Background: Primary hyperparathyroidism (pHPT) is associated with a defective regulation of the secretion of parathyroid hormone (PTH). Thus in pHPT, higher than normal calcium concentrations are required to inhibit PTH release. However, it is not known if this defective regulation is normalized by removal of the parathyroid adenoma (i.e., whether the regulation of PTH secretion is normal in the remaining glands). In this study we therefore investigated the PTH secretion in patients operated on for parathyroid adenoma 1 year after operation.
Methods: Na2 ethylenediamine tetraacetic acid and CaCI2 were infused at constant rates in six patients operated on for parathyroid adenoma and six healthy individuals. Serum levels of intact PTH and ionized calcium were determined during the infusions.
Results: No significant differences between the two groups were found in baseline levels of serum ionized calcium and PTH. Furthermore, no significant differences between patients and control subjects were found in the maximum serum PTH levels during the hypocalcemic infusion of ethylenediamine tetraacetic acid or in the minimum serum PTH levels during the calcium infusion. In contrast, the set point (the calcium concentration required for half-maximal inhibition of PTH secretion) was significantly lower in the patients (1.20 +/- 0.01 mmol/L) compared with control subjects (1.22 +/- 0.01 mmol/L; p < 0.05).
Conclusions: We conclude that the elevation of set point in patients with parathyroid adenoma is corrected by successful operation. This suggests a monoclonal origin of parathyroid adenomas.