Cold sensitivity in the spinal cord of sheep.

Abstract

1. Five clipped sheep with spinal thermodes, exposed to an air temperature of 20°C, had a resting oxygen consumption\((\dot V{\text{O}}_{\text{2}} )\) of 5.9 ml/kg body weight · minute and a respiratory quotient (RQ) of 0.87. Cooling the spinal cord for 15 min from a mean temperature of 38.6°C down to 34.8°C caused\(\dot V{\text{O}}_{\text{2}} \) to rise to 7.6 ml/kg · min (P<0.02) and RQ to fall to 0.83 (P<0.001). More intense cooling of the spinal cord to 32.6°C caused\(\dot V{\text{O}}_{\text{2}} \) to increase to 9.6 ml/kg · min (P<0.01) while RQ fell to 0.80 (P<0.01). During spinal cooling the animals shivered. During the more intense spinal cooling, rectal temperature increased from 38.8°C to 39.2°C (P<0.02). 2. Cooling the spinal cord to 32.6°C caused plasma free fatty acid (FFA) concentration to increase from a control value of 16.2 mg/100 ml to 22.7 mg/100 ml (P<0.01). This increase in plasma FFA was completely abolished by prior administration of a sympathetic blocking drug. 3. These results show that the spinal cord of sheep is cold sensitive and that there is an increase in plasma FFA during spinal cooling, which is mediated via the sympathetic nervous system.