Journal of Applied Physiology, Vol 71, Issue 2 432-437, Copyright © 1991 by American Physiological Society
Effects of pyridostigmine bromide on human thermoregulation during cold water immersion
W. K. Prusaczyk and M. N. Sawka
US Army Research Institute of Environmental Medicine, Natick, Massachusetts 10760-5007.
This study examined the effects of an oral 30-mg dose of pyridostigmine
bromide (PYR) on thermoregulatory and physiological responses of men
undergoing cold stress. Six men were immersed in cold water (20 degrees C)
for up to 180 min on two occasions, once each 2 h after ingestion of PYR
and 2 h after ingestion of a placebo. With PRY, erythrocyte cholinesterase
inhibition was 33 +/- 12% (SD) 110 min postingestion (10 min preimmersion)
and 30 +/- 7% at termination of exposure (mean 117 min). Percent
cholinesterase inhibition was significantly related to lean body mass (r =
-0.91, P less than 0.01). Abdominal discomfort caused termination in three
of six PYR experiments but in none of the control experiments (mean
exposure time 142 min). During immersion, metabolic rate, ventilatory
volume, and respiratory rate increased significantly (P less than 0.05)
over preimmersion levels and metabolic rate increased with duration of
immersion (P less than 0.01) in both treatment but did not differ between
conditions. PYR had no significant effect on rectal temperature, mean body
temperature, thermal sensations, heart rate, plasma cortisol, or change in
plasma volume. It was concluded that a 30-mg dose of PYR does not increase
an individual's susceptibility to hypothermia during cold water immersion;
however, in combination with cold stress, PYR may result in marked
abdominal cramping and limit cold tolerance.
