Comparison of A‐V and precursor‐product methods for measuring muscle protein breakdown in burned patients

Abstract

We have recently developed a new bolus precursor‐product method for measuring protein synthesis and breakdown simultaneously. The new method is an attractive alternative to our previously developed A‐V balance method because it does not require femoral lines or measurement of blood flow. Although we have previously shown that the two methods (A‐V vs precursor‐product) for measuring protein breakdown agree in rabbits, the new method has not been validated in humans. The purpose of this study was to compare muscle protein fractional breakdown rates (FBR) using the two methods in humans simultaneously. Results from the A‐V balance method were converted to units %/h with estimates of muscle protein bound pool size. Five burn patients not on anabolic treatments were studied at 1 and 3 weeks postburn using both the A‐V balance method (using 13C4 threonine tracers) and the new precursor‐product method (using 15N and 13C6 phenylalanine tracers). FBR was similar for A‐V (1 week: 0.29 ± 0.13%/h, n=3; 3 weeks: 0.29 ± 0.11%/h, n=5) and bolus (1 week: 0.24 ± 0.05 %/h, n=5; 3 weeks: 0.29 ± 0.05 %/h, n=4) methods. Comparable results are obtained with the new method using either arterial or peripheral venous enrichment. The new precursor‐product bolus method gives similar results to the A‐V balance method without the use of femoral catheters or measurement of blood flow.