Chronic protein undernutrition and an acute inflammatory stimulus elicit different protein kinetic responses in plasma but not in muscle of piglets

The changes in protein metabolism of severe childhood malnutrition are gene rally perceived as a metabolic adaptation to chronic protein undernutrition . However, severe malnutrition is invariably accompanied by infections whic h also have profound effects on protein metabolism. This study aimed to dis tinguish the effect of protein undernutrition from that of an inflammatory stimulus on muscle and plasma protein synthesis rates. Two groups of five p iglets consumed diets containing either 23% or 3% protein for 4 wk. They th en were infused intravenously with H-2(3)-leucine before and 48 h after sub cutaneous injections of turpentine to measure the fractional synthesis rate s (FSR) of muscle protein and both the FSR and the absolute synthesis rates (ASR) of albumin and fibrinogen, Prior to turpentine injection, compared t o control piglets, protein-deficient piglets had significantly lower muscle FSR and plasma concentrations of both albumin and fibrinogen, although onl y albumin had lower FSR and ASR. Turpentine injection decreased muscle FSR but increased the FSR, ASR and plasma concentrations of both albumin and fi brinogen in control piglets. In protein-deficient piglets, the inflammatory stress caused a further decrease in muscle protein FSR and in plasma album in concentration despite marked increases in albumin FSR and ASR, Fibrinoge n FSR, ASR and plasma concentration were increased. We conclude that protei n undernutrition and inflammation elicit the same kinetic response in muscl e protein but different kinetic responses in plasma proteins. Furthermore, whereas protein deficiency reduces the plasma albumin pool via a reduction in albumin synthesis, inflammation reduces it through a stimulation of cata bolism and/or loss from the intravascular space.