Skeletal muscle vasodilation at the onset of exercise

The purpose of this study was to determine whether P-adrenergic or muscarinic receptors are involved in skeletal muscle vasodilation at the onset of exercise. Mongrel dogs (n = 7) were instrumented with flow probes on both external iliac arteries and a catheter in one femoral artery. Propranolol (1 mg), atropine (500 mu g), both drugs, or saline was infused intra-arterially immediately before treadmill exercise at 3 miles/h, 0% grade. Immediate and rapid increases in iliac blood flow occurred with initiation of exercise under all conditions. Peak blood flows were not significantly different among conditions (682 +/- 35, 646 +/- 49, 637 +/- 68, and 705 +/- 50 ml/min, respectively). Although the doses of antagonists employed had no effect on heart rate or systemic blood pressure, they were adequate to abolish agonist-induced increases in iliac blood flow. Because neither propranolol nor atropine affected iliac blood flow, we conclude that activation of beta-adrenergic and muscarinic receptors is not essential for the rapid vasodilation in active skeletal muscle at the onset of exercise in dogs.