RESUMO
Thrombocytopenia is common in patients with lung diseases. Lung injury is associated with deranged platelet homeostasis. The potential mechanisms underlying this association were investigated in this study. The number and morphology of circulating megakaryocytes (MK) were investigated in vivo during cardiopulmonary bypass (CPB) in patients undergoing elective cardiac surgery for heart disease. The association between lung injury and thrombocytopenia was further investigated in vitro in rats with lung injury. MK and platelet counts, and platelet activation between the prepulmonary (right atrial) and postpulmonary (left atrial) blood were also compared. In human, the total number of MK in central venous was higher than those of peripheral arteries during normal circulation. During CPB, the total MK and Type-4 MK of central venous and peripheral arteries were significant increased when compared with that in normal circulation. In healthy rats, the postpulmonary blood had lower MK count, higher platelet count, and similar P-selectin expression. However, the lung-damaged animals showed no such differences in either MK or platelet count, but P-selectin expression was greater in the postpulmonary blood. Peripheral platelets in the lung-injured rats were significantly lower than those in their respective controls. The lungs may play an active role in the regulation of MK levels and the lung damage may reduce circulating platelets.