Age-related changes in the iron spin state of testosterone-binding rat liver microsomal cytochromes P-450

The aging process is accompanied by decreased drug metabolism as well as lower levels of sex hormones such as testosterone. We examined the age-dependence of liver microsomal cytochromes P-450 from young (3 months) and old (24 months) male rats by absorption and ESR spectroscopy. Spectral perturbations by testosterone were used to identify testosterone-specific P-450 forms. Absorption difference spectra indicated that testosterone induced a greater conversion of P-450 to the high spin form in young rats than in old rats. ESR signals corresponding to total low spin P-450 were of higher intensity in the young rats and were increased by testosterone. Testosterone also interconverted one low spin P-450 species to another. These results demonstrate age-related differences in the types and amounts of testosterone-specific P-450's in rats.