Direct inhibitory effect of amino-terminal parathyroid hormone fragment [PTH(1–34)] on PTH secretion from bovine parathyroid primary cultured cells [formula omitted

Abstract

We have examined the possibility of direct inhibitory effect of PTH(1–34) on PTH secretion in bovine parathyroid cells. As low as 10 −12 M PTH(1–34) completely inhibited low calcium(0.5 mM Ca 2+)-stimulated PTH secretion by these cells. In the presence of 1.25 mM Ca 2+, 10 −12 M PTH (1–34) inhibited PTH secretion by about 14.3% of the basal value, while 10 −11 M or higher concentration of PTH(1–34) showed potent inhibitory effects equivalent to the inhibitory action of high calcium concentration (2.5 mM Ca 2+) on PTH secretion. At 2.5 mM Ca 2+, as much as 10 −9 M PTH(1–34) failed to inhibit PTH secretion further. These results suggest that PTH(1–34) might directly, not via calcium concentration, inhibit PTH secretion by parathyroid cells and that a cooperative mechanism could exist between calcium and PTH(1–34) to inhibit PTH secretion.