Changes in cyclic AMP and electrolytes after parathyroidectomy in primary hyperparathyroidism

Changes in the excretion of urinary cyclic AMP, calcium and phosphate, and serum calcium, ionized calcium, and magnesium were studied after parathyroidectomy for primary hyperparathyroidism. Urinary cyclic AMP decreased rapidly and 8 of 11 patients had a significant reduction 1 h postoperatively, but changes in serum calcium and ionized calcium were delayed. Serum calcium concentrations closely parallelled those of serum ionized calcium and phosphate excretion returned to normal almost 7 h later than that of cyclic AMP. Excretion of urinary calcium rose rapidly at 4 h after surgery because calcium clearance improved after the reduction in circulating parathyroid hormone. The fall in urinary calcium at about 24 h was due to the subsequent reduction in serum calcium.