[Effect of calcium on N-terminal truncation of PTH in human parathyroid cells]

Serum PTH (7-84) is accumulated in patients with secondary hyperparathyroidism. It is also known that serum calcium (Ca) increases the generation of N-terminally truncated forms of parathyroid hormone (PTH). In this study, we examined whether accumulation of PTH (7-84) fraction is a parathyroid glandular origin or not by using primary cultured parathyroid cells from patients with primary and secondary hyperparathyroidism. The Bio-PTH/I-PTH ratio, indicating the ratio of PTH (1-84) to the sum of (1-84) PTH and N-terminally truncated fragment, was suppressed by increase in extracellular Ca2+ concentration for both cultured parathyroid cells prepared from parathyroid adenomas and uremia-associated secondary hyperparathyroidism. There is no difference between the ratios in primary and secondary hyperparathyroidism. These findings suggest that N-terminal truncation is regulated by extracellular Ca2+ concentration in parathyroid cells, but accumulation of PTH (7-84) fragments in patients with secondary hyperparathyroidism is mainly caused by uremia.