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alpha1-adrenergic-receptor responsiveness in skeletal muscle during dynamic exercise
J B Buckwalter1, P J Mueller, P S Clifford
1Departments of Anesthesiology and Physiology, Medical College of Wisconsin and Veterans Affairs Medical Center, Milwaukee, Wisconsin 53295, USA. jbuckwald@mcw.edu
Journal of Applied Physiology (Bethesda, Md. : 1985)
|December 8, 1998
Summary
This study investigated sympathetic vasoconstriction during exercise, finding no evidence of reduced alpha1-adrenergic-receptor responsiveness in working muscles. Results do not support the concept of sympatholysis in skeletal muscle during dynamic activity.
Area of Science:
- Exercise Physiology
- Cardiovascular Regulation
- Skeletal Muscle Physiology
Background:
- Sympathetic vasoconstriction in working muscles during exercise (sympatholysis) is debated.
- Reduced alpha1-adrenergic-receptor responsiveness is a proposed mechanism for sympatholysis.
Purpose of the Study:
- To investigate alpha1-adrenergic-receptor-mediated vasoconstriction in resting and exercising skeletal muscles.
- To determine if exercise attenuates vasoconstrictor responses to a selective alpha1-agonist.
Main Methods:
- Seven chronically instrumented mongrel dogs were used.
- Intra-arterial infusions of phenylephrine (selective alpha1-agonist) were administered at rest and during treadmill exercise (3 and 6 miles/h).
- Vascular conductance, systemic blood pressure, and contralateral blood flow were measured.
Main Results:
- Phenylephrine infusions caused similar reductions in vascular conductance at rest (76%), 3 miles/h (76%), and 6 miles/h (67%).
- No significant differences in vasoconstrictor response were observed across conditions (P > 0.05).
- Systemic blood pressure and contralateral iliac blood flow remained unaffected.
Conclusions:
- The study did not demonstrate an attenuation of vasoconstriction to a selective alpha1-agonist during exercise.
- These findings do not support the concept of sympatholysis mediated by reduced alpha1-adrenergic-receptor responsiveness in skeletal muscle.
- Alpha1-adrenergic-receptor-mediated vasoconstriction appears maintained during dynamic exercise in this model.