Tissue distribution of radioactivity in rats given tritiated analogues of hepatotoxic pyrrolizidine alkaloids.

1. [3H]Retronecine 7,9-bis-N-ethylcarbamate (RC) given intravenously (120 mg/kg) to male rats showed similar tissue distribution of radioactivity to that after an equally hepatotoxic dose (40 mg/kg) of [3H]synthanecine A bis-N-ethylcarbamate (SAC), but the 3H in most tissues after 3H-SAC was about double that after 3H-RC. 2. Concentrations of radioactivity were initially highest in liver and lung, but were higher in lung after 3H-RC than after 3H-SAC, reflecting the higher pneumotoxicity of the former. Concentrations of radioactive metabolites strongly attached to liver tissue were approx. the same 1 day after similarly hepatotoxic doses of either compound. 3. Excretion of radioactivity from 3H-RC was about double that from 3H-SAC in urine, and half that in faeces during the first day.