Chlorpyrifos-induced hypothermia and vasodilation in the tail of the rat: Blockade by scopolamine

Abstract

Organophosphate pesticides such as chlorpyrifos reduce core temperature (T(c)) in laboratory rodents. The mechanism(s) responsible for the chlorpyrifos-induced hypothermia are not well known. This study assessed the role of a key effector for thermoregulation in the rat, vasomotor control of heat loss from the tail, and its possible cholinergic control during chlorpyrifos-induced hypothermia. T(c) and motor activity were monitored by telemetry in female Long-Evans rats maintained at an ambient temperature (T(a)) of 25°. Tail skin temperature (T(sk(t))) was measured hourly. Rats were dosed with chlorpyrifos (0 or 25 mg/kg orally). Two hr later the rats were dosed with saline or scopolamine (1.0 mg/kg intraperitoneally). Two hr after chlorpyrifos treatment there was a marked elevation in T(sk(t)) concomitant with a 0.5°reduction in T(c). Scopolamine administered to control rats led to a marked elevation in T(c) with little change in T(sk(t)). Rats treated with chlorpyrifos and administered scopolamine underwent a marked vasoconstriction and elevation in T(c). Vasodilation of the tail is an important thermoeffector to reduce T(c) during the acute stages of chlorpyrifos exposure. The blockade of the response by scopolamine suggests that the hypothermic and vasodilatory response to chlorpyrifos is mediated via a cholinergic muscarinic pathway in the CNS.