Carnitine transport in rat small intestine.

Although L-carnitine has been given orally to patients with systemic carnitine deficiency with successful control of the disease and is present in a variety of dietary sources, there is little available information on the physiology of its absorption. We therefore studied intestinal carnitine absorption in the rat by measuring the uptake of radioactive L-carnitine by everted intestinal rings and sacs. Active transport was demonstrated in duodenum and jejunum, but not ileum, with intracellular concentrations higher than medium concentrations at steady state and by the prevention of concentration gradients with anoxia, metabolic inhibitors, and replacement of sodium ion. Studies of the relationship of uptake to carnitine concentration demonstrated the presence of two components of transport: a saturable component (with a Km of between 206 and 316 microM) that could be inhibited by the metabolically inactive D-isomer and by acetylcarnitine and a linear component that we presume represents diffusion.