The rates of radical formation from the dipyridylium herbicides paraquat, diquat, and morfamquat in homogenates of rat lung, kidney, and liver: An inhibitory effect of carbon monoxide

Abstract

In an attempt to elucidate the mechanism of toxicity in mammals and to explain some organ specificities observed in chronic dipyridylium herbicide intoxication, the specific rates of radical cation appearance for paraquat, diquat, and morfamquat were measured in homogenates of rat lung, kidney, and liver. In each organ homogenate, the order of the rates was morfamquat > diquat > paraquat. For each herbicide the order of the rates was liver > lung > kidney. The results are inconsistent with the hypothesis that selectively enhanced rates of radical production in the target organs are responsible for the specificities observed. Carbon monoxide inhibited the rate of appearance of the diquat radical in all three organ homogenates: in contrast, the rate of radical formation from paraquat and morfamquat were not affected. No inhibition was observed in any combination of organ and herbicide by either potassium cyanide or SKF 525-A. It is concluded that diquat is reduced by a different electron transferring agent than either paraquat or morfamquat.