Release Of Thromboxane A2 Research Articles

Local and Systemic Inflammatory Mediator Release in Patients with Acute and Chronic Posttraumatic Osteomyelitis

The local and systemic release of thromboxane A2, prostaglandin I2, leukotriene B4 (LTB4), tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and interleukin-8 (IL-8) were studied before and after operation in 29 patients with acute and 22 with chronic posttraumatic osteomyelitis. Twenty patients without osteomyelitis, who underwent operations for fractures of the lower extremities, served as controls. Blood and tissue samples from the osteomyelitic and control groups were collected under defined conditions and mediators were determined by radioimmunoassay (thromboxane B2, 6-keto-prostaglandin F1 alpha, LTB4) or by enzyme-linked immunosorbent assay (TNF-alpha, IL-1 beta, and IL-8). In addition, common parameters (leukocyte count, C-reactive protein, temperature) were measured. The best correlation with acute disease activity was given by TNF-alpha, IL-6, IL-8, and LTB4. Plasma levels of these mediators in acute osteomyelitis were significantly increased compared to chronic osteomyelitis and to controls, respectively. Tissue samples from osteomyelitic focus showed significantly increased levels for IL-8, IL-6, TNF-alpha, IL-1 beta, and LTB4 in acute osteomyelitis, whereas the values for TxB2 and 6-keto-prostaglandin F1 alpha were only slightly increased compared to the chronic osteomyelitis group. This study describes the local and systemic liberation of various mediators in acute and chronic posttraumatic osteomyelitis in detail for the first time and provides data for pre- and postoperative monitoring of disease activity and demonstrates new pathogenetic and therapeutic aspects of bone modulation in osteomyelitis.

Leukocyte and platelet depletion protects the liver from damage induced by cholestasis and ischemia-reperfusion in the dog.

Ischemia-reperfusion injury has been studied in various organs. The effects of leukocyte and platelet depletion on cholestasis and ischemia-reperfusion-induced liver damage were evaluated in the dog liver. The left hepatic duct was ligated for 4 weeks to create a cholestatic lobe. An ischemic condition was produced for 60 min by stopping the peristaltic pump supplying blood to the liver. The metabolism of substances modulated in the liver during cholestasis and I-R was assessed in non-treated and in leukocyte- and platelet-depleted animals. The extraction rate of insulin and indocyanine green decreased during cholestasis and ischemia-reperfusion. Cholestasis accelerated the release of thromboxane A2 but not prostaglandin I2 after ischemia-reperfusion. Ischemia-reperfusion accelerated the release of prostaglandin I2 and thromboxane A2 from the liver. Further, ischemia-reperfusion increased the ratio of thromboxane A2 to prostaglandin I2. Cholestasis promoted an increase in the level. Ischemia-reperfusion caused an increase in the lipid peroxide level, and no change in the alpha-tocopherol level. Ischemia-reperfusion caused an increase in the lipid peroxide level, a decrease in the alpha-tocopherol level, and no change in the glutathione level. Depletion of leukocytes and platelets reduced these changes during cholestasis and ischemia-reperfusion. Depletion of leukocytes and platelets thus appears to protect liver function from cholestasis and ischemia-reperfusion injury by reducing peroxidation of lipids composing the cell membrane and the rate of thromboxane A2 prostaglandin I2, which predicts cellular damage, and by increasing the levels of alpha-tocopherol and glutathione, believed to be free radical scavengers.

Pregnant or not Pregnant—Systemic or Pulmonary Hypertension Induced by Thromboxane A2and Deficiency of Prostaglandins: A Hypothesis

Background: Dysfunctional vascular endothelium with deficient production of prostacyclin (PGI2), persistent activation of platelets, enhanced release of thromboxane A2 (TXA2), and vasospasm are common features of two vascular disorders, both of which are of unknown origin and affect exclusively or mainly women of childbearing age: preeclampsia (PE) and primary pulmonary hypertension (PPH). The association of high TXA2/PGI2 ratio with systemic hypertension in pregnant but with pulmonary hypertension in nonpregnant women is intriguing.Hypothesis: Based on experimental data collected from intact nonpregnant and pregnant rabbits, isolated and perfused lung preparations, and TXA2 receptor studies performed on pulmonary arterial membranes, we hypothesize that in the nonpregnant state the pulmonary resistance vessels may form the primary target site of TXA2, and that during pregnancy the sensitivity of these vessels to TXA2 may be blunted simultaneously with enhanced systemic vascular sensitivity to this eicosanoid. Such a reciprocal change of vascular TXA2 sensitivity could explain the association of high TXA2/PGI2 ratio with PPH in nonpregnant women and with systemic hypertension n in pregnant women.

Induction of Prostanoid Biosynthesis by Bacterial Lipopolysaccharide and Isoproterenol in Rat Microglial Cultures

We have used purified microglial cultures obtained from neonatal rat cerebral cortex to investigate the ability of microglia to release prostanoids after exposure to bacterial lipopolysaccharide, a classic macrophage activator. Release of prostaglandin E2, prostaglandin D2, and thromboxane A2 was low in basal conditions and increased in a dose- and time-dependent way upon lipopolysaccharide treatment (1-100 ng/ml), by a mechanism requiring de novo protein synthesis. When compared with astrocytes, microglial cells appeared to respond more effectively to lipopolysaccharide, being able to release prostanoids after exposure to a 100-fold lower concentration of lipopolysaccharide. In addition to prostanoids, we also measured the release of leukotriene B4; although lipopolysaccharide failed to stimulate leukotriene B4 release by microglial cells, it doubled the basal production in astrocytes. Lipopolysaccharide enhanced the release of preloaded [3H]arachidonic acid from microglial membrane phospholipids by a mechanism inhibited by the protein synthesis inhibitor cycloheximide, which suggests that the increased availability of arachidonic acid contributed to the enhanced prostanoid production. Lipopolysaccharide, however, also stimulated prostanoid synthesis by inducing cyclooxygenase activity, as shown by determining the activity of newly synthesized enzyme after inactivating the endogenous enzyme with aspirin and by assessing the level of the inducible form of cyclooxygenase by western blot analysis. Among the mechanisms potentially involved in the regulation of microglial prostanoid production, we studied the effect of beta-adrenergic receptor activation. The beta-agonist isoproterenol was inactive by itself but doubled the effect of lipopolysaccharide.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced arachidonic acid metabolism in alveolar macrophages from wheezy infants. Modulation by dexamethasone.

To test the hypothesis that alveolar macrophages (AM) from wheezy infants release increased amounts of eicosanoids, as do AM from adults with asthma, we compared eicosanoid release by unstimulated- and ionophore-A23187-stimulated AM from 13 wheezy and six nonwheezy infants and analyzed its regulation by dexamethasone in vitro. Alveolar macrophages from wheezy infants released greater amounts of thromboxane A2 (TxA2) and leukotriene B4 (LTB4) under resting conditions and of TxA2 upon stimulation than did those from control subjects. Dexamethasone induced a dose-dependent inhibition of the spontaneous and A23187-stimulated release of TxA2, but not of the A23187-stimulated release of lipoxygenase products. The inhibition of TxA2 formation was maintained when free arachidonic acid was added during A23187 stimulation, demonstrating that dexamethasone acted mainly at a postphospholipase A2 site. AM exposed to acetylsalicylate and then incubated overnight exhibited de novo cyclooxygenase synthesis, suggesting the presence of the inducible cyclooxygenase as a target for inhibition by dexamethasone. In conclusion, our findings suggest that AM from wheezy infants are activated in vivo to release eicosanoids, as are AM from asthmatic adults, and they support the therapeutic indications of glucocorticoids in severe recurrent wheezing of infancy.

Tyrosine phosphorylation of an SH2-containing protein tyrosine phosphatase is coupled to platelet thrombin receptor via a pertussis toxin-sensitive heterotrimeric G-protein.

SH-PTP1 is a protein tyrosine phosphatase (PTP) predominantly expressed in haematopoietic cells and containing two src homology-2 (SH2) domains. Here we report that SH-PTP1 is phosphorylated on both serine and tyrosine residues in response to thrombin or phorbol myristate acetate (PMA), which increased by 60 and 40%, respectively, SH-PTP1 activity. Thrombin-induced phosphorylation of SH-PTP1 is an early signalling event (maximal within 10 s) involving neither integrin signalling, nor calcium, nor release of ADP or thromboxane A2. Moreover, in contrast with PMA, the effect of thrombin on the tyrosine phosphorylation of SH-PTP1 was hardly affected by GF109203X, a specific protein kinase C (PKC) inhibitor. Finally, phosphorylation of SH-PTP1 could be provoked in permeabilized platelets by thrombin or GTP gamma S. This was abolished by pertussis toxin, the specificity of this effect being verified with the megakaryocytic cell line Dami cell. Our data thus identify SH-PTP1 as an in vivo substrate of a putative protein tyrosine kinase linked to the thrombin receptor by a Gi protein. This might offer some clue to unravel the mechanism of thrombin not only in platelets but also in nucleated cells, where its mitogenic effect is known to involve pertussis toxin-sensitive G-proteins, tyrosine phosphorylation and the ras pathway.

Activation of rabbit platelets by Ca2+ influx and thromboxane A2 release in an external Ca2+‐dependent manner by zooxanthellatoxin‐A, a novel polyol

1. Zooxanthellatoxin-A (ZT-A), a novel polyhydroxylated long chain compound, isolated from a symbiotic marine alga Simbiodinium sp., caused aggregation in rabbit washed platelets in a concentration-dependent manner (1-4 microM), accompanied by an increase in cytosolic Ca2+ concentration ([Ca2+]i). 2. ZT-A did not cause platelet aggregation or increase [Ca2+]i in a Ca(2+)-free solution, and Cd2+ (0.1-1 mM), Co2+ (1-10 mM) and Mn2+ (1-10 mM) inhibited ZT-A-induced aggregation. SK&F96365 (1-100 microM), a receptor operated Ca2+ channel antagonist, and mefenamic acid (0.1-10 microM), a non-specific divalent cation channel antagonist, inhibited platelet aggregation and the increase in [Ca2+]i induced by ZT-A. 3. Indomethacin (0.1-10 microM), a cyclo-oxygenase inhibitor, and SQ-29548 (0.1-10 microM), a thromboxane A2 (TXA2) receptor antagonist, inhibited platelet aggregation and the increase in [Ca2+]i induced by ZT-A. 4. Methysergide (0.01-1 microM), a 5-HT2 receptor antagonist, inhibited ZT-A-induced platelet aggregation but did not affect the increase in [Ca2+]i induced by ZT-A. 5. Tetrodotoxin (1 microM), a Na+ channel blocker and chlorpheniramine (1 microM), a H1-histamine receptor antagonist, neither affected ZT-A-induced platelet aggregation nor the increase in [Ca2+]i induced by ZT-A. 6. Genistein (1-100 microM), a protein tyrosine kinase inhibitor, and staurosporine (0.01-1 microM), a protein kinase C inhibitor, also inhibited ZT-A-induced platelet aggregation. 7. The present results suggest that ZT-A elicits Ca(2+)-influx from platelet plasma membranes. The resulting increase in [Ca2+]i subsequently stimulates the secondary release of TXA2 from platelets. Furthermore, the response to ZT-A may be associated with tyrosine phosphorylation.

Neutrophil interactions with endothelium and platelets: possible role in the development of cardiovascular injury.

Polymorphonuclear neutrophils (PMN) cause myocardial injury during ischaemia and reperfusion by their direct effects on the myocardium; PMN release highly cytotoxic free oxygen radicals and proteolytic enzymes and PMN aggregates are involved in capillary plugging and the no-reflow phenomenon. In addition, PMN-derived factors including free oxygen radicals, lipoxygenase products, cytokines and proteolytic enzymes have been shown to modify the function of endothelium and platelets. However, both endothelium and platelets are capable of modulating PMN activation. Endothelial cells modulate PMN function by the expression of adhesion molecules and by release of soluble factors including nitric oxide, prostacyclin, endothelins, platelet activating factor and interleukin-8. Platelets affect PMN activation by release of thromboxane A2, platelet derived growth factor, serotonin, lipoxygenase products, proteases and adenosine. Thus, in addition to their direct injurious effect on ischaemic myocardium, neutrophils are involved in the functional balance between endothelium and platelets and exert an indirect effect on the myocardium.

P2-32 - Zooxanthellaioxin-A, a novel polyhydroxylated long chain compound, activates rabbit platelets mediated via Ca2+ influx followed by the release of thromboxane A2 in an external Ca2+-dcpen3eni manner

P2-32 - Zooxanthellaioxin-A, a novel polyhydroxylated long chain compound, activates rabbit platelets mediated via Ca2+ influx followed by the release of thromboxane A2 in an external Ca2+-dcpen3eni manner

Block of Endothelin‐1‐induced release of thromboxane A2 from the guinea pig lung and nitric oxide from the rabbit kidney by a selective ETB receptor antagonist, BQ‐788

1. The present study characterizes the receptors responsible for endothelin-1-induced release of thromboxane A2 from the guinea pig lung and of endothelium-derived nitric oxide from the rabbit perfused kidney, by the use of the selective ETA receptor antagonist, BQ-123, and a novel selective ETB receptor antagonist, BQ-788. 2. In the guinea pig perfused lung, endothelin-1 (ET-1) (5 nM) induced a marked increase of thromboxane A2 which was reduced by 17 +/- 5.0, 70 +/- 1.0 and 93 +/- 1.2% by BQ-788 infused at concentrations of 1, 5 and 10 nM respectively. In contrast, BQ-123 (0.1 and 1.0 microM) had little or no effect on the ET-1-induced release of thromboxane A2. 3. In the same perfused model, the selective ETB agonist, IRL 1620 (50 nM), stimulated the release of thromboxane A2, but not prostacyclin. The eicosanoid-releasing properties of IRL 1620 were abolished by BQ-788 at 10 nM, yet were unaffected by BQ-123 (1 microM). 4. In the rabbit perfused kidney, BQ-788 (10 nM) potentiated the increase of perfusion pressure induced by endothelin-1 (1, 5 and 10 nM) by approximately 90%, but not that induced by angiotensin II (1 microM). Furthermore, the selective ETB receptor antagonist did not reduce the release of prostacyclin triggered by either peptide. 5. In another series of experiments, pretreatment of the perfused kidney with a nitric oxide synthase inhibitor, L-NAME (100 microM), potentiated the pressor responses to both endothelin-1 and angiotensin II. Under L-NAME treatment, BQ-788 did not further potentiate the pressor response to endothelin-1. 6 Our results illustrate the predominant role of ETB receptor activation in the release of thromboxane A2 and nitric oxide triggered by endothelin-l in the guinea pig perfused lung and rabbit kidney respectively.

Plasma thromboxane B2 concentration in pulmonary hypertension associated with congenital heart disease.

We investigated the plasma concentration of thromboxane B2 (TXB2), a stable metabolite of thromboxane A2 (TXA2), to assess platelet activation in 78 patients who had pulmonary hypertension associated with congenital heart disease (PH group) and 16 patients with almost normal hemodynamics (control group). The PH group was divided into two subgroups: pulmonary vascular resistance (Rp) < or = 10 U/m2 (Rp < or = 10 group) and > 10 U/m2 (Rp > 10 group). In addition, the Rp < or = 10 group was divided on the basis of clinical symptoms into groups with dyspnea (dyspnea[+] group) and without dyspnea (dyspnea[-] group). Plasma TXB2 levels were measured by radioimmunoassay. Plasma TXB2 levels in the three groups (control, Rp < or = 10, and Rp > 10) were significantly different (P < .005); the TXB2 levels in the Rp < or = 10 group were significantly higher than the others. Among the Rp < or = 10 patients, the plasma TXB2 levels were significantly higher in the dyspnea(+) group than in the dyspnea(-) group (P < .0001). In addition, the pulmonary-to-systemic flow ratio and pulmonary blood flow divided by body surface area were significantly higher in the dyspnea(+) group than in the dyspnea(-) group (P < .02 and P < .002, respectively). These findings suggest that platelet activation led to increased TXA2 release in patients with pulmonary hypertension, especially those with dyspnea and Rp < or = 10. TXA2 release from platelets probably caused constriction of the pulmonary arterioles and the bronchi, thus worsening pulmonary hypertension and dyspnea in these patients. In the patients with high Rp values, it was considered that the number of pulmonary arterioles where platelets could be activated had been reduced.

Antithrombotic activity of nicardipine in spontaneously hypertensive rats

Calcium metabolism appears to be altered in human and experimental hypertension, which represents an important risk factor for thrombotic events. We investigated the possible effect of the calcium antagonist nicardipine on a model of experimental venous thrombosis in spontaneously hypertensive rats (SHR). Thrombus formation was highly enhanced in SHR with respect to normotensive Wistar Kyoto rats (WKY). Nicardipine, when administered orally (10 mg kg −1) at a single dose or once a day for three days, completely counteracted the increase in thrombus size caused by hypertension. Furthermore, a significant rise in prostacyclin production from aortic tissue [19.2±1.5 vs 13.2±2.4 ng (mg dry tissue) −1], associated with a fall in thromboxane A2 release from activated platelets (328.3±74.6 vs 705.0±88.1 ng ml −1), was observed in nicardipine-treated SHR. Plasma triglyceride and free fatty acid levels were also lowered by drug administration. Our results suggest that the actions of nicardipine on calcium metabolism result in antithrombotic effect through an increased availability of vasodilating eicosanoids in vessel walls and through a reduced amount of prothrombotic agents (thromboxane, free fatty acids).

Formation of biologically active autacoids is regulated by calcium influx in endothelial cells.

The blocker of receptor-mediated calcium entry SK&F 96365 was used to evaluate the contribution of calcium influx to the formation of biologically active endothelial prostanoids and endothelium-derived relaxing factor (EDRF). SK&F 96365 inhibited histamine-stimulated calcium entry into human umbilical vein endothelial cells but not its discharge from intracellular stores as determined spectrofluorometrically by changes of intracellular calcium concentration in fura-2-loaded cells. Concordantly, SK&F 96365 inhibited histamine-induced endothelial synthesis of 6-keto-prostaglandin F1 alpha and thromboxane B2 in a dose-dependent manner. To assess the functional significance of endothelial formation of prostacyclin and EDRF to platelets, the cAMP- and cGMP-dependent phosphorylation of two platelet proteins, rap1B and a 50-kD vasodilator-stimulated phosphoprotein (VASP), was analyzed in coincubation experiments of endothelial cells with platelets. Autacoids released by histamine-stimulated endothelial cells caused the phosphorylation of rap1B and VASP in platelets, which was only partly inhibited by either indomethacin or NG-monomethyl-L-arginine but was almost completely suppressed by SK&F 96365. The concomitant endothelial release of thromboxane A2 had no effect on protein kinase C- and calcium-dependent phosphorylation of platelet proteins. The results demonstrate that blockade of receptor-mediated calcium entry by SK&F 96365 markedly reduced the release of biologically active prostacyclin and EDRF from endothelial cells. Thus, calcium influx but not calcium release from intracellular stores plays a critical role in the receptor-stimulated formation and liberation of prostacyclin and EDRF in endothelial cells.

Selective Mycobacterium avium–induced production of nitric oxide by human monocyte-derived macrophages

Infection with a virulent strain of Mycobacterium avium, but not with virulent Mycobacterium tuberculosis or avirulent Mycobacterium smegmatis, induced the formation of nitric oxide by human monocyte-derived macrophages. This process was not affected by lipopolysaccharide or cytokines such as interferon-gamma or tumor necrosis factor alpha. M. avium-induced nitric oxide production was significantly decreased by NG-monomethyl-L-arginine, a potent inhibitor of nitric oxide synthase activity, without any significant enhancement of intramacrophagic mycobacterial growth. Infection with all the three mycobacterial species induced a significant activation of phospholipase A2 activity of macrophages as evidenced by the increased release of thromboxane A2. Finally, nitric oxide production by human monocyte-derived macrophages required infection with live M. avium, as neither gamma-irradiated M. avium nor the subcellular fractions of this microorganism (cell wall, cytosol) were able to trigger nitric oxide synthesis.

Thrombin-induced endothelium-dependent inhibition and direct activation of platelet-vessel wall interaction. Role of prostacyclin, nitric oxide, and thromboxane A2.

Platelet-vessel wall interaction plays an important role in acute cardiovascular disorders. Thrombin is a potent platelet activator but also has profound effects on the endothelium. Endothelial cells possess antithrombotic activity by releasing nitric oxide and prostacyclin, both potent vasodilators and platelet inhibitors. We studied the role of thrombin as a regulator of platelet-vessel wall interaction in isolated human arteries suspended in organ chambers for isometric tension recording. In arteries with endothelium, thrombin (0.01 to 1 U/mL) induced endothelium-dependent relaxations, which were reduced by the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 10(-4) mol/L) and/or indomethacin (10(-5) mol/L). Human platelets (75,000/microL) evoked only marginal contractions in arteries with endothelium (3 +/- 3% of the contraction to KCl 100 mmol/L; NS), which were markedly enhanced by endothelial removal (22 +/- 4%; P < .05). Thrombin (1 U/mL) did not affect the response to platelets in arteries with (6 +/- 5%; NS) but induced a huge contraction in rings without endothelium (53 +/- 6%; P < .01 versus control without endothelium). The potent contraction to thrombin-activated platelets (1000 to 75,000/microL) in arteries without endothelium was markedly inhibited by the thromboxane A2 synthetase/receptor antagonist ridogrel (10(-5) mol/L; P < .005 versus control) and the single-acting thromboxane receptor blocker SQ-30741 (10(-7) mol/L; P < .01 versus control). Thus, thrombin directly stimulates platelets to release thromboxane A2, inducing potent vasoconstriction, which is prevented by the simultaneous thrombin-induced release of prostacyclin and nitric oxide from endothelial cells. In arteries devoid of functional endothelial cells, as occurs in patients with coronary artery disease, a combined inhibition of thromboxane production and action provides a potent therapeutic tool to interfere with the thrombin-induced activation of platelet-vessel wall interaction.

Platelets Increase the Tone of Quiescent Rat Aortic Rings by Release of Serotonin and Potentiate the Subsequent Contractile Response to Norepinephrine

To examine the effect of platelets on the tone of quiescent vessels, rat aortic rings with intact endothelium and others with denuded endothelium were exposed to platelets in an organ bath. Suspension of washed platelets induced a mild but consistent contraction of rings with intact endothelium. The subsequent contractile response of these rings to norepinephrine (NE) was also potentiated. Platelets caused a marked contraction of quiescent rings without intact endothelium and potentiated the subsequent contractile effects of NE. The procontractile effect of platelets in rat aortic rings with and without intact endothelium was not modulated by the selective thromboxane A2 (TXA2)/endoperoxide receptor antagonist SQ29,548 or the cyclooxygenase inhibitor indomethacin, but was completely blocked by serotonin (S2) receptor antagonist LY53,857, suggesting that release of serotonin from aggregating platelets is perhaps more important than release of TXA2 in the procontractile effects of platelets on quiescent rat aortic rings. To examine the role of vascular endothelium in the procontractile effect of platelets further, we treated aortic rings with intact endothelium with the inhibitor of endothelium-derived relaxing factor (EDRF) NG-monomethyl-L-arginine (L-NMMA) or the adenine nucleotide scavenger apyrase. In rings treated with L-NMMA or apyrase, the contractile effect of platelets was enhanced (p < 0.01) and mimicked that in rings without intact endothelium. These observations indicate that although basal release of EDRF modulates the contractile effect of platelets, the dominant effect of platelets on quiescent rat aortic rings with intact endothelium is procontractile and this effect is mediated exclusively by release of serotonin.

Expression of prostaglandin H2-mediated mechanism of vascular contraction in hypertensive rats. Relation to lipoxygenase and prostacyclin synthase activities.

We tested the hypothesis that a prostanoid-mediated mechanism of vascular contraction is expressed in rats with aortic coarctation-induced hypertension. Rings of descending thoracic aorta taken from normotensive and hypertensive rats were contrasted in terms of constrictor responsiveness to arachidonic acid (AA), AA-induced release of eicosanoids, and ability to convert exogenous prostaglandin (PG) H2 to PGI2. AA (10(-8) to 10(-5) mol/L) increased isometric tension in aortic rings (bathed in Krebs' bicarbonate buffer) of hypertensive but not normotensive rats. AA (10(-5) mol/L) also elicited the release of PGI2, PGE2, thromboxane (TX) A2, and monohydroxyeicosatetraenoic acids (HETEs); this release from the aortic rings of hypertensive rats exceeded the corresponding release from the aortic rings of normotensive rats. However, the rate of conversion of exogenous PGH2 to PGI2 by aortic rings of hypertensive rats was < 50% the rate of conversion by aortic rings of normotensive rats. The constrictor effect of AA in aortic rings of hypertensive rats was abolished by an inhibitor of cyclooxygenase (indomethacin, 10 mumol/L) and a blocker of TXA2-PGH2 receptors (SQ29548, 1 mumol/L) but was not affected by an inhibitor of TXA2 synthesis (CGS13080, 10 mumol/L), suggesting mediation by PGH2. The lipoxygenase inhibitor baicalein (75 mumol/L) also attenuated the constrictor effect of AA in aortic rings of hypertensive rats while decreasing the associated release of HETEs and correcting the impairment in the conversion of PGH2 to PGI2.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective impairment of endothelium-dependent relaxations by prostaglandin endoperoxide

Studies of aortas from hypertensive and diabetic rats and rabbits have demonstrated impairment of endothelium-dependent relaxations, which were associated with increased release of endothelium-derived thromboxane A2 (TXA2). This implicates enhanced release of TXA2 or its precursor prostanoid, prostaglandin endoperoxide (PGH2), or both, as factors mediating the endothelial cell dysfunction. The interaction of vasoconstrictor prostanoids (PGH2, PGF2 alpha and U-46619, a stable thromboxane-receptor agonist) and oxygen-derived free radicals with the release of nitric oxide was examined in isolated aortas from Sprague-Dawley rats. Exogenously applied PGH2 or U-46619 caused concentration-dependent contractions of aortic rings, these contractions being blocked by the newly developed, potent and selective PGH2- and TXA2-receptor antagonist BMS-180291, but not by inhibition of TXA synthase or cyclo-oxygenase (using dazoxiben and indomethacin, respectively). In aortic rings contracted submaximally with phenylephrine, brief exposure to a subthreshold concentration of PGH2 caused impairment of acetylcholine- and ADP-induced, but not of nitroprusside-induced, relaxations. The impairment was restored towards normal by BMS-180291 or by superoxide dismutase (SOD), a superoxide anion scavenger, but not by dazoxiben or indomethacin. In contrast, treatment of aortic rings with U-46619 or PGF2 alpha did not impair the relaxations. Oxygen-derived free radicals generated by xanthine oxidase caused contractions and impaired acetylcholine relaxations which were reversed by SOD but not by BMS-180291. These findings indicate that activation of PGH2 receptors causes contractions and selective impairment of endothelium-dependent relaxations by a mechanism involving generation of oxygen-derived free radicals in the endothelium.

Detection of Antitrophoblast Antibodies in the Sera of Patients With Anticardiolipin Antibodies and Fetal Loss

AbstractWomen with anticardiolipin antibodies (ACLA) are at increased risk for fetal loss. One potential explanation for this outcome is that sera from these individuals contain antibodies reactive with trophoblast cells, which are involved in the establishment of the uteroplacental vasculature and maintenance of placental blood fluidity. To examine this hypothesis, we compared the incidence of trophoblast-reactive antibodies in 27 patients with AC LA and a history of fetal loss with that in 29 normal pregnant women. Sera from 20 patients, but only one control, contained trophoblast-reactive antibodies (P < .001). These antibodies were not directed against major histocompatibility class I antigens, and reacted with both term and first-trimester trophoblast cells. In most cases, sera from which AC LA were adsorbed by cardiolipin-containing liposomes maintained reactivity against cells. In addition, patient Ig fractions immunoprecipitated an ~62-kD protein from the trophoblast cell surface, stimulated the release of arachi-donic acid and thromboxane A2 by trophoblasts, and inhibited the binding of prourokinase to trophoblast urokinase receptors. These observations show that sera from women with AC LA and a history of fetal loss contain antitrophoblast antibodies. These antibodies may be serologically distinct from ACLA, and may contribute to the pathogenesis of fetal demise.

Detection of antitrophoblast antibodies in the sera of patients with anticardiolipin antibodies and fetal loss

Women with anticardiolipin antibodies (ACLA) are at increased risk for fetal loss. One potential explanation for this outcome is that sera from these individuals contain antibodies reactive with trophoblast cells, which are involved in the establishment of the uteroplacental vasculature and maintenance of placental blood fluidity. To examine this hypothesis, we compared the incidence of trophoblast-reactive antibodies in 27 patients with ACLA and a history of fetal loss with that in 29 normal pregnant women. Sera from 20 patients, but only one control, contained trophoblast-reactive antibodies (P &lt; .001). These antibodies were not directed against major histocompatibility class I antigens, and reacted with both term and first-trimester trophoblast cells. In most cases, sera from which ACLA were adsorbed by cardiolipin- containing liposomes maintained reactivity against cells. In addition, patient Ig fractions immunoprecipitated an approximately 62-kD protein from the trophoblast cell surface, stimulated the release of arachidonic acid and thromboxane A2 by trophoblasts, and inhibited the binding of prourokinase to trophoblast urokinase receptors. These observations show that sera from women with ACLA and a history of fetal loss contain antitrophoblast antibodies. These antibodies may be serologically distinct from ACLA, and may contribute to the pathogenesis of fetal demise.