Journal of Applied Physiology, Vol 72, Issue 6 2203-2209, Copyright © 1992 by American Physiological Society
Effect of prior exercise and insulin on potential thermogenic systems in rat skeletal muscle
T. W. Balon, J. L. Treadway, J. B. Hughes, J. C. Young and N. B. Ruderman
Department of Exercise Science, University of Iowa, Iowa City 52242.
We previously reported that insulin stimulates oxygen consumption by the
perfused rat hindquarter after high-intensity exercise. The purpose of the
present study was to examine whether fructose 6-phosphate-fructose
1,6-bisphosphate cycling or an uncoupling of mitochondrial respiration
contributes to this phenomenon. Hindquarter skeletal muscle was analyzed
after perfusion in the absence or presence of insulin (150-200 microU/ml)
for high-energy phosphate content, fructose 6-phosphate-fructose
1,6-bisphosphate cycling of glucose before incorporation into glycogen, and
mitochondrial respiratory control. Muscle from exercised rats perfused with
insulin did not display greater rates of glucose cycling or mitochondrial
uncoupling; in fact, insulin decreased the rate of fructose 6-phosphate
cycling and tended to increase respiratory control in skeletal muscle
mitochondria. In addition, the concentrations of ATP and creatine phosphate
and the calculated free ADP level in muscle of previously exercised rats
perfused with insulin were similar to those of control rats. The results do
not exclude the possibility that localized subcellular changes in ADP
occurred, however. In conclusion, the results suggest that insulin-induced
increases in other substrate cycles, ion transport systems, and/or as yet
unidentified energy-requiring processes account for the 25-30% increase in
hindquarter oxygen consumption after intense exercise.
