Occurrence of cysteine conjugate of 2-hydroxyestrone in rat bile, with special reference to its formation mechanism.

The biliary excretion of the water-soluble metabolites in the rat administered with 2-hydroxyestrone-6, 7-3H and estrone-4-14C has been investigated. A polar metabolite separated from the collected bile was characterized to be a conjugate of 2-hydroxyestrone with cysteine at C-1 or C-4 through a sulfide linkage. The in vitro experiment with the rat liver preparation also demonstrated the formation of the cysteine conjugate. Based upon the 3H/14C values of 2-hydroxyestrone and its cysteine conjugate the probable mechanism involved in conjugation has been discussed.