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Background: The PTH-calcium sigmoidal curve is shifted to the right, the slope of the curve is steeper, and the set point of calcium is increased in dialysis patients with secondary hyperparathyroidism, compared to patients with low-turnover bone disease. These findings could be related to increased parathyroid cell mass and increased sensitivity of parathyroid cells to serum calcium variations in these patients. Calcitriol therapy has been documented to reduce PTH levels by shifting the curve to the left and downward. The effect of a surgical reduction of parathyroid gland mass on the PTH-calcium curve has not yet been investigated. In this study we compared the effects of calcitriol and subtotal parathyroidectomy (PTH) on the dynamics of PTH secretion in response to acute changes of serum calcium in two groups of dialysis patients with severe hyperparathyroidism., Methods: Fourteen dialysis patients treated for 6 months with high-dose i.v. calcitriol (1-2 micrograms thrice weekly, and 10 dialysis patients who underwent subtotal PTx were studied. The PTH-calcium relationship obtained by inducing hypo- and hypercalcaemia means of low and high calcium dialysis was evaluated before and 2-6 months after treatment., Results: Both calcitriol and subtotal PTx significantly decreased PTH (respectively from 797 +/- 595 to 380 +/- 244 and from 1036 +/- 250 to 70 +/- 34 pg/ml), as well as maximal PTH response to hypocalcaemia (PTHmax), and maximal PTH suppression during hypercalcaemia ( PTHmin). When the PTH-calcium curves were constructed using PTHmax as 100% to factor for differences in absolute PTH levels and to provide an assessment of individual parathyroid cell function, a shift of the sigmoidal curve to the left and downward, and a significant decrease in the set point of ionized calcium (from 1.31 +/- 0.05 to 1.26 +/- 0.05 and from 1.36 +/- 0.09 to 1.22 +/- 0.07 mmol/l) was documented with both treatments. However, the slope of the PTH-calcium curve increased after subtotal PTx indicating that the sensitivity of the parathyroid cell to serum calcium changes increased with PTx, while on the contrary it decreased with calcitriol., Conclusions: PTH secretion decreases proportionally more with calcitriol than with surgery for a given decrease in the functional mass of parathyroid cells. The change in the PTH-ICa sigmoidal curve induced by subtotal PTx is due to the removal of a large mass of parathyroid tissue with advanced hyperplasia.

The use of high ultrafiltration rates in haemodiafiltration (HDF) has been suggested for improving the clearance of small and large molecules. This strategy has become economically applicable with the development of safe techniques for on-line production of sterile infusate from dialysate, which enables us to infuse large substitution fluid volumes without further increasing the cost of sessions. The effect of increasing the ultrafiltration rate in HDF on electrolyte balance has not yet been evaluated. The aim of this study was to evaluate the effects of variations of the ultrafiltration rate on calcium kinetics in HDF using three different dialysate calcium concentrations. Since the increase in ultrafiltration rate augments the convective calcium loss, variations of intrasession calcium balance could result from modifications of the ultrafiltration rate. In the present study we found no significant variations in calcium balance and serum ionized calcium (iCa) levels during on-line HDF treatment when increasing the mean ultrafiltration rate from 60 to 100 ml/min in the presence of an adequate and corresponding increase in the infusion rate (from 2.5 to 5 l/h). During the balance studies, pretreatment serum iCa was on the average 1.32 mmol/l and weight loss 3.2 kg. Mean calcium loss during treatment was 2.8 and 3.3 mmol at infusion rates of 2.5 and 5 l/h with 1.63 mmol/l of calcium in both the dialysate and infusate; calcium loss rose to 5.9 and 11.2 mmol at infusion rates of 2.5 l/h and to 5.7 and 14.2 mmol at infusion rates of 5 l/h when the dialysate and infusate calcium was reduced respectively to 1.5 and 1.25 mmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

In 12 continuous ambulatory peritoneal dialysis (CAPD) patients we evaluated peritoneal calcium mass transfer (CaMT), serum and effluent dialysate ionized calcium (iCa) changes, and the variations of the dialysate-to-plasma (D/P) ratio for calcium throughout 6-hour dwell exchanges with zero calcium, 1.25 mmol/L calcium (1.25 Ca), and 1.75 mmol/L calcium (1.75 Ca) peritoneal solutions. The infused ionized and total calcium were, respectively, 1.28 +/- 0.04 and 1.77 +/- 0.04 mmol/L with 1.75 Ca and 0.89 +/- 0.03 and 1.28 +/- 0.04 mmol/L with 1.25 Ca solutions. During CaMT studies, the ultrafiltration rate was 250 mL on average, and serum iCa 1.24 mmol/L. Calcium was gained by the patients (+0.41 +/- 0.6 mmol/L) using standard solutions. CaMT was -0.67 +/- 0.4 mmol/L with 1.25 Ca and -2.4 +/- 0.4 mmol/L with zero Ca solutions. Throughout the exchanges the D/P ratio for iCa decreased from 0.97 +/- 0.03 at 0 minutes to an equilibrium value (at about 240 minutes) of 0.84 +/- 0.03 with 1.75 Ca solutions, while it increased from 0.75 +/- 0.04 to 0.83 +/- 0.05 with 1.25 Ca solutions. After a 6-hour exchange with zero Ca, the D/P ratio for iCa was 0.76 +/- 0.04, significantly lower than the D/P ratio for urea (0.97 +/- 0.02), creatinine (0.89 +/- 0.06), and bicarbonate (0.98 +/- 0.02). In conclusion, dialysate and serum iCa are in equilibrium at a D/P ratio of about 0.84. Thus calcium is gained by the patients using 1.75 Ca solutions, and it is lost (both by diffusion and ultrafiltration) using 1.25 Ca solutions.(ABSTRACT TRUNCATED AT 250 WORDS)

A high incidence of adynamic bone disease not related to aluminum intoxication has been reported in continuous ambulatory peritoneal dialysis (CAPD). Since reduced parathyroid hormone (PTH) secretion may predispose to adynamic bone, we investigated whether parathyroid gland sensitivity may be depressed in CAPD in comparison with hemodialysis (HD). Thus we determined parathyroid function by the evaluation of the PTH-ionized calcium (ICa) relationship, which was obtained inducing hypocalcemia and hypercalcemia in 19 CAPD and 18 HD patients with biochemical and histological evidence of mild (MILD) or severe (OF) hyperparathyroidism, but negative stainable bone aluminum. Either CAPD or HD patients with OF showed a shift to the right of the sigmoidal PTH-ICa curve in comparison with patients with MILD, greater set point of calcium, and maximal PTH stimulation and inhibition. The PTH-ICa curve and the other parathyroid function parameters were not different in CAPD and HD patients within the same bone histological group. In conclusion, our data document that parathyroid gland activity is stimulated either in CAPD and HD patients with OF, but is not depressed in CAPD patients in comparison with HD patients.