Demonstration of Ac-Arg-Gly-Asp-Ser-NH2 as an Antiaggregatory Agent in the Dog by Intracoronary Administration

This study compared the anti-platelet effect of Ac-RGDS-NH2 which is a peptide fragment from fibrinogen to Ac-RGES-NH2 in which the aspartic acid (D) of Ac-RGDS-NH2 has been replaced by glutamic acid (E). When Ac-RGDS-NH2 was infused intracoronary at concentrations of 100–400 mM, acute platelet dependent thrombus formation in the dog coronary artery was inhibited. However, infusion of Ac-RGES-NH2 intracoronary at similar concentrations to Ac-RGDS-NH2 failed to inhibit platelet dependent thrombus formation in the dog. Ac-RGDS-NH2 and Ac-RGES-NH2 were also tested for their ability to inhibit collagen-induced platelet aggregation in vitro. Ac-RGDS-NH2 elicited concentration-dependent inhibition of collagen-induced aggregation with no effect of Ac-RGES-NHz otr collagen-induced platelet aggregation. Thus, Ac-RGDS-NH2 is an effective antiplatelet agent after intracoronary administration in the dog and also inhibits collagen-induced platelet aggregation in vitro. Ac-RGDS-NH2 is a specific inhibitor of platelet aggregation as replacement of the aspartic acid in Ac-RGDS-NH2 with glutamic acid results in complete loss of biological activity.

Comparing the antithrombotic efficacy of a humanized anti-factor IX(a) monoclonal antibody (SB 249417) to the low molecular weight heparin enoxaparin in a rat model of arterial thrombosis

A humanized inhibitory anti-factor IX(a) antibody (SB 249417) has been compared to enoxaparin (Lovenox) in a rat model of arterial thrombosis. Pretreatment of rats with either SB 249417 (3.0 mg/kg, i. v.) or enoxaparin (30.0 mg/kg, i.v. or s.c.) resulted in comparable and significant reductions in thrombus formation. However, the efficacious dose of enoxaparin resulted in >30-fold increase in the aPTT over baseline, while the efficacious dose of SB 249417 prolonged the aPTT by only approximately 3-fold. Additionally, pretreatment with SB 249417 resulted in sustained blood flow and arterial patency throughout the experiment in >80% of rats treated. In contrast, <30% of rats pretreated with enoxaparin remained patent throughout the experiment. The data in this report indicate that the selective inhibition of factor IX(a) with the monoclonal antibody SB 249417 produces a superior antithrombotic profile to that of the low molecular weight heparin enoxaparin.

In vitro and in vivo characterization of intrinsic sympathomimetic activity in normal and heart failure rats

Clinical studies conducted with carvedilol suggest that beta-adrenoceptor antagonism is an effective therapeutic approach to the treatment of heart failure. However, many beta-adrenoceptor antagonists are weak partial agonists and possess significant intrinsic sympathomimetic activity (ISA), which may be problematic in the treatment of heart failure. In the present study, the ISAs of bucindolol, xamoterol, bisoprolol, and carvedilol were evaluated and compared in normal rats [Sprague-Dawley (SD)], in rats with confirmed heart failure [spontaneously hypertensive heart failure (SHHF)], and in isolated neonatal rat cardiomyocytes. At equieffective beta1-adrenolytic doses, the administration of xamoterol and bucindolol produced a prolonged, equieffective, and dose-related increase in heart rate in both pithed SD rats (ED50 = 5 and 40 microgram/kg, respectively) and SHHF rats (ED50 = 6 and 30 microgram/kg, respectively). The maximum effect of both compounds in SHHF rats was approximately 50% of that observed in SD rats. In contrast, carvedilol and bisoprolol had no significant effect on resting heart rate in the pithed SD or SHHF rat. The maximum increase in heart rate elicited by xamoterol and bucindolol was inhibited by treatment with propranolol, carvedilol, and betaxolol (beta1-adrenoceptor antagonist) but not by ICI 118551 (beta2-adrenoceptor antagonist) in neonatal rat. When the beta-adrenoceptor-mediated cAMP response was examined in cardiomyocytes, an identical partial agonist/antagonist response profile was observed for all compounds, demonstrating a strong correlation with the in vivo results. In contrast, GTP-sensitive ligand binding and tissue adenylate cyclase activity were not sensitive methods for detecting beta-adrenoceptor partial agonist activity in the heart. In summary, xamoterol and bucindolol, but not carvedilol and bisoprolol, exhibited direct beta1-adrenoceptor-mediated ISA in normal and heart failure rats.

Plasma- and cerebrospinal fluid-immunoreactive endothelin-1: effects of nonpeptide endothelin receptor antagonists with diverse affinity profiles for endothelin-A and endothelin-B receptors

Some endothelin (ET) receptor antagonists have been reported to elevate plasma immunoreactive endothelin-1 (irET-1). However, there is no information regarding the effects of ET receptor antagonists on cerebrospinal fluid (CSF) levels. To better understand the regulation of circulating and CSF ET-1, the effects of several nonpeptide antagonists with high, intermediate, or low affinity at the ETB receptor, as well as the potent ETB selective agonist sarafotoxin 6c (S6c), were characterized and compared. The effects of SB209670 (Ki ETA = 0.2 nM; Ki ETB = 12 nM), SB217242 (Ki ETA = 1.1 nM; Ki ETB = 111 nM), SB234551 (Ki ETA = 0.1 nM; Ki ETB = 500 nM), SB247083 (Ki ETA = 0.4 nM; Ki ETB = 467 nM), and S6c (Ki ETA = 950 nM; Ki ETB = 1 nM) on plasma irET-1 were determined by ELISA in the anesthetized dog after i.v. administration. Systemic administration of equivalent doses of the nonpeptide ET receptor antagonists produced dose-related elevations in plasma irET-1 which were correlated (p = 0.019) with affinity at the ETB receptor. There was no significant correlation with affinity at the ETA receptor. In addition, the plasma irET-1 and ET antagonist concentrations were linearly correlated (r = 0.98) throughout the time course after antagonist administration. There was no evidence of densensitization after three bolus administrations performed at 2-h intervals (SB209670, 1 and 3 mg/kg i.v.). Elevations in plasma irET-1 (four- to fivefold) were also observed after systemic administration of S6c (1 nmol/kg i.v.). The administration of L-NAME (200 micrograms/kg/min for 30 min), an inhibitor of nitric oxide (NO) synthase, increased blood pressure (33%) but did not alter plasma irET-1. In contrast, systemic administration of the ET receptor antagonists had little or no effect on the on irET-1 in the CSF. However, intracerebroventricular (i.c.v.) administration of SB209670 produced a dose-related (3-100 micrograms) increase in cisternal CSF levels of irET-1 without altering plasma irET-1. Systemic administration of ETB receptor antagonists and agonists rapidly increased plasma irET-1. These ETB receptor antagonist effects correlate linearly with affinity at the cloned human ETB receptor, do not exhibit desensitization, and do not appear to reflect inhibition of ETB-mediated NO production. The endothelial ETB receptor may represent a high-capacity storage/clearance site for circulating ET-1. ET receptor antagonists may also act extravascularly/abluminally to increase irET-1 in the CNS.

Angiotensin type 1 receptors mediate smooth muscle proliferation and endothelin biosynthesis in rat vascular smooth muscle

Angiotensin II (AII) has the potential to promote vascular smooth muscle (VSM) hypertrophy and hyperplasia; however, the mechanisms involved in AII stimulation of VSM growth are not fully understood. The AII receptor subtypes in VSM responsible for several biological events leading to cell proliferation have been evaluated. All-induced mitogenesis in explants of rat VSM cells was antagonized by the angiotensin type 1 (AT1)-selective receptor antagonists SK&F 108566 (IC50 = 5.3 +/- 0.96 nM) and DuP 753 (IC50 = 3.5 +/- 0.97 nM), but not by AT2 receptor antagonists. AII-stimulated endothelin (ET)-1 gene expression was antagonized by SK&F 108566 (50% at 1 microM), but not by selective AT2 receptor antagonists. Similarly, AII stimulated the release of immunoreactive ET (irET) from cultured VSM cells that was antagonized by 1 microM SK&F 108566 (72%) and DuP 753 (66%), but not by AT2 receptor antagonists. AII and growth factors that stimulated the release of irET down-regulated the number of ET receptor binding sites. AII (1-100 nM) markedly (6- to 10-fold) stimulated mitogen-activated protein kinase, an enzyme believed to be involved in the pathway for cell proliferation, and this stimulation was blocked (50-75%) by SK&F 108566 (1 nM-1 microM). Phosphoramidon (50 microM) inhibited (60%) both AII-induced irET release and cell proliferation. These data demonstrate that AII-mediated VSM growth is via AT1 receptors, and suggest that AII-induced ET production may contribute to the proliferative response in these cells.

The in vitro pharmacological profile of SK&F 106760, a novel GPIIB/IIIA antagonist

The properties of SK&F 106760 [N alpha-acetyl-cyclo(S,S)-cysteinyl-N alpha-methyl-arginyl-glycyl-aspartyl-penicillamine-amide] as a GPIIb/IIIa antagonist have been studied in vitro and compared with those of the parent molecule, Ac-RGDS-NH2. Ac-RGDS-NH2 inhibited biotinylated fibrinogen binding to purified human GPIIb/IIIa immobilized on plastic microtitre plates with a Ki of 530 +/- 73 nM. In canine platelet rich plasma Ac-RGDS-NH2 produced a concentration related inhibition of adenosine diphosphate-induced platelet aggregation following preincubation for 3 min with an IC50 of 91 +/- 1 microM. However, incubation in platelet rich plasma for 3 hr abolished the activity of Ac-RGDS-NH2. SK&F 106760 inhibited biotinylated fibrinogen binding to purified human GPIIb/IIIa immobilized on plastic microtitre plates with a Ki of 477 +/- 57 pM. SK&F 106760 inhibited adenosine diphosphate-induced platelet aggregation in human platelet rich plasma with an IC50 of 230 +/- 60 nM but did not inhibit the von Willebrand Factor receptor (GPIb/IX)-mediated platelet agglutination produced by ristocetin. In canine platelet rich plasma SK&F 106760 inhibited aggregation produced by adenosine diphosphate, collagen and epinephrine/U-46619 with IC50 values of 355 +/- 35, 260 +/- 20, and 490 +/- 90 nM, respectively and in gel filtered platelets inhibited thrombin-mediated aggregation with an IC50 of 188 +/- 10 nM. Preincubation of SK&F 106760 in platelet rich plasma for three hours had no significant effect on its ability to inhibit adenosine diphosphate-induced platelet aggregation. SK&F 106760 produced insurmountable inhibition of adenosine diphosphate-induced platelet aggregation in the presence of constant fibrinogen concentrations, but produced competitive inhibition of the concentration-response curve to fibrinogen in adenosine diphosphate-activated platelets with a Kb of 8.0 +/- 1.0 nM. Thus, SK&F 106760 is a potent, stable competitive GPIIb/IIIa antagonist with no detectable activity at the von Willebrand Factor receptor (GPIb/IX).

A role for endogenous endothelin-1 in neointimal formation after rat carotid artery balloon angioplasty. Protective effects of the novel nonpeptide endothelin receptor antagonist SB 209670

The observation that levels of the mitogenic peptide endothelin-1 are elevated in the human coronary sinus after percutaneous transluminal coronary angioplasty (PTCA) has implicated endothelin-1 in the etiology of vascular restenosis. The present study examined this hypothesis in both an in vitro and an in vivo rat model of neointimal formation by using the novel nonpeptide endothelin receptor antagonist SB 209670. In vitro, endothelin-1 (1 nmol/L) induced a ninefold increase in rat aortic vascular smooth muscle [3H]thymidine incorporation. This endothelin A receptor-mediated effect was completely inhibited by SB 209670 (IC50, 6.2 +/- 2.2 nmol/L). In vivo, acute intra-arterial administration of exogenous endothelin-1 (5 to 500 pmol/kg over a 30-minute period immediately after angioplasty) dose-dependently augmented the degree of neointimal formation (by up to 150% when assessed 14 days after surgery). This response was evident as early as 7 days after angioplasty. Hemodynamic studies indicated that this action was unrelated to a systemic pressor action of the peptide. Administration of SB 209670 (2.5 mg/kg IP, twice a day for 3 days before and for 2 weeks after surgery) reduced neointimal formation by approximately 50% relative to control animals. Thus, the data indicate for the first time that (1) endothelin-1 promotes neointimal formation in vivo and (2) endogenous endothelin-1 is involved in the pathogenesis of angioplasty-induced lesion formation in the rat. Endothelin receptor antagonists such as SB 209670 may therefore serve as useful adjuncts to PTCA, attenuating the degree of vascular restenosis observed after vascular wall injury.

Endothelin levels increase in rat focal and global ischemia

Endothelin-1, a peptide exhibiting extremely potent cerebral vasoactive properties, is elevated in the cerebrospinal fluid after hemorrhagic stroke and implicated in cerebral vasospasm. The purpose of this study was to determine changes in endothelin in ischemic rat brain by assaying endothelin tissue and extracellular levels. Immunoreactive endothelin levels in ischemic brain tissue following permanent or transient focal ischemia produced by middle cerebral artery occlusion was determined. In addition, endothelin levels were assayed in striatal extracellular fluid collected by microdialysis before, during, and after global ischemia produced by two-vessel occlusion combined with hypotension. Twenty-four hours after the onset of permanent middle cerebral artery occlusion, the ischemic cortex level (0.58 +/- 0.27 fmol/mg protein) of immunoreactive endothelin was significantly (p < 0.05) increased, by 100%, over that in the nonischemic cortex (0.29 +/- 0.13 fmol/mg protein). Transient artery occlusion for 80 min with reperfusion for 24 h also resulted in a similar significant (p < 0.05) increase, 78%, in immunoreactive endothelin in the ischemic zone. Global forebrain ischemia significantly (p < 0.05) increased the level of immunoreactive endothelin collected in striatal microdialysis perfusate, from a basal level of 14.6 +/- 6.7 to 26.5 +/- 7.7 and 26.2 +/- 7.4 amol/microliters (i.e. 82 and 79%). These changes reflect the relative picomolar extracellular concentration increases during ischemia and following reperfusion, respectively. This is the first demonstration of elevated levels of endothelin in focal ischemic tissue and in the extracellular fluid in global ischemia and suggests a role of the peptide in ischemic and postischemic derangements of cerebral vascular function and tissue injury.

Human laminin produces human platelet aggregation in vitro

The effects of laminin isoforms on platelet aggregation were compared and characterized in platelet rich plasma (PRP) obtained from 26 healthy human volunteers. In approximately 38% of the individuals tested, human laminin produced a biphasic platelet aggregation response. Human laminin produced only a primary phase in the remaining "non-responsive" individuals. Mouse laminin, rat laminin and human merosin did not cause platelet aggregation in any of the volunteers. The biphasic platelet aggregation response caused by human laminin was concentration-dependent (0.3-30 nM) and was consistently observed upon repeated testing of "responsive" individuals. The secondary phase of aggregation produced by human laminin in "responsive" individuals was abolished by aspirin, SQ 29,548, a selective thromboxane antagonist, and SK&F 106760, an RGD-derived platelet fibrinogen receptor (GPIIb/IIIa) antagonist. Also, the secondary phase of aggregation was not observed in washed platelets. Both the primary and secondary platelet responses produced by human laminin were abolished by a VLA-6 (alpha 6 beta 1) monoclonal antibody, but not by the YIGSR pentapeptide. In conclusion, human laminin causes thromboxane-dependent platelet aggregation, in vitro, in a significant population of human volunteers. The aggregation response was dependent upon the interaction of human laminin with platelet VLA-6 (alpha 6 beta 1). These novel results suggest that in some individuals laminin may play an important role in hemostasis and thrombogenesis.

Neuron-specific enolase increases in cerebral and systemic circulation following focal ischemia

Neuron-specific enolase (NSE) is an isoform of the glycolytic enzyme, enolase, and is found in neurons and neuroendocrine cells. We evaluated cerebral immunohistologic and plasma changes in NSE in rats from 2 h to 15 days following permanent or transient middle cerebral artery occlusion (MCAO). At 1-2 days post-MCAO, loss of NSE immunofluorescence from within neurons to the extracellular space was observed in the infarcted areas of all MCAO animals. NSE also was identified intravascularly throughout the brain following MCAO. NSE in plasma was determined by a specific radioimmunoassay. Plasma NSE following permanent or transient MCAO was increased significantly from that observed in controls (2.8 +/- 0.3 ng/ml) beginning at 2 h and persisting for 2.5 days post-MCAO (maximum levels of 8.8 +/- 0.9 to 9.6 +/- 0.5 ng/ml after 6-12 h; P < 0.05, n = 4-9). Quantified contralateral forelimb and hindlimb neurological deficits in these animals were significant and persisted for at least 15 days following MCAO but were not observed following sham surgery. These data suggest that MCAO-induced cortical infarction and neurological dysfunction is associated with neuronal depletion and vascular redistribution of brain NSE resulting in a measurable increase in plasma NSE. Such diffusion of NSE into the cerebral vasculature and systemic circulation from ischemic tissue can be expected to serve as a marker for the incidence of cerebral damage in acute and chronic ischemic brain infarcts.

Oxyhemoglobin stimulation of endothelin production in cultured endothelial cells

Oxyhemoglobin and endothelin have both been linked to the development of the severe and sustained cerebral vasospasm associated with subarachnoid hemorrhage. The effects of oxyhemoglobin on endothelin biosynthesis in cultured endothelial cells were evaluated. Oxyhemoglobin (0.01 to 100 microM) produced concentration-dependent increases in immunoreactive endothelin levels in bovine pulmonary artery endothelial cell-conditioned medium. The median effective concentration for oxyhemoglobin-induced increases in immunoreactive endothelin levels was approximately 0.5 microM, and the maximum stimulation of immunoreactive endothelin levels was approximately 5.5-fold over basal conditions. In addition to directly stimulating basal production of immunoreactive endothelin, oxyhemoglobin significantly augmented immunoreactive endothelin production following platelet-mediated stimulation of endothelin production. An l-arginine analog inhibitor of nitric oxide synthase, L-NG-monomethyl arginine (L-NMMA, 200 microM), did not significantly affect basal immunoreactive endothelin levels. However, L-NMMA significantly augmented platelet-induced immunoreactive endothelin production. Methylene blue (10 microM), an inhibitor of soluble guanylate cyclase, did not significantly affect basal immunoreactive endothelin levels, nor did it significantly affect the platelet-mediated stimulation of immunoreactive endothelin production in cultured endothelial cells. The present results reveal that oxyhemoglobin can directly stimulate endothelin biosynthesis in cultured endothelial cells. This newly identified property of oxyhemoglobin suggests a potential mechanism for the sustained and severe cerebral vasospasm associated with subarachnoid hemorrhage.

Platelets stimulate expression of endothelin mRNA and endothelin biosynthesis in cultured endothelial cells

Modulation of the biosynthesis of the vasoconstrictor peptide endothelin was studied in cultured endothelial cells. Immunoreactive endothelin (irET) levels were significantly elevated in conditioned medium from bovine pulmonary artery endothelial (BPAE) or human umbilical vein endothelial cells when coincubated with washed human platelets. Platelets (approximately 200,000 cells/microliters) enhanced irET levels approximately 250% over basal levels. Stimulation of irET levels in BPAE cell-conditioned medium by platelets was time and platelet number dependent. Platelets, as well as thrombin and transforming growth factor-beta 1, stimulated the expression of preproendothelin-1 mRNA in a time-dependent manner. Coincubation of low doses of thrombin (0.1 unit/ml) and subthreshold concentrations of platelets with BPAE cells resulted in a further enhancement of irET levels in conditioned medium. Platelet-mediated stimulation of irET production was not significantly affected by indomethacin (1 microM) or the platelet-activating factor receptor antagonist WEB 2086 (1 microM); however, coincubation of endotoxin (100 ng/ml) with platelets and BPAE cells resulted in significantly higher levels of irET. Whether direct contact or adhesion between platelets and endothelial cells is necessary for stimulating irET release was studied by separating platelets from BPAE cells with a 0.4 microns permeable membrane. Under these conditions, platelets still produced significant elevations (approximately 190% over basal levels) in irET levels in BPAE cell-conditioned medium. In addition, platelet-free buffer from agonist-induced platelet aggregation also significantly enhanced irET production (200% over basal values). These data indicate that a platelet-derived regulatory factor can induce the biosynthesis of endothelin from cultured endothelial cells and also suggest that platelets might play a role in vasomotor regulation via a novel intercellular interaction with the endothelium.

Effect of selective endoperoxide/thromboxane A2 receptor antagonism with sulotroban on tPA-induced thrombolysis in a rabbit model of femoral arterial thrombosis

The thrombolytic efficacy of recombinant tissue-type plasminogen activator (tPA) in the presence and absence of the selective endoperoxide/thromboxane A2 (TXA2) receptor antagonist, sulotroban (BM 13.177, SK&F 95587) was studied in a model of femoral artery thrombosis in the anesthetized rabbit. The thrombus was formed by injection of thrombin, CaCl2 and whole blood into an isolated segment of the femoral artery. After 30 min of stable thrombotic occlusion of the femoral artery, tPA was infused IV for 90 min at doses of 5.0, 7.5 and 10.0 micrograms/kg/min. In other experiments, sulotroban was administered as a bolus dose of 1 mg/kg/IV, followed by a constant infusion of 1 mg/kg/hr concurrent with tPA infusion. Sulotroban had no effect on the incidence of tPA-induced reperfusion at any dose studied or on residual clot weight. However, at a tPA dose of 10 micrograms/kg/min, IV lysis time was reduced in sulotroban treated animals from 65 min to 29 min (P less than 0.05), and the magnitude of femoral artery blood flow achieved as a result of tPA-induced reperfusion was greater in sulotroban-treated animals. These data suggest that adjunctive therapy with a selective endoperoxide/TXA2 antagonist improves the response to tPA when tPA is administered at a maximal or near maximally effective pharmacological dose.

Combination of the thromboxane receptor antagonist, sulotroban (BM 13.177; SK&F 95587), with streptokinase: demonstration of thrombolytic synergy

We examined the ability of the prostaglandin endoperoxide/thromboxane A2 antagonist, sulotroban (BM 13.177; SK&F 95587) to enhance the thrombolytic efficacy of a minimally effective thrombolytic dose of streptokinase. A critical stenosis sufficient to just abolish the hyperemic response to a 20-sec total occlusion was placed on the left circumflex coronary artery of anesthetized open chest dogs using an adjustable screw occluder clamp. Thrombi were formed by applying a 150 microA anodal current to a wire placed within the lumen of the left circumflex just proximal to the screw occluder clamp. After thrombus formation, animals were given either streptokinase (20,000 I.U. bolus + 2,000 I.U./min x 180 min, N = 10), streptokinase + sulotroban (5 mg/kg bolus + 5 mg/kg/hr, N = 10), streptokinase + heparin (300 I.U./kg bolus + 100 I.U./kg/hr, N = 9) or streptokinase + heparin + sulotroban (N = 9). Plasma thromboxane A2 level (as measured by the metabolite, thromboxane B2) was not significantly reduced by any treatment, whereas the dose of sulotroban used completely abolished U46619-induced ex vivo platelet aggregation. Of 10 animals receiving streptokinase alone, only 1 reperfused at 55 min after the start of the streptokinase infusion. Conversely, 9 of 10 animals receiving streptokinase + sulotroban reperfused at 79.4 +/- 10.5 min poststreptokinase (P less than .05). When animals were treated with heparin before streptokinase administration, 8 of 9 animals receiving the streptokinase + heparin combination reperfused in an average of 66.8 +/- 8.6 min after the start of streptokinase infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of Ac-Arg-Gly-Asp-Ser-NH2 as an antiaggregatory agent in the dog by intracoronary administration

This study compared the anti-platelet effect of Ac-RGDS-NH2 which is a peptide fragment from fibrinogen to Ac-RGES-NH2 in which the aspartic acid (D) of Ac-RGDS-NH2 has been replaced by glutamic acid (E). When Ac-RGDS-NH2 was infused intracoronary at concentrations of 100-400 mM, acute platelet-dependent thrombus formation in the dog coronary artery was inhibited. However, infusion of Ac-RGES-NH2 intracoronary at similar concentrations to Ac-RGDS-NH2 failed to inhibit platelet-dependent thrombus formation in the dog. Ac-RGDS-NH2 and Ac-RGES-NH2 were also tested for their ability to inhibit collagen-induced platelet aggregation in vitro. Ac-RGDS-NH2 elicited concentration-dependent inhibition of collagen-induced aggregation with no effect of Ac-RGES-NH2 on collagen-induced platelet aggregation. Thus, Ac-RGDS-NH2 is an effective antiplatelet agent after intracoronary administration in the dog and also inhibits collagen-induced platelet aggregation in vitro. Ac-RGDS-NH2 is a specific inhibitor of platelet aggregation as replacement of the aspartic acid in Ac-RGDS-NH2 with glutamic acid results in complete loss of biological activity.

Effect of thromboxane synthase inhibition on the thrombolytic action of tissue-type plasminogen activator in a rabbit model of peripheral arterial thrombosis

The thrombolytic efficacy of recombinant tissue-type plasminogen activator (tPA) in the presence and absence of a thromboxane synthase inhibitor was studied in a model of femoral artery thrombosis in the anesthetized rabbit. The thrombus was formed by injection of thrombin and whole blood into an isolated segment of the femoral artery. After 30 min of stable thrombotic occlusion of the femoral artery, sodium heparin (300 U/kg, i.v.) was administered and tPA was infused locally to the site of the thrombus for 30 min at 0.01, 0.10 or 1.0 microgram/kg/min. In other experiments, CGS 13080, a selective thromboxane synthase inhibitor, was administered at a dose of 2 mg/kg i.v., 5 min before tPA was infused and at the end of the 30 min tPA infusion. Pretreatment with CGS 13080 resulted in a shorter time to tPA-induced reperfusion, greater incidence of reperfusion and increased the magnitude of femoral artery blood flow achieved after effective thrombolysis. Furthermore, pretreatment with CGS 13080 resulted in a greater than 10-fold enhancement in the effective dose of tPA. These data indicate that thromboxane synthase inhibition may be beneficial as an adjunct to thrombolytic therapy with tPA.

Influence of selective endoperoxide/thromboxane A2 receptor antagonism with sulotroban on lysis time and reocclusion rate after tissue plasminogen activator-induced coronary thrombolysis in the dog

The purpose of this investigation was to examine the potential beneficial effect of the selective endoperoxide/thromboxane A2 (TxA2) receptor antagonist, sulotroban (BM 13.177), on tissue type plasminogen activator (tPA)-induced coronary thrombolysis in the dog. A stenosis that eliminated reactive hyperemic capacity was placed on the circumflex coronary artery and an occlusive thrombus was produced by electrical injury to the intimal surface of the artery. Upon occlusion, sodium heparin was administered (300 U/kg i.v.) followed by 100 U/kg i.v. every hour thereafter. All dogs received i.v. tPA 60 min after the formation of the occlusive thrombus at a dose of 10 micrograms/kg/min for up to 90 min, if necessary, to elicit reperfusion. Thrombolysis was demonstrated in all dogs by restoration of coronary blood flow. Dogs were randomized to one of three groups. Group I consisted of 24 animals that received vehicle infusion along with tPA. Group II consisted of 10 animals that received sulotroban at a bolus dose of 1 mg/kg i.v. followed by 1 mg/kg/hr i.v. administered simultaneously with tPA. Group III consisted of 11 animals that received sulotroban at a bolus of 10 mg/kg i.v. followed by 10 mg/kg/hr i.v. administered simultaneously with tPA. Infusions of either vehicle or sulotroban were continued for 2 hr, post-thrombolysis. tPA was infused for at least 30 min, after which infusion of tPA was terminated upon achieving a reperfusion level of coronary blood flow equivalent to 50% or greater than control blood flow. All animals occluded spontaneously to electrolytic stimulation between 32 and 62 min. tPA-induced thrombolysis occurred in Group I vehicle-infused animals at 32 +/- 5 min.(ABSTRACT TRUNCATED AT 250 WORDS)