Estimation of the glucose-alanine-lactate-glutamine cycles in
postabsorptive man: role of skeletal muscle.
Perriello, G., R. Jorde, N. Nurjhan, M. Stumvoll, G. Dailey, T.
Jenssen, D. M. Bier, and J. E. Gerich.
Division of Endocrinology and Metabolism, Scripps Clinic, La Jolla,
CA 92037, The University of Rochester School of Medicine, Rochester,
NY 14642, University Hospital of Tromso, Department of Medicine,
Tromso, NORWAY, Washington University School of Medicine, Metabolism
Division, St. Louis, MO 63110
APStracts 2:0072E, 1995.
To evaluate transfer of carbon between plasma glucose and plasma
alanine (glucose-alanine cycle) and lactate (Cori Cycle), to assess
the contribution of skeletal muscle to these cycles, and to determine
whether a glucose-glutamine cycle exists in postabsorptive humans, we
infused 11 normal over-night fasted volunteers with [2-3H] glucose,
[6-14C] glucose and [3-13C] alanine to isotopic steady state and in 7
of these simultaneously measured forearm net balance, uptake and
release of labelled and unlabelled glucose, lactate and alanine. We
found that 40.9 +/- 3.3, 66.8 +/- 3.2 and 13.4 +/- 1.1% respectively
of plasma alanine, lactate and glutamine carbon came from plasma
glucose. More plasma glucose was converted to plasma alanine than
could be derived from plasma alanine (1.89 +/- 0.20 vs 1.48 +/- 0.15
_mol.kg-1.min-1, p<0.001). A similar direction of net carbon flux
was found for lactate (8.5 vs 4.2 _mol.kg.-1min-1) with only
glutamine adding more carbon to plasma glucose than was received from
it (1.0 vs 0.75 _mol.kg.-1min-1). Skeletal muscle accounted for 50.2
+/- 3.9 and 45.5 +/- 5.7% of the overall appearance of alanine and
lactate in plasma, and 54.2 +/- 5.4 and 36.4 +/- 4.2% of their
respective origins from plasma glucose. Skeletal muscle release of
alanine and lactate that had been formed from plasma glucose
accounted for 19.1 +/- 2.1 and 48.4 +/- 4.8% respectively of muscle
glucose uptake and 42.4 +/- 5.5 and 49.9 +/- 5.8% of the overall
release of alanine and lactate from muscle. These results demonstrate
that in postabsorptive humans a glucose-glutamine cycle exists which,
in contrast to the Cori and glucose-alanine cycles, results in a
positive transfer of new carbon to the glucose pool and that
approximately one-half of plasma alanine and two-thirds of plasma
lactate production from plasma glucose occurs in tissues other than
skeletal muscle.
Received 31 October 1994; accepted in final form 7 April 1995.
APS Manuscript Number E447-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.