Effect of acute intradialysis hyperphosphoremia on parathormone (PTH) secretion

Hyperphosphoremia is said to cause secondary hyperparathyroidism by depress ing ionized calcium plasma levels and by affecting serum calcitriol levels. Recent studies suggest a direct stimulatory role of phosphorus in PTH prod uction. The aim of this study was to analyse the influence of acute hyperph osphoremia on PTH production. The study was performed on 6 stable patients on regular dialysis therapy. We compared the biochemical data and phospho-c alcium metabolism parameters obtained from a conventional five hours hemodi alysis session (C-HD) with those obtained during a hemodialysis in which, a fter 120 minutes, a dialysate with phosphate (6 mg/dl) was used (P-HD). The calcium balance was similar in both HD. We observed a similar behavior of the phospho-calcium metabolism parameters in both procedures until the 1 20 minutes (T120). From then, in the P-HD it was observed a significant inc rease of phosphorus serum levels (T120: 3.2 +/- 0.18 mg/dl; T180: 5.44 +/- 0.38 mg/dl (p < 0.05). It was also observed a decrease in Ca2+ (T120: 4.1 /- 0.06; T180: 3.8 +/- 0.07 mg/dl). After the introduction of the phosphate dialysate, the PTH levels increased significantly (T120: 212 +/- 88; T180: 274 +/- 107 pg/ml; (p < 0.051. The PTH behavior in P-HD was similar to tha t observed in HD patients when a slight decrease of serum Ca++ was induced by changing calcium concentration of dialysate. Our results demostrate that in uremic patients the intradialytic acute hype rphosphoremia increases PTH production by depressing ionized calcium plasma levels.