apyrase and Blood-Platelet-Disorders

We identified SPA in three young apparently healthy women. SPA was associated with release of TXA2 and was only partially inhibited by ADP-inhibitor apyrase and alpha 2-adrenoceptor blocker yohimbine. In vitro incubation of aspirin (90 micrograms/ml) or selective TXA2 synthetase inhibitor OKY-046 (0.1 uM) with platelet rich plasma (PRP) did not abolish SPA, although platelet generation of TXA2 was markedly inhibited. In contrast, oral administration of large amounts of aspirin in one subject or in vitro incubation of PRP with TXA2 -endoperoxide receptor blocker SQ 29,548 (20-100 nM) significantly inhibited SPA. These studies suggest that SPA is associated with TXA2 release. Since TXA2 -endoperoxide receptor blocker completely abolishes the secondary wave, agents like this may be of therapeutic value in individuals with SPA and evidence of tissue ischemia.

Topics: Adult; Apyrase; Aspirin; Blood Platelet Disorders; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Fatty Acids, Unsaturated; Female; Humans; Hydrazines; In Vitro Techniques; Methacrylates; Platelet Aggregation; Thromboxane A2; Yohimbine

The mechanism as well as some characteristics of haematin-induced human platelet aggregation were investigated. Haematin-induced platelet aggregation required the presence of devalent cations; Mg2+, and to a lesser extent, Co2+, were just as effective as Ca2+ in supporting the aggregation. Mono- and trivalent cations were ineffective. Verapamil inhibited the aggregation. The aggregation was accompanied by thromboxane formation which could be abolished by aspirin. The release of adenine nucleotides was only slightly inhibited by aspirin. The rate of aggregation and the ultrastructure of the aggregated platelets were comparable between control and aspirin-treated samples. It is concluded therefore that haematin-induced aggregation is not dependent on platelet prosta-glandin synthesis. Haematin induced binding of fibrinogen to platelets, and failed to aggregate thrombasthenic platelets. These findings indicate that haematin may induce platelet aggregation by promoting influx of divalent cations in association with increased fibrinogen binding and release of adenine nucleotides.

Topics: Adenosine Triphosphate; Apyrase; Blood Platelet Disorders; Blood Platelets; Cations, Divalent; Child; Epoprostenol; Female; Fibrinogen; Heme; Hemin; Heparin; Humans; Microscopy, Electron; Platelet Aggregation; Prostaglandin D2; Prostaglandins D; Prostaglandins, Synthetic; Thromboxanes; Verapamil

Topics: Acrylonitrile; Adenosine Diphosphate; Agglutination; Albumins; Apyrase; Blood Platelet Disorders; Blood Platelets; Cell Communication; Edetic Acid; Epinephrine; Fibrinogen; Humans; Immune Sera; Platelet Adhesiveness; Platelet Aggregation; Platelet Count; Thrombin

Fibrinogen is essential for aggregating platelets with adenosine diphosphate (ADP) and was recently shown to bind to platelets stimulated with ADP. The present work confirms the specific and saturable nature of the platelet-fibrinogen interaction. Binding of 125iodine-labeled fibrinogen to human gel-filtered platelts was maximal at 1 min, and the receptors were saturated when the fibrinogen concentration in the suspending medium approached 0.8 mg/ml. Assuming that one fibrinogen molecule interacts with a single receptor, experiments with 9 normal donors revealed the presence of 12,896 +/- 2456 receptors per platelet. Much of the bound material dissociated from platelets after incubation with apyrase or EDTA. Binding was markedly inhibited at pH 6.5, in the presence of EDTA, and with platelets from 3 thrombasthenic patients but not with those from a patient with the Bernard-Soulier syndrome. Fibrinogen binding was also virtually absent with platelets that had been incubated with EDTA for 8 min at 37 degrees C and pH 7.8. These platelets could not aggregate when mixed with ADP and adequate CaCl2 and fibrinogen, although they could still change their shape. Thus, ADP-induced binding of fibrinogen correlates with platelet aggregability.

Topics: Adenosine Diphosphate; Apyrase; Binding Sites; Blood Platelet Disorders; Blood Platelets; Edetic Acid; Fibrinogen; Humans; Platelet Aggregation; Temperature