Desmopressin (DDAVP) improves recruitment of activated platelets to collagen but simultaneously increases platelet endothelial interactions in vitro.

Platelet dysfunction can cause clinically relevant bleeding. Treatment with DDAVP is advocated for this condition. DDAVP increases von Willebrand factor (VWF) on endothelial cells (ECs) and in plasma. VWF could facilitate platelet deposition on subendothelial collagen. VWF also facilitates platelet/EC interactions. Therefore DDAVP could precipitate thromboembolic events. We used a flow chamber model to study in vitro and ex vivo if DDAVP alters recruitment of platelets to EC and collagen. Resting or TRAP-activated platelets and EC were treated individually or simultaneously with 0.4 ng/ml DDAVP. Fluorophor-labeled platelets (10(6)/ml) were resuspended in reconstituted blood and superfused across EC and collagen in an in vitro flow chamber model at arterial shear (320 s(-1)). Adhesion of platelets to the respective surface was recorded fluorescence microscopically and platelet covered area was assessed. TRAP significantly induced adhesiveness of platelets for collagen and EC. DDAVP pretreatment of platelets did not affect adhesiveness of resting or TRAP-activated platelets for collagen or EC. Adhesiveness of resting but not TRAP-activated platelets was induced on DDAVP-treated EC. DDAVP-conditioned EC supernatant contained vWF and significantly increased platelet deposition on collagen. Platelets from patients with clinically suspected platelet dysfunction undergoing aortic valve replacement exhibited decreased platelet deposition on collagen surfaces. In summary, our data confirm that DDAVP can induce release of platelet adhesion promoting factors from EC, which is most likely vWF. DDAVP has no direct effect on platelets. Blood samples from DDAVP-treated patients do not exhibit significantly augmented platelet deposition on collagen ex vivo. This influence of released promoting factors might cause an increase of undesirable interactions of platelets with EC.

Infection-associated platelet dysfunction of canine platelets detected in a flow chamber model.

BACKGROUND: In the present study, the influence of bacterial infection, lipopolysacharides (LPS) and hydroxyethyl starch (HES) on platelet function in a parallel plate flow chamber were measured. Experiments were performed with non-activated and protease-activating-receptor (PAR) 4 agonist activated platelets. Comparative measurements were in vivo capillary bleeding time, platelet function analyzer and impedance aggregometry. RESULTS: PAR 4 agonist did not increase platelet adhesion of platelets from dogs with bacterial inflammation in the flow chamber in contrast to platelets of healthy dogs. Except from impedance aggregometry with lower sensitivity and specificity, PFA did not detect platelet dysfunctions in dogs with infection. In vitro addition of LPS or HES significantly reduced platelet covered area after PAR-activation. CONCLUSIONS: The flow chamber detects platelet dysfunctions in dogs with inflammatory diseases. In vitro addition of LPS highlights the inhibiting effect of bacterial wall components on platelet function. Platelet dysfunction induced by infection could possibly also be diagnosed after treatment of sepsis with colloids has commenced. The flow chamber could be a useful tool to detect sepsis associated platelet dysfunction given that larger prospective trials confirm these findings from a proof of concept study.

A dynamic flow-chamber-based adhesion assay to assess canine platelet-matrix interactions in vitro.

BACKGROUND: Dynamic adhesion assays allow the examination of platelet dysfunction and drug effects on platelet function. OBJECTIVE: The purpose of the study was to optimize several parameters such as type and concentration of collagen, wall shear stress, and the concentration of the platelet-activating agonist in a new biochip perfusion chamber for the study of canine platelets. METHODS: After fluorescent staining of platelets, citrated blood of 10 healthy dogs was perfused through the flow chamber coated with different concentrations of canine or bovine skin collagen. Wall shear stress ranged from 14 to 60 dynes/cm(2). Protease-activating receptor 4 (PAR 4) agonist was used for platelet activation. After perfusion, platelet attachment to the collagen matrix was quantified based on fluorescent imaging. Total platelet covered area and average size of platelet covered areas were measured by planimetry. RESULTS: Canine platelet adhesion was supported by ≥ 200 µg/mL canine collagen, but not bovine skin collagen. Consistent results were obtained with a wall shear stress of 14 dynes/cm(2), whereas higher wall shear stress resulted in increased variability. Platelet activation with PAR 4 agonist increased the total platelet covered area and the average size of platelet covered areas. CONCLUSIONS: This study indicates the need to carefully select collagen type and concentration to assess canine thrombus formation in a dynamic flow chamber. The established method should be a useful tool to determine changes in platelet-matrix interactions as an indicator of platelet activation or platelet dysfunction in dogs.