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1 Division of Cardiology,
Received 21 January 1997; accepted in final form 10 February 1997.
Shoemaker, J. Kevin, Prasant Pandey, Michael D. Herr, David
H. Silber, Qing X. Yang, Michael B. Smith, Kristen Gray, and Lawrence
I. Sinoway. Augmented sympathetic tone alters muscle metabolism
with exercise: lack of evidence for functional sympatholysis. J. Appl. Physiol. 82(6):
1932-1938, 1997.
sympathetic nervous system; handgrip exercise; phosphocreatine; phosporous-31-nuclear magnetic spectroscopy; pH; Doppler ultrasound
It is unclear whether sympathetic tone opposes
dilator influences in exercising skeletal muscle. We examined high
levels of sympathetic tone, evoked by lower body negative pressure
(LBNP, 
60 mmHg) on intramuscular pH and phosphocreatine (PCr)
levels (31P-nuclear magnetic resonance spectroscopy) during
graded rhythmic handgrip (30 contractions/min; ~17, 34, 52 and 69%
maximal voluntary contraction). Exercise was performed
with LBNP and without LBNP (Control). At the end of exercise, LBNP
caused lower levels of muscle pH (6.59 ± 0.09) compared
with Control (6.78 ± 0.05; P < 0.05). PCr recovery, an index of mitochondrial respiration, was less
during the recovery phase of the LBNP trial. Exercise mean arterial
pressure was not altered by LBNP. The protocols were repeated with
measurements of forearm blood flow velocity and deep venous samples
(active forearm) of hemoglobin (Hb) saturation, pH, and lactate. With
LBNP, mean blood velocity was reduced at rest, during exercise, and
during recovery compared with Control (P < 0.05). Also, venous Hb
saturation and pH levels during exercise and recovery were lower with
LBNP and lactate was higher compared with Control
(P < 0.05). We conclude
that LBNP enhanced sympathetic tone and reduced oxygen transport. At
high workloads, there was a greater reliance on nonoxidative
metabolism. In other words, sympatholysis did not occur.
0161-7567/97 $5.00
Copyright © 1997 the American Physiological Society
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