Inhibition of thermoregulatory non-shivering thermogenesis by trauma in cold-acclimated rats.

1. Heat production and blood flow in the interscapular brown adipose tissue of 3 degrees C acclimated rats have been measured by the heated thermo-couple technique.2. When the environmental temperature (T(a)) was reduced from 30 to 3 degrees C heat production by the brown adipose tissue began to increase at the lower limit of the thermoneutral zone and then increased linearly.3. Blood flow also increased when T(a) was reduced but was not so well correlated with T(a). There was however a good positive correlation between blood flow and heat production.4. During the first hour after a 4 hr period of bilateral hind-limb ischaemia in a 20 degrees C environment the percentage of rats not producing heat in the interscapular brown adipose tissue increased and the tissue blood flow fell.5. By varying the T(a) of the injured rat it was found that the T(a) at which heat transfer from the interscapular brown adipose tissue commenced was significantly lower than in the controls although the slope of the regression lines relating heat production and T(a) was unaltered.6. Blood flow also increased in the injured rat when T(a) was lowered but the increase in the tissue blood flow per unit increase in heat production was less than in the controls.7. In a 5 degrees C environment heat production in the interscapular brown adipose tissue of the injured rat was further increased by the S. C. injection of L-isoprenaline or L-noradrenaline.8. It is concluded that the central control of thermoregulatory non-shivering thermogenesis is inhibited after injury in the rat.