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Abstract
1. Liver microsomal preparations from chick embryos (1 day before hatching) and from 1–7 day old chicks were assayed for oxidative drug-metabolizing activity with aminopyrine, aniline and naphthalene as substrates.
2. Activities for all three substrates were highest in preparations from 1 day-old chicks. These were more than twice as active as the 7 day-old preparations and about three times as active as those from the embryos.
3. The increase in drug-metabolizing activities in newly-hatched chicks was the same for either sex and persisted for 3 days before declining towards the 7 day-old levels.
4. The developmental time-course of the liver microsomal drug-metabolizing activities was independent of any factor in the 105 000 g supernatant fractions and of such microsomal parameters as cytochrome b5 and cytochrome P-450 content, and NADPH-cytochrome c reductase activity, but was related to changes in NADPH-cytochrome P-450 reductase levels.
5. Treatment of 7 day-old chicks with exogenous inducers, 3-methylchol-anthrene or phenobarbital sodium (100 mg/kg, intraperitoneally) brought about maximal stimulation of microsomal activity at 18–24 h. The time-course of this induction was reflected by changes in microsomal cytochrome P-450 content and NADPH-cytochrome P-450 reductase activities.
6. Some induction of liver microsomal drug metabolism in 7 day-old chicks could also be brought about by injecting certain lipid-soluble egg yolk extracts.
8. Baltimore: Williams & Wilkins Co.