Eicosanoids in renal function

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.

Is there a role for PGE2 in urinary concentration?

Prostanoids are prominent, yet complex, components in the maintenance of body water homeostasis. Recent functional and molecular studies have revealed that the local lipid mediator PGE2 is involved both in water excretion and absorption. The biologic actions of PGE2 are exerted through four different G-protein-coupled receptors; designated EP1-4, which couple to separate intracellular signaling pathways. Here, we discuss new developments in our understanding of the actions of PGE2 that have been uncovered utilizing receptor specific agonists and antagonists, EP receptor and PG synthase knockout mice, polyuric animal models, and the new understanding of the molecular regulation of collecting duct water permeability. The role of PGE2 in urinary concentration comprises a variety of mechanisms, which are not fully understood and likely depend on which receptor is activated under a particular physiologic condition. EP3 and microsomal PG synthase type 1 play a role in decreasing collecting duct water permeability and increasing water excretion, whereas EP2 and EP4 can bypass vasopressin signaling and increase water reabsorption through two different intracellular signaling pathways. PGE2 has an intricate role in urinary concentration, and we now suggest how targeting specific prostanoid receptor signaling pathways could be exploited for the treatment of disorders in water balance.

COX-2 disruption leads to increased central vasopressin stores and impaired urine concentrating ability in mice

It was hypothesized that cyclooxygenase-2 (COX-2) activity promotes urine concentrating ability through stimulation of vasopressin (AVP) release after water deprivation (WD). COX-2-deficient (COX-2(-/-), C57BL/6) and wild-type (WT) mice were water deprived for 24 h, and water balance, central AVP mRNA and peptide level, AVP plasma concentration, and AVP-regulated renal transport protein abundances were measured. In male COX-2(-/-), basal urine output and water intake were elevated while urine osmolality was decreased compared with WT. Water deprivation resulted in lower urine osmolality, higher plasma osmolality in COX-2(-/-) mice irrespective of gender. Hypothalamic AVP mRNA level increased and was unchanged between COX-2(-/-) and WT after WD. AVP peptide content was higher in COX-2(-/-) compared with WT. At baseline, plasma AVP concentration was elevated in conscious chronically catheterized COX-2(-/-) mice, but after WD plasma AVP was unchanged between COX-2(-/-) and WT mice (43 ± 11 vs. 70 ± 16 pg/ml). Renal V2 receptor abundance was downregulated in COX-2(-/-) mice. Medullary interstitial osmolality increased and did not differ between COX-2(-/-) and WT after WD. Aquaporin-2 (AQP2; cortex-outer medulla), AQP3 (all regions), and UT-A1 (inner medulla) protein abundances were elevated in COX-2(-/-) at baseline and further increased after WD. COX-2(-/-) mice had elevated plasma urea and creatinine and accumulation of small subcapsular glomeruli. In conclusion, hypothalamic COX-2 activity is not necessary for enhanced AVP expression and secretion in response to water deprivation. Renal medullary COX-2 activity negatively regulates AQP2 and -3. The urine concentrating defect in COX-2(-/-) is likely caused by developmental glomerular injury and not dysregulation of AVP or collecting duct aquaporins.

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.

An oxygen-sensitive mechanism in regulation of epithelial sodium channel

Epithelial sodium channels (ENaCs) are of immense importance, controlling Na(+) transport across epithelia and thus playing a central role in all aspects of fluid clearance as well as numerous other functions. Regulation of these channels is critical. Here, we show that haem, a regulator of Na(+) transport, directly influences ENaC activity, decreasing channel-open probability (but not unitary conductance) in inside-out patches (but not outside-out). Conversely, exposure to the protein in the presence of NADPH and at normoxic O(2) tension (requirements for activity of hemeoxygenase) increases channel activity. CO, a product of hemeoxygenase activity, activated ENaC in a manner similar to that of haem plus NADPH. However, under hypoxic conditions, inhibition of ENaC by haem occurred even in the presence of NADPH. These data demonstrate a potent, O(2)-sensitive mechanism for regulation of ENaC, in which hemeoxygenase acts as the O(2) sensor, its substrate and product inhibiting and stimulating (respectively) the activity of ENaC.

Expression of cyclooxygenase-2 in biopsies obtained from human transplanted kidneys undergoing rejection

BACKGROUND

The inducible cyclooxygenase (COX)-2 is a target of immunosuppressive drugs routinely administered to patients after transplantation. This study investigates a potential involvement of COX-2 in transplant rejection. Therefore, we examined the expression of COX-2 in biopsies obtained for diagnostic purposes.

METHODS

COX-2 was detected by immunohistochemistry and in situ hybridization. Congruent staining was obtained by both methods: in specimens of a kidney explanted as the result of vascular rejection, tubular epithelial cells and endothelial cells stained positively for COX-2. Furthermore, in appendiceal specimens obtained at surgery, epithelial cells of the crypts, interstitial cells, and mesothelial cells were positive by both methods, affirming the specificity of the antibody.

RESULTS

Compared with healthy control subjects, intensive staining of COX-2 was observed in most of the 28 biopsies obtained from patients diagnosed with vascular rejection combined with cellular interstitial rejection and tubulitis. Glomeruli and the macula densa area were essentially negative compared with prominent staining in cortical and medullary epithelial cells of the tubuli. Staining was distinct with individual positive cells in the tubular cross sections. Few arteries expressed COX-2 in intimal cells. Less prominent expression of COX-2 was detected in the biopsies of six kidneys obtained from patients diagnosed with acute tubular necrosis.

CONCLUSION

This is the first report to show the up-regulation of COX-2 in human transplanted kidneys, despite ongoing immunosuppressive treatment. It remains to be established whether the up-regulation of COX-2 is part of the rejection process or has to be considered implicated in renal preservative mechanisms.

Is recombinant human erythropoietin (rh-epo) more than just a treatment of anemia in cancer and chemotherapy?

Recombinant human eythropoietin (rh-epo) is a well established treatment for many kinds of anemia including the anemia of cancer with or without myelosuppressive chemotherapy. This review considers the effects of rh-epo in humans, tumour-bearing and healthy experimental animals treated with cisplatin with or without rh-epo, and proposes that the ability of rh-epo to improve the quality of life in cancer patients may also be due to interference with the prostaglandin pathways.

Hand-assisted laparoscopic radical nephrectomy-associated rhabdomyolysis with ARF

Intraoperative rhabdomyolysis with resultant acute renal failure is a rare complication seen, most commonly, with urologic surgical procedures. Since the early 1990s, the refinement of laparoscopic techniques has permitted their application more broadly. Among the procedures to benefit from these less invasive surgical methods has been radical nephrectomy. In general, this has resulted in less postoperative pain and shorter convalescence. Nonetheless, laparoscopic radical nephrectomy still represents major surgery and is not free from operative risks. To highlight one of these risks, we present a case of a young, obese man with renal cell carcinoma who underwent a hand-assisted laparoscopic radical nephrectomy that was complicated by rhabdomyolsis resulting in acute renal failure (ARF). We discuss the clinical insults that contributed to the development of azotemia with particular attention paid to our current understanding of the pathogenesis of myoglobinuric ARF. In addition, we review the literature concerning surgery-associated, rhabdomyolytic ARF with the aim of providing clinicians guidance for the avoidance and early recognition of this rare, but very serious, surgical complication.

Renal concentrating defect in mice lacking group IV cytosolic phospholipase A(2)

Eicosanoids regulate various cellular functions that are important in physiological and pathophysiological processes. Arachidonic acid is released from membranes by phospholipase A(2) (PLA(2)) activity. Activated macrophages derived from mice lacking the 85-kDa group IV cytosolic PLA(2) (cPLA(2)) have a markedly reduced release of prostaglandin E(2) and leukotrienes B(4) and C(4). Under basal conditions and after furosemide, urinary prostaglandin E(2) excretion is reduced in cPLA(2)-knockout (cPLA(2)(-/-)) mice. Serum creatinine, Na(+), K(+), and Ca(2+) concentrations, glomerular filtration rate, and fractional excretion of Na(+) and K(+) are not different in cPLA(2)(-/-) and cPLA(2)(+/+) mice. Maximal urinary concentration is lower in 48-h water-deprived cPLA(2)(-/-) mice compared with cPLA(2)(+/+) animals (1,934 +/- 324 vs. 3,541 +/- 251 mmol/kgH(2)O). Plasma osmolality is higher (337 +/- 5 vs. 319 +/- 3 mmol/kgH(2)O) in cPLA(2)(-/-) mice that lose a greater percentage of their body weight (20 +/- 2 vs. 13 +/- 1%) compared with cPLA(2)(+/+) mice after water deprivation. Vasopressin does not correct the concentrating defect. There is progressive reduction in urinary osmolality with age in cPLA(2)(-/-) mice. Membrane-associated aquaporin-1 (AQP1) expression, identified by immunocytochemical techniques, is reduced markedly in proximal tubules of older cPLA(2)(-/-) animals but is normal in thin descending limbs. However, Western blot analysis of kidney cortical samples revealed an equivalent AQP1 signal intensity in cPLA(2)(+/+) and cPLA(2)(-/-) animals. Young cPLA(2)(-/-) mice have normal proximal tubule AQP1 staining. Collecting duct AQP2, -3, and -4 were normally expressed in the cPLA(2)(-/-) mice. Thus mice lacking cPLA(2) develop an age-related defect in renal concentration that may be related to abnormal trafficking and/or folding of AQP1 in the proximal tubule, implicating cPLA(2) in these processes.

Eicosanoid regulation of the renal vasculature

Even though it has been recognized that arachidonic acid metabolites, eicosanoids, play an important role in the control of renal blood flow and glomerular filtration, several key observations have been made in the past decade. One major finding was that two distinct cyclooxygenase (COX-1 and COX-2) enzymes exist in the kidney. A renewed interest in the contribution of cyclooxygenase metabolites in tubuloglomerular feedback responses has been sparked by the observation that COX-2 is constitutively expressed in the macula densa area. Arachidonic acid metabolites of the lipoxygenase pathway appear to be significant factors in renal hemodynamic changes that occur during disease states. In particular, 12(S)- hydroxyeicosatetraenoic acid may be important for the full expression of the renal hemodynamic actions in response to angiotensin II. Cytochrome P-450 metabolites have been demonstrated to possess vasoactive properties, act as paracrine modulators, and be a critical component in renal blood flow autoregulatory responses. Last, peroxidation of arachidonic acid metabolites to isoprostanes appears to be involved in renal oxidative stress responses. The recent developments of specific enzymatic inhibitors, stable analogs, and gene-disrupted mice and in antisense technology are enabling investigators to understand the complex interplay by which eicosanoids control renal blood flow.

Differential effect of a selective cyclooxygenase-2 inhibitor versus indomethacin on renal blood flow in conscious volume-depleted dogs

Renal effects of a selective cyclooxygenase-2 (COX-2) inhibitor [MF-Tricyclic; 3-(3,4-difluorophenyl)-4-(4-(methylsulfonyl)phenyl)-2-(5H)-furanone] were studied in control and volume-depleted conscious dogs. MF-Tricyclic was compared with the nonselective COX-1/COX-2 inhibitor indomethacin. Six instrumented male dogs were randomly selected to receive MF-Tricyclic or indomethacin at 10 mg/kg. Volume depletion was effected by a sodium-restricted diet (14 days) with administration of furosemide (7.5 mg/kg, i.v.) the day before the experiment. Indomethacin ablated systemic COX-1 activity (p < 0.05), whereas MF-Tricyclic did not affect this activity. Each compound achieved plasma concentrations in excess of their respective median inhibitory concentrations (IC50 values) against canine COX-2. In controls, neither compound affected mean arterial pressure (MAP), heart rate (HR), renal blood flow (RBF), fractional excretion (FE) Na+, or FE K+. In volume-depleted dogs, indomethacin reduced RBF (p < 0.05), whereas MF-Tricyclic did not affect this parameter. Indices of renal function in volume-depleted dogs were not affected. These data are consistent with the view that the effects of indomethacin on RBF are a consequence of inhibition of COX-1 activity. Furthermore, in these studies, short-term administration of a selective COX-2 inhibitor was without deleterious effects on renal function.

Effects of percutaneous nephrolithotomy and extracorporeal shock wave lithotripsy on renal function and prostaglandin excretion

The aim of the study was to investigate the effects of percutaneous nephrolithotomy (PCN) and extracorporeal shock wave lithotripsy (ESWL) on renal function and urinary prostaglandin excretion. Twenty/ESWL patients and 20 PCN patients were studied pre-, 24 h and two weeks after treatment. Twenty-four hours after treatment PCN resulted in a fall in serum potassium, sodium and calcium. There was a small rise in urinary prostaglandin excretion. All results had returned to normal by two weeks. ESWL caused a rise in serum creatinine with a fall in calculated glomerular filtration rate (GFR). This was coupled with a fall in urinary excretion of sodium, potassium, and calcium. There was a rise in urinary prostaglandin excretion. Serum calcium and LDH levels also rose. All results had returned to normal by two weeks except urinary calcium excretion, and serum albumin had now fallen. ESWL had more effect on renal function in the acute phase of treatment than PCN.

Increased total body synthesis of prostacyclin in rats with adjuvant arthritis

In rats with adjuvant arthritis we measured the urinary excretion of 2,3-dinor-6-oxo-PGF1 alpha, 7 alpha-hydroxy-5,11-dioxo-tetranor-prosta-1,16- dioic acid (PGE-M) and 2,3-dinor-thromboxane-B2, reflecting total body synthesis of prostacyclin, thromboxane and the E-prostaglandins, respectively. The urinary prostanoid metabolites were assessed by gas chromatography/tandem mass spectrometry using stable isotope internal standards. We found a more than 10-fold increase of urinary 2,3-dinor-6-oxo-PGF1 alpha excretion and a 5-fold higher urinary excretion of PGE-M in adjuvant arthritic rats as compared to non-arthritic control rats (p < 0.001; n = 12, each). There was no significant difference in urinary 2,3-dinor-thromboxane-B2 excretion between arthritic rats and control animals. Our data show a dramatic increase of urinary 2,3-dinor-6-oxo-PGF1 alpha excretion reflecting increased total body prostacyclin synthesis. It can be assumed that prostacyclin plays a role in generalized inflammatory reactions, comparable to that of the E-prostaglandins.

Modulation of renal medullary ionic hypertonicity by prostaglandins: data from tissue admittance studies in the rat

1. Modulation of the cortico-papillary electrolyte gradient by prostaglandins (PG) was studied in the kidney of anaesthetized rats. The intrarenal PG activity was varied by synthesis blockade with indomethacin (Ind) or meclophenamate (Me) and by intrarenal infusion of prostaglandin E2 (PGE2). 2. The interstitial electrolyte concentration in the medulla was continuously recorded in the kidney in situ as tissue electrical admittance (reciprocal impedance); the total renal blood flow (RBF), inulin clearance (Cin) and renal excretion were measured simultaneously. 3. Indomethacin and Me (15 mg kg-1 h-1) increased tissue admittance 15-20% in the inner and 12-15% in the outer medulla (P < 0.001) whereas PGE2 (300 ng kg-1 min-1) decreased admittance 14 and 8%, respectively (P < 0.01). 4. Renal blood flow and Cin were not affected by intrarenal PG activity changes. There was an increase in urine concentration after PG blockade and a delayed decrease after PGE2 infusion. 5. A joint analysis of the dynamics of medullary tissue admittance, renal haemodynamics and renal excretion provides evidence that PGs modify the medullary ionic hypertonicity by affecting NaCl transport in the ascending limb of the loop of Henle.

Peripheral haemodynamic effects of inhibition of prostaglandin synthesis in congestive heart failure and interactions with captopril

OBJECTIVES

To investigate the role of prostaglandins in maintaining circulatory homoeostasis in chronic heart failure and the hypothesis that an increase in vasodilatory prostaglandin synthesis may contribute to the actions of angiotensin converting enzyme inhibitors in heart failure.

DESIGN

Randomised, double blind, placebo controlled studies. Cardiac output and renal and limb blood flow were measured after oral indomethacin 50 mg or placebo followed by "open" intravenous infusion of prostaglandin E2 (study A). In a second study the same measurements were made after oral indomethacin 50 mg or placebo was given 30 min before "open" captopril (study B).

METHODS

Blood pressure was measured using a mercury sphygmomanometer. Cardiac output was determined by Doppler interrogation of blood flow in the ascending aorta and echocardiographic measurement of aortic root diameter. Renal blood flow was calculated from the effective renal plasma flow measured by p-aminohippurate clearance and the haematocrit, and glomerular filtration rate by endogenous creatinine clearance. Limb blood flow was measured by venous occlusion plethysmography using mercury in silastic strain gauges. The concentration of plasma prostaglandin E2 was measured by radioimmunoassay.

SETTING

University department of cardiovascular medicine.

PATIENTS

12 patients with chronic stable heart failure before starting treatment with angiotensin converting enzyme inhibitors.

RESULTS

Indomethacin resulted in adverse effects on cardiac output, systemic vascular resistance, renal blood flow, glomerular filtration, urinary sodium excretion, and calf vascular resistance. Changes were reversed with infusion of prostaglandin E2. Pretreatment with indomethacin resulted in the attenuation of the acute increase in cardiac output and decrease in systemic vascular resistance that occurred with captopril. Similarly, an increase in renal blood flow with captopril was attenuated by indomethacin.

CONCLUSIONS

The acute adverse effects of indomethacin on central and peripheral haemodynamic and renal function suggest that prostaglandins have a significant role in the regulation of peripheral blood flow and renal function in patients with stable chronic heart failure. The attenuation by indomethacin of captopril induced improvements in haemodynamic function and renal blood flow is consistent with the hypothesis that captopril may act in part via an increase in prostaglandin synthesis.

Effects of angiotensin-converting enzyme inhibition on renal dysfunction induced by moderate potassium depletion in healthy women

The role of the renin-angiotensin system in renal hypokalaemic dysfunction has been investigated by evaluating the effects of the angiotensin (AT)-converting enzyme inhibition by enalapril. Healthy women were studied either in normal potassium balance (N3, n = 6) or moderate potassium depletion (KD3, n = 6). Potassium depletion (KD) was induced by low potassium dietary intake (greater than or equal to 10 mmol per day) and natriuretic treatment associated with replacement of net NaCl and water losses; the cumulative potassium deficit achieved was 214 +/- 54 mmol. The renal function and the urinary excretions of some prostanoids (PGE2, 6-keto-PGF1 alpha, TxB2) were evaluated during hypotonic polyuria (oral water load) and subsequent moderate antidiuresis (lysine-8-vasopressin (LVP) low-dose infusion). Paired studies were performed in absence (control) and presence of enalapril. Basal plasma renin activity (PRA) and urinary aldosterone excretion were determined before the water load of control studies. Renal dysfunction typical of chronic KD occurred in the KD3 group, i.e. increase in PRA, decrease in creatinine clearance, depression of the diuretic response to water load, inhibition of distal fractional chloride reabsorption, and blunted efficacy of LVP in increasing the urinary solute concentration. The urinary prostanoid excretions were reduced. Basal urinary aldosterone excretion was not changed significantly. In KD3 group enalapril decreased mean arterial pressure (MAP), increased the plasma potassium concentration, improved the diuretic response to water load and corrected the impairment of the distal fractional chloride reabsorption. Despite the decrease in MAP enalapril did not affect significantly the creatinine clearance. Neither urinary prostanoid excretions nor the renal response to LVP were affected by the drug. The data suggest that in KD the increased activity of the renin-angiotensin system affected the renal function both through direct effects and through effects dependent on the angiotensin-supported secretions of aldosterone and probably of vasopressin. Finally, by comparing the effects of enalapril and indomethacin in experimental groups with an equivalent degree of KD, evidence is provided in favour of the interaction between renin-angiotensin and prostanoid systems in controlling the glomerular filtration rate and the salt and water handling by renal tubules.

Prostacyclin in diarrhoea-associated haemolytic uraemic syndrome

The role of prostacyclin (PGI2) in the pathogenesis of haemolytic uraemic syndrome (HUS) is controversial. In part, confusion has been caused by failure to distinguish between two main sub-types of the syndrome: extrinsic, diarrhoea-associated HUS (D+ HUS), usually caused by infection with verocytotoxin-producing Escherichia coli or Shigella dysenteriae, and the heterogeneous group of non-prodromal forms where intrinsic factors predominate (D- HUS). This paper critically reviews data confined to D+ HUS. Two methods have been used to assess PGI2 synthesis; the generation of PGI2 from endothelium in the presence of HUS plasma in vitro and the measurement of stable metabolites in body fluids. No concensus could be reached with regard to the former. The reported increase of PGI2 stable metabolites in plasma may represent reduced clearance or increased carriage by plasma lipids. Apparent differences between studies of urinary excretion of PGI2 metabolites may reflect the way excretion was expressed. If the metabolite concentration is factored for urinary creatinine, it appears that renal excretion and thus renal synthesis of PGI2 is reduced. However, these are insufficient data on which to attribute the pathogenesis of D+ HUS to disordered PGI2 metabolism.

Effects of starvation on the urinary contents of primary thromboxane and prostacyclin metabolites and a possible selenium-dependent role of prostacyclin in the renal handling of ketone bodies

The aim of this study was to investigate whether urinary prostanoids, as an index of renal synthesis of these compounds, are affected in selenium (Se) deficiency and, if so, whether such changes could add to our understanding of the high excretion of ketone bodies in Se-deficient rats (p < 0.005 vs Se-adequate rats). Male rats were fed a Se-deficient diet with less than 0.01 mg Se/kg or the same diet supplemented with 0.2 mg Se/kg. The urinary contents of prostaglandin E2 (PGE2), PGF2 alpha and 6-keto PGF1 alpha were not significantly affected by the Se status. However, there was a positive correlation between the urinary contents of ketone bodies and 6-keto PGF1 alpha in Se deficiency (with p < 0.02 for acetaoacetate and p < 0.05 for 3-hydroxybutyrate). In contrast, only negative (nonsignificant) relationships were observed between these same parameters in Se-adequate rats. No correlations between urinary contents of ketone bodies and PGE2, PGF2 alpha or thromboxane B2 (TXB2) were obtained. Compared to fed rats, starvation caused a 4-fold increase in the urinary TXB2 content in Se-adequate, as well as in Se-deficient rats (p < 0.001). Starvation had an opposite effect on the content of 6-keto PGF1 alpha, which decreased (to 64% that of fed animals p < 0.001) in Se-adequate rats and, nonsignificantly (to 93% that of fed animals) in the Se-deficient group. It is concluded that starvation profoundly affects the urinary contents (and thus, probably renal synthesis) of TX and prostacycline (PGI2).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological control of altitude sickness

Acute mountain sickness has long been recognized as a potentially life-threatening condition afflicting otherwise healthy individuals who ascend rapidly to high altitude, where the partial pressure of oxygen in the air is reduced. The symptoms of acute mountain sickness are probably a consequence of disturbances in fluid balance brought about by severe tissue hypoxia. Acute mountain sickness can be prevented by an adequately slow ascent, which is the best method, but for those with limited time there are several drug therapies that provide a relatively good protection. John Coote describes these treatments and their possible mechanisms of pharmacological action.

Urinary PGE2 in rats with chronic partial unilateral ureteral obstruction

Urinary prostaglandin E2 (PGE2) was measured in Munich-Wistar rats with surgically created chronic partial unilateral ureteral obstruction (UUO). Mean values of bladder urine PGE2 were higher in sham than in UUO (24.5 +/- 14.4 vs 12.9 +/- 8.2 ng/mg creatinine, respectively, P less than 0.05). Following diuresis, both ureters were cannulated and urine was collected. PGE2 excretion was increased in sham (66.5 +/- 34.4 and 70.1 +/- 44.5 ng/mg creatinine, left and right, respectively). But in UUO, the obstructed kidney excreted less PGE2 than the contralateral kidney (32.1 +/- 6.0 vs 62.3 +/- 40.4 ng/mg creatinine, obstructed vs contralateral, respectively, P = 0.08). PGE2 synthesis was then determined in separated renal medullary and cortical slices. Renal medullary slices from kidneys with severe obstruction synthesized less PGE2 than the contralateral unobstructed side (3.30 +/- 1.22 vs 10.52 +/- 3.23 ng/mg wet wt-30 min, respectively, P less than 0.05) and failed to respond to arachidonic acid stimulation with any significant increase in PGE2 synthesis (3.30 +/- 1.22 vs 4.47 +/- 1.04 ng/mg wet wt-30 min, baseline vs stimulated). In contrast, contralateral unobstructed kidney slices responded with a significant increase in PGE2 synthesis (10.52 +/- 3.23 vs 21.10 +/- 2.50 ng/mg wet wt-30 min, baseline vs stimulated, P less than 0.05). We conclude that chronic partial UUO in the Munich-Wistar rats resulted in significantly less PGE2 elaboration.

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.

Effect of fish oil supplementation on the excretion of the major metabolite of prostaglandin E in healthy male subjects

We investigated the effect of fish oil supplementation on the synthesis of prostaglandin E (PGE) in vivo by measuring the excretion of its catabolite, PGE-M, in 24-hr urine by gas chromatography/mass spectrometry. Forty healthy male volunteers (24-57 years of age) consumed a controlled basal diet providing 40% of energy from fat (P/S ratio about 0.8:1), 130 mg/1000 kcal cholesterol, and a minimum of 22 mg/day of alpha-tocopherol (alpha-T), for three experimental periods lasting a total of 28 weeks. During period 1 (10 weeks) the diet was supplemented with placebo (PO) capsules (15 X 1 g/day) consisting of a blend of fats approaching the fatty acid profile of the basal diet. This was followed by a second 10-week period during which the subjects received 15 X 1 g/day capsules of fish oil concentrate (FOC). During period 3 (8 weeks) they continued the 15 g/day intake of FOC but received an additional 200 mg/day of alpha-T. PO and FOC capsules contained 1 mg alpha-T/g fat as antioxidant. A 14% reduction of PGE-M excretion was observed after 10 weeks of FOC supplementation (period 2), compared to an identical period of placebo supplementation (period 1), P = 0.009. PGE-M excretion during the last week of period 3 was not significantly different from that at the end of period 2. The reduction in PGE synthesis in response to the relatively high marine oil supplementation was large in many subjects participating in this study.

Effect of autacoid modulation on N-(3,5-dichlorophenyl)succinimide (NDPS) and NDPS metabolite nephrotoxicity

N-(3,5-Dichlorophenyl)succinimide (NDPS) is an agricultural fungicide which has been shown to induce acute tubular necrosis. The purpose of the present study was to determine if creatinine clearance was altered early in the development of NDPS nephrotoxicity. This study also examined the effect of autacoid modulation on the renal effects induced by NDPS and two metabolites of NDPS, N-(3,5-dichlorophenyl)-2-hydroxysuccinimide (NDHS) and N-(3,5-dichlorophenyl)-2-hydroxysuccinamic acid (NDHSA). In one set of experiments, male Fischer 344 rats (4 rats/group) were administered a single intraperitoneal (i.p.) injection of NDPS (1.0 mmol/kg) or vehicle and creatinine clearance was determined at 3 and 6 h post-treatment. NDPS administration resulted in a marked decrease in creatinine clearance at both time points. In a second set of experiments, rats (4-8 rats/group) were pretreated with the cyclooxygenase inhibitor indomethacin (3.0 or 5.0 mg/kg, i.p.) or the thromboxane synthase inhibitor dazmegrel (20 mg/kg, i.p.) 1 h before the i.p. administration of NDPS (0.2 or 0.4 mmol/kg), NDHS (0.05 or 0.1 mmol/kg), NDHSA (0.05 or 0.1 mmol/kg) or vehicle. Indomethacin pretreatment potentiated the nephrotoxic potential of NDPS and its two metabolites, while dazmegrel pretreatment attenuated NDPS nephrotoxicity without marked effects on NDHS or NDHSA nephropathy. These results indicate that renal hemodynamic changes occur early in the development of NDPS nephrotoxicity and that autacoids are important modulators of NDPS- and NDPS metabolite-induced renal effects.