Abstract
An eight-week feeding trial discusses how methionine affects intestinal barrier and lipid transport on rice field eel (Monopterus albus). Six isoenergetic and isonitrogenous feeds contained different levels of methionine (0, 2 g/kg, 4 g/kg, 6 g/kg, 8 g/kg, or 10 g/kg). Compared with M0 (0 g/kg), gastric amylase, lipase, and trypsin were remarkably increased as dietary methionine ( P < 0.05 ); intestinal amylase, lipase, and trypsin were remarkably increased in M8 (8 g/kg) ( P < 0.05 ). Compared with M0, gastric fovea was remarkably increased ( P < 0.001 ), gastric epithelium is neater in M8 than that in M0, intestinal villus height and muscular thickness are remarkably increased in M8 ( P < 0.001 ), and amounts of goblet cells per root in M8 were increased ( P > 0.05 ), while intestinal crypt depth was markedly decreased ( P < 0.001 ). Lipid droplets in the intestinal villus and mucosal layer in the M8 (8 g/kg) group were more than that in M0 (0 g/kg). Compared with M0 (0 g/kg), the intestinal gcn2 and eif2α were downregulated in M8 (8 g/kg) ( P < 0.01 and P < 0.05 , respectively), while occ, cl12, cl15, zo-1, zo-2, hdlbp, ldlrap, npc1l1, cd36, fatp1, fatp2, fatp6, apo, apoa, apob, apoc, apoe, mct1, mct2, mct8, lpl, mttp, moat2, and dgat2 were upregulated markedly in M8 (8 g/kg). Intestinal eif2α expression was positively correlated with gcn2, and intestinal zo-1, cl15, fatp6, ldlrap, mct2, mct8, apo, apob, mct1, apoc, fatp1, mttp, cd36, occ, npc1l1, hdlbp, fatp2, apoe, lpl, and moat2 gene expression was negatively correlated with gcn2. In conclusion, methionine deficiency affected the gastric and intestinal structures, damaged the intestinal barrier, and decreased lipid and fatty acid transport. Besides, gcn2 could be activated when M. albus was fed methionine-deficient feed.
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