Maturation of the sulfobromophthalein sodium-glutathione conjugating system in rat liver

Sulfobromophthalein sodium, hereafter referred to as BSP, has frequently been employed to ap-praise hepatic function in the newborn infant (1-7). With but one exception (2), many studies have demonstrated delayed disappearance of BSP from blood and increased BSP retention in both the full-term and premature infant in the immediate postpartum period (1, 3-7). Subse-quently, the rate of removal of BSP from blood gradually increased, and within a few weeks after birth, approached values found in older children and adults. In general, the impairment of BSP clearance in the first few days after delivery has been attributed to immaturity, and the gradual improvement to maturation of the factors involved in the hepatic removal of BSP from blood and the subsequent excretion of BSP into bile. Based on a considerable body of evidence which has been accumulated within the past few years (8-15), it is now known that a major fraction of the BSP which is removed from blood and ex-creted into bile undergoes metabolic transforma-tion within the liver. There appears to be general agreement that the major pathway of BSP metab-olism in man, rat, dog, and other species involves conjugation with the tripeptide glutathione in thioether linkage (12-15). Recently, we identi-fied an enzyme in the soluble supernatant fraction of liver that catalyzes BSP-glutathione conjuga-tion (15). During conjugation, whether enzyme-catalyzed or not, bromine is released from BSP, and the sulfur group of glutathione attaches to BSP at the site of bromine removal (13, 15)