alpha1-adrenergic-receptor responsiveness in skeletal muscle during dynamic exercise.
Attenuation of sympathetic vasoconstriction (sympatholysis) in working muscles during dynamic exercise is controversial. One potential mechanism is a reduction in alpha1-adrenergic-receptor responsiveness. The purpose of this study was to examine alpha1-adrenergic-receptor-mediated vasoconstriction in resting and working skeletal muscles by using intra-arterial infusions of a selective agonist. Seven mongrel dogs were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs and a catheter in one femoral artery. A selective alpha1-adrenergic-receptor agonist (phenylephrine) was infused as a bolus into the femoral artery catheter at rest and during exercise. All dogs ran on a motorized treadmill at two exercise intensities (3 and 6 miles/h). Intra-arterial infusions of the same effective concentration of phenylephrine elicited reductions in vascular conductance of 76 +/- 4, 76 +/- 6, and 67 +/- 5% (P > 0.05) at rest, 3 miles/h, and 6 miles/h, respectively. Systemic blood pressure and blood flow in the contralateral iliac artery were unaffected by phenylephrine. These results do not demonstrate an attenuation of vasoconstriction to a selective alpha1-agonist during exercise and do not support the concept of sympatholysis.
Buckwalter
J B
JB
Departments of Anesthesiology and Physiology, Medical College of Wisconsin and Veterans Affairs Medical Center, Milwaukee, Wisconsin 53295, USA. jbuckwald@mcw.edu
Mueller
P J
PJ
Clifford
P S
PS
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001341:Autonomic Nervous System / Q000187:drug effects / Q000502:physiology; D004285:Dogs; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply / Q000187:drug effects / Q000502:physiology*; D010656:Phenylephrine / Q000494:pharmacology; D005082:Physical Exertion / Q000502:physiology*; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology
D000316:Adrenergic alpha-Agonists; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine