Effects of L-theanine on glutamine metabolism in enterotoxigenic Escherichia coli (E44813)-stressed and non-stressed rats

L-theanine, a non-protein-derived amino acid, is widely used as a functional ingredient in foods. Here, we evaluated the in vivo effects of L-theanine on glutamine metabolism in healthy rats and in a stressed rat model, which was established by infecting rats with enterotoxigenic Escherichia coli (E44813). The results showed that L-theanine significantly enhanced the synthesis of glutamine and stabilized the intestinal tract in healthy rats. In E44813-stressed rats, L-theanine could replace L-glutamine, thereby alleviating intestinal stress by reducing the expression of inflammatory factors, enhancing the activities of antioxidant enzymes, and regulating glutamine metabolism by modulating its synthesis. Treatment with a combination of L-theanine and L-glutamine was superior to treatment with L-glutamine alone in enhancing the activity of antioxidant enzymes, reducing the expression of inflammatory factors, and increasing the intestinal villi height and crypt depth.