AJP - Endocrinology and Metabolism, Vol 259, Issue 5 E633-E638, Copyright © 1990 by American Physiological Society
Nitrogen sparing by 2-ketoisocaproate in parenterally fed rats
M. Yagi, D. E. Matthews and M. Walser
Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
In rats receiving total parenteral nutrition with or without sodium
2-ketoisocaproate (KIC; 2.48 g.kg-1.day-1), L-[1-13C]leucine and [1-14C]KIC
were constantly infused for 6 h. CO2 production, 14CO2 production, 13CO2
enrichment, urinary urea nitrogen (N) plus ammonia N and total urinary N
were measured. Whole body protein synthesis (S) was calculated in
non-KIC-infused rats and also in unfed rats infused with [1-14C]leucine
from fractional oxidation of labeled leucine (1-F), where F is fractional
utilization for protein synthesis, and urea N plus ammonia N excretion (C)
as S = C x F/(1-F). Addition of KIC caused a significant reduction in N
excretion and a significant improvement in N balance. Fractional oxidation
of labeled KIC increased, whereas fractional utilization of labeled KIC for
protein synthesis decreased, but the extent of incorporation of infused KIC
into newly synthesized protein (as leucine) amounted to at least 40% of the
total rate of leucine incorporation into newly synthesized whole body
protein. We conclude that addition of KIC spares N in parenterally fed rats
and becomes a major source of leucine for protein synthesis.
