Role of platelets in microembolism-induced acute lung injury

The role of platelets in acute lung injury has not been well defined. In the present study of isolated perfused rat lungs, a significant increase in pulmonary arterial pressure (PAP), lung weight and the lung lavage fluid protein concentration occurred when 3 mL of a CaCl2 suspension (25 mg/mL) was mixed with blood-KHB (Krebs-Henseleit Buffer) perfusate; or when platelets were added instead of blood. However, such an increase was not observed (p > 0.05) when only KHB was used. When a comparatively small amount (0.75 mL) of the CaCl2 suspension (50 mg/mL) was added to the KHB perfusate, PAP, lung weight and the lung lavage protein concentration increased only when PAF (platelet activating factor) and platelets were both added before, but not separately. The above phenomena show that platelets are actively involved in the mechanism of acute lung injury and play an extremely important role in this microembolic model.