Influence of diet on metabolism and excretion of bromosulphthalein sodium

The effect of a 48 hr fast on the hepatic components of the bromosulphthalein sodium (BSP) conjugating system was studied in rats and contrasted with previously observed changes induced in animals fed a protein free diet (PF) for 48 hr. Fasting causes a 25% fall in hepatic glutathione (GSH) content compared to a 70% decrease in PF rats. BSP conjugating enzyme activity fell by about 20% with both dietary regimens. In vivo studies demonstrated: normal BSP excretion in both groups following conjugated BSP infusion; a fall in BSP transport maximum (Tm) in PF animals given free BSP; this decrease in BSP Tm is due to decreased excretion of conjugated BSP, despite hepatic levels of conjugated BSP equal to those attained during infusion with conjugated BSP and in association with a decrease in the proportion of conjugated BSP relative to free BSP in the liver. It was previously shown that the presence of free BSP in the liver inhibits the excretion of conjugated BSP. Presumably the excess free dye in the liver of PF animals is the result of the loss of GSH from these livers and responsible for the increased inhibition of conjugated BSP excretion in these rats.