Lack of Relationship between Parathyroid Hormone and 1,25-Dihydroxyvitamin D in Chronic Renal Failure

Abstract

In the present study, concentrations of parathyroid hormone (PTH), determined by an intact PTH assay and a midregion/C-terminal PTH assay, 1,25-dihydroxyvitamin D [1,25(OH)₂D₃], ionized calcium and phosphate were measured in 15 patients with a stable creatinine clearance (C_cr) of 21.2 ± 14.4 ml/min (mean ± SD; group 1) and in 10 patients with a C_cr regularly undergoing hemodialysis (group 2, C_cr not measured). In group 1, the mean concentration of 1,25(OH)₂D₃ was significantly increased compared with the level in group 2, whereas no differences were found concerning the concentrations of intact PTH, midregion/C-terminal PTH, ionized calcium and phosphate. In group 1, the PTH concentration correlated inversely with ionized calcium concentration and C_cr, which in turn, was directly correlated. The concentration of 1,25(OH)₂D₃ correlated inversely with phosphate concentration, but did not correlate with either PTH or ionized calcium concentrations. In group 2 no correlation was found between any of the biochemical variables. The data demonstrate that in patients with stable renal failure, the concentration of ionized calcium still regulates PTH secretion but other variables such as parathyroid cell mass and setpoint may interfere with the interrrelation. The elevated concentration of phosphate in renal failure may override PTH as a regulator of the renal 1,25(OH)₂D₃ formation. The lack of correlations in the hemodialyzed patients may be attributed to extrarenal production of 1,25(OH)₂D₃, reduced binding of 1,25(OH)₂D₃ to parathyroid tissue or the major changes in calcium homeostasis caused by the hemodialysis.

Metabolism of Calcium and Vitamin D₃ in Patients with Acute Tubulointerstitial Nephritis: A Study of 41 Patients with IMephropathia Epidemica

“…l,25(OH)2D, correlated inversely with serum phosphate, as has been seen earlier in chronic renal failure [13,31] and ARF due to rhabdomyolysis [4], The same tendency towards decreasing l,25(OH)2D3 simulta neously with increasing serum phosphate was also seen in patients with normal serum creatinine and low or normal serum phosphate. Phosphate is known to play an important role in the regulation of l,25(OH)2D2 synthesis in humans [32], Studies on mild chronic renal failure have shown that restriction of dietary phosphate increases and supplemen tation decreases serum l,25(OH)2D2, though serum phos phate is constantly within normal limits [9,33].…”

Long-Term Control of Hyperparathyroidism in Advanced Renal Failure by Low-Phosphorus Low-Protein Diet Supplemented with Calcium (without Changes in Plasma Calcitriol)

“…There was an inverse corre lation between intact plasma PTH and ionized serum cal cium and GFR [24,25]. A direct correlation was observed between plasma PTH and plasma phosphate levels, con firming that the rise in plasma phosphate concentration resulting from phosphate retention plays an important role in the stimulation of PTH secretion [11,26].…”