Studies on sex-related difference of cytochrome P-450 in rat liver microsomes (IV). Radial immunodiffusion assay and regulation by sex hormones of forms of cytochrome P-450 present specifically in males and females, respectively

Abstract To clarify enzymatic mechanisms involved in the occurrence of sex difference of drug metabolism in the rat, we purified one major form of cytochrome P-450 from respective liver microsomes from untreated male and female rats with essentially the same method. These purified forms, P-450-male and P-450-female showed differences in catalytic activities upon re-constitution with purified NADPH-cytochrome P-450 reductase, molecular weights, spectral properties and immunochemical examinations. The amounts of cytochrome P-450 were quantified by radial immunodiffusion assay using antibodies to P-450-male and P-450-female. The results showed that P-450-male and P-450-female existed rather specifically in liver microsomes from male and female rats, respectively. Cytochrome P-450 reacting with anti-P-450-male IgG appeared in liver microsomes of female rats when female rats had been ovariecto-mized and was treated with testosterone. Inversely, P-450-fe-male could be detected in liver microsomes of male rats after treatment with estradiol. Based on these and other results, we confirm that the synthesis of P-450-male and P-450-female is regulated by sex hormones.