Nonshivering thermogenesis induced by repetitive cooling of spinal cord in the rat.

The effect of prolonged and repetitive cooling of the spinal cord on the sensitivity to the metabolic effect of exogenous noradrenaline and on the resistance to cold exposure was studied in the white male rat. The spinal cord of 10 animals was cooled for an average of 90 h-9 h/day 5 days/wk - to a level that induced an increase in oxygen uptake of almost 70%. Oxygen consumption was then measured at 30 degrees C before and 1 h after a subcutaneous injection of noradrenaline (0.4 mg/kg). Following the noradrenaline injection, the experimental animals increased oxygen uptake by 71%, while the control ones increased it by only 33% (P less than 0.01). During exposure to -20 degrees C, the experimental animals, despite their increased capacity for nonshivering thermogenesis, did not maintain rectal temperature longer than the control ones, thus showing that other factors also play a significant role in cold adaptation in the rat.