Ontogenic development of drug-metabolizing enzymes in male chicken liver

The ontogenic study of the hepatic biotransformation enzymes revealed the early development of both oxidative and conjugative enzymes in male chickens ranging in age from 3 to 12 weeks. Although the rate of microsomal cytochrome P450 reactions progressively increased during the first 9 weeks, it decreased thereafter. Furthermore, the proteins revealed by the antibodies to anti-cytochrome P450 1A2, 2B4, 2C7, and 3A4 appeared to be constitutively expressed. Hepatic monooxygenases were characterized by different developmental patterns. The demethylase activities increased progressively up to 9 weeks, then they declined, in 12 weeks reaching the activity level observed in 3-week-old chickens. In contrast, alkoxyresorufin O-dealkylases and benzopyrene hydroxylase activities continued to increase with age. Significant variability was noted for aniline hydroxylase. Among conjugation enzymes, UDP-glucuronyltransferase towards p-nitrophenol and isoniazid N-acetyltransferase activities increased with the age of the fowl, but with different profiles. Concerning glutathione S-transferase accepting 1-chloro-2,4-dinitrobenzene or 1,2-dichloro-4-nitrobenzene, the chickens aged from 3 to 9 weeks were less well developed in this enzyme than 12-week-old ones.