| Background:Bile salt,as the main constituent of bile flow,is ATP-dependent transported by a variety of transporting proteins such as Na~+-taurocholate cotransporting polypeptide(Ntcp) and bile salt export pump(Bsep).The expression and functional disorders of Ntcp and Bsep play a very important role in the etiology of different types of cholestasis. Recent study revealed that recombinant human growth hormone(rhGH) could promote the bilirubin metabolism in obstructive jaundice,but few is known about the effect on bile salt transportation.Signal transducer and activator of transcription 5(STATS) activation derived from the conjunction of growth hormone and its receptor is the principal pathway of growth hormone signaling transduction.The down-regulation of GH/GHR axis paralelled by Stats inactivation was confirmed in obstructive jaundiced rats.We proposed the hypothesis that rhGH supplementation could up-regulate the activity of Stat5 in the hepatocyte cytosol,which translocates to the nucleus and binds to the target DNA sequence,with the effect of regulating the expression of Ntcp and Bsep and then promoting bile salt metabolism.Objectives:To evaluate the effect of GH/GHR-Stat5 pathway on bile salt transportation in common bile duct ligation(CBDL)-bile duct reconstruction(BDR) rat model,and provide a possible approach to enhance surgical tolerance and safety,promote recovery for patients suffered from obstructive jaundice.Methods and Results:1.One hundred and thirty six Spragure-Dawley rats were randomizedly divided into three groups,namely A group(sham operation),B group(CBDL-BDR-NaCl),and C group (CBDL-BDR-rhGH).The Pst14d accumulated mortality of C group was 14.3%,which was much lower than that of B group 41.9%with statistical significance(x~2=4.493,P=0.034). Such indices as ALT,TBIL,TBA and TNF-αof rhGH-treated rats were much better than that of non-rhGH-treated rats.The ultrastructure of hepatocyte observed by TEM showed that mitochondria swelling,bile canaliculi extending and microvilli reducing were relieved by rhGH.2.Immunohistochemistry staining,reverse transcription polymerase chain reaction and Western blotting were applied to detect the expression of Ntcp and Bsep on three levels of membrane localization,gene transcription and protein translation.In addition,the effect of rhGH supplementation on the above-mentioned transporters was evaluated as well.Our data showed that the expression of Ntcp and Bsep decreased significantly after CBDL and increased slowly after BDR.Even on Pst14d,statistical significance existed between B or C group and A group,rhGH still proved a beneficial effect on their expression.3.The expression and function of Stat5 were evaluated by in situ hybridization(ISH) and electrophoretic mobility shift assay(EMSA).The results showed that bile duct obstruction reduced Stat5 mRNA and its binding activity to target DNA sequences,which presented a similar tendency as bile salt transporters after bile reflow.The longer the obstruction duration was,the lower Stat5 mRNA level and DNA-binding activity were.rhGH partly protected the expression and function of Stat5 which were damaged as GH/GHR axis during the CBDL-BDR procedure.Conclusions:1.The application of rhGH proves a beneficial effect of cholagogue and liver function improvement,and may be a promising approach to enhance surgical tolerance and safety, promote recovery in obstructive jaundiced rats.2.Down-regulation of Ntcp and Bsep during bile duct obstruction and improving slowly after bile reflow,especially for Bsep,may be the main cause of bile salt decreasing slowly and recovering delayed after operation for patients suffered from obstructive jaundice.3.rhGH can up-regulate the expression of Ntcp and Bsep,augment the uptake and excretion of bile salt,and promote the recovery of bile salt transportation system after bile reflow.4.The expression and function of Stat5 is inhibited by bile duct obstruction due to impeded activity of GH/GHR axis,and rhGH partly protect the GH/GHR-Stat5 signaling pathway. |
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