Platelet storage pool deficiency and prostaglandin synthesis in chronic granulocytic leukaemia

Relationships between thrombohemorrhagic complications and platelet function in patients with essential thrombocythaemia

Three subgroups have been distinguished in essential thrombocythaemia (ET) patients, on the basis of clinical and laboratory findings. ET patients with bleeding incidents had smaller platelet volume, lower concentrations of beta-thromboglobulin and platelet factor 4 in their plasma, 10%, 26%, and 26% lower compared to patients without complications, respectively. ATP secretion from platelets of bleeders, clotters, and "no-complications" ET patients was found to be 75%, 36%, and 45%, respectively, lower than in healthy people. Spontaneous platelet aggregation appeared to be normal in about 90% of ET patients with no complications and in all bleeders but only in 35% patients with clotting incidents. All bleeders had abnormal agonist-evoked aggregation assays. Among remaining ET patients 30%-60% displayed normal values of different evoked aggregation tests. Thus, clinically distinguished group of bleeding ET patients may be differentiated from other subgroups on the basis of laboratory findings.

Platelet dense granules: structure, function and implications for haemostasis

The advances that have been made over the last decade in microscopic, biochemical, molecular, and genetic techniques have led to substantial improvement in our understanding of platelet dense granule structure and function, and the implications of dense granule deficiencies for haemostasis. However, much has still to be learned. For example, what is the specific mechanism of docking and fusion that occurs during dense granule exocytosis? What are the roles of dense granule membrane proteins during exocytosis or after expression on the surface of activated platelets? Finally, how do the genetic defects identified in HPS and CHS result in the clinical phenotype of these diseases, and what does this tell us about the origin and function of the affected subcellular organelles?

Interferon-alpha restores beta1-integrin-dependent, collagen-mediated platelet aggregation in a patient with chronic myelogenous leukemia

Although interferon-alpha (IFN-alpha) induces hematologic remissions in 70% to 80% of patients with chronic myelogenous leukemia (CML) and complete or near-complete cytogenetic remissions in 10% to 20% of patients, the exact mechanisms underlying these clinical results remain unclear. We have hypothesized that IFN-alpha acts at least in part through restoration of beta1-integrin function on malignant hematopoietic progenitors that can promote adhesion of malignant progenitors to the marrow microenvironment. This may then restore microenvironmental inhibition of progenitor proliferation and induce tumor dormancy. We demonstrate that IFN-alpha administration to a patient suffering from a clinically severe bleeding diathesis reversed the defective collagen-mediated aggregation of platelets expressing normal numbers of functionally inactive collagen receptors. This is the first in vivo demonstration that IFN-alpha can up-regulate the function of adhesion receptors in CML and supports the premise that IFN-alpha induces remissions by restoring normal integrin-mediated interactions between progenitors and microenvironmental components.

Arachidonic acid metabolism in platelets of patients with essential thrombocythaemia

Platelet aggregation tests and studies comprising [14C] arachidonic acid [14C]AA incorporation, release and metabolism were performed in resting and thrombinstimulated platelets of 11 patients with essential thrombocythaemia (ET) and 11 normal subjects. Nine patients had abnormal aggregation tests. Incorporation and distribution of [14C]AA in main platelet phospholipids (PLs) was similar in both groups. Activated platelets of patients with ET released more radioactivity from PLs that controls (13.7 +/- 5.4% versus 8.2 +/- 1.9%, p < 0.01). The formation of 12-L-hydroxy-5,8,10-heptadecatrienoic acid (HHT) was also increased (3.3 +/- 1.4% of total radioactivity versus 1.6 +/- 0.4% in controls (p < 0.0001). The same results were obtained for the generation of thromboxane B2 (p < 0.01). We did not detect differences in the formation of 12-L-hydroxy- 5,8,10,14-eicosatetraenoic acid (3.3 +/- 1.7% in patents versus 2.0 +/- 0.5% in controls). These results indicate that platelets of patients with ET have an increased activity of phospholipases and suggest a facilitated metabolism of arachidonate by the prostaglandinsynthetase pathway. Our results also demonstrate that impairment of aggregation tests in these patients was not due to a defective activity of the enzymes involved in the release and metabolism of AA by platelets.

Life-threatening thrombotic and haemorrhagic problems associated with silent myeloproliferative disorders

Myeloproliferative disorders are well recognized as being associated with haemorrhage and thrombosis. We describe two cases, one of life-threatening haemorrhage and the other of thrombosis, in patients with normal peripheral blood counts and films, both of whom went on to develop overt manifestations of myeloproliferative disorders (CGL and essential thrombocythaemia) more than a year after their first presentation.

Lactate dehydrogenase isoenzymes in patients with essential thrombocythemia

Various abnormalities have been described in platelets of patients with Essential Thrombocythemia (ET), including alteration in the glycolytic pathway and increased lactate production. Lactate dehydrogenase (LDH) isoenzymes were studied in 15 of these patients. Relative activity of LDH-5 isoenzyme was higher comparing with normal platelets (p < 0.05), while LDH-3 activity was diminished (p < 0.05). LDH-1, LDH-2 and LDH-4 isoenzymes were unchanged. We also found an altered profile of LDH isoenzymes in serum. These findings can contribute to improve the knowledge of platelet defects in ET and be useful in the diagnosis of these patients.

Platelet storage pool deficiency, leukemia, and myelodysplastic syndromes

Abnormalities in platelet dense granules, small intracellular organelles containing ATP, ADP, calcium, serotonin, and pyrophosphate, have frequently been reported in patients with leukemia and myeloproliferative disorders, particularly acute and chronic myelogenous leukemia. Recent studies of a family which includes several members with an autosomal dominant dense granule deficiency condition show an association between the presence of this form of dense granule deficiency and the development of acute myelogenous leukemia. Studies in two additional patients, one with the Monosomy 7 syndrome and the second with a myelodysplastic syndrome, revealed a defect in platelet dense granules. This defect appears to be due to an abnormality in the formation of these granules rather than the presence of empty vesicular structures or decreased contents due to activation associated secretion. The results suggest that the defect in platelet dense granules associated with leukemia or myelodysplastic syndromes may result from a chromosome alteration in the megakaryocyte cell line leading to decreased formation of dense granules. Studies in the family with an inherited bleeding disorder suggest that a gene coding for a protein important for the formation of dense granules is located adjacent to a gene which, when abnormal, may predispose to the development of leukemia.

Inherited platelet-storage pool deficiency associated with a high incidence of acute myeloid leukaemia

A family with an inherited bleeding disorder extending over four generations, and multiple cases of myeloblastic and myelomonoblastic leukaemia was studied. Ten members of the family had, by history, a haemorrhagic diathesis. There were three documented cases of myeloblastic leukaemia, two documented cases of myelomonoblastic leukaemia and two more cases of leukaemia by history. In four of the cases the bleeding diathesis clearly antedated the leukaemia, in two by many years. The bleeding disorder is characterized by a long bleeding time, abnormal platelet aggregation, low platelet ADP and decreased numbers of platelet dense bodies consistent with a dense granule storage pool deficiency. The number of dense granules was decreased by immunofluorescence employing quinacrine or using an antibody to the dense granule membrane protein, granulophysin, confirming an absolute decrease in dense granule numbers rather than the presence of empty granule sacs. This congenital storage pool deficiency is associated with a high incidence of acute myeloid leukaemia in this family.

Qualitative platelet defects in chronic myeloproliferative disorders: evidence for reduced ATP secretion

19 consecutive untreated patients with chronic myeloproliferative disorders and thrombocytosis were subjected to comprehensive platelet function tests including platelet aggregometry. 12 patients had essential thrombocythaemia (ET) and 7 patients had polycythaemia vera (PV). Bleeding time was normal. Arachidonic acid, collagen and ristocetin aggregation were abnormal only in a minority of patients, whereas ADP aggregation was impaired in 16 out of 19 patients. The most conspicuous findings were abolished second-wave adrenalin aggregation, increased ADP aggregation threshold, and markedly reduced ATP secretion during collagen-induced aggregation. This triad of qualitative platelet defects seems to be a good diagnostic marker of chronic myeloproliferative disease with thrombocytosis.

Multimeric composition of plasma von Willebrand factor in chronic myelocytic leukaemia

We studied the multimeric composition of plasma von Willebrand factor (vWf) in 26 patients with chronic myelocytic leukaemia (CML); 13 in chronic phase, 8 in blast crisis, 5 in both chronic phase and blast crisis. The relative amount of large (multimer band greater than or equal to 11) multimers calculated by densitometer scan following SDS-agarose gel electrophoresis was 14.6 +/- 2.9% (mean +/- SD) in normal controls, 8.7 +/- 4.7% in chronic phase and 15.0 +/- 5.2% in blast crisis. CML patients in chronic phase (but not in blast crisis) had a significantly lower percentage of large multimers than normal controls (p less than 0.001). The relative amount of large multimers was positively correlated with a ratio of ristocetin cofactor/vWf antigen (p less than 0.005), and was negatively correlated with platelet count (p less than 0.001), WBC count (p less than 0.05) and granulocyte count (p less than 0.05). We conclude that some patients with CML, especially in chronic phase, lack large multimers. The negative correlation of the relative amount of large multimers with platelet and granulocyte count suggests that large multimers may be consumed in high platelet count states or degraded by protease(s) from increased blood cells.

Intraplatelet levels of vWF:Ag and fibrinogen in myeloproliferative disorders

Several platelet function abnormalities have been described in the myeloproliferative syndromes. We have measured the intraplatelet vWF:Ag and fibrinogen (FI) in the platelet lysates by Laurell technique in 11 patients with polycythemia vera (PV), 10 with essential thrombocythemia (ET), 14 with chronic myelocytic leukaemia (CML) and 3 with myelofibrosis (MF) and these results were correlated with platelet function abnormalities. Decreased intraplatelet levels of vWF:Ag and FI were found in all the patients with ET and MF, in 8 out of 11 PV and 3 out of 14 CML. A statistical significant correlation was observed between the intraplatelet levels of vWF:Ag and FI in the control group and in CML and PV, but no correlation was found in ET and MF. No correlation was observed between the plasmatic and the intraplatelet levels of vWF:Ag and FI in any group. Evidences of platelet activation (spontaneous platelet aggregation or circulating platelet aggregates) were observed in 40% of the cases with ET and PV, and all these cases had low intraplatelet levels of both antigens. None of the cases with MF had evidences of platelet activation and 2 out of 14 patients with CML had platelet activation. The deficiency of the dense bodies was less frequent than the depletion of the alpha granules (5 out of 11 PV, 4 out of 10 ET, 6 out of 14 CML and 2 out of 3 MF). The low intraplatelet contents of vWF: Ag and FI, more frequently observed in ET and PV, may be the result of platelet activation and in vivo release, but megakaryocyte dysfunction is more likely in myelofibrosis.

Acquired von Willebrand disease in patients with polycythemia rubra vera

Platelet function and factor VIII complex were evaluated in ten patients with polycythemia rubra vera. Seven patients showed abnormal epinephrine-induced aggregation. The intracellular concentrations of adenosine diphosphate (ADP) were below normal, and the ratio of adenosine triphosphate (ATP)/ADP was greater than normal. In four of eight cases, there was a decrease in ristocetin cofactor activity and a reduction in the slowly migrating forms of vWF:Ag on crossed immunoelectrophoresis. Defect of large multimers of vWF:Ag was also observed. The ratio of vWF:Ag to ristocetin cofactor was elevated in these patients. Plasma from the patients had no effect on normal plasma except in one case, in which isolated IgG appeared to cause inactivation of ristocetin cofactor. Treatment with 1-deamino-8-arginine vasopressin caused correction of the vWF abnormalities with rapid return of ristocetin cofactor to baseline in some patients. The present study shows that the alterations of multimeric structure of vWF occur in more than 50% of patients with polycythemia rubra vera and are in some part due to the inhibitor specific for vWF.

Acquired von Willebrand disease and storage pool disease in chronic myelocytic leukemia

Platelet function was evaluated in 20 patients with chronic myelocytic leukemia (CML), all Ph positive. Seven showed abnormal epinephrine-induced aggregation, while four had impaired both ADP- and collagen-induced aggregation. The platelets of all patients aggregated with arachidonic acid, thus ruling out cyclooxygenase or lipoxygenase deficiency. The intracellular concentrations of ATP and ADP were significantly below normal, and the ratio of ATP/ADP was greater than normal in all 12 patients. ATP released from platelets by Lumi-aggregometer was reduced. In four patients with abnormal ristocetin-induced aggregation, vWF:Ag, RCoF, and FVIII:C were all reduced. No significant inactivation of factor VIII was induced in normal plasma by incubation with patient's plasma. The crossed immunoelectrophoretic analysis revealed that vWF:Ag in these patients was mainly composed of more anodic component as compared with that of normal plasma. The ratio of vWF:Ag/RCoF was significantly greater than normal. A marked increase of factor VIII and a rapid return of vWF:Ag and RCoF to the baseline after the 1-deamino-8-arginine vasopressin (DDAVP) infusion were observed. Transient increase in vWF:Ag after the infusion of DDAVP appeared with less anodic forms and in the same relative proportion as that in normal plasma. The present study shows that in some patients with CML storage pool disease occurs with acquired von Willebrand disease.

Platelet granule disorders

The present review has cataloged the inherited and acquired disorders of platelet granules. Unfortunately, a mere listing of different conditions in which dense bodies, alpha granules, or both are decreased, absent, or fused does little to define their importance in human platelet physiology or as a causative factor in hemorrhagic disease. The inherited disorders serve as the best index of granule involvement in platelet hemostatic function. Our experience with storage pool deficiency in patients with Hermansky-Pudlak syndrome has suggested that in many individuals virtual absence of dense bodies and their contents does not present a serious threat to hemostasis. Placing HPS patients on aspirin did not cause spontaneous hemorrhage, suggesting that secretion of dense body contents and synthesis of endoperoxides and thromboxane A2 are not absolutely essential for platelet function. However, the literature strongly suggests that many patients with HPS and SPD face a serious risk from bleeding, and hemorrhage may cause death. We can only conclude that some patients with HPS have platelet defects or other hemostatic problems that render SPD a far more serious threat than in other patients who appear to have the same disease. Dense bodies of and by themselves do not appear absolutely required for platelet function. Isolated deficiency of alpha granules presents the same enigma. Only a few patients with this rare inherited disease have been reported. They are generally considered to have mild to severe hemorrhagic problems. However, the past medical history of our two patients with GPS has recently been reviewed and platelet function studies repeated. Despite the mild thrombocytopenia, they are free of any significant bleeding episodes and their platelet function appears virtually normal. Our findings do not support the concept that alpha granules are essential for platelet function. The only condition that seems to support a critical role for storage organelles in hemostasis is the combined alpha-granule, dense body deficiency in one patient reported by Weiss. This patient does have bleeding problems. However, it is difficult to draw conclusions based on a single patient, and the discovery of other patients will help to clarify the hemostatic problem of patients with dual storage organelle deficiencies. In the meantime, we have prepared platelets from normal individuals free of storage granules by sedimentation through gradients containing cytochalasin B. The function of the normal agranular platelets is compromised, but they do respond to some aggregating agents.(ABSTRACT TRUNCATED AT 400 WORDS)

Alterations of blood platelet function induced by neutral proteases from human leukocytes

Washed human platelets are damaged by two neutral proteases from human leukocytes (elastase-like protease, ELP and chymotrypsin-like protease, CLP). The damage is manifested as inhibited aggregation by ristocetin and collagen, and enhanced aggregation by ADP in the presence of fibrinogen. Similarly to alpha-chymotrypsin (alpha-CT), CLP also increases binding of 125I-fibrinogen to platelets and renders platelets aggregable by human fibrinogen. ELP is less effective in this respect possibly due to damage to platelet receptors for fibrinogen. In the plasma medium platelets are not sensitive to leukocytic proteases added at concentrations that provoke some prolongation of the time of plasma clotting by thrombin.

The platelet defect in acute myeloid leukaemia

In a study of platelets from 13 patients with acute myeloid leukaemia abnormal aggregation and release reactions were found. A previously unrecognised quantitative defect of thromboxane B2 production may, at least in part, explain these findings. In contrast to a previous report, we were unable to show a convincing storage pool defect in these platelets. The platelet membrane glycoproteins were largely normal.

Evidence against enhanced platelet activity in sickle cell anaemia

Although numerous studies have provided indirect evidence for enhanced platelet activity in sickle cell anaemia, little attention has been directed to examination of platelet alpha and dense granule release in the sickling disorders. We simultaneously measured by radioimmunoassay plasma levels of the alpha granule constituents beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) in 43 children with sickle cell anaemia in steady state and 24 patients during severe vaso-occlusive crisis. beta-TG levels during steady state (50 +/- 3.6 ng/ml, mean +/- SEM) were greater (P less than 0.001) than in normal controls (36 +/- 1.6), but there was no additional significant rise during crisis (55 +/- 5.9). PF4 levels were similar (P = 0.12) in both steady state (10 +/- 1.2 ng/ml) and crisis (9.3 +/- 2.3) to those of normal controls (6.0 +/- 0.8). The similarity of beta-TG/PF4 ratios in normal and sickle cell anaemia patients as well as the positive correlation (P less than 0.05) between platelet count and beta-TG and PF4 suggested that an artefactual in vitro platelet activation was responsible for some of the observed increased beta-TG and PF4 levels. Further evidence against enhanced platelet activity in these sickle cell patients included normal intraplatelet content of the dense granule constituent 5-HT and a normal ATP/ADP ratio. From this data we conclude that platelet activation in children with sickle cell anaemia appears minimal.

Evidence for a platelet membrane defect in the myeloproliferative syndromes

Bleeding and abnormal platelet aggregation occur in patients with myeloproliferative disorders. In this study, twenty patients were examined, some sequentially, and a proportion found to have defective aggregation toward adrenaline, adenosine diphosphate (ADP), and collagen. In these seven patients, the abnormality in platelet response with defective collagen-induced [14C]serotonin release correlated with poor collagen-stimulated thromboxane B2 (TXB2) production. In contrast, five of these patients showed a normal threshold aggregation response to arachidonic acid. The combined results suggest that in these patients, there is a defect between receptor-stimulus coupling and the mobilization of arachidonic acid from membrane phospholipid.

Subnormal platelet response to thromboxane A2 in a patient with chronic myeloid leukaemia

A new type of acquired platelet dysfunction was found in a chronic myeloid leukaemia patient with petechiae and thrombocytosis. Platelet aggregation induced by arachidonic acid (AA), collagen and A23187 was decreased, secondary aggregation by ADP and epinephrine was defective and ristocetin-induced aggregation was completely reversible. No platelet ATP was released by AA and collagen. Only high concentrations of AA (greater than or equal to 2 mM) induced minimal reversible aggregation. 14C-serotonin uptake by the platelet and platelet adenine nucleotide contents were normal. Normal AA metabolism was demonstrated by thin-layer radiochromatographic analysis of the metabolites of 14C-AA and the determination of thiobarbituric acid reactive substances produced by the incubation of AA or thrombin with the platelets. Minimal reversible aggregation was observed when patient's platelet-rich plasma was added to a reaction mixture in which thromboxane A2 (TXA2) had been generated. TXA2 produced by patient's platelets showed normal platelet-aggregating activity. These results suggest that a subnormal platelet response to TXA2 is included as a mechanism for this acquired hypofunction of the platelet.

Deficiency of platelet lipoxygenase activity in myeloproliferative disorders

The myeloproliferative disorders are characterized by frequent bleeding and thrombotic complications, which have been attributed to abnormal platelet function. In 24 of 60 patients studied, reduced activity of the platelet lipoxygenase pathway for oxygenation of arachidonic acid was revealed by a new direct assay. This assay measured arachidonic acid-induced oxygen consumption in platelets preincubated with aspirin to block cyclooxygenase activity. Patients with secondary polycythemia or thrombocytosis had normal lipoxygenase activity . In the cells of seven of eight patients with lipoxygenase deficiency arachidonic acid induced increased synthesis of thromboxane, the major cyclooxygenase product. Nevertheless, patients with deficient lipoxygenase activity tended to have episodes of hemorrhage rather than thrombosis. Bleeding complications occurred in 67 per cent of patients with lipoxygenase deficiency, but in only 19 per cent of those with normal lipoxygenase activity (P less than 0.001). In contrast, 13 per cent of lipoxygenase-deficient patients, but 31 per cent of patients with other myeloproliferative disorders, had thromboembolic complications. Measurement of platelet lipoxygenase activity may be of diagnostic value in distinguishing myeloproliferative disorders from secondary thrombocytosis or polycythemia. Lipoxygenase deficiency may prove to be a useful natural model for investigating the role of lipoxygenase products in hemostasis.

Decreased platelet serotonin levels in systemic lupus erythematosus

Platelet serotonin levels were measured in 41 patients with systemic lupus erythematosus (SLE) and 36 normal controls. SLE patients had significantly lower mean serotonin levels (243 +/- 131 versus 414 +/- 175 ng/10(9) platelets, P less than 0.001); the lowest levels occurred in those patients with active disease. No differences in mean platelet serotonin levels were found when we compared patients with or without a history of renal disease, thrombocytopenia, or neuropsychiatric involvement. Decreased release of platelet granule constituents, as measured by plasma levels of the alpha-granule protein, beta-thromboglobulin.

Defective platelet aggregation and increased platelet turnover in patients with myelofibrosis and other myeloproliferative diseases

In 9 patients with myeloproliferative diseases (MPD) (6 with myelofibrosis, MF, 1 with Ph1 positive chronic granulocytic leukaemia, CGL, 1 with primary eosinophilia, PE, 1 with pre-leukaemia syndrome, preL) collagen, epinephrine, and ADP-induced aggregation, N-ethylmaleimide-induced malondialdehyde (MDA) production, beta-thromboglobulin (beta-TG) plasma levels, and platelet turnover were studied. Collagen-induced aggregation was found to be normal in 7 patients, absent in 1, and reduced in 1. In all but 3 patients, aggregation with ADP was markedly reduced. Epinephrine-induced aggregation was decreased in 7 patients. No difference was found between mean MDA production in MPD (3.21 +/- 0.50 nmol/10(9) PLTs) and in control group of 21 normal subjects (3.04 +/- 0.26 nmol/10(9) PLTs). Mean beta-TG levels were significantly higher (P less than 0.01) in MPD patients (165.00 +/- 28.29 ng/ml) than in healthy controls (81.76 +/- 14.63 ng/ml). Mean platelet production half-time was significantly shorter in MPD (2.48 +/- 0.24 d) than in the control group (3.43 +/- 0.17 d), after adjustment for age by covariance analysis (P less than 0.005). Our data do not indicate an abnormal prostaglandin synthesis and are consistent with the hypothesis that a disseminated intravascular platelet aggregation might take place in MPD patients.

Platelet dysfunction in myeloproliferative syndromes

The most common abnormality of the platelets in 43 patients with a variety of myeloproliferative syndromes was impaired or absent aggregation when stimulated with collagen and adrenaline. Eight unselected cases studied in more detail showed a normal prostaglandin synthesis pathway as evidenced by normal aggregation with arachidonic acid and the production of normal amounts of malonyldialdehyde. Mixing experiments with aspirin-tested platelets showed correction of the abnormal adrenaline and collagen responses and confirmed that the nature of the defect was different from that induced by aspirin. Stimulation of "myeloproliferative" platelets with thrombin after blocking the prostaglandin pathway with aspirin resulted in reduced aggregation, indicating either a deficiency of the storage pool of adenine nucleotides in the platelets or an abnormality of a membrane receptor for thrombin.

Spectrum of platelet aggregation abnormalities in myeloproliferative diseases

Several platelet abnormalities have been described in myeloproliferative diseases. The present study deals with 81 patients with polycythaemia vera, chronic myelogenous leukemia, essential thrombocythaemia and idiopathic myelofibrosis, and reports the analysis of the findings in platelet-induced aggregation. Platelet abnormalities induced by ADP, adrenaline and collagen were found in 41.9% of the patients. A defect of primary aggregation was documented in 13 cases and one of them showed an aggregation pattern similar to that of Glanzmann's disease. Fifteen patients had an impairment of secondary aggregation, and in one case of this group the platelet malondialdehyde and serotonin findings were consistent with a defect resembling that of typical congenital storage pool deficiency. A disturbance of the arachidonic acid pathways associated with a storage pool deficiency was found in a third patient belonging to a group with abnormalities of primary and secondary aggregation. In conclusion, platelets in myeloproliferative diseases have several defects and in a few cases their combination is similar to those of congenital diseases.

Platelet function in hairy-cell leukaemia

A quantitative study of various aspects of platelet function was carried out in eight patients with typical hairy-cell leukaemia (HCL). In at least two patients platelet aggregation was convincingly reduced to more than one aggregating agent (ADP, adrenaline, collagen, thrombin, and ristocetin). Granular storage capacity for {(14)C} 5-HT was reduced in five of the six patients tested. The two patients with definitely abnormal aggregation had the greatest reduction in granular storage pool and the longest bleeding times of those tested but, like the other patients, they did not have a clinical haemostatic defect. It was concluded that a granular storage pool defect (SPD) was at least partly responsible for aggregation abnormalities in HCL since the platelet release reaction in response to thrombin appeared to be normal. All our patients ran a chronic course uncomplicated by any of the factors known to predispose to a platelet SPD acquired in the circulation. Although in the one patient tested before and after splenectomy there was some improvement in platelet aggregation after operation, there was no clear general relationship between defective platelet function and either previous splenectomy or platelet count. Since a direct involvement of the megakaryocytic series in the underlying cell proliferation of HCL seems unlikely, it is concluded that the platelet defect can most reasonably be attributed to the production of abnormal platelets as a result of marrow fibrosis and/or infiltration by hairy cells.

Arachidonic acid causes lysis of human platelets in an artificial medium: protection by plasma

Addition of 1 or 2 mM of arachidonic acid (AA) to a washed platelet suspension (WPS) resulted in an instantaneous rise of light transmission (LT) in the platelet aggreagameter. The LT curves showed no evidence ofshape change patterns and the recording pen showed no fluctuations. This rise of LT was not affected by the absence of CaCl2, or the presence of PGI2 or ASA. However, LT curves, showing shape change patterns and with pen fluctuations, were obtained when plasma, serum or albumin was included in the test system. These latter form of LT curves were also obtained in WPS samples exposed to lower concentrations of AA. Electron microscopic examination of these samples revealed varying degrees of lysis of every platelet in WPS exposed to 1 mM of AA. Numerous lyzed platelets were also found in samples either exposed to 0.5 mM of AA in the absence of added plasma, serum or albumin, or exposed to 1 mM of AA in the presence of 5% of added plasma or 2.5 mg/ml albumin. The LT curves of these samples showed shape change patterns and pen fluctuations. These results indicate a pitfall of relying on platelet aggregometry alone in the study of certain AA-induced responses of washed platelets.