ON THE MECHANISM OF HYPOSTHENURIA IN HYPERCALCEMIA

Reversible renal failure caused by hypercalcemia. A retrospective study

The influence of hypercalcemia on renal function was studied retrospectively in 13 patients suffering from primary hyperparathyroidism, sarcoidosis, vitamin D intoxication, malignant lymphoma or chronic lymphatic leucemia. Different kinds of treatment, depending upon the primary disease, often induced a rapid fall in the serum calcium concentration. The serum creatinine concentration always fell simultaneously. The serum phosphate concentration fell in all but two patients. Changes in serum calcium and serum creatinine correlated significantly (p less than 0.001), as did changes in serum calcium and serum phosphate concentrations (p less than 0.05). Serum calcium/serum creatinine and serum calcium/serum phosphate ratios were significantly higher in patients with primary hyperparathyroidism than in patients with hypercalcemia of non-hyperparathyroid origin (p less than 0.01, p less than 0.001). This suggests a different effect of calcium on the glomerular filtration rate in hyperparathyroid and non-hyperparathyroid patients, the latter group being more sensitive to the influence of hypercalcemia. Possible explanations for this difference, such as a protective effect of PTH on the glomerular filtration, are discussed.

Liver transplantation-associated hypercalcemia followed by acute renal dysfunction

A 34-year-old woman with liver insufficiency due to glycogen storage disease III underwent a living spousal liver transplantation. Soon after the successful operation, moderate hypercalcemia along with hyperbilirubinemia emerged without clarified reasons. The hypercalcemia persisted for over a month despite calcitonin treatment and the serum calcium level surged to 13.2 mg/dl with albumin correction. Renal dysfunction was indicated by an acute increase in serum creatinine (approximately 0.8 to approximately 2.8 mg/ml), which was assumed to be hypercalcemia-induced and was effectively treated with bisphosphonate, pamidronate (30 mg, i.v.). Recent topics related to transplantation-associated hypercalcemia are discussed.

Vasopressin-elicited water and urea permeabilities are altered in IMCD in hypercalcemic rats

To investigate how hypercalcemia blunts renal concentrating ability, alterations in basal and arginine vasopressin (AVP)-elicited osmotic water (Pf) and urea (Purea) permeabilities were measured in isolated perfused terminal inner medullary collecting ducts (IMCD) from control and chronically hypercalcemic rats after dihydrotachysterol (DHT) (M. Levi, L. Peterson, and T. Berl. Kidney Int. 23: 489-497, 1983) treatment. The IMCD Pf of DHT-treated rats did not increase significantly after AVP and was accompanied by a significant 87 +/- 4% reduction in aquaporin-2 (AQP-2) protein but not mRNA. In contrast, both basal and AVP-elicited IMCD Purea from DHT rats were significantly increased and accompanied by a significant 41 +/- 11% increase in AVP-regulated urea transporter protein content. Immunoblotting with anti-calcium/polyvalent cation-sensing receptor protein (CaR) antiserum revealed specific alterations in CaR bands in endosomes purified from the apical membranes of inner medulla of DHT rats. These data are the first detailed analyses of hypercalcemia-induced alterations in AVP-regulated permeabilities and membrane transporters in IMCD. We conclude that selective alterations in IMCD transport occur in hypercalcemia, permitting the body to dispose of excess calcium without forming calcium-containing renal stones.

Primary disseminated form of Ewing sarcoma in association with hypercalcemia and acute renal failure

We present a case of an extremely rare form of Ewing sarcoma--primary disseminated, with fulminating course, severe hypercalcemia, extensive calcium deposition in parenchymatous organs, including kidneys, and acute renal failure as a clinical consequence. Correction of hypercalcemia was followed by prompt restoration of the glomerular filtration rate (GFR), suggesting that hypercalcemia had a direct effect on its regulation independent of the renal tubular damage. The effectiveness of the treatment with indomethacin indirectly supports the possibility of prostaglandin-mediated humoral hypercalcemia of malignancy.

Effects of calcium on vasopressin-mediated cyclic adenosine monophosphate formation in cultured rat inner medullary collecting tubule cells. Evidence for the role of intracellular calcium

We explored the effects of alterations in extracellular and intracellular calcium concentration on arginine vasopressin (AVP)-stimulated cAMP formation in cultured rat inner medullary collecting tubule cells. cAMP formation remains constant at extracellular calcium concentrations between 0.5 and 4.0 mM, which did not change intracellular calcium. Maneuvers that alter intracellular calcium concentration are associated with marked changes in cAMP generation. EGTA decreases intracellular calcium and enhances AVP-stimulated cAMP formation, while increasing cellular calcium with 2 microM A23187 decreases AVP-stimulated cAMP formation in the presence, but not in the absence, of extracellular calcium. The changes in cAMP formation observed when intracellular calcium is altered are associated with reciprocal changes in prostaglandin E2 (PGE2) synthesis. Despite greater than 95% inhibition of PGE2 synthesis with 5 microM meclofenamic acid, the changes in cAMP formation accompanying alterations in intracellular calcium concentration are still evident. These studies suggest that intracellular calcium critically influences AVP-stimulated cAMP formation. It does so by a mechanism independent of PG that is probably mediated by a direct effect of the cation on the adenylate cyclase complex.

Role of the loop segment in the urinary concentrating defect of hypercalcemia

Hypercalcemia is associated with impaired urinary concentrating ability. To explore the mechanism(s) by which hypercalcemia impairs chloride transport in the loop of Henle, we carried out in vivo microperfusion of the loop segment in Sprague-Dawley rats rendered acutely hypercalcemic (12.1 +/- 0.1 mg/dliter) by calcium gluconate infusion. Control rats were infused with sodium gluconate and had normal plasma calcium (8.0 +/- 0.2 mg/dliter). Compared to control, fractional chloride reabsorption was decreased (61 +/- 4 to 50 +/- 3%; P less than 0.05) and early distal chloride increased 74 +/- 6 to 98 +/- 3 mEq/liter (P less than 0.001) in hypercalcemia. During hypercalcemia, infusion of verapamil failed to increase fractional chloride reabsorption (49 +/- 4%; P less than 0.05) or decrease early distal chloride (95 +/- 2; P less than 0.05) toward control values. Similarly, indomethacin did not improve fractional chloride reabsorption (48 +/- 4%; P less than 0.05) or distal chloride concentration (93 +/- 7; P less than 0.05). In control rats infused with Ringers HCO3, the addition of calcium 8.0 mEq/liter to the perfusate increased early distal calcium (9.22 to 3.11 mEq/liter) but was associated with no change in fractional chloride reabsorption (-6 +/- 6%) and a slight decrease in early distal chloride (-9 +/- 3 mEq/liter; P less than 0.05). These data are consistent with the hypothesis that an elevated plasma, not luminal calcium, concentration impairs chloride reabsorption in the loop segment, primarily the ADH-stimulated component. This may have an important role in the urinary concentrating defect of hypercalcemia.

Inhibition of transcellular NaCl reabsorption in dog kidneys during hypercalcemia

Reduced concentrating and diluting capacity of the kidney in acute and chronic hypercalcemia may partly be due to inhibition of transcellular sodium reabsorption (RNa) in the thick ascending limb of Henle's loop. To examine this hypothesis, local heat production and RNa were measured during normo- and hypercalcemia at comparable glomerular filtration rate (GFR) in volume expanded, anesthetized dogs. Changes in proximal RNa which might occur during CaCl2 infusion, were minimized by infusing acetazolamide (75 mg/kg body wt iv). When ultrafiltrable calcium was increased from 1.12 +/- 0.09 to 2.95 +/- 0.10 mmol/l, cortical heat production was unchanged, whereas outer medullary heat production fell by 32 +/- 4%. RNa was reduced by 32 +/- 6%. Bicarbonate reabsorption did not change but calcium reabsorption and potassium excretion increased significantly. The potassium content of cortex and outer medulla increased during hypercalcemia, whereas ouabain, an inhibitor of Na+, K+-ATPase reduces the potassium content. We conclude that hypercalcemia does not inhibit transcellular RNa in the diluting segment by a direct effect on the Na+, K+-ATPase or the mitochondria, but by interfering with the coupled NaCl transport across the luminal cell membrane.

Control of renal hemodynamics and glomerular filtration rate in chronic hypercalcemia. Role of prostaglandins, renin-angiotensin system, and calcium

The role of prostaglandins (PG), renin-angiotensin system (RAS) and calcium (Ca) in the control of renal hemodynamics and glomerular filtration rate (GFR) in chronic hypercalcemia (serum Ca 12.8 mg%) was studied. Renal blood flow (RBF, 6.39 ml/min per gram kidney weight [gkw]) and GFR (0.52 ml/min per gkw) were significantly decreased in hypercalcemic rats when compared with normocalcemic rats (7.15, P < 0.001 and 0.74, P < 0.05, respectively). These changes in RBF and GFR occurred independent of any significant alterations in systemic hemodynamics, blood and plasma volume. Inhibition of the renal PG with indomethacin resulted in marked decrements in both RBF (6.39-4.12 ml/min per gkw, P < 0.01) and GFR (0.52-0.19 ml/min per gkw, P < 0.01) in hypercalcemic rats, whereas there was no significant alterations in normocalcemic rats. Inhibition of the RAS with captopril resulted in marked increments in both RBF (6.39-7.35 ml/min per gkw, P < 0.05) and GFR (0.52-0.74 ml/min per gkw, P < 0.05) in hypercalcemic rats. In fact, there was no significant difference from the RBF and GFR of similarly treated normocalcemic rats. Similar results were also obtained with the competitive angiotensin II (AII) antagonist (sarcosyl(1)-isoleucyl(5)-glycyl(8)) AII. Since both the renal PG and the RAS are involved in the control of RBF and GFR in hypercalcemia, the role of each is best revealed in the absence of the other. Hence, comparison of the RBF and GFR in the PG-inhibited hypercalcemic rats in the presence of AII (4.12 and 0.19 ml/min per gkw, respectively) and absence of AII (5.99 and 0.53 ml/min per gkw, P < 0.01 for both) reveals the vasoconstrictive role for AII in hypercalcemia. On the other hand, comparison of the RBF and GFR in the AII-inhibited hypercalcemic rats in the presence of PG (7.35 and 0.74 ml/min per gkw, respectively) and absence of PG (5.99 and 0.53 ml/min per gkw, P < 0.01 and P < 0.05, respectively) reveals the vasodilatory role for PG in hypercalcemia. Finally, comparison of the RBF and GFR in both PG- and AII-inhibited hypercalcemic rats (5.99 and 0.53 ml/min per gkw, respectively) with similarly treated normocalcemic rats (7.30 and 0.94 ml/min per gkw, P < 0.001 and P < 0.005, respectively) reveals the vasoconstrictive role for Ca in chronic hypercalcemia. Our study therefore demonstrates that in chronic hypercalcemia the RBF and GFR are controlled by an active interplay of the vasoconstrictive effect of AII, the vasodilatory effect of renal PG, and the direct vasoconstrictive effect of Ca, independent of either AII or PG. The sum total of these forces produces a modest but significant decrease in RBF and GFR.

Plasma vasopressin in hypercalcaemic states

Plasma vasopressin was measured by radioimmunoassay in eight normal subjects and in six patients with hypercalcaemia. Vasopressin levels were significantly elevated in the hypercalcaemic patients, although urine osmolalities were lower than in controls. This finding is consistent with a renal resistance to the action of endogenous vasopressin in hypercalcaemia.

Renal function in hypercalcemic dogs during hydropenia and during saline infusion

The effects of calcium-gluconate infusions on renal function were studied in unanesthetised dogs. Each dog was studied during hydropenia and saline infusion. Hypercalcemia, mean serum calcium 3.85 mmol/l (hydropenia) and 3.62 mmol/l (saline infusion), increased fractional excretion of sodium (CNa/CIn), calcium (CCa/CIn), and magnesium (CMg/CIn). The increase was significantly higher in saline-expanded dogs than in hydropenic dogs. Fractional excretion of potassium (CK/CIn) was increased in hydropenia but remained unchanged in saline-expanded animals. Fractional excretion of phosphate (Cp/CIn) was not consistently changed by hypercalcemia. Fractional excretion of chloride (CCl/CIn) was markedly increased in saline-expanded dogs but was not changed in hydropenia. Urine osmolality was reduced in hydropenic dogs but unchanged in saline-expanded dogs. In hydropenic as well as in saline-expanded dogs tubular reabsorption of solute-free water (TcH2O/CIn) increased during the first hour of hypercalcemia. In hydropenic dogs hypercalcemia caused a slight but significant decrease in blood pH, standard bicarbonate, and base excess. In hydropenic as well as in saline-expanded dogs glomerular filtration rate (CIn), renal plasma flow (CPAH), and filtration fraction were unaffected.

Effects of hypercalcemia on water and sodium excretion by the isolated dog kidney

The effects of acute hypercalcemia on hemodynamics and on water and sodium excretion were studied on the blood-perfused isolated dog kidney. This model advantageously eliminates various factors which modify medullary osmolality and intrarenal hemodynamics, as well as collecting duct permeability. Calcium ion directly inhibits sodium reabsorption in the proximal tubule and in the ascending limb of Henle's loop, leading to increased sodium excretion rate and to decreased free water generation. The vasoconstrictive action of calcium, leading to decreased glomerular filtration rate, may mitigate the strong natriuretic effect of this ion.

A micropuncture study of postobstructive diuresis in the rat

In order to investigate the syndrome of postobstructive diuresis, clearance and micropuncture studies were carried out in rats after relief of 24 hr of bilateral (BUL) or unilateral (UUL) ureteral ligation. In rats with BUL, a striking diuresis and natriuresis occurred when the obstruction to one kidney (the experimental kidney) was relieved. The results were not influenced by administration of vasopressin or d-aldosterone. Whole kidney clearances of inulin and p-aminohippuric acid (PAH) in the experimental kidney were reduced to 10% and 20% of normal, respectively. Superficial nephron inulin and PAH clearances were also reduced, but only to 40% and 45%, respectively. These findings suggest a heterogeneity of nephron function in which deep nephrons were functioning poorly or not at all. To investigate the site of impaired tubular reabsorption in the surface nephrons, absolute and fractional water reabsorption was measured. Absolute reabsorption was found to be decreased all along the nephron. Fractional reabsorption in proximal tubules was normal, as indicated by an average endproximal tubular fluid per plasma inulin (TF/P(In)) of 2.16 vs. 2.30 in controls. TF/P(In) was markedly decreased in distal tubules (2.91 vs. 8.02) and final urine (5.56 vs. 263). These observations indicate that the major sites of impaired sodium reabsorption leading to the diuresis were beyond the proximal tubule.Rats with 24 hr of UUL did not demonstrate a comparable natriuresis or diuresis either spontaneously when the obstruction was relieved or after i.v. infusion of urea. A major difference between the BUL and UUL rats was that prerelease intrarenal hydrostatic pressure was markedly elevated (30.1 mm Hg) in the former but was below normal free-flow values (9.2 mm Hg) in the latter. Thus, elevation of intrarenal pressure during the period of obstruction may be causally related to the natriuresis and diuresis which occurs after the obstruction is relieved.

Urine concentration and dilution in hypokalemic and hypercalcemic dogs

The urine-concentrating mechanism was studied in chronic hypokalemia (seven dogs given a low K(+), high NaCl diet plus injections of deoxycorticosterone acetate [DOCA]) and chronic hypercalcemia (seven dogs given vitamin D). In the potassium-depleted dogs, muscle, serum, and urine K(+) fell markedly, but glomerular filtration rate (GFR) and body weight varied little. Maximum urine osmolality fell in all dogs (mean decrease = 45%); however, solute-free water reabsorption (T(CH2O)) at high rates of solute excretion remained normal in three of four dogs. Free water excretion (C(H2O)) increased normally or supranormally as a function of increasing Na(+) delivery to Henle's loop in six dogs so tested. Hypercalcemia of several weeks duration caused a decrease in both GFR (mean 36%) as well as in maximum urine osmolality (mean 57%). Maximum T(CH2O) was not invariably depressed; in fact, when the values were adjusted for the reduced number of functioning nephrons (T(CH2O)/C(In)), four of seven studies were normal. C(H20)/C(In) increased normally (or supranormally) with increasing fractional Na delivery to Henle's loop in four of five dogs.I conclude that the lowered maximum urine osmolality in these hypokalemic and hypercalcemic dogs was not related to abnormal water reabsorption from the collecting ducts. Although not specifically measured in this study, it is very likely that solute accumulation in the renal medulla was reduced. This probably was not caused by abnormal delivery of sodium to, nor reabsorption of sodium from Henle's loop. It is likely that a more subtle defect exists in the countercurrent mechanisms for establishing a steep concentration gradient in the renal medulla. In the few hypercalcemic dogs in whom GFR was very low, I believe that injury to, and blockage of medullary tubules could account for most of the reduction in maximum U(Osm). Although not specifically ruled out, there is no evidence here to suggest that high serum Ca(+) or low serum K(+) per se causes a defect in sodium and water reabsorption in the mammalian nephron.