Adenosine receptor antagonist and augmented vasodilation during hypoxic exercise

Casey DP, Madery BD, Pike TL, Eisenach JH, Dietz NM, Joyner MJ, Wilkins BW. Adenosine receptor antagonist and augmented vasodilation during hypoxic exercise. J Appl Physiol 107: 1128-1137, 2009. First published August 6, 2009; doi:10.1152/japplphysiol.00609.2009.-We tested the hypothesis that adenosine contributes to augmented skeletal muscle vasodilation during hypoxic exercise. In separate protocols, subjects performed incremental rhythmic forearm exercise (10% and 20% of maximum) during normoxia and normocapnic hypoxia (80% arterial O(2) saturation). In protocol 1 (n = 8), subjects received an intra-arterial administration of saline (control) and aminophylline (adenosine receptor antagonist). In protocol 2 (n = 10), subjects received intra-arterial phentolamine (alpha-adrenoceptor antagonist) and combined phentolamine and aminophylline administration. Forearm vascular conductance (FVC; in ml.min(-1).100 mmHg(-1)) was calculated from forearm blood flow (in ml/min) and blood pressure (in mmHg). In protocol 1, the change in FVC (Delta FVC; change from normoxic baseline) during hypoxic exercise with saline was 172 +/- 29 and 314 +/- 34 ml.min(-1).100 mmHg(-1) (10% and 20%, respectively). Aminophylline administration did not affect Delta FVC during hypoxic exercise at 10% (190 +/- 29 ml.min(-1).100 mmHg(-1), P = 0.4) or 20% (287 +/- 48 ml.min(-1).100 mmHg(-1), P = 0.3). In protocol 2, Delta FVC due to hypoxic exercise with phentolamine infusion was 313 +/- 30 and 453 +/- 41 ml.min(-1).100 mmHg(-1) (10% and 20% respectively). Delta FVC was similar at 10% (352 +/- 39 ml.min(-1).100 mmHg(-1), P = 0.8) and 20% (528 +/- 45 ml.min(-1).100 mmHg(-1), P = 0.2) hypoxic exercise with combined phentolamine and aminophylline. In contrast, Delta FVC to exogenous adenosine was reduced by aminophylline administration in both protocols (P < 0.05 for both). These observations suggest that adenosine receptor activation is not obligatory for the augmented hyperemia during hypoxic exercise in humans.