Parathyroid gland function in secondary hyperparathyroidism.

The parathyroid glands play a critical role in the maintenance of calcium homeostasis. It has been suggested that the set-point for calcium-regulated parathyroid hormone (PTH) release is higher in uremic patients than normal subjects. However, these assessments of parathyroid gland function have been performed using methods that differed from the original four-parameter model. Dynamic testing of the parathyroid glands has been performed with standardized infusions of calcium gluconate and sodium citrate in dialysis patients with secondary hyperparathyroidism and in normal volunteers. In addition, similar studies have been carried out before and after 4 months of intermittent calcitriol therapy. The derived values for the set-point were 1.21 + 0.04 mmol/l and 1.24 + 0.06 mmol/l, respectively in control and dialyzed patients (NS). Furthermore, the values for set-point were 1.21 + 0.01 and 1.22 + 0.01 mmol/l (NS), before and after calcitriol therapy. In addition, when subjects were grouped according to the severity of secondary hyperparathyroidism, the set-point calcium-regulated PTH release did not differ between the groups. Calcitriol therapy alters the secretory capacity of the parathyroid glands during hypocalcemia. The degree of parathyroid enlargement and the type of cell proliferation may be more important determinants of the severity of secondary hyperparathyroidism.