Effects of dietary l-tryptophan supplementation on intestinal response to chronic unpredictable stress in broilers
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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.
Keywordsl-Tryptophan Chronic unpredictable stress 5-Hydroxytryptamine Intestinal barrier function Broilers
We thank Dr Guoyao Wu for helpful discussion and suggestion on the manuscript. This work was partly supported by the National Natural Science Foundation of China (No. 31572423, 31372327).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
The use of animals for this research was approved by the Institutional Animal Care and Use Committee of China Agricultural University.
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