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Abstract
1. A study of the sex- and age-(4 to 103 weeks) related changes in liver microsomal mixed-function oxidase components of Sprague-Dawley rats, showed that total cytochrome P-450 ranged from 12.0 to 34.0 nmol/g, peaking between weeks 26 and 39; males had higher levels than females at weeks 4 to 51. Cytochrome b5 ranged from 5.0 to 15.0 nmol/g with inconsistent age- and sex-related differences.
2. NADPH: cytochrome C reductase ranged from 2.6 to 4.8 μmol/min per g, with maximal activity at week 39; males had greater activity at weeks 12 to 78. NADH: cytochrome C reductase ranged from 5.2 to 26.9 μmol/min per g, peaking between weeks 51 and 78; females had greater activity at weeks 12 to 51.
3. This age- and sex-related pattern of changes in these components is specific to the Sprague–Dawley strain. There are slight but significant differences between sexes only in rats less than 1 year old. There was no significant correlation between rates of p-nitroanisole or aniline metabolism and cytochrome P-450 concentrations.