Microsomal N-demethylase activity in developing rat liver after administration of 3-methylcholanthrene☆

Abstract Microsomal N -demethylase activity was examined during various stages of liver development. Its specifie activity in fetal and in 1-day neonatal liver was significantly lower than in the liver of the adult female. Between day 1 and 3 post partum , the sp. act. of N -demethylase rose to the adult female value. The enzymatic activity in the gravid and nonpregnant rat was similar; that of the adult male was 1·7-fold higher. 3-Methylcholanthrene administration was attended by an increase in liver enzyme activity in adult female, neonatal, preweanling and weanling rats. The enzyme activity could not be induced in fetal liver after administration of the drug to the pregnant rat or directly into the amniotic sac. In the former case, the possibility of the inability of the drug to be transported across the placenta was excluded. It was concluded that some aspect of the maternal environment prevented the elaboration of the drugmetabolizing enzymes after administration of 3-methylcholanthrene.