Factors Influencing Pyrroliz Id Ine (senecio) Alkaloid Metabolism: Species, Liver Sulfhydryls and Rumen Fermentation 1

The metabolism in vitro of pyrrolizidine alkaloids by microsomes from eight animal species was studied. The rates of pyrrole production ranged from high to low in the following order: male hamster > male rabbit > male mouse > male rat > beef steer > beef bull female rat > wether lamb > male chicken male Japanese quail. With the exception of the rabbit and chicken, there appeared to be a direct relationship between rate of pyrrole production in vitro and susceptibility to pyrrolizidine alkaloids. Senecio jacobaea incubated with sheep rumen fluid was more toxic to rats than S. jacobaea incubated with cattle rumen fluid. This result, along with the in vitro pyrrole production results, suggests that the greater resistance of sheep than cattle to S. jacobaea is due to differences in hepatic alkaloid metabolism rather than to rumen effects. In rats injected with pyrrolizidine alkaloid, total sulfhydryl levels were not altered at 1 and 2 hr post-injection. Pretreatment for 10 days with 1% dietary cysteine did not affect liver sulfhydryl levels (total, non-protein and proteinbound) but did reduce (P<.05) the 2-hr bound pyrrole level. The results indicate that alkaloid metabolism does not result in prolonged sulfhydryl depletion. (