AJP - Endocrinology and Metabolism, Vol 238, Issue 5 487-E493, Copyright © 1980 by American Physiological Society
Production of alanine and glutamine by atrial muscle from fed and fasted rats
M. E. Tischler and A. L. Goldberg
During incubation in vitro, rat atrial and rabbit papillary muscles
synthesized and released large amounts of alanine and even higher amounts
of glutamine. The amino groups used in the synthesis of alanine and
glutamine appeared to be derived from the catabolism of other amino acids,
specifically, leucine, isoleucine, valine, aspartate, glutamate,
asparagine, arginine, and proline. The total amount of glutamine and
alanine synthesized increased by 45% in atrial muscle from fasted rats, in
which the oxidation of branched-chain amino acids is enhanced. In atria
from fed rats, addition of leucine stimulated by about 20% the production
of both alanine and glutamine, probably by providing additional amino
groups for transamination with alpha-ketoglutarate. However, in cardiac
muscle from fasted rats and rabbits, leucine increased the production of
glutamine, but not of alanine. Isoleucine and valine, by contrast, enhanced
production of both alanine and glutamine in these tissues. In the presence
of leucine, low levels of pyruvate seem to limit the production of alanine,
apparently because leucine, unlike isoleucine or valine, promotes the
conversion of pyruvate to lactate.
