THE EFFECT OF ENTERAL CARNITINE ADMINISTRATION IN HUMANS

We previously determined that the L-carnitine uptake by human duodenal tissue occurs by both active (K(T) 558-mu-mol/L) and passive mechanisms. The effects of enteral carnitine was studied in humans. A hamburger meal (345-mu-mol total carnitine) induced peak jejunal fluid free (unesterified) and short-chain acylcarnitine concentrations (SCAC) of 209 and 130-mu-mol/L, respectively. Plasma carnitine concentrations and the percent renal reabsorption remained unchanged. By contrast, a pharmacologic dose of free carnitine (25 298-mu-mol) raised peak intraluminal free and SCAC to 20 660 and 4204-mu-mol/L. Plasma total carnitine concentrations doubled to 93-mu-mol/L, and the percent renal reabsorption of free and SCAC declined to 76% and 52%, respectively. In triple-lumen perfusions, 200-mu-mol carnitine/L was absorbed at 484 nmol.min-1.30cm-1 jejunum, a rate sufficient for prandial but not pharmacologic assimilation. Our findings indicate that absorption of physiologic and pharmacologic amounts of carnitive occurs predominantly by active transport and passive diffusion, respectively.