Lysine-carnitine conversion in normal and undernourished adult men-suggestion of a nonpeptidyl pathway.

Administration of 5 g L-lysine orally to normal adults produced a significant increase in plasma carnitine levels within 6 h followed by a further rise by 48 h. Levels remained high up to 72 h. Similar changes in plasma carnitine were not observed if blood was sampled without lysine load or after administering a load of other amino acids such as tryptophan or threonine. Maximum excretion of carnitine per g creatinine was observed in 24 to 48 h collection after lysine load. Two subjects showed an early peak in 3-h and 6-h collections, respectively. Undernourished subjects failed to demonstrate similar change. After rehabilitation the undernourished subjects behaved as did the well-nourished subjects. These observations suggest that there may be a rapid in vivo conversion of orally administered lysine to carnitine in humans. Conversion of lysine to carnitine may be impaired in malnutrition.