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The pattern of individual bilirubin pigments during a 24 hour caloric restriction (400 Kcal) was investigated in three groups of patients: one group with constitutional hyperbilirubinaemia (n = 29), another with microcytaemia and signs of haemolysis (n = 15) and the third consisting of patients without signs of hepatic disease (n = 11). The different bilirubin fractions (unconjugated, mono- and di-conjugated) were separated as methylated tetrapyrroles by t.l.c. following alkaline methanolysis. In all patients fasting induced an enhancement of the unconjugated bilirubin while the concentration of mono- and di-methyl esters of conjugated bilirubins remained within the normal range. When a pre-fasting concentration of total bilirubin equal to 1.2 mg/dl was used as a discriminating point, two different patterns in the fasting-induced increase in unconjugated bilirubin were identified. An increase of more than 1 mg/dl was found in 30 patients and 28 of these had constitutional hyperbilirubinaemia as diagnosed by exclusion of other disorders. The group with an increase of less than 1 mg/dl was composed of 25 patients, only one of whom had constitutional hyperbilirubinaemia: 14 were affected by microcytaemia and 10 were outpatients without signs of disease. The "fasting-induced increase in unconjugated bilirubin" has a specificity of 78%, a sensitivity of 84% and a positive and negative predictive value of 85 and 76%, respectively, for the diagnosis of constitutional hyperbilirubinaemia.

Intravenous infusion of glucagon (100 micrograms/hr/100 g body weight) in rats produces a 20 to 35% increase in bile flow and enhances the activity of hepatic bilirubin uridine diphosphate-glucuronyltransferase to 132% after a 90 min infusion. When a bilirubin load is given to produce a constant and apparently maximal biliary bilirubin excretion rate (or transport maximum) the administration of glucagon increased the bilirubin transport maximum. The excretion rate of bilirubin monoglucuronides was more enhanced than that of diglucuronide. The enhanced rate of glucuronidation, assayed in vitro, correlated with the augmented biliary output and inversely with the plasma unconjugated bilirubin levels. It is concluded that glucagon, at the dosage used, leads to a higher formation rate of bilirubin monoconjugates and that the choleresis, also induced by the hormone, enhances the biliary secretion of the monoconjugates formed. The enhanced conjugation results in a decreased plasma concentration of unconjugated bile pigment and the associated choleresis leads to a decreased di- to monoconjugate ratio, opposite to what has been observed during bilirubinostasis and cholestasis. The secretory efficacy, as assessed from the bile-to-plasma concentration ratio, is enhanced for all bilirubin pigments after glucagon administration.

A steady maximal biliary secretion of bilirubin has been produced in male Wistar rats, recovered from anesthesia, by continuous infusion of 256 nmol of unconjugated bilirubin per hour per 100 gm body weight, after priming with 3.4 mumols. The administration of somatostatin (2 micrograms/hr/100 gm body weight) produced a reversible decrease of bile flow and bile acid excretion while bilirubin output was unchanged. After discontinuation of somatostatin, a slight increase in the output of bilirubin conjugates was observed with the rapid recovery of bile flow. Administration of Na+ taurocholate at increasing rates (30 to 480 nmol/min/100 gm body weight) progressively enhanced bile flow and bile acid secretion. The rate of secretion of bilirubin conjugates increased to 18% above the values in controls at a taurocholate dose of 120 nmol/min/100 gm body weight and remained at that level with higher amounts, in spite of further increases in flow. Under Na+ taurocholate, somatostatin failed to reverse the enhancement of bilirubin output, although it still inhibited the secretion of bile acids and bile flow. A mechanism linked to osmotic flow induced by taurocholate would appear to serve as a component of the total capacity of the hepatocyte to transfer bilirubin conjugates into the canaliculus. At low bile-acid secretory rates this component seems of minor quantitative importance, whereas a major (specific) pathway seems not yet saturated.

The activity of bilirubin UDP-glucuronyltransferase in liver tissue was increased 1.5-fold after 90 min of secretion administration (4 i.u./h per kg body wt.) in anaesthetized Wistar rats biopsied half-hourly over a period of 2 h. In unanaesthetized R/A Wistar rats, activities of liver enzymes were assayed after administration secretin for 1 h. Bilirubin UDP-glycosyltransferase activities and cytochrome P-450 concentration were increased, but p-nitrophenol UDP-glucuronyltransferase and UDP-glucose dehydrogenase activities remained unchanged.

The apparent maximal transport capacity (Tm) of the liver for bilirubin was studied in rats after oral treatment for two weeks with the two flavonoids (+)-cyanidanol-3 and palmitoyl-catechin in order to investigate a possible mechanism of action on jaundice described in humans. (+)-Cyanidanol-3 produces no changes in bilirubin-Tm, and the analysis of bilirubin and its conjugates in the different compartments reveals a decreased amount of the whole bilirubin taken up by the liver. Palmitoyl-catechin, a more lipophilic derivative of catechin, produces a slight increase in bilirubin-Tm. This appears related to the increased conjugation rate demonstrated in vitro for bilirubin. A multicompartimental analysis shows a different distribution of bilirubins as compared to controls. It is likely that physicochemical changes of the membrane environment, where the enzyme is buried, have modified the capacity of the hepatocyte to dispose bilirubin.

Somatostatin was administered intravenously to male Wistar rats, recovered for 3 h from an anesthesia during which the common bile duct and jugular vein were cannulated. Different bile acid-secretory rates were obtained by infusion of saline, or of Na+-taurocholate (150 nmol/min/100 g body wt), or by 8-h bile depletion. At the dose of 2 micrograms/h/100 g body wt, somatostatin causes a prompt decrease of bile flow (about 30%) and of bile acid secretion (32%-47%). The bile acid-independent fraction of canalicular bile is more decreased than the one associated with bile acid secretion. The changes are dose dependent and show a saturation pattern, with half-maximal saturation already at 2.2 ng/min/100 g body wt. Despite this cholestasis, endogenous bilirubin secretion remained unchanged, pointing to different secretory mechanisms for bilirubin and bile acids. In the isolated and perfused liver, somatostatin displays an anticholeretic effect, proportional to the amount of Na+-taurocholate present in the system. Hepatic blood flow and O2 consumption remained constant during perfusion, and were not affected by somatostatin. The hepatic transport of bile acid, and the water and electrolyte secretion are directly affected by somatostatin, and the experimentally-induced cholestasis seems a new and suitable model for studying mechanisms of bile secretion.

Increasing amounts of porcine secretion (0.05 to 2.00 clinical units/h/100 g body wt) given to rats during a continuous infusion of bilirubin, increased bile flow and the apparent maximal biliary excretion of bilirubin ('Tm'). This increment was caused by an enhanced biliary output of bilirubin monoconjugates. The effect was dose dependent but maximal at a secretin infusion of 0.80 CU. Somatostatin 0.2 and 0.8 microgram/h/100 g body wt caused a dose related inhibition of the hepatic effects of secretin both on bile flow and on biliary output of bilirubin conjugates. As secretin elicits the release of somatostatin, a feed-back system could be envisaged whereby the somatostatin released stops the effects of secretin.