Background: To investigate the effect of the reversal of hyperparathyroidism on platelet intracellular free calcium ([Ca2+]i) by pharmacological parathyroidectomy with intravenous calcitriol in uremic patients with secondary hyperparathyroidism (2 degrees 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 degrees HPT and serum I-PTH 4 times greater than the normal upper limits, were selected for treatment with intravenous calcitriol 1 microgram 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 degrees HPT. Serum I-PTH levels were significantly correlated with platelet [Ca2+]i in uremic patients with 2 degrees 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 degrees HPT.