DIRECT INHIBITORY EFFECT OF AMINO-TERMINAL PARATHYROID-HORMONE FRAGMENT [PTH(1-34)] ON PTH SECRETION FROM BOVINE PARATHYROID PRIMARY CULTURED-CELLS INVITRO

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 Ca2+)-stimulated PTH secretion by these cells. In the presence of 1.25 mM Ca2+, 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 Ca2+) on PTH secretion. At 2.5 mM Ca2+, 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. © 1991.