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

Abstract

I . 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-methionhe 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 dipcptide.Preliminary investigations of absorption rates of methionine and the dipeptide L-methionyl-L-methionine (dimethionine) after a short period of reduced dietary intake (a dietary condition referred to as 'semistarvation' by Crampton, showed that reduced food intake increased the absorption of both amino acid and peptide, but that the effect on absorption of the peptide was less marked. This suggested that the mechanisms of intestinal uptake of the two compounds might not be identical. I n view of this, and because we know of no other study of peptide absorption following several dietary alterations, we have investigated the effects of different diets on the rates of absorption of methionine and dimethionine.Newey & Smyth (1959,1960,1962) first showed that mucosal uptake of dipeptides, with cellular hydrolysis, occurred in the small intestinc of the rat and dog. Studies of relative absorption rates of amino acids and small peptides and investigations of defects in intestinal amino acid transport have now shown that mucosal uptake of small peptides occurs in many mammalian species, including man (Matthews,

Kinetics of Uptake of L-Leucine and Glycylsarcosine into Normal and Protein Malnourished Young Rat Jejunum

“…= 100-rivation in the immediate postweaning period caused a reduction in maximal mediated transport capacity for both Gly-Sar and leucine when uptake was expressed on the basis of unit length. There was no preservation of peptide uptake relative to amino acid uptake, neither was there an initial increase in absorption as found by Lis et al (7,8) in short-term protein deprivation in adult rats. Furthermore, the reduction observed in this study was not as great as that seen in long-term protein malnutrition in the adult rat (7,8).…”

“…There was no preservation of peptide uptake relative to amino acid uptake, neither was there an initial increase in absorption as found by Lis et al (7,8) in short-term protein deprivation in adult rats. Furthermore, the reduction observed in this study was not as great as that seen in long-term protein malnutrition in the adult rat (7,8). The malnourished young animals had a much greater reduction in gut length compared with the controls than malnourished adult animals in which the reduction in mean intestinal length was only of the order of 5% (7).…”

“…The results have been conflicting, but in general, peptide transport was shown to be less affected than amino acid transport (7,8,9). …”

“…The impact of protein restriction with or without calorie deprivation on amino acid and peptide transport has been investigated in adult man (1) and experimental animals (4,6,7,8,12,15,16,18). The results have been conflicting, but in general, peptide transport was shown to be less affected than amino acid transport (7,8,9).…”

Effects of Semi-Starvation on the Total Body Composition and Absorptive Function of the Small Intestine of the Young Adult Female Rat

“…The active transport of histidine has been shown to increase (Kershaw et al 1960;Hindmarsh et al 1967;Madge 1970). Lis et al (1972) showed for rats that after 10 days offood restriction to prevent growth but to maintain body weight there was increased L-methionine absorption from the small intestine, but the effect was no longer apparent after 51 days.…”