Inhibition of shivering during restraint hypothermia.
Restraint hypothermia has often been described, but its cause has never been clarified. We hypothesized that it might be due to a suppression of shivering thermogenesis. Thus, we restrained conscious rats in an ambient temperature of 2 degrees C while measuring rectal (Tre) and tail skin temperatures, metabolic rate (MR), and shivering activity. When rats were cold exposed but not restrained, Tre fell 1.4 +/- 0.2 degrees C (SE) during the 1st h. When these same rats were restrained, Tre fell at a rate of 6.5 +/- 0.2 degrees C/h. MR averaged 15.7 +/- 1.4 W/kg for the unrestrained rats, but it averaged only 9.0 +/- 1.1 W/kg for the restrained rats. The restrained rats showed no signs of shivering. The animals were then subjected to a restraint adaptation regimen and then reexposed to cold. Restraint now produced a fall in Tre of only 2.6 +/- 0.7 degrees C/h. The animals shivered and generated an MR of 15.8 +/- 0.9 W/kg. Naive rats became hypothermic because restraint suppressed shivering activity. However, adapted rats continued to shiver and remained normothermic. We suggest that a stressful or threatening situation, such as restraint for a naive rat, inhibits shivering and leads to hypothermia in a cold environment. This would not occur in adapted rats because restraint is no longer stressful.
D000223:Adaptation, Psychological; D000818:Animals; D001831:Body Temperature; D003080:Cold Temperature; D004576:Electromyography; D006801:Humans; D007035:Hypothermia / Q000503:physiopathology*; D010101:Oxygen Consumption; D051381:Rats; D011919:Rats, Inbred Strains; D012149:Restraint, Physical; D012768:Shivering; D013315:Stress, Psychological / Q000503:physiopathology*