AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 6 845-R849, Copyright © 1983 by American Physiological Society
Decrease in liver norepinephrine in response to exercise and hypoglycemia
W. W. Winder, M. A. Beattie, C. Piquette and R. T. Holman
The existence of the sympathetic innervation of the liver has been known
for many years, but the role of this system in regulation of liver
metabolism is unclear. The purpose of these experiments was to identify
physiological conditions for activation of liver sympathetics. Liver
norepinephrine (NE) was measured in normal resting rats and in rats exposed
to swimming, treadmill running, fasting, and insulin-induced hypoglycemia.
Liver NE decreased significantly in response to swimming (-71% of control),
treadmill running (-53% of control), and hypoglycemia (-24% of control).
Rats that are endurance trained by daily bouts of treadmill running for 3
mo show no decrease in liver NE in response to a 60-min run on the
treadmill, whereas nontrained rats show a 50% decrease in liver NE with the
same amount of exercise. We conclude that the liver sympathetics are
activated in response to swimming, treadmill exercise and hypoglycemia, and
that endurance training causes a reduction in the degree of
exercise-induced activation of these neurons.
