Decreases in the sodium content of bone were measured to evaluate the role of this tissue in the buffering of acute metabolic acidosis. The bones of rats and dogs were labeled with radiosodium prior to the infusion of HCl, and changes in the radioactivity were used to indicate the loss of bone sodium. Significant reductions in the skeletal sodium occurred within the first 5 h of acidosis, and these losses can only be partially attributed to the hyponatremia accompanying the acid infusion. Decreases were greatest in the smaller bones of the rat; and, in the dog, the losses from flat bones exceeded those of the long bones. Only the rapidly exchangeable sodium of bone was involved in the changes due to acidosis. Soft tissue buffering may be more important initially; during 1.5-h experiments, the skeletal losses were small and could be ascribed almost entirely to the decrease in the amount of sodium contained in bone water. However, at the end of 5.0 h, the quantity of sodium released from the skeleton is sufficient to account for much of the tissue buffering.
