CORTISOL METABOLISM INVITRO .2. SPECIES-DIFFERENCE

It has been suggested that cortisol 6beta-hydroxylase activity specifi cally reflects cytochrome P4503A (CYP3A) levels in the liver. However, we have previously reported that the metabolism of cortisol in human liver fractions in vitro is extremely complex and variable, and theref ore complete metabolite analysis must be undertaken if 6beta-hydroxyco rtisol is to be used as a marker of CYP3A activity. In the present stu dy, the metabolism of [H-3]cortisol by hepatic microsomes from various animal species, and by cytosol from male and female rats, has been de fined and compared with metabolites formed by human liver microsomes. Metabolites were characterized by co-chromatography with authentic sta ndards, mass spectrometry, and quantified by radiometric HPLC. The res ults show that all microsomes prepared from animal species studied (ma le and female rat, male and female guinea-pig, male hamsters and mice) can metabolize cortisol, although the metabolic profiles are both qua ntitatively and qualitatively different from that obtained with human microsomes. In general the metabolic profiles for animal microsomes ar e simpler: hamster, mouse and guinea pig show only 6beta-hydroxylase a nd 11beta-dehydrogenase activity, although male rat shows both of thes e and 20beta-reductase activity while the female rat possesses all of the above as well as the ability to reduce the A-ring (DELTA4-reductas e and 3-oxidoreductase activities). The female rat also produces two m etabolites undetected in humans. Incubations with male rat cytosol gen erated 20beta-dihydrocortisone as the major metabolite, and several un identified minor polar metabolites, whereas female cytosolic products were identical to those generated by human cytosol, the major metaboli te being 3alpha,5beta-tetrahydrocortisol. In conclusion, our studies h ave shown that hepatic cortisol metabolism is extremely variable among st the species investigated and that the hamster provides the simplest model with which to explore cortisol 6beta-hydroxylase activity.