Inhibition of Monoamine Oxidase by the Pesticide Chlordimeform and Related Compounds

CHLORDIMEFORM is a formamidine acaricide and insecticide used to control phytophagous mites, cattle ticks and certain lepidopterous insects. Because of its unique spectrum of biological activity with regard to selectivity, chlordimeform may be the forerunner of a new class of agricultural chemicals. Although its mechanism of action is unknown, Knowles and Roulston1, studying the action of chlordimeform and related compounds on the southern cattle tick, suggested that inhibition of monoamine oxidase (MAO) could be involved. This hypothesis was based on observations of ticks poisoned with formamidine compounds and on the known ability of amidine compounds, such as propamidine and pentamidine, to inhibit MAO from mammals2. We have observed that symptoms manifested by rats poisoned by chlordimeform and demethylchlordimeform are similar to those elicited by sympathomimetic agents including known MAO inhibitors (unpublished results of F. R. Johannsen and C. O. K.). Thus, it seemed appropriate to examine chlordimeform and related compounds as potential inhibitors of rat liver MAO in vitro.