Somatostatin inhibits the effect of secretin on bile flow and on hepatic bilirubin transport in the rat

Cellular and transcriptional heterogeneity in the intrahepatic biliary epithelium

Epithelial tissues comprise heterogeneous cellular subpopulations, which often compartmentalize specialized functions like absorption and secretion to distinct cell types. In the liver, hepatocytes and biliary epithelial cells (BECs; also called cholangiocytes) are the two major epithelial lineages and play distinct roles in (1) metabolism, protein synthesis, detoxification, and (2) bile transport and modification, respectively. Recent technological advances, including single cell transcriptomic assays, have shed new light on well-established heterogeneity among hepatocytes, endothelial cells, and immune cells in the liver. However, a "ground truth" understanding of molecular heterogeneity in BECs has remained elusive, and the field currently lacks a set of consensus biomarkers for identifying BEC subpopulations. Here, we review long-standing definitions of BEC heterogeneity as well as emerging studies that aim to characterize BEC subpopulations using next generation single cell assays. Understanding cellular heterogeneity in the intrahepatic bile ducts holds promise for expanding our foundational mechanistic knowledge of BECs during homeostasis and disease.

Somatostatin, neuronal vulnerability and behavioral emotionality

Somatostatin (SST) deficits are common pathological features in depression and other neurological disorders with mood disturbances, but little is known about the contribution of SST deficits to mood symptoms or causes of these deficits. Here we show that mice lacking SST (Sst(KO)) exhibit elevated behavioral emotionality, high basal plasma corticosterone and reduced gene expression of Bdnf, Cortistatin and Gad67, together recapitulating behavioral, neuroendocrine and molecular features of human depression. Studies in Sst(KO) and heterozygous (Sst(HZ)) mice show that elevated corticosterone is not sufficient to reproduce the behavioral phenotype, suggesting a putative role for Sst cell-specific molecular changes. Using laser capture microdissection, we show that cortical SST-positive interneurons display significantly greater transcriptome deregulations after chronic stress compared with pyramidal neurons. Protein translation through eukaryotic initiation factor 2 (EIF2) signaling, a pathway previously implicated in neurodegenerative diseases, was most affected and suppressed in stress-exposed SST neurons. We then show that activating EIF2 signaling through EIF2 kinase inhibition mitigated stress-induced behavioral emotionality in mice. Taken together, our data suggest that (1) low SST has a causal role in mood-related phenotypes, (2) deregulated EIF2-mediated protein translation may represent a mechanism for vulnerability of SST neurons and (3) that global EIF2 signaling has antidepressant/anxiolytic potential.

Physiology of cholangiocytes

Cholangiocytes are epithelial cells that line the intra- and extrahepatic ducts of the biliary tree. The main physiologic function of cholangiocytes is modification of hepatocyte-derived bile, an intricate process regulated by hormones, peptides, nucleotides, neurotransmitters, and other molecules through intracellular signaling pathways and cascades. The mechanisms and regulation of bile modification are reviewed herein.

Regulation of cholangiocyte bicarbonate secretion

The objective of this review article is to discuss the role of secretin and its receptor in the regulation of the secretory activity of intrahepatic bile duct epithelial cells (i.e., cholangiocytes). After a brief overview of cholangiocyte functions, we provide an historical background for the role of secretin and its receptor in the regulation of ductal secretion. We review the newly developed experimental in vivo and in vitro tools, which lead to understanding of the mechanisms of secretin regulation of cholangiocyte functions. After a description of the intracellular mechanisms by which secretin stimulates ductal secretion, we discuss the heterogeneous responses of different-sized intrahepatic bile ducts to gastrointestinal hormones. Furthermore, we outline the role of a number of cooperative factors (e.g., nerves, alkaline phosphatase, gastrointestinal hormones, neuropeptides, and bile acids) in the regulation of secretin-stimulated ductal secretion. Finally, we discuss other factors that may also play an important role in the regulation of secretin-stimulated ductal secretion.

Bronchobiliary fistula due to alveolar hydatid disease: report of three cases

Bronchobiliary fistula is a serious complication of echinococcosis of the liver. Surgical and endoscopic treatments have been used successfully in the management of bronchobiliary fistula due to hepatic hydatid cysts. However, very little information exists on the management of bronchobiliary fistula due to alveolar hydatid disease. We report here the efficacy of various potential therapies in three cases.

The effect of short-term octreotide administration on the histologic structure of stomach, duodenum, jejunum, colon, liver and gallbladder in an experimental pancreatitis model

It is known that long-term administration of octreotide leads to changes in the histology of intraabdominal organs and plasma biochemical values. The purpose of the present study was to evaluate the histological effect of short-term octreotide administration on digestive organs in the experimentally induced pancreatitis by ligating pancreatic duct. The sham operation was performed on 20 rabbits in Groups 1 and 2. Acute pancreatitis was induced by pancreatic duct ligation in 20 rabbits in Groups 3 and 4. Octreotide was administered subcutaneously to the rabbits in Groups 2 and 4 at a dosage of 10 microg/kg/day for 7 days. The animals were sacrificed at the end of day 7, blood and tissue samples were collected. There was no histological changes in the stomach, duodenum, gallbladder, or small and large intestines of those group which received octreotide, while hepatic bile duct proliferation, bile duct epithelium proliferation, periportal inflammation and venous stasis were observed in liver histology. In conclusion, one-week octreotide administration in this experimental acute pancreatitis model was not associated with pathologic changes in digestive organs except liver.

Heterogeneity of the proliferative capacity of rat cholangiocytes after bile duct ligation

We previously introduced the concept that intrahepatic bile duct epithelial cells, or cholangiocytes, are functionally heterogeneous. This concept is based on the observation that secretin receptor (SR) gene expression and secretin-induced cAMP synthesis are present in cholangiocytes derived from large (> 15 microns in diameter) but not small (< 15 microns in diameter) bile ducts. In work reported here, we tested the hypothesis that cholangiocytes are heterogeneous with regard to proliferative capacity. We assessed cholangiocyte proliferation in vivo by measurement of [3H]thymidine incorporation and in vitro by both [3H]thymidine incorporation and H3 histone gene expression in small (fraction 1) and large (fraction 2) cholangiocytes isolated from rats after bile duct ligation (BDL). In the two cholangiocyte subpopulations, we also studied basal somatostatin receptor (SSTR2) gene expression as well as the effects of somatostatin on 1) SR gene expression and secretin-induced cAMP synthesis and 2) [3H]thymidine incorporation and H3 histone gene expression. In normal rat liver, cholangiocytes, unlike hepatocytes, were mitotically dormant; after BDL, incorporation of [3H]thymidine markedly increased in cholangiocytes but not hepatocytes. When subpopulations of cholangiocytes were isolated after BDL, DNA synthesis assessed by both techniques was limited to large cholangiocytes, as was SSTR2 steady-state gene expression. In vitro, somatostatin inhibited SR gene expression and secretin-induced cAMP synthesis only in large cholangiocytes. Moreover, compared with no hormone, somatostatin inhibited DNA synthesis solely in large cholangiocytes. These results support the concept of the heterogeneity of cholangiocytes along the biliary tree, extend this concept to cholangiocyte proliferative activity, and imply that the proliferative compartment of cholangiocytes after BDL is located principally in the cholangiocytes lining large (> 15 microns) bile ducts.

Octreotide long-term treatment in patients with portal hypertension: persistent inhibition of postprandial glucagon response without major changes in renal function

BACKGROUND/AIMS

Octreotide acutely decreases splanchnic blood flow and postprandial portal pressure in patients with portal hypertension. Inhibition of glucagon release parallels the hemodynamic changes. We studied the hormonal and renal effects of long-term treatment with octreotide (100 microg s.c., t.i.d., immediately before meals, for 2 weeks) in 12 patients with cirrhosis and portal hypertension.

METHODS

Postprandial blood levels of glucagon, insulin and glucose, and renal function tests were monitored in a study where patients acted as their own controls. Eleven patients completed the study, octreotide being discontinued in one patient who developed jaundice after 6 days of therapy.

RESULTS

Long-term treatment did not cause any change in fasting hormonal levels measured 12 h after the last injection of octreotide. However, pre-prandial injection of octreotide induced a marked fall in blood glucagon (163+/-49 pg/ml, after 20 min, vs. 254+/-71 pg/ml, basal; p<0.01), thus preventing the postprandial response occurring without treatment (322+/-102 pg/ml, 30 min-peak, vs. 249+/-77 pg/ml, basal; p<0.03). Inhibition of postprandial glucagon was maintained after 2 weeks of therapy (159+/-33 pg/ml, after 20 min, vs. 237+/-54 pg/ml, basal; p<0.01). Octreotide abolished the insulin postprandial response with no major change in glycemic control. Treatment had no long-term effect on renal plasma flow (effective renal plasma flow: 596+/-79 ml/min, baseline, vs. 609+/-71 ml/min, at 2 weeks; p>0.5), glomerular filtration rate (glomerular filtration rate: 99+/-11 vs. 99+/-12 ml/min; p>0.5), blood urea and creatinine, whereas it induced a mild decrease in plasma electrolyte levels (p<0.02).

CONCLUSIONS

Long-term octreotide treatment persistently suppresses the postprandial glucagon response of patients with portal hypertension without causing deterioration in their renal function.

Somatostatin does not block the effect of vasoactive intestinal peptide on bile secretion in man

The effects of intravenously administered somatostatin and vasoactive intestinal peptide (VIP) on bile secretion were studied in 10 patients with complete biliary fistulas. The two peptides were administered both separately and simultaneously. During the infusion of vasoactive intestinal peptide, bile secretion increased by 85%, whereas during somatostatin infusion it decreased by 40%. When the peptides were administered together, the VIP-induced choleretic effect was not reduced by somatostatin. Vasoactive intestinal peptide infusion increased bicarbonate concentration and output, whereas somatostatin had the opposite effect. The output of chloride also increased following vasoactive intestinal peptide infusion but decreased following somatostatin infusion. The concentration of chloride was unaffected by somatostatin whereas it was decreased by vasoactive intestinal peptide. The output of bile acids was unaffected by vasoactive intestinal peptide and decreased by somatostatin infusion, whereas total lipid concentration increased during somatostatin infusion and decreased when vasoactive intestinal peptide was added. It is concluded that, in man, somatostatin acts on the bile acid-dependent canalicular bile secretion and also, to some extent, on the ductular secretion, whereas vasoactive intestinal peptide acts strictly at the ductular level. The effects of the two peptides on bile secretion are independent of each other.