The Influence of Temperature on Toxicity

Our understanding of the effects of temperature on toxic response has seen resurgence in the past several decades, with the development of better methods to study the integration of autonomic and behavioural thermoregulatory responses in rodents and other species. Radiotelemetry provides researchers with the best tool to study the thermoregulatory responses in undisturbed rodents exposed chronically or acutely to toxic chemicals. The thermoregulatory response to acute exposure to many toxic chemicals involves a regulated hypothermic response, characterized by an increase in autonomic thermoeffectors to increase heat loss and a behavioural preference for cooler temperatures. This thermoeffector response is quickly manifested by a marked drop in the core temperature in rodents. However, in humans and other large mammals, the hypothermic response is meagre due to their large thermal inertia. A combination of exposure to cool temperatures and a moderate hypothermic response has been found to benefit survival with a variety of toxic agents. Thus, the integrated thermoregulatory response of rodents to lower their core temperature seems to be an adaptive response. On the other hand, fever or hyperthermia is often seen in humans and other large mammals exposed to various toxicants. A fever is also seen in rodents provided that core temperature is monitored without disturbing the animal (e.g. telemetry). The universal effects of temperature on chemical toxicity calls for researchers to have a better understanding of the thermoregulatory effects of environmental toxicants. Keywords: thermoregulation; autonomic; behavioural; radiotelemetry; thermal stress; organophosphate insecticides; fever