Biliary excretion of dye in dogs infused with BSP or its glutathione conjugate.

A comparison of the maximal rates of biliary excretion (Tm), of dye in dogs infused with either BSP or its glutathione conjugate (BSP-GSH) was carried out. Tm was much higher when BSP-GSH rather than BSP was infused. This was accounted for by a significantly higher concentration of dye in bile of dogs receiving BSP-GSH. Evidence is presented that BSP and its conjugated metabolites compete for a common transport carrier and that BSP disproportionately depresses the biliary excretion of conjugated dye compounds. This latter observation accounts for the depressed dye Tm found during infusion of BSP. Choleresis invariably accompanied dye excretion. When BSP-GSH was infused, enhanced bile flow could be accounted for by the predicted osmotic activity of dye transported into bile. By contrast, the choleresis measured during infusion of BSP was significantly greater than that predicted. An additional mechanism for choleresis is operative, therefore, when unconjugated BSP is infused. Administration of taurocholate enhanced dye Tm when BSP-GSH was infused. Since increments of canalicular bile flow induced by theophylline and glucagon did not enhance dye excretion into bile, this effect by taurocholate appears to be related to taurocholate excretion per se rather than to the enhanced canalicular bile flow which accompanies its excretion.