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Alpha-adrenergic vascular responsiveness during postexercise hypotension in humans.
John R Halliwill1, Frank A Dinenno, Niki M Dietz
1Department of Exercise and Movement Science, University of Oregon, Eugene, OR 97403-1240, USA. halliwil@uoregon.edu
The Journal of Physiology
|May 27, 2003
Summary
Postexercise hypotension involves increased blood vessel dilation, but alpha-adrenergic responsiveness remains intact. This study found that reduced blood pressure after exercise is not caused by blunted alpha-adrenergic responses.
Area of Science:
- Cardiovascular Physiology
- Exercise Physiology
Background:
- Postexercise hypotension (PEH) in sedentary individuals is characterized by unexplained peripheral vasodilation.
- The underlying mechanisms of PEH, particularly changes in vascular responsiveness, require further investigation.
Purpose of the Study:
- To test the hypothesis that alpha-adrenergic responsiveness is blunted in the forearm and leg vasculature during PEH.
- To investigate the role of alpha-adrenergic signaling in the vasodilation observed after aerobic exercise.
Main Methods:
- 12 sedentary participants (10 men, 2 women) underwent a 60-minute cycling exercise at 60% VO2peak.
- Arterial pressure and forearm/leg blood flow were measured before and 30 minutes after exercise.
- Vascular conductance was assessed during intra-arterial infusions of alpha1-agonist (phenylephrine) and alpha2-agonist (clonidine) in the forearm and leg.
Main Results:
- Exercise induced a significant reduction in mean arterial pressure and increased forearm and leg vascular conductance.
- Vasoconstrictor responses to phenylephrine and clonidine infusions were maintained or enhanced postexercise compared to preexercise.
- Blunted alpha-adrenergic responsiveness was not observed in either the forearm or leg vasculature during PEH.
Conclusions:
- Alpha-adrenergic vascular responsiveness is preserved during postexercise hypotension in sedentary humans.
- The increased vascular conductance contributing to PEH is not attributable to a diminished alpha-adrenergic-mediated vasoconstriction.
- Further research is needed to elucidate the precise mechanisms driving peripheral vasodilation in postexercise hypotension.