Effect of dietary changes on intestinal absorption of L-methionine and L-methionyl-L-methionine in the rat.

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1. The absorption rates of L-methionine and L-methionyl-L-methionine (dimethionine) from the upper jejunum and lower ileum of the rat were studied in vivo after different dietary treatments. Rates were expressed per unit gut length and per unit gut weight; the former was considered to be the more satisfactory under the different dietary conditions.2. The dietary treatments were either short-term (10 d) or long-term (40–84 d).3. The rate of absorption of methionine increased in the jejunum after a restricted dietary intake, a high-protein diet or a high-methionine diet, but decreased after long-term protein deprivation. Short-term dietary restriction had a similar effect on methionine absorption in jejunum and ileum, though less pronounced in the latter. The rate of absorption of dimethionine was less influenced by dietary changes than that of methionine.4. Under all conditions studied, the absorption rate of methionine was greater when presented as the dipeptide than when presented as the equivalent amount of free amino acid. This confirms that dimethionine is taken up intact from the intestinal lumen, and it seems likely that there are different mechanisms of mucosal uptake for methionine and its dipeptide.