Role of P-selectin in platelet sequestration in pulmonary capillaries during endotoxemia

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

BLOQUEIO DO ÓXIDO NÍTRICO COM L-NAME COMPROMETE A MICROCIRCULAÇÃO HEPÁTICA DURANTE ENDOTOXINEMIA Blockade of NO with L-NAME jeopardize hepatic microcirculation during endotoxemia

O bloqueio da produção do óxido nítrico durante endotoxinemia permanece controvertido. Visando avaliar o efeito do bloqueio do óxido nítrico na microcirculação hepática, ratos Sprague-Dawley machos receberam LPS e depois de 2h foram tratados com L-NAME (10 mg/kg, n=6) ou solução salina (NS, n=7). A perfusão sinusoidal foi avaliada pela microscopia intravital, sangue foi colhido das veias hepáticas para determinação do equilíbrio ácido-básico, e a bile produzida durante todo o experimento foi mensurada. Depois de 1h de tratamento L-NAME acentuou a falência da perfusão sinusoidal induzida pelo LPS (p < 0.05 vs NS), acentuando a acidose no sangue efluente hepático (p < 0.05 vs NS), enquanto o fluxo biliar apresentou uma redução adicional (L-NAME 2.0 ± 0.5 vs NS 2.4 ± 0.1 <FONT FACE="Symbol">m</font>l/g/min). O bloqueio não-seletivo do óxido nítrico na endotoxinemia aumenta a falência da perfusão sinusoidal, piora o equilíbrio ácido-básico do fígado e tende a acentuar a deficiência da função excretora.<br>The blockade of NO production during endotoxemia remains controversial. To evaluate the effect of NO blockade on the liver microcirculation, Sprague-Dawley male rats received LPS and 2h after they were treated by injections of L-NAME (10 mg/kg BW, n=6) or normal saline (NS, n=7). Intravital microscopy (IVM) assessed sinusoidal perfusion, blood samples were taken from the hepatic vein to determine base excess, and bile was collected. After 1h treatment L-NAME increased the LPS-induced sinusoidal perfusion failure (p < 0.05 vs NS), accentuated the acidosis in the hepatic blood effluent (p < 0.05 vs NS), while bile flow was further reduced (L-NAME 2.0 ± 0.5 vs NS 2.4 ± 0.1 <FONT FACE="Symbol">m</font>l/g/min). Non-selective NO blockade in endotoxemia enhances the sinusoidal perfusion failure, impairs acid-basic status of the liver and shows a tendency of impairment of the excretory function