Rats were fed an 8% casein diet supplemented with L-, D-methionine, LL- or DD-dimethionine. There were six groups in Experiment 1: 8% casein, 8% casein+0. 2% L-, D-methionine, LL-, DD-dimethionine or oligo-L-methionine (a mixture of hexamer and heptamer). There were seven groups in Experiment 2:8% casein, 8% casein+0.06, 0.08 or 1. 0% LL- or DD-dimethionine.
In our previous experiment, fatty liver developed in rats fed an 8% casein diet supplemented with 0.2% L-methionine, but not in rats fed 8% casein with oligo-L-methionine. Since oligo-L-methionine hardly dissolves in water and is hydrolyzed very slowly by pancreatic juice and everted gut rings of rat intestines, and since L-methionine is an amino acid with high intestinal absorption, we assumed that the difference in supplemental effects between L-methionine and oligo-L-methionine may be due to their differential absorption rate from the intestine. If the assumption is valid, methionine derivatives which are slowly hydrolyzed and/or absorbed from the intestine should also be able to prevent an accumulation of liver fat when they are supple-mented in a low casein diet. As absorption of DD-dimethionine from the loop of the rat small intestine is slow (about 1/10 of LL-dimer)
(6), the supplemental effects of DD-dimethionine in the low casein diet was examined. In Experiment 1, a fatty liver was observed in all supplemented groups except for the group fed the diet with oligo-L-methionine. In Experiment 2, there was no significant difference in liver fat accumulation between the group fed an 8% casein diet and groups fed with supplemented diets, but the blood threonine value was lower in the supplemented diet groups than in the 8% casein diet group. It was obvious that DD-dimethionine could not prevent threonine imbalance symptoms, such as a decrease in blood threonine and an increase in liver fat. The blood threonine level of groups fed LL-dimethionine being lower than groups fed DD-diastereomer may suggest that the threonine imbalance symptom was caused more easily by LL-dimethionine than by DD-diastereomer. It is also probable that the absorption rate of DD-dimethionine from the intestinal tract is significantly higher than that of oligo-L-methionine.
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