Metabolism of [14C]emodin in the rat.

1. Absorption, excretion, tissue distribution and metabolism of the anthraquinone [14C]emodin was studied after a single oral administration (approx. 50 mg/kg) to rats. 2. Urinary excretion amounted to 18(+/- 5)% dose in 24 h and to 22(+/- 6)% in 72 h. 3. Metabolites found in pooled urine (0-72 h) were mostly free anthraquinones (emodin and emodic acid, 16% dose); 3% was conjugated and 3% was non-extractable radioactivity. 4. In 24 h, 48 +/- 11% and in 120 h, 68 +/- 8% dose was excreted in the faeces, mostly in the free anthraquinone form. 5. In two cannulated rats biliary excretion reached a maximum at approx. 6 h and amounted to 49% dose within 15 h; 70% of biliary activity was in the form of conjugated emodin. 6. The content of radioactivity in most organs decreased significantly between 3 and 5 days. In kidneys, however, the 14C activity was still equiv. to 4.33 p.p.m. emodin after five days. Mesenterium and fat tissue showed increasing 14C activity from 72 to 120 h.