Effect of repeated bouts of short-term exercise on plasma free and sulphoconjugated catecholamines in humans

We tested the hypothesis that measurement of plasma catecholamine sulphate concentration after exercise reflects the overall activation of the sympath oadrenergic system during the whole period of repeated bouts of short-term exercise. A group of 11 male athletes performed two exercise tests at simil ar average power outputs consisting of three sets each. The tests either st arted with one set of three very intense sprints (95% of maximal running sp eed) followed by two sets of three less intense sprints (85% of maximal run ning speed; HLX) or vice versa (LHX). Similar mean areas under the curve of free noradrenaline (NA) during HLX and LHX [622 (SEM 13) vs 611 (SEM 14) n mol.l(-1).min) as well as similar mean heart rates [143 (SEM 9) vs 143 (SEM 8) beats.min(-1)] indicated comparable sympathetic activation during both exercise tests. Even so, plasma concentration of free NA was still signific antly higher at the end of LHX than of HLX [35.7 (SEM 3.5) vs 22.5 (SEM 2.1 ) nmol.l(-1), respectively], i.e. when exercise ended with the more intense set of sprints. Plasma noradrenaline sulphate (NA-S) increased with exerci se intensity showing higher mean increments after the first set of HLX comp ared to LHX [1.83 (SEM 0.42) vs 1.18 (SEM 0.29) nmol.l(-1); P < 0.05]. Howe ver, after the end of HLX and LHX, increments in plasma NA-S were similar [ 4.52 (SEM 0.76) vs 4.06 (SEM 0.79) nmol.l(-1)], suggesting that NA-S respon se changed in parallel with the overall activation of the sympathetic nervo us system during repeated bouts of short-term exercise. The results support ed the hypothesis that measurement of plasma NA-S immediately after repeate d bouts of short-term exercise reflects overall activation of the sympathet ic nervous system during prolonged periods of this type of exercise.