (C) following -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 VO₂ and % VO_{2 max}, blockade was without effect on C (except in one athletic subject), but atropine produced a rise in C. In relation to Q, both drugs produced an increase in C, but for a given cardiac frequency (f_H) C was higher with blockade, and lower with atropinisation than found in control experiments. The intra- and inter-subject variability of C in relation to f_H 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 f_H attainable for given individuals under the different drug and control conditions (% f_H).It was concluded that during short term exercise, the rise of C in relation to % f_H reflects both the myocardial sensitivity to vagal and blockade, and the circulatory vasoconstrictor control of blood vessels which is required to sustain increases in systemic and muscle blood flow.