Evidence for the presence of a prostaglandin E 2 -9-keto reductase in rat organs

Angiotensin type 1 receptor mediates renal production and conversion of prostaglandins E2 to F2α in conscious diabetic rats

INTRODUCTION

Previous studies demonstrated that stimulation of angiotensin subtype 1 receptor (AT1R) led to increased renal generation of prostaglandins E2 (PGE2) and renal inflammation. In turn, PGE2 increases AT1R activity. The conversion of PGE2 to the less active metabolite prostaglandin F2α (PGF2α) via 9-ketoreductase interrupts this feedback loop. The effects of diabetes on the interface between AT1R, PGE2 and PGF2α are not well established. We hypothesized that in diabetes, an aberrant AT1R activity enhances the biosynthesis of PGE2 and impairs the activity of PGE 9-ketoreductase, leading to accumulation of PGE2.

MATERIALS AND METHODS

Using microdialysis technique, we monitored renal interstitial fluid levels of angiotensin II (Ang II), PGE2 and PGF2α in control and AT1R blocker, valsartan, treated diabetic rats (N=8 each). We utilized the PGF2α to PGE2 ratio as indirect measure of PGE 9-ketoreductase activity.

RESULTS

Diabetes increased renal interstitial fluid levels of Ang II, PGE2 and PGF2α. PGF2α/PGE2 ratio increased by the third week, but declined by the sixth week of diabetes. Valsartan reduced PGE2 and PGF2α levels and increased Ang II and the conversion of PGE2 to PGF2α.

CONCLUSION

Our results suggest that in diabetes, AT1R increases PGE2 generation and reduces conversion of PGE2 to PGF2α with the progression of diabetes.

Human organic anion transporters and human organic cation transporters mediate renal transport of prostaglandins

Prostaglandin E(2) (PGE(2)) and prostaglandin F(2 alpha) (PGF(2 alpha)) have been used for the induction of labor and the termination of pregnancy. Renal excretion is shown to be an important pathway for the elimination of PGE(2) and PGF(2 alpha). The purpose of this study was to elucidate the molecular mechanism of renal PGE(2) and PGF(2 alpha) transport using cells stably expressing human organic anion transporter (hOAT) 1, hOAT2, hOAT3, and hOAT4, and human organic cation transporter (hOCT) 1 and hOCT2. A time- and dose-dependent increase in PGE(2) and PGF(2 alpha) uptake was observed in cells expressing hOAT1, hOAT2, hOAT3, hOAT4, hOCT1, and hOCT2. The K(m) values of PGE(2) uptake by hOAT1, hOAT2, hOAT3, hOAT4, hOCT1, and hOCT2 were 970, 713, 345, 154, 657, and 28.9 nM, respectively, whereas those of PGF(2 alpha) uptake by hOAT1, hOAT3, hOAT4, hOCT1, and hOCT2 were 575, 1092, 692, 477, and 334 nM, respectively. PGE(2) and PGF(2 alpha) significantly inhibited organic anion uptake by hOATs and organic cation uptake by hOCTs. In conclusion, considering the localization of these transporters, the results suggest that PGE(2) and PGF(2 alpha) transport in the basolateral membrane of the proximal tubule is mediated by multiple pathways including hOAT1, hOAT2, hOAT3, and hOCT2, whereas that in the apical side is mediated by hOAT4.

Increased renal formation of thromboxane A2 and prostaglandin F2 alpha in heart failure

Renal formation of the vasoconstrictor prostaglandins thromboxane A2 (TXA2) and prostaglandin F2 alpha (PGF2 alpha) was investigated in 25 patients with cardiac failure, divided into New York Heart Association functional classes I to IV, and in eight healthy control subjects. Plasma renin activity (PRA) and hemodynamic parameters were also investigated. Renal vasoconstrictor eicosanoid formation, measured in urinary daily excretion, was not different between patients in class I and control subjects. Class II to IV patients showed progressively increasing production of PGF2 alpha (F = 49.8, p < 0.001, analysis of variance) and TXA2 (F = 37.8, p < 0.002). PGF2 alpha excretion peaked in class IV (+ 1266% vs class I, p < 0.001). Compared with class I, urinary excretion of thromboxane B2 was + 816% in class III and + 1561% in class IV (both p < 0.001). PRA was significantly increased only in class IV (+ 1558%, p < 0.001). The current results indicate a progressive increase in renal production of vasoconstrictor eicosanoids directly related to New York Heart Association class and suggest that these prostanoids may have a role in deterioration of renal function.

A comparative study of the effects of iloprost and PGE1 on pulmonary arterial pressure and edema formation in the isolated perfused rat lung model

Isolated lungs from male Wistar rats (250-350 g) were perfused at a constant flow rate (10 ml/min, non-recirculating) with Krebs-Ringer-bicarbonate buffer containing 4.5 % bovine serum albumin, and were ventilated at a positive pressure (60 breaths/min). Pulmonary arterial pressure and lung weight (as a measure of edema formation) were recorded continuously. After an equilibration period of 20 minutes the various test compounds were added to the perfusion fluid and experimental recording was continued for another 60 minutes. The effects of the stable PGI2-mimetic, iloprost, of PGE1, and of the biologically active PGE1-metabolite, 13,14-dihydro-PGE1, were evaluated in this model (n = 6). Iloprost showed slight, but not significant vasodilation; however, lung weight remained unchanged. PGE1 and 13, 14-dihydro-PGE1 also caused slight vasodilation, but in contrast to iloprost these compounds induced distinct pulmonary edema. The lung weight gain was discernible at concentrations of 2.8 x 10(-6) mol/l (significant at 2.8 x 10(-5) mol/l; p < or = 0.05) and was accompanied by increases in the wet-weight to dry-weight ratios. These findings were duplicated in a second set of experiments (n = 6) from which the same results were obtained. The results indicate that at high concentrations PGE1 (and 13,14-dihydro-PGE1), but not iloprost, can induce pulmonary edema in rats probably by increasing the permeability of the pulmonary vasculature.

Prostaglandin-E2 9-reductase from corpus luteum of pseudopregnant rabbit is a member of the aldo-keto reductase superfamily featuring 20 alpha-hydroxysteroid dehydrogenase activity

The prostaglandin-E2 9-reductase (PGE2 9-reductase) activity in the corpus luteum of rabbits corresponds to a cytosolic, NADPH-dependent enzyme with a molecular mass of 36 kDa. This enzyme was purified from corpora lutea on day 12 of pseudopregnancy with a 266-fold enrichment. The main purification step was affinity chromatography using Red Sepharose CL-6B. The efficiency of this column was improved by elution with 1 mM NADH prior to elution of the active fractions with 1 mM NADPH. Amino acid sequence data demonstrate that the rabbit luteal PGE2 9-reductase has to be classified as a member of the aldo-keto reductase superfamily. The enzyme revealed a wide substrate specificity comprising the reduction of aldehydes, ketones, and quinones. Apparent kinetic constants were determined using methylglyoxal, DL-glyceraldehyde, and 9,10-phenanthrenquinone as substrates. The fully purified enzyme showed two catalytic activities of particular interest: PGE2 9-reductase and 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD) activities. The competitive inhibition of 20 alpha-HSD activity by PGE2 indicates that progesterone and PGE2 are substrates for the same enzyme. From these results, we conclude that prostaglandin and steroid metabolism are tightly linked to each other. For this reason the aldo-keto reductase could be a key enzyme in the cascade of events leading to the regression of the corpus luteum in the rabbit.

Prostaglandin D2 and endothelin-1 induce the production of prostaglandin F2 alpha, 9 alpha, 11 beta-prostaglandin F2, prostaglandin E2, and thromboxane in capillary endothelium of human brain

Endothelial cells derived from human brain capillaries (HBCEC) synthesize prostaglandin D2 (PGD2) which can be stimulated, among other prostanoids, by endothelin 1 (ET-1). Both the PGD2 induced by ET-1 and the exogenously added PGD2 to HBCEC are converted to 9 alpha, 11 beta-prostaglandin F2 (9 alpha, 11 beta-PGF2), a known potent vasoconstrictor. Exogenous PGD2 also dose-dependently enhanced the production of vasoconstrictive PGF2 alpha, thromboxane B2 (TXB2), and the vasodilatory PGE2 as well as cAMP by HBCEC. The PGD2-induced formation of PGF2 alpha, PGE2, and TXB2 was reduced by the cyclooxygenase inhibitors acetylsalicylic acid (ASA) or indomethacin (Indo), indicating for the first time that PGD2 may contribute to the formation of prostanoids in HBCEC. These results strongly suggest that PGD2 may play an important role in the regulation of cerebral capillary function under physiologic and pathologic conditions.

Metabolism of prostaglandin F2 alpha in Zellweger syndrome. Peroxisomal beta-oxidation is a major importance for in vivo degradation of prostaglandins in humans

We have recently shown in vitro that the peroxisomal fraction of a rat liver homogenate has the highest capacity to beta-oxidize prostaglandins. In order to evaluate the relative importance of peroxisomes for this conversion also in vivo, we administered [3H]prostaglandin F2 alpha to an infant suffering from Zellweger syndrome, a congenital disorder characterized by the absence of intact peroxisomes. As a control, labeled compound was administered to two healthy volunteers. Urine was collected, fractionated on a SEP-PAK C18 cartridge, and subjected to reversed-phase high-performance liquid chromatography. The Zellweger patient was found to excrete prostaglandin metabolites considerably less polar than those of the control subjects. The major urinary metabolite in the control subjects was practically absent in the urine from the Zellweger patient. The major urinary prostaglandin F2 alpha metabolite from the Zellweger patient was identified as an omega-oxidized C20-prostaglandin, 9,11-dihydroxy-15-oxoprost-5-ene-1,20-dioic acid. The major urinary prostaglandin F2 alpha metabolite from the control subjects had chromatographic properties of a tetranor (C16) prostaglandin, in accordance with earlier published data. The present results, in combination with our previous in vitro data, indicate that peroxisomal beta-oxidation is of major importance for in vivo chain shortening of prostaglandins.

Enzymatic formation of prostaglandin F2 alpha in human brain

Prostaglandin (PG)E2 9-ketoreductase, which catalyzes the conversion of PGE2 to PGF2 alpha, was purified from human brain to apparent homogeneity. The molecular weight, isoelectric point, optimum pH, Km value for PGE2, and turnover number were 34,000, 8.2, 6.5-7.5, 1.0 mM, and 7.6 min-1, respectively. Among PGs tested, the enzyme also catalyzed the reduction of other PGs such as PGA2, PGE1, and 13,14-dihydro-15-keto PGF2 alpha, but not that of PGD2, 11 beta-PGE2, PGH2, PGJ2, or delta 12-PGJ2. The reaction product formed from PGE2 was identified as PGF2 alpha by TLC combined with HPLC. This enzyme, as is the case for carbonyl reductase, was NADPH-dependent, preferred carbonyl compounds such as 9,10-phenanthrenequinone and menadione as substrates, and was sensitive to indomethacin, ethacrynic acid, and Cibacron blue 3G-A. The reduction of PGE2 was competitively inhibited by 9,10-phenanthrenequinone, which is a good substrate of this enzyme, indicating that the enzyme catalyzed the reduction of both substrates at the same active site. These results suggest that PGE2 9-ketoreductase, which belongs to the family of carbonyl reductases, contributes to the enzymatic formation of PGF2 alpha in human brain.

Isozyme specificity of rat liver glutathione S-transferases in the formation of PGF2 alpha and PGE2 from PGH2

When prostaglandin H2 (PGH2) was incubated with a mixture of glutathione S-transferases (GSTs) obtained from S-hexylglutathione affinity chromatography, as much as 40% of it was transformed into a prostanoid whose Rf value corresponded to that of the standard PGF2 alpha. The reaction product was identified as PGF2 alpha by cochromatography with a standard on TLC and HPLC. The stereochemistry of the hydroxyl groups on C-9 and C-11 of the cyclopentane ring was confirmed by mass-spectral analysis of the butylboronate derivative of the reaction product. Neither PGE2 nor PGD2 could substitute for PGH2 in the reaction mixture, indicating that the mechanism of formation of PGF2 alpha is a direct two-electron reduction of the endoperoxide moiety and not through a reduction of the keto group on PGE2 or PGD2. Individual GST isozymes exhibited distinct differences in their catalytic rates of formation of PGF2 alpha from PGH2. Among various GSTs, isozyme IV, a homodimer of Ya size subunit showed the highest activity with a Vmax value of approximately 6000 nmol.min-1.mg-1. In general, the isozymes containing Ya and Yc subunits exhibited relatively high activity toward PGH2, indicating that it is the non-selenium-dependent glutathione peroxidase activity associated with the GSTs that might be responsible for the reduction of PGH2 to PGF2 alpha. Interestingly, isozyme IV also exhibited the highest PGE2 forming activity with a Vmax value of approximately 3000 nmol.min-1.mg-1 followed by isozyme I, a homodimer of Yb subunit, which had a Vmax value of 420 nmol.min-1.mg-1. Based on these results, it appears that the GSTs play an important role in the biosynthesis of classical PGs. Therefore, it is conceivable that the tissue-specific formation of PGF2 alpha and PGE2 might, in part, be due to the relative distribution of these enzyme activities in a given tissue. Our results have not only confirmed the previously published reports (E. Christ-Hazelhof et al. (1976) Biochim. Biophys. Acta 450, 450-461), but also have characterized the specificity of GST isozymes in the formation of PGF2 alpha.

Bovine placental prostaglandin synthesis in vitro as it relates to placental separation

Bovine placentomes were collected during late gestation, prepartum and immediately postpartum. Postpartum tissues were collected prior to fetal membrane separation. Maternal and fetal placentomal components each were examined for their ability to synthesize prostaglandins (PG's) from arachidonic acid (AA) and metabolize PGF2 alpha and PGE2 in vitro. Maternal placental PG synthesis was lower (P less than .05) than that for fetal placental tissue and was primarily PGF's. Fetal placental PG synthesis increased (P less than .05) prepartum and was primarily PGE's. Fetal placental PGE production predominated (P less than .05) postpartum if the fetal membranes were retained, while PGF production predominated (P less than .05) if the membranes were released. Maternal and fetal placental tissues were unable to convert PGE2 to PGF2 alpha (P greater than .05). Postpartum fetal placental tissue was able to convert PGF2 alpha to PGE2 (P less than .05) if the fetal membranes were retained but not if the membranes were released (P greater than .05). These results indicate that fetal placental synthesis of PGF's may be related to placental membrane separation. The shift in fetal placental PG production from PGE's to PGF's may be due to a cessation of the ability of released fetal tissue to convert PGF2 alpha to PGE2.

Sertoli-cell prostaglandin synthesis. Effects of (follitropin) differentiation and dietary vitamin E

The synthesis of prostanoids by the Sertoli cell was assessed as part of a study on the role of vitamin E in maintaining spermatogenesis. Analyses of eicosanoid synthesis from endogenous substrate were carried out using freshly isolated Sertoli-cell-enriched preparations from both pre-pubertal and adult rats fed purified diets with and without vitamin E, as well as cells carried in primary culture. Freshly isolated cells from both the immature and fully differentiated adult testes produced PGI2 (prostaglandin I2) and PGE2, but PGF2 alpha was produced only by cells of the adult vitamin E-deficient rat. Cells from adult controls synthesized PGF2 alpha after primary culture. In contrast with other hormone responses of this cell, which are refractory in the adult, FSH (follitropin) potentiated prostaglandin production by freshly isolated cells of both immature and adult rats. The FSH response of Sertoli cells from immature animals did not change after primary culture. Adult cells were refractory to the hormone after culture, but the total amounts of prostaglandins produced by these cells were 10-fold higher than by either freshly isolated or cells of the immature in culture. Analogues of cyclic AMP did not potentiate prostaglandin synthesis. However, mepacrine, a phospholipase inhibitor, blocked the FSH effect. The finding that Sertoli cells synthesize prostaglandins and FSH enhances prostaglandin production implicates a potential role for eicosanoids in spermatogenesis and suggests that vitamin E may affect intratesticular regulators.

Effects of gonadectomy and steroid treatment on renal prostaglandin 9-ketoreductase activity in the rat

The effect of gonadectomy and treatment with sex-steroids on renal prostaglandin 9-ketoreductase activity in 10-11 week old male and female rats was determined. Rats were gonadectomized or subjected to sham operation at 3 weeks of age. During week 7, rats were injected s.c. twice over a 6-day interval with vehicle (peanut oil, 0.5 ml X kg-1) or with depot forms of testosterone (5 mg X kg-1), estradiol (0.02 mg X kg-1), progesterone (5 mg X kg-1), or estradiol and progesterone combined. Renal prostaglandin 9-ketoreductase activity was about 50% higher in female rats than in males. Gonadectomy decreased 9-ketoreductase activity in females, but not in males, and eliminated the gender difference in enzyme activity. Treatment with estradiol elevated 9-ketoreductase activity in males and females, while treatment with testosterone or progesterone was without effect. Progesterone did, however, antagonize the elevation in 9-ketoreductase activity produced by estradiol.

15-Keto-13,14-dihydroprostaglandin F2 alpha and prolactin in maternal and cord blood during prostaglandin E2 or oxytocin therapy for labor induction

15-keto-13,14-dihydroprostaglandin F2 alpha plasma levels were measured in pregnant women following labor induction with either oral PGE2 treatment or intravenous oxytocin, both combined with amniotomy. The median time to start of contractions was 62 minutes in the PGE2 treated group and 45 minutes in the oxytocin treated group (p less than 0.01; median test). The increase in 15-ketodihydro-PGF2 alpha appeared earlier in the PGE2 group but not in the oxytocin group (p less than 0.001 and p = 0.210, respectively). At delivery, the 15-ketodihydro-PGF2 alpha values had further increased in both treatment groups. The increase was significantly higher in the PGE2 treated patients compared with oxytocin treated patients (p = 0.03; contrast test). Despite higher 15-ketodihydro-PGF2 alpha concentrations throughout parturition, PGE2 women did not deliver more rapidly than oxytocin infused women. There was no correlation between 15-ketodihydro-PGF2 alpha blood concentrations and either onset of contractions or labor time. The decrease in maternal serum prolactin concentration during parturition was pronounced (p less than 0.001) in the PGE2 group but occurred also in oxytocin treated patients (p less than 0.02). A single oral dose (0.5 mg) of PGE2 taken by non-pregnant women led to significant (p less than 0.05) increases in 15-ketodihydro-PGF2 alpha levels in blood plasma after 10 minutes. This increase persisted for at least 90 minutes. It is suggested that oral PGE2 may be transformed into PGF2 alpha and/or induce endogenous PGF2 alpha biosynthesis.

Stereospecific conversion of prostaglandin D2 to (5Z,13E)-(15S)-9 alpha-11 beta,15-trihydroxyprosta-5,13-dien-1-oic acid (9 alpha,11 beta-prostaglandin F2) and of prostaglandin H2 to prostaglandin F2 alpha by bovine lung prostaglandin F synthase

A prostaglandin F (PGF) synthase was recently purified from bovine lung that catalyzed the reduction of both PGH2 and PGD2 but at different active sites on the enzyme. In view of the recent finding that PGD2 is stereospecifically reduced to a unique biologically active compound, (5Z, 13E)-(15S)-9 alpha, 11 beta, 15-trihydroxyprosta-5,13-dien-1-oic acid (9 alpha,11 beta-PGF2 or 11-epi-PGF2 alpha), by a human liver cytosolic enzyme, detailed characterization of the products formed from PGH2 and PGD2 by the bovine lung PGF synthase was carried out. Chromatographic characteristics of the products formed and stereochemical analysis procedures using mass spectrometry indicated that the enzyme stereospecifically reduces PGH2 to PGF2 alpha, whereas PGD2 is stereospecifically converted to 9 alpha,11 beta-PGF2. The finding that this enzyme catalyzes the formation of both C-11 hydroxy epimers of PGF2, albeit from different substrates, is of interest in that these two compounds may exert different biological actions.

Dietary fish oil modulates macrophage fatty acids and decreases arthritis susceptibility in mice

B10.RIII and B10.G mice were transferred from a diet of laboratory rodent chow to a standard diet in which all the fat (5% by weight) was supplied as either fish oil (17% eicosapentaenoic acid [EPA], 12% docosahexaenoic acid [DHA], 0% arachidonic acid [AA], and 2% linoleic acid) or corn oil (0% EPA, 0% DHA, 0% AA, and 65% linoleic acid). The fatty acid composition of the macrophage phospholipids from mice on the chow diet was similar to that of mice on a corn oil diet. Mice fed the fish oil diet for only 1 wk showed substantial increases in macrophage phospholipid levels of the omega-3 fatty acids (of total fatty acid 4% was EPA, 10% docosapentaenoic acid [DPA], and 10% DHA), and decreases in omega-6 fatty acids (12% was AA, 2% docosatetraenoic acid [DTA], and 4% linoleic acid) compared to corn oil-fed mice (0% EPA, 0% DPA, 6% DHA, 20% AA, 9% DTA, and 8% linoleic acid). After 5 wk this difference between the fish oil-fed and corn oil-fed mice was even more pronounced. Further small changes occurred at 5-9 wk. We studied the prostaglandin (PG) and thromboxane (TX) profile of macrophages prepared from mice fed the two diets just before being immunized with collagen. Irrespective of diet, macrophages prepared from female mice and incubated for 24 h had significantly more PG and TX in the medium than similarly prepared macrophages from male mice. The increased percentage of EPA and decreased percentage of AA in the phospholipids of the macrophages prepared from the fish oil-fed mice was reflected in a reduction in the amount of PGE2 and PGI2 in the medium relative to identically incubated macrophages prepared from corn oil-fed mice. When this same fish oil diet was fed to B10.RIII mice for 26 d before immunization with type II collagen, the time of onset of arthritis was increased, and the incidence and severity of arthritis was reduced compared to arthritis induced in corn oil-fed mice. The females, especially those on the fish oil diet, tended to have less arthritis than the males. These alterations in the fatty acid pool available for PG and leukotriene synthesis suggest a pivotal role for the macrophage and PG in the immune and/or inflammatory response to type II collagen.

Release of arachidonate cascade products by the rabbit bladder; neurophysiological significance?

The endogenous production of prostaglandins and thromboxane A2 by the rabbit urinary bladder was assessed by radioimmunoassay in a relatively intact system and in the absence of substrate. PGE2 and PGI2 (prostacyclin) were the main prostaglandins released whereas PGF2 alpha ratio of 5:1 and a PGI2 to PGF2 alpha ratio of 3:1 were observed. This qualitative pattern was independent of bladder area. In addition, prostaglandin release by the bladder body was significantly greater than by the bladder base at all incubation times. The physiological implications of these experimental observations are discussed.

Activity of prostaglandin biosynthetic pathways in rat pancreatic islets

Isolated pancreatic islets of the rat were either prelabeled with [3H]arachidonic acid, or were incubated over the short term with the concomitant addition of radiolabeled arachidonic acid and a stimulatory concentration of glucose (17mM) for prostaglandin (PG) analysis. In prelabeled islets, radiolabel in 6-keto-PGF1 alpha, PGE2, and 15-keto-13,14-dihydro-PGF2 alpha increased in response to a 5 min glucose (17mM) challenge. In islets not prelabeled with arachidonic acid, label incorporation in 6-keto-PGF1 alpha increased, whereas label in PGE2 decreased during a 5 min glucose stimulation; after 30-45 min of glucose stimulation labeled PGE levels increased compared to control (2.8mM glucose) levels. Enhanced labelling of PGF2 alpha was not detected in glucose-stimulated islets prelabeled or not. Isotope dilution with endogenous arachidonic acid probably occurs early in the stimulus response in islets not prelabeled. D-Galactose (17mM) or 2-deoxyglucose (17mM) did not alter PG production. Indomethacin inhibited islet PG turnover and potentiated glucose-stimulated insulin release. Islets also converted the endoperoxide [3H]PGH2 to 6-keto-PGF1 alpha, PGF2 alpha, PGE2 and PGD2, in a time-dependent manner and in proportions similar to arachidonic acid-derived PGs. In dispersed islet cells, the calcium ionophore ionomycin, but not glucose, enhanced the production of labeled PGs from arachidonic acid. Insulin release paralleled PG production in dispersed cells, however, indomethacin did not inhibit ionomycin-stimulated insulin release, suggesting that PG synthesis was not required for secretion. In confirmation of islet PGI2 turnover indicated by 6-keto-PGF1 alpha production, islet cell PGI2-like products inhibited platelet aggregation induced by ADP. These results suggest that biosynthesis of specific PGs early in the glucose secretion response may play a modulatory role in islet hormone secretion, and that different pools of cellular arachidonic acid may contribute to PG biosynthesis in the microenvironment of the islet.

Enzymatic inactivation of 6-keto-prostaglandin E1 in vitro: Comparison with prostaglandin E1

The inactivation of 6-keto PGE1, a biologically active and stable metabolite of prostacyclin, was studied in 100,000 g cytosolic supernatants by bioassay on rat stomach strip (contraction) and human platelets (inhibition of ADP-induced aggregation). PGE1 was used as a reference compound. Both PGs were inactivated in supernatants from colon, kidney and liver of rat, rabbit and guinea-pig. Inactivation was time- and NAD+ -dependent and was generally greater for PGE1 than 6-keto-PGE1. The enzyme responsible for 6-keto-PGE1 inactivation in cytosolic supernatants is distinct from prostaglandin 15-hydroxydehydrogenase and 9-keto reductase, is not inhibitable by sulphasalazine-like drugs and its activity is recoverable after precipitation by ammonium sulphate. We conclude that 6-keto-PGE1 can be inactivated by enzymes with wide tissue distribution, but further studies are needed for identification of these novel enzymes and the products formed as well as to assess their significance in the intact animal.

Alterations in the fraction of oxygen in inspired gas affect rates of renal prostaglandin E2 synthesis in anesthetized dogs

Reductions of oxygen in inspired gas from 20% to 15%, in anesthetized dogs, reduced arterial PO2 and increased the renal efflux of PGE2 but not PGF2a. Renal blood flow, blood pressure, plasma renin activity as well as arterial pH and PCO2 were unaffected PGs may mediate the renal hemodynamic or excretory consequences of alterations in PO2. In addition, minor variations in PO2 might account, in part, for the variable renal venous PGE2 concentrations reported under basal conditions.

A novel prostaglandin 11-keto reductase found in rabbit liver

The prostaglandin 11-keto reductase of rabbits, which catalyzes the conversion of prostaglandin D2 to prostaglandin F2 alpha, is only found in the liver. This enzyme, which is primarily localized in the soluble fraction, requires NADPH for activity; its Km value for prostaglandin D2 is approx. 200 muM. [14C]Prostaglandin D2 administered to rabbits via the portal vein escapes from the liver unchanged, suggesting that exogenous prostaglandin D2 may be inaccessible to the enzyme. The possible role of this enzyme in the metabolism of endogenous hepatic prostaglandin D2 is suggested by the demonstration that the liver synthesizes prostaglandin D2 from arachidonic acid.

Transformations of prostaglandin H2 in the cat brain

Transformations of prostaglandin H2 were studied in the whole homogenate and subcellular fractions (microsomes, high-speed supernatant) of the cat brain. Prostaglandin H2 was converted enzymatically to prostaglandin E2, 6-ketoprostaglandin F 1 alpha, and thromboxane B2. While prostaglandin E2 and thromboxane B2 predominated, respectively, in the whole homogenate and the microsomes, 6-ketoprostaglandin F1 alpha was formed in both tissue preparations. Pretreatment of the microsomes with reduced glutathione stimulated the formation of prostaglandin E2 at the expense of 6-ketoprostaglandin F1 alpha and thromboxane B2. Imidazole and 15-hydroperoxyarachidonic acid interfered with the microsome-induced transformations of prostaglandin H2 to thromboxane B2 and 6-ketoprostaglandin F1 alpha, respectively. No prostaglandin D2 was detected even after treatment of the tissue with reduced glutathione. Prostaglandin H2, on the other hand, was converted to prostaglandin F2 alpha, but the yield of this compound in native tissue was equal to, or lower than, that in boiled tissue. We conclude that the feline brain is endowed with several enzymes (prostaglandin E2 isomerase, thromboxane A2 and prostaglandin I2 synthetases) competing for the added endoperoxide. All enzymes were located in the microsomes. No evidence was obtained indicating enzymic reduction of prostaglandin H2 to prostaglandin F2 alpha.

Glutathione-prostaglandin A1 conjugate as substrate in the purification of prostaglandin 9-ketoreductase from rabbit kidney

Using GSH-PGA1 as substrate for determination of enzyme activity a pI 4.8 form of rabbit kidney prostaglandin 9-keto-reductase has been purified 95 times to a specific activity of 1755 nmol/min per mg protein. The purification procedures involve ion-exchange chromatography, gel-filtration and affinity chromatography. The latter procedure comprises Blue Sepharose affinity chromatography, and GSH-PGA1-Sepharose affinity chromatography. The purified enzyme preparation also showed a weak NADP+-dependent 15-hydroxyprostaglandin dehydrogenase activity, 20 nmol/min per mg protein with PGE1 as substrate. Km (PGE1) for the dehydrogenase is 142.6 +/- 45.1 microM (S.E., n = 7).

NAD+-dependent 15-hydroxyprostaglandin dehydrogenase from porcine kidney. I. Purification and partial characterization

The cytoplasmic NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (11 alpha, 15-dihydroxy-9-oxoprost-13-enoate:NAD+ 15-oxidoreductase, EC 1.1.1.141) from porcine kidney was purified to a specific activity of 1.2 unit per mg protein by a series of chromatographic techniques including affinity chromatography. The native molecular weight of the enzyme was estimated to be 45 000. Substrate specificity studies indicated that the enzyme was NAD+-specific and was able to catabolize readily various prostaglandins, with the exception of prostaglandin B and thromboxane B. The enzyme was inhibited by sulfhydryl inhibitors, diuretic drugs and various fatty acids.

Human plasma transforms prostacyclin (PGI2) into a platelet antiaggregatory substance which contracts isolated bovine coronary arteries

Prostacyclin (PGI2) incubated in Human Platelet Rich Plasma (PRP); in Platelet Poor Plasma (PPP) or in Krebs-Ringer-Bicarbonate (KRB) during different periods of time on contractions of bovine coronary arteries and on the ADP platelet aggregative capacity of human PRP, were explored. It was documented that incubates in PRP or in PPP retain an antiaggregatory activity at higher levels and during a longer time than in KRB. On the other hand, PGI2 incubates in KRB exhibited only a relaxing activity on isolated bovine coronary arteries, whereas when incubated in PRP or in PPP presented a biphasic influence. The initial effects (evoked by incubates of 30 minutes) were distinctly relaxing but those obtained with later incubates (60--150 minutes) stimulated clearly the resting basal tone of the arteries. The possibility that the human plasma might have an enzyme(s) able to transform prostacyclin into a more stable material with human antiaggregatory platelet function and bovine coronary contracting capacity is discussed.

Prostaglandin F2 alpha levels in human cerebrospinal fluid in normal and pathological conditions

Prostaglandin F2 alpha concentrations in cerebrospinal fluid (CSF) from normal human subjects and patients with various pathological disorders of the central nervous system (CNS) were measured by radioimmunoassay. The mean PGF2 alpha level in 54 controls with no evidence of organic CNS disease was 67 pg/ml (range: 25-150 pg/ml). A significant increase of PGF2 alpha levels was demonstrated in most samples from patients with CNS diseases. Extremely high values were found in patients with stroke and subarachnoid hemorrhage when samples were collected shortly after the cerebral attack. With the regression of clinical symptoms and radiological findings a decrease of PGF2 alpha levels was demonstrated in this group of patients. In 32 patients with cerebral transient ischemic attacks a mean PGF2 alpha concentration of 170 pg/ml (range: 35-355 pg/ml) was found. Increased PGF2 alpha levels were found in patients with epilepsy when samples were collected within a few days after a convulsion. PGF2 alpha levels of four patients with slow progredient forms of multiple sclerosis without clinical symptoms at the time of sample collection were not different from normal controls while the mean PGF2 alpha level of all other patients with multiple sclerosis was 152 pg/ml (range: 55-325 pg/ml). Moreover, increased values could be demonstrated in patients with cerebral tumors and inflammatory processes.

The identification of 5beta,7alpha-dihydroxy-11-oxotetranor-prostane-1,16-dioic acid as a urinary metabolite of prostaglandin F2alpha in the rat

5beta,7alpha-Dihydroxy-11-oxotetranor-prostane-1,16-dioic acid has been identified by gas chromatography-mass spectrometry as a urinary metabolite of [9beta-3H]prostaglandin F2alpha in the rat. This tetranor prostaglandin F derivative, which is the 5beta epimer of the major urinary metabolite of prostaglandin F2alpha, accounted for at least 2% of the total dose. Absence from the metabolite of tritium label at the C-5 position indicated the existence of a minor, previously unknown metabolic pathway by which prostaglandin Falpha derivatives may be converted by oxido-reduction into prostaglandins of Fbeta stereochemistry.

Prostaglandin metabolism by human testis

Human testis preparations appear to carry out both the synthesis and turnover of prostaglandins. Prostaglandins and prostaglandin metabolites were extracted from whole tissue. Testis microsomes converted both endogenous and exogenous substrate to prostaglandins. Microsomal prostaglandin biosynthesis was inhibited by indomethacin. Prostaglandin E2-9-ketoreductase was present in both the cytosolic and microsomal fractions of human testis. Prostaglandin metabolism by human testis has not previously been reported.

Elimination of low steady-state concentrations of [5,6-3H2]prostaglandin E1 in the pulmonary and the systemic circulations of anaesthetized rats

The elimination of [3H]prostaglandin E1 in anaesthetized rats was studied by continuous intravenous or intraarterial infusions, producing steady-state concentrations at the level of endogenous prostaglandin E2 in mixed venous blood. Blood samples (0.5 ml) were collected from the carotid artery or the right atrium, respectively. The levels of [3H]prostaglandin E1 were measured at different infusion time intervals and the 3H-labeled hydrophobic metabolites characterized. Cardiac output was estimated by a modification of the dye injection method, using 125I-labelled albumin as the marker. From the cardiac output and the rate of infusion, the fractional clearance of the lung and the systemic beds in the steady-state situation were estimated to 88.3 +/- 3.2% and 54.1 +/- 15.2% (mean +/- S.D.), RESPECTIVELY. The hydrophobic metabolites were characterized chromatographically on Sephadez LH-20 columns, using synthetically prepared [14C]prostaglandin metabolites as internal standards and markers. The identities of some metabolites were further established by derivative formation to a constant [3H]/[14C] ratio. The major metabolite was 15-keto-13,14-dihydro-[3H]prostaglandin E1, while 15-keto-[3H]prostaglandin E1 and 13,14-dihydro-[3H]prostaglandin E1 could not be demonstrated.

Pathways of prostaglandin F2alpha metabolism in mammalian kidneys

1 High-speed cytoplasmic supernatants of rat, rabbit, pig and guinea-pig kidneys were prepared and the metabolism of 10 mug/ml prostaglandin F(2alpha) labelled with [(3)H(1)-9beta]-prostaglandin F(2alpha) studied by thin layer radiochromatography and bioassay.2 The metabolism of prostaglandin F(2alpha) measured by radiochromatography parallels biological inactivation in all species except the rabbit.3 Kidneys metabolize prostaglandin F(2alpha) by two divergent pathways, yielding a mixture of prostaglandin E and F metabolites.4 15-Hydroxyprostaglandin dehydrogenase and prostaglandin Delta-13 reductase are present in all species in characteristic proportions. Thus prostaglandin F(2alpha) is metabolized sequentially to 15-keto prostaglandin F(2alpha) and 13,14-dihydro-15-keto prostaglandin F(2alpha). The rate and profile of formation of these metabolites is species-dependent.5 13,14-Dihydro-15-keto prostaglandin F(2alpha) is the principal prostaglandin F series metabolite in all species.6 Pig and guinea-pig kidney contain an unidentified enzyme which converts 13,14-dihydro-15-keto prostaglandin F(2alpha) to 13,14-dihydro prostaglandin F(2alpha).7 Rat kidney contains a high concentration of a prostaglandin 9-hydroxy dehydrogenase which converts 13,14-dihydro-15-keto prostaglandin F(2alpha) to 13,14-dihydro-15-keto prostaglandin E(2).8 Rabbit kidney contains a novel 9-hydroxydehydrogenase which oxidises prostaglandin F(2alpha) directly to E(2), thus producing a compound with more potent renal actions. The possible implications of this enzyme for kidney homeostasis are discussed.

Prostaglandin-induced effects in the primate cerebral circulation

The effects of intracarotid infusions of prostaglandins E2 and F2alpha on cerebral blood flow (CBF) and oxygen consumption (CMRO2), and on extracranial blood flow, have been studied in anaesthetisex baboons. The 133Xe clearance method was used for measuring CBF, whilst extracranial blood flow was assessed by both the local tissue injection of 133Xe and external carotid artery flowmetry. Both PGF2alpha and PGE2 (10(-7) and 10(-6) g/kg/min) reduced both CBF and CMRO2. Spasm of the internal carotid artery with PGE2 was noted at the higher dose. Following osmotic opening of the blood-brain barrier by the hypertonic urea technique, the effects of small doses of PGE2 and CBF and CMRO2 were greatly potentiated. PGE2 greatly increased extracranial blood flow. Hence, both PGE2 and PGF2alpha reduce CBF and CMRO2, whilst PGE2 greatly increases extracranial blood flow.

Inhibition of cholesterol esterification in rabbit aorta by prostaglandin E2

Cholesterol esterification in the arterial wall was investigated with cell-free preparations of intima-media from control rabbits and rabbits rendered atherosclerotic by feeding a diet containing 1% cholesterol. In the presence of 2 mM ATP and 0.1 mM CoA, the major activity for esterification of [4-14C] cholesterol added in vitro was found in the 12,000 g and 105,000 g pellets. In control animals, the activity in the latter pellet was twice that in the former. After cholesterol-feeding for 6 months, the activity increased 5-fold in the 105,000 g pellet and 2-fold in the 12,000 g pellet of the atherosclerotic intima-media. Prostaglandin E2 (PGE2) in concentrations between 2 and 12 X 10(-7) M exhibited a dose-dependent inhibition of the esterifying activity in both particulate preparations. The inhibition was 97% at PGE2 concentrations greater than 1.2 X 10(-6) M in preparations from control animals. Inhibition by PGE2 in preparations from atherosclerotic rabbits was also observed. These results suggest a possible regulatory role of PGE2 in cholesterol esterification in the arterial wall.