Diazinon is an
organophosphate (OP)-based,
anticholinesterase insecticide that irreversibly inhibits
acetylcholinesterase activity and produces
cholinergic stimulation in central nervous system (CNS) and peripheral tissues. Our laboratory has found that OPs administered orally in rats induce a transient period of
hypothermia followed by a delayed
fever that persists for several days after exposure. There is little information on the thermoregulatory effects of
diazinon. Core temperature (Tc) and motor activity (MA) were monitored by radiotelemetry in male and female rats of the Long-Evans strain dosed orally with
diazinon (0 [
corn-oil vehicle], 100, 200, or 300 mg/kg in males and 0, 50, 100, or 200 mg/kg in females). There was a dose-dependent decrease in Tc during the first night
after treatment, with females exhibiting slightly greater sensitivity than males. MA was unaffected in females exposed to
diazinon at doses of 50 to 200 mg/kg; MA of males was reduced during the first night after dosing with 300 mg/kg. There was a delayed elevation in Tc of males dosed with 200 and 300 mg/kg and females dosed with 50, 100, and 200 mg/kg
diazinon. The elevated Tc was only manifested during d 2 and 3 after
diazinon. Administration of 200 mg/kg
sodium salicylate to females 48 h after being treated with 200 mg/kg
diazinon led to a rapid abatement of the
fever.
Diazinon doses of 50 to 300 mg/kg led to 40% to 50% inhibition in plasma
cholinesterase (ChE) activity 4 h after dosing, and females displayed a significantly slower recovery of ChE activity compared to males. When compared on a molar basis, the hypothermic response to
diazinon was relatively small compared to other OPs such as
chlorpyrifos. The delayed
fever and efficacy of
sodium salicylate to block
diazinon-induced
fever are similar to the effects of OPs
chlorpyrifos and diisopropyl fluoro-
phosphate (
DFP).