EXHAUSTIVE EXERCISE-INDUCED TISSUE HYPOXIA DOES NOT CHANGE ENDOTHELINAND BIG ENDOTHELIN PLASMA-LEVELS IN NORMAL VOLUNTEERS

Chronic hypoxia has been shown to increase plasma endothelin levels. T he current study was undertaken to examine the effect of exercise-indu ced tissue hypoxia on plasma levels of endothelin-1 (ET-1) and its pre cursor big endothelin-1 (Big-ET-1). After approval by the local ethica l committee an incremental dynamic exercise test was performed in 12 p hysically trained volunteers (aged 20 to 40 years), using an electrica lly braked bicycle ergometer. The protocol included a step-wise increa se of the workload until a heart rate of 130/min was reached, followed by a maintenance period of 25 min, and a further stepwise increase un til exhaustion. Blood was drawn before, at several time points during, and 5 min after termination of the study for determination of ET-1, B ig-ET-l, plasma renin activity (PRA), angiotensin converting enzyme (A CE), norepinephrine, epinephrine, and lactate. Lactate levels at basel ine were 14.5 +/- 1.6 mg/dL (mean +/- SEM), which increased to 76.5 +/ - 4.8 mg/dL at the time of exhaustion (P < .01). Baseline values for E T-1 and Big-ET-1 were 0.264 +/- 0.061 and 0.637 +/- 0.130 fmol/ml, res pectively, which remained essentially unaltered throughout the exercis e test. PRA was 1.46 +/- 0.45 ng/mL/h before exercise and increased to 3.55 +/- 0.96 ng/ml/h at exhaustion (P < .001). Norepinephrine and ep inephrine were also increased at exhaustion. The study demonstrates th at exhaustive physical exercise with acute development of pronounced t issue hypoxia - in contrast to chronic hypoxia - does not influence th e release of ET-1 or Big-ET-1 or the conversion of the precursor to th e active compound. Unlike endothelin, circulating renin and the catech olamines were markedly stimulated by this maneuver. Am J Hypertens 199 8;11:1028-1031 (C) 1998 American Journal of Hypertension, Ltd.