Monte M J, El-Mir M Y, Sainz G R, Bravo P, Marin J J
Department of Physiology and Pharmacology, Faculty of Pharmacy, University of Salamanca, Spain.
Biochim Biophys Acta. 1997 Nov 28;1362(1):56-66. doi: 10.1016/s0925-4439(97)00063-x.
One major difficulty in interpreting the changes occurring during liver regeneration is the co-existence of non-activated cells and proliferating hepatocytes at all stages of differentiation. The aim of this study was to investigate bile acid (BA) secretion into bile during normal (NLR) and synchronized (SLR) liver regeneration in rats. Regeneration was synchronized by reversible inhibition of ribonucleotide reductase by 10 h treatment with hydroxyurea (HU) shortly after two-third partial hepatectomy. Total BA output as measured by GC-MS increased immediately after partial hepatectomy. This was followed by a further transient enhancement during the next day in the NLR. HU treatment did not significantly modify total BA output, but after releasing synchronized regeneration a marked reduction was observed. This was followed by a recovery to reach values close to those of NLR on day 7 of the regenerative process in SLR. Amidated BA output as measured by HPLC analysis revealed an early enhancement in the proportion of non-conjugated BAs in bile in NLR. However, the profile of conjugated BAs, which was not affected by HU treatment, matched that of total BAs during the first stage of SLR. By contrast, the increase in BA output observed on day 3 of the regenerative process in this group was accounted for by an enhancement in non-conjugated BA secretion. On day 7 of the regenerative process, the proportion of conjugated BA in bile was restored to approximately 100% in this group. Most BA molecules were conjugated with taurine rather than with glycine in all experimental groups, during both NLR and SLR. GC-MS determinations indicated that the magnitude of the cholic acid predominance in all bile samples was significantly modified during liver regeneration. This was increased early after partial hepatectomy and declined toward control values after few (2-3) days. Enhancement in the cholic acid predominance was due to a reduction in the proportion of all other major BAs, above all ursocholic acid and omega-muricholic acid. By contrast, minor BAs in normal control rat bile such as allo-cholic acid were increased during both NLR and SLR, and remained at detectable levels up to day 7. Changes in the proportion of secreted BA species were similar in SLR and NLR except that the early reduction in the proportion of BAs other than cholic acid was more pronounced in SLR and the quantitative importance of the diversity in BA species was recovered earlier in SLR than in NLR. In summary, these results indicate that profound changes in BA secretion during rat liver regeneration do occur. Most of them are probably related to the existence of retro-differentiation/re-differentiation processes which are speeded up by hydroxyurea-induced synchronization of the wave of hepatocyte proliferation.
解读肝脏再生过程中发生的变化时，一个主要困难在于在分化的各个阶段，未活化细胞与增殖的肝细胞同时存在。本研究的目的是调查大鼠正常肝脏再生（NLR）和同步肝脏再生（SLR）过程中胆汁酸（BA）分泌到胆汁中的情况。在三分之二部分肝切除术后不久，用羟基脲（HU）处理10小时，通过可逆抑制核糖核苷酸还原酶使再生同步化。通过气相色谱 - 质谱法（GC - MS）测定，部分肝切除术后总BA输出立即增加。在NLR中，第二天总BA输出进一步短暂增强。HU处理并未显著改变总BA输出，但在同步再生解除后，观察到显著降低。随后在SLR的再生过程第7天恢复到接近NLR的值。通过高效液相色谱（HPLC）分析测定的酰胺化BA输出显示，NLR中胆汁中非共轭BA的比例早期增加。然而，共轭BA的谱图不受HU处理影响，在SLR的第一阶段与总BA的谱图匹配。相比之下，该组在再生过程第3天观察到的BA输出增加是由非共轭BA分泌增加所致。在再生过程第7天，该组胆汁中共轭BA的比例恢复到约100%。在所有实验组中，无论是NLR还是SLR期间，大多数BA分子都与牛磺酸而非甘氨酸结合。GC - MS测定表明，在肝脏再生过程中，所有胆汁样本中胆酸优势的程度发生了显著改变。部分肝切除术后早期增加，在几天（2 - 3天）后降至对照值。胆酸优势的增强是由于所有其他主要BA的比例降低，尤其是熊去氧胆酸和ω - 鼠胆酸。相比之下，正常对照大鼠胆汁中的次要BA，如别胆酸，在NLR和SLR期间均增加，并在第7天之前一直保持可检测水平。SLR和NLR中分泌的BA种类比例变化相似，只是除胆酸外的BA比例在SLR中的早期降低更为明显，并且SLR中BA种类多样性的数量重要性比NLR更早恢复。总之，这些结果表明大鼠肝脏再生过程中BA分泌确实发生了深刻变化。其中大多数可能与逆向分化/再分化过程的存在有关，这些过程因羟基脲诱导的肝细胞增殖波同步化而加速。
