Aim: To determine the effect of soman on stress induced hyperthermia and the influence of central and peripheral cholinergic antagonists.
Methods: Effects of subcutaneous injection of soman, scopolamine, methylscopolamine and pyridostigmine on stress-induced hyperthermia were observed in rats by radio telemetry in an open-field environment. Plasma cholinesterase (ChE) activity was measured by a spectrophotometry.
Results: (1) Core temperature of the control group increased by 0.96 degrees C when exposed to open-field, whereas core temperature only increased by 0.55 degrees C in soman treated animals. Scopolamine, a central cholinergic antagonist, nearly abolished inhibitory effects of soman on core temperature when exposed to open-field. Methylscopolamine, a peripheral cholinergic antagonist, coadministered with soman reduced significantly the hyperthermic response to open-field exposure compared with rats dosed with soman. (2) Pyridostigmine, a peripheral anti-ChE agent that caused a 52% decrease in plasma ChE activity led to a significant enhancement of the hyperthermic response to open-field exposure. Methyl scopolamine nearly abolished the effects of pyridostigmine on stress-induced hyperthermia response.
Conclusion: Inhibitory effect of soman on the open field hyperthermia suggested that soman treatment hampered the ability of the rat to develop a normal hyperthermic response when placed in the open-field environment. Its inhibitory effects were mediated primarily through a central muscarinic pathway. In addition, peripheral cholinergic nerve was involved in the control of stress hyperthermic response.