Hyperphosphatemia Accelerates Parathy tion and Parathyroid Hormone Secretion Secondary Parathyroid Hyperplasia roid Cell Proli in Severe fera-

We studied the role of phosphorus retention in parathyroid cell proliferation and parathyroid hormone (PTH) oversecretion in severe secondary parathyroid hyperplasia. Mice transplanted with human parathyroid tissue from a patient who had undergone parathyroidectomy for severe secondary hyperparathyroidism were divided into four groups; each group was given a diet with a different phosphorus content (0.4, 0.7, 1.0, and 1.2%) to alter serum phosphorus concentrations. Histologic examinations of grafts by hematoxylin-eosin or by bromodeoxyuridine (BrdU) immunohistochemical staining were performed to assess parathyroid cell proliferation. Changes in serum phosphorus concentrations unidirectionally affected PTH secretion from the graft, because human PTH did not cross-react with mouse PTH. Serum phosphorus concentrations of 1.OP and 1.2P groups were significantly higher than those of 0.4P and 0.7P groups (p<0.05). Serum phosphorus concentrations were significantly correlated with the gradient of human PTH elevation with a coefficient of 0.48 and a p<0.05. Furthermore, serum phosphorus concentrations and the gradient of human PTH elevation were significantly higher in mice with BrdU-immunoreactive cells in the parathyroid graft than in mice without immunoreactive cells in the graft. These results indicate that uncontrolled hyperphosphatemia may accelerate the proliferation of parathyroid cells, exacerbating PTH oversecretion.