The renal sensitivity for endogenous parathormone in patients with primary hyperparathyroidism, vitamin D deficiency and renal stones

Baseline levels and increases in urinary cyclic AMP excretion (UcAMP) and immunoreactive parathormone (iPTH) were studied before and during infusion of EDTA in euparathyroid patients with renal stones (n=11), patients with primary hyperparathyroidism (PHP; n=14) and patients with vitamin D deficiency (n = 12). In all three groups, EDTA evoked a significant rise in iPTH and UcAMP. In patients with PHP and in those with vitamin D deficiency, there was a sufficiently close relationship between increments in iPTH (delta iPTH) and in UcAMP (delta UcAMP) (r = 0.90, P less than 0.001 and r = 0.67, P less than 0.02, respectively) to use this model to assess renal sensitivity for changes to endogenous PTH levels. We quantified sensitivity of the kidney for PTH, by calculating the ratio delta UcAMP/delta TPTH for the three studied groups. The ratio was comparable in patients with renal stones (16.7 +/- 10.3) and PHP (13.8 +/- 4.9, P greater than 0.10), but was significantly increased in patients with vitamin D deficiency (33.2 +/- 17.9; P less than 0.01 versus patients with renal stones and P less than 0.01 versus patients with PHP). Within the group of patients with PHP there was no correlation between baseline serum calcium concentrations and the ratio delta UcAMP/delta TPTH. It is concluded that in patients with vitamin D deficiency, renal sensitivity to PTH is increased compared with patients with PHP and euparathyroid patients with renal stones, perhaps an expression of a teleological useful adaptation of end organ sensitivity.