Steroid metabolism in the cat. Biliary and urinary excretion of metabolites of [4-14C] oestradiol.

1. [4-(14)C]Oestradiol was administered to seven male, seven female and two castrated male cats as a single intravenous injection. Bile and urine were collected for 6h. 2. The radioactivity was excreted mainly in the bile of all animals (53-60%); only approx. 1% of the dose appeared in the urine. 3. Bile and urine samples were hydrolysed successively by beta-glucuronidase, cold acid and hot acid. There were significant differences (P<0.005) between the percentage of the dose present in the bile fractions hydrolysed by beta-glucuronidase (male, 9.0+/-1.7%; female, 18.6+/-1.45%) and by cold acid (male, 18.9+/-1.44%; female 12.1+/-1.02%). The excretion of radioactivity in these fractions by the castrated male cats was closer to that of female cats. 4. Approx. 20-27% of the dose could not be extracted from aqueous solution (pH10.5) by ethyl acetate-ether after hydrolysis.