Dynamic exercise attenuates sympathetic responsiveness of canine vascular smooth muscle

pathetic responsiveness of canine vascular smooth muscle. J Appl Physiol 89: 2294–2299, 2000.—The phenomenon of re-duced responsiveness of the skeletal muscle arterial vascu-lature to sympathetic activation during exercise (sympa-tholysis) remains controversial. The purpose of this study was to examine the vascular effects of sympathoactivation in dynamically exercising skeletal muscle. Mongrel dogs (19–24 kg) were instrumented chronically with transit-time ultra-sonic flow probes on the external iliac arteries. After pre-treatment with atropine (0.2 mg/kg), an intravenous bolus (4 mg/kg) of a nicotinic ganglion stimulant [1,1-dimethyl-4-phe-nylpiperazinium iodide (DMPP)] was given at rest and dur-ing treadmill exercise at graded intensities. Administration of DMPP was associated with prompt reductions in iliac blood flow and increases in arterial pressure under all con-ditions. There were significant reductions (P, 0.05) in ilia