Reyes H
Departamento de Medicina Experimental y de Medicina, Facultad de Medicina (Campus Oriente), Universidad de Chile, Santiago de Chile.
Rev Med Chil. 1994 Aug;122(8):944-50.
Bile acids are the most important solutes of bile: they are essential in cholesterol degradation, solubilization and excretion; they are determinants of bile flow and secretion; and their role is crucial in the intestinal absorption of lipids and lipid soluble vitamins. In amphibia and in cartilaginous fish, the 27C cholestane molecule is hydroxylated to alcohols. In birds, the terminal 27C-OH group is oxydated to cholestanoic acids. In vertebrates of a more recent evolutionary origin, the lateral chain is shortened to 24C and oxydated to cholestanoic acids. Further transformations include chemical changes in the cholestane skeleton and in the lateral chain (hydroxylations, dehydroxylations, epimerization, etc). In the intestinal lumen, the saprophytic flora provides enzymes catalysing new changes that originate "secondary" bile acids. During entero-hepatic circulation, another variety of bile acids appear, commonly termed "tertiary" bile acids. A recent study of Lee R Hagey characterized bile acid composition of over 600 species of vertebrates, showing that bile acid composition of bile has been the subject of an interesting evolutionary phenomenon and that it is a chemical marker of biodiversity in vertebrates.
它们在胆固醇降解、溶解和排泄中必不可少；它们是胆汁流动和分泌的决定因素；并且它们在脂质和脂溶性维生素的肠道吸收中起着关键作用。在两栖动物和软骨鱼类中，27碳胆烷分子被羟基化为醇类。在鸟类中，末端的27碳-OH基团被氧化为胆烷酸。在进化起源较新的脊椎动物中，侧链缩短至24碳并被氧化为胆烷酸。进一步的转化包括胆烷骨架和侧链的化学变化（羟基化、脱羟基化、差向异构化等）。在肠腔中，腐生菌群提供催化新变化的酶，从而产生“次级”胆汁酸。在肠肝循环过程中，出现了另一种胆汁酸，通常称为“三级”胆汁酸。李·R·哈吉最近的一项研究对600多种脊椎动物的胆汁酸组成进行了表征，表明胆汁的胆汁酸组成是一种有趣的进化现象的主题，并且它是脊椎动物生物多样性的化学标志物。
