Distinguishable substrate pools for muscle glyconeogenesis in
lactate-supplemented recovery from a prolonged swim in rats.
Ryan, Colleen, and Jerry Radziuk.
Ottawa Civic Hospital and the University of Ottawa
APStracts 2:0086E, 1995.
The formation of muscle glycogen from substrates other than glucose
(glyconeogenesis) has now been demonstrated (i) from circulating
lactate when this is elevated and (ii) from intramuscular substrate
which equilibrates with the products of local glucose metabolism but
not with circulating lactate (32). The purpose of the present studies
was to examine the interaction of recovery from low intensity
exercise (4-h swim) and supplementation with exogenous lactate in
determining the distribution of carbon flux between these two
pathways for the glyconeogenic process in the gastrocnemius muscles.
Ten protocols were defined using [14C]bicarbonate (no local
incorporation into glycogen), [U-14C]lactate (tracks circulating
lactate) and recycled [1-14C]glucose (tracks local substrate
formation and glyconeogenesis). During recovery, lactate was infused
to increase circulating concentrations 15-20 fold. Glucose and saline
infusions during recovery were used as controls. The results indicate
that prior exercise primarily promotes the local incorporation of
recycled glucose label, produced within the muscle into glycogen.
Exogenous lactate stimulates the incorporation of circulating lactate
into muscle glycogen. The contribution of the two substrate pools to
glycogen synthesis appears to be additive indicating the independence
of muscle glycogenesis from these two sources.
Received 8 September 1994; accepted in final form 19 April 1995.
APS Manuscript Number E367-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.