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Departments of Anesthesiology and Physiology, Medical College of Wisconsin and Veterans Affairs Medical Center, Milwaukee, Wisconsin 53295
Submitted 19 February 2003 ; accepted in final form 19 May 2003
There is evidence that ATP acts as a neurotransmitter in vascular smooth
muscle and is coreleased with norepinephrine from sympathetic nerves. We
hypothesized that P2X-receptor stimulation with the selective P2X-receptor
agonist
,
-methylene ATP would produce vasoconstriction in resting
and exercising skeletal muscle. Six mongrel dogs were instrumented chronically
with flow probes on the external iliac arteries of both hindlimbs and a
catheter in one femoral artery. The selective P2X agonist
,
-methylene ATP was infused as a bolus into the femoral artery
catheter at rest and during mild, moderate, and heavy exercise. Intra-arterial
infusions of
,
-methylene ATP elicited reductions in vascular
conductance of 54 ± 5, 49 ± 8, 39 ± 8, and 30 ± 6%
at rest, 3 miles/h, 6 miles/h, and 6 miles/h at a 10% grade, respectively. The
agonist infusions did not affect blood flow in the contralateral iliac artery.
To examine whether nitric oxide is responsible for the attenuated
vasoconstrictor response to P2X stimulation, the infusions were repeated in
the presence of NG-nitro-L-arginine methyl
ester. After nitric oxide synthase blockade, intra-arterial infusions of
,
-methylene ATP elicited reductions in vascular conductance of 56
± 7, 61 ± 8, 52 ± 9, and 40 ± 7% at rest, 3
miles/h, 6 miles/h, and 6 miles/h at a 10% grade, respectively. P2X-receptor
responsiveness was attenuated during exercise compared with rest. Blockade of
nitric oxide production did not affect the attenuation of P2X-receptor
responsiveness during exercise. These data support the hypothesis that P2X
purinergic receptors can produce vasoconstriction in exercising skeletal
muscle.
blood flow; sympatholysis; autonomic nervous system; dogs
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