Isozyme specificity of testosterone 7α-hydroxylation in rat hepatic microsomes: Is cytochrome P-450a the sole catalyst?

Abstract

In the present study we show that monospecific antibody against cytochrome P-450a completely inhibits testosterone 7α-hydroxylation in hepatic microsomes of untreated male or female rats or rats of either sex treated with dexamethasone. These data are in contrast with those of K. Nagata et al. (1987, J. Biol. Chem. 262, 2787–2793) who recently reported that an antibody prepared against cytochrome P-450a completely inhibited testosterone 7α-hydroxylase activity in microsomes from untreated or 3-methylcholanthrene-treated rats but only inhibited 50% of the activity in microsomes from dexamethasone-treated rats. They proposed that dexamethasone treatment of rats induced another testosterone 7α-hydroxylase in rat liver. The discrepancy in the two sets of data was due, at least in part, to the use of a chromatography system by Nagata et al. that is incapable of resolving a number of testosterone metabolites. Dexamethasone treatment of rats leads to a marked increase in the production of several testosterone metabolites, including 15β-hydroxytestosterone which is cochromatographic with 7α-hydroxytestosterone in their chromatography system. Our results indicate that cytochrome P-450a accounts for all of the testosterone 7α-hydroxylase activity in microsomes from dexamethasone-treated rats, and that testosterone 7α-hydroxylation continues to be a useful marker for monitoring cytochrome P-450a in rat hepatic microsomes.