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A B S T R A C T The influence of bile salts on the hepatic metabolism of sulfobromophthalein sodium (BSP) was studied in the perfused rat liver. During sodium taurocholate infusions, hepatic uptake of BSP from plasma was increased and appeared to be related to an enhanced transit of BSP from liver into bile. BSP-glutathione conjugation was not affected by the bile salt infusions, although bile salts inhibited the enzyme system in vitro.The major effect of bile salts was to increase the BSP transport maximum (Tm). When sodium taurocholate was infused in saline at a rate of 30 /moles/hr, both bile flow and the BSP Tm increased, and remained at peak levels of 1.5 ±0.12 Al/min per g liver and 21 ±3.0 lg/min per g liver, respectively. In contrast, during saline infusion alone both levels were significantly lower (1.06 ±0.17 /Al/min per g liver and 15.8 ±4.16 .g/min per g liver, respectively), and both fell progressively after the 2nd hr of perfusion. This decline in bile flow and BSP Tm was associated with a decrease in biliary bile salt excretion and was reversed by adding bile salts to the perfusate. Since the biliary concentration of BSP remained within a narrow range in all experiments, the BSP Tm was primarily determined by the rate of bile flow.Dependence of BSP Tm on the rate of bile production was further confirmed by changing the temperature of the perfusate during a constant infusion of taurocholate. BSP Tm paralleled temperature-induced changes in bile flow irrespective of changes in the level of bile salt excretion.Since the biliary concentration of BSP remained within a narrow range in all experiments, the concen-

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