The acid-base balance during the time course of endotoxin fever and sodium salicylate antipyresis in the rabbit.

Blood acid-base balance in sodium salicylate antipyresis was investigated in adult rabbits at ambient temperature of 21.5 +/- 0.5 degrees C. The experimental fever elicited by iv injection of lipopolysaccharide Escherichia coli 1 microgram/kg/ was accompanied by a slight metabolic acidosis. A decrease in pH by 0.09 and HCO3- by 4.8 mEq/1 was noticed during the rising phase of pyrogen fever. There were no concomitant changes in blood PCO2 during that period of time. Although the concentrations of HCO3- were decreasing till the end of the experiment, the parallel falls in PCO2 led to a partial compensation of the noticed acidosis. Pretreatment with 200 mg/kg of sodium salicylate /an hour's iv infusion/reduced the febrile response by 42% and completely reversed the postpyrogen changes in pH and HCO3-. The falls in PCO2 during antipyresis, however, were similar to those observed in febrile rabbits. Possible mechanisms by which sodium salicylate could affect the pyrogen-induced disturbances of acid-base balance are being considered.