Adenosine receptor antagonist and augmented vasodilation during hypoxic exercise.
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 O2 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 x 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 (DeltaFVC; change from normoxic baseline) during hypoxic exercise with saline was 172 +/- 29 and 314 +/- 34 ml x min(-1) x 100 mmHg(-1) (10% and 20%, respectively). Aminophylline administration did not affect DeltaFVC during hypoxic exercise at 10% (190 +/- 29 ml x min(-1)x100 mmHg(-1), P = 0.4) or 20% (287 +/- 48 ml x min(-1) x 100 mmHg(-1), P = 0.3). In protocol 2, DeltaFVC due to hypoxic exercise with phentolamine infusion was 313 +/- 30 and 453 +/- 41 ml x min(-1) x 100 mmHg(-1) (10% and 20% respectively). DeltaFVC was similar at 10% (352 +/- 39 ml min(-1) x 100 mmHg(-1), P = 0.8) and 20% (528 +/- 45 ml x min(-1) x 100 mmHg(-1), P = 0.2) hypoxic exercise with combined phentolamine and aminophylline. In contrast, DeltaFVC 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.
Casey
Darren P
DP
Department of Anesthesiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA. casey.darren@mayo.edu
Madery
Brandon D
BD
Pike
Tasha L
TL
Eisenach
John H
JH
Dietz
Niki M
NM
Joyner
Michael J
MJ
Wilkins
Brad W
BW
D000241:Adenosine / Q000378:metabolism; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000328:Adult; D000628:Aminophylline / Q000008:administration & dosage / Q000494:pharmacology*; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D001916:Brachial Artery / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D015444:Exercise; D005260:Female; D005542:Forearm; D018737:Hand Strength; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006940:Hyperemia / Q000000981:diagnostic imaging / Q000378:metabolism / Q000503:physiopathology*; D000860:Hypoxia / Q000000981:diagnostic imaging / Q000378:metabolism / Q000503:physiopathology*; D007261:Infusions, Intra-Arterial; D017078:Laser-Doppler Flowmetry; D018482:Muscle, Skeletal / Q000098:blood supply*; D010100:Oxygen / Q000097:blood; D010646:Phentolamine / Q000494:pharmacology; D012123:Pulmonary Ventilation / Q000187:drug effects; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1 / Q000378:metabolism; D012039:Regional Blood Flow / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000503:physiopathology; D014463:Ultrasonography; D014664:Vasodilation / Q000187:drug effects*
D000317:Adrenergic alpha-Antagonists; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1; D000628:Aminophylline; D000241:Adenosine; D010100:Oxygen; D010646:Phentolamine