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M L Rand

Publications and source records attributed to M L Rand.

At least 19 recordsLinked to original sources
PubMed2002

Concurrent measurement of the survival of two populations of rabbit platelets labeled with either two PKH lipophilic dyes or two concentrations of biotin.

BACKGROUND: To avoid radioisotopic labeling and permit comparison of the survival of two platelet populations concurrently in one animal, we compared simultaneous recoveries and survival times of homologous rabbit platelets labeled in vitro with the lipophilic dyes PKH26 (red fluorescing) and PKH67 (green fluorescing) and with two levels of biotin (low, 1 microg/ml; high, 10 microg/ml). METHODS: Blood samples were drawn up to 96 h postinfusion and analyzed by flow cytometry. Biotin-labeled samples were incubated with phycoerythrin-streptavidin before analysis. RESULTS: Recovery of PKH26-labeled platelets at 1 h was lower (37.5%) than that of PKH67-labeled platelets (47.3%; P < 0.001). Platelet survival times were 62.4 and 61.9 h. Recoveries at 1 h of platelets labeled with two levels of biotin were similar (86.6% and 84.6%) and greater than those of PKH-labeled platelets (P < 0.001). Survival of platelets labeled with biotin did not differ (low, 83.3 h; high, 85.2 h) and was longer than for PKH-labeled platelets (P < 0.01). Labeling methods did not activate platelets (measured by P-selectin expression), nor did they affect platelet responses to adenosine diphosphate (ADP), collagen, or thrombin. CONCLUSIONS: Labeling with two levels of biotin is superior to labeling with PKH dyes, and is useful for measuring concurrently the survival of two differing platelet populations.

Adenosine Diphosphate↗
PubMed2001

Blood platelet adhesion to protein studied by on-line acoustic wave sensor.

The attachment of blood platelets to the surface of bare and protein-coated thickness-shear mode acoustic wave devices operating in a flow-through configuration has been studied. Platelets in washed from bind to the gold electrodes of such sensors, but the resulting frequency shifts are far less than predicted by the conventional mass-based model of device operation. Adherence to albumin and various types of collagen can be produced by on-line introduction of protein or by a pre-coating strategy. Differences in attachment of platelets to collagen types I and IV and the Horm variety can be detected. Platelets attached to collagen yield an interesting delayed, but reversible signal on exposure to a flowing medium of low pH. Scanning electron microscopy of sensor surfaces at various time points in this experiment reveals that originally intact platelets are eventually destroyed by the high acidity of the medium. The reversible frequency is attributed to the presence of removable platelet granular components at the sensor-liquid interface.

Albumins↗
PubMed2000

Responses to aggregating agents after cleavage of GPIb of human platelets by the O-sialoglycoprotein endoprotease from Pasteurella haemolytica- potential surrogates for Bernard-Soulier platelets?

Most proteolytic enzymes that cleave glycoprotein lb (GPlb) also cleave other glycoproteins or receptors on the surface of platelets. We have used an O-sialoglycoprotein endoprotease from Pasteurella haemolytica that selectively cleaves the heavily O-glycosylated GPlb, but does not cleave N-linked glycoproteins or unglycosylated proteins. Isolated, [14C]serotonin-labeled platelets in Tyrode-albumin solution were incubated with 10 microg/mL endoprotease for 60 minutes at 37 degrees C. These platelets did not release [14C]serotonin, had no detectable GPIb, and were unresponsive to ristocetin/von Willebrand factor. Compared with control platelets, aggregation and release of [14C]serotonin by the endoprotease-pretreated platelets were inhibited in response to low concentrations of thrombin, SFLLRN (the PAR-1-activating peptide), collagen, and U46619 (a thromboxane A(2) mimetic); aggregates were smaller in size. The presence of fibrinogen overcame the inhibition of responses induced by SFLLRN, collagen, and U46619. With fibrinogen, primary ADP-induced aggregation was scarcely affected by pretreatment with the endoprotease. Thus, the PAR-1 receptor for thrombin, and receptors for collagen, thromboxane A(2), fibrinogen (GPIIb/IIIa), and ADP appear to function normally on the endoprotease-pretreated platelets. Since only GPIb is cleaved by the endoprotease, these platelets seem to provide potential surrogates for Bernard-Soulier syndrome platelets for further studies of platelet functions in this condition.

Agglutination↗
PubMed2000

von Willebrand disease in a pediatric-based population--comparison of type 1 diagnostic criteria and use of the PFA-100 and a von Willebrand factor/collagen-binding assay.

Definitive diagnosis of type 1 von Willebrand Disease (VWD) remains a problem. Provisional consensus guidelines for the diagnosis of definite and possible type 1 VWD were prepared by the Scientific Subcommittee on von Willebrand factor (VWF) of the Scientific and Standardization Committee (SSC) of the International Society on Thrombosis and Haemostasis (ISTH) during the 1996 annual meeting for the specific purpose of further evaluation in retrospective and prospective studies by a Working Party on Diagnostic Criteria (1996 Annual Report of the SSC/ISTH Subcommittee on VWF). In the first phase of this study, we compared 2 definitions of type 1 VWD. each with 3 criteria: significant bleeding history, laboratory investigations, and family history. Using the ISTH consensus guidelines for type 1 VWD definition, significantly fewer patients were diagnosed with definite type 1 disease as compared to our "in house" Hospital for Sick Children (HSC) criteria (4 vs. 31). While we recognize that the provisional ISTH consensus guidelines were not intended for clinical use, we believe that the results of our studies are of interest and will assist in any future refinements to the ISTH guidelines. In the second phase of this study, we investigated the utility of 2 new tests, a laboratory screening test and a functional test, for VWD in our well characterized, pediatric-based population. The Platelet Function Analyzer (PFA-100) provides an in vitro measure of primary hemostasis under conditions of high shear, using disposable cartridges containing collagen and either epinephrine or ADP. All tested subjects with types 2 or 3 VWD had prolonged PFA-100 closure times (CTs) with both cartridge types (n = 17) and prolonged bleeding times (n = 14). In subjects with definite type 1 VWD, 20/24 (83%) had prolonged CTs with the collagen/ADP cartridge (19/24 (79%) with collagen/epinephrine), compared with 7/26 (27%) with prolonged bleeding times. In subjects with definite types 1, 2, or 3 VWD, collagen/ADP CTs were abnormal in 37/41 subjects, giving an overall sensitivity of 90%. With this high sensitivity, the PFA-100 is a better screening test for VWD than the bleeding time. We also tested a VWF collagen-binding assay (VWF:CBA) as a functional test for VWF, in comparison with the more routinely-used ristocetin cofactor assay (VWF:RC0). The VWF:CBA is based on an ELISA technique, which has the potential to be more reproducible than the VWF:RC0. We found that the VWF:CBA detected 43/49 (88%) subjects with definite types 1, 2, or 3 VWD, performing as well as the VWF:RC0, that detected 42/48 (88%). We also showed that, used in conjunction with VWF antigen levels, the VWF:CBA may be useful in classification of VWD subtypes.

Adolescent↗
PubMed1999

Effects of ethanol on platelet responses associated with adhesion to collagen.

Adhesion of platelets to collagen in damaged blood vessels or ruptured atherosclerotic plaques is important in hemostasis and arterial thrombosis. Adhesion to collagen results in secretion of granule contents and formation of thromboxane A2; thromboxane A2 and released ADP synergistically promote aggregation around platelets adherent to collagen. Ethanol inhibits collagen-induced platelet aggregation, secretion, arachidonate mobilization, and thromboxane A2 formation but does not inhibit platelet adhesion to de-endothelialized rabbit aortae. We investigated whether ethanol affects the initial signalling events and responses of platelets adherent to collagen, independent of the actions of secondary agonists. Suspensions of washed human platelets, labelled by incorporation of [3H]oleate into phospholipids, were used to measure platelet adhesion to collagen by a filtration method; studies were done in the presence of an ADP-removing system and blockers of receptors for thromboxane A2, platelet-activating factor, serotonin, and fibrinogen. Ethanol (87 mM) did not affect the rate or extent of platelet adhesion to collagen or secretion of [14C]serotonin from prelabelled platelets adherent to collagen, but ethanol did inhibit thromboxane A2 formation. Previous studies showed that ethanol does not affect platelet stimulation by arachidonate, leading to the suggestion that reduced mobilization of arachidonate, rather than inhibition of its conversion to thromboxane A2, is responsible for inhibition by ethanol of thromboxane A2 formation. Here, we show by a gel mobility shift assay and immunoblotting, that ethanol delays the collagen-induced increase in the phosphorylation of cytosolic phospholipase A2, the enzyme responsible for arachidonate mobilization. However, ethanol has no effect on collagen-induced tyrosine phosphorylation of phospholipase Cgamma2, determined by immunoprecipitation and immunoblotting. Thus, ethanol's effect on signal transduction in collagen-adherent platelets occurs distal to phosphorylation of phospholipase Cgamma2 but proximal to phosphorylation of cytosolic phospholipase A2.

Adenosine Diphosphate↗
PubMed1999

Effects of cathepsin G pretreatment of platelets on their subsequent responses to aggregating agents.

Cathepsin G, a proteolytic enzyme from activated leukocytes, can interact with platelets during inflammation and thrombosis. Platelets that have been exposed to cathepsin G in thrombi may recirculate if they are freed during fibrinolysis. To determine whether some of the subsequent functions of such platelets would be impaired, we investigated the responses of cathepsin G-pretreated platelets to agonists that they would encounter in the circulation. Suspensions of washed human platelets were labeled with [14C]serotonin and resuspended in Tyrode-albumin solution (with 2 mM Ca2+ and apyrase). After 15 minute incubation with 400 nM cathepsin G at 37 degrees C, 52+/-3% of [14C]serotonin had been released, and glycoprotein Ib was degraded. The platelets were washed and resuspended in fresh medium to remove cathepsin G and released materials. Ristocetin-induced agglutination was abolished, indicating that the binding site for von Willebrand Factor on glycoprotein Ib had been removed. Aggregation and release of residual [14C]serotonin in response to 0.1-1.0 U/mL thrombin was blocked or greatly reduced by the cathepsin G pretreatment. This inhibition is probably largely due to cleavage by cathepsin G of some of the protease-activated receptors at the C-terminal side of Ser42 so that the tethered ligand is lost. Pretreatment with cathepsin G did not affect responses to ADP or a low concentration of platelet-activating factor in the presence of fibrinogen, indicating that receptors for these agonists were unaffected and that the function of the fibrinogen receptor, GPIIb/IIIa was unchanged. Responses to cathepsin G, the thrombin receptor-activating peptide SFLLRN, collagen, or the thromboxane A2 mimetic U46619 were partially inhibited, even in the presence of added fibrinogen. Platelet adhesion to a collagen-coated surface was 51+/-7% inhibited, which may indicate cleavage of a collagen receptor or receptors; this may partly account for strong inhibition of collagen-induced aggregation and release of granule contents; additionally, as shown by inhibition of responses to U46619, the function of the thromboxane A2 receptor may be compromised. Thus, although cathepsin G activates platelets, if they recirculate after interaction with it, their subsequent adhesion to damaged vessel walls, aggregation, and release of granule contents induced by thrombin and collagen will be diminished.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1999

The fibrinogen gamma chain dodecapeptide inhibits agonist-induced aggregation of rabbit platelets and fibrinogen binding to rabbit glycoprotein IIb-IIIa.

The HHLGGAKQAGDV (H12) sequence at the carboxyl termini of the y chains and the RGD sequences in the Aalpha chains of human fibrinogen are potential recognition sites for the binding of soluble fibrinogen to glycoprotein IIb-IIIa (GPIIb-IIIa) on activated human platelets. Thus, addition of either H12 or RGD-containing peptides inhibits aggregation of and fibrinogen binding to human platelets. In contrast, we reported previously that RGDS had relatively little inhibitory effect on these functions of rabbit platelets. In the present study, we found that H12 inhibited ADP- and thrombin-induced aggregation of rabbit platelets in a dose-dependent manner. Specificity was demonstrated by the failure of the variant HHLGGAKQAGEV peptide to inhibit ADP-induced aggregation. Furthermore, flow cytometric analyses demonstrated that H12 inhibited the binding of FITC-fibrinogen to ADP-activated rabbit platelets in a dose-dependent manner. To examine the direct interaction of H12 with rabbit GPIIb-IIIa, we performed affinity chromatography by applying an octylglucoside extract of rabbit platelet proteins onto an affinity matrix containing the fibrinogen gamma chain sequence. Proteins of approximately 135 kDa and approximately 95 kDa were specifically eluted by soluble H12, and the 95 kDa protein band was immunoblotted by anti-LIBS1, a monoclonal antibody against human GPIIIa. In control samples, no detectable protein from rabbit platelet lysates was eluted from an RGD affinity matrix by GRGDSP. Collectively, our results demonstrated that H12 inhibits aggregation of and fibrinogen binding to rabbit platelets by directly interacting with rabbit GPIIb-IIIa. These findings suggest that rabbit platelets would serve as a suitable thrombosis model for testing the efficacy of peptide mimetics derived from H12.

Animals↗
PubMed1998

Virus-associated idiopathic thrombocytopenic purpura.

Two-thirds of children with acute idiopathic thrombocytopenic purpura (ITP) have a history of an infectious illness a few days to a few weeks before the onset of thrombocytopenia. In a subset of affected children, identification of a specific virus can be made, such as varicella zoster virus, rubella, Epstein-Barr virus, influenza, or human immunodeficiency type 1 virus, indicating an etiological role for preceding viral infection in these children with ITP. While inhibition of thrombopoiesis has been established to play a role in thrombocytopenia associated with infection with some viruses, it does not appear to play a major role in the etiology of most typical ITP cases. Rather, enhanced clearance of platelets by the reticuloendothelial system is considered to be, at least in part, responsible for the thrombocytopenia which occurs during the viremic phase of acute virus infection or which develops days to weeks following the virus illness. Molecular mimicry between viral antigens and host proteins has been implicated in a number of autoimmune phenomena, and may be involved in the enhanced platelet clearance in virus-associated ITP.

Acute Disease↗
PubMed1998

The Platelet Function Analyzer (PFA-100): a novel in-vitro system for evaluation of primary haemostasis in children.

The PFA-100 system provides an in-vitro method of assessing primary platelet-related haemostasis by measuring the time (the closure time, or CT) taken for a platelet plug to occlude a microscopic aperture cut into a membrane coated with collagen and either epinephrine or ADP. We used the system to establish normal ranges for CTs in healthy children, adults and neonates. Mean CTs of healthy children were independent of the needle gauge used (21G or 23CG) for blood sampling; they were very similar to the mean CTs of healthy adults, but longer than mean CTs of healthy neonates. Although children with haemophilia had normal CTs, the PFA-100 system was found to be potentially useful in screening for von Willebrand disease in children.

Adolescent↗
PubMed1998

Use of the PFA-100 in the assessment of primary, platelet-related hemostasis in a pediatric setting.

The platelet function analyzer, PFA-100, has been designed to provide an in vitro measure of primary hemostasis simply, quickly, quantitatively, and accurately to aid in the routine screening of patients with potential hemorrhagic risk due to abnormal platelet plug formation. The system measures the closure time (CT), or the time taken for platelets in a sample of anticoagulated blood to form a plug that occludes a microscopic aperture cut into a membrane coated with collagen and either epinephrine or ADP. The high shear stresses produced in the analyzer lead to platelet plug formation that is greatly dependent on von Willebrand's factor (vWF). In this article, we detail the system itself and describe our initial studies using the PFA-100 to assess primary hemostasis in pediatric populations. Normal ranges have been established for healthy children and neonates. CTs for healthy children are independent of the needle gauge (21G or 23G) used for blood sampling. They are similar to CTs for healthy adults, but neonates have significantly shorter CTs, likely due to increased levels of vWF. Children with hemophilia have normal CTs, whereas seven out of eight patients with von Willebrand's disease (vWD) have abnormally long CTs. CT reproducibility between duplicate samples is excellent. Our preliminary results indicate that the PFA-100 will be useful in the evaluation of primary hemostasis in children, as well as in adults.

Adolescent↗
PubMed1998

Platelet function in autoimmune (idiopathic) thrombocytopenic purpura.

Platelets play an essential role in the formation of haemostatic plugs. The quantitative defect of platelets in autoimmune (idiopathic) thrombocytopenic purpura (ITP) can result in bleeding complications, but most ITP patients have platelets with normal or enhanced function. Platelets in ITP are large, young, so-called "stress" platelets with increased platelet-associated autoimmune antibody (immunoglobulin G). Young stress platelets are more functional platelets, and their presence may account for bleeding times in ITP patients that are shorter than would be predicted on the basis of the patients' (low) platelet counts. Some ITP patients have significant mucocutaneous bleeding with platelet counts >50 x 10(9) l(-1); this may be due to qualitative platelet dysfunction (e.g. brought about by inhibitory antiplatelet autoantibodies).

Autoantibodies↗
PubMed1998

Apolipoprotein(a) enhances platelet responses to the thrombin receptor-activating peptide SFLLRN.

Elevated levels of lipoprotein(a) [Lp(a)] are correlated with an increased risk of atherosclerotic disease. We examined the effect of recombinant apolipoprotein(a) [r-apo(a)] and Lp(a) on responses of washed human platelets, prelabeled in the dense granules with [14C]serotonin and suspended in Tyrode's solution, to ADP and the thrombin receptor-activating peptide SFLLRN. No effect of the 17 kringle (K), 12K, or 6K r-apo(a) derivatives (at concentrations of 0.35 and 0.7 micromol/L) or Lp(a) (up to 0.1 micromol/L) on primary ADP-induced platelet aggregation was observed. In contrast, weak platelet responses stimulated by 7.5 micromol/L SFLLRN were significantly enhanced by the r-apo(a) derivatives; eg, 0.7 micromol/L 17K r-apo(a) increased aggregation from 15+/-4% to 58+/-6%, release of [14C]serotonin from 9+/-3% to 36+/-6%, and formation of thromboxane A2, measured as its stable metabolite thromboxane B2, from 7+/-1 to 29+/-5 ng/10(9) platelets (n=3; P<0.04 to 0.015). Significant enhancement of aggregation and release of granule contents was observed at a concentration of 17K r-apo(a) as low as 0.175 micromol/L. Purified Lp(a) (0.25 to 0.1 micromol/L) also enhanced SFLLRN-induced aggregation and release in a dose-dependent manner. Although plasminogen (0.7 and 1.5 micromol/L) and low density lipoprotein (0.025 to 0.1 micromol/L) both exhibited potentiating effects on SFLLRN-mediated platelet aggregation, the magnitude of the responses was less than that observed with either the r-apo(a) derivatives or Lp(a). The enhanced responses of platelets via the protease-activated receptor- thrombin receptor in the presence of Lp(a) may contribute to the increased risk of thromboembolic complications of atherosclerosis associated with this lipoprotein.

Adenosine Diphosphate↗
PubMed1998

Ethanol inhibits thrombin-induced secretion of the contents of human platelet dense and alpha-granules and lysosomes.

Moderate consumption of alcoholic beverages is associated with a reduction in thromboembolic complications of coronary artery disease, possibly partially attributable to inhibition by ethanol of platelet responses to some aggregating agents. Although ethanol is known to inhibit thrombin-induced secretion of platelet dense granule contents, the effect of ethanol on secretion of alpha-granule and lysosomal contents has not been studied. Using suspensions of washed platelets, and a range of thrombin concentrations (up to 0.1 U/ml), we examined the effect of 87 mM ethanol on secretion of [14C]serotonin from prelabelled platelets as a measure of secretion of dense granule contents. Secretion of alpha-granule and lysosomal contents was examined by flow cytometric measurement of the surface expression of CD62P (P-selectin) and CD63, respectively. Secretion of the lysosomal enzyme, beta-N-acetylglucosaminidase was also quantified. Results were expressed as % of maximum response induced by 1 U/ml thrombin. Ethanol inhibited the thrombin-induced secretion of both dense and alpha-granule contents (P <0.001, 2-way ANOVA), and of lysosomal contents (P <0.005 for CD63 expression and P <0.001 for beta-N-acetylglucosaminidase secretion). When platelets were pretreated with aspirin, thrombin-induced secretion of storage granule and lysosomal contents was slightly inhibited, but secretion was inhibited by ethanol to the same extent as the untreated platelets, indicating that this inhibition was independent of thromboxane A2. Surface expression of CD63 occurred at lower thrombin concentrations than those required for secretion of beta-N-acetylglucosaminidase, possibly due to the presence of some CD63 on granule membranes. Although the role of lysosomal contents in thrombus formation is not established, some constituents of storage granules are known to augment thrombus formation; ethanol's inhibition of their secretion by stimulated platelets may contribute to its beneficial effect on thromboembolism.

Blood Platelets↗
PubMed1997

Platelet disorders in newborn infants: diagnosis and management.

Platelets are small, disc-shaped, anucleated cells formed by fragmentation of megakaryocytes in the bone marrow. They circulate in blood with a lifespan of 7 to 10 days and, together with fibrin, form hemostatic plugs at sites of vessel injury. Abnormalities of platelets, either quantitative or qualitative, may cause clinically significant bleeding with resultant morbidity and, on occasion, mortality. This review will focus on platelet disorders in neonates, defined as infants of up to 4 months of age. Special emphasis will be given to the physiology of platelet function in healthy and sick newborn infants. The review will be divided into sections as follows: role of platelets in hemostasis, platelet function in newborn infants, quantitative platelet disorders, qualitative platelet disorders, and platelet transfusion therapy.

Blood Platelet Disorders↗
PubMed1997

Pretreatment of human platelets with plasmin inhibits responses to thrombin, but potentiates responses to low concentrations of aggregating agents, including the thrombin receptor activating peptide, SFLLRN.

Effects of plasmin on platelets, that influence subsequent responses to aggregating agents, are relevant to attempts to prevent rethrombosis following administration of fibrinolytic agents. We describe plasmin-induced inhibition of platelet responses to thrombin, but potentiation of responses to other aggregating agents. Washed human platelets were labeled with 14C-serotonin, treated for 30 min at 37 degrees C with 0, 0.1 or 0.2 CU/ml of plasmin, followed by aprotinin, washed and resuspended in a Tyrode-albumin solution with apyrase. Incubation with 0.2 CU/ml of plasmin almost completely inhibited thrombin-induced (0.1 U/ml) aggregation, release of 14C-serotonin, and increase in cytosolic [Ca2+]. In contrast, with plasmin-pretreated platelets, aggregation and release of 14C-serotonin were strongly potentiated in response to low concentrations of the thrombin receptor-activating peptide SFLLRN, ADP, platelet-activating factor, collagen, arachidonic acid, the thromboxane mimetic U46619, and the calcium ionophores A23187 and ionomycin. Aspirin or RGDS partially inhibited potentiation. Plasmin-pretreated platelets resuspended in plasma anticoagulated with FPRCH2Cl (PPACK) also showed enhanced responses to aggregating agents other than thrombin. The contrasting effects on responses to thrombin and SFLLRN are noteworthy. Plasmin cleaves GPIIb/IIIa so that it becomes a competent fibrinogen receptor, and binding of 125I-fibrinogen during ADP-induced aggregation was greatly potentiated within 10 s. Potentiation of aggregation by other agonists may be due to increased binding of released fibrinogen. Thus, platelets freed from a thrombus may have increased responsiveness to low concentrations of aggregating agents other than thrombin. These results provide further support for the use of inhibitors of platelet reactions in conjunction with administration of fibrinolytic agents.

Adenosine Diphosphate↗
PubMed1996

Conditions influencing release of granule contents from human platelets in citrated plasma induced by ADP or the thrombin receptor activating peptide SFLLRN: direct measurement of percent release of beta-thromboglobulin and assessment by flow cytometry of P-selectin expression.

Contrary to a recent report [Rinder et al.: Blood 82:505, 1993], aspirin does inhibit the release of alpha-granule contents as well as inhibiting the release of dense granule contents by human platelets during ADP-induced aggregation in citrated platelet-rich plasma (PRP). Measurements were: percent release of 14C-serotonin from prelabeled platelets, radio-immunoassay of beta-thromboglobulin (beta TG), and expression on the platelet surface of the alpha-granule constituent, P-selectin, by flow cytometry. During the second phase of ADP-induced aggregation, 69.0 +/- 8.3% of beta TG and 54.1 +/- 4.6% of 14C-serotonin were released (mean +/- SEM, n = 13); aspirin treatment reduced these values to 6.0 +/- 1.2 and 1.0 +/- 0.3%, respectively. In contrast, incubation of platelets with ADP without stirring caused only 6.7 +/- 1.7% release of beta TG and 2.1 +/- 0.4% release of 14C-serotonin; these low values were not appreciably affected by aspirin. During ADP-induced primary aggregation in PRP anticoagulated with FPRCH2CI (PPACK), only 4.7 +/- 0.9% release of beta TG and no detectable release of 14C-serotonin occurred; aspirin had no effect. In both stirred and unstirred PRP, the thrombin receptor activating peptide, SFLLRN (50 microM), caused at least 75% release of the contents of both granules, which was partially inhibited by aspirin. Upon incubation of platelets with ADP (2-10 microM), the mean fluorescence intensity due to P-selectin was < 14% of that induced by SFLLRN. In this unstirred system used for flow cytometry, aspirin treatment caused no significant inhibition of P-selectin expression. Thus, under conditions in which ADP does not cause secondary aggregation (physiological Ca2+ concentration or unstirred citrated PRP) release of the contents of both types of granules is less than 7% and aspirin is not inhibitory; the P-selectin expression associated with this low percent release is also unaffected by aspirin. However, aspirin does strongly inhibit the extensive release of both alpha-granule and dense granule contents during ADP-induced secondary aggregation in citrated PRP.

Adenosine Diphosphate↗