Thromboxane inhibition during concurrent therapy with low-dose aspirin and over-the-counter naproxen sodium.

Aspirin is the dominant antiplatelet therapy for cardiovascular disease. Naproxen is frequently used in aspirin-treated patients and may influence the antiplatelet effect of aspirin. We evaluated the pharmacodynamic interaction (lower bound of the one-sided 95% CI for serum TxB2 inhibition < 95%) between 220 mg immediate-release naproxen sodium (once or twice daily) and 81 mg daily immediate release aspirin at various dosing intervals. There was no interaction during the first day of concurrent treatment. After 10 days, irrespective of the timing and dose of naproxen in relation to aspirin dosing, a pharmacodynamic interaction occurred which persisted after discontinuing naproxen. In the control group (aspirin alone), the lower bound for serum TxB2 inhibition was > 98% at all time points. The clinical relevance of these observations remains unknown and merits further investigation since over-the-counter naproxen is widely used to relieve pain by individuals taking low dose aspirin for cardioprotection. CLINICAL TRIAL REGISTRATION: NCT02229461.

A study of the pharmacokinetics and thromboxane inhibitory activity of a single intramuscular dose of carprofen as a means to establish its potential use as an analgesic drug in white rhinoceros.

The alleviation of pain and prevention of suffering are key aspects of animal welfare. Unfortunately, analgesic drugs are not available for all species. White rhinoceros (Ceratotherium simum), representing one of such species, which survive poaching attempts inflicted with severe facial injuries and gunshot wounds, nonetheless require analgesic support. To improve treatment conditions, this study explored the use of carprofen for the treatment of pain and inflammation in white rhinoceros. The pharmacokinetics of 1 mg/kg intramuscular carprofen was evaluated in six healthy white rhinoceros. The half-life of λz and mean residence time was 105.71 ± 15.67 and 155.01 ± 22.46 hr, respectively. The area under the curve and the maximum carprofen concentration were 904.61 ± 110.78 µg ml-1  hr-1 and 5.77 ± 0.63 µg/ml, respectively. Plasma TXB2 inhibition demonstrated anti-inflammatory properties and indicated that carprofen may be effective for a minimum of 48 hr in most animals. With its long half-life further indicating that a single dose could be effective for several days, we suggest that carprofen may be a useful drug for the treatment of white rhinoceros.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress.

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

[Antiplatelet agents]. / Agents antiplaquettaires et athérothrombose.

Atherothrombosis is a major global public health problem. Chronic atherosclerotic disease is often clinically silent and coexists across multiple vascular beds but, when complicated by thrombosis, it can result in an acute coronary syndrome, stroke, transient ischemic attack, and critical limb ischemia. Platelets play a role in the development of chronic atherosclerotic disease and are a key mediator of clinical events in atherothrombosis. Numerous clinical trials have tested antiplatelet agents for primary and secondary prevention, and several new antiplatelet drugs are under development. There is evidence of clear benefit of single and, in some cases, dual antiplatelet therapy in the prevention of recurrent cardiovascular and cerebrovascular complications. Dual antiplatelet therapy has emerged as the standard of care for acute coronary syndromes, with aspirin typically being used in combination with clopidogrel or one of the newer more potent ADP receptor antagonists (ticagrelor or prasugrel). Conversely, in chronic stable coronary disease, no benefit of dual antiplatelet therapy has yet been convincingly demonstrated Evidence supporting routine use of aspirin or any other antiplatelet agent for primary prevention is mixed, and this strategy should only be considered for individual high-risk patients in whom the thrombotic risk outweighs the risk of major bleeding complications.

A novel prostacyclin agonist protects against airway hyperresponsiveness and remodeling in mice.

Airway remodeling in bronchial asthma results from chronic, persistent airway inflammation. The effects of the reversal of airway remodeling by drug interventions remain to be elucidated. We investigated the effects of ONO-1301, a novel prostacyclin agonist with thromboxane inhibitory activity, on the prevention and reversibility of airway remodeling in an experimental chronic asthma model. Mice sensitized and challenged to ovalbumin (OVA) three times a week for 5 consecutive weeks were administered ONO-1301 or vehicle twice a day from the fourth week of OVA challenges. Twenty-four hours after the final OVA challenge, airway hyperresponsiveness (AHR) was assessed, and bronchoalveolar lavage was performed. Lung specimens were excised for staining to detect goblet-cell metaplasia, airway smooth muscle, and submucosal fibrosis. Mice administered ONO-1301 showed limited increases in AHR compared with mice administered the vehicle. The histological findings of airway remodeling were improved in ONO-1301-treated mice compared with vehicle-treated mice. Presumably, these therapeutic effects of ONO-1301 are attributable to the up-regulation of production of hepatocyte growth factor (HGF) in lung tissue, because the neutralization of HGF by antibodies prevented the effects of ONO-1301 on AHR and airway remodeling. Mice administered ONO-1301 showed similar levels of AHR and airway remodeling as mice administered montelukast, a cysteinyl-leukotriene-1 receptor antagonist, and lower levels were observed in mice administered dexamethasone. These data suggest that ONO-1301 exerts the effect of reversing airway remodeling, at least in part through an elevation of HGF in the lungs, and may be effective as an anti-remodeling drug in the treatment of asthma.

Rutin present in Alibertia edulis extract acts on human platelet aggregation through inhibition of cyclooxygenase/thromboxane.

Alibertia edulis leaf extract is commonly used in folk medicine, with rutin caffeic and vanillic acids being its major compounds. The Alibertia edulis leaf extract was investigated for its pharmacological effects via platelet aggregation, calcium mobilization, cyclic nucleotides levels, vasodilator-stimulated phosphoprotein Ser157 and Ser239 and protein kinase Cß2 phosphorylation, thromboxane B2, cyclooxygenases 1 and 2, docking and molecular dynamics. Alibertia edulis leaf extract significantly inhibited (100-1000 µg mL-1) platelet aggregation induced by different agonists. Arachidonic acid increased levels of calcium and thromboxane B2, phosphorylation of vasodilator-stimulated phosphoprotein Ser157 and Ser239, and protein kinase Cß, which were significantly reduced by Alibertia edulis leaf extract, rutin, and caffeic acid as well mixtures of rutin/caffeic acid. Cyclooxygenase 1 activity was inhibited for Alibertia edulis leaf extract, rutin and caffeic acid. These inhibitions were firsrtly explored by specific stabilization of rutin and caffeic acid compared to diclofenac at the catalytic site from docking score and free-energy dissociation profiles. Then, simulations detailed the rutin interactions close to the heme group and Tyr385, responsible for catalyzing the conversion of arachidonic acid to its products. Our results reveal the antiplatelet aggregation properties of Alibertia edulis leaf extract, rutin and caffeic acid providing pharmacological information about its origin from cyclooxygenase 1 inhibition and its downstream pathway.

Comparative study on the effect of aspirin, TP receptor antagonist and TxA2 synthase inhibitor on the vascular tone of human saphenous vein and internal mammary artery.

AIMS: Thromboxane (TxA2) is synthesized from arachidonic acid (AA) via thromboxane synthase (TxS) enzyme and induces vasoconstriction via TP receptor. Our aim is to compare the effects of aspirin, TxS inhibitor and TP receptor antagonist on vascular reactivity of bypass grafts (saphenous vein and internal mammary artery). MAIN METHODS: Using isolated organ bath, saphenous vein and internal mammary artery preparations were incubated with TP receptor antagonist, TxS inhibitor, aspirin, IP or EP4 receptor antagonist. Then prostaglandin (PG)E2, PGF2α, phenylephrine and AA were administered in concentration-dependent manner. The expression of prostanoid receptor and PGI2 synthase (PGIS) enzyme was determined by Western Blot. KEY FINDINGS: TP receptor antagonist inhibited the contraction induced by PGE2, PGF2α, and AA but not that induced by phenylephrine in both types of vessels. Aspirin increased phenylephrine-induced contraction only in internal mammary artery and decreased AA-induced contraction in saphenous vein. TxS inhibitor decreased both PGE2 and AA-induced contraction in both types of vessels. This decrease was reversed by co-incubation of TxS inhibitor and IP/EP4 receptor antagonists. The expressions of EP3 receptor and PGIS enzyme were greater in internal mammary artery compared to saphenous vein while IP and TP receptors expressed at similar levels. SIGNIFICANCE: TP receptor antagonist and TxS inhibitor are more effective to reduce contraction induced by different spasmogens in comparison to aspirin. Our results suggest that TP receptor antagonist and TxS inhibitor might have an advantage over aspirin due to their preventive effect on increased vascular reactivity observed in post-operative period of coronary artery bypass grafting.

A prostacyclin agonist with thromboxane inhibitory activity for airway allergic inflammation in mice.

BACKGROUND: ONO-1301 is a novel drug that acts as a prostacyclin agonist with thromboxane A(2) (TxA(2)) synthase inhibitory activity. We investigated the effect of ONO-1301 on development of airway allergic inflammation. METHODS: Mice sensitized and challenged to ovalbumin (OVA) received ONO-1301, OKY-046 (TxA(2) synthase inhibitor), beraprost, a prostacyclin receptor (IP) agonist, ONO-1301 plus CAY10449 (selective IP antagonist) or vehicle during the challenge period. Twenty-four hours after the OVA challenge, airway hyperresponsiveness (AHR) to methacholine was assessed and bronchoalveolar lavage was performed. Lung specimens were excised for goblet cell staining and analysis of lung dendritic cells (DCs). Bone marrow-derived dendritic cells (BMDCs) were generated, in the presence or absence of drugs, for analysis of DC function. RESULTS: Mice that received ONO-1301 showed significantly lower AHR, airway eosinophilia, T-helper type 2 cytokine levels, mucus production and lung DCs numbers than vehicle-treated mice. These effects of ONO-1301 were mostly reversed by CAY10449. BMDCs treated with ONO-1301 alone showed lower DC functions, such as expression of costimulatory factors or stimulation to spleen T cells. CONCLUSIONS: These data suggest that ONO-1301 may suppress AHR and airway allergic inflammation through modulation of DCs, mainly mediated through the IP receptor. This agent may be effective as an anti-inflammatory drug in the treatment of asthma.

Incomplete inhibition of thromboxane biosynthesis by acetylsalicylic acid: determinants and effect on cardiovascular risk.

BACKGROUND: Incomplete inhibition of platelet thromboxane generation, as measured by elevated urinary 11-dehydro thromboxane B(2) concentrations, has been associated with an increased risk of cardiovascular events. We aimed to determine the external validity of this association in aspirin-treated patients enrolled in the Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management and Avoidance (CHARISMA) trial and to determine whether there are any modifiable factors or interventions that lower urinary 11-dehydro thromboxane B(2) concentrations that could thereby reduce cardiovascular risk. METHODS AND RESULTS: Urinary 11-dehydro thromboxane B(2) concentrations were measured in 3261 aspirin-treated patients at least 1 month after they had been randomly assigned to placebo or clopidogrel. Baseline urinary 11-dehydro thromboxane B(2) concentrations in the highest quartile were associated with an increased risk of stroke, myocardial infarction, or cardiovascular death compared with the lowest quartile (adjusted hazard ratio 1.66, 95% CI 1.06 to 2.61, P=0.03). Increasing age, female sex, history of peripheral artery disease, current smoking, and oral hypoglycemic or angiotensin-converting enzyme inhibitor therapy were independently associated with higher urinary concentrations of 11-dehydro thromboxane B(2), whereas aspirin dose > or =150 mg/d, history of treatment with nonsteroidal antiinflammatory drugs, history of hypercholesterolemia, and statin treatment were associated with lower concentrations. Randomization to clopidogrel (versus placebo) did not reduce the hazard of cardiovascular events in patients in the highest quartile of urinary 11-dehydro thromboxane B(2) levels. CONCLUSIONS: In aspirin-treated patients, urinary concentrations of 11-dehydro thromboxane B(2) are an externally valid and potentially modifiable determinant of stroke, myocardial infarction, or cardiovascular death in patients at risk for atherothrombotic events.

Clinical aspects of platelet inhibitors and thrombus formation.

The platelet, once thought to be solely involved in clot formation, is now known to be a key mediator in various others processes such as inflammation, thrombosis, and atherosclerosis. Supported by the wealth of evidence from clinical trials demonstrating their benefits in patient outcomes, antiplatelet agents have become paramount in the prevention and management of various diseases involving the cardiovascular, cerebrovascular, and peripheral arterial systems. Despite being among the most widely used and studied classes of medical therapies, new discoveries regarding important clinical aspects and properties of these agents continue to be made. As our understanding of platelet biology expands, more effective and safer novel therapies continue to be developed. The use of more refined agents in conjunction with a better understanding of their effects will further the ability to provide more optimized care on an individual basis.

Selective thromboxane inhibition after vascular protectant AGI-1067: results of assessment of lipoprotein profiles (ALPS) biomarkers in vitro and in vivo substudy.

BACKGROUND: Oxidative stress play an important role triggering platelet/endothelial activation. AGI-1067 is a novel, phenolic antioxidant, and vascular protectant which dose-dependently inhibits PEA biomarkers in vitro. Whether treatment with AGI-1067 alters platelets in vivo is not known. We serially assessed release of established PEA biomarkers in subjects treated with AGI-1067 versus placebo in the frame of Assessment of Lipoprotein Profiles Randomized Trial (ALPS). METHODS: Healthy subjects (18-65 years) with multiple risk factors for coronary artery disease were randomized 1:1 to receive 300 mg AGI-1067 (n = 112) or matching placebo (n = 117) daily for 12 weeks. Anticoagulants, aspirin, NSAIDS, and COX inhibitors were not permitted in this study. Plasma samples were collected at baseline, and at week 12 after randomization. Platelet factor 4 (PF4), beta-thromboglobulin (betaTG), P-selectin, thromboxane (TxB2), and prostacyclin (6-keto-PGF1a) were measured by ELISA. RESULTS: Treatment with AGI-1067 was associated with a highly significant reduction of TxB2 release (P < 0.0001) when compared to the placebo. There were no differences in PF4, betaTG, P-selectin, and 6-keto-PGF1a between and within groups. AGI-1067 also inhibits TxB2 release from calcium ionophore (A23187)-stimulated human platelets with the IC50 equals 1 microM; but does not interfere with 6-keto-PGF1alpha release in either A23187-, or TXA2-stimulated human aortic endothelial cells. CONCLUSION: AGI-1067 selectively reduces TxB(2 )production from stimulated platelets, and diminishes plasma TxB2 levels in ALPS participants. These data support earlier in vitro, and pilot ex vivo experiments suggesting antiplatelet properties of AGI-1067. Lack of 6-keto-PGF1a down regulation may represent an attractive advantage of AGI-1067 over currently available antiplatelet regimens.

[Risk of gastrointestinal bleeding with aspirin and platelet antiaggregants]. / Riesgo de hemorragia digestiva con aspirina y antiagregantes plaquetarios.

Aspirin is widely used for the prevention of thrombotic cardiovascular disease. The effect of platelet antiaggregation is achieved with low doses of 75-325 mg/day. Due to COX-1 inhibition, associated gastrointestinal adverse effects can occur. Other drugs whose platelet antiaggregant effect is achieved through different mechanisms of action have been developed, such as clopidogrel and ticlopidine, which do not inhibit COX-1. The proportion of patients taking low-dose aspirin alone or in combination with other antiaggregants is high and consequently the use of these drugs should be optimized by reducing their gastrointestinal adverse effects to a minimum. Knowledge of the risk factors that increase the risk of gastrointestinal adverse effects with platelet antiaggregants, such as age, concomitant use of other drugs such as anticoagulants or non-steroidal anti-inflammatory drugs, a history of peptic ulcer -whether complicated or uncomplicated-, and Helicobacter pylori infection, would help to allow management to be individually tailored to each patient. The use of proton pump inhibitors and/or H. pylori eradication should allow a positive balance, even in patients with gastrointestinal risk factors.

L-arginine supplementation and thromboxane synthase inhibition increases cerebral blood flow in experimental cerebral malaria.

Cerebral malaria pathogenesis involves vascular dysfunction with low nitric oxide (NO) bioavailability, vasoconstriction and impaired vasodilation, leading to ischemia, tissue hypoxia and ultimately death. Cerebral blood flow (CBF) involves NO and other pathways, including arachidonic acid (AA)-derived metabolites. Here we show that mice with experimental cerebral malaria (ECM) by P. berghei ANKA showed marked decreases in CBF (as assessed by laser speckle contrast imaging - LSCI) and that administration of L-arginine supplementation (50 mg/kg) and/or of the thromboxane synthase inhibitor Ozagrel (100 mg/kg) induced immediate increases in CBF. L-arginine in combination with artesunate (32 mg/kg) induced immediate reversal of brain ischemia in the short-term (1 hour), but the effect subsided after 3 and 6 hours. Neither L-arginine nor Ozagrel reversed blood brain barrier breakdown. Mice with ECM showed brain levels of selected AA-derived metabolites with a vasoconstrictor profile, with increased levels of 8-isoprostanes, 20-HETE and 14,15-DHET, whereas mice infected with a non-ECM-inducing strain of P. berghei (NK65) showed a vasodilator profile, with normal levels of 20-HETE and 14,15-DHET and increased levels of PGE2. L-arginine is capable of partially reversing cerebral ischemia and AA metabolites may play a role in the cerebrovascular dysfunction in ECM.

Elevated cholesterol reduces acetylsalicylic acid-mediated platelet acetylation.

We describe the role of plasma and platelet cholesterol content in the ability of acetylsalicylic acid (ASA) to acetylate platelet proteins and inhibit platelet function. Platelet susceptibility to ASA was monitored in subjects differing in plasma total cholesterol and in suspensions of cholesterol-enriched or cholesterol-depleted platelets. Platelets from subjects with higher plasma cholesterol (>6 mmol/l) showed reduced platelet sensitivity to ASA (inhibition of platelet aggregation and thromboxane generation by 60% and 68% in 'lower-' vs. 32% and 56% in 'higher-cholesterol' donors; n=13 in each group; p=0.056 and p<0.04, respectively). [Acetyl-1-(14)C] incorporation to platelet proteins in subjects with higher plasma cholesterol was significantly reduced (11.0 vs. 14.6 nmol/g protein, p<0.0001) and correlated significantly with blood total cholesterolemia (R(K)=-0.430, p<0.003) and LDL-cholesterol (R(K)=-0.349, p<0.012), but not with platelet cholesterol content. In conclusion, elevated plasma cholesterol is an important determinant of ASA-induced acetylation of platelets and platelet diminished sensitivity to ASA. The molecular basis of such an association remains obscure, notwithstanding it may constitute a link between sub-optimal platelet response to aspirin and lipid metabolic disorders.

Losartan and ozagrel reverse retinal arteriolar constriction in non-obese diabetic mice.

OBJECTIVE: Reductions in retinal blood flow are observed early in diabetes. Venules may influence arteriolar constriction and flow; therefore, we hypothesized that diabetes would induce the constriction of arterioles that are in close proximity to venules, with the constriction mediated by thromboxane and angiotensin II. METHODS: Using nonobese diabetic (NOD) mice, retinal measurements were performed three weeks following the age at which glucose levels exceeded 200 mg/dL, with accompanying experiments on age-matched normoglycemic NOD mice. The measurements included retinal arteriolar diameters and red blood cell velocities and were repeated following an injection of the thromboxane synthase inhibitor, ozagrel. Mice were subdivided into equal groups and given drinking water with or without the angiotensin II receptor antagonist, losartan. RESULTS: Retinal arterioles were constricted in hyperglycemic mice, with a significant reduction in flow. However, not all arterioles were equally affected; the vasoconstriction was limited to arterioles that were in closer proximity to venules. The arteriolar vasoconstriction (mean arteriolar diameters = 51 +/- 1 vs. 61 +/- 1 microm in controls; p < 0.01) was eliminated by both ozagrel (61 +/- 2 microm) and losartan (63 +/- 2 microm). CONCLUSIONS: Venule-dependent arteriolar vasoconstriction in NOD mice is mediated by thromboxane and/or angiotensin II.

Pioglitazone and losartan modify hemodynamic and metabolic parameters and vascular prostanoids in fructose-overloaded rats.

This study analyzes the effects of losartan (AT1 blocker) and pioglitazone (insulin sensitizer), alone and in combination, in the fructose-overloaded rat, a model of metabolic syndrome. All treatments (nine weeks) reduced blood pressure and triglyceridemia and also restored the diminished release of vasodilator prostaglandins (prostacyclin in aorta and mesenteric vascular bed and prostaglandin E(2) in the latter). Pioglitazone, alone and in combination with losartan, reduced the release of the vasoconstrictor thromboxane in controls and fructose rats in both vascular preparations. In conclusion, although combination therapy and single treatments exerted similar effects, there may still be some advantage to the combined treatment.

The thromboxane antagonist, 13-azaprostanoic acid, inhibits arachidonic acid-induced Ca2+ release from isolated platelet membrane vesicles.

In the present study we investigated the ability of the arachidonic acid metabolites, prostaglandin H2 and thromboxane A2, to release Ca2+ from isolated platelet vesicles. The vesicles were prepared through modification of previously described procedures. 45Ca uptake and release were determined by Millipore filtration and isotope counting of the filter paper. Incubation of the vesicles (25 degrees C) with 50 microM CaCl2 (plus 45Ca) resulted in the accumulation of 13 nmol Ca2+ per mg of protein under steady-state conditions. Addition of arachidonic acid (25 microM) resulted in a 42% release of the accumulated Ca2+ and the production of 150 ng thromboxane B2/mg protein. Pretreatment of the vesicles with indomethacin (4 microM) completely inhibited arachidonic acid-induced Ca2+ release and reduced thromboxane B2 synthesis by 82%. Pretreatment of the vesicles with the specific thromboxane A2/prostaglandin H2 antagonist, 13-azaprostanoic acid (20 microM), also resulted in complete inhibition of Ca2+ release but no inhibition of thromboxane B2 production. Addition of prostaglandin H2 (0.3 microM) to the platelet vesicles produced a significant release of Ca2+ only in the presence of the adenylate cyclase inhibitor, 2',5'-dideoxyadenosine (100 microM). This Ca2+ release was totally blocked by 13-azaprostanoic acid (20 microM). The thromboxane synthetase inhibitor 9,11-azoprosta-5,13-dienoic acid (azo analog I, 3.6 microM), in the presence of 2',5'-dideoxyadenosine, only slightly inhibited Ca2+ release in response to added prostaglandin H2, even though thromboxane B2 production was blocked by 95%.

Specific binding of the thromboxane A2 antagonist 13-azaprostanoic acid to human platelet membranes.

In the present study we characterized the interaction between the thromboxane A2/prostaglandin H2 antagonist, trans-13-azaprostanoic acid (13-APA), and isolated human platelet membranes. In these studies, we developed a binding assay using trans [3H] 13-APA as the ligand. It was found that trans [3H] 13-APA specific binding was rapid, reversible, saturable and temperature dependent. Scatchard analysis of the binding data yielded a curvilinear plot which indicated the existence of two classes of binding sites: a high-affinity binding site with an estimated dissociation constant (Kd) of 100 nM; and a low-affinity binding site with an estimated Kd of 3.5 microM. At saturation, approximately 1 pmol/mg protein of [3H] 13-APA was bound to the high affinity site. In order to further characterize the nature of the [3H] 13-APA binding site, we evaluated competitive binding by cis 13-APA, cis 15-APA, prostaglandin F2 alpha, U46619, 6-ketoprostaglandin F1 alpha and thromboxane B2. It was found that the [3H] 13-APA binding site was stereospecific and structurally specific. Thus, the cis isomer of 13-APA exhibited substantially reduced affinity for binding. Furthermore, the prostaglandin derivatives, thromboxane B2 and 6-ketoprostaglandin F1 alpha, which do not possess biological activity, also did not compete for [3H] 13-APA binding. On the other hand, U46619 which acts as a thromboxane A2/prostaglandin H2 mimetic, and prostaglandin F2 alpha which acts as a thromboxane A2/prostaglandin H2 antagonist, both effectively competed for [3H] 13-APA binding. These findings indicate that trans 13-APA binds to a specific site on the platelet membrane which presumably represents the thromboxane A2/prostaglandin H2 receptor.

Venular constriction of submucosal arterioles induced by dextran sodium sulfate.

BACKGROUND: Leukocyte and platelet adherence in postcapillary venules has been speculated to induce constriction of closely paired arterioles. This mechanism was investigated in the current study, in a model of intestinal inflammation induced by dextran sodium sulfate (DSS; 5,000 molecular weight). METHODS: Closely paired, parallel arterioles and venules in the submucosa of the mouse intestine were observed using fluorescent intravital microscopy. Arterioles in control mice were compared to arterioles in mice given 5% DSS in drinking water for 11 days. RESULTS: DSS induced an inflammatory response in which fluorescently labeled leukocytes and platelets were observed adhering to venules. Arterioles constricted and flow decreased significantly when the arterioles were paired with venules having adherent leukocytes and platelets, although the decreases in flow and diameter appeared to be more dependent on platelet than leukocyte adherence. No significant constriction was observed in arterioles paired with venules having minimal platelet adherence. Inhibition of thromboxane with 100 mg/kg ozagrel induced a significant dilation of arterioles in DSS mice that was absent in control mice. CONCLUSION: The results are consistent with a proposed mechanism in which thromboxane constricts submucosal arterioles when the arterioles are closely paired with platelet-bearing venules in DSS-induced inflammation.