The effect of salicylates on the hemostatic properties of platelets in man

Von Willebrand factor: dissociation from antihemophilic factor procoagulant activity

Factor VIII corrects both the clotting defect in hemophilia A and an abnormality of platelet aggregation in von Willebrand's disease. These two activities of factor VIII (antihemophilic factor and von Willebrand factor) are both detected in the void volume when human plasma or cryoprecipitate is chromatographed on Bio-Gel 5M under conditions of isotonic salt concentration. In contrast, antihemophilic factor procoagulant activity is detected with proteins of lower molecular weight when the chromatography is performed with a buffer containing 0.8M NaCl. In this way, the two activities of factor VIII can be dissociated. It remains to be determined whether these components are separate molecules associated as a complex of high molecular weight in plasma or whether they are subunits of a complex macromolecule.

Defective ristocetin-induced platelet aggregation in von Willebrand's disease and its correction by factor VIII

The antibiotic ristocetin, in concentrations of 1.0-1.5 mg/ml, aggregated normal platelets in citrated platelet-rich plasma by a mechanism in which the release reaction played only a minor role. Platelet aggregation by ristocetin in a concentration of 1.2 mg/ml was absent or markedly decreased in 10 patients with von Willebrand's disease. Lesser degrees of abnormality were obtained with a concentration of 1.5 mg/ml. The magnitude of the defect in ristocetin-induced platelet aggregation correlated well with the degree of abnormality of the bleeding time and the levels of antihemophilic factor (AHF, VIII(AHF)) procoagulant activity. In all patients, the defect in ristocetin-induced platelet aggregation was corrected in vitro by normal plasma. Correction was also obtained with a fraction of normal cryoprecipitate that eluted in the void volume with VIII(AHF) after chromatography on a gel that excludes molecules larger than 5 x 10(6). A similar fraction, devoid of VIII(AHF) activity, obtained from patients with von Willebrand's disease had no corrective effect, but fractions obtained from patients with hemophilia were just as effective as those obtained from normal subjects. The correction activity of plasma and partially purified factor VIII was inhibited by a rabbit antibody to human factor VIII but not by a human antibody against VIII(AHF) procoagulant activity. The studies provide further evidence that patients with von Willebrand's disease are deficient in a plasma factor that is necessary for normal platelet function. The activity of this factor appears to be associated with factor VIII but is unrelated to VIII(AHF) procoagulant activity.

Inhibition of primary ADP-induced platelet aggregation in normal subjects after administration of nitrofurantoin (furadantin)

The evidence indicating that platelets may play a role in the occurrence of certain thromboembolic phenomena has stimulated a search for inhibitors of platelet function. This report presents data to indicate that nitrofurantoin is a potent inhibitor of primary ADP-induced platelet aggregation. The addition of 10 muM nitrofurantoin to citrated platelet-rich plasma obtained from 12 normal subjects produced a 29+/-6% (2 SD) inhibition of the velocity of platelet aggregation induced by 2 muM ADP. The inhibitory effect of nitrofurantoin demonstrated competitive kinetics in respect to ADP. The intravenous (180 mg) or oral (200 mg) administration of nitrofurantoin produced a serum nitrofurantoin concentration ranging from 2.7 to 23 muM in 28 normal subjects. Platelet-rich plasma obtained from these subjects demonstrated inhibition of the velocity of ADP-induced platelet aggregation that correlated with the log of the serum nitrofurantoin concentration (P < 0.001). Collagen-induced platelet aggregation was also inhibited in a dose-related manner, and the bleeding time was significantly prolonged in the two subjects with the highest serum nitrofurantoin concentration. These studies indicate that nitrofurantoin in vivo inhibits platelet function to a degree that is proportional to the serum nitrofurantoin concentration.

Dipyridamole and aspirin tested against an experimental model of thrombosis

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Stress and the induction of intravascular platelet aggregation in the heart

Intravascular aggregation of platelets similar to that found in dogs after norepinephrine infusion was demonstrated using the electron microscope in the hearts of 20 of 23 rats subjected to two forms of stress (immersion in hot water, 7 of 8 rats; repeated small electric shocks to the feet, 13 of 15 rats). Only one of 14 unstressed rats was found to have similar intravascular platelet aggregates. These findings suggest that catecholamines secreted endogenously during stress are sufficient to cause platelets to aggregate intravascularly and raise the possibility that clinical myocardial infarction occurring during severe or prolonged stress may be caused by catecholamine-induced platelet thrombi which occur at, or travel to, and occlude a coronary artery already narrowed by previous atherosclerosis.

Ultrastructural findings in storage pool disease and aspirin-like defects of platelets

Previous studies have shown that abnormalities in collagen-induced platelet aggregation may be due to an impaired release of storage pool ADP, the agent ultimately responsible for platelet aggregation. In some patients and in normal subjects who ingest aspirin, the storage pool of ADP is present in normal amounts, but the mechanism for releasing it appears to be defective ("aspirin-like" defect). In these subjects, the centripetal reorientation of the platelet granules, which may be early structural changes of the release reaction, failed to occur. In one preleukemic patient with an aspirin-like defect, the elements of the open-channel system were also increased. In a second group of patients the impairment of aggregation is due to a deficiency of storage pool ADP. In these patients with storage pool disease, the initial ultrastructural changes associated with the collagen-induced release reaction were normal. The most striking abnormality was a marked decrease in the number of platelet dense bodies. Since the platelets of these patients are deficient in both serotonin and the storage pool of adenine nucleotides, the findings suggest that, in human platelets, these substances are normally stored in the dense bodies. A defect in the formation or function of the dense bodies may account for the abnormalities of platelet aggregation in storage pool disease.

Intravascular platelet aggregation in the heart induced by stress

Sixteen rats, stressed by immersion in ice-cold water for 25-45 min, were found to have platelet aggregates in myocardial small vessels on electron microscopic study. None of six similar nonstressed control rats had platelets in myocardial vessels. It is concluded that stress, probably via catecholamine secretion that enhances platelet stickiness, can induce intravascular platelet aggregation. It is possible that this mechanism plays a part in the relationship between stress and acute clinical myocardial infarction.

Effects of normal and aspirin platelets on defective secondary aggregation in the Hermansky-Pudlak syndrome. A test for storage pool deficient platelets

Platelets from patients with the Hermansky-Pudlak syndrome (albinism, accumulation of ceroid-like pigment in bone marrow macrophages and mild hemorrhagic symptoms) and aspirin-treated normal platelets fail to develop irreversible secondary waves of aggregation when exposed to aggregating agents on the platelet aggregometer. The present study demonstrates that equal volumes of Hermansky-Pudlak and aspirin-treated platelets, when mixed together, respond in a biphasic manner comparable to normal cells. Correction of the release defect of aspirin platelets by storage pool deficient Hermansky-Pudlak cells indicates that different mechanisms are involved in the failure of the release reaction in the two cell types. The simple test may serve to distinguish other patients with storage pool deficient platelets from individuals who have taken aspirin or other drugs with an aspirin-like effect on platelet function.

Noncytokinetic radiation injury: anticoagulants as radioprotective agents in experimental radiation hepatitis

Rats that have been irradiated with a single dose of 1500 roentgens directed to the liver show the following abnormalities: increased clearance of colloidal gold by the liver at 30 days, a decreased albumin space index at 30 days, and increased alkaline phosphatase at 60 days. In each of these cases, animals receiving Depo-heparin in dose ranges reasonable for human application had essentially normal values. There was no radioprotective effect with salicylates at the doses used. Higher doses of salicylates resulted in death of the animals.

Aspirin-induced prolongation of the ivy bleeding time. Its diagnostic usefulness

Ivy bleeding time values before and two hours after ingestion of 600 mg of aspirin (aspirin tolerance test) were studied in normal persons, in patients with a disorder of primary hemostasis and in patients with various coagulation factor deficiencies. Aspirin produced a significant prolongation of the bleeding time in patients with von Willebrand's disease, uremia, and primary platelet disease, and in two patients with Factor XI deficiency. Dextropropoxyphene hydrochloride caused no prolongation of the bleeding time in normal persons.