Calcium-dependent release of carboxyl-terminal fragments of parathyroid hormone by hyperplastic human parathyroid tissue in vitro.

The role of intracellular calcium in the secretion of fragments of PTH by human parathyroid tissue has not been examined previously. We used an in vitro perifusion system to study this phenomenon. Hyperplastic human parathyroid tissue, obtained at surgery from patients with chronic renal failure, was sliced into small pieces, placed in perifusion chambers, and exposed to low (0.5 mM) or high (2.0 mM) calcium concentrations. PTH secreted into the perifusion medium was analyzed by gel exclusion chromatography and RIA using a carboxyl-terminal antiserum. Under high calcium conditions, proportionally more carboxyl-terminal fragments of PTH (65.3%) were released by the perifused tissue than intact PTH (34.7%). When perifused with low calcium medium, the tissue released more intact PTH (55.0%) than carboxyl-terminal fragments (45.0%). These studies are consistent with the suggestion that calcium-dependent intracellular degradation of PTH plays an important role in the regulation of hormone secretion.