Effect of intravenous calcitriol on platelet intracellular calcium in uremic hemodialysis patients with secondary hyperparathyroidism

Background. To investigate the effect of the reversal of hyperparathyroidism on platelet intracellular free calcium ([Ca²⁺](i)) by pharmacologial parathyroidectomy with intravenous calcitriol in uremic patients with secondary hyperparathyroidism (2°HPT). Methods. Serum concentrations of intact parathyroid hormone (I-PTH) were measured by two-site immunometric assay, and platelet [Ca²⁺](i) was assessed using the fluorescent indicator fura-2. Fifteen hemodialysis patients with 2°HPT and serum I-PTH 4 times greater than the normal upper limits, were selected for treatment with intravenous calcitriol 1 μg thrice weekly for one month. Results. An increase of serum I-PTH (449.17 ± 52.35 vs 32.52 ± 1.95 pg/ml) and elevated platelet [Ca²⁺](i) (139.49 ± 8.78 vs 74.70 ± 6.48 nM/L) was observed in uremic patients with 2°HPT. Serum I-PTH levels were significantly correlated with platelet [Ca²⁺](i) in uremic patients with 2°HPT (r = 0.736, p = 0.002). The serum I-PTH levels decreased from 449.17 ± 52.35 to 221.27 ± 35.66 pg/ml (p < 0.001) and platelet [Ca²⁺](i) fell from 139.49 ± 8.78 to 97.86 ± 7.25 nM/L (p < 0.001) after treatment. Fall in platelet [Ca²⁺](i) was related to concomitant reduction in PTH levels (r = 0.572, p = 0.026). Conclusions. It was concluded that an increase in cytosolic calcium in uremia may be at least in part induced by PTH. Besides, intravenous calcitriol can provide an effective way to suppress elevated serum I-PTH and attenuate platelet free calcium in uremia with 2°HPT.