Development of liver microsomal oxidations in the chick

Area of Science:

• Biochemistry
• Pharmacology
• Developmental Biology

Background:

• Liver microsomes play a critical role in drug metabolism.
• Understanding the developmental changes in drug-metabolizing enzymes is essential for predicting drug efficacy and toxicity.

Purpose of the Study:

• To investigate the developmental profile of oxidative drug-metabolizing activities in chick liver microsomes.
• To examine the factors influencing these activities during early post-hatch development and their response to induction.

Main Methods:

• Assay of oxidative drug-metabolizing activity using aminopyrine, aniline, and naphthalene as substrates in liver microsomes from chick embryos and chicks aged 1-7 days.
• Analysis of microsomal parameters including cytochrome b5, cytochrome P-450 content, and NADPH-cytochrome c reductase activity.
• Administration of exogenous inducers (3-methylcholanthrene, phenobarbital sodium) and egg yolk extracts to 7-day-old chicks to assess induction of drug metabolism.

Main Results:

• Drug-metabolizing activities were highest in 1-day-old chicks, significantly exceeding those in 7-day-old chicks and embryos.
• The developmental increase in activity was sex-independent and persisted for 3 days before declining.
• Activity changes correlated with NADPH-cytochrome P-450 reductase levels, not supernatant factors or other microsomal parameters.
• Exogenous inducers and egg yolk extracts stimulated microsomal activity in 7-day-old chicks, with induction kinetics reflected in P-450 content and reductase activity.

Conclusions:

• Chick liver microsomal drug metabolism exhibits a distinct developmental peak shortly after hatching.
• NADPH-cytochrome P-450 reductase activity is a key determinant of this developmental pattern.
• Chick liver drug metabolism can be induced by exogenous agents and egg yolk components, offering insights into xenobiotic metabolism regulation.