Regulation by calcium and 1,25‐(OH) 2 D 3 of cell proliferation and function of bovine parathyroid cells in culture

The effects of high calcium and 1,25‐(OH) 2 D 3 on parathyroid cell growth, PTH secretion, and steady‐state levels of pre‐proPTH mRNA in proliferating bovine parathyroid cells were examined. Cells were established in primary tissue culture and then tested in passages 2 and 5. Cell proliferation was suppressed by 10 −9 ‐10 −7 M 1,25‐(OH) 2 D 3 but not by high calcium (2.5 mM). Cells at passages 2 and 5 were grown to subconfluence and then exposed for 72 h to 2.5 mM calcium or 10 −7 M 1,25‐(OH) 2 D 3 . Pre‐proPTH mRNA was decreased to approximately 50% of control by 2.5 mM calcium compared with 0.3 and 1.0 mM calcium. PTH secretion, as tested by low calcium stimulation for 1 h at the end of 72 h incubation, was inhibited by 50% in cells that had been exposed to high calcium compared with control. Incubation with 10 −7 M 1,25‐(OH) 2 D 3 caused a decrease in the levels of pre‐proPTH mRNA and PTH release to 50% of control at 72 h. These results suggest that cultured bovine parathyroid cells, at least in early passages, have responses to high calcium and l,25‐(OH) 2 D 3 similar to those in primary nonproliferating cultures studied earlier and that 1,25‐(OH) 2 D 3 inhibits the proliferation of parathyroid cells in a dose‐responsive fashion.