Isolation and identification of metabolites of 14C-labeled estradiol in cattle

A total of six steers and six heifers received three daily injections containing either 200 muCi (1 mg) of [4-14C] estradiol-17beta or 312 muCi (2.16 mg) of [4-14C] estradiol 17beta 3-benzoate. Major metabolites of the administered estradiol-17beta and estradiol-17beta 3-benzoate were identified in muscle, fat, liver, and kidney samples obtained 3 hr after the final injection. Estradiol benzoate was nondetectable in the tissues analyzed, suggesting rapid hydrolysis of the benzoate ester. Consequently, the relative proportions of the various metabolites were similar for both the injected estrogens. Estradiol-17beta and estrone, which together accounted for 80-90% of the total extracted radioactivity, appear to be the major metabolites in both muscle and fats. In contrast, the major metabolites present in liver and kidney appear in the conjugate fraction. Most of the conjugated metabolites were glucuronates, which represent 85-95% of the total recovered conjugate radioactivity.