THE TOXIC ACTIONS OF PYRROLIZIDINE (SENECIO) ALKALOIDS

Abstract

The pyrrolizidine alkaloids give rise to a large number of toxic effects, many of them apparently unconnected with each other. They were for a long time regarded principally as liver poisons. In the past 10 years it has become clear that they also have a severe toxic action on the lung. The importance of making a systematic investigation of lesions in some other tissues has been stressed. Only one paper (42) deals with a possible autoimmune element among the toxic reactions. This aspect has been neglected and might repay investigation. There are repeated, separate, reports of a protective effect of cysteine and methionine. Again, systematic investigation might turn these into a useful tool for investigating toxic mechanisms. In assessing the veterinary problems and the results of feeding experiments with plants it is necessary to remember that plants can contain more than one toxin. Some plants containing pyrrolizidine alkaloids have been shown to contain a neurolathyrogen (19) and toxic levels of nitrites (127). The study of the effects of the alkaloids upon cell division in mammals has now reached a point where it could profitably be linked up with the more detailed knowledge of DNA metabolism in bacteria. An investigation of the effects of the alkaloids and the pyrrolizidine pyrroles on DNA metabolism in Escherichia coli would be worthwhile. According to the current evidence, it seems that these alkaloids present a hazard to man only in special circumstances. As a veterinary hazard, they remain important wherever pasture is poor or forage crops are likely to be heavily contaminated with the appropriate weeds. As tools for the student of biological mechanisms they are becoming increasingly interesting.