Dynamic exercise attenuates sympathetic responsiveness of canine vascular smooth muscle.
The phenomenon of reduced responsiveness of the skeletal muscle arterial vasculature to sympathetic activation during exercise (sympatholysis) 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 ultrasonic flow probes on the external iliac arteries. After pretreatment with atropine (0.2 mg/kg), an intravenous bolus (4 microg/kg) of a nicotinic ganglion stimulant [1,1-dimethyl-4-phenylpiperazinium iodide (DMPP)] was given at rest and during treadmill exercise at graded intensities. Administration of DMPP was associated with prompt reductions in iliac blood flow and increases in arterial pressure under all conditions. There were significant reductions (P < 0.05) in iliac vascular conductance of 58 +/- 4 (SE), 48 +/- 3, 36 +/- 5, and 16 +/- 3% at rest, 3 miles/h and 0% grade, 6 miles/h and 0% grade, and 6 miles/h and 15% grade, respectively. These data demonstrate that activation of postganglionic sympathetic nerves with DMPP caused vasoconstriction in the skeletal muscle vasculature at rest and during exercise. Additionally, the magnitude of vasoconstriction was inversely related to exercise intensity. These results support the concept of exercise sympatholysis.
Ruble
S B
SB
Department of Anesthesiology, Medical College of Wisconsin and Veterans Affairs Medical Center, Milwaukee, Wisconsin 53295, USA.
Valic
Z
Z
Buckwalter
J B
JB
Clifford
P S
PS
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D004285:Dogs; D005731:Ganglionic Stimulants / Q000494:pharmacology; D007083:Iliac Artery / Q000187:drug effects / Q000502:physiology; D009043:Motor Activity / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000294:innervation*; D018722:Nicotinic Agonists / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000502:physiology*; D014655:Vascular Resistance / Q000187:drug effects
D005731:Ganglionic Stimulants; D018722:Nicotinic Agonists; D004246:Dimethylphenylpiperazinium Iodide