The contrasting actions of two pyrethroids (deltamethrin and cismethrin) in the rat.

Deltamethrin and cismethrin are representative members of the two classes of pyrethroid insecticide which can be distinguished on the basis of the symptoms which they produce in mammals. This paper reviews the relevant literature together with some new findings. The motor symptoms produced by the deltamethrin class are a complex but distinctive sequence of co-ordinated movements which are accompanied by EEG spiking, increased brain blood flow, increased brain glucose utilization in some regions, salivation, hyperglycaemia and, in vitro, increased cardiac contractility. The cismethrin class produces a different pattern of uncoordinated tremor accompanied by increased brain blood flow and regional glucose utilization, but without EEG spiking, salivation, hyperglycaemia or cardiac actions. Both compounds produce regional dissociations between brain blood flow and glucose utilization. It is concluded that most of these actions are attributable to prolongation of membrane sodium currents, and that the more widespread actions of deltamethrin are due to the much greater sodium current prolongation which it produces.