Effects of antiplatelet agents on pulmonary haemodynamic response to fMLP in endotoxin primed rats

Background: The interaction between neutrophils and platelets may be important in the modulation of pulmonary haemodynamics under systemic inflammatory conditions. A study was undertaken to examine whether antiplatelet agents inhibit platelet-neutrophil adherence and ameliorate the pulmonary haemodynamic response to fMLP by inhibiting thromboxane release in endotoxin primed lungs. fMLP stimulates neutrophils but not platelets; however, thromboxane synthesis in neutrophils is very low. Methods: Rats were pretreated with either cilostazol (300 mg/kg) or aspirin (50 mg/kg) before endotoxin priming (5 mg/kg). Platelets in the lung were identified by fluorescent immunohistochemistry. Platelet-neutrophil adherence was analysed by flow cytometry of the lung vascular flush. The effect of fMLP (10^-6 M) on thromboxane release, lung weight (an indicator of pulmonary vasoconstriction), and lung filtration coefficient was determined in an isolated lung system perfused at a constant pressure difference. Results: Endotoxin induced platelet accumulation and platelet-neutrophil adherence in the lung capillary were completely inhibited by cilostazol and aspirin while neutrophil recruitment was not affected. The fMLP challenge caused a significant increase in thromboxane 82 levels in endotoxin primed lungs. The fMLP induced decrease in lung weight was enhanced by endotoxin priming (from -4.9 to -63.9 mg, 95% CI of mean difference -99.5 to -10.5 mg, p<0.05). The fMLP induced increase in the lung filtration coefficient was also enhanced by endotoxin priming (from 0.63 to 2. 40 mg/min/cm H₂O/g, 95% CI of mean difference 1.17 to 2.37 mg/min/cm H₂O/g, p<0.05). Treatment with cilostazol and aspirin completely inhibited the enhanced pulmonary haemodynamic response to fMLP. Conclusion: The neutrophil-platefet interaction is of critical importance in the modulation of pulmonary haemodynamics via thromboxane.