In Vitro and In Situ Absorption of Methionine Sulfoxide in Rat Small Intestine

Absorption of methionine and its sulfoxide was investigated in vitro with everted sacs and in situ with circulated loops of rat small intestine. Transmural transport and tissue accumulation of methionine sulfoxide in the everted sacs were in fair agreement with those of methionine. Apparent kinetic parameters for the difference of transmural transport in the absence and presence of 10^?5 m carbonylcyanide m-chlorophenylhydrazone, i.e. for the energy-dependent active transport, were similar for both methionine and its sulfoxide. Methionine was found at a low level in the serosal fluid of the everted sac on incubation with methionine sulfoxide. It was attributed to the methionine leaked out from the tissue but not to that formed by reduction of methionine sulfoxide during the course of intestinal transport. Similar transport was also observed in situ in circulated intestinal loops for methionine and its sulfoxide. The absorption efficiency of methionine sulfoxide in the small intestine is not the reason for the decreased nutritional availability of the most likely oxidation product of methionine.