Electrolyte water metabolism in polycystic kidney and in chronic glomerulonephritis. Effects of intravenous calcium load

A calcium infusion test was performed in 18 patients with chronic glomerulonephritis (9 with normal glomerular filtration rate (GFR) and 9 with renal insufficiency) and in 11 patients with polycystic kidney disease (5 of them with renal insufficiency). The following parameters were evaluated: fractional reabsorption of calcium in proximal tubule, theoretical threshold for calcium, the correlations between urinary calcium and sodium excretion, the effects of sodium excretion induced by the calcium load on the urinary volume, C(osm), TcH 2O and potassium excretion. The results may be summarized as follows: The theoretical threshold for calcium is strictly related to GFR, as the calcium reabsorption in the distal tubule decreases with the progressive fall in GFR values: this depends probably on the reduced sensitivity of distal tubule to parathormone (pseudohypoparathyroidism). The fractional reabsorption of calcium is independent of the degree of renal insufficiency. The sodium excretion is directly related and dependent on calcium excretion only in those patients from both groups with normal GFR; on the contrary, a significant natriuresis not related to calcium excretion was observed in uremic patients. The urine volume, C(osm) and potassium excretion are directly related to sodium excretion only in glomerulonephritic and polycystic patients with normal GFR, whereas these parameters are partly independent from sodium excretion in patients with renal insufficiency. The only significant difference between the 2 groups is the inability to maximally concentrate the urine observed in polycystic patients with normal GFR and not found in glomerulonephritic patients with normal renal function. This difference was not evident in both groups of patients with renal insufficiency.