Effects of time of day on chlorpyrifos-induced alterations in body temperature

Chlorpyrifos (CPF) is an organophosphate (OP) insecticide and is among the most common and widely used commercial insecticides. Human intoxication is reported to result in a typical set of responses, which include an immediat e and long lasting hyperthermic response (fever). Rodents exposed to simila r doses exhibit a biphasic body temperature response: short-term hypothermi a followed by subtle hyperthermia several days after administration. Time o f day of administration has been suggested to alter the body temperature ef fect of CPE In the present study, it is shown that adult male Sprague-Dawle y rats exposed to CPF via (oral) gavage at four different times of the day demonstrate a hypothermic response, the timing and magnitude of which is in dependent of time of exposure and that is blocked by atropine pretreatment. However, a delayed (hyperthermic) response seems to be exhibited only when dosing occurs during the light phase. Our findings support existing theori es that the hypothermic and hyperthermic effects of CPF work through indepe ndent mechanisms. It is also suggested that humans may indeed exhibit a bip hasic temperature response to CPF intoxication, but that it is not typicall y detected. (C) 2000 Elsevier Science Inc. All rights reserved.