In vivo studies of intestinal carnitine absorption in rats.

We have studied small intestinal absorption of carnitine in vivo using a combination of segmental perfusion techniques and bolus intraluminal injection. We found evidence of a partially saturable absorption process (with Km values of 1035 and 1267 microM for jejunum and ileum calculated for the saturable component) that appeared to be separate from the imino acid transport system. Absorption was characterized by slow mucosal uptake, prolonged mucosal retention, and a very slow mucosal exit process with blood levels of [3H] carnitine still rising 8 h after intraluminal administration. We have also demonstrated the presence of carnitine acetyltransferase in intestinal mucosa and have shown that the intestine forms significant amounts of acetylcarnitine from exogenous carnitine.