Inhibition of shivering during restraint hypothermia

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Abstract
Restraint hypothermia has often been described, but it cause has never been clarified. This might be due to a suppression of shivering thermogenesis. Conscious rats were therefore restrained in an ambient temperature of 2.degree. 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.degree. C (SE) during the 1st h. When these same rats were restrained, Tre fell at a rate of 6.5 .+-. 0.2.degree. 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.degree. C/h. The animals shivered and generated on MR of 15.8 .+-. 0.9 W/kg. Naive rats became hypothermic because restraint suppressed shivering activity. Adapted rats continued to shiver and remained normothermic. A stressful or threatening situation, such as restraint for a naive rat, apparently inhibits shivering and leads to hypothermia in a cold environment. This could not occur in adapted rats because restraint is no longer stressful.

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