Rapid suppression of S-PTH by oral calcitriol and calcium in healthy premenopausal women

The influence of oral calcium +/- cholecalciferol or calcitriol on S-PTH an d whole blood ionized calcium (B-Ca++) in the very short term has not been elucidated. B-Ca++ and S-PTH were measured after overnight fast every 5 or 15 min for 4-h in 7 healthy premenopausal women (30-45 years) in a crossove r design where the subjects were studied on 4 different days. Study 1: (con trol), 125-ml tap water (also given in studies 2-4); study 2: 1000 mg calci um, as calcium carbonate, study 3: 1000 mg calcium and 400 IU (5 mug) chole calciferol; and study 4: 0.5 mug calcitriol plus 1000mg calcium. Calcium pl us 1,25(OH)(2) vitamin D-3 induced a rapid and significant fall in S-PTH co mpared to the control period (p<0.02). Calcium alone or calcium plus cholec alciferol did not change the PTH levels significantly compared to control ( water). B-Ca++ increased significantly after calcium plus 1,25(OH)2 vitamin D-3 (p<0.01) and calcium plus cholecalciferol (p<0.05) compared to the con trol period. The B-Ca++ elevation was significantly higher after calcium pl us 1,25 vitamin D-3 than after calcium plus cholecalciferol (p<0.05). In co nclusion, oral calcitriol plus calcium causes a rapid elevation in B-Ca++ a nd suppression of the PTH secretion also in. the short term (hours).