ANTICHOLINESTERASE ADMINISTRATION DURING ACUTE ALTITUDE EXPOSURE

1. Red blood cell cholinesterase activity was decreased an average of -31 +/- 9%, -41 +/- 8%, -35 +/- 7% and -41 +/- 13% after 2, 26, 50 and 74 h of pyridostigmine treatment (30 mg, t.i.d.). 2. Pyridostigmine d ecreased resting heart rate at sea level (SL) by 7 +/- 10 b.min-1 afte r 74 h (P < 0.05). Resting esophageal temperature (T(es)) was -0.28 +/ - 0.16-degrees-C at 10,000 ft and -0.10 +/- 0.22-degrees-C after 74 h (SL) compared to SL control; and was +0.20 +/- 0.10-degrees-C after 2 h and +0.20 +/- 0.13-degrees-C after 26 h at 10,000 ft compared to alt itude control (P < 0.05). 3. The thermosensitivity of forearm sweating to increasing T(es) was 26 +/- 3% lower at altitude compared to sea l evel (P < 0.05). This depression in thermosensitivity was not observed at altitude with pyridostigmine. The T(es) threshold for onset of for earm sweating was increased 0.2-degrees-C after 26 h of pyridostigmine compared to control altitude experiments (P < 0.05). 4. The depressin g effect of acute hypobaric hypoxia on thermosensitivity of sweating w as confirmed by this study. Pyridostigmine administration did not affe ct skin blood flow responses during acute altitude exposure.