Intravenously infused carnitine: influence on protein and branched-chain amino acid metabolism in starved and parenterally fed rats.

We studied the effect of intravenously infused carnitine (34 mumol.100 g-1.d-1) on protein and branched-chain amino acid (BCAA) metabolism in rats either starved for 3 d or parenterally fed for 7 d. Carnitine infusion did not significantly affect nitrogen balance, protein content of liver and muscle, plasma concentrations of BCAA and branched-chain keto acid, or leucine oxidation and incorporation into liver and muscle proteins of either starved or fed rats. Despite a two- to threefold increase in plasma carnitine level, tissue concentrations of carnitine and its acyl-derivatives were not significantly affected by carnitine infusion. Of the amount of carnitine infused, 91% was lost in the urine of starved rats and 87% in the urine of fed rats. We conclude that intravenous carnitine infusion does not affect protein and BCAA metabolism and that this lack of effect may be related to the failure of carnitine infusion to enrich tissue pools of carnitine.