胆汁的生成、分泌、排泄及胆汁淤积发生机制

<正>常的胆汁生成、分泌、排泄是机体重要的生理过程。胆汁在促进脂质消化和吸收、清除机体代谢废物、调节胆固醇代谢等方面发挥着重要作用。当各种原因引起胆汁生成、分泌或排泄发生障碍时,则出现急性或慢性胆汁淤积性病变。深入了解胆汁生成、分泌、排泄及胆汁淤积的发生机制对于开展胆汁淤积性肝病相关研究和指导临床实践具有重要的意义。     

胆汁淤积的发生机制和诊治策略

胆汁淤积(cholestasis)是由多种原因所致的胆汁分泌或排泄障碍，导致胆汁不能正常流入十二指肠．从而反流入血液循环中。临床上常表现为黄疸、瘙痒、尿色深、粪色变浅和黄斑瘤等，实验室检查可有血清胆红素、碱性磷酸酶(ALP)、5’-核苷酸酶和γ-谷氨酰转移酶(GGT)水平升高，血清丙氨酸转氨酶(ALT)和天冬氨酸转氨酶(AST)水平升高提示有肝细胞损伤，慢性胆汁淤积常有总胆固醇水平升高。     

胆汁形成与胆汁淤积性疾病发生的机制

胆汁淤积是指在肝细胞水平或胆管水平胆汁生成,分泌或流动障碍[1].肝细胞与胆管细胞膜上存在众多的蛋白质是胆汁形成与分泌的重要转运体,随着对这些转运体的鉴定,以及对影响胆汁酸盐合成、转运的复杂信号网络系统的深入了解,为充分认识胆汁淤积形成的分子机制提供了重要价值[2-3].     

胆汁淤积的发生机制及相关疾病

胆汁是在胆道中流动的一种重要消化液,在非消化期间由肝脏生成后储存于胆囊中,在消化期间则由肝脏和胆囊直接排入十二指肠,参与脂肪的消化和吸收。胆汁中含有多种成分,如胆盐、卵磷脂、胆固醇等可降低脂肪表面张力,促使脂肪乳化成微滴,增大与胰脂肪酶的作用面积而有利于脂肪的消化吸收。而当胆汁分泌异常和(或)排出障碍时,就会使胆汁淤积,并导致一系列疾病的发生。因此了解其发生机制对于胆汁淤积的诊断和治疗具有重     

胆汁外引流治疗难治的肝内胆汁淤积症

９例经内科常规治疗２个月以上且病情进行性加剧的肝内胆汁淤积症患者,应用胆道置Ｔ管外引流胆汁,糜蛋白酶加生理盐水冲洗胆道,获得满意疗效,认为胆道外引流胆汁明显减少肝肠循环,同时增大肝细胞胆汁分泌压与胆道静水压的压力差,胆管冲洗,疏通毛细胆管,有利于利胆,此种方法的前途令人鼓舞。     

胆汁淤积性肝病疲劳的发生机制、评估和治疗

胆汁淤积性肝病的典型肝外表现有瘙痒、脂肪泻、脂溶性维生素缺乏及代谢性骨病。近年来，人们开始注意到这类疾病中的疲劳也是一个明显的症状。由于其是非特异性症状，且缺乏客观的评估方法，所以直到现在仍然被大家所忽视。此外，目前对疲劳的发病机制及其治疗依旧不清楚。疲劳是一个复杂的症状，包括持续的衰竭感觉，正常工作能力缺失，心理和生理功能的下降。现在，由于患有原发性胆汁性肝硬化的患者在早期就得到诊断，了解疲劳症状的基本发病机制显得尤为重要。     

重视胆汁淤积的分子机制和药物治疗研究

胆汁淤积（cholestasis）不是一种疾病．而是一组疾病共同的临床症状．故称为胆汁淤积综合征更为恰当。该综合征在临床上常见。随着对胆汁分泌和排泄的分子机制认识的不断深入．对胆汁淤积概念的理解也有了新的拓展。传统观念认为胆汁淤积是肝内、外梗阻因素造成胆汁形成后流动受阻．这种仅仅基于解剖学上的理解显然是不全面的。目前认为胆汁淤积是指胆汁生成障碍和（或）胆汁流动障碍。     

肝衰竭时胆汁淤积的发生机制及处置对策

肝衰竭是多种因素引起的严重肝脏损害。肝衰竭时胆汁淤积是一种以大量肝细胞坏死为主要原因的严重肝细胞性肝内胆汁淤积,表现为结合胆红素和非结合胆红素同时急剧增高,且其水平与肝衰竭严重程度呈正比。肝脏组织结构改变加重胆汁淤积,肠道微生物群对胆红素和胆汁酸代谢有影响。治疗肝衰竭时胆汁淤积的根本措施是去除病因,促进肝细胞再生和肝功能恢复。     

Urinary excretion of bile acids in bile duct-ligated rats

Background. In patients with complete bile duct obstruction, the only pathway of bile acid elimination is through the urine. However, the urinary excretion of various bile acid conjugates in the presence of bile duct obstruction has not been clarified. Given this factor, the urinary excretion of various bile acids was compared in rats that were bile duct-ligated for 3 days. Methods. After urinary bladder cannulation, radiolabeled bile acids were intravenously injected, and urine samples were collected every 2 h for 6 h, and radioactivity was counted. Results. Urinary excretion (cumulative percent dose during 6 h) of taurocholate and cholate was similar (19.3% and 16.8%). Urinary excretion of tauroursodeoxycholate, lithocholate, and taurolithocholate-sulfate was less effective (12.7%, 9.8% and 2.1%, respectively). Cholate was mostly conjugated with taurine, and lithocholate was mostly conjugated with taurine and further hydroxylated. Conclusions. These results indicate that unconjugated bile acids were taken up by the liver and excreted into the blood after further biotransformation even under conditions of complete bile duct obstruction. Although bile acid sulfates are the major bile acids in the urine of patients with obstructive jaundice, monohydroxylated bile acids are considered not to be so effectively excreted into the urine, even with conjugation with taurine and sulfate, in rats. Received: October 4, 2002 / Accepted: November 8, 2002 RID="*" ID="*" Reprint requests to: H. Takikawa Acknowledgments. This work was partly supported by a Grant-in-Aid by the Japan Society for the Promotion of Science (C2-14570510).     

The biliary excretion and pharmacokinetics of mezlocillin in jaundiced patients with external bile drainage

ABSTRACT— The biliary excretion and pharmacokinetics of mezlocillin have been studied in jaundiced patients with total external bile drainage through a percutaneous transhepatic catheter. In 10 of 11 studies, 2 g mezlocillin intravenously resulted in biliary concentrations sufficient to exceed the minimum inhibitory concentrations of most common biliary pathogenic organisms. In 6 h, 0.2–6.2% of the dose given was recovered in bile. The biliary clearance was 0.21–7.82 ml/min and increased with the duration of biliary decompression. The serum half-life of mezlocillin was prolonged (1.81 ± 0.23 h, mean ± SD), and was due to reduced biliary and renal clearance.     

Bile salt independent flow during bile salt‐induced choleresis and cholestasis in the rat: role of biliary thiol secretion

Abstract: Aims/Background: Previous studies have shown that the generation of the so‐called “bile salt‐independent flow” (BSIF) may be partly dependent on the hepatic availability and rate of canalicular secretion of osmotically active substances such as glutathione (GSH) and derived thiols. This study examined the role of common bile salts (BS) on the BSIF formation under both choleretic and cholestatic conditions, and on the relationship of the BSIF to the biliary thiol secretion. Methods: Experiments were carried out in adult male Sprague‐Dawley rats both in situ in the isolated perfused rat liver and in vivo. The effect of choleretic and cholestatic doses of BS on the biliary BS secretion rate (BSSR), BS‐dependent flow (BSDF), and BSIF was evaluated. Results: In the perfused rat liver, the infusion of low and physiological doses of taurocholic acid stimulated the biliary BSSR, BSDF, and BSIF. This was associated with increased biliary thiol secretion and thiol‐dependent bile flow. In vivo administration of taurocholic acid, taurochenodeoxycholic acid or taurolithocholic acid in step‐wise increasing doses leading to cholestasis showed that the onset of cholestasis was not accompanied by a significant decline in the BSSR or BSDF but rather by a marked inhibition of the apparent BSIF. During cholestasis, the three BS produced a significant reduction of biliary thiol secretion, with a marked decrease in thiol‐dependent bile flow sufficient to account for a major proportion of BSIF inhibition. This decline in thiol secretion occurred before the drop in biliary BS secretion and was more pronounced than the reduction in BS output. No change in hepatic thiol content was observed. Administration of free or glyco‐conjugated BS also resulted in a significant decrease of BSIF during the cholestatic period, suggesting a common role for BSIF inhibition in BS‐induced cholestasis. Conclusion: The changes in bile flow during BS‐induced choleresis and cholestasis are mediated by changes in the portion of the BSIF regulated by the thiol secretion.     

Increased melibiose/rhamnose ratio in bile of rats with acute cholestasis

Background and Aim: Melibiose/rhamnose permeability test is used for noninvasive intestinal mucosa barrier testing. However, the possible escape route of the absorbed saccharides through either intact or impaired blood–biliary barriers has not so far been explored. The objective of the present study was therefore two‐fold: First, to describe in detail the biliary pharmacokinetics of melibiose and rhamnose in rats; second, to evaluate the changes of both sugars' pharmacokinetics upon impairment of the blood–biliary barrier by acute extrahepatic cholestasis in rats. Methods: Bile duct obstructed (BDO), sham‐operated and intact (unoperated) male Wistar rats were administered, 24 h after the appropriate intervention, with a single intravenous dose of melibiose and rhamnose, and a 4‐h pharmacokinetic study was performed. Results: In intact animals, the biliary excretion of melibiose and rhamnose was only 0.06% and 0.4% of the administered dose, respectively, while the urinary excretion accounted for 70.6% and 61.7%, respectively. In BDO animals, the biliary excretion rate of both saccharides, especially that of melibiose, was increased with a consequent 4.4‐fold rise of the biliary melibiose/rhamnose ratio, the accepted paracellular permeability indicator. Both, the renal clearance of melibiose and the urinary melibiose/rhamnose ratio remained uninfluenced by cholestasis. Conclusion: The present study is the first to describe in detail pharmacokinetic parameters and the biliary excretion of melibiose and rhamnose in healthy and cholestatic rats. The altered melibiose/rhamnose biliary excretion ratio in BDO rats indicates that the test is able to detect the impairment of the blood–biliary barrier in acute extrahepatic cholestasis.     

Effect of ursodeoxycholic acid administration on bile duct proliferation and cholestasis in bile duct ligated rat

The origin, mechanism, and significance of the bile duct proliferation (BDP) associated with cholestasis remain unexplained. This study examined the effect of oral administration of ursodeoxycholic acid (UDCA) on both BDP and cholestasis in the rat. After bile duct ligation, male Sprague-Dawley rats were treated for 30 days with either UDCA (5 mg/day) (group A) or saline solution (group B). Animals were sacrificed at day 30. The serum activity of aminotransferase (ALT, AST), alkaline phosphatase, and -glutamyltransferase (GGT) was significantly lower (P<0.01) in the UDCA-treated rats. Total serum bilirubin and total serum bile acids were lower (P<0.001) in group A. Moreover, the control of BA in bile was reduced also (P<0.02). Conversely, serum cholesterol levels were not different between the two groups. Histological examination showed that the number of ductular cells in the portal areas was significantly (P<0.001) reduced in UDCA-treated as compared to saline-treated rats. The replication activity, assessed as the number of bromodeoxyuridine-positive cells, was also significantly lower in treated animals (33±11 vs 64±22 per 1000 cells;P<0.001). Lobular bile ductules were three times larger in group B, and extrahepatic duct measurements confirmed this increase in size of the larger biliary ducts (P<0.001). These findings demonstrate that UDCA reduces BDP in response to BD ligation. Although the mechanism(s) of this effect is still hypothetical, UDCA may reduce the level of irritating bile salts such as chenodeoxycholic acid and lithocolate and increase periductular bile acid recirculation. These data support the beneficial effect of UDCA treatment in chronic cholestatic disease.     

Matrine improves 17α-ethinyl estradiol-induced acute cholestasis in rats

Aim:  To explore the effects of matrine (MT) on acute intrahepatic cholestasis induced by 17α-ethinyl estradiol (EE) in rats.
Methods:  Acute intrahepatic cholestasis in rats were induced by EE, and the effects of MT on acute intrahepatic cholestasis were explored and compared with ursodeoxycholic acid (UDCA) by serum biochemical determination and bile excretion experiments.
Results:  The serum biochemical and bile biochemical results indicated that MT and UDCA had notable hepatoprotective effects by counteracting cholestasis induced by EE. The bile flow and the bile excretion of glycocholic acid (GC, a substrate of bile salt export pump [Bsep]), ketoprofen glucuronide (KPG) and rhodamine 123 (Rh123, a substrate of multidrug resistance protein 1 [MDR1]) decreased by EE, were significantly improved after administration of MT.
Conclusion:  MT exhibited potential protection against EE-induced acute intrahepatic cholestasis.     

Biliary excretion of bile acids and organic anions in rats with dichloroethylene-induced bile canalicular injury

Background Hepatocytes in zone 1 of the hepatic lobule play a role in the uptake and biliary excretion of bile acids and organic anions under physiological conditions, and hepatocytes in zone 3 may play a role only when there is a high-dose load. To further elucidate the role of hepatic zonation in the hepatic handling of bile acids and organic anions, the biliary excretion of these compounds was studied in rats with dichloroethylene (DCE)-induced selective zone 3 bile canalicular injury.Methods Biliary excretion of various bile acids and organic anions was studied in rats 1h after oral administration of DCE (5mg/100g). The effect of DCE on the immunostaining of multidrug resistance protein 2 (Mrp2; an important canalicular organic anion transporter) in the liver was also examined.Results The biliary excretory maximum of taurocholate and tauroursodeoxycholate was decreased in DCE-treated rats, whereas the biliary excretion of taurolithocholate-sulfate and phenolphthalein-glucuronide was unchanged in DCE-treated rats, and DCE treatment decreased the biliary excretion of sulfobromophthalein and pravastatin. DCE decreased Mrp2 staining in the canalicular membrane of zone 3 hepatocytes on immunohistochemistry.Conclusions These findings indicate that canalicular transport in zone 3 hepatocytes is important in the biliary excretion of bile acids and organic anions, when they are administered at high doses.     

Biliary excretion of taurocholate, organic anions and vinblastine in rats with alpha-naphthylisothiocyanate-induced cholestasis

BACKGROUND AND AIMS: alpha-Naphthylisothiocyanate (ANIT) is known to cause cholestasis due to injury of the bile duct epithelial cells. The aim of the present study was to examine the effect of a single dose of ANIT on the biliary excretion of various cholephilic compounds and on the amount of canalicular transporters. METHODS: Twenty-four hours after the oral administration of ANIT (100 mg/kg), the biliary excretion of taurocholate, leukotriene C(4), pravastatin and vinblastine was studied. The protein levels of the bile salt export pump and multidrug resistance protein 2 and the immunostaining of multidrug resistance protein 2 in the liver were also examined. RESULTS: The ANIT treatment markedly decreased the biliary excretion of tracer amounts of taurocholate, leukotriene C(4), pravastatin and vinblastine. The biliary excretory maximum of taurocholate was also markedly decreased after ANIT treatment. The ANIT treatment had no effect on the protein levels of bile salt export pump and multidrug resistance protein 2 and the immunostaining of multidrug resistance protein 2 in the liver. CONCLUSIONS: These findings support canalicular transporters having little effect on the marked impairment of biliary excretion of cholephilic compounds in ANIT-induced cholestasis.