Dehydroretronecine-induced rhabdomyosarcomas in rats

Two groups of rat were given s.c. injections of either monocrotaline or its major detectable metabolite, dehydroretronecine, biweekly for 1 year. Tissues obtained from partial hepatectomies performed at 4 months on a portion of these animals showed that both compounds caused a decided inhibition of mitotic division in regenerating liver. Rhabdomyosarcomas developed at the site of dehydroretronecine injection in 51.6% of the rats and in 3.3% of the monocrotaline-treated rats. Metastatic lesions were recorded in 8.3% of these animals. In addition to the above, 10% of the monocrotaline-treated rats developed other tumors that included myelogenous leukemias, hepatocellular carcinomas, and pulmonary adenomas. These data indicate that either monocrotaline or its metabolite dehydroretronecine are capable of causing neoplastic transformations in the tissues of experimental animals.