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 μCi (1 mg) of [4‐ ¹⁴ C]estradiol‐17ß or 312 μCi (2.16 mg) of [4‐ ¹⁴ C] estradiol‐17ß 3‐benzoate. Major metabolites of the administered estradiol‐17ß and estradiol‐17ß 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‐17β 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.