Autonomic control of skeletal muscle vasodilation during exercise

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Abstract
Buckwalter, John B., Patrick J. Mueller, and Philip S. Clifford. Autonomic control of skeletal muscle vasodilation during exercise. J. Appl. Physiol. 83(6): 2037–2042, 1997.—Despite extensive investigation, the control of blood flow during dynamic exercise is not fully understood. The purpose of this study was to determine whether β-adrenergic or muscarinic receptors are involved in the vasodilation in exercising skeletal muscle. Six mongrel dogs were instrumented with ultrasonic flow probes on both external iliac arteries and with a catheter in a branch of one femoral artery. The dogs exercised on a treadmill at 6 miles/h while drugs were injected intra-arterially into one hindlimb. Isoproterenol (0.2 μg) or acetylcholine (1 μg) elicited increases in iliac blood flow of 89.8 ± 14.4 and 95.6 ± 17.4%, respectively, without affecting systemic blood pressure or blood flow in the contralateral iliac artery. Intra-arterial propranolol (1 mg) or atropine (500 μg) had no effect on iliac blood flow, although they abolished the isoproterenol and acetylcholine-induced increases in iliac blood flow. These data indicate that exogenous activation of β-adrenergic or muscarinic receptors in the hindlimb vasculature increases blood flow to dynamically exercising muscle. More importantly, because neither propranolol nor atropine affected iliac blood flow, we conclude that β-adrenergic and muscarinic receptors are not involved in the control of blood flow to skeletal muscle during moderate steady-state dynamic exercise in dogs.