| Objective Cholestasis is common disease syndrome, most resulting from biliary obstruction by malignant tumors, choledocholithiasis, biliary stricture and cholestatic hepatitis. Cholestasis may lead to severe and complicated pathophysiological changes. So far, choleretic and corticosteroid prove limited efficacy in cholestasis treatment. As to obstructive jaundice, icterus regresses slowly after restoration of bile flow, and there is less effective treatment. rhGH was proved to be an effective measure to treat patients with severe cholestasis by our hepatobiliary institute. As the rate-limiting step, bilirubin secretion across hepatocyte canalicular membrane is mediated by ATP binding cassette, an ATP-dependent,against more than 1,000-fold higher concentration gradient. Excretion of non-bile salt organic anions ,such as bilirubin glucuronides and divalent sulfated or glucuronidated bile salts, is mediated by the multidrug resistance protein 2. The regulation of bilirubin secretion by GH has not been proved in obstructive jaundice patients or rats by experimental study. So the study of the molecular mechanism and signaling pathway of bilirubin transport is necessary.Methods 1. The rat model of bile duct obstruction and restoration of bile flow: the common bile duct was ligated. 2 weeks later, the proximal bile duct and the duodenum was intubated and bile flow restored. 2. Estimate of serum TNF-αand GH: RIA was used. 3. Estimate of STAT5 activation: ISHH was used.4. The expression of Mrp2 gene: RT-PCR and immunofluorescent microcopy were used to prove the canalicular localization of Mrp2. Results 1. Serum bilirubin increased after common bile duct ligation, at the peak of its level on the seventh day. Serum bilirubin slowly desended after restoration of bile flow, reaching normal level on the fourteenth day, but the bilirubin of 10% obstructive jaundice rates with sever cholestasis slowly regressed. 2. The downregulation of expression of MRP2 across canalicular membrane was confirmed in obstructive jaundice rats. After restoration of bile flow, we found that the expression of Mrp2 gene increased, but recovery was very slow .3. There was marked downregulation of STAT5mRNA in bile duct obstruction rats. After restoration of bile flow , STAT5 mRNA level of hepatocyte slowly inceased, and the level of STAT5 mRNA correlated significantly positively with the expression of Mrp2. JAK/STAT5 signaling pathway regulated expression of Mrp2 gene. 4. Serum TNF-αincreased markedly in bile duct ligation rat.Serum TNF-αpeaked on the fourteenth day, 7 to 8-fold higher than normal level. After restoration of bile flow, serum TNF-α slowly lowered, and the correlation analysis suggested that TNF-α negatively correlated with the expression of Mrp2 gene and the level of STAT5mRNA. Overdos excretion of inflammation factors in rats with obstructive jaundice ,such as TNF-α, inhibited retiniod response elements of Mrp2 promoters,and downregulated its expression . 5. Growth hormone in serum was markedly lower in rats with extrahepatic cholestasis by bile duct obstruction .After restoration of bile flow, growth hormone in serum increased. Correlation analysis found that growth hormone in serum positively correlated with the expression of Mrp2 gene and the level of STAT5mRNA in hepatocytes. Hence, JAK/STAT5 signaling pathway might regulate the expression of Mrp2 gene.6. The total bilirubin and direct bilirubin of the obstructive jaundice rats in serum treated by rhGH lower than rats with bile duct obstruction at the same point .The secretion of inflammation factor in serum,such as TNF-α,was markly lower. The total bilirubin and direct bilirubin in rats after restoration of bile flow was quickly cleared . The expression of Mrp2 gene and the level of STAT5mRNA in hepatocytes was higher than that of the obstructive jaundice rat at the same point. Correlation analysis found that serum growth hormone positively correlated with the expression of Mrp2 gene and the level of STAT5mRNA...
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