LEUCINE METABOLISM AND BODY CELL MASS IN CYSTIC-FIBROSIS

To further investigate the nature of malnutrition in cystic fibrosis ( CF), specifically to evaluate the influence of body composition on leu cine metabolism and determine whether measures used as reference stand ards alter comparative differences in protein metabolism, we measured [C-13]leucine kinetics in nine well-nourished and eight malnourished, height-, FEV(1)-, and sex-matched CF subjects. Body cell mass was meas ured by total-body potassium (K-40) analysis. Leucine turnover did not significantly differ between groups in absolute values or when correc ted for body weight, body height, or surface area. However, malnourish ed CF patients had accelerated leucine turnover based on body cell mas s measurements. Mean leucine synthesis per unit body cell mass in the malnourished group was 147% higher than that of the well-nourished gro up (p<0.001). These data indicate that altered body composition is an important factor influencing protein metabolism in CF and should be co nsidered in future metabolic studies. The importance of potentially se rious but possibly correctable deficits in body cell mass in CF is emp hasized.