Antioxidants in the serum of children with insulin-dependent diabetes mellitus

To determine whether alteration in serum antioxidant status is related to the increased oxidative stress as a cause of diabetic angiopathy, we measured both the antioxidant activity (AOA) and total peroxyl radical-trapping antioxidant parameter (TRAP), and their component individual antioxidants in serum of children with insulin-dependent diabetes mellitus (IDDM). The AOA was measured as the ability to inhibit lipid autoxidation in brain homogenates. TRAP was assayed as the ability to delay lipid peroxidation induced by an azo initiator. Antioxidants measured were ceruloplasmin, transferrin, and albumin components of AOA; and ascorbic acid, uric acid, protein sulfhydryl, and alpha-tocopherol as components of TRAP. Serum AOA appeared to be decreased in the diabetics in relation to poor glycemic control, corresponding to the decrease in transferrin and albumin. Serum haptoglobin level was also decreased in the diabetics. Similarly, the directly measured TRAP value was decreased in the diabetic serum mainly due to the decreased contribution of unidentified chain-breaking antioxidants, despite the increase in ascorbic acid and alpha-tocopherol. The decrease in both types of antioxidant activity in the diabetic serum, as new findings, suggests that a defective serum antioxidant status contributes to the increased oxidative stress in IDDM.     

Dehydroepiandrosterone protects tissues of streptozotocin-treated rats against oxidative stress

Chronic hyperglycemia in diabetes determines the overproduction of free radicals, and evidence is increasing that these contribute to the development of diabetic complications. It has recently been reported that dehydroepiandrosterone possesses antioxidant properties; this study evaluates whether, administered daily for three weeks per os, it may provide antioxidant protection in tissues of rats with streptozotocin-induced diabetes. Lipid peroxidation was evaluated on liver, brain and kidney homogenates from diabetic animals, measuring both steady-state concentrations of thiobarbituric acid reactive substances and fluorescent chromolipids. Hyperglycemic rats had higher thiobarbituric acid reactive substances formation and fluorescent chromolipids levels than controls. Dehydroepiandrosterone-treatment (4 mg/day for 3 weeks) protected tissues against lipid peroxidation: liver, kidney and brain homogenates from dehydroepiandrosterone-treated animals showed a significant decrease of both thiobarbituric acid reactive substances and fluorescent chromolipids formation. The effect of dehydroepiandrosterone on the cellular antioxidant defenses was also investigated, as impaired antioxidant enzyme activities were considered proof of oxygen-dependent toxicity. In kidney and liver homogenates, dehydroepiandrosterone treatment restored to near-control values the cytosolic level of reduced glutathione, as well as the enzymatic activities of superoxide-dismutase, glutathione-peroxidase, catalase. In the brain, only an increase of catalase activity was evident (p < .05), which reverted with dehydroepiandrosterone treatment. The results demonstrate that DHEA treatment clearly reduces oxidative stress products in the tissues of streptozotocin-treated rats.     

Tissue distribution of avian pancreatic polypeptide-degrading activity

Degradation of avian pancreatic polypeptide (APP) by subcellular fractions from homogenates of chicken kidney, liver, and brain was characterized in this study. Chicken kidney cytosol exhibited the highest degrading activity of all kidney subcellular fractions studied including nuclear, mitochondrial, and microsomal. The cytosolic kidney APP-degrading activity was inhibited in a dose-dependent manner by bacitracin, serine protease inhibitors, and dithiothreitol, and eluted in the void volume of a Sephadex G-100 column, indicating that it is a soluble, serine protease-like activity with a Mr greater than 100,000 kDa and with some dependence on disulfide bonds. Soluble cytosol fractions from chicken liver, kidney, and brain all exhibited greater APP-degrading activity than that of corresponding membrane fractions and, furthermore, were similar in activity between one another. It is concluded that APP degradation by tissue homogenates occurs via a soluble, cytosolic protease which is inhibited by selected serine protease inhibitors; the activity does not differ among liver, kidney, and brain, three tissues which show different receptivity for APP.     

Total reactive antioxidant potential in human saliva of smokers and non-smokers.

Uric acid is the most important non-enzymatic antioxidant present in human saliva. There is a great variability among individuals, both in salivary uric acid content and saliva total reactive antioxidant potential (TRAP). The uric acid present in saliva correlates with plasma uric acid, suggesting that the former is imported from plasma. There are not statistical differences between uric acid or TRAP values in saliva of smokers and non-smokers. Also, smoking a cigarette does not modify the levels of antioxidants present in saliva.     

Time Course of Peripheral Oxidative Stress as Consequence of Global Ischaemic Brain Injury in Rats

Free radicals play an important role in the pathogenesis of brain injury. This study evaluates the potential relationship between ischaemia/reperfusion (I/R)-induced brain injury, peripheral oxidative stress (lymphocyte DNA damage), plasma antioxidant potential and uric acid levels. We observed that 15 min of ischaemia were sufficient to significantly increase lymphocyte DNA damage that remained elevated at the end of early (3 h) reperfusion and at later (72 h) reperfusion time; this parameter was not significantly increased, when compared to preoperated levels. In parallel, antioxidant potential was elevated after 15 min of ischaemia, remained high at early (3 h) reperfusion and decreased again with longer (72 h) reperfusion. A close association between the plasma antioxidant status and the uric acid content has been confirmed by findings that changes in TRAP values positively correlate with uric acid concentration in rat plasma after ischaemic injury. Moreover, results of in vitro experiments with extra uric acid addition to control plasma have shown that uric acid contributes to a greater part of TRAP values. These results indicate a similar time course of brain I/R-associated oxidative stress and peripheral antioxidant defence status and/or oxidative stress in animal experiments.     

Effect of aging on aqueous-phase antioxidants in tissues of male Fischer rats

The purpose of this study was to determine the influence of aging on concentrations of the important aqueous-phase antioxidants in rat tissues. Ascorbic acid, glutathione and uric acid were measured in tissues and organs of male Fischer 344 rats at 6, 15 and 26 months of age. Blood, liver, lungs, heart, kidneys, brain, testes and lenses were excised rapidly and were extracted with cold metaphosphoric acid. Aging diminished the concentration of ascorbic acid in liver, lung and lens; levels in 26-month-old rats were 40-60% of those in 6-month-old rats. Glutathione content was diminished only in lens, where it decreased almost 50% between 15 and 26 months. Some age-associated increases in antioxidant levels also were seen; testis ascorbic acid and kidney glutathione levels were elevated in the old compared with the younger rats. Uric acid concentrations were much lower than glutathione or ascorbic acid concentrations in every tissue except plasma. Old rats had lower levels of uric acid in liver but higher levels in heart, kidney and testis. These results demonstrate that aqueous-phase antioxidant levels are not uniformly diminished in tissues of old rats.     

Postnatal development of the actual and total activity of the branched-chain 2-oxo acid dehydrogenase complex in rat tissues

Actual and total activities of the branched-chain 2-oxo acid dehydrogenase complex were determined in homogenates of quadriceps muscle, heart, liver, kidney and brain from rats of 0-70 days age. All rat tissues except quadriceps muscle showed a marked increase of total activity between 0 and 21 days, heart and kidney also after weaning. The actual activity rose after birth in liver, kidney and brain and after weaning in liver, kidney and heart. The activity state was always about 100% in liver and varied between 40-60% in kidney and brain, 10-23% in heart and 6-12% in quadriceps muscle. The actual activities measured indicate, that the degradation of branched-chain 2-oxo acids mainly takes place in the liver of the newborn, suckling and young-adult rat.     

Alterations of Antioxidant Enzymes and Oxidative Damage to Macromolecules in Different Organs of Rats During Aging

Oxygen free radicals have been hypothesized to play an important role in the aging process. To investigate the correlation between the oxidative stress and aging, we have determined the levels of oxidative protein damage and lipid peroxidation in the brain and liver, and activities of antioxidant enzymes in the brain, liver, heart, kidney, and serum from the Fisher 344 rats at ages of 1, 6, 12, 18, and 24 months. The results showed that the level of oxidative protein damage (measured as carbonyl content) in the brain and liver was significantly higher in older animals than in young animals. No statistical difference was observed in the lipid peroxidation of the liver and brain between young and old animals. The activities of antioxidant enzymes in most tissues displayed an age-dependent decline. Superoxide dismutases in the heart, kidney, and serum, glutathione peroxidase activities in the serum and kidney, and catalase activities in the brain, liver, and kidney, significantly decreased during aging. Cytochrome c oxidase, an enzyme involved in electron transport in mitochondria, initially increased, but subsequently decreased in the aged brain, whereas no significant alteration was observed in the liver mitochondrial antioxidant enzymes. The present studies suggest that the accumulation of oxidized proteins during aging is most likely to be linked with an age-related decline of antioxidant enzyme activities, whereas lipid peroxidation is less sensitive to predict the aging process.     

Gender differences in antioxidant capacity of rat tissues determined by 2,2'-azinobis (3-ethylbenzothiazoline 6-sulfonate; ABTS) and ferric reducing antioxidant power (FRAP) assays

Differences in susceptibility to oxidative stress between males and females have been postulated. Several methods have been developed to assess the total antioxidant capacity of human serum or plasma, but just recently some of them were employed for measurement of antioxidant capacity of tissues. In this study, we measured and compared antioxidant capacity of heart, kidney, liver and brain tissues of male and female rats. Antioxidant capacity was determined using 2,2'-azinobis (3-ethylbenzothiazoline 6-sulfonate; ABTS) and ferric reducing antioxidant power (FRAP) assays. In the same samples, lipid peroxidation products of these tissues were analysed using thiobarbituric acid reactive substances (TBARS) assays. Antioxidant capacity of heart, kidney and liver tissues was higher in female than male rats for both FRAP and ABTS assays. We found positive correlation between FRAP and ABTS values for all tested tissues. FRAP and ABTS proved to be comparable, simple and quick methods for antioxidant capacity scanning in tissues. TBARS levels differed only for brain tissue, being higher in males. These results indicate stronger defense against oxidative damage in females for all observed tissues. These finding may account for the longer lifespan of females.     

Relationship between antioxidant potential and oxidative damage to lipids, proteins and DNA in aged rats

Oxidative stress has been implicated to play a major role in aging and age-related diseases. In the present study, we investigated the effects of aging on the total antioxidant capacity, uric acid, lipid peroxidation, total sulfhydryl group content and damage to DNA in adult (6 months), old (15 months) and senescent (26 months) male Wistar rats. The antioxidant capacity, determined by phycoerythrin-based TRAP method (total peroxyl radical-trapping potential) was significantly decreased in the plasma and myocardium of old and senescent rats, whereas plasma level of uric acid was elevated in 26-month-old rats. Age-related decline in plasma and heart antioxidant capacity was accompanied by a significant loss in total sulfhydryl group content, increased lipid peroxidation and higher DNA damage in lymphocytes. Correlations between TRAP and oxidative damage to lipids, proteins and DNA suggest that the decline in antioxidant status may play an important role in age-related accumulation of cell damage caused by reactive oxygen species.     

Renal inactivation of substance P in the rat.

The activity and distribution of substance P-catabolizing enzyme(s) were studied in the rat kidney. Kidney homogenates inactive substance P 5-20 times as fast as do homogenates of intestine, liver, lung, heart or brain. The catabolizing activity was highest in the cortex and decreased progressively down the papilla. Cortex of rat kidney was homogenized and fractions enriched in microsomal membrane, final supernatant, plasma membrane, endoplasmic reticulum, brush border and intact glomeruli were prepared. The identity and homogeneity of the preparations were determined by assaying marker enzymes and by morphological examination. Substance P was catabolized most rapidly by the microsomal and plasma-membrane-enriched fractions, and least rapidly by endoplasmic reticulum or final supernatant fractions. Purified brush border of proximal tubules inactivated substance P more than 10 times as fast as isolated glomeruli. Our experiments show that substance P is catabolized at a rate that is similar to the rates of inactivation of bradykinin and angiotensin II. Further, the distribution of substance P-catabolizing activity in various kidney fractions is similar to the distribution of kininase and angiotensinase activities previously reported.     

Incomplete palmitate oxidation in cell-free systems of rat and human muscles

The palmitate oxidation capacity was determined in whole homogenates, postnuclear fractions and mitochondrial fractions of various rat and human muscles and in rat liver, kidney, brain and lung. The oxidation rate (production of 14CO2 and 14C-labeled acid-soluble intermediates) was [1-14C]palmitate greater than [U-14C]palmitate greater than [16-14C]palmitate in all cell-free systems. Oxidation rates were highest in rat heart and liver, intermediate in kidney, diaphragm and m. quadriceps, and low in brain and lung. The capacity of human heart was much lower than that of rat heart and about twice that of human skeletal muscles. Omission of L-carnitine and addition of malonyl-CoA, KCN or antimycin A decreased the oxidation rates in whole homogenates and mitochondrial fractions. Antimycin or KCN increased and malonyl-CoA decreased the ratio of the oxidation rates with [1-14C]- and [16-14C]palmitate. The carnitine concentration had no significant effect on the ratio. 14C-labeled dodecanoic and tetradecanoic acids were identified in homogenates and mitochondrial fractions of m. quadriceps and liver of rat as acid-insoluble intermediates of [16-14C]palmitate oxidation in the presence and absence of antimycin A. Their amounts recovered can account for the differences in oxidation rates found with [1-14C]- and [16-14C]palmitate. The incomplete palmitate oxidation in cell-free systems appears to be mainly caused by an inadequate mitochondrial degradation of peroxisomal oxidation products.     

Focal neurometabolic alterations in mice deficient for succinate semialdehyde dehydrogenase

Metabolite profiling in succinate semialdehyde dehydrogenase (SSADH; Aldh5a1-/-) deficient mice previously revealed elevated gamma-hydroxybutyrate (GHB) and total GABA in urine and total brain and liver extracts. In this study, we extend our metabolic characterization of these mutant mice by documenting elevated GHB and total GABA in homogenates of mutant kidney, pancreas and heart. We quantified beta-alanine (a GABA homolog and putative neurotransmitter) to address its potential role in pathophysiology. We found normal levels of beta-alanine in urine and total homogenates of mutant brain, heart and pancreas, but elevated concentrations in mutant kidney and liver extracts. Amino acid analysis in mutant total brain homogenates revealed no abnormalities except for significantly decreased glutamine, which was normal in mutant liver and kidney extracts. Regional amino acid analysis (frontal cortex, parietal cortex, hippocampus and cerebellum) in mutant mice confirmed glutamine results. Glutamine synthetase protein and mRNA levels in homogenates of mutant mouse brain were normal. We profiled organic acid patterns in mutant brain homogenates to assess brain oxidative metabolism and found normal concentrations of Kreb's cycle intermediates but increased 4,5-dihydroxyhexanoic acid (a postulated derivative of succinic semialdehyde) levels. We conclude that SSADH-deficient mice represent a valid metabolic model of human SSADH deficiency, manifesting focal neurometabolic abnormalities which could provide key insights into pathophysiologic mechanisms.     

Oxalate modulates thiobarbituric acid reactive species (TBARS) production in supernatants of homogenates from rat brain, liver and kidney: effect of diphenyl diselenide and diphenyl ditelluride

The aim of this paper was to investigate the mechanism(s) involved in the sodium oxalate pro-oxidative activity in vitro and the potential protection by diphenyl diselenide ((PhSe)(2)) and diphenyl ditelluride ((PhTe)(2)) using supernatants of homogenates from brain, liver and kidney. Oxalate causes a significant increase in the TBARS (thiobarbituric acid reactive species) production up to 4mmol/l and it had antioxidant activity from 8 to 16mmol/l in the brain and liver. Oxalate had no effect in kidney homogenates. The difference among tissues may be related to the formation of insoluble crystal of oxalate in kidney, but not in liver and brain homogenates. (PhSe)(2) and (PhTe)(2) reduced both basal and oxalate-induced TBARS in rat brain homogenates, whereas in liver homogenates they were antioxidant only on oxalate-induced TBARS production. (PhSe)(2) showed a modest effect on renal TBARS production, whereas (PhTe)(2) did not modulate TBARS in kidney preparations. Oxalate at 2mmol/l did not change deoxyribose degradation induced by Fe(2+) plus H(2)O(2), whereas at 20mmol/l it significantly prevents its degradation. Oxalate (up to 4mmol/l) did not alter iron (10micromol/l)-induced TBARS production in the brain preparations, whereas at 8mmol/l onwards it prevents iron effect. In liver preparations, oxalate amplifies iron pro-oxidant activity up to 4mmol/l, preventing iron-induced TBARS production at 16mmol/l onwards. These results support the antioxidant effect of organochalcogens against oxalate-induced TBARS production. In addition, our results suggest that oxalate pro- and antioxidant activity in vitro could be related to its interactions with iron ions.     

The subcellular location of isozymes of NADP-isocitrate dehydrogenase in tissues from pig, ox and rat

Antibodies against purified NADP-isocitrate dehydrogenase from pig liver cytosol and pig heart were raised in rabbits. The purified enzymes from these sources are different proteins, as demonstrated by differences in electrophoretic mobility and absence of crossreactivity by immunotitration and immunodiffusion. The NADP-isocitrate dehydrogenase in the soluble supernatant homogenate fraction from pig liver, kidney cortex, brain and erythrocyte hemolyzate was identical with the purified enzyme from pig liver cytosol, as determined by electrophoretic mobility and immunological techniques. The enzyme in extracts of mitochondria from pig heart, kidney, liver and brain was identical with the purified pig heart enzyme by the same criteria. However, the 'mitochondrial' isozyme was the major component also in the soluble supernatant fraction of pig heart homogenate. The 'cytosolic' isozyme accounted for only 1-2% of total NADP-isocitrate dehydrogenase in pig heart, as determined by separation of the isozymes with agarose gel electrophoresis and immunotitration. The mitochondrial isozyme was also the predominant NADP-isocitrate dehydrogenase in porcine skeletal muscle. The ratio of cytosolic/mitochondrial isozyme for porcine whole tissue extract, determined by immunotitration, was about 2 for liver and 1 for kidney cortex and brain. The distribution of isozymes in cell homogenate fractions from ox and rat tissues corresponded to that observed in organs of porcine origin. The mitochondrial and cytosolic isozymes from ox and rat tissues exhibited crossreactivity with the antibodies against the pig heart and pig liver cytosol enzyme, respectively, and the electrophoretic migration patterns were similar qualitatively to those found for the isozymes in porcine tissues. Nevertheless, there were species specific differences in the characteristics of each of the corresponding isozymes. NAD-isocitrate dehydrogenase was not inhibited by the antibodies, confirming that the protein is distinct from that of either isozyme of NADP-isocitrate dehydrogenase.     

The organochalcogen 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one induces oxidative stress in heart, liver, and kidney of rats

The objective of this study was to investigate the in vitro effects of the organochalcogen 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one on some parameters of oxidative stress in liver, kidney, and heart of 10-day-old rats. The homogenates of liver, kidney, and heart were incubated for 1 h in the absence (control) or in the presence of 1, 10, or 30 μM of the organoselenium and thiobarbituric acid reactive substances, carbonyl, and the activity of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) were measured. First, we tested the influence of the compound on 1,1-diphenyl-2-picrylhydrazyl (DPPH(?)) radical scavenging and verified that the organochalcogen did not have any antioxidant properties. We observed an increase of lipid peroxidation in all concentrations tested in heart and kidney, while in liver only in the concentrations of 10 and 30 μM. Moreover, we also verified an enhance of protein oxidation in the concentrations of 10 and 30 μM in kidney. On the other hand, the compound caused a reduction on the activity of CAT in heart (10 and 30 μM), liver (30 μM), and kidney (30 μM). The activity of SOD was increased in heart (10 and 30 μM), while in liver (30 μM) and in kidney (10 and 30 μM) the activity was reduced. Our findings indicate that this organoselenium compound induces oxidative stress in liver, heart, and kidney of immature rats, collaborating to the fact that these tissues are potential targets for the organochalcogen action.     

Conversion of arachidonic acid to lipoxygenase products by human fetal tissues

[14C]Arachidonic acid was converted to several lipoxygenase products by homogenates of human fetal tissues as determined by thin-layer chromatography. The net conversions of [14C]arachidonic acid to radiolabeled lipoxygenase products were high (greater than or equal to 5%) in the case of fetal liver and brain, and low (less than or equal to 2%) in the case of fetal adrenal, heart, and kidney.     

The metabolism of sialic acids in isolated rat colonic mucosal cells.

The activities of ten enzymes involved in sialic acid metabolism were measured in colonic mucosal cells from rats and compared with those in liver. A methodology was devised that enabled all ten enzyme activities to be evaluated in a single rat colon preparation. Enzyme assays with radioactively labelled substrates were developed for maximum sensitivity, and the identification of substrates and products was carefully checked to assess the contribution of contaminants to enzyme reactions with low activity. The activities of most enzymes involved in the biosynthesis of N-acetyl-D-neuraminic acid (NeuAc) from UDP-N-acetyl-D-glucosamine were found to be more than 20-fold lower than those in liver. The activities of CMP-NeuAc synthase, N-acetyl-D-glucosamine 2-epimerase, N-acetyl-D-glucosamine kinase, sialyltransferase and sialidase were similar to or 2-4-fold lower than in liver. The biosynthesis of NeuAc via its 9-phosphate was demonstrated in the 100 000 g supernatant of colonic-cell homogenates by enzymic assay and precursor experiments with N-acetyl[14C]-mannosamine. No alternative route for NeuAc formation could be detected. The 100 000g supernatant fractions of liver, kidney and colonic mucosal cells utilized N-acetyl[14C]mannosamine with differing efficiencies. Radioactive products identified as sialic acid biosynthetic intermediates amounted to 49%, 0.04% and 5.6% of added precursor in liver, kidney and colon respectively. Catabolism of labelled precursor to non-hexosamine products was high in kidney and colonic mucosal-cell fractions.     

Impaired plasma antioxidative defense and increased nontransferrin-bound iron during high-dose chemotherapy and radiochemotherapy preceding bone marrow transplantation

To analyze the effects of radiochemotherapy on the pro-oxidative/antioxidative balance in plasma, we measured the total radical antioxidant parameter of plasma (TRAP) and single plasma antioxidants (uric acid, sulfhydryl groups, alpha-tocopherol, ubiquinone-10/total coenzyme-Q10 ratio, ascorbate, and bilirubin) every 12 h during high-dose chemotherapy and radiochemotherapy preceding bone marrow transplantation (BMT). Nontransferrin-bound iron (NTBI) was monitored as a potential pro-oxidant. Plasma levels of polyunsaturated fatty acids (PUFA) were measured as substrates, and thiobarbituric acid-reactive substances (TBARS) were measured as products of lipid peroxidation. Allantoin was analyzed as the product of uric acid oxidation. Patients receiving busulfan, VP-16, and cyclophosphamide (BU/VP/CY) (n = 8) were compared with those receiving total body irradiation in addition to VP-16 and cyclophosphamide (TBI/VP/CY) (n = 8). TRAP values were within the normal range before therapy and decreased after BU/VP/CY by 37% (p <. 02) and after TBI/VP/CY by 39% (p <.02). During TBI and after VP-16, a temporary increase in TRAP values occurred, which was not related to changes in individual antioxidants. In vitro experiments confirmed that VP-16 had an antioxidative effect. The concentration of uric acid declined in both groups and correlated with TRAP (BU/VP/CY: r =.80, p <.001; TBI/VP/CY: r =.84, p <.001). Levels of NTBI, which is normally not found in plasma, increased rapidly during conditioning therapy (p <.02 in both groups) and correlated inversely with TRAP (weighted intraindividual Spearman rank correlation coefficient for both groups: NTBI and TRAP: r = -.59, p <.001) and PUFA (in the radiochemotherapy group: r = -.67, p <.001). Whereas PUFA declined (p <.02 in both groups), TBARS increased (p <. 05 in both groups). Furthermore, an increase of allantoin and ubiquinone-10/total coenzyme-Q10 ratio in the BU/VP/CY group was found (allantoin: p <.02; ubiquinone-10/total coenzyme-Q10 ratio: p <.05). Antioxidants only partially recovered to baseline values until day 14 after BMT. Our findings indicate oxidative stress after high-dose radiochemotherapy and suggest a contribution of NTBI therein.     

Leukotriene A4: metabolism in different rat tissues

The transformation of leukotriene A4 into dihydroxyeicosatetraenoic acids and sulfidopeptide leukotrienes was determined in homogenates of rat tissues supplied with glutathione and albumin. The highest production of leukotriene B4 was found in spleen, lung and small intestine, while leukotriene C4 dominated in liver and lung. 5(S),6(R)-Dihydroxy-7,9-trans-11,14-cis-eicosatetraenoic acid (5,6-DHETE) was formed in all tissues, most prominently in kidney, heart and brain. We also found another isomer of 5,6-dihydroxyeicosatetraenoic acid produced in the kidney. This compound was derived from 5,6-DHETE by isomerization, probably of the 11-cis double bond to 11-trans, and the process appeared to be catalyzed by a membrane-bound factor.