Lack of a direct effect of 1,25-dihydroxycholecalciferol on parathyroid hormone secretion by normal bovine parathyroid glands.

Because of differing reports of an effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on parathyroid hormone (PTH) secretion, the present studies were performed in vitro using bovine parathyroid gland slices and isolated parathyroid cells. Both COOH-terminal and NH2-terminal RIAs for PTH were employed. No effect of 1,25(OH)2D3 on PTH secretion was found during a 4-h incubation of parathyroid slices in variable external calcium concentrations. The results from dual RIA measurements also showed no effect of 1,25(OH)2D3 on PTH secretion by isolated parathyroid cells during 90- to 150-min incubations with variable calcium concentrations. In addition, extensive analysis by polyacrylamide gel electrophoresis showed no effect of 1,25(OH)2D3 on cAMP generation. Whereas calcium inhibited and isoproterenol stimulated the production of cAMP, 1,25(OH)2D3 had no effect. We conclude that 1,25(OH)2D3 does not affect parathyroid gland function acutely in vitro.