Difference in the mode of acute cold-induced hypothermia between rat and hamster.

The present work was undertaken to elucidate the underlying causative factors limiting survival in hypothermic rats (non-hibernator) and hamsters (hibernator). A variety of physiological and biochemical parameters were measured for 28 male Wistar rats (205-286 g) and 26 male golden hamsters (85-118 g) before and during induction of hypothermia to colonic temperature (Tco) of 18 degrees C. With progressive decreases in Tco, parallel falls in VO2, VCO2, and heart rate were observed. In rats, plasma pH (pHp) in arterial blood was significantly lowered from 7.453 at Tco of 38 degrees C to 7.327 at Tco of 18 degrees C (p less than 0.001). From the observations of increased arterial PCO2 and bound CO2 (bicarbonate ion) concentration, together with the unchanged blood lactate, respiratory acidosis caused by hypoventilation was suggested to be responsible for the decrease in pHp. In contrast to rats, in hamsters pHp was almost unchanged during the induction of hypothermia, while nearly complete depletion of blood glucose (-84.6%) and liver glycogen (-99.5%) were observed when Tco of 38 degrees C was lowered to 18 degrees C. It is concluded that the decrease in pHp is a limiting factor for rats to survive the deep hypothermia at Tco of 18 degrees C and the exhaustion of carbohydrates as an energy supply for hamsters.