Developmental changes in the expression of enterocytic and hepatic cytochromes P4501A in rat.

1. The development of CYP1A enzymes was studied in enterocytic and hepatic microsomes from 1-day-old to adult male and female rats. Microsomes were prepared by calcium precipitation. Enzyme expression was determined by Western blotting using a polyclonal CYP1A1 antibody. 2. The developmental expression of CYP1A in enterocytic and hepatic microsomes was similar for males and females. 3. Enterocytic CYP1A (CYP1A1) showed a sharp increase at weaning, plateauing at adult levels by 60 days. 4. Hepatic CYP1A (mostly CYP1A2) increased sharply just before weaning. However, in contrast to the enterocytic enzyme, there was a 4-fold decrease in enzyme expression down to adult levels by day 60.