The effect of chronic metabolic acidosis on the end organ responsiveness to parathyroid hormone in man.

To examine the effect of prolonged metabolic acidosis on the responsiveness of end organs to PTH, we measured the changes in serum ionized calcium and the urinary excretion of calcium and phosphorus in response to a 10-h infusion of parathyroid extract (PTE) before and after 9 days of metabolic acidosis. During the first hours of PTE infusion, the increases in ionized calcium were slower during acidosis, but the maximal increments in ionized calcium (0.5 +/- 0.1 and 0.4 +/- 0.1 mg/dl, respectively) were not different. Moreover, the PTE-induced increments in the fractional excretion of phosphate during acidosis and the control study were not different. Fractional excretion of calcium before the infusion of PTE was higher in acidosis than in control (3.7 +/- 0.3% compared to 0.8 +/- 0.3%; P less than 0.01). However, at 10 h of the infusion, when the maximal effect of PTE was observed, the fractional excretions of calcium in control and acidosis were not significantly different. These data suggest that prolonged metabolic acidosis has little or no effect on bone or renal responsiveness to PTH.