This site presents research into interactions between pyrethroids in vivo, and combines it with a diverse range of additional information from around the topic, giving the reader a fuller idea of this research's relevence and implications.
Pyrethroid insecticides are used extensively across the globe for pest control, in applications ranging from fly-sprays to agriculture. These chemicals are less toxic to mammals than some other insecticides; however cases of poisoning do still occur. Prolonged exposure to these agents may also cause subtle accumulative toxic effects, especially in the young. Thus, there is considerable interest in elucidating the acute and chronic mechanisms of toxicity in mammals, so that informed decisions can made about how to protect those exposed to pyrethroids.
Recently it has come to light that different pyrethroids may interact within an organism in a competitive manner, rather than an additive one as might be expected. Key experiments using isolated sodium channels and neurons showed a competitive interaction between different pyrethroid compounds [Song et al., 1996; Motomura et al,. 2001]. The compounds were type I and type II pyrethroids (tetramethrin and fenvalerate/deltamethrin, respectively) and the competition seemed to favour Type I effects over Type II, suggesting a distinction between the classes.
Knowing whether this competitive interaction occurs in vivo, and at realistic dose ranges, is of vital importance. For instance if a person had received sub-toxic doses of three pyrethroids, if their effects were additive the results could be fatal, whereas if they act competitively it could leave them unharmed. In either case, understanding the nature of interactions between pyrethroids, particularly those compounds most used industrially and domestically, is needed to guide those who use and produce these agents.
We tested the hypothesis - that Type I and Type II pyrethroids interact competitively - using an in vivo model and two common insecticides. An established experimental model was used to assess the effects pyrethroids were exerting, called Paired-pulse inhibition [Joy et al, 1989]. This model uses electrical recordings and stimulations in the rat hippocampus, and can distinguish between the effects of different pyrethroids. If the hypothesis proves correct it might be extended to see whether Type I and Type II pyrethroids specifically compete with each other (as seems to be the case), or whether it is a more general phenomenon throughout the range of compounds.
