Effects of hypothermia on thyrotropin-releasing hormone content in the rat brain.

The thyrotropin-releasing hormone (TRH) content in the brain was determined in normothermic and hypothermic rats subjected to immobilization stress. TRH contents in the hypothalamus, midbrain and cerebral cortex significantly decreased during mild hypothermia (body temperature about 34 degrees C), but not during profound hypothermia (about 24 degrees C). The decreases in the TRH content during mild hypothermia were readily reversed by rewarming the animal. These results indicate that cerebral TRH is involved in the response to a mild body temperature drop when the animal is exposed to a cold environment.