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

Biliary excretion of biotin and biotin metabolites is quantitatively minor in rats and pigs

We sought to determine whether the biliary excretion of biotin contributes substantially to the overall excretion of the vitamin in mammals, and hence, whether metabolism by gut microorganisms could account for some metabolism of biotin administered parenterally. [carbonyl-14C]Biotin was injected intravenously into six rats; bile and urine were collected for 24 h after injection. In a study of five pigs, serum and bile were analyzed for endogenous biotin and metabolites. In rat bile and urine, biotin, bisnorbiotin, biotin-d,l-sulfoxide, bisnorbiotin methyl ketone and two unidentified compounds were quantitated. In bile, these six compounds accounted for only 1.9 +/- 0.2% of the administered 14C, but in urine they accounted for 60.6 +/- 4.1%. The metabolite and time profiles in bile were also strikingly different from those in urine. Only biotin, bisnorbiotin and biotin-d,l-sulfoxide were quantitated in pig bile and serum. The concentrations of biotin, bisnorbiotin and biotin-d,l-sulfoxide in bile were 6.9-14.7 times the concentrations in serum. However, the bile to serum ratios of biotin and metabolites were >99% less than those of bilirubin, which is actively excreted. These data provide evidence that the biliary excretion of biotin and metabolites is quantitatively negligible.

The influence of induced hyperglycaemia on the characteristics of intestinal motility and bile kinetics in healthy men

Simultaneous recording of duodenal motility and biliary scintigraphy by continuous infusion of 99mTc-dimethyl-iminodiacetic acid was performed in 16 healthy fasted men, of whom eight had an intravenous glucose bolus injection immediately after the passage of a duodenal phase III of the migrating motor complex (MMC). This was followed by a continuous intravenous infusion of glucose. Characteristics of the time-activity curves from the gallbladder area and intestinal area were related to phase activity of the duodenal MMC. The median duration of the entire MMC cycle was significantly shorter in the glucose group than in the group without glucose. The difference was caused by shortening of phase II. Spontaneous gallbladder emptying appeared in all eight subjects from the group without glucose but in only a single subject from the glucose group. The relative amount of liver bile diverted to the gallbladder in the entire cycle was significantly higher in the subjects who received glucose, and in four subjects all the hepatic bile was diverted to the gallbladder. The results demonstrate that induced hyperglycaemia exerts a pronounced effect on gastrointestinal motility and bile kinetics. Available evidence suggests that the effects are caused by a 'medical vagotomy'.

Effect of phlorizin on hepatic bile production before and during glucose infusion

During intravenous infusion of glucose, bile secretion is reduced (cholestasis), indicating that hepatocellular metabolism of glucose could have harmful effects on the liver. Phlorizin has been identified as a compound capable of impeding glucose uptake of liver cells. To examine whether phlorizin had any effect on glucose-associated cholestasis, three groups of experiments were performed on anaesthetized pigs. In group I phlorizin (100 mg/kg body wt) during normoglycaemia stimulated bicarbonate-dependent bile secretion by 56 +/- 4%. After phlorizin, hyperglycaemia decreased both bile acid- and bicarbonate-dependent bile secretion by 37 +/- 4%. But after the glucose load normalization of plasma glucose concentration increased the bicarbonate-dependent fraction by 38 +/- 4%. In group II phlorizin (100 mg/kg body wt, infused intravenously) during hyperglycaemia stimulated bicarbonate-dependent bile secretion by 35 +/- 5%. In group III bile secretion was continuously stimulated by infusion of Na-taurocholate. Hyperglycaemia reduced bicarbonate-dependent bile secretion by 33 +/- 4%, but after phlorizin both bile acid- and bicarbonate-dependent bile secretion increased on average by 121 +/- 8%. The osmotic effect of hyperglycaemia cannot be blocked by phlorizin, but judged by the effect on bile secretion, phlorizin may decrease the cholestatic effect induced by metabolism of glucose. Phlorizin could be an interesting compound for use in solutions for organ preservation.

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.

Mechanism of ursodeoxycholic acid- and canrenoate-induced biliary bicarbonate secretion and the effect on glucose- and amino acid-induced cholestasis

The mechanism of ursodeoxycholic acid (UDCA)- and canrenoate-induced bicarbonate choleresis was studied before and during the administration of glucose or amino acids in anaesthetized pigs. Previous studies have shown that the canalicular secretion has, on a molar basis, a relationship among the secretion of chloride, bicarbonate, and bile acids of 0.9, 0.3, and 1, respectively. Ductular secretion is associated with the transport of 0.25 mol chloride per 1 mol bicarbonate. In control experiments UDCA was associated with a biliary secretion of about 1.3 mol chloride and 0.5 mol bicarbonate per 1 mol bile acid, and canrenoate caused the secretion of 1.2 mol chloride per 1 mol bicarbonate. Intravenous infusion of glucose or amino acids increased these relationships, and after administration of UDCA or canrenoate, these relationships were still increased by at least 70% on average when compared with the control experiments. A reduction in bile secretion after glucose or amino acid infusion is opposed by UDCA or canrenoate. The effect of UDCA or canrenoate on bile secretion is not disturbed by glucose or amino acids. Both substances stimulate canalicular bicarbonate secretion and could be of importance in improving cholestatic conditions.

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.