The Toxicity of Paraquat

Abstract

Samples of paraquat dichloride and paraquat dimethosulphate are equitoxic when the LD50 is expressed as mg. paraquat ion/kg. body-weight. There are wide species variations in the LD5o and, of course, variations according to the route of administration in a single species.The pathological lesions attributable to paraquat are described in some detail. Among the most unusual is a peculiar proliferative condition in the lungs, which in an extreme case and in many parts can hardly be recognized as consisting of pulmonary tissue. With slight variations, the same microscopical picture may be seen in the rat, mouse, dog, and man, and less often in the rabbit. The experimental evidence suggests that once the condition is initiated it often proceeds in the absence of further exposure to paraquat until it becomes lethal.There is evidence that much of the mortality resulting from dermal application of paraquat in the rabbit is caused not by percutaneous absorption but by oral contamination from the stratum corneum. This leads to glossitis and oesophagitis and an inability or unwillingness to eat.In this paper we report the effects of paraquat administered to laboratory animals as the dichloride or dimethosulphate, either as a single dose by one or other route, or over a short term of repeated doses. Observations made by others on the effects of very exceptional cases of poisoning in man, arising from accidental imbibition of a solution of the substance rather than from its use in the field, suggest that similar pathological changes may be expected in human beings. Chemical Constitution and UsesParaquat is a dipyridylium compound. The formula and chemical nomenclature of the dichloride are given below.

A Guide to Neurotoxic Animal Models of Parkinson's Disease

“…A similar argument can be made in a rat model in which paraquat is injected weekly for 24 wks but only 30% reduction in dopamine is detected (Ossowska et al 2005). Given that paraquat is known to cause pulmonary toxicity (Clark et al 1966;Smith and Heath 1976;Cicchetti et al 2005;Saint-Pierre et al 2006), which could affect motor performance, it may be necessary to assess whether L-dopa can alleviate motor deficits induced by paraquat. As discussed, this strategy has been used in the MPTP and 6-OHDA animal models to confirm that the observed motor deficit is linked to the damage of the nigrostriatal pathway.…”

Responses of the Lung to Toxic Injury

“…Species differences in the response of lung to foreign chemicals are well known. For example, hamsters seem to be much more resistant to inhaled carcinogens and other toxic agents than are most other species (27,28), and BHT damages mouse lung only, but not the lungs of other species (14). It is, of course, possible that many such differences may be explained by the ways foreign chemicals are handled.…”

Autopsy findings in a case of acute paraquat poisoning with extensive cerebral purpura.

“…The morphological change of the brain was just compatible to cerebral purpura represented by various causes including embolization and toxic agents (Colmant and Naeve 1975;Strich 1976). Symptoms possibly reflecting the lesions of the central nervous system in man as well as in animals have been described, though not frequently, in the literature (Bullivant 1966;Clark et al 1966). But, as far as we know, the lesions pathologically documented are rare.…”