Nephrology Dialysis Transplantation, Vol 13, Issue 7 1723-1730, Copyright © 1998 by Oxford University Press
V Lim, K Yarasheski and M Flanigan
Background: Uraemia and dialysis are viewed as
catabolic processes resulting in malnutrition in chronic renal failure
(CRF) patients. To sort out the effects of uraemia, acidosis, and dialysis
on protein metabolism, we measured leucine flux in CRF patients before and
after initiation of maintenance dialysis. Subjects and
methods: Whole-body leucine flux was measured by primed-constant
infusion of L[1-13C]leucine in nine CRF patients
longitudinally; twice before and once after initiation of maintenance
dialysis (D). Before dialysis, one leucine flux was measured when the
patients were acidotic (A), and the other, when acidosis was corrected with
NaHCO, (NA). Five normal subjects underwent one single leucine flux
measurement to serve as control (N). Both patients and normal subjects
consumed a constant diet for 6 days and leucine flux was measured on the
7th day 12 h post-absorption. Diet for the CRF patients was identical
during the three periods. Plasma L[1-13C]leucine and
L[1-13C]KIC were measured by gas chromatography/mass
spectrometry and expired 13CO2 by isotope ratio
spectrometry. Leucine kinetics were calculated using standard equations.
Results: Plasma CO2 levels were 19, 26 and 31 mmol/l
in A, NA and D periods respectively. All kinetic results
(&mgr;mol/kg/h) are presented as means±SD in the order of A,
NA, D, and N, and CRF values that are statistically different from N are
identified (*). The amounts of leucine release from endogenous protein
breakdown (Ra or Q) were 101±12* 95±9*
113±22 and 117±6. Leucine oxidation (C), quantities
of leucine irreversibly oxidized to CO2, were 16.5±5.4,
9.7±3.7*, 12.3±3.0*, and 23.2±3.1. Leucine
protein incorporation levels (S) were 85±10, 85±8,
101±19 and 94±6. The S of 101 in CRF patients at
period D was statistically higher than those during A and NA periods.
Conclusions: These data indicate that when acidosis
was corrected, CRF patients adapted to lower protein intake by reducing
amino-acid oxidation and protein degradation, and maintained protein
synthesis at normal levels. Metabolic acidosis impaired the downregulation
of amino-acid oxidation. Maintenance dialysis treatment longitudinally
restored protein flux to normal and increased protein synthesis. The
general notion that uraemia and dialysis are protein catabolic is not
supported by this work. Key words: leucine kinetics;
protein turnover; uraemia
ORIGINAL ARTICLES
The effect of uraemia, acidosis, and dialysis treatment on protein metabolism: a longitudinal leucine kinetic study
Departments of Internal Medicine, University of Iowa College of Medicine, Iowa City, Iowa, USA; Washington University Medical School, St Louis, MO, USA; Corresponding author at: Nephrology Division, Department of Internal Medicine, T310, GH, University of Iowa Hospitals, Iowa City, IA 52242, USA
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