AJP - Endocrinology and Metabolism, Vol 259, Issue 4 E513-E516, Copyright © 1990 by American Physiological Society
Formation of gluconeogenic precursors in rat skeletal muscle during fasted-refed transition
M. N. Goodman, R. Dietrich and P. Luu
Department of Medicine, University of California, School of Medicine, Davis, Sacramento 95817.
During the fasted-refed transition, hepatic glycogen repletion from glucose
can occur by the direct and indirect pathway. In the indirect pathway,
glucose is first metabolized to 3-carbon intermediates that then are
converted in the liver to glucose 6-phosphate via the gluconeogenic pathway
before conversion to glycogen. The present study evaluated whether skeletal
muscle is a major source of 3-carbon intermediates (i.e., lactate,
pyruvate, and alanine) during refeeding of 1-day fasted rats. Arteriovenous
differences for lactate, pyruvate, and alanine across the anesthetized rat
hindlimbs were used to evaluate muscle metabolism in the fed, fasted, and
refed state. In the fasted state, liver glycogen was depleted, and muscle
released 3-carbon intermediates. One hour after refeeding, hepatic glycogen
was 30% repleted, and blood lactate, pyruvate, and alanine increased.
Despite this, the release of alanine by muscle diminished at this time and
lactate was removed. At 4 h after refeeding, 3-carbon intermediates were
all released by hindlimb tissue but in an amount not greater than in the
fasted state. Overall, these results suggest that skeletal muscle in the
rat is not a major source of 3-carbon precursors for early postprandial
hepatic glycogen repletion via the indirect pathway, nor is the rise in
3-carbon intermediates in blood during refeeding caused by their increased
output by muscle.
