Effect of MgCl2 infusion on urinary Ca and Na during reduction in their filtered loads

Macrophages use apoptotic cell-derived methionine and DNMT3A during efferocytosis to promote tissue resolution

Efferocytosis, the clearance of apoptotic cells (ACs) by macrophages, is critical for tissue resolution, with defects driving many diseases. Mechanisms of efferocytosis-mediated resolution are incompletely understood. Here, we show that AC-derived methionine regulates resolution through epigenetic repression of the extracellular signal-regulated kinase 1/2 (ERK1/2) phosphatase Dusp4. We focus on two key efferocytosis-induced pro-resolving mediators, prostaglandin E2 (PGE2) and transforming growth factor beta 1 (TGF-β1), and show that efferocytosis induces prostaglandin-endoperoxide synthase 2/cyclooxygenase 2 (Ptgs2/COX2), leading to PGE2 synthesis and PGE2-mediated induction of TGF-β1. ERK1/2 phosphorylation/activation by AC-activated CD36 is necessary for Ptgs2 induction, but this is insufficient owing to an ERK-DUSP4 negative feedback pathway that lowers phospho-ERK. However, subsequent AC engulfment and phagolysosomal degradation lead to Dusp4 repression, enabling enhanced p-ERK and induction of the Ptgs2-PGE2-TGF-β1 pathway. Mechanistically, AC-derived methionine is converted to S-adenosylmethionine, which is used by DNA methyltransferase-3A (DNMT3A) to methylate Dusp4. Bone-marrow DNMT3A deletion in mice blocks COX2/PGE2, TGF-β1, and resolution in sterile peritonitis, apoptosis-induced thymus injury and atherosclerosis. Knowledge of how macrophages use AC-cargo and epigenetics to induce resolution provides mechanistic insight and therapeutic options for diseases driven by impaired resolution.

Mechanism of urinary calcium regulation by urinary magnesium and pH

Urinary magnesium and pH are known to modulate urinary calcium excretion, but the mechanisms underlying these relationships are unknown. In this study, the data from 17 clinical trials in which urinary magnesium and pH were pharmacologically manipulated were analyzed, and it was found that the change in urinary calcium excretion is directly proportional to the change in magnesium excretion and inversely proportional to the change in urine pH; a regression equation was generated to relate these variables (R(2) = 0.58). For further exploration of these relationships, intravenous calcium chloride, magnesium chloride, or vehicle was administered to rats. Magnesium infusion significantly increased urinary calcium excretion (normalized to urinary creatinine), but calcium infusion did not affect magnesium excretion. Parathyroidectomy did not prevent this magnesium-induced hypercalciuria. The effect of magnesium loading on calciuria was still observed after treatment with furosemide, which disrupts calcium and magnesium absorption in the thick ascending limb, suggesting that the effect may be mediated by the distal nephron. The calcium channel TRPV5, normally present in the distal tubule, was expressed in Xenopus oocytes. Calcium uptake by TRPV5 was directly inhibited by magnesium and low pH. In summary, these data are compatible with the hypothesis that urinary magnesium directly inhibits renal calcium absorption, which can be negated by high luminal pH, and that this regulation likely takes place in the distal tubule.

The role of calcium in the prevention of kidney stones

Nephrolithiasis is a common and important condition. Several lines of evidence suggest that increased urinary calcium increases the risk of kidney stones. Since dietary calcium raises urinary calcium, it has been common practice to reduce calcium intake in stone-formers who hyperabsorb calcium from the intestine, although no trial has yet been designed to directly demonstrate the effectiveness of calcium restriction. In contrast, some have suggested that calcium restriction may be harmful due to resultant hyperoxaluria and risk of bone loss. In fact, two powerful prospective observational studies have suggested that increased dietary calcium reduces the risk of the first kidney stone. However, calcium was not the only variable, since those with the highest quintile of calcium intake also ingested more fluid, potassium, magnesium and phosphate. Moreover, the otherwise thorough analysis was not adjusted for alkali intake, which may prevent stones, or oxalate intake, which may increase stone risk. Due to limitations in available data, future prospective studies should be designed to probe the effect of specific interventions with calcium, both dietary and supplemental, on urinary parameters and stone formation, particularly in hypercalciuric stone-formers, who may respond conversely. For now, dietary calcium should be gradually increased in stone-formers as guided by the urinary calcium, and hypocalciuric agents should be added as necessary.

Renal function in premature infants during aminoglycoside therapy

The effect of three different aminoglycosides on renal function was evaluated in 30 premature infants of similar gestational age who were treated within 24 h of birth with either amikacin (10 infants, group A), gentamicin (10 infants, group B) or netilmicin (10 infants, group C), for a period of 7 days. Ten infection-free premature infants of similar post-conceptional age were used as controls. Serial determinations of plasma creatinine concentration (PCr), as well as the fractional excretion of sodium (FENa), potassium, magnesium (FEMg), phosphate (FEP) and uric acid (FEUA), and the urinary excretion of calcium (UCa/UCr ratio) were assessed before, during and after treatment. During the treatment period a significant increase in FENa, FEMg and UCa/UCr was observed in group B (P < 0.05 and P < 0.01, respectively) and an increase in FENa and UCa/UCr in group C (P < 0.01) compared with controls. These disturbances were observed with trough concentrations of aminoglycosides but were accentuated at peak serum concentrations and were restored to normal 2 days after stopping therapy. In addition, a significant correlation was demonstrated between FENa, FEMg and UCa/UCr ratio in treated patients. PCr levels decreased similarly in all patient groups, but in 8 of 30 infants (27%) they remained elevated and returned to control values only 10 days after stopping therapy. Such renal functional disturbances, although transient, may result in significant electrolyte and mineral imbalance in the sick premature infant.

Calcium homeostasis in pregnant women receiving long-term magnesium sulfate therapy for preterm labor

OBJECTIVES

The hypothesis of this study is that calcium homeostasis and bone mineralization are altered in pregnant women receiving long-term therapy with magnesium sulfate as compared with similar women not receiving magnesium sulfate to control preterm labor.

STUDY DESIGN

Thirty-nine women between 24 and 32 weeks' gestation, matched for age, race, and duration of bed rest, were enrolled. Indices of calcium homeostasis in serum and urine were measured serially, and bone mineralization of the distal radius was measured at 1 and 11 weeks post partum.

RESULTS

Magnesium therapy was administered for a mean duration of 26 +/- 14 days and a cumulative dose of 1405 +/- 963 gm. Serum concentrations of magnesium, phosphorus, and parathyroid hormone increased and those of calcium decreased from baseline values in the magnesium sulfate group and remained uniform throughout the 3-week investigation. The serum magnesium, phosphorus, parathyroid hormone, and calcium concentrations in the control group were unchanged during the study and differed significantly from those in the magnesium sulfate group (p < 0.001). Urinary output of magnesium, calcium, and copper was significantly greater in the magnesium sulfate group than in the control group throughout the study. Urinary losses of calcium in the magnesium sulfate group, approximately 800 to 900 mg/day, were substantial. Although radius bone density 1 week post partum did not differ between groups, the change in bone density from 1 to 11 weeks post partum was significantly lower in the magnesium sulfate group than in controls.

CONCLUSIONS

These data suggest that calcium homeostasis is altered during and after long-term magnesium sulfate therapy. The marked, prolonged urinary calcium losses may affect maternal bone mineralization.

Modification of renal and tissue cation transport by cholecystokinin octapeptide in the rabbit

1. Reports that gastric sodium loads cause a greater natriuresis than those administered intravenously, suggest that a gastric or portal sodium monitor exists which releases a humoral natriuretic factor. To determine whether cholecystokinin octapeptide (CCK-8) had direct renal natriuretic effects (and was therefore a candidate for this gut-derived natriuretic factor) we compared the natriuretic response to CCK-8 infused intravenously with that infused directly into the renal artery of six conscious male rabbits. 2. CCK-8 produced a significant log dose-dependent decrease in the fractional excretions of calcium (P less than 0.05) and magnesium (P less than 0.005) and a log dose-dependent increase in fractional sodium excretion (P less than 0.025). The significant decreases in the fractional excretions of calcium and magnesium were accompanied by log dose-dependent falls in their plasma levels (calcium, P less than 0.05, and magnesium, P less than 0.005), indicating movement of calcium and magnesium to extravascular sites. Studies of tissue calcium and magnesium levels in response to CCK-8 infusion showed that calcium accumulated in kidney and skeletal muscle. 3. We conclude that CCK-8 has direct renal natriuretic effects at the tubular level and could be the gut-derived natriuretic factor. In addition to its effects on sodium excretion, CCK-8 causes renal retention and increased gut absorption of calcium and magnesium with movement of these ions to extravascular sites.

Studies on the pathogenesis of cisplatin-induced hypomagnesemia in rats

After three weekly intraperitoneal injections of cisplatin (2.5 mg/kg body wt), male Wistar rats developed chronic hypomagnesemia, which was evident from the second week and persisted throughout the 8-week experiments. Plasma magnesium concentration was 0.69 +/- 0.01 mM in cisplatin-treated rats compared to 0.80 +/- 0.02 mM in pair-fed control rats (P less than 0.01) in the eighth week of experimentation. Despite a similar dietary magnesium intake, urinary excretion of magnesium in cisplatin-treated rats was inappropriately high, relative to the lower plasma magnesium concentration, indicating the presence of renal magnesium wasting induced by cisplatin. During the 3 weeks of cisplatin injections, metabolic balance studies indicated abnormal renal excretion and a reduction in the fractional intestinal absorption of magnesium. A compensatory period of significantly greater retention of magnesium then occurred in cisplatin-treated rats beginning in the fourth week. Clearance and recollection micropuncture studies in a separate group of rats revealed normal magnesium and calcium transport in the superficial proximal and distal nephron. Following acute MgCl2 infusion, the urinary excretion of magnesium and calcium were significantly higher in cisplatin-treated rats than in control rats; however, micropuncture studies of superficial nephrons failed to demonstrate abnormal transport of these divalent cations. It is possible, therefore, that 7 weeks of cisplatin treatment led to tubular adaptation that might have obscured the defect in magnesium reabsorption. Morphological examination indicated that pathological changes were confined to the S3 segment of proximal corticomedullary nephrons.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal magnesium transport and the effects of hypermagnesemia, hypercalcemia, body magnesium stores and parathyroid hormone

Magnesium reabsorption occurs throughout the proximal, loop and distal segments of the nephron. The proximal tubule is less permeable to magnesium than calcium and sodium and most of the filtered load is reclaimed in the thick ascending limb of the loop of Henle. Thus one would expect that factors which regulate magnesium reabsorption should act within this important segment. No single hormone or agent appears to regulate magnesium reabsorption sufficiently to account for urinary changes; rather it appears to be a number of intracellular and extracellular factors acting in concert to effect day to day magnesium homeostasis.

Divalent cation transport in kidney slices. I. Properties of calcium transport in slices of rat kidney cortex and the effects of diuretics

Correlative studies on transports of Ca2+ and Na+ and the properties of Ca2+ transport were carried out in rat kidney cortex slices. Ouabain had no effect on the Ca2+ transport but did inhibit the Na+ transport extensively. With addition of 2,4-dinitrophenol to the incubation medium, or under the anaerobic conditions, the effluxes of Ca2+ and Na+ were inhibited while the Ca2+ influx was enhanced significantly. Sulfhydryl inhibitors such as ethacrynic acid, mersalyl and p-chloromercuribenzoic acid suppressed Ca2+ efflux and stimulated Ca2+ influx. When the slices of kidney cortex were treated with these inhibitors, there was a reduction in the content of cellular ATP. The present results suggest that Ca2+ transport may be partly independent of Na+ transport, and that Ca2+ efflux may require energy-yielding processes.

Interrelationships among thiazide diuretics and calcium, magnesium, sodium, and potassium balance in normal and hypertensive man

The benzothiadiazide diuretics are known to cause magnesium and potassium wasting and retention of calcium and uric acid. The effect of magnesium replacement on diuretic-induced changes in sodium, potassium, calcium, and magnesium balance, weight, and blood pressure was studied in 12 normal subjects and 13 hypertensive patients to determine whether oral magnesium would reduce thiazide-induced kaliuresis. The groups differed in their response to diuresis in that the normotensive subjects did not show a fall in blood pressure (despite an equivalent weight loss), returned to a state of sodium balance earlier, and developed a greater net negative potassium balance over 12 days of diuretic therapy. Both groups displayed calcium and uric acid retention and magnesium wasting during diuretic therapy. The addition of oral magnesium replacement during diuretic therapy had no effect on any measured values beyond that seen in subjects who took diuretics without magnesium replacement. Thus, magnesium replacement did not reduce urinary potassium loss. However, urinary calcium losses increased when magnesium was given to subjects who were not receiving diuretics. The data provide the first report that small doses of oral magnesium enhance calcium excretion in hypertensive subjects.

Renal handling of magnesium

In summary, magnesium reabsorption occurs throughout the proximal and distal segments of the nephron. The proximal tubule is less permeable to magnesium than calcium and sodium with most of the filtered load being reclaimed in the ascending loop of Henle. In contrast to calcium and sodium a tubular reabsorptive maximum has been demonstrated for magnesium and under certain circumstances secretion has been demonstrated in the terminal nephron segments. Although many factors are known to affect magnesium reabsorption the mechanism of the renal homeostasis remains to be determined.