Extract: Sulfadimethoxine significantly reduced plasma bilirubin levels and altered the tissue bilirubin distribution in both the newborn and the adult Gunn rat. The majority of the unbound bilirubin appeared to distribute preferentially to the intestine and liver in the newborn, whereas in the adult the unbound bilirubin was taken up primarily by the liver. The bilirubin content of brain tissue from both age groups was significantly higher after sulfadimethoxine treatment.Speculation: A decrease in the available extravascular bilirubin binding sites, indicated by an increased concentration of bilirubin in the carcass and an apparent decreased capacity of the liver of the newborn Gunn rat to bind bilirubin, would suggest that kernicterus in the Gunn rat neonate is associated with increased bilirubin concentrations in the brain. However, the similar uptake of bilirubin by the brain tissue of both the newborn and the adult Gun rat raises the question of increased sensitivity of the newborn brain to bilirubin toxicity.
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