Cyclic Flow Reductions Research Articles

Lack of effect of glycoprotein IIb/IIIa blockade on myocardial platelet or polymorphonuclear leukocyte accumulation and on infarct size after transient coronary occlusion in pigs

ObjectivesWe sought to assess the effect of glycoprotein (GP) IIb/IIIa blockade on myocardial platelet and polymorphonuclear leukocyte accumulation and on infarct size after coronary injury and transient coronary occlusion (CO) in pigs. BackgroundIt has been suggested that platelet GP IIb/IIIa blockade might reduce the severity of microvascular damage after reperfusion. MethodsSixteen thiopental-anesthetized, open-chest pigs, in whom platelets had been labeled with technetium-99m (99mTc) on the previous day, were submitted to catheter-induced left anterior descending coronary artery (LAD) injury followed by 55 min of CO and 5 h of reperfusion. Five minutes before reflow, the animals were blindly allocated to receive lamifiban (intravenous bolus of 250 μg/kg body weight and continuous infusion of 3 μg/kg per min) or saline. ResultsLamifiban had a rapid and potent platelet anti-aggregatory effect, as demonstrated by significant prolongation of the bleeding time and profound (∼90%) inhibition of ex vivo platelet aggregation, and completely prevented the development of cyclic flow reductions of the LAD (0 vs. 5 ± 1, one of them followed by re-occlusion, in control animals, p = 0.005). However, compared with animals receiving placebo, those treated with lamifiban had a similar (p = NS) content of 99mTc platelets in the reperfused myocardium (288 ± 40% vs. 205 ± 27% of the value in the control region, respectively) and similar myeloperoxidase activity (0.50 ± 0.17 U/g vs. 0.47 ± 0.17 U/g, respectively) and infarct size (46.8 ± 12.0% vs. 49.8 ± 10.5% of the area at risk, respectively). Arteriolar platelet thromboemboli were very rarely seen on histologic analysis. Lamifiban did not modify platelet P-selectin expression in additional studies. ConclusionsPlatelet GP IIb/IIIa blockade has a potent antithrombotic effect at the culprit lesion, but does not significantly reduce the magnitude of microvascular platelet accumulation or myocardial damage after transient CO.

A novel MCA occlusion model of photothrombotic ischemia with cyclic flow reductions: development of cerebral hemorrhage induced by heparin

Intracerebral hemorrhage is the major complication associated with antithrombotic and thrombolytic therapy. Despite efforts directed toward achieving hemorrhagic infarction, an ideal animal model of cerebral hemorrhage has not yet to be established. Using the photothrombotic technique in rabbits, we developed a model of cerebral hemorrhage by inducing cyclic flow reductions in the middle cerebral artery (MCA). Furthermore, the hemorrhage increased 4-fold after infusion of heparin at a dose prolonging activated partial thromboplastin time by about three times that of control animals. The photothrombotic occlusion of the MCA is based on a thrombosis induced by endothelial injury through singlet oxygen produced by Rose Bengal injection and green light irradiation (Acta Neuropathol. 72 (1987) 315; Acta Neuropathol. 72 (1987) 326; J. Pharmacol. Toxicol. Methods. 29 (1993) 165). Using a pulse Doppler flowmeter, spontaneous reperfusion of the MCA after the thrombotic occlusion following cyclic flow reductions was observed within 2 h in the majority of animals. This model is unusual with respect to the development of clinical stroke, because of the MCA cyclic flow reductions. Thus it is different from permanent or ischemia/reperfusion MCA occlusion in rodents and may be suitable for studying hemorrhagic risks associated with the use of antithrombotic agents.

Administration of Raw Onion Inhibits Platelet-Mediated Thrombosis in Dogs

A number of studies suggest that dietary intake of onions is of benefit to cardiovascular health. Onion juice inhibits in vitro human platelet aggregation. To study the in vivo effect of onion on platelet aggregation, 11 dogs were prepared with mechanically damaged and stenosed coronary arteries. Periodic platelet-mediated thrombus formation followed by embolization produced cyclic flow reductions (CFR). In five dogs, 0.09 +/- 0.01 mL/kg onion juice administered intravenously abolished CFR within 20 min. This was followed by a 60 +/- 14% (P = 0.002) reduction in collagen-induced ex vivo whole-blood platelet aggregation. Six dogs were given 2.0 g/kg raw onion homogenate intragastrically. CFR were eliminated within 2.5-3 h in five of the dogs. This was accompanied by a 44 +/- 24% (P = 0.04) reduction in ex vivo aggregation. These findings suggest that the consumption of raw onion may help prevent platelet-mediated cardiovascular disorders. However, in vitro incubations of onion juice demonstrated that the platelet inhibitory response was significantly greater in dog blood than in human blood.

Antiplatelet and Antithrombotic Activity of RWJ-53308, A Novel Orally Active Glycoprotein IIb/IIIa Antagonist

RWJ-53308 is a novel nonpeptide glycoprotein IIb/IIIa (GPIIb/IIIa) antagonist that inhibits fibrinogen binding to GPIIb/IIIa with an IC 50 of 0.4±0.3 nM. RWJ-53308 inhibits thrombin-induced platelet aggregation in human gel-filtered platelets (IC 50=60±12 nM) and platelet aggregation in human platelet-rich plasma (PRP) in response to collagen, arachidonic acid, ADP, and SFLLRN-NH 2 (IC 50=60±10, 150±30, 70±4, and 160±80 nM, respectively). The potency of RWJ-53308 in dog and guinea pig PRP is similar to human PRP. RWJ-53308 inhibits ex vivo collagen- and ADP-induced platelet aggregation in conscious dogs for up to 4 h following 0.3 mg/kg iv, and through 4 and 6 h following 1 and 3 mg/kg po. Oral bioavailability is 16±7%. RWJ-53308 reduces thrombus weight in a canine arteriovenous (AV) shunt model following intravenous (0.01–0.1 mg/kg) and oral (3 mg/kg) administration. In a guinea pig carotid artery pinch-injury model, RWJ-53308 completely suppresses thrombus-induced cyclic flow reductions (CFR) at 0.7 mg/kg iv. RWJ-53308 also blocks thrombus formation in photoactivation- and ferric chloride-induced models of thrombosis in guinea pigs at 0.3 and 1 mg/kg iv, respectively. In summary, RWJ-53308 is a potent orally active GPIIb/IIIa antagonist that may be useful for both acute and chronic treatment of arterial thrombotic disorders.

Cessation of platelet-mediated cyclic canine coronary occlusion after thrombolysis by combining nitric oxide inhalation with phosphodiesterase-5 inhibition

OBJECTIVESWe sought to evaluate the ability of type 5 phosphodiesterase (PDE5) inhibitors to augment the antithrombotic effects of inhaled nitric oxide (NO) in a canine model of platelet-mediated coronary thrombosis after thrombolysis.BACKGROUNDType 5 phosphodiesterase inhibitors potentiate the ability of NO to inhibit platelet aggregation in vitro by preventing platelet cyclic guanosine monophosphate catabolism. We previously reported that breathing low concentrations of NO gas attenuated, but did not prevent, cyclic flow reductions (CFRs) in a canine model of coronary thrombosis after thrombolysis.METHODSCyclic flow reductions were induced after creation of a left anterior descending coronary artery stenosis, endothelial injury, thrombus formation and thrombolysis. Dogs were either untreated or treated with inhaled NO (20 ppm by volume), intravenous zaprinast, intravenous dipyridamole or the combination of inhaled NO with either PDE5 inhibitor (n = 4 per group).RESULTSCyclic flow reductions ceased, and complete coronary patency was achieved in all dogs after they breathed NO combined with zaprinast (by 12.0 ± 4.7 min [mean ± SEM]) or dipyridamole (by 9.8 ± 4.7 min). The frequency of CFRs was unaffected by NO, dipyridamole or zaprinast alone. Systemic arterial blood pressure and bleeding time were unchanged with any treatment. Ex vivo thrombin-induced platelet aggregation in dogs breathing NO and receiving dipyridamole was reduced by 75 ± 7% (p < 0.05).CONCLUSIONSThe PDE5 inhibitors potentiated the antithrombotic properties of inhaled NO in a canine model of platelet-mediated coronary artery thrombosis after thrombolysis, without prolonging the bleeding time or causing systemic hypotension.

Anti-Human vWF Monoclonal Antibody, AJvW-2 Fab, Inhibits Repetitive Coronary Artery Thrombosis without Bleeding Time Prolongation in Dogs

The antithrombotic and antihaemostatic effects of the monoclonal antibody against human vWF (AJvW-2 Fab) were investigated in comparison with those of the monoclonal antibody against platelet GPIIb/IIIa (abciximab) in dogs. The ex vivo platelet aggregation and template bleeding time were measured before, 5, 90, 210 min and 24 h after injection of either AJvW-2 Fab or abciximab in anesthetized beagle dogs. Plasma concentration, vWF occupancy and plasma vWF antigen level were also measured by ELISA. In addition, the antithrombotic effect was evaluated in a canine model of repetitive coronary thrombosis (Folts model). AJvW-2 Fab significantly inhibited the ex vivo botrocetin-induced platelet aggregation at 0.18 mg/kg (53% plasma vWF occupancy) and also inhibited cyclic flow reductions (CFRs) at 0.06 mg/kg (31% occupancy). A significant prolongation of the bleeding time was observed at 1.8 mg/kg (95% occupancy), which was 30 times as high as the antithrombotic effective dose. Whereas, abciximab significantly inhibited both the ex vivo ADP-induced platelet aggregation and CFRs at 0.8 mg/kg, which was the minimally effective dose, also resulting in a significant prolongation of the bleeding time. These results suggest that blockade of the GPIb–vWF axis with AJvW-2 Fab leads to the inhibition of thrombus formation in the stenosed coronary arteries without less bleeding time prolongation than the GPIIb/IIIa blockade with abciximab.

Dynamic intracoronary thrombosis does not cause significant downstream platelet embolization.

A mural intracoronary thrombus is a potential source of platelet emboli that may obstruct downstream microvessels, but this phenomenon has not been characterized. The present study aimed to assess the magnitude of myocardial platelet accumulation downstream of a mural intracoronary thrombus and its modification by a concomitant transient coronary occlusion (OC) or by treatment with aspirin. The myocardial content of 99mTc-labelled platelets was analyzed in 26 pigs submitted to intimal injury of the left anterior descending coronary artery (LAD) followed by no intervention (n=6), 25-min OC (n=6), or 48-min OC preceded (n=8) or not (n=6) by intravenous administration of 250 mg aspirin. After 2 h, 24 animals had had 12+/-1 cyclic flow reductions (CFRs) reflecting dynamic LAD thrombosis. Myocardial platelet content in the inferior region was similar among groups. Platelet content in the LAD region was not significantly different to that in the inferior region (129+/-19%, P=NS) in the no intervention group, but was increased following OC (172+/-20 and 312+/-71% after 25- and 48-min OC, respectively, P<0.05). Pre-treatment with aspirin lessened the number of CFRs but did not reduce platelet accumulation in LAD myocardium (483+/-148%). Myocardial platelet accumulation was not associated with the magnitude of platelet deposition in the LAD nor with the number of CFRs, but was correlated with myeloperoxidase activity (r=0.91, P<0.001) and with infarct size (r=0.52, P=0.05). Histological analysis frequently showed sparse platelets or small platelet or leukoplatelet aggregates in small vessels, but arteriolar emboli were rare. In none of seven additional experiments coronary angiography showed obstructions of arterial branches during CFRs. The magnitude of platelet embolization from a mural intracoronary thrombus into downstream myocardium is small despite the presence of repetitive CFRs.

Endogenous tissue factor pathway inhibitor modulates thrombus formation in an in vivo model of rabbit carotid artery stenosis and endothelial injury.

Tissue factor pathway inhibitor (TFPI) is the sole known inhibitor of the extrinsic coagulation pathway of physiological importance; however, its role in modulating thrombosis in vivo is still unclear. Intravascular thrombosis was initiated by placing an external constrictor around endothelially injured rabbit carotid arteries (n=10). Carotid blood flow velocity was measured by a Doppler flow probe. After placement of the constrictor, cyclic flow reductions (CFRs), due to recurrent thrombosis, developed at the site of stenosis. Transstenotic TFPI plasma activity was measured in blood samples before induction of CFRs and after 30, 60, and 180 minutes of CFRs. TFPI plasma activity distal to the site of thrombosis was significantly lower than the corresponding proximal values at 30, 60, and 180 minutes of CFRs. In addition, a progressive decrease in TFPI plasma activity was observed in both the proximal and the distal samples, indicating consumption of TFPI during thrombus formation. In 10 additional rabbits, CFRs were abolished by administration of aspirin (10 mg/kg). In the animals in which aspirin abolished CFRs, endogenous TFPI was depleted by a bolus of a polyclonal antibody against rabbit TFPI, and the effects on restoration of CFRs were monitored. In 5 of 6 animals in which aspirin abolished CFRs, depletion of endogenous TFPI activity caused full restoration of CFRs. The data of the present study support the involvement of endogenous TFPI in the process of thrombus formation in vivo and its active role in modulating arterial thrombosis.

Antithrombotic Efficacy of Single Subcutaneous Administration of a Recombinant Nematode Anticoagulant Peptide (rNAP5) in a Canine Model of Coronary Artery Thrombolysis

We examined the adjunctive benefit of recombinant nematode anticoagulant peptide (rNAP5), a factor Xa inhibitor, in a canine model of recombinant (rt)-PA-induced thrombolysis. In anesthetized dogs, a stable occlusive thrombus was formed by electrolytic injury of the vessel wall, after which the animals were administered rt-PA (1.44 mg/kg, i.v.) and rNAP5 (0.1 mg/kg, s.c.; n=13), or rt-PA plus vehicle (1–2 ml, s.c.; n=13). Hemodynamic and coagulation parameters were monitored for 360 minutes. Single subcutaneous administration of rNAP5 resulted in a prolonged and sustained increase in the activated partial thromboplastin time (>10-fold), whereas prothrombin time was unchanged. The template bleeding time was not altered significantly throughout the protocol (maximum 1.4-fold). The incidence of reperfusion was similar in the two groups with a trend toward faster reperfusion in the rNAP5 group (34±4 minutes) compared to the vehicle group (63±15 minutes; p=0.07). After reperfusion, 80% of the vessels in the vehicle group reoccluded, whereas only 14% of vessels reoccluded in the rNAP5-treated group. Times to reocclusion were 65±21 minutes and 221±28 minutes, respectively ( p<0.05). Single subcutaneous administration of rNAP5 sustained the coronary artery blood flow after reperfusion, such that at the end of protocol the flow was 47% of the preocclusion value as compared to the vehicle group in which the flow was 11% ( p<0.05). Cyclic flow reductions were most prominent during rt-PA-induced reperfusion and were similar in both groups. The results indicate that a single subcutaneous administration of rNAP5 provides a sustained antithrombotic effect in maintaining the coronary artery patency during rt-PA-induced thrombolysis.

O-50 - Cyclic flow reduction of the MCA enlarges infarct volume by artery to artery microemboli

O-50 - Cyclic flow reduction of the MCA enlarges infarct volume by artery to artery microemboli

Pulse dispersion due to atrial fibrillation causes arterial thrombosis in a rabbit experimental model.

Thrombosis associated with atrial fibrillation (AF) is usually caused by a left atrial (LA) thrombus, but it is not always detected. The present study was based on the hypothesis that abnormalities in peripheral artery are responsible for the ischemic stroke associated with AF. Peripheral arterial coagulability was investigated in a rabbit experimental model in which AF was induced by high-frequency stimulation of the right atrium, creating stenosis of the carotid artery together with endothelial damage. The rabbits were classified into 4 groups: (i) sinus rhythm only (group 1), (ii) sinus rhythm after 6 h of pacing (group 2), (iii) short AF (continuous pacing for 5 min; group 3) and (iv) long AF (continuous pacing for 6 h: group 4). The carotid blood flow developed a typical pattern, called cyclic flow reductions (CFRs), the frequency of which (CFRF) was 18.59+/-2.85 in AF (group 3+4) compared with 14.46+/-2.1 in sinus rhythm (group 1+2) (p<0.0005). Among the groups with AF, correlation analysis showed an association between CFRF and pulse dispersion (p<0.02, r=0.58). This study suggests that the distinctive hemodynamic effects with AF, in particular pulse dispersion, substantively influence thrombus formation on injured vascular endothelium.

Superiority of platelet integrin GPIIb–IIIa receptor antagonist over aspirin in preventing cyclic flow reductions in the guinea pig middle cerebral artery

We established a photothrombotic occlusion model in the guinea pig middle cerebral artery. In this model, the middle cerebral artery was recanalized within 10 to 20 min after thrombotic occlusion, with subsequent cyclic flow reductions. Cyclic flow reductions in the middle cerebral artery are expected to manage cerebral infarction by modulating arterial patency. Therefore, we evaluated the effect of several antiplatelet agents on the frequency of cyclic flow reductions and subsequent cerebral infarction using this model. A platelet integrin GPIIb–IIIa receptor antagonist, ME3277 (sodium hydrogen [4-[(4,5,6,7-tetrahydrothieno[3,2 c]pyridin-2-yl) carbonylamino] acetyl- o-phenylene] dioxydiacetate, 0.3, 1 and 3 mg/kg i.v.) dose-dependently inhibited the ex vivo platelet aggregation induced by ADP (5 μM), collagen (0.8 and 20 μg/ml) and arachidonic acid (100 μM). While the same doses of ME3277 reduced the frequency of the cyclic flow reductions and increased the total patency time of the middle cerebral artery, time to thrombotic occlusion was prolonged only at the highest dose, 3 mg/kg. ME3277 (0.3–3 mg/kg) significantly reduced the infarct volume and improved the neurological deficit at 24 h. In contrast, aspirin (30 mg/kg) did not affect these variables in spite of complete inhibition of platelet aggregation induced by arachidonic acid and collagen (0.8 μg/ml). A thromboxane A 2 synthetase inhibitor, sodium ozagrel, significantly increased the total patency time and reduced the infarct volume at 30 mg/kg. Inhibition of prostaglandin I 2 generation could explain the effectiveness of sodium ozagrel but not aspirin in this model. These results suggest that platelet integrin GPIIb–IIIa receptor antagonists are more beneficial than aspirin for the treatment of cerebral thrombosis.

This Month in ANESTHESIOLOGY

This Month in ANESTHESIOLOGY

Role of the hematocrit in a rabbit model of arterial thrombosis and bleeding.

A decrease in hematocrit lengthens bleeding time. The authors studied the role of hematocrit variations in an experimental model of arterial thrombosis and bleeding. The Folts model was used in 24 rabbits. After anesthesia was induced and common monitors were positioned, the right common carotid artery was exposed and a 60% stenosis was induced. A compression injury of the artery was then produced, which triggered a series of cyclic episodes of thrombosis and clot lysis (cyclic flow reductions [CFRs]). After counting the number of CFRs that occurred in 20 min (CFR1), the animals were assigned randomly to one of three groups (n = 8 in each group): control, hemodilution with rabbit homologous platelet-rich plasma, and hemodilution with gelatin solution and then reinfusion of the shed blood. The effect of hemodilution with replacement by platelet-rich plasma or by colloid was observed by recording the number of CFRs during another 20-min period (CFR2). A third period of observation (CFR3) followed shed blood reinfusion in the gelatin solution group. Ear immersion bleeding time was recorded after each CFR period. In the two experimental groups, the decrease in hematocrit (from 36 +/- 3% to 23 +/- 2% and from 38 +/- 3% to 23 +/- 2%, respectively; mean +/- SD) abolished CFRs (from a median of 4 to 0 and 7 to 0, respectively) and significantly lengthened bleeding time (from 76 +/- 24 s to 114 +/- 36 s and from 84 +/- 37 s to 127 +/- 29 s, respectively). Blood reinfusion in the group that received the gelatin solution caused CFR to reappear (CFR3 = 4). Decreases in hematocrit reduced the cyclic arterial thrombosis rate and increased the bleeding time in the rabbits in this study. Hematocrit normalization caused thrombosis to reappear.

Grape Juice but Not Orange or Grapefruit Juice Inhibits Platelet Activity in Dogs and Monkeys (Macaca fasciularis)

Platelet aggregation (PA) contributes to both the development of atherosclerosis and acute platelet thrombus formation (APTF) followed by embolization producing cyclic flow reductions (CFR) in stenosed and damaged dog and human coronary arteries. In seven anesthetized dogs with coronary stenosis and medial damage, CFR occurred at 7 ± 3/30 min and were abolished 127 ± 18 min after gastric administration of 10 mL of purple grape juice/kg. Collagen-induced ex vivo whole blood PA decreased by 49 ± 9% after the abolishment of CFR with grape juice. Ten mL of orange juice/kg (n = 5) and 10 mLof grapefruit juice/kg (n = 5) had no significant effect on the frequency of the CFR or on ex vivo PA. In vitro studies have suggested that flavonoids bind to platelet cell membranes and thus may have an accumulative or tissue-loading effect over time. To test this we fed 5 mLof grape juice/kg to 5 cynomologous monkeys for 7 d. Collagen-induced ex vivo PA decreased by 41 ± 17% compared to control (pre-reatment) after 7 d of feeding. In the same 5 monkeys, neither 5 mL of orange juice/kg nor 5 mLof grapefruit juice/kg given orally for 7 d produced any significant change in PA. Grape juice contains the flavonoids quercetin, kaempferol and myricetin, which are known inhibitors of PA in vitro. Orange juice and grapefruit juice, while containing less quercetin than grape juice, primarily contain the flavonoids naringin, luteolin and apigenin glucoside. The flavonoids in grapes were shown in vitro to be good inhibitors of PA, whereas the flavonoids in oranges and grapefruit to be poor inhibitors of PA. The consumption of grape juice, containing these inhibitors of PA, may have some of the protection offered by red wine against the development of coronary artery disease (CAD) and acute occlusive thrombosis, whereas orange juice or grapefruit juice may be ineffective. Thus, grape juice may be a useful alternative dietary supplement to red wine without the concomitant alcohol intake.

Increased cerebral infarction by cyclic flow reductions: studies in the guinea pig MCA thrombosis model.

We have developed a photochemical model of thrombotic middle cerebral artery (MCA) occlusion in the guinea pig for investigating factors contributing to the development of cerebral infarction. In this model, cyclic flow reductions (CFRs) after recanalization of the MCA are a common observation and might contribute to the development of cerebral infarction. Therefore, we sought to measure the time course of recanalization of the guinea pig MCA after the artery had been occluded by a thrombus. Thrombotic occlusion of the MCA was induced by photochemical reaction between intravenously administered rose bengal and transluminal green light for 10, 15, 20, or 30 min. After the thrombotic occlusion of MCA and subsequent spontaneous thrombolysis, blood flow in the MCA gradually recovered to preocclusion level but with frequent CFRs. The recovery of MCA blood flow or duration of CFRs was dependent on the duration of photochemical reaction (extent of endothelial injury); thus, for a 30-min photochemical reaction, CFRs were still observed 24 h after photochemical reaction. In separate experiments, we also investigated the effect of permanent occlusion of the MCA, which was induced by electrocoagulation in the vessel on cerebral infarction. The infarct volume in the permanent occlusion model was smaller than the maximum value in the thrombotic occlusion model (12.5 vs. 17.4%; P < 0.05, n = 6). CFRs may constitute an important factor contributing to the extent of cerebral infarction.

Intranasal Antiplatelet/ Antithrombotic Efficacy of a Novel Platelet GPIIB/IIIA Receptor Antagonist DMP755

This article describes the equivalent antiplatelet/antithrombotic effects of DMP755 at comparable doses by intranasal and IV administration but required substantially higher doses with the oral administration route. Antiplatelet and antithrombotic efficacy of DMP755 or its free acid form XV459 were determined in dogs. Arterial thrombosis models were induced either electrolytically (200 μA anodal current) in the carotid artery or mechanically by external clamping of femoral artery along with stenosis, which result in either total occlusive thrombus formation or cyclic flow reduction (CFR), respectively. Either DMP755 or its free acid form, XV459 demonstrated maximal and comparable antiplatelet efficacy at 0.025–0.1 mg/kg, intravenous (IV) or intranasal but not oral (PO) in mongrel dogs. The antiplatelet efficacy of DMP755 at 0.1 mg/kg, intranasal, or IV was determined in a cross-over design (n=8 in each group). In this study, a comparable and maximal antiplatelet efficacy for DMP755 after intranasal or IV was demonstrated suggesting 100% intranasal bioavailability as compared with the modest antiplatelet efficacy at 0.1 mg/kg, PO. DMP755 administered at 0.1 mg/kg, intranasally or IV or at 0.3 mg/kg, PO prevented the incidence of electrolytic injury-induced arterial thrombosis in the carotid artery thrombosis model and prevented the incidence of cyclic flow reduction in mechanically injured and stenosed femoral artery. In conclusion, DMP755 has a comparable intranasal and intravenous antiplatelet/antithrombotic profiles along with a significant improvement over its oral profiles. These data also suggest the potential utility of intranasal DMP755 in various acute and chronic thromboembolic disorders. This is the first report of intranasal bioavailability of a glycoprotein receptor antagonist.

The effect of MGDF on platelet function and thrombosis in animal models.

Recombinant human megakaryocyte growth and development factor (rHuMGDF) is a recombinant form of the endogenous c-mpl ligand, thrombopoietin (TPO). rHuMGDF (and c-mpl ligands in general) can produce a measurable sensitization of platelets to known platelet agonists. Our laboratory has observed this sensitization in vitro in both platelet-rich plasma and whole blood and ex vivo in platelets from animals receiving rHuMGDF. Concurrently, clear increases in the tyrosine phosphorylation of Jak2 and c-mpl receptor can be observed both in vitro and ex vivo. To assess the in vivo prothrombotic potential of rHuMGDF, a rabbit carotid artery model of cyclic flow reduction (CFR) was used. Intravenous administration of platelet-sensitizing dosages of rHuMGDF had no effect on the CFR pattern, whereas control experiments demonstrated that the CFR pattern can be modulated by both platelet sensitizing (epinephrine) and antithrombotic (aspirin and ketanserin) agents. We conclude that thrombopoiesis can be observed at dosages that do not sensitize platelets, and further, that platelet-sensitizing dosages of rHuMGDF do not necessarily enhance platelet-dependent thrombosis in this model.

Intravenous and oral antiplatelet/antithrombotic efficacy and specificity of XR300, a novel nonpeptide platelet GPIIb/IIIa antagonist.

Currently used antiplatelet drugs including aspirin, ticlopidine, and others are effective against certain but not all of the many endogenous platelet activators. Because of their limited efficacy, a significant number of serious thromboembolic complications still occur, highlighting the need for a more effective therapy. Thus our study was undertaken to define the antiplatelet efficacy, specificity, and the intravenous and oral antiplatelet/antithrombotic effects of a nonpeptide glycoprotein alphaIIb beta3 integrin (GPIIb/IIIa) antagonist XR300, an ethyl ester prodrug of XR299. XR300, on its conversion to the active form XR299, inhibited human platelet aggregation induced by 100 microM adenosine diphosphate (ADP) with a median inhibitory concentration (IC50) of 0.09 microM. Similarly, XR299 inhibited 125I-fibrinogen binding to human gel-purified platelets (IC50, 0.01 microM) regardless of the agonist used. In purified human GPIIb/IIIa, XR299 demonstrated a competitive high-affinity binding with an IC50 of 1.2 nM. XR299 demonstrated a high degree of specificity for platelet GPIIb/IIIa (alphaIIb beta3) as compared with other integrins including alpha(v)beta3, alpha(v)beta5, and alpha4beta1, where IC50 values were >10 microM. XR300 administered to mongrel dogs either intravenously (0.5-1.0 mg/kg, i.v.) or orally at 1.0-2.0 mg/kg, demonstrated maximal antiplatelet effects with rapid onset and extended duration. XR300 demonstrated maximal antithrombotic efficacy in preventing the incidence of occlusive thrombosis or cyclic flow reduction (CFR) in the carotid or femoral artery thrombosis models induced either electrolytically or by mechanical injury along with stenosis. In conclusion, XR300 is a novel intravenous and oral antiplatelet/antithrombotic agent with high affinity and specificity for platelet GPIIb/IIIa receptors.

Intima–Adventitia Apposition in End-to-Side Arterial Anastomosis: An Experimental Study in the Pig

Background. To prevent ischemic complications during coronary bypass grafting on the beating heart, a nonocclusive distal anastomosis technique is needed. One recently developed nonocclusive technique requires apposition of the intima of the graft to the adventitia of the recipient artery, in contrast to current surgical practice, which dictates apposition of both intimas.Methods. To compare the sole effect of intima–adventitia apposition (n = 18) versus traditional intima–intima apposition (n = 18), we investigated radiolabeled platelet deposition and histomorphologic aspects of vascular wall healing quantitatively in a porcine carotid artery bypass graft model. Both groups were evaluated at 2 hours, 2 days, or 4 weeks.Results. Within the first 2 hours, 3 of 6 pigs with intima–adventitia apposition exhibited cyclic flow reductions as a result of massive mural thrombosis. After intima–adventitia apposition, the number of deposited platelets was significantly higher compared with intima–intima apposition, 147.1 ± 73.0 × 106 and 4.6 ± 1.0 × 106 platelets/cm2 (mean ± standard error of the mean), respectively (p = 0.03). At 2 days, the suture line was covered with small mural thrombi, whereas no thrombi were found after intima–intima apposition. At 4 weeks, intimal hyperplasia at heel and toe was not significantly different from that with intima–intima apposition.Conclusions. Despite thrombotic phenomena in the early phase, intima–adventitia apposition yielded a patent anastomosis with a small intimal hyperplasia response.