Effects of dietary l -tryptophan supplementation on intestinal response to chronic unpredictable stress in broilers

Stress has been recognized as a critical risk factor for gastrointestinal diseases in both humans and animals. However, nutritional strategies to attenuate stress-induced intestinal barrier function and underlying mechanisms remain largely unknown. This study tested the hypothesis that l -tryptophan enhanced intestinal barrier function by regulating mucosal serotonin metabolism in chronic unpredictable stress-exposed broilers. One-day-old male broilers (Arbor Acres) were fed a basal diet supplemented with or without l -tryptophan in the absence or presence of chronic unpredictable stress. Feed intake, body weight gain, plasma corticosterone and 5-hydroxytryptamine (5-HT), intestinal permeability, mucosal secretory IgA (sIgA), and mRNA levels for tryptophan hydroxylase 1 ( TPH1 ), IL - 1β , IL - 6 , TNF - α, IL - 10, protein abundance for claudin-1, occludin, and ZO-1 were determined. Stress exposure led to elevated plasma corticosterone ( P < 0.05), increased intestinal permeability ( P < 0.05), reduced growth performance ( P < 0.05), and decreased sIgA secretion compared with the controls. These effects were largely reversed ( P < 0.05) by l -tryptophan supplementation. Western blot analysis showed that stress exposure resulted in decreased protein abundance for occludin, claudin-1, and ZO-1, which was attenuated by l -tryptophan. mRNA levels for IL - 1β , IL - 6 , and TNF - α were increased, but those for IL-10 were decreased, in the jejunal tissue of broilers subjected to stress. This effect of stress on cytokine expression was abolished by l -tryptophan treatment. The effects of stress were associated with decreased plasma concentration of 5-HT ( P < 0.05), and reduced ( P < 0.05) mRNA levels for TPH1 . l -Tryptophan supplementation markedly attenuated stress-induced alterations in 5-HT and TPH1 mRNA level in jejunal tissues of broilers. Collectively, these results indicate that l -tryptophan supplementation alleviates chronic unpredictable stress-induced intestinal barrier dysfunction by regulating 5-HT metabolism in broilers.