Significance of early increase in stable and radioactive plasma calcium after parathyroidectomy in primary hyperparathyroidism.

Early effects of parathyroid hormone (PTH) deficiency were studied in 12 patients with primary hyperparathyroidism due to single parathyroid adenoma by following the precise time course of changes in plasma calcium (Ca) and immunoreactive parathyroid hormone (IPTH) after parathyroid surgery and by prelabeling 2 patients with radiocalcium (Ca*). Surgical removal of the adenoma was immediately followed by a sudden increase in plasma Ca which preceded the usual fall. The increase in plasma Ca commenced simultaneously with the fall in iPTH and was accompanied by a parallel increase in specific activity (sp. act.) of plasma Ca*. Specific activity continued to rise for 2 h in both prelabeled patients, whereas blood calcium was already falling thereafter reaching a markedly low removal rate constant as long as plasma Ca decreased. When plasma Ca began to rise, sp. act. resumed a descending course. Our findings indicate that the initial hypercalemia depends on PTH withdrawal and results from a rapid flux into general extracellular fluid (ECF) of calcium coming from a compartment with higher sp. act., contained within the miscible pool, immediately followed by a reduction in calcium transfer from bone. These results suggest that acute PTH deficiency determines an outflow of calcium from bone cells and support the theory that PTH initiates its action by modifying their intracellular calcium content.