Heat-stressed rat: effects of atropine, desalivation, or restraint

Heat-stressed rats thermoregulate behaviorally by spreading saliva onto body surfaces and thus lose body water through evaporative cooling. Prior to exploring the role of dehydration in our rat heatstroke model, we sought to compare the abilities of physical restraint, surgical desalivation, and/or atropine to increase the rate of body heat storage by inhibiting body water loss and evaporative cooling during heat exposure. In these experiments, male Sprague-Dawley rats were stressed at an ambient temperature of 41.5 degrees C either in their own cages or in a restraining device until a rectal temperature of 42.6 degrees C was attained. Unrestrained control rats heat-stressed at this temperature lost approximately 8% of body weight (water) during a 258-min exposure. Physical restraint or desalivation reduced both the exposure time and body weight loss by about 72%. Surgically desalivated, heat-stressed rats were observed to engage in voluntary urine-spreading behavior. Maximal heat storage and therefore maximal reduction in exposure time and inhibition of body weight loss to less than 10% of control values were achieved by either physical restraint plus desalivation or by a 500-micrograms dose of atropine.