Acute effects of diisopropyl fluorophosphate (DFP) on autonomic and behavioral thermoregulatory responses in the Long-Evans rat.

Experiments were designed to assess the mechanisms of diisopropyl fluorophosphate (DFP)-induced changes in thermoregulation of the rat. In one study, male rats of the Long-Evans strain were injected with DFP (s.c.) at doses ranging from 0 to 2.0 mg/kg while maintained at an ambient temperature (Ta) of 20--24 degrees C. Body (Tb) and tail skin (Tt) temperatures were recorded for 5 h post-injection. DFP doses of greater than or equal to 1.0 mg/kg resulted in significant decreases in Tb lasting up to 5 h and increases in Tt lasting up to 1 h post-injection. In a second study, metabolic rate (MR), evaporative water loss (EWL), motor activity (MA), Tb, and Tt were measured at 2 h post-injection of 0, 0.5, 1.0, and 1.5 mg/kg DFP (s.c.) at Ta values of 10, 20, and 30 degrees C. DFP treatment resulted in hypothermia at all three Ta values, but the effect was attenuated at 30 degrees C. MR was significantly reduced at a Ta of 20 degrees C following 1.5 mg/kg, unaffected by DFP at a Ta of 30 degrees C, and stimulated at 10 degrees C following 0.5 mg/kg DFP. EWL was significantly elevated at 30 degrees C following 1.5 mg/kg DFP. MA was significantly reduced following greater than or equal to 1.0 mg/kg DFP at 20 and 30 degrees C and 1.5 mg/kg at 10 degrees C. Tt was elevated and reduced by DFP at Ta values of 30 and 10 degrees C, respectively. In a third study, rats were injected with DFP and placed in a temperature gradient for 1 to 2 h post-injection while selected Ta and Tb were monitored. While both control and DFP-treated rats remained in the cool end of the gradient, rats administered DFP at doses of 1.0 and 1.5 mg/kg were significantly hypothermic. It was also found that Ta values of 10, 20, and 30 degrees C had no effect on DFP-induced inhibition of cholinesterase activity of plasma and erythrocyte fractions of whole blood. Overall, these data support the hypothesis that acute DFP may lower the set-point for the control of body temperature in the rat and demonstrates that the toxicity of DFP is modified by changes in Ta.