Bilirubin, UDP-glucuronyl transferase of liver in postmature rats. A functional and morphologic comparison

Postmaturity was induced in dated pregnancies in Wistar rats by daily injection of 25 units of chorionic gonadotrophin, beginning on day 18 of gestational life. Animals were either delivered operatively on day 23 of postconceptual age or allowed to deliver spontaneously on day 24 by stopping the gonadotrophin. The hepatic bilirubin UDP-glucuronyl transferase activity (E.C.2.4.1.17) was quantitated in these animals and compared with that of control animals of normal gestations operatively and spontaneously delivered of similar postconceptual age. Normal animals at birth have very little hepatic bilirubin UDP-glucuronyl transferase activity, but it rapidly achieves adult activities in the first 4 days of neonatal life. In contrast, the postmature animals of 23 and 24 days of postconceptual age exhibited marked suppression of the hepatic bilirubin UDP-glucuronyl transferase activity, but they exhibited rapid neonatal maturation after delivery. The ultrastructure of the hepatocytes from the postmature rats of 24 days postconceptual age exhibited the same paucity of smooth endoplasmic reticulum of 21-day rats, which is in striking contrast to of postnatal life. The findings are interpreted to suggest that the intrauterine milieu actually suppresses fetal maturation of liver function.