Bilirubin, the end-product of haem catabolism, is water insoluble and toxic because of internal hydrogen-bonding. Bilirrubin is converted into polar glucuronide conjugates by the action of hepatic microsomal enzyme bilirubin-UDP-glucuronosiltransferase (UGT1A1), which catalyses the transfer of the glucuronic acid moiety of UDP-GlcA to bilirubin, generating bilirubin monoglucuronide and diglucuronide. Bilirubin glucuronides are polar and are excreted readily in bile.

During fetal live in the rodent, the placental clearance of bilirubin of fetal origin is apparently of such efficiency that intrauterine fetal hiperbilirrubinemia is unknown and substrate induction of UGT1A1 does not occur. Data of different authors indicate in the rat that UGT1A1 is absent during fetal life and only becomes detectable at birth (Cukier et al, 1981). Previous data from our laboratory show that at day 13 of gestational life there is already bilirubin-UDP-glucuronosiltransferase gene expression (Cubero et al, 2001), although we only detect a low activity of the UGT1A1 at the final period gestacional, at day 21 ( Bustamante et al 2005). The purpose of the present study was to determinated the presence of the protein UGT1A1 in the fetal liver in the last days of gestacional period by western blot, and to analyse if the marked suppression of the activity of this enzyme during fetal life it is modified by treatment with glucocorticoides. And the other hand, to know if the postnatal maduration the UGT1A1 activity was more rapid in neonatal pups derived from dams treated with glucocorticoides.

Study supported by Fundación Mutua Madrileña Grants