Studies on the methylation of diethylstilbestrol by preparations of rat liver

The methylated metabolites of diethylstilbestrol (DES) were formed by incubation with S-adenosyl-(3H-methyl)-L-methionine (SAM) and preparations of rat liver. Formation of the O-methyl-catechol metabolite required the 10,000 g supernatant fraction, NADPH and SAM. The nonionic detergent Triton X-100 (0.025%, v/v) did not affect the activity of the methyltransferase but stimulated glucuronyltransferase and inactivated the mixed function oxidases. Thus, incubation with Triton abolished methylation of DES by the 10,000 g supernatant fraction, but methylation and glucuronidation of DES was observed when incubated with microsomes and NADPH and reincubated with Triton, soluble fraction, UDP-glucuronic acid and SAM. Since DES itself was not methylated by the soluble fraction, the results suggest that DES is oxidized by mixed function oxidases to a catechol which is methylated and then glucuronidated. Results of reincubation studies support this sequence. Methylation does not impair glucuronidation of the catechol but glucuronidation prevents its methylation.