AJP - Endocrinology and Metabolism, Vol 272, Issue 5 E848-E855, Copyright © 1997 by American Physiological Society
Effects of exercise and feeding on the hexosamine biosynthetic pathway in rat skeletal muscle
B. A. Nelson, K. A. Robinson, J. S. Koning and M. G. Buse
Department of Medicine, Medical University of South Carolina, Charleston 29425, USA.
Products of the hexosamine biosynthesis pathway (HSNP) have been implicated
in glucose-induced insulin resistance. We measured the major products of
HSNP, UDP-N-acetyl hexosamines (UDP-HexNAc), and the activity of
L-glutamine: D-fructose-6-phosphate amidotransferase (GFAT, rate-limiting
enzyme) in rat hindlimb muscles immediately after exercise and 1, 3, and 16
h postexercise (swimming) in fed and fasted rats and sedentary controls.
Muscle glycogen decreased by 50-75% postexercise. In sedentary rats, muscle
GFAT activity decreased by approximately 30% (P < 0.002) after an 18-h
fast. GFAT activity was not affected by exercise under any condition.
Muscle UDP-HexNAc increased approximately 30% postexercise (P < 0.01) in
ad libitum-fed but not in fasted rats. UDP-HexNAc remained elevated
(approximately 30%, P < 0.002) for 16 h if animals were fed
postexercise. Concentrations of UDP-hexoses, GDP-mannose, and UDP were
unchanged postexercise. Conclusions are that muscle GFAT activity is
regulated by the nutritional state but not by acute exercise. Glucose flux
via HNSP may be increased postexercise in muscles of ad libitum-fed rats.
Increased HSNP products may serve as negative feedback regulators to limit
excessive muscle glycogen deposition postexercise.
