Androgen glucuronyl transferase activity in rat liver, evidence for the importance of hepatic tissue in 5 alpha-reduced androgen metabolism.

To elucidate the role of the liver in 5 alpha-reduced androgen metabolism, we used a rat liver glucuronyl transferase assay to determine the conversion of 17 beta-hydroxy-5 alpha-androstane-3-one (DHT), 5 alpha-androstane-3 alpha, 17 beta-diol (androstanediol), and androsterone to their glucuronide metabolites. Serum levels of the two isomers of androstanediol glucuronide (androstanediol 3- and 17-glucuronide) were also measured. Using 5 microM unconjugated steroid as substrate, the production rate (pmol/mg/min) for each product from its respective unconjugated steroid was 6.9 +/- 0.4 for DHT glucuronide, 101 +/- 3.3 for androstanediol 3-glucuronide, 71 +/- 2.0 for androstanediol 17-glucuronide, and 181 +/- 11 for androsterone glucuronide. Production rates for androstanediol glucuronide were 800 times greater for rat liver than for rat prostate, when examined under similar conditions. In the presence of either 0 or 5 microM unlabeled androstanediol, about 60% of the androstanediol glucuronide formed by rat liver was androstanediol 3-glucuronide. In normal male rat serum, 69 +/- 8% (mean +/- SEM) of total androstanediol glucuronide was androstanediol 3-glucuronide. We have previously shown that rat prostate forms androstanediol 17-glucuronide, but not androstanediol 3-glucuronide. The results from the present study indicate that rat liver forms both androstanediol glucuronide isomers, and does so in about the same ratio as is found in rat serum. The rate of glucuronidation is also much greater in rat liver than in rat prostate. While other sites of glucuronidation are possible, these results are consistent with the hypothesis that DHT and other unconjugated androgens formed in rat prostate are conjugated to glucuronic acid mainly in the liver.