The metabolic fate of endrin in the rabbit

1. [14C]Endrin, administered orally to rabbits, is excreted in the faeces as unchanged endrin (50% of that administered) and in the urine as a mixture of polar metabolites. 2. The major biotransformation is hydroxylation at the methylene bridge (C-12) to yield anti-12-hydroxyendrin. syn-Hydroxylation at C-12 also occurs. 3. The hydroxylated metabolites are excreted mainly as their sulphate conjugates. 4. Glucuronide conjugates are also excreted. anti-12-Hydroxyendrin is rapidly conjugated in vitro on incubation with rabbit liver microsomal glucuronyl transferase and UDPGA. 5. Comparative aspects of the metabolism of endrin in rats and rabbits are discussed.