Effects of acute metabolic acidosis on parathyroid hormone action and calcium mobilization

Mechanisms through which metabolic acidosis increases calcium mobilization have been investigated in thyroparathyroidectomized rats with induction of acute metabolic acidosis by infusing NH4C1 intravenously. Acute metabolic acidosis directly raised serum calcium concentration and augmented the effect of parathyroid hormone (PTH) to raise serum calcium concentration. The same effects of metabolic acidosis were observed in rats with surgically removed intestines and bilateral nephrectomy, suggesting that acute metabolic acidosis directly increases calcium mobilization from bone and augments the effect of PTH to mobilize calcium from bone. In the kidney, acidosis directly inhibited the tubular reabsorption of calcium, but augmented the effect of PTH to increase tubular reabsorption of calcium. Acidosis had no measurable effect on calcitonin action.