Cj. Gordon et Yl. Yang, Chlorpyrifos-induced hypothermia and vasodilation in the tail of the rat: Blockade by scopolamine, PHARM TOX, 87(1), 2000, pp. 6-10
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 los
s from the tail, and its possible cholinergic control during chlorpyrifos-i
nduced hypothermia. T-c and motor activity were monitored by telemetry in f
emale Long-Evans rats maintained at an ambient temperature (T-a) of 25 degr
ees. Tail skin temperature (T-sk(t)) was measured hourly. Rats were dosed w
ith chlorpyrifos (0 or 25 mg/kg orally). Two hr later the rats were dosed w
ith saline or scopolamine (1.0 mg/kg intraperitoneally). Two hr after chlor
pyrifos treatment there was a marked elevation in T-sk(t) concomitant with
a 0.5 degrees reduction in T-c. Scopolamine administered to control rats le
d to a marked elevation in T-c with little change in T-sk(t). Rats treated
with chlorpyrifos and administered scopolamine underwent a marked vasoconst
riction and elevation in T-c. Vasodilation of the tail is an important ther
moeffector to reduce T-c during the acute stages of chlorpyrifos exposure.
The blockade of the response by scopolamine suggests that the hypothermic a
nd vasodilatory response to chlorpyrifos is mediated via a cholinergic musc
arinic pathway in the CNS.