Pine needle abortion in cattle: Metabolism of isocupressic acid

The rumen and hepatic metabolism of the cattle abortifacient compound isocu pressic acid (ICA) was examined in vitro and in vivo. ICA was incubated for 56 h in bovine rumen inoculum and was found to be converted to three compo unds identified as imbricatoloic acid, a structurally uncharacterized isome r of imbricatoloic acid, and dihydroagathic acid. In preparations of liver homogenates, ICA was found to be oxidized to agathic acid. No differences i n ICA metabolites were detected in comparing the cow, sheep, pig, goat, gui nea pig, and rat livers; however, guinea pig and rat liver homogenates were less efficient in converting ICA to agathic acid. ICA had been administere d to cows orally and by intravenous infusion and induced abortions after ei ther method of treatment. After intravenous infusion, agathic acid was iden tified as the major metabolite together with minor amounts of dihydroagathi c acid. After oral administration, dihydroagathic acid was identified as th e major metabolite with minor amounts of agathic acid, imbricatoloic acid, and a structurally uncharacterized metabolite tentatively identified as tet rahydroagathic acid.