Endogenous prostaglandins modulate histamine-induced contraction in canine tracheal smooth muscle

We studied the role of endogenous prostaglandins in modulating the histamine response of canine tracheal smooth muscle (TSM) in vitro. Indomethacin (INDO) (10(-7) - 10(-5) M), a cyclooxygenase and prostaglandin synthesis inhibitor, significantly increased maximum histamine-induced tension (Tmax) and decreased the concentration of histamine required to produce 50% of Tmax (EC50). Acetylsalicylic acid (10(-5) -5 X 10(-4) M), another less potent cyclooxygenase inhibitor, also decreased EC50. Neither the lipoxygenase inhibitor nordihydroguaiaretic acid nor the leukotriene antagonist FPL 55712 had any effect on histamine-induced tension in INDO-pretreated TSM. INDO reduced the standard deviation of EC50 from 0.47 in control TSM (n = 51) to 0.26 in INDO-pretreated TSM (n = 31) (P less than 0.02). High-pressure liquid chromatography established prostacyclin (PGI2), through its degradation product 6-oxo-PGF1 alpha, as the predominant prostaglandin produced by canine TSM. Exogenous PGI2 caused a concentration-dependent relaxation of histamine-contracted TSM. In the tissue bath, spontaneous efflux of 6-oxo-PGF1 alpha from TSM, as measured by radioimmunoassay, averaged 4.7 ng . g muscle-1 . min-1 and increased to 10 ng/g muscle (n = 10, P less than 0.001) with administration of histamine. The isometric tension produced by histamine (10(-4) M) was inversely linearly correlated with the log concentration of endogenous 6-oxo-PGF1 alpha (r = 0.81, P less than 0.01). Our results are consistent with an important role for endogenous bronchodilating prostaglandins, probably prostacyclin, in determining both the histamine sensitivity of canine TSM in vitro and its variability among individual animals.     

Bronchoconstrictor and antibronchoconstrictor properties of inhaled prostacyclin in asthma

Prostacyclin (PGI2) is generated in appreciable amounts during allergic reactions in human lung tissue. To define its activity on human airways we have studied the effects of doubling concentrations of inhaled PGI2 and its hydrolysis product 6-oxoprostaglandin F1 alpha (6-oxo-PGF1 alpha) on specific airway conductance (sGaw), maximum expiratory flow at 30% vital capacity (Vmax30), forced expiratory volume in 1 s (FEV1), and static lung volumes in subjects with mild allergic asthma. In a second study the effect of inhaled PGI2 on bronchoconstriction provoked by increasing concentrations of inhaled prostaglandin (PG) D2 and methacholine was observed. Inhalation of PGI2 up to a concentration of 500 micrograms/ml had no significant effect on sGaw but produced a concentration-related decrease in FEV1 and Vmax30 in all subjects. In two of four subjects inhalation of PGI2 also increased residual volume and decreased vital capacity but had no effect on total lung capacity. PGI2, but not 6-oxo-PGF1 alpha, protected against bronchoconstriction provoked by either PGD2 or methacholine whether airway caliber was measured as sGaw, FEV1, or Vmax30. The apparent disparity between the bronchoconstrictor and antibronchoconstrictor effects of PGI2 might be explained by its potent vasodilator effect in causing airway narrowing through mucosal engorgement and reducing the spasmogenic effects of other inhaled mediators by increasing their clearance from the airways.     

Thromboxane synthase inhibition: implications for prostaglandin endoperoxide metabolism. I. Characterisation of an acute intravenous challenge model to measure prostaglandin endoperoxide metabolism

It has been proposed that thromboxane synthase inhibition (TXSI) may be a useful form of anti-thrombotic therapy and that this is due, in part, to redirection of PGH2 metabolism in favour of PGI2, a potent vasodilator and anti-platelet agent. While redirection has been observed ex vivo there are conflicting reports of its occurrence in vivo. We now describe the characterisation of an acute intravenous challenge model using thrombin, collagen, arachidonic acid (AA) and PGH2 for the study of PGH2 metabolism. Following challenge, plasma concentrations of TXB2, 6-oxo-PGF1 alpha, alleged metabolites of PGI2 (PGI2m) and PGE2 were measured by radioimmunoassay (RIA). Thrombin and collagen challenge resulted in a dose-related increase in plasma TXB2 while AA and PGH2, in addition, elevated 6-oxo-PGF1 alpha and PGI2m. Injection of PGH2 elevated 6-oxo-PGF1 alpha, PGI2m, TXB2 and PGE2 levels. Experimental conditions were defined such that challenge with thrombin (40 NIH units kg-1), collagen (100 micrograms kg-1), AA (1 mg kg-1) and PGH2 (5 micrograms kg-1) and measurement of eicosanoids 0.5 min following challenge were optimal for detection of redirection of PGH2 metabolism in vivo. The identity of immunoreactive TXB2 and 6-oxo-PGF1 alpha was further supported by experiments in which the extracted immunoreactive eicosanoids co-eluted with authentic [3H]standards when subject to reverse phase high performance liquid chromatography (RPHPLC). Evidence is also presented that the levels of plasma eicosanoids measured in this model reflect in vivo biosynthesis.     

Prostanoid synthesis by human umbilical artery

A discrepancy between published values of PGI2 production by human umbilical artery in vitro measured by platelet bioassay, compared with values of 6-oxo-PGF1 alpha by radioimmunoassay, raised the possibility that another anti-aggregatory prostanoid was produced by this tissue. To test this hypothesis, umbilical artery rings were incubated in buffer and PGI2 determined by platelet bioassay and by a more specific radioimmunoassay based on comparison of 6-oxo-PGF1 alpha in hydrolysed and non-hydrolysed samples. 6-oxo-PGF1 alpha, PGF2 alpha and TXB2 were also measured by gas chromatography negative ion chemical ionisation mass spectrometry. PGI2 concentrations by radioimmunoassay and bioassay were significantly correlated (r = 0.92, p less than 0.01). There was no difference between them, disproving the presence of an additional antiaggregatory substance. PGI2 production determined by bioassay (mean 1.21 ng/mg wet weight/h, range 0.59-1.53 ng/mg/h) differed from previously reported values (range 70-325 ng/mg/h). 6-oxo-PGF1 alpha concentrations were confirmed by gas chromatography negative ion chemical ionisation mass spectrometry. Previous determinations of PGI2 production by this tissue overestimated it by approximately 100 times.     

6-oxo-PGF(1 alpha)and 8-epi-PGF(2 alpha)in the arterial wall layers of various species: a comparison between intact and atherosclerotic areas

PGI(2)and 8-epi-prostaglandin(PG)F(2 alpha)are antagonizing compounds. For both a key role in vascular pathology has been hypothesized. The isoprostane 8-epi-PGF(2 alpha)and the stable derivative of PGI(2), 6-oxo-PGF(1 alpha)were determined immunologically in the arterial wall of various species including humans. Human arterial tissue contained the highest amounts of 8-epi-PGF(2 alpha)and synthesized the lowest PGI(2). A significant negative correlation between 8-epi-PGF(2 alpha)and 6-oxo-PGF(1 alpha)was observed. Atherosclerotic segments showed significantly higher 8-epi-PGF(2 alpha)and lower 6-oxo-PGF(1 alpha). 8-epi-PGF(2 alpha)in the intima was higher than in the media, the highest amounts being found in foam-cell rich areas. Synthetic (activated) smooth muscle cells were associated with an enhanced 8-epi-PGF(2 alpha)as well as 6-oxo-PGF(1 alpha). Tissue samples derived from smokers contained more 8-epi-PGF(2 alpha)and produced less PGI(2). The by far highest 8-epi-PGF(2 alpha)/6-oxo-PGF(1 alpha)ratio was found in foam cell rich areas. Similar findings were obtained in rabbit and in minipig arteries. The total 8-epi-PGF(2 alpha)/6-oxo-PGF(1 alpha)ratio is low in normal tissue, increases significantly in an active atherosclerotic process and seems to be even further increased in an inactive atherosclerotic process. These findings are providing an information on the extent of oxidation injury at various sites of different types of atherosclerotic process.     

6-Oxo-PGF1alpha and 8-epi-PGF2alpha in human atherosclerotic vascular tissue.

Isoprostanes are a new family of compounds generated by the free radical catalyzed action on arachidonic acid. Formed during oxidation they have been claimed to be a reliable indicator of in vivo oxidation injury. We assessed the amount of 8-epi-PGF2alpha in human surgical specimens as compared to PGI2 (via its stable metabolite 6-oxo-PGF1alpha), the major compound generated by vascular tissue. 8-epi-PGF2alpha is low in normal vascular tissue as is the 8-epi-PGF2alpha/6-oxo-PGF1alpha ratio. The vessels of smokers in general exhibited an increased 8-epi-PGF2alpha (r=0.82) and a decreased 6-oxo-PGF1alpha (r=0.71). The 8-epi-PGF2alpha/6-oxo-PGF1alpha ratio is, not significantly, increased in vessels derived from hyperlipidemics and hypertensives. These findings indicate that lipid peroxidation occurs within the human arterial wall as evidenced by 8-epi-PGF2alpha, probably further decreasing the synthesis of PGI2 and promoting atherogenic mechanisms.     

Urinary levels of 2,3-dinor-6-oxo-PGF1 alpha: a reliable index of the production of PGI2 in the spontaneously hypertensive rat

The urinary levels of 2,3-dinor-6-oxo-PGF1 alpha (PGI2-M), a major metabolite of PGI2, are determined by the balance between the amount of PGI2 synthesized and the extent of its further metabolic oxidation. The purpose of the present study was to determine if the urinary excretion of PGI2-M can be used as a reliable index of the in vivo production of PGI2 in both normal Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). This involved the exclusion of differences in metabolism between these two strains of rats. In order to do so, we monitored the urinary excretion of PGI2-M during paired intravenous infusions of 6-oxo-PGF1 alpha (the stable product of the spontaneous hydrolysis of PGI2) in conscious, unrestrained SHR and WKY rats aged 12-15 weeks, in doses ranging from 250 to 700 ng. In one experiment, PGI2 was infused instead of 6-oxo-PGF1 alpha. The results of these experiments indicate that SHR and WKY rats are equal with regard to the transformation of 6-oxo-PGF1 alpha and PGI2 into PGI2-M. For both groups, there is a good correlation between the amount of 6-oxo-PGF1 alpha infused and the amount of PGI2-M excreted in urine. These observations confirm the validity of using the urinary levels of 2,3-dinor-6-oxo-PGF1 alpha as an index of PGI2 production in both WKY and SHR. In addition, they support the conclusions drawn from our previous studies, namely that SHR do not produce more PGI2 than WKY rats in vivo, contrary to the situation prevailing in vitro.     

Measurement of 6-oxo-PGF1 alpha in human plasma using gas chromatography-mass spectrometry.

The plasma concentration of the prostacyclin (PGI2) hydration product 6-oxo-PGF1 alpha has been assayed by stable isotope dilution GC-MS in six normal volunteers infused with increasing doses of PGI2 intravenously. The predosing levels of 6-oxo-PGF1 alpha ranged between 114 and 266 pg/ml. Infusion of PGI2 increased 6-oxo-PGF1 alpha concentration in plasma but the increments were lower than expected suggesting less conversion of the PGI2 to 6-oxo-PGF1 alpha at high infusion rates.     

Thromboxane synthase inhibition: implications for prostaglandin endoperoxide metabolism. II. Testing the 'redirection hypothesis' in an acute intravenous challenge model

In the preceding paper we described the characterisation of an acute intravenous challenge model for the evaluation of the effects of thromboxane synthase inhibition (TXSI) on eicosanoid metabolism. Herein we describe the biochemical pharmacology of two TXSI and aspirin in this model. Both TXSI caused significant inhibition of plasma TXB2 in vivo without elevation of 6-oxo-PGF1 alpha levels. Similar results were obtained when combined levels of 6-oxo-PGF1 alpha,13,14 dihydro 6-oxo-PGF1 alpha,13,14 dihydro 6,15-dioxo-PGF1 alpha and 6-oxo-PGE1 were measured as an index of PGI2 biosynthesis (PGI2m). Thus no evidence of in vivo redirection of PGH2 to PGI2 was found. Ex vivo experiments performed in serum gave an apparent stimulation of immunoreactive 6-oxo-PGF1 alpha following TXSI but RPHPLC analysis of extracted serum showed that this stimulation was accounted for by increase in a product co-eluting with [3H]PGF2 alpha. The implications of these findings in relation to TXSI and receptor antagonists are discussed.     

The effects of prostacyclin (PGI2) on tissues which detect prostaglandins (PG'S).

The effects of prostacyclin (PGI2) and its stable metabolite 6-oxo-PGF1alpha on various bioassay tissues are compared with those of PGE2 and PGF2alpha, using the cascade superfusion method. On vascular smooth muscle, PGI2 caused relaxation of all tissues tested except the rabbit aorta. PGE2 relaxed rabbit coeliac and mesenteric artery but contracted bovine coronary artery and had no effect on rabbit aorta. 6-oxo-PGF1alpha was ineffective at the concentrations tested. On gastro-intestinal smooth muscle, PGI2 contracted strips of rat and hamster stomach and the chick rectum. It was less potent than PGE2 or PGF2alpha. None of these substances contracted the cat terminal ileum. 6-oxo-PGF1alpha was inactive on these tissues at the doses tested. PGI2 was less active than PGE2 or PGF2alpha in contracting guinea-pig trachea and rat uterus; 6-oxo-PGF1alpha was active only on the rat uterus. Thus, PGI2 can be distinguished from the other stable prostaglandins using the cascade method of superfusion.     

The effect of partial outlet obstruction on prostaglandin generation in the rabbit urinary bladder

Partial outlet obstruction of the urinary bladder has been demonstrated to induce specific dysfunctions in cellular and sub-cellular membrane structures within the bladder's smooth muscle and mucosal compartments. Recent studies have linked these membrane dysfunctions to alterations in phospholipid metabolism leading to mobilization of free arachidonic acid, the precursor for synthesis of prostaglandins (PG). The purpose of this study was to determine if partial outlet obstruction of the urinary bladder induces changes in the capacity of bladder smooth muscle and mucosa to generate PG. PG were isolated from control and partially obstructed urinary bladder smooth muscle and mucosa of male New Zealand White (NZW) rabbits. PG concentrations (PGE2, PGF2alpha and PGI2, as its stable metabolite 6-keto-PGF1alpha) were determined after 30 minute incubations using enzyme-linked immunoassay (ELISA) kits. In both control and obstructed rabbit urinary bladders, PG generation was significantly higher in isolated mucosa than muscle tissues. A significantly higher concentration of PGF2alpha, and 6-keto-PGF1alpha was measured in obstructed muscle tissue relative to controls. The concentration of 6-keto-PGF1alpha was also significantly higher than the concentrations measured for PGE2 and PGF2alpha in both control and obstructed smooth muscle samples. The generation of PGE2 was significantly higher in rabbit urinary bladder mucosa than either PGF2alpha or 6-keto-PGF1alpha in both control and obstructed samples. The capacity of obstructed mucosal tissue to generate 6-keto-PGF1alpha was significantly higher than control tissue, while no significant differences in PGE or PGF2alpha generation were noted. These data suggest obstruction of the urinary bladder induce specific elevations in PG in both smooth muscle and mucosal tissues.     

Actions of prostacyclin (PGI2) and its product, 6-oxo-PGF1alpha on the rat gastric mucosa in vivo and in vitro.

The effects of prostacyclin (PGI2) and its breakdown product 6-oxo-PGF1alpha on various aspects of gastric function were investigated in the rat. PGI2 increased mucosal blood flow when infused intravenously. PGI2 was a more potent inhibitor of gastric acid secretion in vivo than PGE2. Like PGE2, PGI2 inhibited acid secretion from the rat stomach in vitro. PGI2 had comparable activity to PGE2 in inhibiting indomethacin-induced gastric erosions. Thus prostacyclin shares several of the activities of PGE2, and may be involved in the regulation of gastric mucosal function.     

Effects of prostacyclin on coronary circulation, heart rate and myocardial contractile force in isolated hearts of guinea pig and rabbit - comparison with prostaglandin E2.

Infusions of prostacyclin (PGI2) (3 x 10(-10) - 3 x 10(-7)M) into the coronary circulation of isolated hearts from ginea pigs or rabbits resulted in a concentration-dependent decrease in the coronary perfusion pressure (CPP). There was a slight decrease in left ventricular systolic pressure in the heart of the rabbit, whereas the heart rate remained unchanged. PGE2 was without effect on the heart of the rabbit but was as potent as PGI2 in decreasing the CPP in the guinea pig heart. 6-oxo-PGF1 alpha (up to 3 x 10(-6) M) did not affect any of the parameters measured.     

Factors regulating the production of prostaglandin E2 and prostacyclin (prostaglandin I2) in rat and human adipocytes.

The regulation of PGE2 (prostaglandin E2) and PGI2 (prostaglandin I2; prostacyclin) formation was investigated in isolated adipocytes. The formation of both PGs was stimulated by various lipolytic agents such as isoproterenol, adrenaline and dibutyryl cyclic AMP. During maximal stimulation the production of PGE2 and PGI2 (measured as 6-oxo-PGF1 alpha) was 0.51 +/- 0.04 and 1.21 +/- 0.09 ng/2 h per 10(6) cells respectively. Thus PGI2 was produced in excess of PGE2 in rat adipocytes. The production of the PGs was inhibited by indomethacin and acetylsalicylic acid in a concentration-dependent manner. The half-maximal effective concentration of indomethacin was 328 +/- 38 nM and that of acetylsalicylic acid was 38.5 +/- 5.3 microM. The PGs were maximally inhibited by 70-75% after incubation for 2 h. In contrast with their effect on PG production, the two agents had a small potentiating effect on the stimulated lipolysis (P less than 0.05). The phospholipase inhibitors mepacrine and chloroquine inhibited both PG production and triacylglycerol lipolysis and were therefore unable to indicate whether the PG precursor, arachidonic acid, originates from phospholipids or triacylglycerols in adipocytes. Angiotensin II significantly (P less than 0.05) stimulated both PGE2 and PGI2 production in rat adipocytes without affecting triacylglycerol lipolysis. Finally, it was shown that PGE2 and PGI2 were also produced in human adipocytes, although in smaller quantities than in rat adipocytes. It is concluded that the production of PGs in isolated adipocytes is regulated by various hormones. Moreover, at least two separate mechanisms for PG production may exist in adipocytes: (1) a mechanism that is activated concomitantly with triacylglycerol lipolysis (and cyclic AMP) and (2) an angiotensin II-sensitive, but lipolysis (and cyclic AMP)-independent mechanism.     

Enhancement of anaphylactic mediator release from guinea-pig perfused lungs by fatty acid hydroperoxides.

Fragments of chopped lung from indomethacin treated guinea-pigs had an anti-aggregating effect when added to human platelet rich plasma (PRP), probably due to the production of prostacyclin (PGI2) since the effect was inhibited by 15-hydroperoxy arachidonic acid (15-HPAA, 10 micrograms ml(-1)). Both 15-HPAA (1-20 micrograms ml(-1) min (-1)) and 13-hydroperoxy linoleic acid (13-HPLA, 20 micrograms ml(-1) min(-1)) caused a marked enhancement of the anaphylactic release of histamine, slow-reacting substance of anaphylaxis (SRS-A) and rabbit aorta contracting substance (RCS) from guinea-pig isolated perfused lungs. This enhancement was not reversed by the concomitant infusion of either PGI2 (5 micrograms ml(-1) min (-1)) or 6-oxo-prostaglandin F1alpha (6-oxo-PGF1alpha, 5 micrograms ml(-1) min(-1)). Anaphylactic release of histamine and SRS-A from guinea-pig perfused lungs was not inhibited by PGI2 (10 ng - 10 microgram ml(-1) min(-1)) but was inhibited by PGE2 (5 and 10 micrograms ml(-1) min (-1)). Antiserum raised to 5,6-dihydro prostacyclin (PGI1) in rabbits, which also binds PGI2, had no effect on the release of anaphylactic mediators. The fatty acid hydroperoxides may enhance mediator release either indirectly by augmenting thromboxane production or by a direct effect on sensitized cells. Further experiments to distinguish between these alternatives are described in the accompanying paper (27).     

Production of 6-oxo-prostaglandin F1 alpha and prostaglandin E2 by isolated glomeruli from normal and diabetic rats.

Production of 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha) and prostaglandin E2 (PGE2) was measured by radioimmunoassay in supernatants of isolated glomeruli from rats with streptozocin-induced diabetes and non-diabetic rats. Production of 6-oxo-PGF1 alpha by discs of aortas from these rats was measured at the same time. As shown before, aortic discs from diabetic rats produced significantly less 6-oxo-PGF1 alpha than aortic discs from non-diabetic rats (diabetic 1.99 +/- SEM 0.27 ng v non-diabetic 2.92 +/- 0.46 ng/mg net weight aorta; p less than 0.05). In contrast production of 6-oxo-PGF1 alpha by isolated glomeruli was not reduced in the diabetic rats (diabetic 77 +/- 7 pg v non-diabetic 70 +/- 8 pg/micrograms glomerular DNA). Similarly production of PGE2 was not diminished in the diabetic glomeruli (diabetic 1.20 +/- 0.15 ng v non-diabetic 0.91 +/- 0.12 ng/microgram glomerular DNA). It is concluded that regional differences in production of prostacyclin and 6-oxo-PGF1 alpha occur in experimental diabetes. Diminished prostacyclin production may contribute to the increased susceptibility of diabetic patients to atherosclerosis but is less likely to have a role in the pathogenesis of microangiopathy.     

Prostacyclin and thromboxane A2 in thrombotic thrombocytopenic purpura.

A study was conducted to find whether a deficiency in prostacyclin (prostaglandin I2; PGI2) is implicated in the pathogenesis of thrombotic thrombocytopenic purpura. Plasma samples from two patients with the disease before treatment and from 22 healthy controls were therefore assayed for concentrations of 6-oxo-PGF1 alpha and thromboxane B2, the stable metabolites of PGI2 and thromboxane A2, respectively. Neither of the patients responded to treatment, which in one case included an infusion of PGI2. Both patients had normal concentrations of 6-oxo-PGF1 alpha and thromboxane B2, thus implying that circulating amounts of PGI2 and thromboxane A2 were also normal. These findings suggest that 6-oxo-PGF1 alpha may be detectable in normal amounts in thrombotic thrombocytopenic purpura and that the condition need not be associated with a high concentration of thromboxane A2.     

Regulation of ciliary beat frequency by autonomic mechanisms: in vitro

The ciliated epithelium of the mammalian trachea separates the neurohumoral milieu of the tissue from that of the environment of the airway lumen. To determine whether specific autonomic receptors regulating ciliary beat frequency (CBF) were located on mucosal or serosal sides, we measured CBF by heterodyne mode correlation analysis laser light scattering in bovine tracheal tissues mounted in a two-sided chamber. A beta 2-adrenergic agonist, fenoterol, at 10(-7) M, stimulated serosal CBF from 7.9 +/- 1.3 to 20.2 +/- 5.8 Hz (P less than 0.01) and mucosal CBF from 6.6 +/- 0.9 to 14.7 +/- 4.6 Hz (P less than 0.01). A muscarinic cholinergic agonist, methacholine, at 10(-7) M, increased mucosal CBF from 8.4 +/- 1.0 to 19.5 +/- 5.5 Hz (P less than 0.01) and serosal CBF from 8.0 +/- 0.9 to 15.4 +/- 5.0 Hz (P less than 0.01). The differences in stimulation of CBF on the mucosal and serosal sides between fenoterol and methacholine were significant (P less than 0.01). Studies in which these autonomic agonist stimulating effects were inhibited by their respective antagonists, propranolol and atropine sulfate, demonstrated that CBF can be regulated independently by mediators both in the submucosa and within the mucus lining.     

The renal haemodynamic and excretory actions of prostacyclin and 6-oxo-PGF1 alpha in anaesthetized dogs.

Intrarenal arterial (i.a.) infusions of prostacyclin (PGI2) at 30-300 ng/min to anaesthetized dogs reduced renal vascular resistance (RVR) and filtration fraction (FF), increased mean renal blood flow (MRBF) but did not alter mean arterial pressure (MAP)or glomerular filtration rate (GFR). The urinary excretion of sodium (UNaV), potassium (UKV) and chloride ions (UC1V) were increased through inhibition of net tubular ion reabsorption. PGI2 (3000 ng/min, i.a.) reduced MAP and increased heart rate. Intravenous (i.v.) infusions of PGI2 (3000 gn/min) reduced MAP, GFR, FF, urine volume and ion excretion, with elevation of heart rate. The measured variables were unaltered by 6-oxo-PGF1 alpha (10,000 ng/min i.a.). Treatment of the dogs with the PG synthetase inhibitor meclofenamic acid (2.5 mg/kg i.v.) did not antagonise the elevation of MRBF to PGI2 (300 ng/min i.a.). Thus the renal effects of PGI2 were due to a direct action rather than through conversion to 6-oxo-PGF1 alpha or through stimulation of endogenous renal PG biosynthesis and release.     

Cyclooxygenase products of metabolism of arachidonic acid in mouse macrophages exposed to N-phenyllinoleamide from toxic oil samples

N-phenyllinoleamide (NPLA), one of the major extraneous constituents of Spanish toxic oil samples, appears to enhance the cyclooxygenase metabolic pathway of arachidonic acid by peritoneal mouse macrophages. Results reported herein show an increased biosynthesis of 6-oxo-PGF1 alpha and TXB2 by macrophages exposed to NPLA. However, light and electron microscopy failed to show cellular alterations in macrophages incubated with NPLA for two hours at 27 degrees C. These data suggest a possible involvement of cyclooxygenase arachidonic acid metabolism in the etiopathogenesis of the Spanish Toxic Oil Syndrome.