Human temperature regulation during exercise after oral pyridostigmine administration

Four healthy males exercised in two experiments at ambient temperatures of 22, 29, and 36 degrees C with the relative humidity at 30% in all environments (Tdp = 3.9, 9.9, and 15.8 degrees C). One experiment in each environment was done 150 min after 30 mg oral pyridostigmine bromide (PYR) administration, and the second experiment was done on a separate day with no medication (CON). Red blood cell cholinesterase was 39 +/- 7% lower after PYR (11.8 vs 7.2 micromol.ml-1.min-1). Esophageal (Tes) and mean skin temperature (Tsk), forearm blood flow (FBF), forearm sweating, and skin blood flow (SkBF) were measured twice each minute during a 15-min rest period and during 30-min of seated cycle exercise at approximately 58% Vo2peak. Whole body sweating was determined from weight changes before and after exercise. PYR decreased heart rate at rest and during exercise at 29 degrees C and 36 degrees C (8bpm, p less than 0.05). Resting SkBF was 40% lower at 29 degrees C and 30% lower at 36 degrees C after PYR compared to CON (p less than 0.05). There was no effect of PYR on heat production at rest or during exercise. Tsk was different in the three conditions by design, but was unchanged by PYR. Tes was not different at rest in any condition, but was elevated during exercise at 36 degrees C (0.1 degree C, p less than 0.05) in PYR compared to CON. These data suggest that pyridostigmine ingestion decreased skin blood flow, which may limit exercise thermoregulation in more severe environments.