Platelet Kinetics Research Articles

Platelet kinetics in dogs treated with a glycoprotein IIb/IIIa peptide antagonist.

Platelet glycoprotein IIb/IIIa (GPIIb/IIIa) receptor antagonists have been highly effective inhibitors of platelet aggregation in preclinical studies and in clinical trials. However, decreased platelet counts have been documented in preclinical studies and in some patients receiving GPIIb/IIIa antagonists. We evaluated changes in platelet kinetics and fate in dogs receiving the GPIIb/IIIa receptor antagonist RPR 109891 orally for 4 days. Dogs receiving RPR 109891 had a 22-52% decrease in platelet count with the nadirs at 3-5 days after initiation of treatment. Platelet survival time was reduced by 19%, and platelet half-life was reduced by 63%. Indium-111-labeled platelets were rapidly cleared from the blood within 1 hour after administration of RPR 109891 on treatment days 1 and 2. This clearing was associated with a sharp increase in radioactivity in spleen but not in liver or lung. Platelet clearance was markedly attenuated on treatment days 3 and 4. Platelet counts returned to baseline within 1 week after discontinuation of treatment. These data indicate that RPR 109891 causes rapid and selective sequestration of platelets in the spleen.

The Effect of Monoclonal Anti-human-platelet Antibodies on Platelet Kinetics in a Baboon Model: IgG Subclass Dependency

We assessed the in vivo effect of six intact anti-human antiplatelet antibodies of two major IgG subclasses on platelet kinetics in baboons. Five of the six antibodies tested caused thrombocytopenia of varying degree when injected at a precalculated threshold value. An agglutinating IgG1 antibody (MA-8L4A12) caused a long-lasting, mild thrombocytopenia with a predominant uptake of radiolabelled platelets in the spleen, while the four IgG2 antibodies tested (MA-13G8E1, MA-2M5A6, MA-21K2E8 and MA-22M10) caused a severe, transient thrombocytopenia with uptake of platelets in the liver. Two of the IgG2 antibodies (MA-13G8E1 and MA-2M5A6) caused platelet activation and aggregation in vitro, whilst the other two did not elicit a platelet aggregation response. The platelet survival time was shortened with all five of the thrombocytopenia-inducing antibodies, while only one antibody (MA-2M5A6) had a significant effect on the bleeding time. This study indicates that the IgG subclasss may be a determining factor in the outcome of platelet sequestration in immune-induced thrombocytopenia.

Vortex shedding in steady flow through a model of an arterial stenosis and its relevance to mural platelet deposition.

In this study, the development of unsteady vortical formations in the separated flow region distal to a stenosis throat is presented and compared with the platelet deposition measurements, to enhance our understanding of the mechanisms involved in platelet kinetics in flowing blood. Qualitative and quantitative flow visualization and numerical simulations were performed in a model of a streamlined axisymmetric stenosis with an area reduction of 84% at the throat of the stenosis. Measurements were performed at Reynolds numbers (Re), based on upstream diameter and average velocity, ranging from 300 to 1,800. Both the digital particle image visualization method employed and the numerical simulations were able to capture the motion of the vortices through the separated flow region. Periodic shedding of vortices began at approximately Re=375 and continued for the full range of Re studied. The locales at which these vortices are initiated, their size, and their life span, were a function of Re. The numerical simulations of turbulent flow through the stenosis model entailed a detailed depiction of the process of vortex shedding in the separated flow region downstream of the stenosis. These flow patterns were used to elucidate the mechanisms involved in blood platelet kinetics and deposition in the area in and around an arterial stenosis. The unsteady flow development in the recirculation region is hypothesized as the mechanism for observed changes in the distribution of mural platelet deposition between Re =300, 900, and 1,800, despite only a marginal variation in the size and shape of the recirculation zone under these flow conditions.

Monte Carlo Simulation of the Heterotypic Aggregation Kinetics of Platelets and Neutrophils

The heterotypic aggregation of cell mixtures or colloidal particles such as proteins occurs in a variety of settings such as thrombosis, immunology, cell separations, and diagnostics. Using the set of population balance equations (PBEs) to predict dynamic aggregate size and composition distributions is not feasible. The stochastic algorithm of Gillespie for chemical reactions (Gillespie, 1976. J. Comput. Phys. 22:403–434) was reformulated to simulate the kinetic behavior of aggregating systems. The resulting Monte Carlo (MC) algorithm permits exact calculation of the decay rates of monomers and the temporally evolving distribution of sizes and compositions of the aggregates. Moreover, it permits calculation of all moments of these distributions. Using this method, we explored the heterotypic aggregation of fully activated platelets and neutrophils in a linear shear flow of shear rate G = 335 s −1. At plasma concentrations, the half-lives of homotypically aggregating platelet and neutrophil singlets were 8.5 and 2.4 s, respectively. However, for heterotypic aggregation, the half-lives for platelets and neutrophils decreased to 2.0 and 0.11 s, respectively, demonstrating that flowing neutrophils accelerate capture of platelets and growth of aggregates. The required number of calculations per time step of the MC algorithm was typically a small fraction of Ω 1/2 , where Ω is the initial number of particles in the system, making this the fastest MC method available. The speed of the algorithm makes feasible the deconvolution of kernels for general biological heterotypic aggregation processes.

Urokinase receptor (uPAR, CD87) is a platelet receptor important for kinetics and TNF-induced endothelial adhesion in mice.

Urokinase plasminogen activator receptor (uPAR, CD87) is a widely distributed 55-kD, glycoprotein I-anchored surface receptor. On binding of its ligand uPA, it is known to increase leukocyte adhesion and traffic. Using genetically deficient mice, we explored the role of uPAR in platelet kinetics and TNF-induced platelet consumption. Anti-uPAR antibody stained platelets from normal (+/+) but not from uPAR-/- mice, as seen by fluorescence-activated cell sorter analysis. 51Cr-labeled platelets from uPAR-/- donors survived longer than those from +/+ donors when injected into a +/+ recipient. Intratracheal TNF injection induced thrombocytopenia and a platelet pulmonary localization, pronounced in +/+ but absent in uPAR-/- mice. Aprotinin, a plasmin inhibitor, decreased TNF-induced thrombocytopenia. TNF injection markedly reduced the survival and increased the pulmonary localization of 51Cr-labeled platelets from +/+ but not from uPAR-/- donors, indicating that it is the platelet uPAR that is critical for their response to TNF. As seen by electron microscopy, TNF injection increased the number of platelets and polymorphonuclear neutrophils (PMNs) in the alveolar capillaries of +/+ mice, whereas in uPAR-/- mice, platelet trapping was insignificant and PMN trapping was slightly reduced. Platelets within alveolar capillaries of TNF-injected mice were activated, as judged from their shape, and this was evident in +/+ but not in uPAR-/- mice. These results demonstrate for the first time the critical role of platelet uPAR for kinetics as well as for activation and endothelium adhesion associated with inflammation.

Platelet Adhesion to Collagen Type I, Collagen Type IV, von Willebrand Factor, Fibronectin, Laminin and Fibrinogen: Rapid Kinetics under Shear

Extracellular matrix proteins in the blood vessel wall fulfill an essential role in haemostasis by promoting platelet adhesion at the site of vessel injury. We have combined a continuous-flow system with affinity chromatography to study platelet adhesion under conditions mimicking arterial flow and have examined the adhesion kinetics of unstimulated platelets to collagens type I and IV, von Willebrand factor (vWf), fibronectin, laminin and to fibrinogen. In the absence of red cells, in ACD-prepared plasma adhesion to collagens type I and IV or vWf was rapid, efficient (>50% in <1 s ) and independent of shear rates from 650 to 3400 s(-1) with kinetics following an inverse exponential decay curve. We introduced a simple mathematical model in which this type of kinetics arises, and which may be more generally applicable to various adhesion processes under flow conditions. The model is characterized by the rate of platelet deposition on the adhesive surface being proportional to the number of platelets in the flow. Adhesion to fibronectin was independent of shear rate, but revealed a lag phase of approximately 1.5 s before significant adhesion began. Laminin and fibrinogen supported efficient adhesion at low shear rates (650-1000 s(-1)), but a lag phase of approximately 1.5 s was seen at high shear rates (1700-3400 s(-1)). Control proteins (albumin and gelatin) supported minimal adhesion. Nonspecific adhesion to poly-L-lysine differed from that to other substrate proteins in that the kinetics were linear. In conclusion, human platelets adhered specifically, rapidly (within seconds) and efficiently to several proteins under flow conditions and the kinetics of adhesion depended on the protein serving as substrate as well as on shear rate.

A Randomized Phase-II Study of BB-10010 (Macrophage Inflammatory Protein- 1α) in Patients With Advanced Breast Cancer Receiving 5-Fluorouracil, Adriamycin, and Cyclophosphamide Chemotherapy

BB-10010 is a variant of the human form of macrophage inflammatory protein-1α (MIP-1α), which has been shown in mice to block the entry of hematopoietic stem cells into S-phase and to increase their self-renewal capacity during recovery from cytotoxic damage. Its use may constitute a novel approach for protecting the quality of the stem cell population and its capacity to regenerate after periods of cytotoxic treatment. Thirty patients with locally advanced or metastatic breast cancer were entered into the first randomized, parallel group controlled phase II study. This was designed to evaluate the potential myeloprotective effects of a 7-day regimen of BB-10010 administered to patients receiving six cycles of 5-fluorouracil (5-FU), adriamycin, and cyclophosphamide (FAC) chemotherapy. Patients were randomized, 10 receiving 100 μg/kg BB-10010, 11 receiving 30 μg/kg BB-10010, and nine control patients receiving no BB-10010. BB-10010 was well-tolerated in all patients with no severe adverse events related to the drug. Episodes of febrile neutropenia complicated only 4% of the treatment cycles and there was no difference in incidence between the treated and nontreated groups. Studies to assess the generation of progenitor cells in long-term bone marrow cultures were performed immediately preceding chemotherapy and at the end of six dosing cycles in 18 patients. Circulating neutrophils, platelets, CD 34+ cells, and granulocyte/macrophage colony-forming cell (GM-CFC) levels were determined at serial time points in cycles 1, 3, and 6. The results showed similar hemoglobin and platelet kinetics in all three groups. On completion of the six treatment cycles, the average pretreatment neutrophil levels were reduced from 5.3 to 1.7 × 109/L in the control patients and from 4.3 to 1.9 and 4.5 to 2.5 × 109/L in the 30/100 μg/kg BB-10010 groups, respectively. Relative to their pretreatment values, 50% of the patients receiving BB-10010 completed the treatment with neutrophil values significantly higher than any of the controls (P = .02). Mobilization of GM-CFC was enhanced by BB-10010 with an additional fivefold increase over that generated by chemotherapy alone, giving a maximal 25-fold increase over pretreatment values. Bone marrow progenitor assays before and after this standard regimen of chemotherapy indicated little long-term cumulative impairment to recovery from chemotherapy. Despite the limited cumulative damage to the bone marrow, which may have minimized the protective value of BB-10010 during this regimen of chemotherapy, better recovery of neutrophils in the later treatment cycles with BB-10010 was indicated in a number of patients.© 1998 by The American Society of Hematology.

A Randomized Phase-II Study of BB-10010 (Macrophage Inflammatory Protein- 1) in Patients With Advanced Breast Cancer Receiving 5-Fluorouracil, Adriamycin, and Cyclophosphamide Chemotherapy

BB-10010 is a variant of the human form of macrophage inflammatory protein-1 (MIP-1), which has been shown in mice to block the entry of hematopoietic stem cells into S-phase and to increase their self-renewal capacity during recovery from cytotoxic damage. Its use may constitute a novel approach for protecting the quality of the stem cell population and its capacity to regenerate after periods of cytotoxic treatment. Thirty patients with locally advanced or metastatic breast cancer were entered into the first randomized, parallel group controlled phase II study. This was designed to evaluate the potential myeloprotective effects of a 7-day regimen of BB-10010 administered to patients receiving six cycles of 5-fluorouracil (5-FU), adriamycin, and cyclophosphamide (FAC) chemotherapy. Patients were randomized, 10 receiving 100 μg/kg BB-10010, 11 receiving 30 μg/kg BB-10010, and nine control patients receiving no BB-10010. BB-10010 was well-tolerated in all patients with no severe adverse events related to the drug. Episodes of febrile neutropenia complicated only 4% of the treatment cycles and there was no difference in incidence between the treated and nontreated groups. Studies to assess the generation of progenitor cells in long-term bone marrow cultures were performed immediately preceding chemotherapy and at the end of six dosing cycles in 18 patients. Circulating neutrophils, platelets, CD 34+ cells, and granulocyte/macrophage colony-forming cell (GM-CFC) levels were determined at serial time points in cycles 1, 3, and 6. The results showed similar hemoglobin and platelet kinetics in all three groups. On completion of the six treatment cycles, the average pretreatment neutrophil levels were reduced from 5.3 to 1.7 × 109/L in the control patients and from 4.3 to 1.9 and 4.5 to 2.5 × 109/L in the 30/100 μg/kg BB-10010 groups, respectively. Relative to their pretreatment values, 50% of the patients receiving BB-10010 completed the treatment with neutrophil values significantly higher than any of the controls (P = .02). Mobilization of GM-CFC was enhanced by BB-10010 with an additional fivefold increase over that generated by chemotherapy alone, giving a maximal 25-fold increase over pretreatment values. Bone marrow progenitor assays before and after this standard regimen of chemotherapy indicated little long-term cumulative impairment to recovery from chemotherapy. Despite the limited cumulative damage to the bone marrow, which may have minimized the protective value of BB-10010 during this regimen of chemotherapy, better recovery of neutrophils in the later treatment cycles with BB-10010 was indicated in a number of patients. © 1998 by The American Society of Hematology.

Successful treatment of severe thrombocytopenia in a cirrhotic patient with portal hypertension using partial splenic artery embolization

INTRODUCTION: Patients with cirrhosis and portal hypertension frequently have splenomegaly, thrombocytopenia, anemia and coagulopathy. Splenectomy is an accepted treatment for thrombocytopenia in patients without portal hypertension, however, splenect0my carries a high risk of intraoperative bleeding in those with underlying portal hypertension. Several studies and case reports advocate partial splenic artery embolization for the management of thrombocytopenia due to splenomegaly. CASE: A 69 year old male with Laennec's cirrhosis, portal hypertension (splenomegaly, ascites), presented with severe thrombocytopenia, coagulopathy, anemia, epistaxis, and melena. He was a poor surgical candidate because of comorbidities of insulin dependent diabetes meUitus, chronic renal failure, coronary artery disease, and sip right pneumonectomy for lung cancer 26 years ago. Hg/Hct were 7.6/22.4, platelets: 16,000, PT: 14.2. EGD revealed grade 4 esophageal varices, and portal hypertensive gastropathy. He received 4 units of packed cells. Initially, he underwent a partial splenic artery embolization using polyvinyl alcohol particles. His platelets increased to a range of 26-36,000 one week post embolization, H/H were stable and no additional blood transfusions were needed. Twelve days later a second partial splenic artery embolization was done, which led to a further increase in platelet count to a range of 60-70,000. CT and MRI of the abdomen showed a 50% decrease in spleen size. His H/H at discharge were 9.9/27.9, WBC 4.4 (preadmission was 2.8). CONCLUSION: Partial splenic artery embolization may be a useful procedure for the management of splenomegaly and thrombocytopenia in cirrhotic patients with portal hypertension. It may decrease the frequency of bleeding and blood replacement therapy by increasing platelets count and function. More controlled studies are warranted before considering this procedure as a standard approach for this patient population. [1] Hideya Noguchi. Changes in platelet kinetics after a partial splenic arterial embolization in cirrhotic patients with hypersplenism. Hepatology 1995 Dec;22(6): 1682-1688. [2] Sangro B. Partial splenic embolization for the treatment of hypersplenism in cirrhosis. Hepatology 1993 Aug;18(2):309-314.

Red cell and platelet kinetics in chronic cytopenias following transplantation.

Thirty seven patients with unexplained anemia and/or thrombocytopenia after bone marrow, kidney, liver or heart transplantation were referred to the Department of Nuclear Medicine for erythrocyte or platelet kinetic studies in order to determine the mechanism of the cytopenia: accelerated destruction, or production defect. We observed only one definite case of thrombocytopenia due to accelerated autologous platelet destruction, while the life span was normal in the other 16 cases. Anemia was due to accelerated hemolysis in 7 cases, while the red blood cell life-span was normal in 12 other cases. Kinetic studies can therefore be useful, by demonstrating the mechanism of cytopenia observed after transplantation, and by facilitating the choice of appropriate treatment.

Flow cytometric method for detecting thiazole orange-positive (reticulated) platelets in thrombocytopenic horses

Abstract Objective To evaluate a method for detecting thiazole orange-positive (TO+, reticulated) platelets in equine blood, using flow cytometry. Animals 16 healthy, equine infectious anemia virus (EIAV)-negative horses and ponies; 9 thrombocytopenic, ElAV-positive horses and ponies; and 2 thrombocytopenic, ElAV-negative horses. Procedure Blood from healthy and thrombocytopenic horses was collected by jugular venipuncture. Appropriate sample requirement and incubation time for the assay were evaluated, using blood anticoagulated with EDTA or sodium citrate, or platelet-rich plasma in sodium citrate. The sample of blood or platelet-rich plasma was incubated with thiazole orange, and flow cytometric analysis was performed. Percentage of circulating TO+ platelets was determined from fluorescence (FL-1) logarithmic histograms. Results Healthy ponies (n = 9) had 1.28 to 2.83% (mean ± SD, 2.03 ± 0.50%) and horses (n = 7) had 0.9 to 3.44% (2.12 ± 1.14%) TO+ platelets in circulation. Thrombocytopenic ponies (n = 7) had 11.14 to 48.41 % (26.51 ± 11.99%) and thrombocytopenic horses (n = 4) had 2.33 to 8.52% (6.19 ± 2.68%) TO+ platelets in circulation. Mean platelet counts for the thrombocytopenic ponies and horses were 24,400 ± 20,500 and 39,300 ± 13,500 platelets/μl, respectively (reference range, 94,000 to 232,000 platelets/μl). Conclusion Thiazole orange-positive platelets can be detected in equine blood and percentages of TO+ platelets are increased in thrombocytopenic horses. Clinical Relevance Enumeration of TO+ platelets may prove to be a helpful noninvasive clinical measurement of bone marrow platelet production and aid in the assessment of platelet kinetics in thrombocytopenic horses. (Am J Vet Res 1997;58:1092–1096)

In vivo radioprotective effect of AcSDKP on canine myelopoiesis.

The tetrapeptide acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) interferes with G1/S-phase progression, and the resulting cell cycle arrest is thought to protect hematopoietic stem cells against injury by cycle-active cytotoxic agents. We investigated the radioprotective effect of AcSDKP in a canine radiation model. Dogs were given total-body irradiation (TBI) at an exposure rate of 10 cGy/min, either without further therapy (control) or with administration of AcSDKP at 0.05-500 micrograms/ kg/24 h beginning before and continuing until after completion of TBI. At 400 cGy of TBI, one of 28 control dogs and one of eight AcSDKP-treated dogs recovered hematopoiesis (p = 0.40). At 300 cGy, seven of 21 control dogs recovered hematopoiesis compared with five of five AcSDKP-treated dogs (p = 0.01). In dogs given 300 cGy and AcSDKP, the granulocyte nadirs were less profound (p = 0.04) and occurred later (p = 0.04) than among controls; platelet kinetics did not differ. These data suggest, therefore, that AcSDKP provides a radioprotective effect in dogs exposed to 300 cGy TBI. Such an effect might be beneficial in recipients of intensive radiation therapy. Conceivably, the effect on hematopoietic recovery could be amplified by growth factor administration after irradiation.

Mechanisms of thrombocytopenia induced by interferon therapy for chronic hepatitis B.

To clarify the mechanisms of thrombocytopenia observed in patients with chronic hepatitis B treated with interferon. We studied six patients with chronic active hepatitis B who received intramuscular injections of natural interferon-alpha (3 or 5 million IU/ day) for 4 weeks. Peripheral blood platelet counts, bone marrow findings, and platelet kinetics, determined using 111In-labeled platelets, were analyzed. Platelets decreased significantly 1 week after the beginning of treatment and remained decreased until the completion of treatment. The number of nucleated cells and megakaryocytes in bone marrow decreased in three of five patients studied during treatment. The kinetic study showed platelet survival time to be 8.1 +/- 1.3 days (range, 5.8-10.0). One day after platelet injection, platelets accumulated predominantly in the splenic area in all patients, whereas hepatic accumulation was predominant 7 days after injection in three of the six patients. Thrombocytopenia during interferon treatment arises from the inhibition of stem cell proliferation and differentiation in the bone marrow and from the capture of platelets by the liver.

Platelet kinetics.

Platelet survival can be determined with considerable precision using radioisotopic methodologies; however, complications associated with these techniques still catalyze the search for nonisotopic procedures to estimate platelet survival as well as surrogate markers of platelet life span. Recent reports on markers of platelet age have focused on thiazole orange-staining for enumeration of "reticulated platelets," ie, young platelets with residual mRNA. Numerous clinical studies have observed a correlation between thiazole orange-positive platelets and platelet synthesis, thereby providing a noninvasive means to differentiate between synthetic and destructive mechanisms in thrombocytopenia. Additionally, nonisotopic methods for quantitating platelet survival have recently been developed in animal systems, although they have not yet been transferred to human use. And finally, an ancillary topic related to platelet turnover is the impact of cell age on platelet reactivity. Prevailing paradigms concerning age and reactivity are complicated by recent studies with cytokines, such as interleukin-6, which demonstrate that platelet age is not the sole determinant of platelet reactivity.

PLATELET ACCUMULATION INDUCED BY BACTERIAL ENDOTOXIN IN RATS

We studied the effects of i.v. administration of endotoxin (Escherichia coli, Serotype 0127:B8) on the kinetics of 111In-labelled platelets within the pulmonary, abdominal and splenic vascular beds of the rat, and on the radioactivity present in dissected samples of splenic and hepatic tissues. Bolus i.v. injection of endotoxin to anaesthetised rats caused a dose-dependent, transient accumulation of 111In-labelled platelets in the pulmonary vasculature. Increased radioactivity, suggestive of platelet sequestration, was detected in tissue samples from both the spleen and the liver at 4.5 h compared to the radioactivity detected in those organs in vehicle treated rats. The modulation of endotoxin-induced platelet accumulation within the lungs, spleen and liver by pharmacological agents was investigated. The pulmonary, hepatic and splenic platelet accumulation induced by endotoxin was unaffected by pre-treatment of the animals with indomethacin, HirulogTM or l-NAME. Pre-treatment with dexamethasone significantly reduced the platelet accumulation within the liver and spleen, but not the lungs.

Platelet kinetics, diagnosis and treatment of patients with idiopathic thrombocytopenia purpura: P.C. Ploos van Amstel1, H. Louwes2, A. Zeinali Lathori3, L. Wijnja1, JThM de Wolf3. Departments of Internal Medicine1 and Nuclear Medicine2 Martini Hospital, Department of Haematology3, University Hospital, Groningen, Netherlands

Platelet kinetics, diagnosis and treatment of patients with idiopathic thrombocytopenia purpura: P.C. Ploos van Amstel1, H. Louwes2, A. Zeinali Lathori3, L. Wijnja1, JThM de Wolf3. Departments of Internal Medicine1 and Nuclear Medicine2 Martini Hospital, Department of Haematology3, University Hospital, Groningen, Netherlands

Platelets from Bleeding Simmental Cattle Have a Long Delay in both ADP-activated Expression of GpllB-IIIA Receptors and Fibrinogen-dependent Platelet Aggregation

We have previously reported that platelets from bleeding Simmental cattle do not aggregate in vitro in response to ADP, collagen and calcium ionophore A23187, though calcium mobilization and myosin light chain phosphorylation do occur. The aggregation abnormality, measured by aggregometry, was ascribed to abnormal cytoskeletal expression, with the maximal numbers of activated GpIIb-IIIa receptors per platelet no different from that seen in normal bovine platelets activated with ADP. We have therefore sought to compare the kinetics of micro-aggregation with the rate of expression of GpIIb-IIIa receptors required for mediating fibrinogen (Fg)-dependent platelet aggregation, to provide a more direct molecular explanation for the aggregation abnormality. We compared aggregation kinetics of ADP-activated platelets using both aggregometry and particle counting to monitor micro-aggregation. Fibrinogen receptor expression was monitored with FITC-labelled human Fg and with the reporting antibody for activated GpIIb-IIIa, FITC-PAC1, using flow cytometry. The affected platelets show a marked delay in onset of microaggregation for ADP-activated platelets stirred with human Fg, paralleded by an unusual delay in activated GpIIb-IIIa receptor expression (DARE) for otherwise competent Fg binding. The on-rates for Fg binding to platelets maximally pre-activated with PMA are identical for normal and affected platelets, whether comparing the binding of human or bovine Fg. The unique DARE syndrome explains the observed delay in aggregation of platelets from affected Simmental cattle and predicts the bleeding problems due to delayed binding of adhesive proteins.

Effect of Thoracotomy and Cardiopulmonary Bypass on Activated Platelet and Neutrophil Dynamics and Platelet Emboli in a Pig Model.

The effects of thoracotomy and components of extracorporeal circuits on dynamics of platelets and neutrophils were quantified with autologous In-111-labeled platelets (INPLT) and neutrophils (INN) during cardiopulmonary bypass (CPB) operations in Yorkshire pigs. Cardiopulmonary bypass was carried out with a hollow-fiber oxygenator and an arterial filter in 48 pigs (30-35 kg; 12 unoperated controls for platelets and neutrophils; 12 sham operated controls; 12 with 180 minutes of CPB with platelets and neutrophils; 12 with 90 minutes of CPB and 90 minutes of reperfusion at 2.5-3.5 one/min. Platelets and neutrophils were labeled with In-111 tropolone and were injected intravenously: platelets at 24 hours and neutrophils at 15 minutes before CPB. All pigs were systemically heparinized [activated coagulation time (ACT) > 400 seconds]; CPB was instituted with a roller pump, oxygenator (OX; Bentley Univox, 1.8 m2), and arterial filter (AF; 0.025 m2) for durations of 180 minutes and 90 minutes of bypass, followed by 90 minutes of reperfusion. The kinetics and pooling of platelets and neutrophils were monitored by a Geiger probe. The adherent thrombi and neutrophils in the OX, AF, viscera, and brain were imaged with a gamma camera and were measured with an ion chamber and a gamma counter. The percentile distribution of labeled platelets and neutrophils expressed as the mean +/- standard deviation of injected dose in eight groups was calculated and statistical analyses were performed (ANOVA and paired t-test). Sham operation alone increased platelet retention in the lung, heart, and brain significantly (p < 0.001) over that of unoperated pigs. Neutrophil margination to lung immediately after injection was high; CPB and reperfusion altered the distribution in blood, viscera, and connective tissues. During CPB, an equilibrium among single platelets, platelet thrombi, and emboli was reached in the blood, oxygenator, arterial filter, perfused organs, and tissues. After CPB, the pulmonary neutrophil retention increased significantly (p < 0.001). Reperfusion of 90 minutes following 90 minutes of CPB decreased the level of neutrophils and increased the level of platelets in the lung. Only a small amount of platelets and neutrophils was retained in the oxygenator and arterial filter. Neutrophil retention in the OX and AF was higher than that of platelets. The small amount of retained neutrophils in the heart, kidneys, and brain suggested that cytokines, rather than marginated neutrophils alone, may play a major role in inflammatory insult to these organs during and after CPB. OX thrombi increased with the time of CPB; AF thrombus in both groups was almost similar. During CPB, AF functioned minimally as a thrombus trap with a small percent of retained thrombi; reperfusion post-CPB did not change the amount. Thoracotomy alone has a significant effect on platelet and neutrophil kinetics, and on the subsequent effect of thrombus formation, embolization, and neutrophil margination in organs during the CPB procedure.

Changes in platelet kinetics after a partial splenic arterial embolization in cirrhotic patients with hypersplenism

We performed a partial splenic arterial embolization in 22 patients with cirrhosis associated with thrombocytopenia and then evaluated the changes in platelet kinetics after undergoing the procedure using 111In-tropolone-labeled platelets. The controls consisted of eight chronic hepatitis patients who showed a normal platelet count and normal spleen size. The mean splenic infarction ratio after the procedure was 54.9%. A platelet kinetics study was performed before and 2 months after the procedure. Before the procedure, the cirrhotic patients showed increases in the splenic volume and the spleen/liver uptake ratio of the 111In-labeled platelets on both the third and seventh days, and a decrease in the platelet recovery compared with the controls, which suggested an increased platelet pool in the spleen. In addition, the platelet survival time in cirrhotic patients was shortened, whereas the platelet-associated immunoglobulin G (PA-IgG) was higher than that of the controls, which suggested the involvement of immunologic mechanisms in the thrombocytopenia. With an increase of the platelet count after a partial splenic arterial embolization, the spleen/liver uptake ratio of the 111In-labeled platelets decreased, whereas the platelet recovery increased. Furthermore, the platelet survival time was prolonged, whereas the PA-IgG decreased. The platelet count showed a positive correlation with the platelet survival time and a negative correlation with PA-IgG before and after the procedure. These results suggest that a transcatheter splenic arterial embolization not only may reduce the increased platelet pool in the spleen but also may improve the thrombocytopenia induced by immunologic mechanisms in patients with cirrhosis.

Changes in platelet kinetics after a partial splenic arterial embolization in cirrhotic patients with hypersplenism

We performed a partial splenic arterial embolization in 22 patients with cirrhosis associated with thrombocytopenia and then evaluated the changes in platelet kinetics after undergoing the procedure using 111In-tropolone-labeled platelets. The controls consisted of eight chronic hepatitis patients who showed a normal platelet count and normal spleen size. The mean splenic infarction ratio after the procedure was 54.9%. A platelet kinetics study was performed before and 2 months after the procedure. Before the procedure, the cirrhotic patients showed increases in the splenic volume and the spleen/liver uptake ratio of the 111In-labeled platelets on both the third and seventh days, and a decrease in the platelet recovery compared with the controls, which suggested an increased platelet pool in the spleen. In addition, the platelet survival time in cirrhotic patients was shortened, whereas the platelet-associated immunoglobulin G (PA-IgG) was higher than that of the controls, which suggested the involvement of immunologic mechanisms in the thrombocytopenia. With an increase of the platelet count after a partial splenic arterial embolization, the spleen/liver uptake ratio of the 111In-labeled platelets decreased, whereas the platelet recovery increased. Furthermore, the platelet survival time was prolonged, whereas the PA-IgG decreased. The platelet count showed a positive correlation with the platelet survival time and a negative correlation with PA-IgG before and after the procedure. These results suggest that a transcatheter splenic arterial embolization not only may reduce the increased platelet pool in the spleen but also may improve the thrombocytopenia induced by immunologic mechanisms in patients with cirrhosis.