Accumulation of platelets might contribute to acute lung injury during systemic inflammation. The aim of the study was to elucidate the role of the poly (ADP-ribose) synthetase, a ...nucleotide-polymerizising enzyme, in mediation of platelet-endothelial cell interaction through regulation of adhesion molecules within the pulmonary microcirculation during endotoxemia. We used in vivo fluorescence microscopy to quantify kinetics of fluorescently labeled erythrocytes and platelets in rabbit pulmonary arterioles and venules. Six hours after onset of endotoxin infusion we observed a massive interaction of platelets with the microvascular endothelial cells, whereas under control conditions, no platelet sequestration was measured. An up-regulation of P- and E-selectin was detected in lung tissue following endotoxin infusion by immunohistochemistry and Western blot analysis. Blockade of endothelial P-selectin with fucoidin resulted in a reduction of the endotoxin-induced platelet-endothelial cell interaction. Inhibition of poly (ADP-ribose) synthetase by 3-aminobenzamide inhibited the endotoxin-induced expression of endothelial P- and E-selectin and the subsequent recruitment of platelets. In summary, we provide first in vivo evidence that platelets accumulate in pulmonary microcirculation following endotoxemia. Poly (ADP-ribose) synthetase seems to mediate this platelet-endothelial cell interaction via P- and E-selectin expressed on the surface of microvascular endothelium.
Background: There is growing evidence that platelets accumulate in the lung and contribute to the pathogenesis of acute lung injury during endotoxemia. The aims of the present study were to localize ...platelet sequestration in the pulmonary microcirculation and to investigate the role of P-selectin as a molecular mechanism of platelet endothelial cell interaction. Methods: We used in vivo fluorescence microscopy to quantify the kinetics of fluorescently labeled erythrocytes and platelets in alveolar capillary networks in rabbit lungs. Results: Six hours after onset of endotoxin infusion we observed a massive rolling along and firm adherence of platelets to lung capillary endothelial cells whereas under control conditions no platelet sequestration was detected. P-selectin was expressed on the surface of separated platelets which were incubated with endotoxin and in lung tissue. Pretreatment of platelets with fucoidin, a P-selectin antagonist, significantly attenuated the endotoxin-induced platelet rolling and adherence. In contrast, intravenous infusion of fucoidin in endotoxin-treated rabbits did not inhibit platelet sequestration in pulmonary capillaries. Conclusion: We conclude that platelets accumulate in alveolar capillaries following endotoxemia. P-selectin expressed on the surface of platelets seems to play an important role in mediating this platelet-endothelial cell interaction. Copyright (c) 2006 S. Karger AG, Basel.
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