CHRONIC PROTEIN-DEFICIENCY DIFFERENTIALLY AFFECTS THE KINETICS OF PLASMA-PROTEINS IN YOUNG-PIGS

The use of plasma protein concentrations to assess protein-nutritional status has been questioned because concentrations and kinetics are af fected by factors other than protein intake. To determine the effect o f protein deficiency on plasma protein concentration and synthesis, tw o groups of four piglets consumed diets containing either 20 or 3% pro tein. After 8 wk, H-2(3)-leucine was infused intravenously to measure the fractional and absolute synthesis rates (FSR and ASR) of albumin, transferrin, retinol binding protein (RBP), transthyretin (TTR), a new peptide called TTR2, the high density apolipoprotein (HDL-apoA-1), fi brinogen, and haptoglobin. Compared with controls, protein-deficient p igs had significantly lower (P < 0.05) plasma albumin, RBP and TTR2 co ncentrations, significantly slower (P < 0.05) FSR of fibrinogen, HDL-a poA-1, transferrin, and TTR2, significantly lower (P < 0.05) ASR of al bumin, fibrinogen, transferrin, and TTR2, and a significantly higher ( P < 0.05) ASR of TTR. Fibrinogen and transferrin concentrations did no t differ between groups, but transthyretin concentration was higher in protein-deficient pigs. These results suggest that protein-nutritiona l status cannot be predicted from the concentrations of all plasma pro teins, that chronic protein deficiency affects the rate of synthesis o f only some plasma proteins, and that the kinetic response of plasma p roteins to protein restriction cannot be predicted from measurements o f plasma concentrations.