Effect of pyridostigmine on the exercise-heat response of man

The effect of pyridostigmine on thermoregulatory responses was evaluated during exercise and heat stress. Eight heat acclimated, young adult male subjects received four doses of pyridostigmine (30 mg) or identical placebo tablets every 8 h, in a double blind, randomized, cross-over trial. A 30.3%, SD 4.6% inhibition of the circulating cholinesterase (ChE) activity was induced in the pyridostigmine-treated group. The subjects were exposed to 170-min exercise and heat-stress (dry bulb temperature, 33° C; relative humidity 60%) consisting of 60 min in a sitting position and two bouts of 50-min walking (1.39 m · s^-1, 5% gradient) which were separated by 10-min rest periods. No differences were found between treatments in the physiological responses and heat balance parameters at the end of exposure: heart rate (f_c) was 141 beats · min^-1, SD 16 and 150 beats · min^-1, SD 12, rectal temperature (T_re) was 38.5°C, SD 0.4° and 38.6°C, SD 0.3°, heat storage was 60 W · m^-2, SD 16 and 59 W · m^-2, SD 15 and sweat rate was 678 g · h^-1, SD 184 and 661 g · h^-1, SD 133, in the pyridostigmine and placebo treatments, respectively. The changes in T_re and f_c over the heat-exercise period were parallel in both study and control groups. Pyridostigmine caused a slight slowing of f_c (5 beats·min^-1) which was consistent throughout the entire exposure (P<0.001) but was of no clinical significance. The overall change in f_c was similar for both groups. We have concluded that pyridostigmine administration, in a dose sufficient to induce a moderate degree of ChE inhibition, does not significantly affect performance of exercise in the heat.