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Does beta‐receptor mediated vasodilation contribute to the augmented blood flow during hypoxic exercise?
Author(s) -
Wilkins Brad W.,
Martin Elizabeth A.,
Roberts Shelly K.,
Joyner Michael J.
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a571-c
Subject(s) - phentolamine , vasodilation , propranolol , vasoconstriction , forearm , hypoxia (environmental) , medicine , blood flow , hypoxic pulmonary vasoconstriction , anesthesia , vascular resistance , hemodynamics , heart rate , blood pressure , endocrinology , chemistry , anatomy , oxygen , organic chemistry
Decreased vasoconstrictor responsiveness during hypoxic exercise does not explain the augmented vasodilation in exercising muscle. We tested the hypothesis that β‐mediated vasodilation contributes to a portion of the enhanced muscle blood flow during hypoxic exercise. Subjects breathed hypoxic gas to titrate arterial O 2 saturation to 80% while remaining normocapnic via a re‐breath system. Two consecutive bouts of forearm handgrip exercise (10 and 20% of maximum) were performed under normoxia and hypoxia during saline infusion, during phentolamine (α‐antagoinst) alone and during the combination of phentolamine and propranolol (β‐antagonist). Forearm blood flow (FBF) and blood pressure (MAP) were assessed and forearm vascular conductance (FVC) was calculated (FBF/MAP). Hypoxia alone increased heart rate (62±3 vs. 82±3 bpm) with no change in MAP (86±2 vs. 89±2 mmHg for normoxia and hypoxia respectively). During hypoxic exercise the rise (Δ from baseline) in FVC with phentolamine alone was 166±26 and 448±31 ml/min/100mmHg (10% and 20 % respectively). This rise in blood flow was blunted (143±36 and 279±73 ml/min/100mmHg) with combined phentolamine and propranolol infusion. Thus, preliminary data suggests that in the absence of overlying vasoconstriction, β‐mediated vasodilation may account for a modest portion of the enhanced blood flow during hypoxic exercise.