Effects of ursodeoxycholate, its glucuronide and disulfate and β-muricholate on biliary bicarbonate concentration and biliary lipid excretion

We previously reported that high-dose ursodeoxycholate (UDC) infusion in rats resulted in extensive glucuronidation of UDC, and speculated that the glucuronidation causes bicarbonate-rich hypercholeresis induced by UDC (Takikawa, H., Sano, N., Narita, T. and Yamanaka, M. Hepatology 1990; 11: 743–749). To test this hypothesis, UDC, UDC-3-O-glucuronide, UDC-3,7-disulfate and β-muricholate were separately and intravenously infused into rats (1 μmol/min per 100 g), and biliary bicarbonate concentration was measured. The effects of these bile acids on biliary lipid secretion were also studied. All four bile acids increased bile flow and biliary bile acid excretion. UDC and β-muricholate significantly increased biliary bicarbonate concentration, whereas UDC glucuronide and disulfate did not. Independence of UDC glucuronide excretion and biliary bicarbonate concentration was also confirmed in EHBR, a hyperbilirubinemic mutant Sprague-Dawiey rat. In this case biliary bicarbonate concentration also increased in spite of the absence of UDC glucuronide in the bile after UDC infusion. Biliary phospholipid secretion was increased with UDC, unchanged with β-muricholate, and decreased with UDC glucuronide and disulfate. Biliary cholesterol secretion was increased with UDC, unchanged with β-muricholate and UDC glucuronide, and decreased with UDC disulfate. These data indicate that glucuronidation is not the cause of bicarbonate-rich hypercholeresis induced by UDC but that glucuronidation and sulfation change the effect of UDC on biliary lipid secretion.