AJP - Endocrinology and Metabolism, Vol 252, Issue 5 E595-E598, Copyright © 1987 by American Physiological Society
Effect of a protein synthetic inhibitor on in vivo estimates of protein synthesis in dogs
W. F. Schwenk, E. Rubanyi and M. W. Haymond
In vivo estimates of nonoxidative leucine disappearance have frequently
been used as estimates of leucine incorporation into protein. To attempt to
assess this extrapolation to protein synthesis, seven overnight fasted dogs
received primed 4-h infusions of emetine (3 mg/kg, 1 mg X kg-1 X h-1), an
alkaloid known to inhibit protein synthesis at the translational level.
Protein metabolism was studied using infusions of [1-14C]leucine and
alpha-[4,5-3H]ketoisocaproate (KIC) and the steady-state specific
activities of the leucine moiety (e.g., [14C]KIC and [3H]leucine)
reciprocal to the infused isotopes as estimates of intracellular leucine
specific activities. Plasma leucine (157 +/- 13 to 217 +/- 13 microM) and
KIC (24 +/- 1 to 41 +/- 4 microM) concentrations increased (P less than
0.001), as did leucine oxidation (0.60 +/- 0.07 to 1.67 +/- 0.15 mumol X
kg-1 X min-1, P less than 0.001). Estimates of nonoxidative leucine
disappearance decreased (P less than 0.001) by approximately 70%, and
estimates of the endogenous leucine rate of appearance decreased (P less
than 0.001) by approximately 40% using either the 14C or 3H data. We
conclude that, although in vivo estimates of leucine metabolism are not
quantitative, rapid changes in whole-body estimates of protein synthesis
can be predicted during infusion of labeled leucine.
