PHOSPHORUS AND LACTIC ACID METABOLISM IN THE HYPOTHERMICRAT

Further observations on the increase in blood levels of inorganic phosphorus and lactic acid in hypothermic rats are reported. Progressive increase in blood inorganic phosphorus levels with continued cooling to a rectal temperature of 5 °C appears to be a consequence of catabolism of organic, non-lipid phosphorus. With continued cooling, blood lactic acid is progressively increased; liver lactic acid increases initially, returning, at 5 °C, to control values; muscle lactic acid increases initially and thereafter remains relatively constant. Progressive increases in blood levels of inorganic phosphorus and lactic acid with continued cooling appear to be related to the depth, rather than duration, of hypothermia. Rewarming hypothermic (15 °C) rats to 37 °C rectal temperature with artificial ventilation reduces lactic acid levels of blood, liver, and muscle to less than control values. Rewarming alone was found to reduce blood lactic acid levels to less than control values. Elevation of blood lactic acid levels consequent upon hypothermia was prevented by provision of oxygen during cooling but not by pentobarbital anesthesia. These observations are consistent with the hypothesis that, in the hypothermic rat, the available oxygen is insufficient to meet even the reduced metabolic requirements.