LEUCINE OXIDATION IN-VIVO - INTERINDIVIDUAL AND INTRAINDIVIDUAL VARIATION IN HEALTHY-SUBJECTS AS ASSESSED BY ORAL L-[1-C-13]LEUCINE LOADS

Interindividual variability of leucine catabolism was studied in eight overnight fasted healthy volunteers by means of a controlled oral L-[1-C-13]leucine loading test (5 mg/kg body weight). With the exception of total CO2 expiration (CV = 5%),a considerable variation (CV generally > or >> 10%)was observed with all other metabolic parameters: increase of leucine/2-oxoisocaproate in serum, C-13-enrichment in serum metabolites and (CO2)-C-13 in expired air, and estimated oxidation rates. The degree of variation was only partially referable to individual differences. A comparable high degree of variability was found when two probands underwent multiple loading tests (n = 4). Possible reasons and implications are discussed.