Bile formation: sites and mechanisms

Effect of insulin on hepatic bile secretion during normoglycaemia and hyperglycaemia

The roles of hyperosmolality, hyperglycaemia, and insulin in glucose-induced reduction of bile secretion were examined in anaesthetized pigs. Compared with normoglycaemia, intravenous infusion of isotonic glucose reduced bile acid-dependent bile secretion at a plasma glucose concentration of 18 mmol/l, with 34 +/- 4%. Lowering of plasma glucose concentration to normoglycaemia after administration of insulin (10 U/kg body wt. low dose) increased bicarbonate-dependent bile secretion by 23 +/- 3%. Induction of hyperglycaemia (plasma glucose concentration, 16 mmol/l) and the combined infusion of isotonic glucose and the low insulin dose decreased bile secretion by 22 +/- 3%. During hyperglycaemia (plasma glucose concentration, 16 mmol/l) the combined infusion of isotonic glucose and a high dose of insulin (60 U/kg body wt) increased bile acid-dependent bile secretion by 26 +/- 3%. Hyperglycaemia reduces bile secretion without altering plasma osmolality. Endogenous production (or too rapid degradation) of insulin may be too small during intravenous glucose infusion to cope with the metabolic demands of hepatocellular glucose conversion. This may be overcome by administration of insulin in a large dose, which stimulates bile acid secretion.

Dose-dependent effects of glycine, alanine, and glucose on hepatic bile secretion, oxygen consumption, and hemodynamics

To assess the effects of a small (0.5%) and a large dose (5%) of glycine and alanine and of hypertonic glucose on hepatic bile secretion, oxygen consumption, and hemodynamics, experiments were performed on anesthetized pigs. Only the large dose of amino acids exerted significant changes. Glycine, alanine, and glucose reduced bile acid-dependent bile secretion gradually, which was nearly halved from a control value of 0.32 +/- 0.04 ml/min. Oxygen consumption was thereby continuously stimulated during amino acid and glucose infusion and increased from 448 +/- 132 mumol/min before to 995 +/- 226 mumol/min after the infusion of glycine, alanine, and glucose. Hepatic arterial blood flow increased from 214 +/- 14 ml/min to 238 +/- 14 ml/min after glycine infusion, whereas portal venous blood flow decreased from 542 +/- 50 ml/min to 481 +/- 47 ml/min. Total hepatic blood flow remained unchanged. Alanine and glucose provoked no further changes in hepatic blood flow. Bile secretion is a sensitive marker of hepatic metabolism, whereas hepatic blood flow is not a dominant regulator of bile secretion. Stimulation of hepatic metabolism is not followed by changes in total hepatic blood flow.

Cystic fibrosis, pathophysiological and clinical aspects

Cystic fibrosis is a lethal, hereditary, until recently little understood disease, which leads to progressive functional disturbances in various organs, including the lungs, liver and pancreas. Knowledge of the genetic and cellular abnormalities is rapidly progressing, but therapy is still symptomatic and based on insufficiently controlled and short-term studies. At present the therapeutic approach aims to combat respiratory infections by optimal antibiotic therapy, combined with techniques to promote sputum evacuation. Additional measures attempt to optimise both nutritional state and physical condition. Median survival has improved from approximately 1 year to about 25 years during the past 3 decades. This article summarises present information on disease mechanisms and treatment.

Hepatobiliary pathology in patients with cystic fibrosis

Overt liver disease in cystic fibrosis is a rare condition. Only 1-5% of all patients show a severe disturbance of the liver cell function or portal hypertension. In contrast, liver architecture is much more often disturbed at post mortem examination. The experience is that liver pathology increases with age which will result in rising numbers of patients in the future parallel to the increasing life expectancy of the patients. Bile plugs are commonly found in the portal tract and probably represent the essential abnormality of the liver in CF. Recently new methods have been developed for the investigation of the bile synthesis which will be helpful in the understanding of the CF defect in the liver.

Amino acid- and glucose-induced cholestasis before and during secretin stimulation

To identify the mechanisms of reduced bile flow after hypertonic amino acid and glucose infusion, acute experiments were performed on anesthetized pigs. When secretin was not administered, amino acids or glucose reduced bile acid-dependent bile secretion to 65 +/- 3% of control. During secretin stimulation amino acids or glucose diminished bile acid-independent bile secretion to 78 +/- 2% of control. No changes in serum bilirubin, alanine aminotransferase, and aspartate aminotransferase were observed. Amino acids and glucose attack different mechanisms responsible for bile formation, but the result is that when secretin is not administered, biliary secretion of bile acids is reduced, and, accordingly, bile acid-dependent bile flow diminished. During secretin stimulation biliary NaHCO3 secretion is depressed, accounting for a fall in bile acid-independent bile flow. Amino acids exert no effect on bile acid secretion or, as a result, on bile acid-dependent bile flow after secretin infusion.

Bile acids in bile after monensin treatment

Bile derived from monensin treated bile-fistula rats has been analysed for bile acids content. Bile flow and bile acids decrease in bile following monensin treatment, in agreement with the disruption of the Na+ gradient determined by the ionophore and necessary for the vectorial Na+-cotransport of taurocholate at the sinusoidal pole of the hepatocyte.

Serum bile acid concentrations as an indicator of liver dysfunction induced during danazol therapy

The effects of danazol therapy (600 mg/day) on the liver function of 16 women with endometriosis were investigated. The primary bile acids (cholic acid [CA] and chenodeoxycholic acid [CDCA]) were analyzed with radioimmunoassays in the fasting state and after a test meal. Also, the conventional liver function tests were performed. Ultrasonography was used to detect any possible changes in the gallbladder function. The fasting concentrations of CA increased (P less than 0.05) during therapy, while those of CDCA did not change. The ratio of CA/CDCA also increased (P less than 0.001). The maximal response of CA after the test meal increased (P less than 0.01) during the trial. As regards the other liver function tests, only the transaminases significantly increased (P less than 0.01) after 1 month of therapy but showed a tendency to decrease later during the trial. The gallbladder's volume and function did not change. All the parameters studied normalized within 1 month of cessation of danazol therapy. Danazol seems to have a rather mild effect on liver function. The analyzed parameters indicate transient cell wall injury and slight disturbances in liver cell uptake and secretion mechanism and also of synthesis activity.

Composition of bile after orthotopic liver transplantation

In 20 adult patients undergoing orthotopic liver transplantation (OLT), we studied longitudinally for the first 3 weeks after OLT the composition of bile with regard to differences between surviving and non-surviving patients and between patients with more or less rejection and the relation between bile and serum concentrations. The analyzed biliary components were bilirubin, cholesterol, bile acids, phospholipids, copper, iron, glucose, urea, creatinine, ammonia, protein, sodium, potassium, chloride, pH, bicarbonate, calcium and phosphate. After the 1st day the composition of bile was often different from reference values. In most patients deviations of the hepatic excretion function were found. Especially, a sharp fall was noticed in the biliary concentrations of cholesterol and copper. The composition of bile was not helpful in predicting the histologic degree of rejection or the ultimate outcome of the patients. Changes in bile glucose, electrolyte, urea, and creatinine concentrations were positively related to serum concentrations. We conclude that for the compounds analyzed the composition of bile after OLT is not only influenced by the state of the liver but also by the overall metabolic state of the patient.

Hepatic bile formation in the rat. Addition of vasoactive intestinal peptide to the equation

While changes in gastric, pancreatic, and intestinal secretion in response to more recently identified gastrointestinal peptides have been characterized, there has been less investigation into effects of these hormones on hepatic bile production. The isolated perfused rat liver model has been used to examine effects of vasoactive intestinal peptide (VIP), somatostatin, bombesin, and thyrotropin-releasing hormone (TRH) on bile flow and bile acid transport. No changes were seen following bolus administration of bombesin (3 X 10(-8)-1.5 X 10(-6) M) or TRH (3 X 10(-7)-3 X 10(-6) M), while somatostatin (6 X 10(-6) M) produced a small decrease in bile flow without any change in bile acid output. VIP (3 X 10(-7) M) caused a highly significant increase in both volume of bile flow (0.85 +/- 0.8 to 1.11 +/- 0.09 microliter/min/g liver, P less than 0.001) and bile acid output (31.6 +/- 1.5 to 43.2 +/- 1.7 nmol/min/g liver, P less than 0.001). Elimination of Ca2+ from liver perfusate did not prevent VIP-induced increases in bile flow and bile acid output, and no synergistic effect of concomitant theophylline administration was observed. While effects of VIP on bile flow appear to be due to alterations in hepatic transport of bile acids, the exact mechanism(s) producing these changes remains to be elucidated.

Enhanced biliary gamma-glutamyltransferase excretion following prolonged alcohol consumption in rats

In order to study the question of whether chronic ethanol consumption may alter the biliary excretion of gamma-glutamyltransferase (gamma-GT), female rats were pair-fed nutritionally adequate liquid diets containing either ethanol (36% of total calories) or isocaloric carbohydrates for 24 days. Compared to pair-fed controls, the administration of the alcohol-containing diet resulted in an increased biliary excretion of gamma-GT (5.84 +/- 0.73 mU 6 h-1 100 g-1 b.w. vs. 8.82 +/- 0.79, P less than 0.001). This was associated with a corresponding enhanced biliary output of total bile acids. An apparent linear relation between the biliary output rates of gamma-GT and those of total bile acids was observed both in alcohol-fed animals (r = 0.83) and in their pair-fed controls (r = 0.95). In addition, there was a significant increase of gamma-glutamyltransferase activities in the liver homogenate and in liver plasma membranes, both in fractions rich in bile canalicular and basolateral membranes and in those rich in blood sinusoidal site. Serum gamma-glutamyltransferase activities as well as serum bile acid concentrations were also enhanced by 96.8% (P less than 0.001) and 233% (P less than 0.001), respectively. These data show that chronic alcohol consumption enhances hepatic gamma-GT activities, leading to an increased efflux of gamma-GT into the bile and possibly into the blood out of the liver cell. Furthermore, these data suggest the involvement of bile acids with their solubilizing properties for the biliary excretion of gamma-GT.

Drug-induced cholestasis

Intrahepatic cholestasis, defined as arrested bile flow, mimics extrahepatic obstruction in its biochemical, clinical and morphological features. It may be due to hepatocyte lesions of which there are three types, termed canalicular, hepatocanalicular and hepatocellular, respectively; or it may be due to ductal lesions at the level of the cholangiole or portal or septal ducts. Defective bile flow due to hepatic lesions reflects abnormal modification of the ductular bile. Defective formation of canalicular bile may involve bile acid-dependent or independent flow. It appears to result most importantly from defective secretion of bile acid-dependent flow secondary to defective uptake from sinusoidal blood, defective transcellular transport and defective secretion; or from regurgitation of secreted bile via leaky tight junctions. An independent defect in bile acid-independent flow is less clear. Defective flow of bile along the canaliculus may reflect increased viscosity and impaired canalicular contractility secondary to injury of the pericanalicular microfibrillar network. Impaired flow beyond the canaliculus may result from ductal injury. Sites of lesions that contribute to cholestasis include the sinusoidal and canalicular plasma membrane, the pericanalicular network and the tight junction and, less certainly, microtubules and microfilaments and Golgi apparatus. A number of drugs that lead to cholestasis have been found to lead to injury at one or more of these sites. Other agents (alpha-naphthylisothiocyanate, methylenedianiline, contaminated rapeseed oil, paraquat) lead to ductal injury resulting in cholestasis. Reports of inspissated casts in ductules (benoxaprofen jaundice) and injury to the major excretory tree (5-fluorouridine after hepatic artery infusion) have led to other forms of ductal cholestasis. Most instances of drug-induced cholestasis present as acute, transient illness, although important chronic forms also occur. The clinical features include the reflection of the cholestasis (pruritus, jaundice), systemic manifestations and extrahepatic organ involvement. While nearly all classes of medicinal agents include some that can lead to cholestasis, there are differences among the various categories. Phenothiazines and related antipsychotic and 'tranquillizer' drugs characteristically lead to cholestatic hepatic injury. The tricyclic antidepressants may lead to cholestatic or hepatocellular injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Reovirus type 1 is secreted into the bile

Reovirus type 1, known to be a cause of systemic and intestinal disease in mice, is secreted into the bile of adult A/J mice after viremia. Virus found in the bile in concentrations higher than those in blood may indicate that reovirus type 1 is actively transported into the bile. The transport of virus was independent of levels of virus-specific immunoglobulin A antibody. Modifications of the virus that occurred during transport did not discernibly affect the infectivity of the virus. Entry of virus into the bile may be an important mechanism by which an enteric virus that produces systemic disease reenters the intestine for transmission.