The influence of renal prostaglandins on urinary calcium excretion in idiopathic urolithiasis

Vitamin D and Calcium Supplementation and Urolithiasis: A Controversial and Multifaceted Relationship

Patients with urolithiasis, and particularly those with hypercalciuria, frequently have a marked reduction of bone mineral content up to the levels of osteoporosis, with a significant increase in bone fracture risk. For these reasons, the indication to prescribe vitamin D and/or calcium supplementations is very frequent in such patients. On the other hand, both calcium supplementation, and even more vitamin D therapy, can worsen the risk of developing urolithiasis by increasing calcium, phosphate, and oxalate urinary excretion. Despite the clinical and practical relevance of this issue, the evidence on this topic is scarce and contradictory. Therefore, some concerns exist about how and whether to prescribe such supplements to a patient with a history of kidney stones. In this narrative review, we resume some pivotal pathophysiological concepts strictly related to the dealt topic, and we draw some considerations and personal opinions on the pros and cons of such prescriptions. Finally, we share with the reader our pragmatic algorithm for handling the urolithiasis risk in patients who have strong indications to be prescribed vitamin D and calcium supplementations.

Nutrition and Kidney Stone Disease

The prevalence of kidney stone disease is increasing worldwide. The recurrence rate of urinary stones is estimated to be up to 50%. Nephrolithiasis is associated with increased risk of chronic and end stage kidney disease. Diet composition is considered to play a crucial role in urinary stone formation. There is strong evidence that an inadequate fluid intake is the major dietary risk factor for urolithiasis. While the benefit of high fluid intake has been confirmed, the effect of different beverages, such as tap water, mineral water, fruit juices, soft drinks, tea and coffee, are debated. Other nutritional factors, including dietary protein, carbohydrates, oxalate, calcium and sodium chloride can also modulate the urinary risk profile and contribute to the risk of kidney stone formation. The assessment of nutritional risk factors is an essential component in the specific dietary therapy of kidney stone patients. An appropriate dietary intervention can contribute to the effective prevention of recurrent stones and reduce the burden of invasive surgical procedures for the treatment of urinary stone disease. This narrative review has intended to provide a comprehensive and updated overview on the role of nutrition and diet in kidney stone disease.

The idiopathic hypercalciuria reviewed. Metabolic abnormality or disease?

Idiopathic hypercalciuria (IH) is defined as that clinical situation in which an increase in urinary calcium excretion is observed, in the absence of hypercalcemia and other known causes of hypercalciuria. In recent years, its diagnosis in pediatric age has been more frequent because it has been known that it can debut with very different symptoms, in the absence of kidney stone formation. The discovery of genetic hypercalciuric stone-forming rats has allowed us to glimpse the pathophysiological mechanism of IH since they show many data in common with humans with IH as normal levels of blood calcium, intestinal calcium hyperabsorption, increased bone resorption and a defect in the renal tubular calcium reabsorption. In 1993, it was shown that in these animals there is an increase in the number of vitamin D receptors (VDR) in the intestine, which favors an increase in the functional capacity of calcitriol-VDR complexes that explains the increase in intestinal transport of calcium. The same happens at the bone level producing a greater resorption. In our opinion, IH is a 'metabolic anomaly' or, better, an inheritable constitutive metabolic characteristic. In this sense, what patients with IH would inherit is the availability of having a greater number of VDRs in their cells than those with normal urinary calcium excretion. IH cannot be considered a sensu stricto disease, so pharmacological treatment must be individualized.

Testing the dogma that total phospholipid fatty acid composition of blood plays a role in kidney stone pathogenesis, using a high-low risk human model: results from a pilot study

Previous studies have suggested that ω-3 and ω-6 polyunsaturated fatty acid (PUFA) composition in plasma and red blood cell (RBC) total phospholipids plays a role in urolithiasis. Our aim was to test the robustness of this dogma by retrospectively comparing baseline profiles of these parameters in subjects from high- and low-stone-risk groups. The documented difference in stone occurrence in white (relatively common) (W) and black (rare) (B) subjects prompted us to select these groups as the high-low risk model for the study. Blood and urine samples were obtained from ten subjects in each group and were analysed for PUFAs and stone risk factors, respectively. Concentrations of linoleic acid (LA), eicosadienoic acid (EDA) and arachidonic acid (AA) in plasma and or/RBC total phospholipids were significantly higher in B. Differences in other PUFA profiles were also observed. There was no inter-group difference in AA/LA ratios. Urinary oxalate was significantly higher while urinary phosphate was significantly lower in B. We speculate that elevated AA in B might arise because of a possibly enhanced elongation of LA to EDA, as well as an enhanced ∆-8-desaturation of EDA to dihomo-gamma-linolenic acid (DGLA), which is the immediate precursor of AA. Alternatively, we speculate that the ∆-5-desaturation step of DGLA to AA might be more highly activated in this group. Irrespective of the mechanism, our observed inter-group differences in phospholipid PUFA composition are in conflict with previously published dogma which relates PUFA characteristics to high- and low-stone risk.

Increased dietary long-chain polyunsaturated fatty acids alter serum fatty acid concentrations and lower risk of urine stone formation in cats

The lifespan of cats with non-obstructive kidney stones is shortened compared with healthy cats indicating a need to reduce stone formation and minimize chronic kidney disease. The purpose of this study was to investigate the effects of increasing dietary polyunsaturated fatty acids (PUFA) on urine characteristics. Domestic-short-hair cats (n = 12; mean age 5.6 years) were randomized into two groups and fed one of two dry-cat foods in a cross-over study design. For one week before study initiation, all cats consumed control food that contained 0.07% arachidonic acid (AA), but no eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA). Group 1 continued eating control food for 56 days. Group 2 was fed test food for 56 days, which was control food plus fish oil and high-AA oil. Test food contained 0.17% AA, 0.09% EPA and 0.18% DHA. After 56 days, cats were fed the opposite food for another 56 days. At baseline and after each feeding period, serum was analyzed for fatty acid concentrations, and urine for specific gravity, calcium concentration, relative-super-saturation for struvite crystals, and a calcium-oxalate-titrimetric test was performed. After consuming test food, cats had increased (all P<0.001) serum concentrations of EPA (173%), DHA (61%), and AA (35%); decreased urine specific gravity (P = 0.02); decreased urine calcium concentration (P = 0.06); decreased relative-super-saturation for struvite crystals (P = 0.03); and increased resistance to oxalate crystal formation (P = 0.06) compared with cats consuming control food. Oxalate crystal formation was correlated with serum calcium concentration (r = 0.41; P<0.01). These data show benefits for reducing urine stone formation in cats by increasing dietary PUFA.

Companion Animals Symposium: dietary management of feline lower urinary tract symptoms

Experimental and clinical investigations have confirmed the importance of dietary modifications in medical protocols designed to treat and prevent feline lower urinary tract signs (LUTS). The objective of this review is to discuss common medical conditions contributing to feline LUTS and to present currently used and potential preventative dietary modifications. Feline LUTS are a set of clinical conditions with similar symptoms related to inappropriate urine elimination due to a combination of genetics, stress and frustration reactions, environment, and medical condition or conditions, for example, idiopathic cystitis, urolithiasis, urethral obstruction, and urinary tract infection. The main goals of dietary modifications to prevent LUTS are 1) promote large dilute volumes of urine, 2) decrease the relative supersaturation of urine for specific stone types, and 3) promote healthy bacterial populations in the gastrointestinal and urogenital tracts. The impact of dietary composition, including dietary moisture, protein concentration and digestibility, mineral concentrations (i.e., Na, Cl, Ca, P, and Mg), inclusion of acidifiers and alkalinizing agents, inclusion of vitamin B6, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and γ-linolenic acid, fiber concentration and characteristics, and oxalate degrading probiotics, on these outcomes is discussed, and dietary guidelines for cats are provided. Because of the complex interaction of diet composition, environment, and animal physiology, there is a need for clinical research linking current recommendations or dietary options for the treatment and prevention of LUTS with physiological outcomes (i.e., decreased relative supersaturation and LUTS recurrence). Additionally, for many recommendations (e.g., probiotic administration, EPA, DHA), extrapolation from other species was necessary. Research is needed in feline patients with LUTS on these dietary components.

Cyclooxygenase 2 and prostaglandin E2 regulate the attachment of calcium oxalate crystals to renal epithelial cells

OBJECTIVE

To determine the roles of endogenous cyclooxygenase 2 and prostaglandin E(2) in crystal-cell binding, which is considered to be an important step in the development of intratubular nephrocalcinosis.

METHODS

An expression plasmid for human cyclooxygenase 2 was introduced into Madin-Darby canine kidney cells using the lipofection method. Cyclooxygenase activity was measured using thin-layer chromatography, and the prostaglandin E(2) concentration was determined with an enzyme immunoassay. In addition, crystal attachment was evaluated with a liquid scintillation counter using [(14)C] calcium oxalate monohydrate crystals, and immunohistochemistry and an enzyme immunoassay were used to analyze and quantify the expression of hyaluronan, a crystal-binding molecule.

RESULTS

Cyclooxygenase 2-overexpressing Madin-Darby canine kidney cells produced about 10-fold more prostaglandin E(2) than wild-type Madin-Darby canine kidney cells, and their hyaluronan production was also upregulated. The attachment of calcium oxalate monohydrate crystals to cyclooxygenase 2-overexpressing Madin-Darby canine kidney cells was significantly reduced compared with their attachment to wild-type and mock-transfected Madin-Darby canine kidney cells. Pre-incubation of the cyclooxygenase 2-overexpressing cells, as well as the mock-transfected and wild-type cells with the cyclooxygenase 2 selective inhibitor etodolac, increased the cellular attachment of calcium oxalate monohydrate crystals in a dose-dependent manner.

CONCLUSIONS

These findings suggest that cyclooxygenase 2 expression and the resultant increase in endogenous prostaglandin E(2), leading to increased hyaluronan production, help to prevent nephrocalcinosis by inhibiting the attachment of calcium oxalate monohydrate crystals to the surface of renal epithelial cells.

Omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid in the management of hypercalciuric stone formers

OBJECTIVE

To investigate the use of fish oil in the dietary management of hypercalciuric stone formers. Prostaglandins have been linked to urinary calcium excretion, suggesting a role for omega-3 fatty acids in the treatment of hypercalciuric urolithiasis.

METHODS

We retrospectively studied a cohort of patients treated at our stone clinics from July 2007 to February 2009. Patients' urinary risk factors for stone disease were evaluated with pre- and post-intervention 24-hour urine collections. All patients received empiric dietary recommendations for intake of fluids, sodium, protein, and citric juices. All subjects with hypercalciuria (urinary calcium>250 mg/d for males or >200 mg/d for females) on at least two 24-hour urine collections were counseled to supplement their diet with fish oil (1200 mg/d).

RESULTS

Twenty-nine patients were followed for 9.86±8.96 months. The mean age was 43.38±13.78 years. Urinary calcium levels decreased in 52% of patients, with 24% converting to normocalciuria. The average urinary calcium (mg/d) decreased significantly from baseline (329.27±96.23 to 247.47±84.53, P<.0001). Urinary oxalate excretion decreased in 34% of patients. The average urinary oxalate (mg/d) decreased significantly from baseline (45.40±9.90 to 32.9±8.21, P=.0004). Urinary citrate (mg/d) increased in 62% of subjects from baseline (731.67±279.09 to 940.22±437.54, P=.0005). Calcium oxalate supersaturation decreased in 38% of the subjects significantly from baseline (9.73±4.48 to 3.68±1.76, P=.001).

CONCLUSION

Omega-3 fatty acids combined with empiric dietary counseling results in a measurable decrease in urinary calcium and oxalate excretion and an increase in urinary citrate in hypercalciuric stone formers.

Effect of n-3 fatty acid supplementation on urinary risk factors for calcium oxalate stone formation

PURPOSE

Findings are inconsistent in a few studies of the effect of n-3 fatty acid supplementation on urinary calcium and oxalate excretion in stone formers. We evaluated the physiological effects of supplementation with eicosapentaenoic acid and docosahexaenoic acid on urinary risk factors for calcium oxalate stone formation under standardized conditions.

MATERIALS AND METHODS

We studied 15 healthy subjects initially while consuming a standardized diet for 5 days (control phase). During consecutive intervention phases 1-5-day standardized diet, 2-20-day free diet and 3-5-day standardized diet participants received 900 mg eicosapentaenoic acid and 600 mg docosahexaenoic acid daily. While ingesting the standardized diets, daily 24-hour urine samples were collected.

RESULTS

After short-term supplementation with eicosapentaenoic acid and docosahexaenoic acid in phase 1 we noted no changes in urinary parameters compared to the control phase. After 30-day supplementation with eicosapentaenoic acid and docosahexaenoic acid in phase 3 relative supersaturation with calcium oxalate decreased significantly by 23% from a mean ± SD of 2.01 ± 1.26 to 1.55 ± 0.84 due to significantly decreased urinary oxalate excretion (p = 0.023). Other urinary variables were not affected by supplementation.

CONCLUSIONS

Results show that 30-day n-3 fatty acid supplementation effectively decreases urinary oxalate excretion and the risk of calcium oxalate crystallization. The mechanism of the physiological effect may be decreased cellular oxalic acid exchange attributable to an altered fatty acid pattern of membrane phospholipids with concomitant changes in oxalate transporter activity. Calcium oxalate stone formers may benefit from long-term n-3 fatty acid supplementation.

Bone disease and idiopathic hypercalciuria

Observational and epidemiologic studies alike have shown that idiopathic hypercalciuric (IH) stone-forming patients typically show bone mineral density scores that are significantly lower than those observed for age- and sex-matched normal subjects or those for nonhypercalciuric stone-forming patients. Most of these studies have relied on changes in bone mineral density and have not explored the mechanism(s) involved. There have been a small number of studies that have relied on dynamic bone histomorphometry to ascertain the nature of the bone defect in IH patients. When performed, these studies clearly have shown increased bone resorption and high bone turnover in patients with fasting hypercalciuria whereas suppressed bone formation indices are the most consistent finding in patients with the absorptive variant of IH. The causes of this apparent difference in bone remodeling between the 2 variants of IH still is uncertain. Available evidence suggests that potential mechanisms may be dependent in large part to genetic, metabolic, and nutritional causes of hypercalciuria and bone loss in patients with IH.

Reduced bone formation and relatively increased bone resorption in absorptive hypercalciuria

Absorptive hypercalciuria (AH), a common stone-forming condition characterized biochemically by intestinal hyperabsorption of calcium and hypercalciuria may be associated with bone loss. In AH type I (AH-1), hypercalciuria persists despite restriction in dietary calcium intake. We therefore hypothesized that the skeleton may contribute to the hypercalciuria in this subgroup of patients. Histomorphometric analysis of iliac crest biopsies were performed on nine stone-formers with AH-1 and on nine matched normal subjects. After stabilization on a stone-prevention diet, calcium homeostasis in the stone formers was then evaluated on inpatient constant metabolic diet before and after short-term blockade of bone resorption by alendronate (10 mg daily, 17 days total). Compared with controls, the stone-formers had lower indices of bone formation (osteoblast surface/bone surface 1.8+/-2.1 vs 3.0+/-1.5%, P=0.04; wall thickness 35.8+/-6.9 vs 47.2+/-7.6%, P=0.001) and relatively higher bone resorption (osteoclast surface/bone surface 0.4+/-0.2 vs 0.2+/-0.2%, P=0.05). In the stone-formers, a short-term course of alendronate treatment corrected fasting urinary calcium (0.14+/-0.06 to 0.06+/-0.04 mg Ca/mg Cr, P=0.001) and marginally reduced 24-h urinary calcium by 48 mg/day (P=0.06). Increased intestinal calcium absorption and hypercalciuria persisted, but estimated calcium balance improved (P=0.007). Our results suggest that the hypercalciuria of AH-1 originates primarily from intestinal hyperabsorption of calcium, but bone resorption in excess of bone formation may contribute.

Fatty acids and idiopathic calcium nephrolithiasis

Clinical and experimental investigations seem to underline the important role of fatty acids in the pathogenesis of hypercalciuria, a well-known risk factor for lithogenesis. To evaluate the relationships between the previously reported increase in plasma phospholipid arachidonic acid level and the factors responsible for calcium metabolism in idiopathic calcium nephrolithiasis, a best-fit model was constructed. This new statistical application shows a causal relationship between plasma phospholipid arachidonic acid content, intestinal calcium absorption, biochemical markers of bone turnover, urinary calcium excretion and bone mineral density at the lumbar spine. This model suggests that a defect in the phospholipid fatty acid composition could represent the primary event responsible for the mosaic of metabolic and clinical alterations that are distinctive features of renal stone formers, such as kidney, intestine, and bone calcium metabolism, and several forms of idiopathic hypercalciuria.

Fatty acid intake and incident nephrolithiasis

BACKGROUND

Elevated levels of arachidonic acid in cell membranes may promote the hypercalciuria and hyperoxaluria that are characteristic of idiopathic calcium nephrolithiasis. The intake of n-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), may decrease the arachidonic acid content of cell membranes and reduce urinary excretion of calcium and oxalate. It has been proposed that greater intake of EPA and DHA (through dietary sources or fish oil supplementation) may reduce the risk for kidney stone formation.

METHODS

After excluding subjects with a prior history of kidney stones, we prospectively examined the relation between fatty acid intake (including fish oil supplements) and incident symptomatic kidney stones in 3 large cohorts: the Health Professionals Follow-Up Study (N = 46,043), the Nurses' Health Study I (NHS I; N = 92,079), and the Nurses' Health Study II (N = 96,304). Self-administered food-frequency questionnaires were used to assess fatty acid intake every 4 years. Cox proportional hazards regression was used to adjust simultaneously for a variety of risk factors.

RESULTS

We documented 3,956 incident kidney stones during a combined 36 years of follow-up. After adjustment for intake of other dietary factors, no association was detected between the intake of arachidonic acid or linoleic acid (a metabolic precursor to arachidonic acid) and the risk for incident kidney stones. Older women (NHS I) in the highest quintile of EPA and DHA intake had a multivariate relative risk of 1.28 (95% confidence interval, 1.04 to 1.56; P for trend = 0.04) of stone formation compared with women in the lowest quintile. However, this relation was not observed in the other 2 cohorts.

CONCLUSION

Fatty acid intake is not consistently associated with the development of kidney stones. Greater levels of arachidonic and linoleic acid intake do not increase the risk for developing a kidney stone, and greater intake of n-3 fatty acids does not reduce the risk.

Bone mineral content in calcium renal stone formers

Idiopathic renal calcium stone disease often presents with reduced bone mineral content. Investigations using non-invasive methods for the measurement of bone mineral content (single and dual-photon absorptiometry, dual-energy x-ray absorptiometry, quantitative computed tomodensitometry) show a slight decrease in skeletal mineral content of idiopathic renal stone formers (RSFs). The alterations in bone mineral content in RSFs have different explanations: prostaglandin-mediated bone resorption, subtle metabolic acidosis and 1-25 vitamin D disorders. Bone mineral content is worsened by insufficient dietary calcium leading to a negative calcium balance.

Effect of high protein diet on stone-forming propensity and bone loss in rats

BACKGROUND

High protein diets are believed to cause kidney stone formation and bone loss, but the mechanisms mediating these changes are unknown. The purpose of this study was to create an animal model of animal protein excess and to evaluate the response of kidney and bone to the dietary protein load.

METHODS

Rats (12 per group) were pair-fed with a high (48%) and low (12%) casein diets that were otherwise identical in their content of sodium, potassium, calcium, phosphorus, and magnesium.

RESULTS

Compared with the low casein group, the high casein group delivered a substantial acid load during 59 days of study, since it significantly decreased urinary pH, and increased urinary ammonium, titratable acidity, and net acid excretion. Animals on high casein diet also had higher urinary volumes. On the high casein diet, urinary calcium excretion was significantly higher and urinary citrate excretion and concentration was significantly lower. On the high casein diet, urinary saturation of calcium phosphate was higher. Serum calcitriol concentration did not significantly differ between the two groups. Histomorphometric analysis of femur procured after 59 days on the diet showed marked increase in bone resorption in the high casein group. Hypocitraturia was associated with increased activity of sodium-citrate cotransporter in renal cortical brush-border membranes (BBM) in the high casein group.

CONCLUSION

Both the kidney and bone contribute to the pathogenesis of hypercalciuria during high casein diet in rats. Hypocitraturia is probably renal in origin. This rat model will be useful in elucidating the mechanisms by which high protein intake increases the risk of nephrolithiasis and bone loss in human beings.

Role of Nutrition in the Formation of Calcium-Containing Kidney Stones

Diet plays an important role in the pathogenesis of calcium-containing kidney stones. Although much work has demonstrated that specific dietary components alter urinary composition and supersaturation, relatively few studies link the ingestion of these components with actual nephrolithiasis. This article reviews the dietary factors thought to promote or inhibit the formation of calcium stones and discusses the current controversies in the field of nutrition and nephrolithiasis. Special attention is paid to the roles of dietary calcium, supplemental calcium, oxalate, phytate, and n-3 fatty acids. We offer dietary recommendations to individuals who have suffered from a calcium-containing kidney stone, and emphasize that a patient's 24-hour urine chemistries should be used to help guide dietary intervention.

n-3 Fatty acids and their role in nephrologic practice

During the past year, a newly reported clinical trial has strengthened the argument for recommending daily treatment with n-3 polyunsaturated fatty acids in patients with immunoglobulin A nephropathy (the most common form of primary glomerulonephritis in the world) who are at high risk for progression of renal disease. Studies are underway that involve a combination of cyclosporine A, a commonly prescribed immunosuppressive agent in solid-organ transplantation, with a high-potency n-3 polyunsaturated fatty acid to reduce cyclosporine toxicity. Two studies reported during the past year show promise that dietary supplementation with n-3 polyunsaturated fatty acids will substantially decrease vascular access graft thrombosis in patients receiving maintenance hemodialysis, and may reduce hypercalciuria in patients who suffer from kidney stones.

Effect of ethyl icosapentate on urinary calcium and oxalate excretion

BACKGROUND

The effect of ethyl icosapentate (EPA-E) on urinary calcium and oxalic acid excretion was examined to evaluate whether EPA-E is useful in the prevention of calcium-containing urinary stones.

METHODS

For 6 months, urine was measured daily from 40 calcium-containing urinary stone producers at an outpatient clinic, before and after the administration of 1800 mg/day EPA-E. The urine was measured for volume, urea nitrogen, creatinine, calcium, magnesium, phosphorus, uric acid, oxalic acid and citric acid. Serum total cholesterol and triglyceride were also measured.

RESULTS

Urinary calcium excretion was not reduced in any of the patients or particular hypercalciuric groups, nor did the level of calcium change. However, nine of the 25 hypercalciuric patients experienced a significant urinary calcium reduction to the normal calciuric level (a reduction of approximately 44%). It is not known why these particular patients experienced a reduction. Urinary oxalic acid did not change, whether hypercalciuria was present or not.

CONCLUSIONS

These findings suggest that EPA-E is not particularly effective in reducing urinary calcium excretion in the hypercalciuric patients, but it needs future investigation because some patients experienced significant urinary calcium reduction.

Plasma phospholipid arachidonic acid content and calcium metabolism in idiopathic calcium nephrolithiasis

BACKGROUND

Reports of an increase in plasma and erythrocyte phospholipid arachidonic acid content and in urinary prostaglandin E2 (PGE2) excretion in patients with idiopathic calcium nephrolithiasis suggested their crucial role in the pathogenesis of hypercalciuria, a well-known risk factor for lithogenesis.

METHODS

To confirm this hypothesis, 15 healthy subjects and 20 nephrolithiasis patients were evaluated for plasma phospholipid polyunsaturated fatty acid content and PGE2 concentration, serum parathyroid hormone, 25 hydroxyvitamin D3, 1, 25-dihydroxyvitamin D3, and bone-specific alkaline phosphatase levels, as well as urinary excretion of calcium, biochemical markers of bone resorption (hydroxyproline and crossLaps), and intestinal calcium absorption. Furthermore, the effect of a 30-day fish-oil diet supplementation on the previously mentioned parameters was investigated in the patients.

RESULTS

At baseline, patients compared with controls showed higher levels of plasma phospholipid arachidonic acid content (P = 0.002), PGE2 (P = 0.0004), serum 25-vitamin D3 (P = 0.001), and 1,25-vitamin D3 (P = 0.001), urinary excretion of calcium (P = 0.001), hydroxyproline (P = 0.007), and crossLaps (P = 0.019), as well as intestinal calcium absorption (P = 0.03 at 60 min). Fish oil supplementation induced a reduction in the plasma phospholipid arachidonic acid level (P < 0.0001), and except for serum concentrations of 25-vitamin D3, normalized baseline blood and urinary parameters, including intestinal calcium absorption. A close correlation between plasma PGE2 and serum 1,25-vitamin D3 (P = 0.004) and between phospholipid arachidonic acid and intestinal calcium absorption (P = 0.0002) and calciuria (P = 0.007) was observed, as well as between urine excretion of crossLaps and hydroxyproline (P < 0.0001), crossLaps and calcium (P < 0.0001), and hydroxyproline and calcium (P < 0.0001).

CONCLUSIONS

These findings indicate that the phospholipid arachidonic acid content anomaly could represent the primary event responsible for the mosaic of metabolic and clinical alterations that are distinctive features of renal stone formers, and suggest that a common pathogenetic mechanism might account for the several forms of hypercalciuria detected in idiopathic calcium nephrolithiasis.

Abnormal arachidonic acid content of red blood cell membranes and main lithogenic factors in stone formers

BACKGROUND

Increased arachidonic acid content in red blood cell membranes of stone formers (SF) has recently been reported and is hypothesized as representing the underlying causal factor for both hyperoxaluria and hypercalciuria. We performed the present study to see whether we could confirm this finding and to test whether any relationship exists between the fatty acid composition of red blood cell membranes and the main metabolic factors involved in stone formation.

METHODS

In 21 SF and 40 healthy controls subjects the fatty acid composition of red blood cell membranes was assessed. In addition, the following parameters were evaluated in SF: daily and fasting urinary calcium excretion, fractional intestinal calcium absorption, 1,25-dihydroxy-vitamin D, intact parathyroid hormone, hydroxyproline in fasting urine, daily urinary excretion of oxalate, citrate, urate, electrolytes, urea, sulphate, relative supersaturation for calcium oxalate monohydrate.

RESULTS

The red blood cell membrane of SF had a lower content of arachidonic acid, linoleic acid, and docosahexaenoic acid than that of control subjects. Arachidonic acid content was not correlated with any of the parameters studied. However, when patients were grouped according to the degree of oxalate excretion, hyperoxaluric SF had a higher arachidonic acid content and arachidonic/linoleic acid ratio than SF with normal oxalate excretion.

CONCLUSIONS

Our results do not confirm the finding of an increased arachidonic acid content of red blood cell membrane in SF. On the contrary, reduced arachidonic acid levels were found in our patients. However, hyperoxaluric SF had a relatively higher arachidonic acid content than SF with normal urinary oxalate excretion.

Dietary manipulation of delta-6-desaturase modifies phospholipid arachidonic acid levels and the urinary excretion of calcium and oxalate in the rat: insight in calcium lithogenesis

An anomalous n-6 polyunsaturated fatty acid composition in plasma and erythrocyte membrane phospholipids, namely increased levels of arachidonic acid (AA), has been reported in calcium nephrolithiasis and has been proposed to play an important role in its pathogenesis. To confirm this, in rats we modified phospholipid AA levels by dietary manipulation of the delta-6-desaturase, the rate-limiting enzyme of the fatty acid biosynthetic pathway, and evaluated the effect on cellular and renal functions predisposing to lithogenesis. Increased AA levels led to conditions at risk for nephrolithiasis: higher oxalate flux and lower sodium cotransport in erythrocytes and a rise in urinary prostaglandin E2, calcium, sodium, and oxalate levels; reduced AA levels reversed these changes. In vitro, in human erythrocytes the incorporation of exogenous AA into membranes increased band 3 protein phosphorylation directly activating the Ser/Thr protein kinase CK1 and induced a parallel raise in band 3-mediated oxalate transport. These findings demonstrate the pivotal role of phospholipid AA in modulating erythrocyte and renal transport of calcium and oxalate.

Regulation of renal epithelial cell affinity for calcium oxalate monohydrate crystals

The binding and internalization of calcium oxalate monohydrate (COM) crystals by tubular epithelial cells may be a critical step leading to kidney stone formation. Exposure of MDCK cells to arachidonic acid (AA) for 3 days, but not oleic or linoleic acid, decreased COM crystal adhesion by 55%. Exogenous prostaglandin PGE(1) or PGE(2) decreased crystal binding 96% within 8 h, as did other agents that raise intracellular cAMP. Actinomycin D, cycloheximide, or tunicamycin each blocked the action of PGE(2), suggesting that gene transcription, protein synthesis, and N-glycosylation were required. Blockade of crystal binding by AA was not prevented by the cyclooxygenase inhibitor flurbiprofen, and was mimicked by the nonmetabolizable AA analog eicosatetryanoic acid (ETYA), suggesting that generation of PGE from AA is not the pathway by which AA exerts its effect. These studies provide new evidence that binding of COM crystals to renal cells is regulated by physiological signals that could modify exposure of cell surface molecules to which the crystals bind. Intrarenal AA, PGs, and/or other agents that raise the intracellular concentration of cAMP may serve a protective function by preventing crystal adhesion along the nephron, thereby defending the kidney against crystal retention and stone formation.

Pathogenesis of idiopathic calcium nephrolithiasis: update 1997

Idiopathic calcium nephrolithiasis (ICN) is a frequent disease in Western countries. The physicochemical theory of lithogenesis, which explains stone formation by the precipitation, growth, and crystalline aggregation of lithogenic salts in the urine, has contributed greatly to the understanding of the pathogenesis of calcium urolithiasis. However, several aspects are still unexplained; the co-existence of familial occurrence, primary tubular dysfunctions with ICN, and anomalies in the systemic handling of oxalate and calcium led to the development of a cellular hypothesis of ICN. A number of cellular defects in the handling of ions has been reported that involves both anion and cation transport. These anomalies are probably the expression of a still unknown cellular defect in idiopathic calcium stone formers. We suggested that an anomaly in the cell membrane composition might be responsible for the complex array of cell ion flux abnormalities observed in ICN. Recently, a disorder in the n-6 polyunsaturated fatty acid series has been described; it is characterized by a lower linoleic acid content and a higher arachidonic acid concentration in both plasma and erythrocyte membrane phospholipids of renal calcium stone patients. This anomaly could cause an increased activity of ion carriers; furthermore, it may lead to increased prostaglandin synthesis and to secondary phenomena at the kidney, skeletal, and intestinal level. As a consequence, critical conditions for lithogenesis in the kidney may ensue. The data suggest a common pathogenesis for hypercalciuria and hyperoxaluria. The systemic defect in the phospholipid arachidonic acid level may be both of dietary or genetic origin; experimental data suggest that the increase in delta-6 desaturase activity, the limiting enzyme in the metabolic pathway of polyunsaturated fatty acids, might be relevant to the pathogenesis of lipid abnormalities observed in nephrolithiasis and to the pathogenesis of ICN and its related problems (at the kidney, intestinal, and bone level).

Calcium metabolism, osteoporosis and essential fatty acids: a review

Essential fatty acid (EFA)-deficient animals develop severe osteoporosis coupled with increased renal and arterial calcification. This picture is similar to that seen in osteoporosis in the elderly, where the loss of bone calcium is associated with ectopic calcification of other tissues, particularly the arteries and the kidneys. Recent mortality studies indicate that the ectopic calcification may be considerably more dangerous than the osteoporosis itself, since the great majority of excess deaths in women with osteoporosis are vascular and unrelated to fractures or other bone abnormalities. EFAs have now been shown to increase calcium absorption from the gut, in part by enhancing the effects of vitamin D, to reduce urinary excretion of calcium, to increase calcium deposition in bone and improve bone strength and to enhance the synthesis of bone collagen. These desirable actions are associated with reduced ectopic calcification. The interaction between EFA and calcium metabolism deserves further investigation since it may offer novel approaches to osteoporosis and also to the ectopic calcification associated with osteoporosis which seems to be responsible for so many deaths.

Parathormone, 1,25 dihydroxyvitamin D and prostaglandin E2 correlation in children with idiopathic hypercalciuria

As urinary prostaglandin excretion might be involved in idiopathic hypercalciuria, we studied the excretion of prostaglandin E2 and calcium together with serum prostaglandin E2, parathormone and 1,25 dihydroxyvitamin D in 20 patients and 11 controls Idiopathic hypercalciuric patients showed increased levels of urinary prostaglandin E2-like activity, which is correlated with calcium excretion. Although no change was observed in serum parathormone level in control and hypercalciuric patients, there was a positive correlation between serum 1,25 dihydroxyvitamin D and prostaglandin E2-like activity. These findings suggest that prostaglandin E2 could play a role in the hypercalciuria syndrome, possibly by increasing 1,25 dihydroxyvitamin D synthesis.

Emergency treatment of renal colic with intravenous ketoprofen

The non-steroidal anti-inflammatory drug (NSAID) Ketoprofen (Profenid) is used as intravenous monotherapy incorporated in 0.9% normal saline solution (100 mg Ketoprofen ampoule + 200 ml normal saline) in the treatment of renal colic. We present our experience in 65 patients complaining of clinically diagnosed renal colic who were treated by intravenous saline-Ketoprofen. Prospective investigations revaled urinary calculi in 51 patients, oxaluria (crystalluria) in 5, acute colitis in 2, severe myositis in 2, negative investigations in 3 and radiculitis in 2 patients. Positive response was observed in 93.8% of patients as far as pain relief is concerned. Pain relief started within 5-7 minutes after beginning the infusion. Duration of analgesic effect ranged between 4 and 12 hours. Repeating the injection was done for maintenance of analgesia. Side effects included drowsiness in 2 patients, palpitation in 1 patient, epigastric pain in 1, muscular cramp in 1 patient. Ketoprofen, an antiprostaglandin, is a powerful anti-inflammatory and potent analgesic. Intravenous saline-Ketoprofen is a good emergency treatment for acute episodes of renal colic.

Evening primrose oil reduces urinary calcium excretion in both normal and hypercalciuric rats

Hypercalciuria is an important risk factor in the aetiology of idiopathic urolithiasis and many treatment modalities in clinical practice are directed towards reducing urinary calcium excretion. There are no natural animal models of hypercalciuria, such as the spontaneous hypertensive rat; however, the streptozotocin-diabetic rat is accepted as a good model for studies of disordered renal function associated with diabetes mellitus. Hypercalciuria is a prominent feature of the streptozotocin-diabetic rat and the model was, therefore, used to study the influence of evening primrose oil on urinary calcium excretion. Twenty rats divided into two groups of ten rats each were maintained on either normal rat chow (group 1) or primrose oil enriched diet (group 2) for 10 weeks. At 4 weeks both groups of rats were made diabetic with streptozotocin. Urine calcium measurements were serially performed before commencement of the diet, during the pre-streptozotocin (pre-diabetic) phase and during the post streptozotocin (diabetic) phase. The urine calcium excretion was significantly less in the primrose oil fed animals during both the pre-diabetic phase and the diabetic phase compared with the rats on the normal rat chow. These results indicate that evening primrose oil, a rich source of gamma-linolenic acid, helps to reduce urine calcium excretion in normal animals as well as in the hypercalciuric streptozotocin-diabetic rat. Dietary modifications with long-chain omega-6 and omega-3 fatty acids might be a useful adjunct in the treatment of idiopathic hypercalciuric urolithiasis.

Does fish oil benefit stone formers?

The possibility that dietary fish oil supplementation may benefit patients with hypercalciuric urolithiasis by decreasing calcium excretion and enhancing protective mechanisms has been studied in rats and humans. In experiments on rats in metabolic cages, fish oil inhibited experimental nephrocalcinosis induced by intraperitoneal calcium gluconate. There were no significant changes in urinary biochemistry. In a clinical study on 18 hypercalciuric recurrent stone patients fish oil significantly decreased urinary calcium excretion. This effect was accompanied by decreases in the excretion of magnesium and citrate. Oxalate excretion and urinary fibrinolytic activity were unchanged. Overall, fish oil had a limited impact on the risk profile for recurrent urolithiasis.

Reduced vertebral bone density in hypercalciuric nephrolithiasis

Dual-energy x-ray absorptiometry and single-photon absorptiometry were used to determine bone density at the lumbar spine and radial shaft in 62 patients with absorptive hypercalciuria, 27 patients with fasting hypercalciuria, and 31 nonhypercalciuric stone formers. Lumbar bone density was significantly lower in patients with absorptive (-10%) as well as in those with fasting hypercalciuria (-12%), with 74 and 92% of patients displaying values below the normal mean, whereas only 48% of the nonhypercalciuric stone formers had bone density values below the normal mean. In contrast, radial bone density was similar in all three groups of renal stone formers investigated. The comparison of urinary chemistry in patients with absorptive hypercalciuria and low normal bone density compared to those with high normal bone density showed a significantly increased 24 h urinary calcium excretion on random diet and a trend toward a higher 24 h urinary uric acid excretion and a higher body mass index in patients with low normal bone density. Moreover, among the patients with absorptive hypercalciuria we found a statistically significant correlation between the spinal bone density and the 24 h sodium and sulfate excretion and the urinary pH. These results gave evidence for an additional role of environmental factors (sodium and animal proteins) in the pathogenesis of bone loss in absorptive hypercalciuria. In conclusion, our data suggest an osteopenia of trabecular-rich bone tissues in patients with fasting and absorptive hypercalciurias.

Calcium homeostasis and hypercalciuria in hyperprostaglandin E syndrome

Children with hyperprostaglandin E syndrome, a neonatal variant of Bartter syndrome with enhanced renal and systemic formation of prostaglandin E2, have hypercalciuria, nephrocalcinosis, and osteopenia. Because prostaglandin E2 affects tubular calcium handling, stimulates the formation of calcitriol in vitro, and has osteolytic activity, we studied calcium homeostasis and the influence of prostaglandin E2 formation on hypercalciuria in nine patients with hyperprostaglandin E syndrome during long-term indomethacin treatment and after its withdrawal. Suppression of prostaglandin E2 formation by indomethacin resulted in improvement of biochemical and clinical features of hyperprostaglandin E syndrome. However, hypercalciuria, osteopenia, and nephrocalcinosis did not completely resolve. Despite a low calcium diet, daily urinary calcium excretion was enhanced during and after withdrawal of indomethacin treatment (median 6.3, range 5.3 to 14, and median 9.4, range 4.4 to 38 mg/kg per day, respectively). Daily urinary calcium excretion was greater after withdrawal than during indomethacin treatment. Urinary calcium excretion was not correlated with urinary prostaglandin E2 excretion. Plasma levels of intact parathyroid hormone (median 11, range 6.8 to 12 pmol/L) and calcitriol (median 157, range 108 to 236 pg/ml) were elevated during indomethacin treatment and decreased after withdrawal of indomethacin. These data suggest that hypercalciuria in hyperprostaglandin E syndrome is mainly due to a renal leak of calcium, which is caused by enhanced renal formation of prostaglandin E2 and a tubular defect not related to prostaglandin E2 formation. There is no evidence for prostaglandin-stimulated calcitriol formation. Decreasing plasma levels of parathyroid hormone in the presence of renal calcium losses after withdrawal of indomethacin treatment may be due to a bone resorption process caused by systemic prostaglandin formation; the process may contribute to hypercalciuria in the patient not receiving indomethacin.

Etiology and treatment of urolithiasis

Nephrolithiasis is a heterogeneous disorder, with varying chemical composition and pathophysiologic background. Although kidney stones are generally composed of calcium oxalate or calcium phosphate, they may also consist of uric acid, magnesium-ammonium phosphate, or cystine. Stones develop from a wide variety of metabolic or environmental disturbances, including varying forms of hypercalciuria, hypocitraturia, undue urinary acidity, hyperuricosuria, hyperoxaluria, infection with urease-producing organisms, and cystinuria. The cause of stone formation may be ascertained in most patients using the reliable diagnostic protocols that are available for the identification of these disturbances. Effective medical treatments, capable of correcting underlying derangements, have been formulated. They include sodium cellulose phosphate, thiazide, and orthophosphate for hypercalciuric nephrolithiasis; potassium citrate for hypocitraturic calcium nephrolithiasis; acetohydroxamic acid for infection stones; and D-penicillamine and alpha-mercaptopropionylglycine for cystinuria. Using these treatments, new stone formation can now be prevented in most patients.

Vertebral mineral content in diet-dependent and diet-independent hypercalciuria

The vertebral mineral content was measured using dual photon absorptiometry in 41 calcium stone patients with idiopathic hypercalciuria. These patients had been previously divided into 2 groups (diet-dependent and diet-independent hypercalciuria) during a low sodium and low calcium diet. In some of the patients (11 with diet-dependent and 11 with diet-independent hypercalciuria) the vertebral mineral content was evaluated in relation to serum ionized calcium, intact parathyroid hormone, alkaline phosphatase and osteocalcin determined after a low sodium and low calcium diet. The vertebral mineral content, expressed as Z-VMD, was normal in diet-dependent and lower in diet-independent hypercalciuric stone patients (-0.30 +/- 1.19 versus -0.26 +/- 1.18, p less than 0.02). In 7 of 21 patients (33.3%) the vertebral mineral content was less than 2 standard deviations of the normal value, indicating a true involvement in bone metabolism. Serum intact parathyroid hormone and osteocalcin levels were not different from the controls in both groups, while alkaline phosphatase activity and ionized calcium were higher in diet-independent hypercalciuric patients. Serum ionized calcium was negatively correlated with bone vertebral density. The results suggest that an increased bone turnover may be a primary event in causing hypercalciuria in calcium stone patients unable to decrease urinary calcium to less than the calcium intake.

Prostanoids in paediatric kidney diseases

Prostanoids belong to the growing family of eicosanoids, which are all derived from arachidonic acid. Prostanoids act as modulators and mediators in a large spectrum of physiological and pathophysiological processes within the kidney. On the one hand, the potent vasoconstrictor and platelet-aggregating thromboxane (TX) A2 is involved in the pathophysiology of a variety of glomerular diseases, such as haemolytic-uraemic syndrome and immune-mediated glomerulopathies. Prostaglandin (PG) E2, on the other hand, interferes with tubular electrolyte and water handling. Clinical data support the hypothesis that this member of the prostanoid family contributes to the pathophysiology of Bartter's syndrome, hyperprostaglandin E syndrome, idiopathic hypercalciuria and renal diabetes insipidus. Both prostanoids, TXA2 and PGE2, are involved in the pathophysiology of obstructive uropathies. The physiological and protective role of renal vasodilator prostanoids (PGI2 and PGE2) has been studied during treatment with non-steroidal anti-inflammatory drugs. Part of the pharmacological effects of frusemide and converting enzyme inhibitors is mediated by PGI2 and PGE2. The role of renal prostanoids in cyclosporine toxicity is still equivocal. Future investigations on the physiological and pathophysiological role of renal prostanoids will have to consider the multiple interactions between prostanoids on the one hand, and classical hormones and other mediators (e.g. cytokines) on the other hand.

The effect of diclofenac sodium on urinary concentration of calcium, uric acid and glycosaminoglycans in traumatic paraplegics

Non-steroidal anti-inflammatory drugs (NSAID) have been shown to decrease calcium excretion in the experimental animal, in human volunteers and in calcium stone formers. Paraplegics tend to be hypercalciuric during the first 2 years after their injury and this is said to be a predisposing factor for stone formation in these patients. The effect of the NSAID diclofenac sodium was studied in 12 traumatic paraplegics who had sustained their injury 1 to 6 months previously; 24-h urine samples collected before and 2 weeks and 4 weeks after oral diclofenac sodium 50 mg tds were analysed for calcium, uric acid, glycosaminoglycans (GAGs) and volume. There were no significant changes in urinary volume, uric acid and GAGs excretion. However, urinary calcium concentration and 24-h calcium excretion decreased significantly following 2 weeks' and 4 weeks' treatment with diclofenac sodium.

The protective role of eicosapentaenoic acid [EPA] in the pathogenesis of nephrolithiasis

The low incidence of atherosclerosis and other degenerative diseases including stone disease in the Greenland Eskimo has been attributed to their high consumption of oily fish with its high concentration of eicosapentaenoic acid (EPA). Man cannot synthesis EPA from the precursor essential fatty acid, linolenic acid, and can only assimilate preformed EPA present in fish and fish oil, to bring about a change in the pathway of eicosanoid metabolism from the n-6 to the n-3 series. With a westernised diet the oxygenated products of renal prostaglandin synthesis are metabolites of the n-6 series and these are known to play an important role in several pathophysiological states including stone disease. Our previous studies have shown a relationship between prostaglandin activity and urinary calcium excretion and it would seem that the initiating factor/s for stone formation trigger the mechanisms for prostaglandin synthesis resulting in the biochemical abnormalities associated with stone disease. The Eskimo may be protected from these events by possession of an eicosanoid metabolism that follows an n-3 pathway. To test this hypothesis experiments were performed using an animal model of nephrocalcinosis. The animals were divided into three groups; one group was given an intra-peritoneal injection of 10% calcium gluconate daily for 10 days to induce nephrocalcinosis; a second group was fed MaxEPA fish oil before and during the calcium gluconate injections and a third group only received an intra-peritoneal injection of N saline. A group of 12 recurrent, hypercalciuric/hyperoxaluric stone-formers were treated with fish oil for eight weeks to study the effects on solute excretion. Nephrocalcinosis, which was readily produced in the control animals, was prevented in the experimental animals by pre-treatment with fish oil and urine calcium excretion was significantly reduced. The urinary calcium and oxalate excretion in the recurrent, hypercalciuric stone-formers was significantly reduced with fish oil treatment over an eight week period. There were no untoward side-effects. These studies indicate that the incorporation of EPA in the diet as a substitute metabolic pathway could be a unique way of correcting the biochemical abnormalities of idiopathic urolithiasis.

Plasma concentrations of atrial natriuretic factor and hemodynamics in pregnancy-induced hypertension

Plasma values of atrial natriuretic factor (ANF) were evaluated in 31 women with pregnancy-induced hypertension (PIH) and 31 normal pregnant women at the same age of gestation. In 27 women with PIH and 27 normal pregnant women forearm venous tone (FVT) was evaluated by Strain Gauge Plethysmography. Forearm vascular resistance (FVR) was measured as the ratio of mean blood pressure (MBP) to forearm blood flow. In addition Cardiac Index (CI) by means of transthoracic electrical bioimpedance and total peripheral vascular resistance (TPR) (with the Frank Equation) were also measured. In comparison with the normal pregnant women, the women with PIH had similar values of hematocrit (as an index of plasma volume) and significantly higher levels of FVR and TPR, while ANF plasma values did not differ significantly. Subdividing the women with PIH in relation to the presence of proteinuria (greater than or equal to 0.3 g/l), those with proteinuria, in addition to significantly higher levels of FVR and TPR, had significantly higher levels of FVT than normal pregnant women, while ANF plasma values were higher even though the difference was only near the level of significance. Hypertensive women with proteinuria also had higher values of FVT than hypertensive women without proteinuria. By means of multiple regression ANF did not show any significant correlations with hematocrit or sodium excretion. Hypertension with proteinuria seems to represent a more severe form of the disease in which, in addition to the probable influence of other factors such as the renin-angiotensin and prostaglandin systems, a greater increase in peripheral sympathetic tone than in hypertension alone appears to be present, causing a reduction in venous compliance in addition to the elevation in FVR and TPR, with increase in central blood volume and atrial stretch. This may explain the higher ANF plasma levels in these patients in comparison with normal pregnant women, even though the absence of a significant correlation of ANF with hematocrit and the fact that ANF increase was only near the level of significance may suggest a change in the relation between ANF secretion and atrial volume receptors in pregnancy either normal or complicated by hypertension. ANF does not seem to play an important role in water and sodium excretion in PIH probably because of the presence of very high plasma levels of hormones such as aldosterone, progesterone and oestriol which, together with renal prostaglandins, seem to be involved in diuresis and natriuresis in pregnancy.

Effect of nifedipine on urinary excretion of calcium and calcium-controlling hormones in essential hypercalciuria

Nifedipine has been shown to lower urinary calcium in "essential" hypercalciuria. However, the mechanism(s) by which this action takes place is completely unknown. This study describes the effect of nifedipine on some calcium-controlling hormones in essential hypercalciuria. Nifedipine (20 mg/day) was administered to ten essential hypercalciuric patients, and urinary PgE2, plasma bicyclic PgE2, 1,25 vitamin D3, and PTH were assayed before and after drug administration. Nifedipine promoted a significant fall in urinary calcium (352.1 +/- 87.67 SD vs. 231.2 +/- 74.62 mg/hr; t = 7.35, p less than .0001) and PgE2 (343.92 +/- 42.71 vs. 245.03 +/- 35.41 SD ng/24 hr; t = 6.18, p less than .0002), as well as in plasma bicyclic PgE2 (310.00 +/- 30.91 vs. 200.00 +/- 31.62 SD pg/ml; t = 9.86, p less than .0001) and 1,25 (OH)2 vitamin D3 (32.77 +/- 3.23 vs. 26.94 +/- 2.94 SD pg/ml; t = 6.53, p less than .0001), while PTH remained unaltered (18.50 +/- 3.63 vs. 19.50 +/- 4.09 SD ng/ml; t = 0.85, p, ns). Urinary calcium and PgE2 correlated positively before (r = 0.81, p less than .005) but not after treatment. The fall in urinary PgE2 brought about by nifedipine seems to be due to an inhibition of PgE2 synthesis, since the absolute decrements in both urinary PgE2 and plasma PgE2 metabolites were positively correlated (r = 0.79, p less than .007). No correlation was found between the absolute decrements of plasma bicyclic PgE2 and 1,25 (OH)2 vitamin D3. These data seem to suggest that the fall in urinary calcium brought about by nifedipine is in some way related to PgE2 synthesis inhibition and to uncoupling of 1,25 (OH)2 vitamin D3 and PTH action.

Glycose aminoglycane excretion and concentration in the urine of patients with frequently recurrent calcium-oxalate lithiasis prior to and following Diclofenac-Na therapy

Excretion and concentration of glycose aminoglycans were measured in 19 patients with frequent relapses of calcium-oxalate lithiasis, prior to and two weeks after onset of Diclofenac-Na therapy. In most patients, markedly enhanced glycose aminoglycan concentration and excretion could be demonstrated. Elevation of the high-molecular inhibitor potential in the urine results in reduced risk of calcium-oxalate lithogenesis, which may explain the therapeutic success of nonsteroidal anti-inflammatory drugs in the treatment of therapy resistant calcium-oxalate lithiasis.

Effect of aspirin and indomethacin on the serum and urinary calcium, magnesium and phosphate

Recent data have shown that administration of prostaglandin inhibitors to patients with hypercalciuric nephrolithiasis decreased urinary calcium excretion, implying a possible role for prostaglandins in calcium excretion. To explore this hypothesis, we investigated the effect of single dose or 7 days' administrations of aspirin (100 mg/kg orally) or indomethacin (20 mg/kg, orally) on the urinary and serum concentrations of calcium, magnesium and inorganic phosphate. Experiments were performed in normocalcaemic and hypercalcaemic rats. Hypercalcaemia and hypercalciuria were induced in male Wistar albino rats by administration of vitamin D3 (20,000 IU/daily) for 7 days. Aspirin and indomethacin both significantly lowered the urinary calcium excretion in normocalciuric and hypercalciuric rats. The acute administration of indomethacin caused greater reduction of calcium excretion than that produced by the acute administration of aspirin, whereas aspirin showed greater activity than indomethacin after the long-term use of each. Aspirin induced hypocalcaemia in normocalcaemic rats and abolished the hypercalcaemia in hypercalcaemic rats. On the contrary, indomethacin, a specific prostaglandin biosynthesis inhibitor, increased serum levels of calcium. Hypophosphataemia was observed only after the administration of a single dose of aspirin in normocalcaemic rats, while the reduction of urinary phosphate excretion was investigated in hypercalciuric rats after the acute and chronic administration of indomethacin. Serum levels of phosphate were not altered significantly by acute or chronic administration of indomethacin. A single dose of indomethacin significantly reduced urinary excretion of magnesium in both groups of rats. However, the acute and chronic administration of aspirin resulted in non-significant changes in serum and urinary concentrations of magnesium. These data suggest that aspirin has hypocalcaemic and hypocalciuric actions while indomethacin has only a hypocalciuric effect. Aspirin may produce these actions by two mechanisms, one of them like that of indomethacin which is dependent on the inhibition of biosynthesis of prostaglandins, and another possible mechanism that is not related to the inhibition of prostaglandin biosynthesis. This suggestion may be supported by the discrepancy between the effects of aspirin and indomethacin on the renal handling and serum concentrations of magnesium and inorganic phosphate.

Clinical and biochemical aspects of pregnancy-induced hypertension

In order to study what characteristics accompany the development of pregnancy-induced hypertension (PIH) and what parameters, if any, differentiate hypertension alone from hypertension with proteinuria, we evaluated 119 women with PIH who had hypertension alone, 73 women with PIH who had hypertension and proteinuria greater than or equal to 0.3 g/l, 63 women with normal pregnancy, 20 normal non-pregnant women. In comparison with normal pregnant women and normal non-pregnant women, women with PIH showed an increase in heart rate, suggesting an increased peripheral sympathetic tone, and an initial derangement in renal function as shown by the increase in serum uric acid and reduction in sodium excretion and total and fractional calcium excretion at any given level of sodium excretion. These changes were more marked in patients with hypertension and proteinuria. Higher levels of systolic blood pressure (SBP) were present in women with hypertension alone who subsequently developed proteinuria, compared with those who had only hypertension until term. According to our data hypertension alone and hypertension with proteinuria seem to be two aspects of only differing severity of the same disease.

Evidence for a prostaglandin-mediated bone resorptive mechanism in subjects with fasting hypercalciuria

This study was performed to assess whether treatment with prostaglandin synthesis inhibitors decreases calcium excretion in patients with idiopathic hypercalciuria. Nineteen hypercalciuric (12 with fasting hypercalciuria (FH), 7 with nonfasting hypercalciuria (NFH) and 8 control non-hypercalciuric stone formers were treated with sodium diclofenac, 50 mg t.i.d. for 2 weeks. After a washout phase, 7 FH patients received 200 mg/day of sulindac (a nonsteroidal antiinflammatory agent (NSAID) inactive on renal prostaglandin synthetase) for 14 more days. Diclofenac reduced urine calcium excretion in subjects with idiopathic hypercalciuria with either normal or elevated fasting urinary calcium (from 387 +/- 26 to 240 +/- 23 mg/day, P less than 0.001; and from 370 +/- 39 to 246 +/- 40 mg/day, P less than 0.05, respectively), whereas it was ineffective in normocalciuric stone formers. Similar antihypercalciuric effectiveness was exerted by sulindac in the seven FH patients. The antihypercalciuric action exerted by diclofenac in subjects with FH was associated with a significant increment in serum PTH (48 +/- 4 vs, 70 +/- 9 pmol/liter, P less than 0.05), whereas in NFH subjects, the antihypercalciuric effect of diclofenac on NFH was not associated with a change in parathyroid activity. Since the major effect of NSAIDs is to decrease prostaglandin synthesis, these data suggest that prostaglandins may play a pathogenetic role in idiopathic hypercalciuria. Furthermore, they suggest that PTH is suppressed in patients with FH, possibly due to stimulation of prostaglandin-mediated bone resorption process.

Lack of effect of prostaglandin inhibition on calcium excretion in normal volunteers

Recent data have shown that administration of indomethacin to patients with hypercalciuric nephrolithiasis decreased urinary calcium excretion, implying a possible pathogenic role for renal prostaglandins in hypercalciuria. To explore this hypothesis we administered indomethacin, ketoprofen and aspirin to normal volunteers for 6 days and assessed daily creatinine clearance and urinary excretion of sodium and calcium. In contrast to previous studies, subjects were maintained on a constant metabolic diet. These nonsteroidal anti-inflammatory drugs decreased urinary sodium excretion but had no effect on creatinine clearance or urinary calcium excretion. In summary, our data do not support an important physiologic role of renal prostaglandins in renal calcium excretion in normal subjects.

Decreased calcium and magnesium urinary excretion during prostaglandin synthesis inhibition in the rat

The effect of endogenous renal prostaglandins on calcium and magnesium reabsorption was investigated. Renal tubular handling of calcium and magnesium was studied by clearance methods in anesthetized Sprague-Dawley and Brattleboro rats, either intact or thyroparathyroidectomized (ATPTX), before and during prostaglandin synthesis inhibition by meclofenamate, indomethacin, or piroxicam infusion. These three inhibitors had similar effects on calcium and magnesium excretion: A significant decrease in absolute and fractional excretions of both cations was observed in intact Sprague-Dawley rats, and in ATPTX rats of both strains, but not in intact Brattleboro rats. These results suggest an inhibitory effect of prostaglandins on vasopressin-, glucagon-, but not PTH-mediated calcium and magnesium reabsorption. This effect is likely to occur in the thick ascending limb of Henle, which is both a target site for these polypeptidic hormones, and a segment where the bulk of calcium and magnesium is reabsorbed.