Hepatic metabolism and pulmonary toxicity of monocrotaline using isolated perfused liver and lung

Monocrotaline is a pyrrolizidine alkaloid obtained from the seeds of Crotalaria spectabilis. When perfused through an isolated liver, monocrotaline is metabolized to Ehrlich reactive (E+) metabolites. Metabolism of monocrotaline was faster in livers from male rats than female rats, was inducible with phenobarbital pretreatment, and was inhibited by coperfusion with the P-450 mixed-function oxidase inhibitor SKF-525A, anoxic perfusion conditions, and low temperatures. When metabolites generated by an isolated liver were perfused through isolated lungs in a recirculatory manner, serotonin transport by the pulmonary endothelium was reduced in correlation with the amount of E+ material contained in the perfusion medium. When metabolism of monocrotaline by the liver was inhibited with SKF-525A, low temperature perfusions or anoxic conditions, serotonin transport by the pulmonary endothelium was unchanged from controls. Monocrotaline alone had no effect on the lung. Thus, isolated perfused livers metabolized monocrotaline to chemical species which produced pulmonary damage in vitro. This provides direct evidence that liver metabolites can cause one of the pneumotoxic effects of monocrotaline observed in vivo.