EFFECT OF ACUTE MILD HYPOXIA DURING EXERCISE ON PLASMA-FREE AND SULPHOCONJUGATED CATECHOLAMINES

Catecholamine (CA) response to hypoxic exercise has been investigated during severe hypoxia. However, altitude training is commonly performe d during mild hypoxia at submaximal exercise intensities. In the prese nt study we tested whether submaximal exercise during mild hypoxia com pared to normoxia leads to a greater increase of plasma concentrations of CA and whether plasma concentration of catecholamine sulphates cha nge in parallel with the CA response. A group of 14 subjects [maximal oxygen uptake, 62.6 (SD 5.2) ml . min(-1). kg(-1) body mass] performed two cycle ergometer tests of l-h duration at the same absolute exerci se intensities [191 (SD 6) W] during normoxia (NORM) and mild hypoxia (HYP) followed by 30 min of recovery during normoxia. Mean plasma conc entrations of noradrenaline ([NA]), adrenaline ([A]), and noradrenalin e sulphate ([NA-S]) were elevated (P < 0.01) after HYP and NORM compar ed with mean resting values and were higher after HYP [120.9 (SEM 3.1) , 2.2 (SEM 0.24), 8.12 (SEM 1.5) nmol . l(-1), respectively] than afte r NORM [(13.7 (SEM 0.9), 1.5 (SEM 0.14), 6.8 (SEM 0.7) nmol . l(-1), r espectively P < 0.01]. The higher plasma [NA-S] after HYP (P < 0.05) w ere still measurable after 30 min of recovery. From our study it was c oncluded that exercise at the same absolute submaximal exercise intens ity during mild hypoxia increased plasma CA to a higher extent than du ring normoxia. Plasma [NA-S] response paralleled the plasma [NA] respo nse at the end of exercise but, in contrast to plasma [NA], remained e levated until 30 min after exercise.