Prostaglandin synthesis by glomeruli isolated from rats with glycerol-induced acute renal failure

A comparative study of chronic kidney disease in dogs and cats: induction of cyclooxygenases

The present study investigated whether renal cyclooxygenase (COX) induction is associated with the severity of chronic kidney disease (CKD) in dogs and cats. The collected kidneys were examined histopathologically and immunohistochemically. The immunoreactivities of COX-1 and COX-2 were evaluated quantitatively, and the correlations to the plasma creatinine concentrations, glomerular size, glomerulosclerosis, interstitial fibrosis, and interstitial cell infiltration were evaluated statistically. Immunoreactivities for COX-1 were heterogeneously observed in the medullary distal tubules and collecting ducts; no correlations with the severity of renal damage were detected. Immunoreactivities for COX-2 were heterogeneously observed in the macula densa (MD) regions. In dogs, the percentage of COX-2-positive MD was significantly correlated with the glomerular size. In cats, glomeruli with COX-2-positive MD had significantly higher sclerosis scores than those with COX-2-negative MD. In conclusion, renal COX-2 is induced in canine and feline CKD, especially in relation to the glomerular changes.

Membrane prostaglandin E synthase-1: a novel therapeutic target

Prostaglandin E(2) (PGE(2)) is the most abundant prostaglandin in the human body. It has a large number of biological actions that it exerts via four types of receptors, EP1-4. PGE(2) is formed from arachidonic acid by cyclooxygenase (COX-1 and COX-2)-catalyzed formation of prostaglandin H(2) (PGH(2)) and further transformation by PGE synthases. The isomerization of the endoperoxide PGH(2) to PGE(2) is catalyzed by three different PGE synthases, viz. cytosolic PGE synthase (cPGES) and two membrane-bound PGE synthases, mPGES-1 and mPGES-2. Of these isomerases, cPGES and mPGES-2 are constitutive enzymes, whereas mPGES-1 is mainly an induced isomerase. cPGES uses PGH(2) produced by COX-1 whereas mPGES-1 uses COX-2-derived endoperoxide. mPGES-2 can use both sources of PGH(2). mPGES-1 is a member of the membrane associated proteins involved in eicosanoid and glutathione metabolism (MAPEG) superfamily. It requires glutathione as an essential cofactor for its activity. mPGES-1 is up-regulated in response to various proinflammatory stimuli with a concomitant increased expression of COX-2. The coordinate increased expression of COX-2 and mPGES-1 is reversed by glucocorticoids. Differences in the kinetics of the expression of the two enzymes suggest distinct regulatory mechanisms for their expression. Studies, mainly from disruption of the mPGES-1 gene in mice, indicate key roles of mPGES-1-generated PGE(2) in female reproduction and in pathological conditions such as inflammation, pain, fever, anorexia, atherosclerosis, stroke, and tumorigenesis. These findings indicate that mPGES-1 is a potential target for the development of therapeutic agents for treatment of several diseases.

Eicosanoids and renal vascular function in diseases

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

Contribution of renal oxygenases to glycerol-induced acute renal failure in the rat

Administration of glycerol produces acute renal failure (ARF) accompanied by profound vasoconstriction. It was hypothesized that impaired arachidonic acid metabolism may contribute to the vasoconstriction through alteration of renal eicosanoids or endothelin-1 or angiotensin II stimulation of renal oxygenases. Arachidonic acid (5, 10, 25 microg) in the control kidney produced increases in perfusion pressure of 15 +/- 9, 18 +/- 8, and 43 +/- 18 mm Hg, respectively. These responses were increased 1.5-fold in glycerol-induced renal failure (p < 0.01). Indomethacin (10 microM), the cyclooxygenase inhibitor, converted arachidonic acid vasoconstriction to epoxide-mediated vasodilator responses, which were unchanged in ARF. In ARF, 5,8,11,14-eicosatetraynoic acid (10 microM), the all-purpose inhibitor of arachidonic acid metabolism; indomethacin (10 microM), a cyclooxygenase inhibitor; 5,8,11-eicosatriyenoic acid (2.5 microM), the 5- and 12-lipoxygenase inhibitor; or aminobenzotriazole (50 mM), the cytochrome P-450 monooxygenase inhibitor, markedly attenuated arachidonic acid-induced vasoconstriction by 73 +/- 11% (p < 0.01), 89 +/- 1% (p < 0.01), 62 +/- 11% (p < 0.01), and 82 +/- 2% (p < 0.01), respectively. In ARF, angiotensin II-induced vasoconstriction was amplified by 67% (p < 0.01). Eicosatetraynoic acid, eicosatriyenoic acid, and aminobenzotriazole reduced these responses by 33 +/- 6% (p < 0.05), 53 +/- 6% (p < 0.01), and 52 +/- 11% (p < 0.05), respectively. Vasoconstriction by endothelin-1 was unchanged in ARF (24 +/- 17%). However, indomethacin attenuated endothelin-1 vasoconstriction by 41 +/- 11% (p < 0.05), whereas eicosatriyenoic acid and aminobenzotriazole were without effect. These data suggest that the increased renal vascular reactivity in ARF in response to arachidonic acid involves a relatively greater production of cyclooxygenase metabolites than monoxygenase- or lipoxygenase-derived eicosanoid metabolites. Furthermore, increased angiotensin II vasoconstriction is predominantly through lipoxygenase and monoxygenase metabolic pathways, whereas for endothelin-1, increased cyclooxygenase-derived vasoconstrictor metabolites play a significant role in its amplified vasoconstrictor effect in glycerol-induced ARF.

Thromboxane synthesis and action within the kidney

PGH2 and TxA2 exert their actions via tissue specific, receptor isoforms. PGH2/TxA2-dependent platelet aggregation and contraction of vascular and bronchial smooth muscle and of glomerular mesangial cells occur via receptors linked to activation of phospholipase C. Although PGH2/TxA2 appear to be of little importance in the maintenance of renal function under physiological circumstances, increased renal TxA2 biosynthesis has been documented in a variety of animal models of renal disease and in some clinical disorders (Table 2). The effects of this eicosanoid on renal tissues in vitro and of pharmacological manipulation of TxA2 synthesis and action in vivo suggest that such interventions will provide new drugs for the treatment of human kidney disease.

Quantification and modulation of thrombomodulin activity in isolated rat and human glomeruli

Thrombomodulin (TM), the endothelial cell surface receptor for thrombin-mediated activation of protein C and of its anticoagulant system, is involved in maintaining vascular nonthrombogenicity, and depressed TM activity may induce intravascular fibrin formation. TM antigen was previously found by immunohistochemical methods in rabbit glomeruli. We therefore attempted to identify the corresponding TM activity in isolated detergent-solubilized rat and human glomeruli. Like purified lung TM, rat glomeruli extracts accelerated the hydrolysis by activated protein C of the chromogenic substrate S-2238 in the presence of 10 nM thrombin, as determined by spectrophotometry. One mg glomerular protein promoted the formation of 681 +/- 115 nmol activated protein C, the equivalent of the amount generated by 845 ng of purified rabbit TM. TM activity correlated with the protein content of the glomerular extracts (r = 0.94). These extracts prolonged rat plasma activated partial thromboplastin time. Incubation of glomeruli with tumor necrosis factor-alpha (TNF) or E. coli lipopolysaccharide depressed their TM-like activity in a dose and time dependent manner. Incubation with TNF suppressed their anticoagulant activity. In human glomeruli, TM activity was also found at a level which corresponded to their TM antigen content, and was determined by ELISA with mouse monoclonal antibody. These results indicate that measurement of glomerular TM activity might help to clarify the mechanisms of intraglomerular fibrin deposition in renal diseases.

Effect of prostaglandin E2 on proline uptake and protein synthesis by cultured human mesangial cells

PGE2 production by glomeruli is increased in a variety of glomerular diseases. Potentially, this process may affect mesangial cell protein synthesis and mesangial cell growth. Thus studies have been undertaken, using cultured human mesangial cells, to assess the effects of PGE2 on proline uptake, protein synthesis and cell proliferation. In the presence of 140 mM NaCl, incubation of mesangial cells with 0.01 to 1 microM PGE2 for 72 hours resulted in a marked decrease of 14C proline uptake, but did not modify 14C leucine uptake. Substitution of choline to sodium inhibited 14C proline uptake by 85% which became independent of PGE2, indicating that this PG specifically altered sodium-dependent proline uptake. Inhibition of this component reached 35 to 50% with 1 microM PGE2. The inhibitory effect of PGE2 on sodium-dependent proline uptake required a lag time of 48 hours, and was suppressed by ouabain, an inhibitor of Na+, K+ ATPase activity. PGE2 did not modify the Vmax of the transport system (1.007 vs. 1.023 nmol/mg/min) but increased (P less than 0.01) its Km (1.179 vs. 0.823 mM). 8-bromo-cyclic AMP also inhibited sodium-independent proline uptake, and PGE2 markedly increased cyclic AMP production. Taken together, these results suggested that PGE2 acted via cyclic AMP stimulation. PGE2 under identical conditions (1 microM, 72 hr incubation) produced a decrease in collagen synthesis estimated by the relative rate of collagen production after incubation of mesangial cells with 14C proline (percentage of 14C radioactivity in collagenase-sensitive proteins over total proteins). PGE2 also diminished the intracellular free proline pool. More generally, PGE2 inhibited cell proliferation and cell total proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Essential fatty acid deficiency ameliorates acute renal dysfunction in the rat after the administration of the aminonucleoside of puromycin

The administration of the aminonucleoside of puromycin (PAN) to rats causes the nephrotic syndrome that is associated with an acute decline in renal function, and an interstitial infiltrate. We examined whether essential fatty acid deficiency (EFAD), which inhibits macrophage infiltration in glomerulonephritis, affects PAN-induced renal dysfunction. Both control and EFAD rats developed proteinuria that resolved over 28 d. After PAN administration, there was a prominent infiltration of macrophages in rats fed a normal diet. The infiltrate was prevented by the EFAD diet. The absence of a macrophage interstitial infiltrate was associated with a significantly higher Cin in the EFAD rats than in controls at 7 d (5.21 +/- 1.19 versus 0.39 +/- 0.08, P less than 0.002 ml/min/kg BW). In addition, CPAH fell to less than 10 ml/min/kg BW by day 7 in controls, but remained the same as normal in the EFAD. After administration of PAN to control rats, there was no increase in urinary thromboxane excretion or an increase in glomerular thromboxane production. Furthermore, the effect of EFAD could not be mimicked by the administration of a thromboxane synthase inhibitor. Irradiation-induced leukopenia in rats on a normal diet markedly improved glomerular filtration and renal blood flow in acutely nephrotic rats. EFAD prevents the interstitial cellular infiltrate and the renal ischemia associated with experimental nephrosis. The recruitment of mononuclear cells into the kidney following PAN directly contributes to the decline in renal function.

In vivo renal angiotensin converting enzyme activity decreases in glycerol-induced acute renal failure

We previously demonstrated that intrarenal angiotensin II generation during glycerol-induced acute renal failure was attenuated, which may have resulted from the inability of intrarenal converting enzyme to convert renal angiotensin I to angiotensin II. In order to test this hypothesis in vivo, we determined the ability of the kidney to convert angiotensin I to angiotensin II by measuring the decrease in renal cortical blood flow (RCBF) in response to exogenous angiotensin I administration. Changes in RCBF were monitored by laser-Doppler velocimetry. Three groups of rats were studied: Group I, controls (N = 7); 24 hours prior to study Group II animals were injected with 50% glycerol, 8 ml/kg i.m. (N = 4); and Group III rats were injected with mercuric chloride, 3 mg/kg s.c. (N = 5). All experimental animals had a three- to sixfold rise in serum creatinine. Mean glomerular filtration rate (GFR) of the left and right kidney in control rats was 0.7 and 0.7 ml/min, respectively. Twenty-four hours after glycerol, GFR was 0.2 ml/min in the left kidney and 0.2 ml/min in the right kidney. In HgCl2 treated rats GFR was 0.1 ml/min in the left kidney and 0.1 ml/min in the right kidney. Each of the following maneuvers elicited a similar rise in blood pressure in Groups I through III. Specifically, when first angiotensin I (4 micrograms/kg/min) was infused for three minutes; second, when 10 minutes later angiotensin I (5 micrograms) was directly applied on the left kidney; and third, when angiotensin II (5 micrograms) was topically administered.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal side effects of nonsteroidal antiinflammatory drugs: clinical relevance

Nonsteroidal antiinflammatory drugs (NSAIDs) induce a variety of renal side effects. We review their prevalence and clinical relevance, and identify the patients who are most at risk for these complications. NSAIDs induce hemodynamic renal failure in states of compromised renal perfusion and in the presence of a preexisting nephropathy. Association of triamterene and indomethacin is especially nephrotoxic and should be avoided. NSAIDs cause sodium retention and impair the natriuretic effect of diuretics: this side effect is clinically relevant in edema-forming states. Hyperkalemia induced by NSAIDs is harmful in case of renal failure and hypoaldosteronism. NSAIDs may induce an acute interstitial nephritis often associated with the nephrotic syndrome; the event is rare and unpredictable, and mainly propionic acid derivatives have been incriminated. NSAIDs are reported to attenuate the hypotensive effect of various drugs; further studies are warranted to better delineate the clinical relevance of this observation.

Renal effects of the inhibitor of thromboxane A2-synthetase OKY-046

Acute renal failure (ARF) was associated with increased urinary thromboxane (TXA2) excretion and lessened excretion of sodium (UNaV) and fractional excretion of sodium (FENa%). The inhibitor of thromboxane A2-synthetase OKY-046 enhanced sodium excretion and fractional excretion of sodium in normal and saline loaded animals whereas it partially prevented the reduction in sodium excretion and creatinine clearance and significantly increased fractional excretion of sodium in glycerol treated rats suggesting a partial protection against the development of acute renal failure.

Eicosanoids in experimental and human renal disease

The renal prostaglandins and thromboxanes are powerful autacoids with potential effects on renal hemodynamics, salt and water metabolism, and the immune system. The possibility of adverse effects on renal function in certain patients with renal disease due to cyclooxygenase inhibition with nonsteroidal anti-inflammatory drugs has long been appreciated. Experimental evidence indicates that renal prostaglandin and thromboxane production is increased in several models of renal disease and that similar decrements in renal function occur with cyclooxygenase inhibition and may be due to inhibition of vasodilator prostaglandins. Additionally, several investigators have shown that administration of prostaglandins may be therapeutic in some forms of renal disease, particularly immunologically mediated diseases. Dietary modification to affect prostaglandin production has also been promising in certain experimental models. In contrast to vasodilator prostaglandins, thromboxane is a potent vasoconstrictor and would be expected to have adverse effects on renal function. Despite demonstration of elevated glomerular thromboxane, studies using inhibitors of thromboxane synthesis in immunologically mediated glomerular disease have been disappointing. There is some evidence, however, that these drugs may be of benefit in ureteric obstruction and renal transplant rejection.

Prostaglandins and other arachidonic acid metabolites in the kidney

This very brief summary of the various possible contributions of PG to normal and abnormal renal function should highlight the problem of assigning a specific role to PG in overall renal physiology and pathophysiology. PG produced in specific segments of the nephron will affect specific functions occurring in this segment. These effects need not necessarily be reflected in the overall renal function. Also in some cases, the determinant may not be prostaglandins, that is, cyclooxygenase derivatives of AA, but perhaps lipoxygenase or epoxygenase products that influence the functional parameters of the specific segment. Despite the multitude of renal functions that may be influenced by PG, we would like to propose a teleological hypothesis for an overall role of PG in the kidney, that is, that of cytoprotective agents. Renal vasodilatatory prostaglandins will maintain renal blood flow when the latter is challenged, thus, preventing hypoxic injury to the tissue. Endogenous prostaglandins may also protect tubular cells from extreme environmental changes as may occur on both the luminal and contraluminal sides. For example, tubular cells may be exposed to luminal fluid that may vary from hypotonic to hypertonic, from alkaline to acid, and so forth. Similarly, the interstitial fluid osmolality and solute composition is subject to considerable variations which may be opposite to those existing on the urinary side. The role of PG might be to maintain the internal milieu of the cells exposed to such extreme changes in environment. This could be accomplished by changing the permeability characteristics of the membranes and the function of pumps. Thus, specific PGs could dampen the hormonal response to protect the specific nephron segment, which might otherwise suffer injury. This hypothesis might also help to explain why the effect of PG administration or inhibition of PG synthesis may vary considerably depending on the overall physiological state of the subject: Maintenance of a local internal milieu may require different responses from those required for total body homeostasis.

Functional role of thromboxane production by acutely rejecting renal allografts in rats

We investigated the role of thromboxane in mediating the reduction in renal function and renal blood flow characteristic of acute renal allograft rejection. We transplanted kidneys from Lewis rats to Brown-Norway recipients. By the third day after transplantation, histologic changes that were consistent with cellular rejection occurred in the kidney. These changes were associated with a moderate reduction in renal function. By day 6, histologic changes of rejection were advanced and included interstitial and perivascular infiltration by mononuclear cells. The clearances of inulin and para-aminohippuric acid were also markedly reduced. As renal function deteriorated, thromboxane B2 (TXB2) production by ex vivo perfused renal allografts increased progressively from 2 to 6 d after transplantation. However, prostaglandin (PG) E2 and 6-keto PGF1 alpha production remained essentially unchanged. There was a significant inverse correlation between the in vivo clearance of inulin and the log of ex vivo TXB2 production. Infusion of the thromboxane synthetase inhibitor UK-37248-01 into the renal artery of 3-d allografts significantly decreased urinary TXB2 excretion and significantly increased renal blood flow (RBF) and glomerular filtration rate (GFR). Although renal function improved significantly after the acute administration of UK-37248-01, GFR and RBF did not exceed 33 and 58% of native control values, respectively. In other animals, daily treatment with cyclophosphamide improved the clearances of inulin and para-aminohippuric acid and reduced thromboxane production by 6-d renal allografts. These studies demonstrate that histologic evidence of rejection is associated with increased renal thromboxane production. Inhibition of thromboxane synthetase improves renal function in 3-d allografts. Cytotoxic therapy improves renal function, reduces mononuclear cell infiltration, and decreases allograft thromboxane production. Thus, the potent vasoconstrictor thromboxane A2 may play a role in the impairment of renal function and renal blood flow during acute allograft rejection.

Increased glomerular thromboxane synthesis as a possible cause of proteinuria in experimental nephrosis

Altered glomerular metabolism of arachidonic acid (AA) has already been demonstrated in experimental nephrotoxic nephritis. The enhanced synthesis of thromboxane A2 (TxA2) in isolated glomeruli that has been found may mediate changes in renal hemodynamics. The objectives of this investigation were: to check whether glomerular AA metabolism is also altered in a model of glomerulopathy in which no leukocyte infiltration or platelet deposition could be demonstrated; to establish a correlation between the altered AA metabolism and proteinuria; and to explore whether the alteration of the prostaglandin (PG) pathway found in isolated glomeruli is an in vitro artifact or reflects a modification in vivo. We used a model of glomerular damage characterized by heavy and persistent proteinuria, which was induced in the rat by a single intravenous injection of adriamycin. At light microscopy, minimal glomerular abnormalities were found in this model. Electron microscopy showed profound alterations of glomerular epithelial cells with extensive fusion of foot processes and signs of epithelial cell activation. Electron microscopy of numerous glomeruli showed no platelet deposition or macrophage and leukocyte infiltration in this model. Isolated glomeruli from nephrotic rats studied 14 or 30 d after a single intravenous injection of adriamycin (7.5 mg/kg) when animals were heavily proteinuric generated significantly more TxB2, the stable breakdown product of TxA2, than normal glomeruli. No significant changes were found in the other major AA metabolites formed through cyclooxygenase. Urinary excretion of immunoreactive TxB2 was also significantly higher in nephrotic than in normal animals. Administration of a selective Tx synthetase inhibitor, UK-38,485, from day 14 to day 18 after adriamycin resulted in a significant reduction of proteinuria compared with pretreatment values. Glomerular synthesis and urinary excretion of TxB2 were normal during the UK-38,485 treatment. Additional experiments showed that elevated glomerular synthesis and urinary excretion of TxB2 were not a consequence of increased substrate availability. Maximal stimulation of the renin-angiotensin axis with furosemide increased glomerular TxB2 synthesis in normal rats, which was significantly lower than in nephrotic animals. Finally, experiments using a unilateral model of adriamycin nephrosis indicated that the enhancement of glomerular TxB2 synthesis is not simply a consequence of the nephrotic syndrome. We conclude that: there is an abnormality of glomerular AA metabolism in nephritic syndrome, which leads to increased TxA2 production; the increased Tx generation correlates with protein excretion and might be responsible for altering the glomerular basement membrane permeability to protein; and the alteration found in isolated glomeruli probably reflects a modification in vivo, in that urinary excretion of immunoreactive TxB2 is also consistently increased in adriamycin nephrosis.

Angiotensin II stimulation of prostaglandin E2 and 6-keto-F1 alpha formation by isolated human glomeruli

The intrinsic in vitro production of prostaglandins (PGs) E2, F2 alpha, 6-keto-F1 alpha, and thromboxane B2 (TxB2) and the conversion of exogenous substrate to PGs and TxB2 by isolated human glomeruli was demonstrated, 6-keto-PGF1 alpha was the major product. This was observed under basal conditions and following incubation with exogenous substrate. Indomethacin (Indo; 10(-4 M) inhibited the conversion of arachidonic acid to PGs and the release of [1-14C]-labeled products from human glomeruli by about 80%. The addition of angiotensin II (AII) to the isolated glomeruli produced, under basal conditions, an almost selective stimulation of 6-keto-PGF1 alpha. Following the prelabeling of glomeruli with 1-14C-arachidonic acid, the increase of glomerular PG formation after AII was added was also only significant for 6-keto-PGF1 alpha. When glomeruli were preincubated with large amounts of non-radiolabeled substrate. AII stimulated PGE2 and 6-keto-PGF1 alpha formation significantly. The data demonstrate PG formation in isolated human glomeruli and show an interaction between AII and the prostaglandin system in this tissue. This interrelationship might have physiologic consequences in the regulation of glomerular hemodynamics.

Altered glomerular eicosanoid biosynthesis in uranyl nitrate-induced acute renal failure

The present studies were designed (1) to examine the pattern of changes in eicosanoid biosynthesis in isolated rat glomeruli, and (2) to correlate these changes with the previously observed alterations in renal perfusion and glomerular filtration rate which occur after uranyl nitrate administration, a model of toxin-induced acute renal failure. In the first part of this study, the in vitro and the in vivo effects of two cyclooxygenase inhibitors were examined for their ability to inhibit rat glomerular eicosanoid biosynthesis. Inhibition of prostaglandin E2 and prostaglandin F2 alpha generation by 1 mM aspirin in vitro was 76 and 82%, respectively. Similar inhibitions of 85 and 72% of biosynthesis of the above-mentioned lipids by 0.1 mM indomethacin were also noted. Intraperitoneal administration of aspirin (150 mg/kg) resulted in a significant inhibition of 88% or greater of prostaglandin E2, prostaglandin F2 alpha, 6-keto-prostaglandin F2 alpha, and thromboxane B2 biosynthesis. These results indicated that the expected alterations produced under in vivo conditions were detectable by in vitro techniques used in this study. 24 h after the administration of uranyl nitrate (25 mg/kg), significant increases in the biosynthesis of prostaglandin E2 (124%) and prostaglandin F2 alpha (88%) were observed when compared to the control values. No significant changes in prostacyclin or thromboxane formation were noted at this time. A further increase in the biosynthesis of prostaglandin E2 (248%), prostaglandin F2 alpha (262%), and a significant increase in prostacyclin (120%), measured as 6-keto-prostaglandin F1 alpha, were noted at 48 h. No changes in thromboxane B2 biosynthesis were noted. It is concluded that these data are consistent with the hypothesis that the increased glomerular biosynthesis of vasodilator eicosanoids (i.e., prostaglandin E2 and prostacyclin) may play a significant role in the homeostatic regulation of renal perfusion and glomerular filtration after acute toxic injury to the kidney.

In vitro prostaglandin synthesis by human glomeruli and papillae

We have investigated in vitro prostaglandin synthesis by human isolated glomeruli and papillary homogenates and compared the results with those obtained in parallel studies using rat material. Prostaglandins were measured by two methods, namely radiometric high performance liquid chromatography after incubation with 14C arachidonic acid and radioimmunoassay. The relative abundance of various prostaglandins synthesized by glomeruli was different in man (6 keto PGF1 alpha greater than TXB2 greater than PGF2 alpha greater than PGE2) and in the rat (PGE2 greater than or equal to PGF2 alpha greater than TXB2 greater than 6 keto PGF1 alpha). Unidentified peaks eluting between 6 keto PGF1 alpha and TXB2 were observed only in rat glomeruli. These peaks were suppressed by indomethacin. Direct radioimmunoassay of prostaglandins in the incubation medium of human glomeruli confirmed the predominance of 6 keto PGF1 alpha synthesis and showed its stimulation by arachidonic acid, its progressive decrease with time and its linear relationship with glomerular protein at low concentrations. On the contrary, the profile of prostaglandin synthesis by the papilla was similar in man and in the rat, PGE2 and PGF2 alpha being the major products in both species. However, related to one mg of protein, papillary synthesis of these two prostaglandins was greater in the rat. These results show that PGI2 is the major prostaglandin synthesized in human glomeruli and suggest a role for this prostaglandin in glomerular physiology in man.