Mortensen P B, Rasmussen H S, Holtug K
Department of Medicine, Hvidovre Hospital, University of Copenhagen, Denmark.
Gastroenterology. 1988 Mar;94(3):750-4. doi: 10.1016/0016-5085(88)90250-8.
Short-chain (C2-C6) fatty acids constitute the major anions of colonic contents. Acetate is nontoxic in contrast to C(3)4-C6 fatty acids, which induce coma in animals and have been reported to be of importance in the development of hepatic coma in humans. An in vitro fecal incubation system was used to demonstrate how blood, hemoglobin, albumin, lactulose, galactose, fructose, and glucose influence short-chain fatty acid production in the colon. Blood, hemoglobin, and albumin caused increased production of all C2-C6 fatty acids, with the most pronounced increase (fourfold) in C4-C6 fatty acids. Lactulose was converted to acetate only, as were its monosaccharide components, D-galactose and D-fructose. In assays incubated with blood, the production of C4-C6 fatty acids was completely inhibited by lactulose, D-galactose, D-fructose, and D-glucose, respectively, whereas the production of acetate was increased. Lactulose thus "detoxified" the profile of short-chain fatty acids produced in the presence of blood and proteins, indicating that colonic fermentative bacteria prefer lactulose to blood when both substrates are available. The effect of lactulose in the treatment of hepatic coma caused by episodes of gastrointestinal bleeding may therefore be due to a shift in bacterial metabolism from blood or proteins, or both, to lactulose in the colon, resulting in a simultaneous reduction in toxic nitrogenous and organic acid products.
短链（C2 - C6）脂肪酸是结肠内容物的主要阴离子。与C3 - C6脂肪酸不同，乙酸无毒，C3 - C6脂肪酸会使动物昏迷，据报道在人类肝昏迷的发展中起重要作用。采用体外粪便培养系统来证明血液、血红蛋白、白蛋白、乳果糖、半乳糖、果糖和葡萄糖如何影响结肠中短链脂肪酸的产生。血液、血红蛋白和白蛋白会使所有C2 - C6脂肪酸的产量增加，其中C4 - C6脂肪酸的增加最为显著（四倍）。乳果糖及其单糖成分D - 半乳糖和D - 果糖仅转化为乙酸。在与血液一起孵育的试验中，乳果糖、D - 半乳糖、D - 果糖和D - 葡萄糖分别完全抑制了C4 - C6脂肪酸的产生，而乙酸的产量增加。因此，乳果糖使在有血液和蛋白质存在时产生的短链脂肪酸谱“解毒”，这表明当两种底物都存在时，结肠发酵细菌更喜欢乳果糖而非血液。因此，乳果糖在治疗由胃肠道出血发作引起的肝昏迷中的作用可能是由于结肠中细菌代谢从血液或蛋白质（或两者）转向乳果糖，导致有毒含氮和有机酸产物同时减少。
