The formation of thromboxane B2, leukotriene B4 and 12-hydroxyeicosatetraenoic acid by alveolar macrophages after activation during tumor growth in the rat

Pieces of tumor tissue were implanted subcutaneously in the right flank of BN female rats. After 3, 7, 10, 12, 14 and 17 days the lungs were lavaged and the alveolar macrophages collected. The cells were activated with the calcium ionophore A23187 and the formation of thromboxane B2 (TxB2), leukotriene B4 (LTB4) and 12-hydroxyeicosatetraenoic acid (12-HETE) determined. The formation of TxB2 decreased considerably until day 7. Thereafter, no changes occurred. The formation of LTB4 increased after the tumor implantation until day 10 and remained stable for the rest of the period, 12-HETE formation was approximately similar, with a decrease at day 12 but continued to increase after day 14. These results suggest that during tumor growth an inhibition of the cyclo-oxygenase or thromboxane synthase occurs and an activation of the C5- and C12-lipoxygenases of the alveolar macrophages.     

Roles of vasoconstrictor prostaglandins, COX-1 and -2, and AT1, AT2, and TP receptors in a rat model of early 2K,1C hypertension

Angiotensin (ANG) II activating type 1 receptors (AT(1)Rs) enhances superoxide anion (O(2)*(-)) and arachidonate (AA) formation. AA is metabolized by cyclooxygenases (COXs) to PGH(2), which is metabolized by thromboxane (Tx)A(2) synthase to TxA(2) or oxidized to 8-isoprostane PGF(2alpha) (8-Iso) by O(2)*(-). PGH(2), TxA(2), and 8-Iso activate thromboxane-prostanoid receptors (TPRs). We investigated whether blood pressure in a rat model of early (3 wk) two-kidney, one-clip (2K,1C) Goldblatt hypertension is maintained by AT(1)Rs or AT(2)Rs, driving COX-1 or -2-dependent products that activate TPRs. Compared with sham-operated rats, 2K,1C Goldblatt rats had increased mean arterial pressure (MAP; 120 +/- 4 vs. 155 +/- 3 mmHg; P < 0.001), plasma renin activity (PRA; 22 +/- 7 vs. 48 +/- 5 ng x ml(-1) x h(-1); P < 0.01), plasma malondialdehyde (1.07 +/- 0.05 vs. 1.58 +/- 0.16 nmol/l; P < 0.01), and TxB(2) excretion (26 +/- 4 vs. 51 +/- 7 ng/24 h; P < 0.01). Acute graded intravenous doses of benazeprilat (angiotensin-converting enzyme inhibitor) reduced MAP at 20 min (-36 +/- 5 mmHg; P < 0.001) and excretion of TxA(2) metabolites. Indomethacin (nonselective COX antagonist) or SC-560 (COX-1 antagonist) reduced MAP at 20 min (-25 +/- 5 and -28 +/- 7 mmHg; P < 0.001), whereas valdecoxib (COX-2 antagonist) was ineffective (-9 +/- 5 mmHg; not significant). Losartan (AT(1)R antagonist) or SQ-29548 (TPR antagonist) reduced MAP at 150 min (-24 +/- 6 and -22 +/- 3 mmHg; P < 0.001), whereas PD-123319 (AT(2)R antagonist) was ineffective. Acute blockade of TPRs, COX-1, or COX-2 did not change PRA, but TxB(2) generation by the clipped kidney was reduced by blockade of COX-1 and increased by blockade of COX-2. 2K,1C hypertension in rats activates renin, O(2)*(-), and vasoconstrictor PGs. Hypertension is maintained by AT(1)Rs and by COX-1, but not COX-2, products that activate TPRs.     

Thromboxane-induced pulmonary vasoconstriction: involvement of calcium

Infusion of tert-butyl hydroperoxide (t-bu-OOH) or arachidonic acid into rabbit pulmonary arteries stimulated thromboxane B2 (TxB2) production and caused pulmonary vasoconstriction. Both phenomena were blocked by cyclooxygenase inhibitors or a thromboxane synthase inhibitor. The increase in pulmonary arterial pressure caused by either t-bu-OOH or arachidonic acid infusion correlated with the concentration of TxB2 in the effluent perfusate. The concentration of TxB2 in the effluent perfusate, however, was always 10-fold greater after arachidonic acid infusion. In the rabbit pulmonary vascular bed lipoxygenase products did not appear involved in the vasoactive response to t-bu-OOH or exogenous arachidonic acid infusion. Calcium entry blockers or a calcium-free perfusate prevented the thromboxane-induced pulmonary vasoconstriction. Calmodulin inhibitors also blocked the pulmonary vasoconstriction induced by t-bu-OOH without affecting the production of TxB2 or prostacyclin. These results suggest that thromboxane causes pulmonary vasoconstriction by increasing cytosol calcium concentration.     

Arachidonic acid metabolites and an early stage of pulmonary hypertension in chronically hypoxic newborn pigs

Our purpose was to determine whether production of arachidonic acid metabolites, particularly cyclooxygenase (COX) metabolites, is altered in 100-400-microm-diameter pulmonary arteries of piglets at an early stage of pulmonary hypertension. Piglets were raised in either room air (control) or hypoxia for 3 days. A cannulated artery technique was used to measure responses of 100-400-microm-diameter pulmonary arteries to arachidonic acid, a prostacyclin analog, or the thromboxane mimetic. Radioimmunoassay was used to determine pulmonary artery production of thromboxane B(2) (TxB(2)) and 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha)), the stable metabolites of thromboxane and prostacyclin, respectively. Assessment of abundances of COX pathway enzymes in pulmonary arteries was determined by immunoblot technique. Arachidonic acid induced less dilation in pulmonary arteries from hypoxic than in pulmonary arteries from control piglets. Pulmonary artery responses to prostacyclin and were similar for both groups. 6-Keto-PGF(1alpha) production was reduced, whereas TxB(2) production was increased in pulmonary arteries from hypoxic piglets. Abundances of both COX-1 and prostacyclin synthase were reduced, whereas abundances of both COX-2 and thromboxane synthase were unaltered in pulmonary arteries from hypoxic piglets. At least partly due to altered abundances of COX pathway enzymes, a shift in production of arachidonic acid metabolites, away from dilators toward constrictors, may contribute to the early phase of chronic hypoxia-induced pulmonary hypertension in newborn piglets.     

Pattern of right ventricular pressure fall and its modulation by afterload

Pattern of right ventricular pressure (RVP) fall and its afterload dependence were examined by analyzing ventricular pressure curves and corresponding pressure dP/dt phase planes obtained in both ventricles in the rat heart in situ. Time and value of dP/dt(min), and the time constant tau were measured at baseline and during variable RV afterload elevations, induced by beat-to-beat pulmonary trunk constrictions. RVP and left ventricular pressure (LVP) decays were divided into initial accelerative and subsequent decelerative phases separated by corresponding dP/dt(min). At baseline, LVP fall was decelerative during 4/5 of its course, whereas only 1/3 of RVP decay occurred in a decelerative fashion. During RV afterload elevations, the absolute value of RV-dP/dt(min) and RV-tau increased, whilst time to RV dP/dt(min) decreased. Concomitantly, the proportion of RVP decay following a decelerative course increased, so that in highly RV afterloaded heartbeats RVP fall became more similar to LVP fall. In conclusion, RVP and LVP decline have distinct patterns, their major portion being decelerative in the LV and accelerative in the RV. In the RV, dP/dt(min), tau and the proportional contribution of accelerative and decelerative phases for ventricular pressure fall are afterload-dependent. Consequently, tau evaluates a relatively much shorter segment of RVP than LVP fall.     

Double-label expression studies of prostacyclin synthase, thromboxane synthase and COX isoforms in normal aortic endothelium

We have performed double-label immunofluorescence microscopy studies to evaluate the extent of co-localization of prostacyclin synthase (PGIS) and thromboxane synthase (TXS) with cyclooxygenase (COX)-1 and COX-2 in normal aortic endothelium. In dogs, COX-2 expression was found to be restricted to small foci of endothelial cells while COX-1, PGIS and TXS were widely distributed throughout the endothelium. Quantification of the total cross-sectioned aortic endothelium revealed a 6- to 7-fold greater expression of COX-1 relative to COX-2 (55 vs. 8%) and greater co-distribution of PGIS with COX-1 compared to COX-2 (19 vs. 3%). These results are in contrast to the extensive co-localization of PGIS and COX-2 in bronchiolar epithelium. In rat and human aortas, immunofluorescence studies also showed significant COX-1 and PGIS co-localization in the endothelium. Only minor focal COX-2 expression was detected in rat endothelium, similar to the dog, while COX-2 was not detected in human specimens. Inhibition studies in rats showed that selective COX-1 inhibition caused a marked reduction of 6-keto-PGF(1alpha) and TXB(2) aortic tissue levels, while COX-2 inhibition had no significant effect, providing further evidence for a functionally larger contribution of COX-1 to the synthesis of prostacyclin and thromboxane in aortic tissue. The data suggest a major role for COX-1 in the production of both prostacyclin and thromboxane in normal aortic tissue. The extensive co-localization of PGIS and COX-2 in the lung also indicates significant tissue differences in the co-expression patterns of these two enzymes.     

Effect of furegrelate on renal plasma flow after angiotensin II infusion

We had previously shown that selective thromboxane synthetase inhibition with furegrelate increases urinary excretion of 6-ketoPGF1 alpha, the hydrolysis product of prostacyclin after stimulation of renal prostaglandin synthesis with furosemide. The present study assessed the functional significance of this "redirection" of prostaglandin formation using a more physiologic stimulus, angiotensin II. Sprague-Dawley rats (n = 27) were fitted with a transabdominal bladder cannula. Five days later they were given angiotensin II (10 mg.kg-1.min-1) by intravenous infusion. After 30 min, an infusion of furegrelate, 2 mg/kg, then 2 mg.kg-1.h-1, (n = 9); indomethacin, 2 mg/kg, then 2 mg.kg-1.h-1 (n = 9); or vehicle, 250 microL, then 0.018 mL/min (n = 9) was begun for 60 min. Clearance of [14C]para-aminohippuric acid was taken as a measure of renal plasma flow. Angiotensin II raised the mean arterial pressure in all groups. Administration of furegrelate or indomethacin did not change mean arterial pressure or heart rate. Angiotensin II reduced [14C]p-aminohippuric acid clearance by about 32% (1.42 +/- 0.18 to 0.97 +/- 0.07 mL.min-1.100 g-1, p less than 0.05). Furegrelate attenuated this renal vasoconstriction (0.97 +/- 0.07 to 1.38 +/- 0.17 mL.min-1.100 g-1, p less than 0.05), while indomethacin increased it by a further 32% (1.78 +/- 0.12 to 1.20 +/- 0.12 mL.min-1.100 g-1, p less than 0.05). Vehicle alone had no effect. Furegrelate reduced serum thromboxane B2 by 90% (6.52 +/- 0.030 to 0.7 +/- 0.21 ng/100 microL, p less than 0.05), while indomethacin reduced it by 73% (5.9 +/- 0.99 to 1.4 +/- 0.20 ng/100 microL, p less than 0.05). We conclude that furegrelate attenuates the renal vasoconstriction of angiotensin II, presumably by enhancing the formation of vasodilator prostaglandins.     

Vasoactive prostanoids are generated from arachidonic acid by COX-1 and COX-2 in the mouse

Generation of vasoactive prostanoids from arachidonic acid by cyclooxygenase (COX)-1 and COX-2 was investigated in anesthetized mice. Intravenous injections of the prostanoid precursor arachidonic acid increased pulmonary arterial pressure and decreased systemic arterial pressure. Pulmonary pressor and systemic depressor responses were attenuated by SC-560 and nimesulide, inhibitors of COX-1 and COX-2, in doses that did not alter responses to injected prostanoids. Pulmonary pressor responses to arachidonic acid were blocked and a depressor response was unmasked, whereas systemic depressor responses were not altered, by a thromboxane receptor antagonist. Pulmonary and systemic pressor responses to angiotensin II injections and systemic pressor responses to angiotensin II infusion were not modified by COX-1 or COX-2 inhibitors but were attenuated by losartan. Systemic depressor responses to arachidonic acid were smaller in COX-1 and COX-2 knockout mice, whereas responses to angiotensin II, norepinephrine, U-46619, endothelin-1, and PGE(1) were not different in COX-1 and COX-2 knockout and wild-type control mice. These results suggest that vasoactive prostanoids with pulmonary pressor and systemic vasodepressor activity are formed by COX-1 and COX-2 and are consistent with Western blot analysis and immunostaining showing the presence of COX-1 and COX-2. These data suggest that thromboxane A(2) (TxA(2)) is formed from the precursor by COX-1 and COX-2 in the lung and are in agreement with immunofluorescence studies showing thromboxane synthase. The present data suggest that COX-1- or COX-2-derived prostanoids do not modulate responses to angiotensin II or other vasoactive agents and that prostanoid responses are similar in CD-1 and C57BL/6 and in male and female mice.     

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.     

Gene expression changes of prostanoid synthases in endothelial cells and prostanoid receptors in vascular smooth muscle cells caused by aging and hypertension.

The present study was designed to assess whether or not changes in genomic expression of cyclooxygenases (COX-1, COX-2), endothelial nitric oxide synthase (eNOS), and prostanoid synthases in the endothelium and of prostanoid receptors in vascular smooth muscle contribute to the occurrence of endothelium-dependent contractions during aging and hypertension. Gene expression was quantified by real-time PCR using isolated endothelial cells and smooth muscle cells (SMC) from the aorta of Wistar-Kyoto and spontaneously hypertensive rats. Genes for all known prostanoid synthases and receptors were present in endothelial cells and SMC, respectively. Aging caused overexpression of eNOS, COX-1, COX-2, thromboxane synthase, hematopoietic-type prostaglandin D synthase, membrane prostaglandin E synthase-2, and prostaglandin F synthase in endothelial cells and COX-1 and prostaglandin E(2) (EP)(4) receptors in SMC. Hypertension augmented the expression of COX-1, prostacyclin synthase, thromboxane synthase, and hematopoietic-type prostaglandin D synthase in endothelial cells and prostaglandin D(2) (DP), EP(3), and EP(4) receptors in SMC. The increase in genomic expression of endothelial COX-1 explains why in aging and hypertension the endothelium has greater propensity to release cyclooxygenase-derived vasoconstrictive prostanoids. The expression of prostacyclin synthase was by far the most abundant, explaining why the majority of the COX-1-derived endoperoxides are transformed into prostacyclin, substantiating the role of prostacyclin as an endothelium-derived contracting factor. The expression of thromboxane synthase was increased in the cells of aging or hypertensive rats, explaining why the prostanoid can contribute to endothelium-dependent contractions. It is uncertain whether the gene modifications caused by aging and hypertension directly contribute to endothelium-dependent contractions or rather to vascular aging and the vascular complications of the hypertensive process.     

Prostaglandins mediate tonic contraction of the guinea pig and human gallbladder

The gallbladder (GB) maintains tonic contraction modulated by neurohormonal inputs but generated by myogenic mechanisms. The aim of these studies was to examine the role of prostaglandins in the genesis of GB myogenic tension. Muscle strips and cells were treated with prostaglandin agonists, antagonists, cyclooxygenase (COX) inhibitors, and small interference RNA (siRNA). The results show that PGE2, thromboxane A2 (TxA2), and PGF(2alpha) cause a dose-dependent contraction of muscle strips and cells. However, only TxA2 and PGE2 (E prostanoid 1 receptor type) antagonists induced a dose-dependent decrease in tonic tension. A COX-1 inhibitor decreased partially the tonic contraction and TxB2 (TxA2 stable metabolite) levels; a COX-2 inhibitor lowered the tonic contraction partially and reduced PGE2 levels. Both inhibitors and the nonselective COX inhibitor indomethacin abolished the tonic contraction. Transfection of human GB muscle strips with COX-1 siRNA partially lowered the tonic contraction and reduced COX-1 protein expression and TxB2 levels; COX-2 siRNA also partially reduced the tonic contraction, the protein expression of COX-2, and PGE2. Stretching muscle strips by 1, 2, 3, and 4 g increased the active tension, TxB2, and PGE2 levels; a COX-1 inhibitor prevented the increase in tension and TxB2; and a COX-2 inhibitor inhibited the expected rise in tonic contraction and PGE2. Indomethacin blocked the rise in tension and TxB2 and PGE2 levels. We conclude that PGE2 generated by COX-2 and TxA2 generated by COX-1 contributes to the maintenance of GB tonic contraction and that variations in tonic contraction are associated with concomitant changes in PGE2 and TxA2 levels.     

Effect of platelet depletion on lung vasoconstriction in heparin-protamine reactions

In six awake sheep the control heparin-protamine reaction was associated with a 150-fold rise in arterial plasma thromboxane B2 (TxB2) levels, a 4.5-fold increase in pulmonary vascular resistance, a 20% decrease in cardiac output, a 30% decrease in arterial PO2, and a 30% reduction in arterial white blood cell concentrations. Depletion of 99% of circulating platelets by antibodies did not prevent either acute and severe pulmonary hypertension or increased plasma TxB2 levels induced by heparin-protamine administration. We produced sheep platelet aggregation in vitro with bovine thrombin and measured marked TxB2 release (36.3 +/- 16.3 ng/10(9) platelets). In contrast, neither heparin, protamine, nor heparin-protamine complexes over a 10,000-fold range of concentrations induced platelet aggregation and release of thromboxane in vitro. Therefore sheep platelets are not the source of thromboxane production associated with acute pulmonary hypertension during the heparin-protamine reaction, and other cells must produce the thromboxane.     

Protective actions of a new thromboxane synthetase inhibitor in arachidonate induced sudden death

A new thromboxane synthetase inhibitor, OKY-046, at doses of 0.5 and 1.0 mg/kg prevented mortality induced by sodium arachidonate in 100% of the rabbits studied. Sodium arachidonate at a dose of 1.25 mg/kg uniformly decreased mean arterial blood pressure to values approximately 0 mm Hg, stopped respiration and produced sudden death within 3-5 minutes in all rabbits studied. OKY-046 prevented all these sequelae of the sodium arachidonate. Untreated rabbits challenged with sodium arachidonate develop large increases in circulating thromboxane B2 (TxB2) and 6-keto PGF1 alpha of about 12- to 18-fold. In contrast, OKY-046 prevented the increase in TxB2 concentrations and the pulmonary thrombosis, but did not block the rise in 6-keto PGF1 alpha following arachidonate injection. These results suggest that the protective mechanism of OKY-046 in arachidonate induced sudden death is via selective inhibition of thromboxane synthesis.     

L-arginine supplementation abolishes the blood pressure and endothelin response to chronic increases in plasma sFlt-1 in pregnant rats

While soluble fms-like tyrosine kinase-1 (sFlt-1) and endothelin-1 (ET-1) have been implicated in the pathogenesis of preeclampsia (PE), the mechanisms whereby increased sFlt-1 leads to enhanced ET-1 production and hypertension remain unclear. It is well documented that nitric oxide (NO) production is reduced in PE; however, whether a reduction in NO synthesis plays a role in increasing ET-1 and blood pressure in response to chronic increases in plasma sFlt-1 remains unclear. The purpose of this study was to determine the role of reduced NO synthesis in the increase in blood pressure and ET-1 in response to sFlt-1 in pregnant rats. sFlt-1 was infused into normal pregnant (NP) Sprague-Dawley rats (3.7 μg·kg(-1)·day(-1) for 6 days beginning on day 13 of gestation) treated with the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (100 mg/l for 4 days) or supplemented with 2% L-Arg (in drinking water for 6 days beginning on day 15 of gestation). Infusion of sFlt-1 into NP rats significantly elevated mean arterial pressure compared with control NP rats: 116 ± 2 vs. 103 ± 1 mmHg (P < 0.05). NO synthase inhibition had no effect on the blood pressure response in sFlt-1 hypertensive pregnant rats (121 ± 3 vs. 116 ± 2 mmHg), while it significantly increased mean arterial pressure in NP rats (128 ± 4 mmHg, P < 0.05). In addition, NO production was reduced ～70% in isolated glomeruli from sFlt-1 hypertensive pregnant rats compared with NP rats (P < 0.05). Furthermore, prepro-ET-1 in the renal cortex was increased ～3.5-fold in sFlt-1 hypertensive pregnant rats compared with NP rats. Supplementation with L-Arg decreased the sFlt-1 hypertension (109 ± 3 mmHg, P < 0.05) but had no effect on the blood pressure response in NP rats (109 ± 3 mmHg) and abolished the enhanced sFlt-1-induced renal cortical prepro-ET expression. In conclusion, a reduction in NO synthesis may play an important role in the enhanced ET-1 production in response to sFlt-1 hypertension in pregnant rats.     

Pulmonary intravascular macrophages and hemodynamic effects of liposomes in sheep

We studied the effects of liposomes on the pulmonary circulation of sheep and found a close correlation between liposome retention in the lung and the intravascular macrophages. A test dose of liposomes (5.5 mumol of total lipids) injected intravenously transiently increased pulmonary arterial pressure from 24 +/- 2 to 55 +/- 16 (SD) cmH2O. The pulmonary arterial pressure responses were dose dependent and reproducible. The rise in pulmonary arterial pressure was blocked completely by indomethacin and 75% by a thromboxane synthase inhibitor. Systemic arterial thromboxane B2 concentration increased from a base-line level of less than 50 pg/ml to 250 +/- 130 pg/ml at the peak of the pressor response. Larger doses of liposomes (220 mumol of total lipids) infused intravenously over 1 h increased pulmonary arterial pressure maximally within the first 15 min. Lymph flow increased and lymph protein concentration decreased, suggesting venoconstriction. Over half (62.4 +/- 15.7%) of 111In-labeled liposomes remained in the lung after 2 h. Fluorescence and transmission electron microscopy showed that greater than 90% of the liposomes were associated with mononuclear cells in the lumen of the alveolar wall microvessels. We conclude that liposomes affect pulmonary arterial pressure transiently by a mechanism involving the arachidonate cascade, principally thromboxane. Our observations suggest that a population of pulmonary intravascular macrophages is likely to be the source of the thromboxane and the pulmonary hemodynamic and lymph dynamic changes that occur in a dose-dependent fashion, although interactions between liposomes, leukocytes, or endothelial cells, in addition to the macrophages, have not been completely ruled out. We believe this is the first demonstration that pulmonary intravascular macrophages may be the source of the arachidonate metabolites rather than endothelial cells, neutrophils, or perivascular interstitial cells.     

Products, kinetics, and substrate specificity of homogeneous thromboxane synthase from human platelets: development of a novel enzyme assay

Homogeneous thromboxane synthase from human platelets converted prostaglandin H2 (PGH2) to thromboxane A2 (measured as thromboxane B2, TxB2), 12(L)-hydroxy-5,8,10-heptadecatrienoic acid (HHT), and malondialdehyde (MDA) in equimolar amounts under a variety of experimental conditions. PGG2 was transformed to MDA and corresponding 15- and 12-hydroperoxy products. PGH1 was enzymatically transformed into 12(L)-hydroxy-8,10-heptadecadienoic acid (HHD) and PGH3 into TxB3 and 12(L)-hydroxy-5,8,10,14-heptadecatetraenoic acid (delta 14-HHT) as earlier reported for solubilized and partially purified thromboxane synthase preparations. The ratio of thromboxane to C17 hydroxy fatty acid formation was 1:1 with PGG2, PGH2, and PGH3 as substrates. These results confirm and extend earlier observations with partially purified enzyme that the three products are formed in a common enzymatic pathway (Diczfalusy, U., Falardeau, P., and Hammarstr?m, S. (1977) FEBS Lett. 84, 271-274). A convenient spectrophotometric assay for thromboxane synthase activity measuring the ultraviolet light absorption of the C17 hydroxy acid formed (e.g., HHT) was developed. The validity of the assay was determined employing specific inhibitors for thromboxane synthase. The substrate specificity of thromboxane synthase was determined using this assay. PGG2 and PGH3 showed Vmax and KM values similar to those of PGH2. The KM value of PGH1 was also identical to that of PGH2 but the Vmax value PGH1 was more than twice as high as that of PGH2.     

Hyperbaric oxygen toxicity: role of thromboxane.

Exposing rabbits for 1 h to 100% O2 at 4 atm barometric pressure markedly increases the concentration of thromboxane B2 in alveolar lavage fluid [1,809 +/- 92 vs. 99 +/- 24 (SE) pg/ml, P less than 0.001], pulmonary arterial pressure (110 +/- 17 vs. 10 +/- 1 mmHg, P less than 0.001), lung weight gain (14.6 +/- 3.7 vs. 0.6 +/- 0.4 g/20 min, P less than 0.01), and transfer rates for aerosolized 99mTc-labeled diethylenetriamine pentaacetate (500 mol wt; 40 +/- 14 vs. 3 +/- 1 x 10(-3)/min, P less than 0.01) and fluorescein isothiocyanate-labeled dextran (7,000 mol wt; 10 +/- 3 vs. 1 +/- 1 x 10(-4)/min, P less than 0.01). Pretreatment with the antioxidant butylated hydroxyanisole (BHA) entirely prevents the pulmonary hypertension and lung injury. In addition, BHA blocks the increase in alveolar thromboxane B2 caused by hyperbaric O2 (10 and 45 pg/ml lavage fluid, n = 2). Combined therapy with polyethylene glycol- (PEG) conjugated superoxide dismutase (SOD) and PEG-catalase also completely eliminates the pulmonary hypertension, pulmonary edema, and increase in transfer rate for the aerosolized compounds. In contrast, combined treatment with unconjugated SOD and catalase does not reduce the pulmonary damage. Because of the striking increase in pulmonary arterial pressure to greater than 100 mmHg, we tested the hypothesis that thromboxane causes the hypertension and thus contributes to the lung injury. Indomethacin and UK 37,248-01 (4-[2-(1H-imidazol-1-yl)-ethoxy]benzoic acid hydrochloride, an inhibitor of thromboxane synthase, completely eliminate the pulmonary hypertension and edema.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of thromboxane synthase inhibition on tumor necrosis factor-induced lung injury in sheep.

To examine the role of thromboxane (Tx) A2 in the pathogenesis of acute lung injury caused by tumor necrosis factor alpha (TNF), we tested the effects of OKY-046, a selective thromboxane synthase inhibitor, on pulmonary hemodynamics, lung lymph balance, circulating leukocytes, arterial blood gas analysis, and TxA2 (as TxB2) and prostacyclin (as 6-keto-prostaglandin F1 alpha) levels in plasma and lung lymph after TNF infusion in awake sheep. Infusion of human recombinant TNF (3.5 micrograms/kg) into a chronically instrumented awake sheep caused a transient increase in pulmonary arterial pressure (Ppa). The Ppa peaked within 15 min of the start of TNF infusion from 23.3 +/- 1.1 (SE) cmH2O of baseline to 42.3 +/- 2.3 cmH2O and then decreased toward baseline. The pulmonary hypertension was accompanied by transient hypoxemia, peripheral leukopenia, and the increases in TxB2 in plasma and lung lymph. These changes were followed by an increase in flow of protein-rich lung lymph, consistent with an increase in pulmonary microvascular permeability. OKY-046 significantly prevented the rises of Ppa and TxB2 concentrations in plasma and lung lymph during early phase after TNF infusion. OKY-046, however, did not attenuate the increase of lung lymph flow, transient hypoxemia, and leukopenia. From these data, and by comparison with our previous studies of OKY-046-pretreated sheep during endotoxemia, we conclude that TxA2 has an important role of the increase in the early pulmonary hypertension, but it is not related to the early hypoxemia, leukopenia, and lung lymph balances in TNF-induced lung injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cyclooxygenase inhibitor blocks rebound response after NO inhalation in an endotoxin model

This study addressed the possible role of cyclooxygenase (COX) and its products in the rebound response to inhaled nitric oxide (INO). Anesthetized, mechanically ventilated piglets were exposed to endotoxin alone, endotoxin combined with INO, or endotoxin with INO plus the COX inhibitor diclofenac (3 mg/kg iv) (n = 8 piglets/group). A control group of healthy pigs (n = 6) was also studied. Measurements were made of blood gases, hemodynamic parameters, lung tissue COX expression, and plasma concentrations of thromboxane B(2) (TxB(2)), PGF(2alpha), and 6-keto-PGF(1alpha). Endotoxin increased lung inducible COX (COX-2) expression and circulating prostanoids concentrations. Inhalation of NO during endotoxemia increased the constitutive COX (COX-1) expression, and the circulating TxB(2) and PGF(2alpha) increased further after INO withdrawal. The combination of COX inhibitor with INO blocked all these changes and eliminated the rebound reaction to INO withdrawal, which otherwise was seen in endotoxemic piglets given INO only. We conclude that the rebound response to INO discontinuation is related to COX products.     

Mechanism of peptidoleukotriene-induced increases in pulmonary transvascular fluid filtration

We examined the effects of leukotrienes C4 (LTC4) and D4 (LTD4) (1 microgram) on the pulmonary vascular filtration coefficient, a measure of vessel wall conductivity to water, and the alterations in pulmonary vascular resistance (PVR) in isolated-perfused guinea pig lungs. We also assessed whether LTC4 and LTD4 increased the permeability to albumin in cultured monolayers of pulmonary artery endothelial cells. In Ringer-perfused and blood-perfused lungs, LTC4 resulted in increases in pulmonary arterial pressure (Ppa) and the pulmonary capillary pressure (Pcap) measured as the equilibration pressure after simultaneous pulmonary arterial and venous occlusions. Pulmonary venous resistance (Rv) increased to a greater extent than arterial resistance (Ra) in both Ringer-perfused and blood-perused lungs challenged with LTC4. The greater increase in PVR in blood-perfused lungs corresponded with a greater elevation of lung effluent thromboxane B2 (TxB2) concentration. The LTC4-stimulated increase in PVR was prevented by pretreatment with meclofenamate (10(-4) M). LTD4 also induced rapid increases in Ppa and Pcap in both Ringer-perfused and blood-perfused lungs; however, Ppa decreased before stabilizing at a pressure higher than base line. The increases in Rv with LTD4 were greater than Ra. The LTD4-stimulated increases in Ra and Rv also paralleled the elevation in TxB2 concentration. As with LTC4, the increases in Ppa, Pcap, PVR, and TxB2 concentration were greater in blood-perfused than in Ringer-perfused lungs. Pretreatment with meclofenamate reduced the magnitude of the initial increase in Ppa, but did not prevent the response.(ABSTRACT TRUNCATED AT 250 WORDS)