Biomedical subjects

W R Wagner

Publications and source records attributed to W R Wagner.

At least 37 records · Page 2Linked to original sources

PubMed1998

Microbubbles targeted to intercellular adhesion molecule-1 bind to activated coronary artery endothelial cells.

BACKGROUND: Preclinical atherosclerosis is associated with increased endothelial cell (EC) expression of leukocyte adhesion molecules (LAMs), which mediate monocyte adhesion during atherogenesis. Identification of cell-surface LAMs may uniquely allow assessment of endothelial function, but there are no in vivo methods for detecting LAMs. We tested a new microbubble designed to bind to and allow specific ultrasound detection of intercellular adhesion molecule-1 (ICAM-1). METHODS AND RESULTS: A perfluorobutane gas-filled lipid-derived microsphere with monoclonal antibody to ICAM-1 covalently bound to the bubble shell was synthesized. Bubbles with either nonspecific IgG or no protein on the shell were synthesized as controls. Coverslips of cultured human coronary artery ECs were placed in a parallel-plate perfusion chamber and exposed to 1 of the 3 microbubble species, followed by perfusion with culture medium. Experiments were performed with either normal or interleukin-1beta-activated ECs overexpressing ICAM-1, and bubble adherence was quantified with epifluorescent videomicroscopy. There was limited adherence of control bubbles to normal or activated ECs, whereas a 40-fold increase in adhesion occurred when anti-ICAM-1-conjugated bubbles were exposed to activated ECs compared with normal ECs (8.1+/-3.5 versus 0.21+/-0.09 bubbles per cell, respectively, P<0.001). Although diminished, this difference persisted even after perfusion at higher wall shear rates. CONCLUSIONS: A gas-filled microbubble with anti-ICAM-1 antibody on its shell specifically binds to activated ECs overexpressing ICAM-1. Diagnostic ultrasound in conjunction with targeted contrast agents has the unique potential to characterize cell phenotype in vivo.

Antibodies, Monoclonal↗

PubMed1998

Creating molecular barriers to acute platelet deposition on damaged arteries with reactive polyethylene glycol.

We report here a novel method for blocking acute platelet deposition at the site of vessel injury by molecularly masking thrombogenic vascular wall proteins with covalently attached polyethylene glycol (PEG). To evaluate this technique, blood containing 111In-labeled platelets was perfused over damaged human placental arteries for 2 min at a wall shear rate of 200 s-1. Denuded vessel segments were incubated for 30, 15, 5, and 1 min with a solution of either reactive PEG-diisocyanate (PEG-ISO) or nonreactive PEG-dihydroxyl (PEG-OH). Vessels treated with PEG-ISO for 1 min exhibited 87 +/- 12% less platelet deposition (p < 0.01) than untreated control vessels, and this reduction did not vary significantly among treatment times, indicating that this reaction occurs rapidly enough to be clinically applicable. To investigate the duration of this thrombotic barrier, denuded pig carotid arteries were treated with reactive PEG-ISO for 1 min, perfused with plasma for 30 min, and then perfused with blood containing radiolabeled platelets. PEG-ISO-treated arteries exhibited 84 +/- 9% less platelet deposition (p < 0.05) than untreated controls. These data demonstrate that damaged arterial surfaces can be rendered resistant to platelet deposition after short contact periods with reactive PEG. Molecular PEG barriers ultimately might find application following vascular procedures to sterically inhibit blood cell interaction with damaged vascular surfaces.

Angioplasty, Balloon↗

PubMed1998

Flow cytometric assays to detect platelet activation and aggregation in device-implanted calves.

Cardiovascular device development often relies upon large-animal models to assess blood biocompatibility prior to initiating clinical trials. Unfortunately, the amount of information gleaned from such trials is limited by simple assays that do not take full advantage of immunotechnological advances that increasingly are applied in clinical studies. Thus we have developed and tested new flow cytometric techniques for measuring circulating activated bovine platelets and platelet microaggregates. Monoclonal antibodies (MAbs) raised against both activated and quiescent bovine platelets were incubated with control and PMA-or ADP-stimulated whole blood. Selected MAbs detected activated bovine platelets and platelet microaggregates in vitro with flow cytometry. Five calves implanted with one of two designs of nonpulsatile ventricular-assist devices (VADs) were followed with these assays prior to and during VAD implantation. Circulating activated bovine platelets and microaggregates increased after implantation in all animals and, alternatively, remained elevated or returned toward preimplant levels. Platelet activation percentages as detected temporally by three MAbs were correlated with one another, and platelet activation was correlated with microaggregate formation. In summary, these new methods for the sensitive measurement of circulating activated bovine platelets and microaggregates may provide valuable information for the development and assessment of future cardiovascular device designs.

Adenosine Diphosphate↗

PubMed1998

Monocyte tissue factor expression and ongoing complement generation in ventricular assist device patients.

BACKGROUND: Ongoing complement activation in patients with a ventricular assist device may contribute to observed hemostatic abnormalities and cellular aggregation by mediating leukocyte and platelet activation, formation of leukocyte-platelet conjugates, and the tissue factor pathway of coagulation. METHODS: Blood from 30 patients was collected before ventricular assist device implantation and during the implantation period. Plasma levels of thrombin-antithrombin III complexes, C3a, and SC5b-9 were measured by commercial enzyme-linked immunosorbent assay. Flow cytometry was used to measure circulating monocyte tissue factor expression and circulating monocyteplatelet and granulocyte-platelet conjugates. RESULTS: Thrombin-antithrombin III complex level and monocyte tissue factor expression peaked in the early postoperative period, with maxima occurring on postoperative days 5 and 3, respectively. Levels of C3a and SC5b-9 remained dramatically elevated over normal values for the duration of the study (6 and 5 times upper normal, respectively). Levels of monocyte-platelet conjugates were normal before implantation, decreased during the first 4 postoperative days, and then increased and remained elevated. Levels of granulocyte-platelet conjugates were elevated over the normal range before implantation and remained elevated from postoperative days 3 to 21. A positive correlation was found between levels of SC5b-9 and granulocyte-platelet conjugates (Spearman R=0.66; p < 0.001), and between levels of C3a and thrombin-antithrombin III complex (Spearman R=0.13; p=0.021). CONCLUSIONS: The data suggest a model in which complement mediates formation of leukocyte-platelet aggregates and may indirectly contribute to thrombin generation through monocyte tissue factor expression.

Adult↗

PubMed1998

Molecular barriers to biomaterial thrombosis by modification of surface proteins with polyethylene glycol.

For cardiovascular biomaterials, thrombosis, thromboembolism and vascular graft occlusion are believed to be precipitated by the adsorption of proteins containing adhesive ligands for platelets. Polyethylene-glycol-diisocyanate (PEG-diisocyanate, 3400 MW) may potentially react with protein amines to form molecular barriers on adsorbed proteins on biomaterials, thereby masking adhesive ligands and preventing acute surface thrombosis. To test this notion, PE, PTFE, and glass microconduits were pre-adsorbed with fibrinogen and treated with PEG-diisocyanate, non-reactive PEG-dihydroxyl, or remained untreated. Following perfusion of 111In-labeled platelets in whole human blood for 1 min (wall shear rate = 312 s(-1)), PEG-diisocyanate treated surfaces experienced 96% (PE), 97% (PTFE) and 94% (glass) less platelet deposition than untreated surfaces. Similar reductions were seen for PEG-diisocyanate versus PEG-dihydroxyl treatment. Low shear perfusions of plasma for 1 h prior to blood contact did not reduce the inhibitory effect of PEG-diisocyanate. Platelet adhesion onto collagen-coated glass coverslips and platelet deposition onto preclotted Dacron were also reduced by treatment with PEG-diisocyanate (93 and 91%, respectively). Protein-reactive PEG may thus have utility in forming molecular barriers on surface-associated proteins to inhibit acute thrombosis on cardiovascular biomaterials.

Adsorption↗

PubMed1998

Assessment of bovine platelet life span with biotinylation and flow cytometry.

Reduced platelet life span is associated with the implantation of a variety of cardiovascular devices and may be used as a gauge of device biocompatibility. In the bovine model, platelet life span has previously been assessed with radioisotope labeling of removed platelets followed by reinjection and periodic gamma counting of blood samples. We report here the use of protein-reactive biotin (sulfo-N-hydroxysuccinimido [NHS]-biotin) as an alternative to radioisotope techniques whereby reinjected biotinylated platelets are subsequently detected in blood samples using phycoerythrin-streptavidin and flow cytometric techniques. Platelet life span was quantified in a normal calf (4.9 days) and in a calf prior to (6.1 days) and following (3.1 days) implantation of a Nimbus Axial Flow Pump ventricular assist device. The assessment of bovine platelet life span with biotinylation and flow cytometry avoids the technical, regulatory, and safety considerations associated with radioisotope usage and appears readily amenable to application in cardiovascular device testing.

Animals↗

PubMed1997

Elevated platelet factor 4 and beta-thromboglobulin plasma levels in depressed patients with ischemic heart disease.

Clinical depression has recently been recognized as an independent risk factor for cardiac mortality in patients after myocardial infarction. The underlying mechanisms of this increased mortality remain unclear. This study investigated the hypothesis that patients suffering from ischemic heart disease (IHD) and depression concurrently may have abnormal platelet activation resulting in an increased risk of thrombosis. Platelet factor 4 (PF4) and beta-thromboglobulin (beta-TG) were measured in young healthy control subjects, in nondepressed patients with IHD, and in depressed patients with IHD. Mean PF4 and beta-TG plasma levels in the IHD group with depression were found to be significantly higher than those of the control and IHD groups. This increase was not related to age, gender, racial difference, aspirin use, or severity of cardiac disease. This finding suggests that in depressed patients with IHD there is greater platelet activation, and may indicate an increased risk of thrombotic complications.

Adult↗

PubMed1997

Albumin microbubble adherence to human coronary endothelium: implications for assessment of endothelial function using myocardial contrast echocardiography.

OBJECTIVES: We hypothesized that sonicated 5% human albumin microbubbles (Albunex) adhere to disrupted vascular endothelium and that this interaction is a marker of endothelial integrity. This study sought to identify sites and determinants of Albunex-endothelial cell (EC) attachment. BACKGROUND: Under normal conditions, Albunex microbubbles used in myocardial contrast echocardiography (MCE) pass unimpeded through the coronary microcirculation. During pathophysiologic states associated with endothelial dysfunction, however, microbubbles linger in the myocardium despite normal flow. The sites and conditions regulating microbubble adhesion are unknown. METHODS: Coverslips with cultured human coronary artery ECs were mounted in a parallel plate perfusion system and perfused with a suspension of fluorescein-labeled Albunex in culture medium, followed by a bubble-free wash at a wall shear rate of 100 s-1. To create inflammatory ECs, phorbol myristate acetate was added 4.5 h before perfusion, and flow cytometry was used to confirm an inflammatory response. Perfusions were performed under normal and inflammatory conditions using surfaces of confluent and subconfluent ECs and isolated extracellular matrix. Bubble adherence was quantified in 20 random fields per cover-slip using epifluorescent video microscopy. RESULTS: No microbubbles adhered to normal confluent ECs, although small numbers adhered to inflamed ECs (0.03 +/- 0.01 bubbles/cell, p < 0.01 vs. normal cells). Fever microbubbles attached to normal versus inflamed matrix of both partially exposed (1,800 +/- 520 vs. 4,100 +/- 1,000 bubbles/mm2, p = 0.05) and completely denuded (2,700 +/- 1,300 vs. 7,200 +/- 1,100 bubbles/ mm2, p < 0.03) endothelium. CONCLUSIONS: Albunex microbubbles preferentially adhere to inflammatory endothelial extracellular matrix. These data suggest that MCE can be used to noninvasively study endothelial integrity and may have implications for the assessment of preclinical atherosclerotic heart disease.

Adhesiveness↗

PubMed1997

Effect of retroviral transduction on human endothelial cell phenotype and adhesion to Dacron vascular grafts.

PURPOSE: Retroviral transduction for genetic enhancement of endothelial cell (EC) anti-thrombotic phenotype offers potential for improving the clinical success of vascular graft seeding; however, application of this technique may bring concomitant alteration in cell functionality. METHODS: Human microvascular ECs were transduced with a retroviral vector encoding for the marker gene beta-galactosidase. Transduced endothelial cells (rtECs) and nontransduced endothelial cells (ntECs) were evaluated by flow cytometry for expression of intercellular adhesion molecule (ICAM)-1 and tissue factor (TF) on both smooth (coverslips) and graft (Dacron, 6 mm inside diameter) surfaces under static and shear exposed conditions. Graft EC retention was measured after 6-hour pulsatile perfusions. Platelet and neutrophil adherence was measured on perfused coverslips. RESULTS: Lower levels of ICAM-1 were expressed by rtECs on coverslips under both static (p < 0.01 vs static ntECs) and shear exposed conditions (p < 0.01 vs static and shear ntECs). Accordingly, fewer polymorphonuclear leukocytes adhered to rtEC monolayers (p < 0.01 vs ntECs). No difference in ICAM-1 and TF expression by static graft seeded rtECs and ntECs was observed. However, graft-seeded rtECs that were exposed to wall shear stress displayed less TF than sheared ntECs (p < 0.05). Transduction did not affect EC retention to the sheared graft surface. CONCLUSIONS: These data suggest that retroviral transduction does not elicit a prothrombotic/proinflammatory phenotype, rather indices of these states appear in some conditions to be reduced. Further, transduction does not adversely affect EC adherence to Dacron graft surfaces under arterial hemodynamics.

Blood Platelets↗

PubMed1996

Comparative in vitro analysis of topical hemostatic agents.

Hemostatic agents are broadly utilized across the surgical specialties. While specific characteristics desirable for individual applications may vary, these agents generally are expected to aid the patient's coagulation system in the rapid development of an occlusive clot. Six commonly utilized hemostatic agents were quantitatively compared in terms of their ability to mediate platelet aggregation, deposition and activation, and initiate gross clot formation in a series of in vitro tests. Three types of collagen sponges (Actifoam, Helistat, Instat), microfibrillar collagen (Avitene), a gelatin sponge (Gelfoam), and oxidized regenerated cellulose (Surgicel) were studied. Platelet aggregation: Citrated platelet rich plasma (PRP) was contacted with hemostatic agents both with and without thrombin in a stirred cuvette and the platelet count was measured over 5 min. Platelet deposition: To approximate arterial wounds, PRP was perfused in a controlled manner through hemostatic agents, and the effluent platelet count was measured over time. Platelet activation: ATP secretion from PRP contacted with hemostatic agents in a stirred cuvette was measured at 1 and 5 min. Clot formation: The clotting time of nonanticoagulated whole blood contacted with the hemostatic agents was measured. Materials which depleted platelets most rapidly and effectively in the perfusion system (Avitene, Helistat, and Actifoam) were also the most effective inducers of platelet aggregation and secretion. Clot formation (likely to be platelet dependent) was also more rapid in this group. An overall activity ranking combined the relative performance of each hemostatic agent on the various tests: Actifoam approximately Avitene > Helistat >> Gelfoam > Instat > Surgicel. The activity ranking generally reflects the materials used in these agents (collagen > gelatin > oxidized regenerated cellulose), as well as their processing (chemical crosslinking in collagen sponges may lower activity). Such in vitro assessment of the relative platelet and coagulation activities of hemostatic agents might serve as a useful screening tool before investigating properties which require more expensive animal or clinical testing.

Adenosine Triphosphate↗

PubMed1994

Heparin-coated cardiopulmonary bypass circuits: hemostatic alterations and postoperative blood loss.

This prospective, randomized study involving patients undergoing isolated coronary artery bypass grafting investigated whether the use of heparin-coated bypass circuits with an uncoated cardiotomy reservoir (n = 10) compared with standard uncoated bypass circuits (n = 10) resulted in differences in patient outcome and hemostatic alterations. There were no differences in postoperative blood loss, transfusion requirements, and routine coagulation test results between groups. Immunoassays for platelet alpha-granule constituents platelet factor 4 and beta-thromboglobulin, thrombin generation by-product F1.2, fibrinopeptide A, thrombin-antithrombin complex, and fibrinolysis by-product D-dimer also demonstrated no significant differences between groups, although trends for lower platelet secretion with heparin coating were noted. Increases were found in beta-thromboglobulin and platelet factor 4 concentrations at 10 (p < 0.03) and 30 minutes (p < 0.001) of CPB, respectively, and continuing throughout CPB (p < 0.001) for both groups versus values measured before incision. No significant differences were seen between levels 5 minutes prior to aortic cross-clamp release and those obtained 8 and 45 minutes after cross-clamp release. Conversely, no significant increases in F1.2, thrombin-antithrombin complex, and D-dimer were seen prior to release of the aortic cross-clamp, but afterward increases occurred that were highly significant (p < 0.001). The temporal data suggest that platelet activation occurs primarily as a result of contact with the cardiopulmonary bypass circuitry, whereas thrombin generation and fibrinolytic activity are not significant until reperfusion of the heart and lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1993

Evaluation of bioprosthetic valve-associated thrombus in ventricular assist device patients.

BACKGROUND: Thromboembolic events may be related to thrombotic deposition on prosthetic valves. In a left ventricular assist device (LVAD) that contains two porcine pericardial bioprosthetic valves in addition to significant associated biomaterial placement, this may be particularly true. Thrombotic deposits on valves removed from LVADs at autopsy or heart transplantation were scored to determine (1) the nature and location of valvular deposition, (2) whether deposition was related to thromboembolic events, (3) correlations between deposition and patient hemodynamic and coagulation parameters, and (4) implant time dependency. METHODS AND RESULTS: Novacor LVADs were implanted in 23 patients as a bridge to transplantation for 1 to 303 days. Photographs of the concave (downstream) and convex (upstream) side of the inflow and outflow valve were made at explant and later scored for (1) total thrombus area (10 = equivalent of cusp area), (2) percent of cusp area occupied by solid thrombus, (3) thrombus color (10 = dark red, 0 = white), and (4) average percent of valve strut height involved with thrombus (from a side view). The inflow valve was shown to have heavier and redder deposition than the outflow valve. This was also true for the concave versus the convex side. Heaviest deposition was seen on the inflow valve concave side, which rests within the LVAD pumping sac and may be subject to poor convection. Patients with neurological thromboembolic events (8/23) during implantation had heavier deposition on the inflow valve concave side (5.7 +/- 2.7 versus 4.6 +/- 2.2, P < .05). Pump volumetric output was also found to negatively correlate with thrombus area on this valve and side (r = -.61, P = .002). Platelet release (platelet factor 4) was correlated with thrombus involvement on the upstream (convex) side of the inflow valve (r = .82, P = .002). No significant dependence of deposition on the implant time was found. CONCLUSIONS: Valve thrombus deposition was related to thromboembolic events. Pump volumetric output and platelet release were found to be related to deposition. These results may have implications for the role of hemodynamics and platelet activation in thromboembolism associated with prosthetic valve placement in general.

Bioprosthesis↗

PubMed1993

The effect of surface macrotexture on the mechanical and histologic characteristics of hydroxylapatite-coated dental implants.

The interface attachment strength and histology of HA-coated endosseous dental implants with surface texturing added to allow for mechanical interlocking of the implant to bone were evaluated in the canine mandibular model. Twenty-two adult mongrel dogs received eight implants (four per side) placed into healed extraction sites. Fifteen weeks post-implantation, the implants were evaluated mechanically by axial pull-out and torsional testing. Following testing, the specimens were evaluated quantitatively for histologic parameters of bone apposition, HA-coating thickness, and mode of interface failure. The addition of surface macrotexture (threads, grooves, and dimples) was not found to have a significant effect on axial pull-out strength compared with smooth implant controls. Similarly, mechanical testing in torsion failed to reveal any significant effect on implant-bone interface attachment due to surface macrotexture. Interface failure occurred primarily at the HA/substrate interface in all implant designs. Examination of HA-coating thickness revealed non-uniform coatings, particularly in the surface-textured designs. Although bone growth into the surface textures was observed in some cases, often only minimal or a thin osseous layer on the HA coating was observed. This factor most likely contributed to the lack of significant additional interface attachment strength in the textured designs. The reduction in areas of complete implant incorporation may also have exposed the HA coating to high interfacial loads and may be responsible for the greater HA coating break-up and presence of particles observed in the textured designs.

Animals↗

PubMed1993

An in vivo analysis of an elliptical dental implant design.

The interface attachment strength and histology of an elliptical hydroxylapatite-coated (HA) endosseous dental implant were compared with those of an otherwise identical cylindrical dental implant. The implant designs were tested in two canine in vivo models: healed mandibular extraction sites and the femoral unicortical plug. The implants were evaluated 15 weeks post-implantation. The elliptical geometry of the dental implant was not found significantly to enhance axial pull-out strength or torsional implant-bone interface attachment in either in vivo model. The cylindrical implant absorbed more energy to failure in both the mandible and the femur; however, the difference was not statistically significant. Differences in the interface shear attachment strength between the two models (mandible and femur) were statistically significant when the maximum load to failure was normalized by the actual bone contact surface area. In all cases, femoral values were significantly greater. Examination of HA-coating thickness revealed uniform coatings on both implant types which were well maintained in vivo. Mechanical failure occurred primarily at the metal substrate-HA interface in each type of implant in both models. The amounts of bone apposition to both implants in both models were identical. Coating break-up and inflammatory response to the particulate debris were minimal.

Analysis of Variance↗

PubMed1993

Cerebrovascular complications associated with the use of artificial circulatory support services.

Neurologic complications are associated with the use of total artificial hearts and with ventricular support systems. Among these complications, thromboembolic events are the most severe and the most frequent, resulting from flow disturbances associated with the artificial devices or occurring within the artificial heart. However, alterations in blood viscosity, abnormalities in the coagulation system, and infection all may play a part in the generation of thrombi. Anticoagulation may play a role in controlling the events that lead to thromboembolism, but the most effective therapeutic regimen has yet to be defined. Although neurologic complications constitute a significant risk, disabling strokes have been relatively rare and appear to relate to the duration of support on the device. The majority of subjects who sustained device-related strokes have made an excellent recovery following transplantation. LVADs constitute an important therapeutic development in the treatment of end stage heart failure. They may cause neurologic complications, but they have the capability of sustaining life until a suitable donor heart is found.

Cardiac Surgical Procedures↗

PubMed1992

ADP receptor antagonists and converting enzyme systems reduce platelet deposition onto collagen.

The effect of the ADP receptor antagonists ATP and adenosine 5'-(beta, gamma-methylene)triphosphate (AMP-PCP), and the ADP-utilizing enzyme systems creatine phosphokinase/creatine phosphate (CPK/CP) and pyruvate kinase/phosphoenol pyruvate (PK/PEP) on platelet deposition onto type I collagen was examined. An in vitro perfusion system was used, which allowed continuous visualization of the deposition of fluorescently labelled platelets. This system also provide well-controlled rheology, precise quantification of deposition, and allowed the use of heparinized whole human blood (3 u/ml). Heparinization at this level permits the local generation of thrombin near surface platelet aggregates. The contribution of ADP is thus studied with the combined effects of thrombin, thromboxane A2, and other aggregating agents present. Results from these studies indicate that ATP was capable of inhibiting deposition by 60% at 1 microM and 90% at 5 microM (whole blood conc.). AMP-PCP inhibited deposition in a dose dependent manner with a Ki of approximately 80 microM and a maximum inhibition of 60%. Inhibition by CPK/CP was measured at 20, 40, and 60 u/ml, with approximately 45% inhibition achieved for the latter two concentrations. PK/PEP at 60 u/ml resulted in 70% inhibition. These results support a role for ADP in mediating platelet recruitment in thrombus growth on collagen. Previous work utilizing animal bleeding times supports this conclusion; the present study demonstrates that this role is not dependent upon endothelial or vasoconstrictive effects. Intraplatelet cAMP levels were raised with respect to controls upon exposure to ATP at 8.3 microM (p less than 0.025), and 15 microM (p less than 0.005), as well as AMP-PCP at 42-500 microM (p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗

PubMed1992

Evidence for a role in thrombus stabilization for thromboxane A2 in human platelet deposition on collagen.

The role of thromboxane A2 (TxA2) in platelet deposition onto collagen was studied in flowing whole heparinized human blood in vitro by using a cyclooxygenase inhibitor, aspirin, and a TxA2 receptor antagonist, GR32191B. Previous studies have demonstrated a role for TxA2 in platelet aggregation in citrated plasma, and for platelet deposition in flowing citrated human and rabbit blood, but not in flowing heparinized rabbit blood. In contrast with the literature regarding rabbit blood, aspirin was demonstrated to be effective in reducing platelet accumulation in heparinized human blood, as was GR32191B. The temporal pattern of the platelet deposition, which reached an asymptote with TxA2 inhibition at 2.0 minutes but did not do so without inhibition, suggested that TxA2 plays a role in thrombus stabilization. The reduction in platelet deposition (which included some aggregation) seen with aspirin and GR32191B in the first 1.5 minutes of perfusion indicated that some inhibition of platelet recruitment occurred. Scanning electron microscopy revealed that less fibrin was present in thrombi derived from GR32191B-treated heparinized blood than in thrombi derived from control heparinized blood. No fibrin formation was observed in citrated blood with or without TxA2 inhibition. It is proposed that, in addition to its role as a mediator of platelet recruitment, TxA2 is involved in the stabilization of platelet-platelet interactions in the thrombus, perhaps by enhancing local fibrin formation or binding.

Aspirin↗

PubMed1991

The use of laser-light scattering and controlled shear in platelet aggregometry.

Laser-light scattering was used to observe and quantify the dynamics of human blood platelet aggregation in platelet-rich plasma (PRP). Aggregation was performed in a controlled shear environment by placing the PRP in the annular space between a rotating cylindrical rod and a stationary cylindrical tube. The instrument was capable of very sensitive continuous semi-quantitative measurements of chemically-induced microaggregation. As a demonstration of the technique, results are presented for ADP-induced aggregation at doses of 10, 1, and 0.1 microM and collagen-induced aggregation at a dose of 5 micrograms/ml, each at shear rates of 1,000 s-1 and 500 s-1. Extensive aggregation was observed in response to ADP at even the low dose of 0.1 microM, indicating a high sensitivity to microaggregates. The sensitivity of the ultimate size of the ADP-induced aggregates to ADP concentration was shear dependent. The formation of microaggregates by collagen stimulation was shown to be almost immediate, as contrasted with a 10-20 s typical lag when observed turbidometrically. Disaggregation was observed with 1 microM ADP, but this was only partial, as contrasted with the complete recovery of transmittance observed in the turbidometric technique. Electronic particle sizing and counting was employed to semiquantitatively verify the aggregate size distributions found from mathematical conversion of the laser-light scattering data.

Adenosine Diphosphate↗