Postnatal development of mixed-function oxidation as measured in microsomes from the small intestine and liver of rabbits.

The postnatal development of aminopyrine N-demethylase, aniline 4-hydroxylase, benzpyrene hydroxylase, biphenyl 4-hydroxylase, 7-ethoxycoumarin 0-deethylase activities, NADPH-cytochrome c reductase, and cytochrome P-450 was compared in microsomes from the liver and small intestine of New Zealand white rabbits. Apart from hepatic aniline hydroxylase activity, all of the xenobiotic-metabolizing enzyme activities examined had a similar pattern of development in the liver and small intestine. In both tissues the ability to metabolize xenobiotics was generally undetectable at 2 days of age and remained relatively low for the first 20 days of life. Theresfter, a rapid 2- to 5-fold increase in all the enzyme activity studied was noted, and adult values were reached or exceeded by 30 days of age. Subsequent development of xenobiotic-metabolizing enzyme activities in the small intestine, but not in the liver, exhibited a transient fall at 50 days of age before adult activities were attained after 75 days of age. The developmental pattern of cytochrome P-450 in the small intestine closely resembled that of the xenobiotic-metabolizing enzyme activities, but in the liver this correlation was less exact.