Effects of pyridostigmine on ability of rats to work in the heat.

Adult, male rats (300-325 g) were treated with pyridostigmine bromide (n = 22) or saline (n = 22) to quantitate the effects of cholinesterase inhibition (64%) on the ability to work (9.14 m/min, level treadmill) in the heat (35 degrees C). Pyridostigmine-treated rats had a mean endurance of 23 min, whereas saline-treated animals ran for nearly 35 min (P less than 0.001). Rates of rectal and skin temperature increments were significantly higher (P less than 0.001) in pyridostigmine-treated rats as were water losses (P less than 0.001). Exercise in the heat to hyperthermic exhaustion effected anticipated increments in circulating urea nitrogen, creatinine, lactate dehydrogenase, and potassium levels, whereas pyridostigmine pretreatment had additive effects on lactate and creatine kinase concentrations. Additionally, pyridostigmine elicited a significant (P less than 0.01) hyperglycemia before exercise, an effect noted also with other organophosphate simulants. We concluded that pyridostigmine-induced cholinesterase inhibition had a variety of debilitating effects during work in the heat.