Prostacyclin: a potentially valuable agent for preserving myocardial tissue in acute myocardial ischemia.

Prostacyclin, a potent, naturally occurring prostaglandin exerts a variety of cardiovascular and cellular actions of potential value in acute myocardial ischemia. These properties include the reduction of systemic blood pressure without changing heart rate, the lowering of coronary vascular and total peripheral resistance, the inhibition of platelet aggregation and the concomitant formation of thromboxane B2, and the reduction of the release of lysosomal enzymes.

Effects of cyclooxygenase inhibitors on the alterations in lung mechanics caused by endotoxemia in the unanesthetized sheep.

The effects of Escherichia coli endotoxin on lung mechanics, hemodynamics, gas exchange, and lung fluid and solute exchange were studied in 12 chronically instrumented unanesthetized sheep. A possible role for cyclooxygenase products of arachidonate metabolism as mediators of the endotoxin-induced alterations in lung mechanics was investigated by studying sheep before and after cyclooxygenase inhibition with sodium meclofenamate and ibuprofen. Sheep were studied three times in random order: (a) sodium meclofenamate (or ibuprofen) infusion alone; (b) E. coli endotoxin alone; and (c) meclofenamate (or ibuprofen) and endotoxin. Meclofenamate alone had no effect on any of the variables measured. Endotoxin alone caused early marked changes in lung mechanics: resistance to airflow across the lungs (RL) increased 10-fold, dynamic lung compliance (Cdyn) decreased 80% and functional residual capacity (FRC) decreased by greater than 30%. The alveolar-to-arterial oxygen difference (delta AaPO2) increased markedly following endotoxemia. In the presence of sufficient meclofenamate to inhibit accumulation of thromboxane-B2 and 6-keto-prostaglandin F1 alpha in lung lymph, endotoxin caused no increase in RL, Cdyn decreased by less than 40%, and FRC decreased by only 6%. Meclofenamate significantly attenuated the hypoxemia and early pulmonary hypertension caused by endotoxemia but had no effect on the late increases in lung fluid and solute exchange. Ibuprofen had similar effects to those observed with meclofenamate. We conclude that both the pulmonary hypertension and changes in lung mechanics observed after endotoxemia may be mediated, at least in part, by constrictor prostaglandins or thromboxanes and that gas exchange may be improved by preventing endogenous synthesis of these mediators.

Effect of N-acetylcysteine on the pulmonary response to endotoxin in the awake sheep and upon in vitro granulocyte function.

Oxygen free radicals released during endotoxemia may contribute to the lung injury of the adult respiratory distress syndrome (ARDS). As this syndrome occurs frequently after gram-negative sepsis in humans, we studied the effect of intravenous N-acetylcysteine (NAC), a free radical scavenger, upon the endotoxin (E)-induced model of ARDS in awake sheep. In vivo studies demonstrated that NAC attenuates the endotoxin-induced rise in pulmonary artery pressure (62 +/- 3 torr with E control vs. 43 +/- 3 torr for E + NAC), and markedly diminishes the rise in lymph flow at 1 h (8.5 +/- 1.2 vs 4.5 +/- 0.6 ml/15 min) and 4 h (5.0 +/- 0.6 vs. 3.3 +/- 0.4 ml/15 min), respectively, for E control vs. E + NAC. NAC also markedly attenuated the alterations in lung mechanics after endotoxemia. Dynamic compliance at 2 h after endotoxemia was 44 +/- 6% of base line for E vs. 76 +/- 10% of base line for E + NAC. Resistance to airflow across the lung at 1 h postendotoxin was 811 +/- 280% of base line for E vs. 391 +/- 233% of base line for E + NAC. NAC substantially reduced the 1 h postendotoxin rise in lymph concentrations of thromboxane B2 (8.29 +/- 3.28 vs. 2.75 +/- 1.93 ng/ml for E vs. E + NAC) and 6-keto-prostaglandin-F1 alpha (0.91 +/- 0.27 vs. 0.23 +/- 0.12 ng/ml for E vs. E + NAC). In addition, in vitro studies were performed which revealed NAC to be a potent free radical scavenger in both biologic and nonbiologic free radical generating systems. NAC decreased phorbol-stimulated granulocyte aggregation in a concentration-dependent manner in vitro. Minimal effects were observed, however, upon leukocyte degranulation at the concentrations of NAC achieved during the in vivo tests. Thus, NAC significantly attenuated all monitored pathophysiologic changes in the endotoxin model of ARDS in sheep, possibly by its ability to scavenge toxic oxygen free radicals. A direct impairment of the ability of inflammatory cells to generate oxygen radicals cannot be ruled out.

Effects of platelet depletion on the unanesthetized sheep's pulmonary response to endotoxemia.

The effect of platelet depletion on the unanesthetized sheep's pulmonary response to endotoxemia was studied in eight unanesthetized sheep. Platelets were depleted with rabbit anti-sheep platelet antibodies (APA). Bolus injections of APA alone caused marked pulmonary hypertension (PPA increased from 21 +/- 2 to 62 +/- 5 cm H2O +/- SE) and alterations in lung mechanics (dynamic compliance of the lung [Cdyn] decreased to 38.5 +/- 4.6% and resistance to air flow across the lung [RL] increased to 705 +/- 162% +/- SE of control), which were attenuated by pretreatment with meclofenamate. It was possible to deplete platelets before endotoxemia through a slow continuous infusion of APA without altering base-line values of the measured variables. Platelet depletion did not significantly attenuate the alterations in pulmonary hemodynamics, lung mechanics, lung fluid and solute exchange, or the normal increase in lung lymph concentrations of thromboxane B2 or 6-keto-PGF1 alpha observed following endotoxemia in the sheep. We conclude that normal circulating platelet counts are not required for the full expression of the sheep's response to endotoxemia.

Murine model of ferric chloride-induced vena cava thrombosis: evidence for effect of potato carboxypeptidase inhibitor.

BACKGROUND/OBJECTIVE: Thrombin-activatable fibrinolysis inhibitor (TAFI) is a plasma carboxypeptidase that renders a fibrin-containing thrombus less sensitive to lysis. In the present study, we describe the development of a murine model of vena cava thrombosis and its use to characterize the antithrombotic activity of potato carboxypeptidase inhibitor (PCI) of TAFIa (activated TAFI) in mice. METHODS/RESULTS: Vena cava thrombosis was induced by various concentrations of FeCl(3) in C57BL/6 mice. A relatively mild stimulus (3.5% FeCl(3)) induced thrombosis that was consistent and sensitive to reference antithrombotic agents such as clopidogrel and heparin. Dose-response studies identified a PCI dose (5 mg kg(-1) bolus plus 5 mg kg(-1) h(-1), i.v.) that produced a maximum 45% decrease in vena cava thrombus mass as assessed by protein content (n = 8, P < 0.01 compared to vehicle) in the 3.5% FeCl(3)-induced model without exogenous tissue plasminogen activator administration. In contrast, PCI had no effect on 3.5% FeCl(3)-induced carotid artery thrombosis in mice. In a tail transection bleeding model, the 5 mg kg(-1) bolus plus 5 mg kg(-1) h(-1) dose of PCI increased tail-bleeding time up to 3.5 times control (n = 8, P < 0.05). The ex vivo activity of antithrombotic doses of PCI was also demonstrated by the enhanced lysis of whole blood clots formed in a thrombelastograph with the addition of a sub-threshold concentration of tPA. CONCLUSION: These studies provide evidence for a role of TAFIa in venous thrombosis in mice, and describe an optimized vena cava injury model appropriate for the evaluation of antithrombotic drugs and the characterization of novel therapeutic targets.

Effects of factor XI deficiency on ferric chloride-induced vena cava thrombosis in mice.

BACKGROUND: Increased plasma levels of coagulation factor (F) XI are a risk factor for venous thrombosis. OBJECTIVE: To further explore the relationship between FXI and venous thrombosis, we evaluated FXI-deficient and wild-type mice in a ferric chloride (FeCl(3))-induced vena cava thrombosis model. METHODS AND RESULTS: Thrombosis was induced by 3-min topical application of filter papers containing increasing concentrations of FeCl(3) and the thrombus was measured at 30 min. In contrast to wild-type mice, FXI-deficient mice failed to form a thrombus with 5% FeCl(3,) and were partially protected against 7.5% and 10% FeCl(3,) respectively. The protective effect was substantially stronger than a high dose of heparin (1,000 units kg(-1), i.v.), clopidogrel (30 mg kg(-1), p.o.) or argatroban (30 mg kg(-1), i.p.). These antithrombotic agents resulted in off-scale bleeding in a tail bleeding time assay, whereas the bleeding time of FXI-deficient mice was unchanged compared to wild-type mice. In addition to its known effect on the coagulation cascade, enhanced clot lysis was demonstrated in FXI-deficient mouse and human plasma compared to those supplemented with FXIa. CONCLUSION: Given the strong antithrombotic efficacy (possibly contributed by strong anticoagulant activity associated with increased fibrinolytic activity) and mild bleeding diathesis associated with FXI deficiency, therapeutic inhibition of FXI may be a reasonable therapeutic strategy to treat or prevent venous thrombosis.

Effects of factor IX or factor XI deficiency on ferric chloride-induced carotid artery occlusion in mice.

Factor XI (FXI) and factor IX (FIX) are zymogens of plasma serine proteases required for normal hemostasis. The purpose of this work was to evaluate FXI and FIX as potential therapeutic targets by means of a refined ferric chloride (FeCl(3))-induced arterial injury model in factor-deficient mice. Various concentrations of FeCl(3) were used to establish the arterial thrombosis model in C57BL/6 mice. Carotid artery blood flow was completely blocked within 10 min in C57BL/6 mice by application of 3.5% FeCl(3). In contrast, FXI- and FIX-deficient mice were fully protected from occlusion induced by 5% FeCl(3), and were partially protected against the effect of 7.5% FeCl(3). The protective effect was comparable to very high doses of heparin (1000 units kg(-1)) and substantially more effective than aspirin. While FXI and FIX deficiencies were indistinguishable in the carotid artery injury model, there was a marked difference in a tail-bleeding-time assay. FXI-deficient and wild-type mice have similar bleeding times, while FIX deficiency was associated with severely prolonged bleeding times (>5.8-fold increase, P < 0.01). Given the relatively mild bleeding diathesis associated with FXI deficiency, therapeutic inhibition of FXI may be a reasonable strategy for treating or preventing thrombus formation.

Myocardial calcium-independent phospholipase A2 activity during global ischemia in isolated rabbit hearts.

OBJECTIVES: To study calcium-independent phospholipase A2 activity during global ischemia in isolated rabbit hearts by measuring the hydrolysis of the endogenous choline phospholipids. METHODS: Langendorff perfused rabbit hearts were exposed to global ischemia for 15 or 60 min, or control perfusion for the same length of time. The hearts were then rapidly frozen in liquid nitrogen and lyophilized. Calcium-independent phospholipase A2 activity in the lyophilized tissue was studied by measuring accumulation of lysophospholipids resulting from hydrolysis of both the choline diacylphospholipid and the choline plasmalogen pool. RESULTS: The calcium-independent phospholipase A2 activity showed the same pH, temperature and calcium sensitivity in control and ischemic (15 min of ischemia) lyophilized myocardial tissue. Incubation of control and ischemic tissue showed no difference in the rate of accumulation of lysophospholipids when the ischemic tissue was obtained from hearts exposed to 15 min of ischemia (107 +/- 4 vs 111 +/- 7 nmol/g dry wt x min, ischemia versus control, mean +/- s.e.m., n = 8), but a significant decrease was noticed in tissue from hearts that had been exposed to 60 min of ischemia (31 +/- 9 vs 86 +/- 18 nmol/g dry wt x min, P < 0.05, n = 4). The decreased phospholipase A2 activity in tissue exposed to 60 min of ischemia was not due to enhanced metabolism of the lysophospholipids (84 +/- 15 vs 79 +/- 8 nmol/g dry wt x min, n = 4). The calcium-independent phospholipase A2 activity was considerably lower in fresh myocardial tissue compared with lyophilized tissue, but comparison of control and ischemic fresh tissue gave results comparable to those found using lyophilized tissue. The myocardial calcium-independent phospholipase A2 activity showed no plasmalogen selectivity in either control or ischemic myocardium. CONCLUSIONS: In isolated perfused rabbit hearts we found no evidence for activation of calcium-independent phospholipase A2 activity during global ischemia. With prolonged time of ischemia there was a significant decrease in calcium-independent phospholipase A2 activity.

Synthesis and pharmacological evaluation of 5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptane derivatives.

1 alpha,2 beta(5Z),3 beta(1E,3S),4 alpha,5 alpha,6 alpha]-7-[5,6-Epoxy-3- (3-cyclohexyl-3-hydroxy-3-methyl-1-propenyl)-7-oxabicyclo[2.2.1]-hept-2- yl]-5-heptenoic acid (31) and [1 alpha,2 beta(5Z),3 beta(1E,3S),4 alpha,5 alpha,6 alpha]-7-[5,6-epoxy-3-[3-hydroxy-5-(p-hydroxyphenyl)-1- pentenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (37) were found to be selective TxA2 antagonists at the platelet and pulmonary thromboxane receptors. An efficient stereospecific synthesis of these compounds and a series of structural analogues is described. Compounds 31 and 37 both inhibited the bronchoconstriction induced by arachidonic acid in the anesthetized guinea pig.

9,11-Epoxy-9-homo-14-oxaprosta-5-enoic acid derivatives. Novel inhibitors of fatty acid cyclooxygenase.

A novel bicyclic prostaglandin analogue, [1R-[l alpha,2 beta (5Z),3 beta,4 alpha]]-7-[3-[(hexyloxy)methyl]- 7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (1), and cogeners were found to be potent inhibitors of fatty acid cyclooxygenase. Compound 1 was the only stereoisomer out of eight possible structures that was active. Ether 1 was 20 times more potent than indomethacin (IND) in inhibiting arachidonic acid (AA) induced aggregation of human platelet-rich plasma. Compound 1 was also more potent than IND in several in vivo assays, AA-induced sudden death in the conscious mouse (2 times) and AA-induced bronchoconstriction in the anesthetized guinea pig (16-45 times).

9,11-Epoxy-9-homo-14-thiaprost-5-enoic acid derivatives: potent thromboxane A2 antagonists.

A novel bicyclic prostaglandin analogue, (1S)-[1 alpha,2 alpha(Z),3 alpha,4 alpha]-7-[3-[(hexylthio)methyl]-7- oxabicyclo [2.2.1]hept-2-yl]-5-heptenoic acid ((-)-10), and its cogeners were found to be potent antagonists at the TxA2 receptor. Compound (-)-10 was the only stereoisomer out of eight possible structures that was active. Thioether (-)-10 was 30-40-fold more potent than another TxA2 antagonist, BM 13.177, in inhibiting arachidonic acid (AA) induced aggregation of human platelet-rich plasma. Compound (-)-10 was effective (I50 = 0.5 +/- 0.4 microM) in inhibiting 9,11-azo-PGH2-induced (0.1 microgram/mL) contraction of guinea pig tracheal spirals. The bronchoconstriction in anesthetized guinea pigs induced by AA was also effectively antagonized by (-)-10 (1 mg/kg, iv); however, in this assay (-)-10 exhibited some direct agonist activity. Radioligand binding studies in washed (human) platelets revealed that (-)-10 is one of the most potent ligands for the PGH2/TxA2 receptor yet described (Kd = 1.6 +/- 0.4 nM).

7-Oxabicyclo[2.2.1]heptyl carboxylic acids as thromboxane A2 antagonists: aza omega-chain analogues.

A novel bicyclic prostaglandin analogue, [1S-[1 alpha, 2 alpha (Z), 3 alpha, 4 alpha]]-7-[3-[[[[(1- Oxoheptyl)amino]acetyl]amino]-methyl]-7-oxabicyclo[2.2.1]hept-2- yl]-5-heptenoic acid [-)-7) was found to be a potent and selective thromboxane A2 (TxA2) receptor antagonist. Unlike the related series of omega-chain allylic alcohols, amide 7 and its congeners were uniformly free of direct contractile activity in vitro (bovine coronary) and in vivo (anesthetized guinea pig). Amide 7 was effective in the inhibition of (a) arachidonic acid induced platelet aggregation of human platelet-rich plasma (I50 = 0.18 +/- 0.006 microM), (b) 11,9-epoxymethano-PGH2 induced platelet aggregation of human platelet-rich plasma (I50 = 0.24 microM), (c) 11,9-epoxymethano-PGH2 induced contraction of guinea pig trachea (Kb = 3.0 +/- 0.3 nM) or rat aorta (Kb = 8.8 +/- 1.1 nM), and (d) arachidonic acid induced bronchoconstriction in the anesthetized guinea pig (0.1-1.0 mg/kg iv). Amide 7 inhibited the binding of [5,6-3H2]-[1S- (1 alpha, 2 alpha (Z), 3 alpha, 4 alpha)]-7-[3-[[2-[(Phenyl- amino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5- heptenoic acid to human platelet membranes in a specific and saturable manner with a Kd = 49.6 +/- 1.4 nM.

9,11-epoxy-9-homoprosta-5-enoic acid analogues as thromboxane A2 receptor antagonists.

A novel bicyclic prostaglandin analogue, (1S)-[1 alpha, 2 alpha(Z),3 alpha(1E,3S*,4R*),4 alpha]-7-[3-(3-hydroxy-4-phenyl-1-pentenyl)-7- oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (4), was found to be a potent and selective thromboxane A2 (TxA2) receptor antagonist. Alcohol 4 was the only member in a series of allylic alcohols which did not display direct contractile activity in the rat stomach strip model. Alcohol 4 was effective in the inhibition of (a) arachidonic acid induced platelet aggregation of human platelet-rich plasma (I50 = 0.65 +/- 0.1 microM); (b) 11,9-epoxymethano-PGH2 induced contraction of guinea pig trachea (pA2 = 8.0 +/- 0.2) or rat aorta (pA2 = 8.1 +/- 0.2); and (c) arachidonic acid induced bronchoconstriction in the anesthetized guinea pig (1 mg/kg iv). A radioiodinated analogue of 4 bound in a specific and saturable manner to human platelet membranes with a Kd = 2.3 +/- 0.9 nM. Modification of the alpha-chain, in an attempt to minimize in vivo metabolism, resulted in TxA2 receptor antagonists of reduced in vitro potency.

Tissue uptake of 3H-methylprednisolone in acute myocardial ischemia.

The tissue uptake of 3H-methylprednisolone (3H-MP) was studied in anesthetized cats during acute myocardial ischemia 1 and 2 hours after injection of 3H-MP. There was a rapid uptake of 3H-MP by many tissues. Liver, kidney, and pancreas exhibited tissue/perfusion ratios of 3 to 7, heart, lungs, and intestine about 2, spleen, adrenal, and aorta 1 to 2, and skeletal muscle and omentum less than 1. Very similar tissue uptakes occurred in cats subjected to myocardial ischemia and sham myocardial ischemia at 1 and 2 hours. Plasma clearances of 3H-MP was not significantly altered either 1 or 2 hours after the onset of myocardial ischemia. Although ischemic myocardial tissue took up less than nonischemic myocardial tissue, this region accumulated significant amounts of 3H-MP. Myocardial tissue metabolized only about 15 to 20 per cent of the 3H-MP taken up after 2 hours. These data indicate that in acute myocardial ischemia, myocardial tissue takes up large amounts of exogenously administered glucocorticoid, most of which remains in the native form during the early phase of acute myocardial infarction.

Pharmacology of prostaglandins in the pulmonary microcirculation.

In unanesthetized sheep, arachidonate infusion increases lung microvascular pressure and augments pulmonary transvascular filtration without altering lung vascular permeability. Pulmonary vascular effects of arachidonate are caused by its conversion to highly active cyclooxygenase products, including PGH2 and, perhaps, thromboxane A2. Cyclooxygenase blockers inhibit pulmonary vascular actions of arachidonate. Most prostaglandins derived from PGH2 [i.e., PGB2, PGD2, PGE, and PGF2 alpha] are vasoconstrictors that exhibit potency intermediate between PGH2 and arachidonate. Vasoconstrictor prostaglandins cause increased flow of protein-poor lung lymph with no indication of altered lung vascular permeability. Vasodilator prostaglandins [i.e., PGE1, PGI2] cause changes in lung lymph formation that are not explained by microvascular hydrostatic-pressure effects alone. Whether lung lymph responses to PGE1 and PGI2 resulted from changes in perfused pulmonary vascular surface area or vascular permeability effects was tested with infusions during near-maximal pulmonary vascular recruitment with increase pressure. Maintaining mechanically increased left atrial pressure constant should minimize changes in lung lymph formation due to pulmonary vascular recruitment and derecruitment, and exaggerate lymph responses due to changes in vascular permeability. When infused during mechanically increased pressure, PGE1 and PGI2 produce similar pressure-mediated decreases in steady-state lung lymph flow, despite increases in pulmonary blood flow, heart rate, and respiratory rate with PGI2 and not with PGE1. In conclusion, PGE1 and PGI2 cause hemodynamic changes that can increase [PGI2] or decrease [PGE1] lung lymph flow. Prostaglandins do not directly alter lung vascular permeability.

Pulmonary hypertension and increased vasoreactivity caused by repeated indomethacin in sheep.

Six chronically catheterized awake sheep were given the cyclooxygenase inhibitor indomethacin (5 mg/kg) twice a day over a 3-wk period. Three sheep receiving vehicle alone served as controls. Pulmonary arterial, left atrial, and systemic arterial pressures, cardiac output, blood gases, and pH were measured biweekly. Pulmonary vasoreactivity to 12% O2 and an analogue of prostaglandin H2 (PGH2-A) was also assessed. As a percent of base line, indomethacin caused a doubling in pulmonary vascular resistance (3 wk = 190 +/- 26%, mean +/- SE) and a 50% increase in pulmonary arterial pressure (3 wk = 151 +/- 9%). Vasoreactivity to 12% O2 increased approximately fourfold during the 1st wk of treatment and then declined. Vasoreactivity to PGH2-A increased steadily, nearly doubling by 3 wk. Light-microscopic counts of peripheral lung biopsy tissue revealed marked sequestration of granulocytes. Morphometric techniques applied to lungs removed at autopsy and fixed with the pulmonary arteries distended with barium gelatin mixture showed a significant reduction in number of barium-filled peripheral arteries and reduction in their external diameter. We conclude that repeated administration of indomethacin alters pulmonary vasoreactivity and causes sustained pulmonary hypertension. Structural studies reveal peripheral lung inflammation and changes in the arterial circulation that are perhaps more consistent with maintained vasoconstriction than chronic pulmonary hypertension.

Effect of endotoxemia on hypoxic pulmonary vasoconstriction in unanesthetized sheep.

This study examined the effect of acute endotoxemia on hypoxic pulmonary vasoconstriction (HPV) in awake sheep. Thirteen sheep were chronically instrumented with Silastic catheters in the pulmonary artery, left atrium, jugular vein, and carotid artery; with a Swan-Ganz catheter in the main pulmonary artery; with a chronic lung lymph fistula; and with a tracheostomy. Base-line HPV was determined by measuring the change in pulmonary vascular resistance (PVR) while sheep breathed 12% O2 for 7 min. Concentrations of immunoreactive 6-keto-PGF1 alpha and thromboxane B2 (TXB2) were measured in lung lymph during the hypoxic challenge. Escherichia coli endotoxin (0.2-0.5 micrograms/kg) was infused intravenously. Four hours after endotoxemia, HPV was measured. In five sheep, meclofenamate was infused at 4.5 h after endotoxemia and HPV measured again. During the base-line hypoxic challenge, PVR increased by 36 +/- 9% (mean +/- SE). There was no significant change in lung lymph 6-keto-PGF1 alpha or TXB2 levels with hypoxia. Twelve of the 13 sheep showed a decrease in HPV 4 h after endotoxemia; the mean change in PVR with hypoxia was -8 +/- 5%, which was significantly (P less than 0.05) reduced compared with base-line HPV. The infusion of meclofenamate at 4.5 h after endotoxin did not restore HPV.

Role of thromboxane receptors in Forssman shock in guinea pigs.

Forssman shock is a bronchospastic reaction mounted in guinea pigs on intravenous administration of an antiserum obtained from rabbits immunized against sheep erythrocytes. The involvement of thromboxane receptors in Forssman shock was determined with SQ 30,741, which was characterized as a selective antagonist of these receptors in guinea pig airways in vitro and in vivo. A volume of antiserum producing consistent, sublethal bronchoconstriction was given either alone (control) or 3 min after SQ 30,741 (0.03, 0.3, or 1.0 mg/kg iv) to urethan-anesthetized guinea pigs. In controls, maximum reductions in dynamic compliance (-59 +/- 6%, P less than 0.01) and increases in airways resistance (383 +/- 97%, P less than 0.01) were detected 1 min after antiserum. Both responses were significantly inhibited by SQ 30,741, either partially at 0.03 mg/kg or completely at 0.3 mg/kg. An accompanying thrombocytopenia was not abated by SQ 30,741. In separate experiments, bronchospasm was reduced by aerosol administration of 0.1% SQ 30,741 and completely prevented by aspirin (10 mg/kg iv). When Forssman antiserum was injected in lethal quantities to other guinea pigs, SQ 30,741 (1 mg/kg iv) attentuated only the resistance component of bronchospasm and did not prevent death. These data demonstrate that thromboxane receptor stimulation is a pivotal step in the pulmonary manifestations of sublethal Forssman shock but is less crucial in more severe forms of the reaction.

Failure of aspirin to interfere with the cardioprotective effects of ifetroban.

The thromboxane receptor antagonist ifetroban ([1S-(1 alpha,2 alpha,3 alpha, 4 alpha)]-2-[[3-[4-[(pentylamino)carbonyl]-2-oxazolyl]- 7-oxabicyclo[2.2.1]hept-2-yl]methyl]benzenepropanoic acid) and aspirin were evaluated for direct and combined effects on myocardial infarct size in anesthetized ferrets subjected to coronary artery occlusion (90 min) and reperfusion (5 h). Aspirin (10 mg/kg) or vehicle was administered as an i.v. bolus dose at the 45th min of occlusion in an initial assessment of its cardioprotective potential in this species. In interaction studies, aspirin was injected i.v. 10 min prior to occlusion (10 mg/kg) and at the 45th min of ischemia (5 mg/kg) both with and without subsequent administration of ifetroban (0.3 mg/kg + 0.3 mg/kg per h) beginning at the 75th min of occlusion. Aspirin administration alone caused non-significant (P > 0.05) 5-7% reductions in tissue damage (19.8-21.8% of left ventricle) from that observed in vehicle-controls (20.4-22.9% of left ventricle). Ifetroban alone significantly (P < 0.05) reduced infarct size compared to vehicle treatment (13 +/- 1% vs. 23 +/- 2% of left ventricle), and this was not prevented by combination with aspirin (12 +/- 2% vs. 22 +/- 3% of left ventricle). In the absence and presence of aspirin, ifetroban reduced infarct size by 42% and 43%, respectively. Concurrently, thromboxane A2-generating capacity in blood (measured as thromboxane B2 in clotted serum) was decreased ca. 99% by aspirin treatment. Thus, virtually complete platelet cyclooxygenase inhibition by aspirin afforded no cardioprotective action in the ferret and, more importantly, this inhibition did not interfere with the myocardial salvage efficacy of ifetroban.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of thromboxane A2/prostaglandin endoperoxide receptors in aorta.

Thromboxane A2/prostaglandin endoperoxide receptor antagonists were studied in rat and guinea-pig aortas contracted with U-46619 (9,11-dideoxy-11 alpha,9 alpha-epoxymethanoprostaglandin F2 alpha) or 8-epi-prostaglandin F2 alpha. In rat aorta, the antagonists competitively inhibited contractions evoked by either agonist with a rank order of potency as follows: BMS-180291 ([1s-(exo,exo)]-2-[[3-[4-[(pentylamino) carbonyl]-2-oxazolyl]-7-oxabicyclo[2.2.1]hept-2-yl]methyl]-benz enepropanoic acid) > or = SQ 29,548 ([1s-[1 alpha,2 beta-(5z), 3 beta,4 alpha)]-7-[3-[[2-[(phenylamino)carbonyl]hydrozino] methyl]-7-oxobicyclo-[2.2.1]hept-2-yl]-5-heptanoic acid) > daltroban (4-[2-(4-chlorobenzenesulfonylamino) methyl]-benzene acetic acid) > or = SQ 30,741 ([1s-[1 beta,2 alpha(5z),3 alpha,4 beta]]-7-[3-[[[[(oxa)amino]acetyl] amino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl-5-heptanoic acid) = AA-2414 (2,4,5-trimethyl-3,6-dioxo-zeta-phenyl-1,4-cyclohexadien-1-heptano ic acid). In guinea-pig aorta, the antagonists competitively antagonized contractions elicited by either agonist with the following rank order of potency: SQ 29,548 = AA-2414 > or = SQ 30,741 > daltroban. Antagonism by BMS-180291 in guinea-pig aorta was not strictly competitive. These findings indicate that thromboxane A2/prostaglandin endoperoxide receptors in rat aortas are different from those in guinea pigs. Because the actions of both agonists were equivalently antagonized by each of the antagonists in both rat and guinea-pig aortas, the results do not support the hypothesis that U-46619 and 8-epi-prostaglandin F2 alpha elicit contractions via different receptor subtypes in the aorta.