Studies on the mechanism of shock. The effect of cocaine and theophylline on the temperature response to injury in the cold-acclimated rat.

The effects of cocaine and theophylline on the changes in core temperature, O2 consumption and the rate of heat loss from the tail were studied in 20° and 3° acclimated rats during and after a 4-hr. period of bilateral hindlimb ischaemia at an environmental temperature of 20°. Cocaine (7 mg. base per kg. body wt. intravenously) had no effect on injured 20° acclimated rats but increased the core temperature in both injured and uninjured 3° acclimated ones. The changes in O2 consumption were unaffected and heat loss from the tail decreased. Cocaine acted mainly by increasing peripheral vasoconstriction and so decreasing heat loss. Theophylline (90 mg. per kg. body wt. intraperitoneally), given 1 hr. before removal of the tourniquets, depressed the core temperature in 20° acclimated rats but increased it in 3° acclimated ones. Theophylline increased heat production in 3° acclimated rats, raising O2 consumption and causing a maximal increase in heat loss from the tail. Whereas this increased heat loss could prevent a rise in the temperature of the uninjured it was insufficient to do so in the injured. Since previous work has shown that limb ischaemia causes a similar increase in adrenaline and noradrenaline secretion in 20° and 3° acclimated rats these results support the view that the difference between the responses to trauma in these 2 types of rat is due to the greater sensitivity of cold-acclimated rats to catecholamines.