Calcium-sensing receptor and apoptosis in parathyroid hyperplasia of patients with secondary hyperparathyroidism.

Objective: This retrospective study investigated the characteristics of secondary hyperparathyroidism (SHPT) by examining the presence of the calcium-sensing receptor (CaSR) and the rate of cell proliferation and apoptosis in parathyroid glands. Methods: Eighteen diffuse and 57 nodular hyperplastic parathyroid glands from 24 patients with SHPT were compared with 14 primary adenomas and 33 normal parathyroid glands using immunohistochemical staining of CaSR and a marker of proliferative activity (Ki67 antigen). Apoptosis was measured using the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling assay. Results: The mean +/- SE labelling index (LI) of CaSR (12.8% +/- 1.5%) in nodular hyperplasia was significantly lower than that in normal parathyroid glands (26.8% +/- 0.8%), whereas the mean +/- SE LI of CaSR in diffuse hyperplasia was similar to that in normal parathyroid glands (23.3% +/- 1.8%). The mean +/- SE LI of Ki67 antigen was significantly higher in primary adenoma and nodular hyperplasia than in normal parathyroid glands. Conclusion: These results indicate that downregulation of CaSR, and a higher rate of proliferation over apoptosis, could contribute to the pathological progression of SHPT.