OKY-046 inhibits anaphylactic bronchoconstriction and reduces histamine level in bronchoalveolar lavage fluid in sensitized guinea pigs.

We investigated the effects of OKY-046, a potent and selective thromboxane A2 (TxA2) synthetase inhibitor, on anaphylactic bronchoconstriction and release of chemical mediators into airway lumen in sensitized guinea pigs in vivo. OKY-046 dose-dependently inhibited antigen-induced anaphylactic bronchoconstriction with or without mepyramine, a histamine H1 antagonist. In the presence of mepyramine, OKY-046 (300 mg/kg, p.o.) elicited significant reductions in histamine (1 min) and TxB2 increases (1-15 min) in bronchoalveolar lavage (BAL) fluid but significantly increased the plasma level of 6-keto-PGF1 alpha, a stable PGI2 metabolite, after antigen challenge. On the contrary, indomethacin only significantly reduced increases in TxB2 levels. These results suggest that the antiasthmatic effect of OKY-046 is probably due to inhibition of TxA2 synthesis and suppression of histamine release via a PGI2 shunting mechanism.     

Dose-dependent effects of a pyridoquinazoline thromboxane synthetase inhibitor on arachidonic acid metabolites and hemodynamics during E. coli endotoxemia in anesthetized sheep

We investigated the effects of a new pyridoquinazoline thromboxane synthetase inhibitor infused before administering Escherichia Coli endotoxin into 18 anesthetized sheep with lung lymph fistulas. In normal sheep increasing plasma Ro 23-3423 concentrations were associated with increased plasma levels of 6-keto-PGF1 alpha, a reduced systemic vascular resistance (SVR, r = -0.80) and systemic arterial pressure (SAP, r = -0.92), the mean SAP falling from 80 to 50 mm Hg at the 20 and 30 mg/kg doses. Endotoxin infused into normal sheep caused transient pulmonary vasoconstriction associated with increased TxB2 and 6-keto-PGF1 alpha levels while vasoconstriction and TxB2 increase were significantly inhibited by pretreatment with Ro 23-3423 in a dose-dependent manner. When compared to controls, plasma and lymph levels of 6-keto-PGF1 alpha, PGF2 alpha and PGE2 after endotoxin infusion were increased several-fold by administering Ro 23-3423 up to plasma levels of 10 micrograms/ml. Doses over 30 mg/kg with blood levels above 10 micrograms/ml reduced plasma and lymph levels of 6-keto-PGF1 alpha, PGF2 alpha and PGE2, suggesting cyclooxygenase blockade at this dose. The peak 6-keto-PGF1 alpha levels at 60 min after endotoxin infusion in sheep with Ro-23-3423 levels below 10 micrograms/ml were associated with the greatest systemic hypotension due to a reduced SVR (r = -0.86). After endotoxin infusion the leukotrienes B4, C4, D4 and E4 in lung lymph were assayed by radioimmunoassay and high pressure liquid chromatography and remained at baseline values.     

Prostaglandins and thromboxane outflow from the perfused mesenteric vascular bed in spontaneously hypertensive rats

To clarify the metabolism of PGE2, prostacyclin (PGI2) and thromboxane A2 (TxA2) in small vessels in spontaneously hypertensive rats (SHR), we removed superior mesenteric vascular beds from 10 week old SHR and age matched normotensive controls (WKY). The mesenteric artery was perfused with Krebs-Henseleit buffer and samples of effluent collected every 15 minutes during 3 hours perfusion for analysis of PGE2, 6-keto-PGF1 alpha (a stable metabolite of PGI2) and TxB2 (a stable metabolite of TxA2) by specific radioimmunoassays. Levels of all three arachidonic acid (AA) metabolites, PGE2, 6-keto-PGF1 alpha and TxB2, in the mesenteric effluent were significantly reduced in SHR as compared to WKY. TxB2 was detected in all samples throughout the perfusion. 6-keto-PGF1 alpha/PGE2 ratios and TxB2/PGE2 ratios were significantly increased in SHR. 6-keto-PGF1 alpha/TxB2 ratios in the first four samples were significantly decreased in SHR as compared to WKY. These data suggest that there may be reduced availability of PG precusor AA and unbalanced synthesis of PGs in small vessels in SHR. Both may have relevance to the development of hypertension in the animals.     

Aspirin augments 15-epi-lipoxin A4 production by lipopolysaccharide, but blocks the pioglitazone and atorvastatin induction of 15-epi-lipoxin A4 in the rat heart

Aspirin (ASA) inhibits cycloxygenase-1 and modifies cycloxygenase-2 (COX2) by acetylation at Ser(530), leading to a shift from production of PGH(2), the precursor of prostaglandin, to 15-R-HETE which is converted by 5-lipoxygenase to 15-epi-lipoxin A(4) (15-epi-LXA4), a potent anti-inflammatory mediator. Both atorvastatin (ATV) and pioglitazone (PIO) increase COX2 expression. ATV activates COX2 by S-nitrosylation at Cys(526) to produce 15-epi-LXA4 and 6-keto-PGF(1alpha) (the stable metabolite of PGI(2)). We assessed the effect of ASA on the myocardial production of 15-epi-LXA4 and PGI(2) after induction by lipopolysaccharide (LPS) or PIO+ATV. Sprague-Dawley rats were pretreated with: control; ASA 10 mg/kg; ASA 50 mg/kg; LPS alone; LPS+ASA 10 mg/kg; LPS+ASA 50 mg/kg; LPS+ASA 200 mg/kg; PIO (10 mg/kg/d)+ATV (10 mg/kg/d); PIO+ATV+ASA 10 mg/kg; PIO+ATV+ASA 50 mg/kg; PIO+ATV+ASA 50 mg/kg+1400 W, a specific iNOS inhibitor; or PIO+ATV+1400 W. ASA alone had no effect on myocardial 15-epi-LXA4. LPS increased 15-epi-LXA4 and 6-keto-PGF(1alpha) levels. ASA (50 mg/kg and 200 mg/kg, but not 10 mg/kg) augmented the LPS effect on 15-epi-LXA4 but attenuated the effect on 6-keto-PGF(1alpha). PIO+ATV increased 15-epi-LXA4 and 6-keto-PGF(1alpha) levels. ASA and 1400 W attenuated the effects of PIO+ATV on 15-epi-LXA4 and 6-keto-PGF(1alpha). However, when both ASA and 1400 W were administered with PIO+ATV, there was a marked increase in 15-epi-LXA4, whereas the production of 6-keto-PGF(1alpha) was attenuated. In conclusion, COX2 acetylation by ASA shifts enzyme from producing 6-keto-PGF(1alpha) to 15-epi-LXA4. In contrast, S-nitrosylation by PIO+ASA augments the production of both 15-epi-LXA4 and 6-keto-PGF(1alpha). However, when COX2 is both acetylated and S-nitrosylated, it is inactivated. We suggest potential adverse interactions among statins, thiazolidinediones, and high-dose ASA.     

Endotoxin-induced lung injury in rats: role of eicosanoids

We studied lung vascular injury and quantitated lung eicosanoids in rats after intraperitoneal injection of Salmonella enteritidis endotoxin. Within 40 min after endotoxin injection (20 mg/kg), lung tissue thromboxane B2 doubled, although 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) increased by 8- to 10-fold. Lung 5-hydroxyeicosatetraenoic acid and leukotriene C4 were variably increased by endotoxin. The levels of all eicosanoids returned to base line 6 h after endotoxin challenge. Lung vascular injury, as assessed by the extravascular accumulation of 125I-albumin and water in isolated perfused lungs, was observed 90 min after endotoxin injection (0.02-20 mg/kg) in vivo. Inhibition of the cyclooxygenase pathway with indomethacin and the lipoxygenase pathway with diethylcarbamazine and 2-(12-hydroxydodeca-5,10-dinyl)-3,5,6-trimethyl-1,4-benzoqui none failed to attenuate endotoxin-induced lung injury. In addition, essential fatty acid deficiency, which markedly reduced lung tissue levels of 6-keto-PGF1 alpha, thromboxane B2, and leukotriene C4, did not protect against endotoxin injury. We conclude that although lung eicosanoids are activated during endotoxemia, they do not play a crucial role in the development of acute lung vascular injury in rats.     

Effects of a thromboxane synthetase inhibitor and a thromboxane antagonist on release and activity of thromboxane A2 and prostacyclin in vitro

The TxA2 synthetase inhibitor, dazoxiben, and the TxA2 antagonist, +/- SQ 29,548, were examined for effects on release and vasoactivity of TxA2 and prostacyclin. Isolated perfused guinea pig lungs were used as the enzyme source from which TxA2 and prostacyclin were released in response to injections of arachidonic acid or bradykinin. Both dazoxiben and +/- SQ 29, 548 inhibited contraction of the superfused rat aorta and bovine coronary artery after arachidonic acid injection through the lung. +/- SQ 29,548 abolished contractions of the rat aorta, but significant aorta contracting activity persisted during dazoxiben treatment. Dazoxiben significantly inhibited arachidonate-induced release of TxA2 (immunoreactive TxB2) into the superfusate, but TxA2 release was significantly potentiated by +/- SQ 29,548. Thus, in the presence of enhanced TxA2 concentrations, +/- SQ 29,548 effectively antagonized the vasospastic effect of TxA2. Dazoxiben diverted a significantly greater amount of arachidonic acid into prostacyclin synthesis (immunoreactive 6-keto-PGF1 alpha), changing original coronary vasoconstriction into relaxation. +/- SQ 29,548 did not significantly modify lung prostacyclin synthesis. Moreover, with +/- SQ 29,548, the absence of TxA2-mediated coronary contraction unmasked active relaxation of the superfused bovine coronary artery, coincident with thromboxane and prostacyclin release. Dazoxiben consistently inhibited TxA2 synthesis and enhanced prostacyclin synthesis. +/- SQ 29,548 augmented TxB2 release in response to arachidonate, but not bradykinin, and did not significantly alter 6-keto-PGF1 alpha release in response to either arachidonate or bradykinin. In terms of vasoactivity measured in vitro, +/- SQ 29,548 and dazoxiben produced similar anti-vasospastic effects, although this was accomplished by completely different mechanisms.     

Effects of thromboxane synthase inhibition on air emboli lung injury in sheep

We tested the effects of OKY-046, a thromboxane synthase inhibitor, on lung injury induced by 2 h of pulmonary air infusion (1.23 ml/min) in the pulmonary artery of unanesthetized sheep with chronic lung lymph fistula so as to assess the role of thromboxane A2 (TxA2) in the lung injury. We measured pulmonary hemodynamic parameters and the lung fluid balance. The concentrations of thromboxane B2 (TxB2) and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) in plasma and lung lymph were determined by radioimmunoassay. Air infusion caused sustained pulmonary hypertension and an increase in pulmonary vascular permeability. The levels of TxB2 and 6-keto-PGF1 alpha in both plasma and lung lymph were significantly elevated during the air infusion. TxB2 concentration in plasma obtained from the left atrium was higher than that from the pulmonary artery at 15 min of air infusion. When sheep were pretreated with OKY-046 (10 mg/kg iv) prior to the air infusion, increases in TxB2 were prevented. The pulmonary arterial pressure, however, increased similarly to that of untreated sheep (1.8 X base line). The increase in lung lymph flow was significantly suppressed during the air infusion. Our data suggest that the pulmonary hypertension observed during air embolism is not caused by TxA2.     

Altered responses to modulators of guanine nucleotide binding protein activity in endotoxin tolerance

The effects of cholera toxin or pertussis toxin and nonhydrolyzable GTP analogs on Salmonella enteritidis endotoxin stimulation of iTxB2 and i6-keto-PGF1 alpha synthesis in control and endotoxin tolerant rat peritoneal macrophages were determined. Pretreatment with pertussis toxin alone had no effect on basal macrophage iTxB2 or i6-keto-PGF1 alpha production, but pertussis toxin (0.1, 1.0 and 10 ng/ml) significantly inhibited endotoxin-stimulated iTxB2 and i6-keto-PGF1 alpha synthesis. Pretreatment with cholera toxin, which did not affect basal iTxB2 or i6-keto-PGF1 alpha synthesis, significantly enhanced endotoxin-induced synthesis of iTxB2 and i6-keto-PGF1 alpha. The effects of pertussis and cholera toxin with or without endotoxin were significantly (P less than 0.05) less in macrophages from endotoxin tolerant rats compared to control macrophages. GTP[gamma-S] (100 microM) significantly increased iTxB2 synthesis and significantly augmented endotoxin-stimulated iTxB2 synthesis in control macrophages (P less than 0.05). However, in macrophages from endotoxin tolerant rats the effect of GTP[gamma-S] on iTxB2 synthesis was significantly less (P less than 0.05) compared to control macrophages. Collectively, these data suggest that: (1) guanine nucleotide binding regulatory proteins mediate endotoxin-stimulated arachidonic acid metabolism in rat peritoneal macrophages; and (2) endotoxin tolerance induces alterations in guanine nucleotide binding protein activity.     

Additive beneficial effects of two inhibitors of vasoconstrictor mediators in acute myocardial ischemia

A specific inhibitor of thromboxane A2 (TxA2) synthesis, CGS-12970, a new angiotensin-converting enzyme (ACE) inhibitor, CGS-16617, and a combination of both agents were evaluated for their ability to reduce the extension of myocardial infarct size in rats. Myocardial creatine kinase (CK) loss from the left ventricular free wall (LVFW) 48 hr after left coronary artery ligation was used as an index of ischemic damage. Treatment with either CGS-12970 (4 mg/kg) or CGS-16617 (1 microgram/kg) alone did not attenuate the loss of CK from LVFW significantly, compared with animals receiving only the vehicles for these drugs. However, the combined use of both agents significantly reduced CK depletion from LFVW (P less than 0.01). These findings support the interrelated role of TxA2 and angiotensin II as mediators of myocardial ischemia and suggest that combined inhibition of their formation may be useful in the treatment of acute myocardial infarction.     

Thromboxane synthase inhibition: "endoperoxide shunt phenomenon" does not occur in healthy humans in vivo

The effects of the thromboxane synthase inhibitor CGS13080 on the in vivo synthesis of thromboxane and prostacyclin were determined in six healthy volunteers. Two different doses (0.08 and 0.25 mg/kg x h) were infused for six hours under strictly controlled conditions and 2,3-dinor-TxB2 and 2,3-dinor-6-keto-PGF1 alpha were measured in urine using gaschromatography--mass spectrometry. The in vivo synthesis of thromboxane was inhibited by 80-75% while there was no effect on the in vivo prostacyclin synthesis.     

OKY-046 inhibits thromboxane synthesis with no effect on brain edema and neurological status in head traumatized rats

Head trauma (HT) was induced in the left hemisphere of rats by a weight drop device. Edema was maximal 24 h after HT in the injured zone, and PGE2, TXB2 and 6-keto-PGF1 alpha were elevated in both the injured and remote areas. The effect of a specific thromboxane synthetase inhibitor, OKY-046, on the outcome of HT was studied. OKY-046, 100 mg/kg, was given to rats immediately and 8 h after HT. The neurological severity score (NSS) was evaluated at 1 h after HT, and at 24 h, just prior to sacrifice. Specific gravity (SG) of both hemispheres was measured after decapitation. Prostaglandins (PGs) were extracted from the site of injury and from the frontal lobes, remote from the injury, and assayed by RIA. Basal levels of PGE2 and 6-keto-PGF1 alpha were not reduced by the drug while basal TXB2 levels were lowered. However, the increased production due to HT of all PGs, was inhibited by OKY-046, especially that of TXB2. The ratio of TXB2/6-keto-PGF1 alpha, known to affect vascular tone, was reduced by OKY-046 treatment as a result of TXA2 synthesis inhibition. Still, no effect was found on the neurological outcome (as evaluated by the NSS), or on edema formation (expressed by reduced SG). Thus, based on the present findings increased TXA2 synthesis cannot be implicated in the pathophysiology of cerebral edema or dysfunction following HT.     

Diethylcarbamazine on pulmonary vascular response to endotoxin in awake sheep

Diethylcarbamazine (DEC) is an inhibitor of lipoxygenase, with protective effects in several experimental models of anaphylaxis and lung dysfunction. The hypothesis of this study was that DEC would alter the pulmonary response to endotoxin infusion, especially the prolonged pulmonary hypertension, leukopenia, hypoxemia, and high flow of protein-rich lung lymph. We prepared sheep for chronic measurements of hemodynamics and collection of lung lymph. In paired studies we gave six sheep endotoxin (0.5 micrograms/kg iv) either with or without DEC. DEC was given (80-100 mg/kg iv) over 30 min followed by a continuous infusion at 1 mg X kg-1 X min-1. Endotoxin was given after the loading infusion of DEC, and variables were monitored for 4 h. The response to endotoxin was characterized by pulmonary hypertension, leukopenia, hypoxemia, and elevations of thromboxane B2 and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha). Lymph flow and protein content reflected hemodynamic and permeability changes in the pulmonary circulation. DEC did not significantly modify the response to endotoxin by any measured variable, including pulmonary arterial and left atrial pressures, cardiac output, lymph flow and protein content, alveolar-to-arterial PO2 difference, blood leukocyte count, and lymph thromboxane B2 and 6-keto-PGF1 alpha. We could not find evidence of release of leukotriene C4/D4 by radioimmunoassay in lung lymph after endotoxin infusion with or without DEC treatment. We conclude that lipoxygenase products of arachidonic acid may not be a major component of the pulmonary vascular response to endotoxin.     

Sulindac does not preserve renal prostacyclin synthesis during endotoxemia

Previous reports have suggested that sulindac is a unique non-steroidal anti-inflammatory (NSAID) agent, because it does not inhibit renal prostaglandin synthesis in doses that inhibit platelet thromboxane B2 synthesis when tested ex vivo. NSAIDS are of potential therapeutic benefit in the treatment of septic or endotoxic shock. Therefore, this study was designed to investigate the proposed unique action of sulindac in experimental endotoxemia. In the current study, the effect of sulindac on aortic, portal and renal venous immunoreactive (i) 6-keto-PGF1 alpha levels, the stable metabolite of prostacyclin, was investigated during endotoxemia in the rat. In doses sufficient to reduce the elevation in aortic and portal venous plasma i6-keto-PGF1 alpha levels, sulindac also significantly (p less than 0.05) attenuated the elevated renal venous plasma 6-keto-PGF1 alpha levels, compared to the vehicle group. Using lower doses, sulindac failed to reduce the endotoxin associated increase in either aortic or renal venous plasma i6-keto- PGF1 alpha levels. Thus, sulindac failed to demonstrate any selective sparing effect on renal prostacyclin generation during endotoxemia.     

The role of thromboxane A2 [TxA2] in liver injury in mice

The role of thromboxane A2 (TxA2) in CCl4-induced liver disease was investigated in mice. Significant elevation of TxB2 in the liver was observed 6 hours after the injection of CCl4. Administration of OKY-046, a selective TxA2 synthetase inhibitor (10 and 50 mg/kg) and ONO-3708, a TxA2 receptor antagonist, (0.5, 1 and 2 mg/Kg) suppressed the elevation of serum GOT and GPT levels and histopathological changes of the liver. In addition, OKY-046 inhibited the elevation of TxB2 in the liver. When U-46619, a stable TxA2 mimetic was injected i.v. into the mice, clear elevation of serum GOT and GPT levels and histopathological score of the liver were observed. These results suggest that TxA2 play a role for the onset of CCl4-induced liver injury in mice.     

Changes in the levels of prostaglandins and thromboxane and their roles in the accumulation of exudate in rat carrageenin-induced pleurisy — a profile analysis using gas chromatography-mass spectrometry —

Injection of γ-carrageenin into t he pleural cavity of rats caused the accumulation of the pleural exudate. When levels of prostaglandins (PGs) and thromboxane (TX) B₂ were quantified by gas chromatography-mass spectrometry as their methyl ester (ME)-dimethyllisopropylsilyl (DMiPS) ether or ME-methoxine-DMiPS ether derivatives, 6-keto-PGF_1α reached the maximum at 1 hr after carrageenin, then PGE₂ and TXB₂ showed peaks at 3 hr and waned off before 9 hr. he PGF_2α level was kept low, but PGD₂, PGE₁ and PGF_1α were not detected. Aspirin (100 mg/kg, i.p.) significantly decreased the PG and TXB₂ levels and suppressed the rate of plasma exudation until 5 hr, but did not at 7 hr, when it was measured by the amount of exuded pontamine sky blue injected intravenously. OKY-025 (300 mg/kg, i.p.), a selective TXA synthetase inhibitor, and tranylcypromine (20 mg/kg, i.p.), a PGI synthetase inhibitor, could not extensively inhibit the accumulation of the exudate. These results suggest that the cyclooxygenase products of arachidonic acid, particularly PGE₂, definitely play an important role in the exudation during the first 5 hr.     

Testing the "redirection hypothesis" of prostaglandin metabolism in the kidney

Furosemide increases the synthesis of two major renal eicosanoids, prostacyclin (PGI2) and thromboxane A2 (TXA2), by stimulating the release of arachidonic acid which in turn is metabolized to PGG2/PGH2, then to PGI2 and TXA2. PGI2 may mediate, in part, the early increment in plasma renin activity (PRA) after furosemide. We hypothesized that thromboxane synthetase inhibition should direct prostaglandin endoperoxide metabolism toward PGI2, thereby enhancing the effects of furosemide on renin release. Furosemide (2.0 mg . kg-1 i.v.) was injected into Sprague-Dawley rats pretreated either with vehicle or with U-63,557A (a thromboxane synthetase inhibitor, 2 mg/kg-1 followed by 2 mg/kg-1 X hr-1). Urinary 6ketoPGF1 alpha and thromboxane B2 (TXB2), reflecting renal synthesis of PGI2 and TXA2, as well as PRA and serum TXB2, were measured. Serum TXB2 was reduced by 96% after U-63,557A. U-63,557A did not affect the basal PRA. Furosemide increased PRA in both vehicle and U63,557A treated rats. However, the PRA-increment at 10, 20 and 40 min following furosemide administration was greater in U-63,557A-treated rats than in vehicle-treated rats and urine 6ketoPGF1 alpha excretion rates were increased. These effects of thromboxane synthesis inhibition are consistent with a redirection of renal PG synthesis toward PGI2 and further suggest that such redirection can be physiologically relevant.     

Blockade of thromboxane and the prevention of eicosanoid-induced sudden death in mice

We studied the effects of thromboxane-receptor antagonism and thromboxane synthetase inhibition in a thrombotic model of sudden death in mice. Intravenous injection of arachidonic acid (AA; 80 mg/kg) or the prostaglandin-endoperoxide analog U-46,619 (2.3 mg/kg) results in sudden death in approximately 90% of the animals. Pretreatment with the thromboxane receptor antagonist SQ-29,548 (0.3-10 mg/kg) protects dose-dependently against AA and U-46,619-induced sudden death. In contrast, CGS-13,080, a thromboxane synthetase inhibitor, shows a dose-dependent beneficial effect in AA-induced sudden death only. Although PTA2 has partial thromboxane agonistic properties in the rabbit, it protected the mice against AA-induced sudden death, thus demonstrating TxA2 antagonistic properties in this species. These data emphasize the importance of thromboxane A2 as a major mediator of arachidonic acid-induced sudden death and the effectiveness of thromboxane-receptor antagonists in endoperoxide-induced sudden death.     

Effect of cicletanine on reperfusion-induced arrhythmias and its relation to 6-keto-PGF1 alpha and thromboxane B2 release

Isolated hearts, excised from spontaneously hypertensive male rats treated orally with cicletanine, a new furopyridine anti-hypertensive drug, were subjected to 30 min of global ischemia followed by 10 min of reperfusion. The effect of cicletanine on reperfusion-induced arrhythmias in relation to 6-keto-PGF1 alpha and thromboxane (TXB2) release was studied. After 30 min of global ischemia, the incidence (total) of ventricular fibrillation (VF) and ventricular tachycardia (VT) was reduced by 2-week pretreatment of the rats with 30 and 100 mg/kg of cicletanine (VF, 33% at 30 mg/kg and 25% at 100 mg/kg vs. 91% in untreated rats; VT, 42% at 30 mg/kg and 42% at 100 mg/kg vs. 100% in untreated rats), while lower doses of cicletanine (3 and 10 mg/kg) failed to reduce the incidence of reperfusion-induced rhythm disturbances. Reperfusion of the ischemic myocardium resulted in a fivefold increase of 6-keto-PGF1 alpha and TXB2 release in the perfusion effluent of fibrillated hearts but not in the perfusion effluent of nonfibrillated hearts. Cicletanine failed to influence the reperfusion-stimulated release of 6-keto-PGF1 alpha and TXB2. These results indicate that the anti-arrhythmic effect of cicletanine in the reperfused myocardium is not related to PGI2 and thromboxane A2 release.     

Metabolism of prostaglandin endoperoxide by microsomes from human lung parenchyma and comparison with metabolites produced by pig, bovine, rat, mouse and guinea-pig

The metabolism of PGH2 by human lung parenchymal microsomes was characterized by radiometric high performance liquid chromatography and compared with metabolism by pig, bovine, rat, mouse, and guinea pig lung microsomes. Microsomes from human lung synthesized 0.74 nmoles/mg protein and 0.72 nmoles/mg protein, PGI2 (6-Keto-PGF1 alpha) and TxA2 (TxB2) respectively, upon incubation with 4.0 nmoles of PGH2. Pig, bovine, rat, mouse, and guinea pig microsomes respectively synthesized 1.0, 1.0, 0.9, 0.4, and 0.1 nmoles of PGI2/mg protein, and 0.9, 1.0, 0.7, 0.3, 1.8 nmoles of TxA2/mg protein, and preparations formed some PGE2, PGF2 alpha, and PGD2. Mouse lung microsomes were unique in synthesizing PGE2 as the major prostaglandin. The thromboxane synthetase inhibitor 1-benzylimidazole was a specific inhibitor in these six species.     

Differential alteration of lipoxygenase and cyclooxygenase metabolism by rat peritoneal macrophages induced by endotoxin tolerance

Altered macrophage arachidonic acid metabolism may play a role in endotoxic shock and the phenomenon of endotoxin tolerance induced by repeated injections of endotoxin. Studies were initiated to characterize both lipoxygenase and cyclooxygenase metabolite formation by endotoxin tolerant and non-tolerant macrophages in response to 4 different stimuli, i.e. endotoxin, glucan, zymosan, and the calcium ionophore A23187. In contrast to previous reports of decreased prostaglandin synthesis by tolerant macrophages, A23187-stimulated immunoreactive (i) leukotriene (LT)C4/D4 and prostaglandin (PG)E2 production by tolerant cells was greater than that by non-tolerant controls (p less than 0.001). However, A23187-stimulated i-6-keto-PGF1 alpha levels were lower in tolerant macrophages compared to controls. Stimulation of prostaglandin and thromboxane (Tx)B2 synthesis by endotoxin or glucan was significantly less in tolerant macrophages compared to controls (p less than 0.05). iLTC4/D4 production was not significantly stimulated by endotoxin or glucan, but was stimulated by zymosan in the non-tolerant cells. Synthesis of iLTB4 by control macrophages was stimulated by endotoxin (p less than 0.01). These results demonstrate that arachidonic acid metabolism via the lipoxygenase and cyclooxygenase pathways in macrophages is differentially altered by endotoxin tolerance.