Restoration of vital activity of cooled animals without rewarming the body

The fatality of deep hypothermia in non-hibernating mammals follows the cessation of respiration and heart beat, and a massive influx of calcium (Ca(++)) into cells. This review presents evidence relating to restoration of key physiological functions during hypothermia in several animal preparations. For example, in anaesthetized hypothermic rats (body temperature 16-17 degrees C), a pharmacologically induced reduction in intracellular [Ca(++)] [via intravenous administration of an ethylenediaminetatraacetate (EDTA) solution (0.15-0.16 mmole)] has been shown to restore cold shivering and respiration after several minutes. Also, activity in an isolated rat heart preparation has been shown to be halted when temperature is reduced in the range 14-12 degrees C. However, decreasing the perfusate [potassium] by a factor of 2-3 relative to normal blood levels restored contractile activity. In conclusion, it is possible to restore the activity of key physiological systems involved in the thermoregulatory responses to sustained hypothermia without the need to rewarm the organism.