Intravenous 1,25(OH)2 Vitamin D3 Therapy in Haemodialysis Patients: Evaluation of Direct and Calcium-Mediated Short-Term Effects on Serum Parathyroid Hormone Concentration

Abstract

Abstract. Eleven patients on chronic haemodialysis treatment thrice weekly received 1 |ig 1,25(OH) 2 D3 i.v. after each dialysis for 3 weeks. Phosphate binders were mainly CaCO 3 , supplemented in a few patients by moderate amounts of A1(OH) 3 . Ionised calcium was measured by ion-selective electrode, normal values being 1. 28-1.42mmol/l. PTH was estimated by an N-terminalsensitive assay; normal values are <0.25ng/ml. Results before and after 1,25(OH) 2 D3 were: ionised calcium before haemodialysis, 1.19±0.12and 1.17±0.14; ionised calcium after haemodialysis, 1.33 + 0.07 and 1.30 ±0.09; PTH before haemodialysis, 1.39 ±0.71 and 1.38 ±0.69; PTH after haemodialysis, 0.64 ±0.22 and 0.60 ±0.17; Phosphate before haemodialysis, 1.85 + 0.48 and 2.18 + 0.43 (/><0.05). No change of PTH concentration and ionised calcium before and after haemodialysis treatment could be documented after i.v. 1,25(OH) 2 D3 treatment. Mild and severe hyperparathyroidism were indistinguishable. Increased serum calcium concentrations therefore appear to be required for the suppression of PTH secretion by i.v. 1,25(OH) 2 D3 therapy.

Vitamin A Antagonizes Calcium Response to Vitamin D in Man

“…Serum levels of calcium, vitamin D, and vitamin A can influence PTH secretion from the parathyroid glands. 1,25(OH) 2 D 3 exerts an immediate (seconds (25) ) suppressive effect on PTH secretion via increased calcium levels, (26) whereas the direct effect on parathyroid tissue leads to decreased PTH secretion only after a lag period of 12‐18 h or more 27‐31) . Thus, the changes in PTH we see after intake of 1,25(OH) 2 D 3 are likely to be reflections of changes in S‐calcium rather than direct regulation of PTH secretion.…”