Whole-body protein turnover in nephrotic subjects: a comparison between different degrees of proteinuria

In contrast to the increased hepatic albumin synthesis in subjects with proteinuria, little is known about the corresponding whole-body protein turnover rates (WPTR). The WPTR and the reutilisation rates (R) were investigated in 20 patients divided in three groups of different degrees of proteinuria (groups I-III: < 1, 1-3, > 3 g/m2/day, respectively). [15N]glycine was administered as a single oral pulse. Urine samples were taken over 2 days. After removing urinary proteins by trichloracetic acid, 15N-enrichment in the supernatant was measured by isotope ratio mass spectrometry. A three-compartment model was used to calculate WPTR and R, which showed a statistically significant difference between groups I and III (2.64 vs. 4.63 g/kg/day, and 70.4% vs. 80.8%, respectively, P < 0.01), whereas the net protein gain remained unchanged (0.13 vs. 0.22 g/kg/day). The higher the protein loss the higher the WPTR and the corresponding R. The severe protein loss provokes increased WPTR and R as well.