Postnatal development of the hepatobiliary transport of phenolsulfonphthalein in rats

1. The postnatal development of the biliary excretion of phenolsulfonphthalein (PSP) was studied in male Wistar rats. 2. Following i.v. injection of PSP at 200 mumol/kg body wt, a maximal biliary excretion of 175 +/- 10 nmol/min/100 g body wt and 32 +/- 5 nmol/min/100 g body wt was reached for unconjugated and conjugated PSP, respectively, in the adult group. 3. The maximal biliary excretion of conjugated PSP was significantly lower in the 20-, 30- and 40-day-old groups as compared to the adults. The excretion of unconjugated dye was also significantly lower in 20- and 30-day-old rats. 4. The postnatal development of PSP excretion was unrelated to changes in the activity of UDP-glucuronosyltransferase. The importance of other factors is also discussed.