Kotal P, Fevery J
Department of Medical Research, Catholic University of Leuven Campus Gasthuisberg, Belgium.
Biochem J. 1990 May 15;268(1):181-5. doi: 10.1042/bj2680181.
Gunn rats lack bilirubin UDP-glycosyltransferases, but diazo-negative derivatives of bilirubin have been described in their bile. In order to investigate this alternative disposal of bilirubin, crude bile samples from Gunn and Wistar rats were directly analysed by h.p.l.c. Besides bilirubin (in Gunn rats) or its glycosides (in Wistar rats), two major compounds were detected. A yellow one corresponded to the previously documented vitamin B-2 and was equally prominent in Gunn rats or Wistar-rat bile. The other compound was colourless, but on standing in contact with air it was spontaneously oxidized to a pinkish-yellow pigment. It was far more prominent in Gunn-rat bile. Analysis of bile obtained after intravenous injection of [14C]bilirubin to Gunn rats demonstrated that this compound was highly labelled. Freezing and thawing of the bile resulted in the formation of a series of diazo-negative derivatives, demonstrating that the original compound was quite labile. Spectral (adsorption and fluorescent) and chromatographic (h.p.l.c., t.l.c. and paper chromatography) analysis of the oxidized form of the labelled compound allowed its identification as urobilin-i. The colourless compound secreted in bile was urobilinogen-i. Administration of neomycin and bacitracin to Gunn rats or gut resection suppressed the biliary excretion of urobilinogen and thus confirmed its intestinal origin. Urobilinogen seems thus to represent the major bilirubin derivative present in Gunn-rat bile. Its breakdown products might represent the so-far-unidentified diazo-negative polar bilirubin derivatives. Since only a small amount of bilirubin is present in Gunn-rat bile, the urobilinogen formed in the intestinal lumen seems to be derived from bilirubin reaching the gut via routes other than the biliary one.
冈恩大鼠缺乏胆红素UDP-糖基转移酶，但在它们的胆汁中已发现胆红素的重氮阴性衍生物。为了研究胆红素的这种替代排泄方式，采用高效液相色谱法直接分析了冈恩大鼠和Wistar大鼠的粗胆汁样本。除了胆红素（冈恩大鼠中）或其糖苷（Wistar大鼠中）外，还检测到两种主要化合物。一种黄色化合物与先前记录的维生素B-2相对应，在冈恩大鼠或Wistar大鼠胆汁中同样显著。另一种化合物无色，但与空气接触放置时会自发氧化为粉红色至黄色色素。它在冈恩大鼠胆汁中更为显著。对冈恩大鼠静脉注射[14C]胆红素后获得的胆汁进行分析表明，该化合物高度标记。胆汁的冻融导致形成一系列重氮阴性衍生物，表明原始化合物相当不稳定。对标记化合物氧化形式的光谱（吸附和荧光）和色谱（高效液相色谱、薄层色谱和纸色谱）分析使其被鉴定为尿胆素-i。胆汁中分泌的无色化合物是尿胆原-i。给冈恩大鼠施用新霉素和杆菌肽或进行肠道切除抑制了尿胆原的胆汁排泄，从而证实了其肠道来源。因此，尿胆原似乎是冈恩大鼠胆汁中存在的主要胆红素衍生物。其分解产物可能代表迄今未鉴定的重氮阴性极性胆红素衍生物。由于冈恩大鼠胆汁中仅存在少量胆红素，肠腔中形成的尿胆原似乎源自通过非胆汁途径到达肠道的胆红素。
