Differences In Platelet Response Research Articles

Recurrent carotid artery stenosis following endarterectomy.

Spectral analysis was used to examine 257 carotid arteries in 227 patients who had undergone carotid endarterectomy at 1, 3, 6, and 12 months after surgery and annually thereafter. Routine intraoperative completion angiography ensured that the operations were technically satisfactory. Postoperative restenoses were identified in 38 patients (15%). In 23 arteries (9%), the restenosis exceeded a 50% diameter reduction while in 15 arteries (6%) the stenosis was less than 50% of the diameter. Restenosis developed in 24/96 women (25%) and 14/161 men (9%). Twenty-nine (70%) stenotic lesions occurred within 12 months. In three patients early lesions regressed. Reoperation with patch angio-plasty was required in six patients. When the 219 carotid arteries that remained widely patent were compared to the 38 that restenosed , no differences were noted for age, diabetes mellitus, hypertension, smoking, or degree of preoperative stenosis. Early stenotic lesions appear to be due to myointimal hyperplasia, which is probably platelet mediated. The predominant female sex distribution may be explained by differences in platelet responsiveness in men and women.

A species difference in platelet aggregation induced by tumour cells

Ehrlich ascites tumour cells (EATC) induced the aggregation of human platelets but not of sheep or rabbit platelets in native platelet-rich plasma. Aggregation was initiated by the interaction of EATC with a component(s) of human plasma, possibly related to the complement system, which led to the release of cellular ADP, a potent platelet aggregating agent. EATC previously incubated with human platelet-poor plasma induced immediate aggregation in platelet-rich plasma from all three species. The species difference in platelet aggregation by EATC is therefore related to the activity or availability of plasma component(s) responsible for release of cellular ADP rather than to intrinsic differences in platelet responsiveness to the tumour cells.

Factors Affecting the Size of Platelet Aggregates in Blood

Factors affecting the size distribution of platelet aggregates formed in whole blood were measured using an electronic particle counter. Lysis of red cells after dilution of blood for analysis allows detection of smaller aggregates without altering aggregate measurement. Differences in platelet response to increasing concentrations of ADP are detected by an increase in the mean size of platelet aggregates while the total volume of aggregates varies linearly with the volume of available platelets (r = .99). The mean aggregate size varies directly with the total volume of aggregates formed (r = .99). Mean aggregate size is inversely related to the packed red cell volume. As the reactivity of platelets is reduced by incubation with aggregation inhibitors at increasing concentrations, the mean size of aggregates becomes smaller, followed by a decrease in the total volume of aggregates. The total volume and mean size of aggregates formed after incubation with collagen and epinephrine, but not ADP, increases with time after venepuncture.

Platelet Adhesion to Native and Collagen Coupled Cuprophane: A Multispecies Comparative SEM Study

Platelet adhesion to intact endothelium seldom occurs, but platelet response to subendothelial structures has been extensively studied and is recognized as being focal to hemostasis and thrombosis. Platelet adhesion to subendothelium in-vivo is generally followed by platelet-platelet cohesion (aggregation) and the platelet release reaction (1). Since thrombus formation and the platelet release reaction have been implicated in several secondary pathologic responses, precise characterization of these events is essential to an understanding of many disease processes.Previously we have demonstrated through the use of an in-vitro flow system that differences in platelet response to foreign surfaces exist among commonly studied animal species (2,3). The present report is an extension of these earlier studies and provides, through scanning microscopy, morphologic evidence for species related platelet responses.Blood for these studies was obtained by venipuncture from sheep, calves, baboons, dogs, rabbits and human volunteers following informed consent.

The influence of pH, temperature, and calcium on platelet aggregation: maintenance of environmental pH and platelet function for in vitro studies in plasma stored at 37 degrees C.

Summary. The threshold concentration of ADP required to induce second phase or irreversible platelet aggregation was shown to differ between individuals when certain environmental factors were controlled during platelet handling. The factors shown to be important were plasma pH, temperature, and calcium concentration. PRP exposed to air showed a rise in pH and this was initially associated with an increase in the threshold concentration of ADP required to induce second phase aggregation. When the pH rose above 8.0 a second phase could not be elicited. Plasma pH and platelet; responsiveness could be maintained for up to 4 hr by simply storing the PRP under an atmosphere of 5% CO2–95% air. The second phase of aggregation is due to fibrin polymerization (Ardlie & Han, 1974) which is calcium‐dependent, and the pH effect was shown to be due in part to a decrease in availability of calcium as a consequence of a pH‐dependent increase in binding of calcium, possibly to citrate and albumin. Alkaline pH also inhibited fibrin polymerization independently of calcium. The ADP threshold for secondary aggregation was also influenced by the citrate concentration and it was shown that 0.1 M and not 0.129 M (3.8%) citrate should be used for blood collection for preparation of plasma for studies of platelet function. Platelets stored at room temperature were much more sensitive to ADP and thrombin than when kept at 37° C and it is suggested that this sensitization at lower temperatures may obscure differences in platelet responsiveness between individuals. As the pH became more alkaline the sensitivity of platelets stored at room temperature increased and then subsequently decreased. Since the coagulation pathway is involved in the response of platelets to stimuli (Ardlie & Han, 1974) meaningful clinical studies of platelet function will have to be carried out with PRP and the present report defines some of the optimal conditions for handling and storage of plasma.