Platelet activation revealed by reduced serotonin content in various left ventricular hypertrophic states.

The study of platelet function in thirty-one patients with left ventricular hypertrophy of various origins (9 cases of hypertensive cardiomyopathy, 11 of hypertrophic obstructive cardiomyopathy and 11 of aortic stenosis) revealed low serotonin content of platelets on the patients with left ventricular tract obstruction but normal levels in the hypertensive cardiomyopathy group. This is attributed to platelet activation induced by important flow disturbances related to the hemodynamic conditions.

Platelet function: aggregation by PAF or sequestration in lung is not modified during immediate or late allergen-induced bronchospasm in man.

Among the mediators involved in the pathophysiologic mechanisms that underly the reactions of the acute and delayed phases of bronchospasm induced by allergens in man, platelet-activating factor (PAF) could play an important role, in particular by its effects on platelets. In animals, inhalation or injection of PAF causes a platelet-dependent bronchoconstriction that is blocked by prior administration of an antiplatelet antiserum and accompanied by platelet accumulation in the pulmonary vessels. In man, inhalation of PAF causes a bronchospasm and induces a bronchial hyperreactivity. Abnormalities of platelet aggregation and the secretion into plasma of platelet factor 4 and beta-thromboglobulin have been described in patients with asthma during induced bronchospasm. Platelet functions have been studied in 15 patients with asthma before and after allergen bronchial provocation tests. There was no difference between platelet counts, plasma concentrations of platelet factor 4 and beta-thromboglobulin, and platelet aggregation induced by several agonists (adrenaline, arachidonic acid, or PAF) before and immediately after the allergen bronchial provocation test. There was no platelet pulmonary sequestration as studied with 111Indium-labeled platelets during 24 hours after the antigen challenge, and the life span of circulating platelets was normal. Our results do not support an important direct role for PAF in the pathophysiology of asthma. It is still possible that the current methodology is too insensitive to detect amounts of PAF in the circulation or that PAF is acting locally.

Culture of human vascular endothelial cells on a positively charged polystyrene surface, primaria: comparison with fibronectin-coated tissue culture grade polystyrene.

Two culture surfaces, fibronectin-coated tissue culture grade polystyrene and a surface-modified polystyrene called Primaria (Falcon), were compared. The morphological (contact inhibition and cobblestone aspect), biological (production of von Willebrand factor and prostacyclin) and physiological (growth activity, non-thombogenicity and regeneration after mechanical injury) properties of human endothelial cells were studied. Adhesion and growth of endothelial cells at low and clonal density were identical on both substrates and the biological properties were preserved. Regeneration of injured endothelium was less easy to study on Primaria polystyrene because the extracellular matrix was damaged during the lesion process. Nevertheless, Primaria polystyrene can easily be substituted for fibronectin coating in growth experiments, especially at very low seeding density.

Mitogenic activity on human arterial smooth muscle cells is increased in the plasma of patients undergoing hemodialysis with cuprophane membranes.

During hemodialysis on cuprophane membranes, platelets are activated and release in plasma alpha-granule-specific substances such as PF4 or platelet-derived growth factor (PDGF). PDGF is the main source of mitogenic activity found in serum. In vitro, it induces the proliferation of smooth muscle cells (SMC) which is known to be involved in the development of atherosclerotic lesions. Atherosclerosis is one of the major complications of uremic patients undergoing chronic hemodialysis. To investigate whether this complication could be due to the dialysis itself, we measured the mitogenic activity in plasma of 10 patients undergoing hemodialysis on cuprophane membrane, using human arterial SMC in culture. Mitogenic activity in plasma increased about 3-fold during dialysis. These results may provide an argument in favor of a contribution of platelet activation and release of mitogenic activity to atherosclerosis in patients dialysed with cuprophane membranes.

[Glanzmann's thrombasthenia and pregnancy. Contribution of plasma exchange before scheduled cesarean section]. / Thrombasthénie de Glanzmann et grossesse. Apport des échanges plasmatiques avant césarienne programmée.

Glanzmann's thrombasthenia is a thrombopathy which affects primary hemostasis due to a qualitative or quantitative abnormality of membrane glycoproteins IIb-IIIa. The treatment of hemorrhages is usually associated with the transfusion of packed red blood cells and platelet concentrates. If massive allo-immunisation occurs, the transfusion will prove to be inefficient. A case of a cesarean section was scheduled after therapeutic plasmapheresis and platelet transfusions in a massively allo-immunised patient with Glanzmann's thrombasthenia. The plasma exchange made it possible to reduce to trace levels the concentrations of anti-PLA1 and anti-PLA2 antibodies, thus making platelet transfusions hemostatically efficient. The cesarean section was therefore safely performed when the bleeding time was normalized.

Prostacyclin (epoprostenol) as the sole antithrombotic agent in postdilutional hemofiltration.

Prostacyclin (PGI2), the most potent and short-lived antiplatelet agent known today, has been used successfully as an antithrombotic in hemodialysis (HD). However, its vasodilatory effect has been the source of blood pressure instability in acetate HD and has restricted its use to bicarbonate HD. The authors took advantage of the better cardiovascular stability obtained with hemofiltration (HF) to compare the effects of PGI2 versus heparin either with acetate or bicarbonate HF in 4 patients. Efficacy of PGI2 in preventing thrombosis of the extracorporeal circuit was demonstrated in all cases with a dose of 4 ng/kg/min. HF performances remained unaffected whatever antithrombotic agent was used. Platelet activation as shown by BTG and PF4 release was inhibited by the PGI2 infusion. Platelet proteins release was greater with acetate HF, suggesting that acetate may have a specific role in platelet activation. Although the use of PGI2 was straightforward, it is worth noting that PGI2 partially suppressed the cardiostability usually associated with acetate HF. We conclude that the efficacy of PGI2 was well maintained in spite of conditions of high platelet shear stress conditions, but also that PGI2 potentiated the vasodilatory effect of acetate and suppressed partially the cardiovascular benefits of HF.

Platelet functions, alpha 2-adrenergic receptors and cytoplasmic free calcium are normal in the myotonic dystrophy of Steinert.

Platelet function tests were performed on 11 patients with myotonic dystrophy of Steinert (MD) and on 21 healthy control subjects. Using citrated platelet-rich plasma or washed platelets, MD patients had normal aggregation and secretion responses after stimulation with adrenaline, ADP, collagen, PAF, arachidonic acid and thrombin. Using intact and functional washed platelets, MD patients responded normally to adrenaline and had a similar affinity and number of alpha 2-adrenergic receptors as control patients as measured by [3H]dihydroergocryptine and [3H]yohimbine binding. In addition platelets from MD patients had normal basal and stimulated levels of cytoplasmic free Ca2+ as measured with the fluorescent Ca2+ probe quin2. Thus platelet functions, alpha 2-adrenergic receptors and cytoplasmic free Ca2+ are normal in MD.

[Methods of studying platelet function. Biological markers of the activation of human platelets in vivo and in vitro]. / Méthodes d'exploration des fonctions plaquettaires. Marqueurs biologiques de l'activation des plaquettes humaines in vivo et in vitro.

Platelets play a key role in hemostasis, thrombosis, atherosclerosis and their pathological consequences. It is possible to follow platelet activation in vivo by measuring bleeding time, platelet count, existence of circulating platelet aggregates or platelet survival and sequestration. In vitro tests include measurement of platelet adhesion, aggregation alpha, and dense granule secretion. It is also possible to follow biochemical events linked to platelet activation such as prostaglandin metabolism, Ca2+ levels or platelet membrane modifications (receptors, glycoproteins, coagulant activities, antigens). Some of these markers of platelet activation are modified in diseases (thrombotic events, hyperlipoproteinemia) and the use of artificial surfaces. It is not always possible to know if the modifications are the cause or the consequence of the pathological event. Unfortunately, some results are questionable because of methodological procedures. Some of these tests have been used to follow the involvement of platelets in a pathological event or to evaluate a prethrombotic state in a patient. It is not yet possible to identify directly, or by the mean of a marker of platelet activation, a patient who is likely to experience a thrombotic episode.

[Physiology of the interactions of blood and the blood vessel wall. Role of pharmacologically active lipids]. / Physiologie des interactions du sang et de la paroi des vaisseaux. Rôle des lipides pharmacologiquement actifs.

The interactions of blood cells (platelets and leukocytes) with the components of the vessel wall (endothelial cells, extracellular subendothelial matrix and smooth muscle cells) play an important role in the initiation of thrombosis and the development of atherosclerosis. These cellular interactions are partially regulated by the formation of pharmacologically active lipids (PAL): prostaglandins, leukotrienes, PAF-acether and related compounds. These biochemical mediators are produced from the phospholipids of the cell membrane in response to external stimulation. The metabolic precursors, such as arachidonic acid, are common. The subsequent enzymatic differentiation leads to the formation of different terminal products according to the cells, thromboxane A2 in the platelets and prostacyclin in the endothelial cells.

[Importance of disorders of primary hemostasis in the occurrence of upper digestive hemorrhage in cirrhosis]. / Importance des troubles de l'hémostase primaire dans la survenue des hémorragies digestives hautes du cirrhotique.

In order to assess the true incidence of haemostatic disorders in cirrhotic gastro-intestinal haemorrhage, a comparative prospective study of primary haemostasis, coagulation and fibrinolysis was carried out in 37 patients distributed into two groups: cirrhotics with gastro-oesophageal varices that had never bled (Group A = 22), and cirrhotics who had had an intestinal bleed from "ruptured" gastro-oesophageal varices (Group B = 15). Combination of thrombocytopenia (less than 100 10(9)/l) and a bleeding time greater than 8 mn was more frequent in Group B (80%) than in Group A (45%) (p = less than 0.05). On the other hand, no significant difference between the two groups was found in the activated cephalin time, thrombin time, prothrombin complex factors (II, V, VII-X), fibrinogen, antithrombin III, Factor VIII complex factors, FDP levels or plasminogen. In conclusion, these results suggest that disorders of primary haemostasis may be involved in bleeding from gastro-intestinal varices in cirrhosis. However, coagulation disorders and anomalies of fibrinolysis would not seem to play a determining role.

[Surgical correction of interventricular communication with pulmonary stenosis in a hemophiliac]. / Correction chirurgicale d'une communication interventriculaire avec sténose pulmonaire chez un hémophile.

Open heart surgery was performed in a 5 year-old boy with severe hemophilia A and large ventricular septal defect with pulmonary stenosis. High doses of Factor VIIIC superconcentrates delivered as small transfusion volumes allowed the use of extracorporeal circulation with heparin. Transfusions began 5 hours before surgery and were stopped 21 days later. No adverse reaction was observed. Thus major surgery is possible in severe hemophiliacs provided strict rules for replacement therapy are followed.

[Platelet aggregation: a tool for clinical investigation and pharmacological study. Methodology]. / L'agrégation plaquettaire: outil d'investigation clinique et d'étude pharmacologique. Méthodologie.

Platelet aggregation can be measured quantitatively by continuous recording of the transmission of a beam of light across a suspension of platelets in constant agitation in an aggregometer. In routine clinical investigation, the study of platelet aggregation is performed on platelet-rich citrated plasma (PRPc). The blood sample has to be excellent to eliminate all traces of thrombin. The blood is collected in 3.8% sodium dihydrate citrate (1 volume for 9 volumes of blood). It is centrifuged at 190 g for 15 minutes at ambiant temperature. The PRPc obtained can be diluted with platelet-poor plasma (PPP) to adjust the concentration of platelets to 3 X 10(5)/microliters. The PRPc is stored at ambiant temperature in stoppered tubes under CO2 to avoid variations in pH. The maximal delay between the collection of the blood and the end of the study of aggregation is 3 hours. In certain cases, in order to define the platelet lesion and to eliminate the influence of plasma proteins, clotting factors and anti-coagulants, a suspension of washed platelets is used. The blood is collected on acid-citrate-dextrose (ACD) and centrifuged at + 37 degrees C to obtain the PRPc. The platelet deposit obtained by centrifugation of the PRPc is washed twice, according to Mustard's method, in Tyrode-albumin buffer at a concentration of 0.35% at + 37 degrees C. It is re-suspended in the same buffer solution at + 37 degrees C in the presence of apyrase and the platelet concentration is adjusted to 3 X 10(5)/microliters. The aggregation or agglutination of the platelets is induced by several agents: ADP, adrenalin, collagen, thrombin, arachidonic acid, ionophor A 23187, PAF-acether and ristocetin. The quantitative study of the aggregation curves of human platelets allows us to study the physiological and biochemical mechanisms control platelet aggregation, to recognize and classify the hereditary or acquired platelet abnormalities which lead to clinical haemorrhagic or thrombotic manifestations and to study the effect of drugs which inhibit platelet aggregation and to understand their mechanism of action.