Quantitation of leukocytes in bronchoalveolar lavage samples from rats after intravascular injection of endotoxin

Although it has been demonstrated in several animal species that neutrophils aggregate in the pulmonary microvasculature after intravenous infusion of chemotactic factors or substances that activate the systemic complement system, studies in rabbits have revealed that affected neutrophils do not migrate out of capillaries into air spaces unless the infusion processes are combined with manipulative procedures involving the airways, such as intubation or instillation of an anesthetic agent. In this study, we report that after intravenous infusion of endotoxin (Escherichia coli) into Sprague-Dawley rats, in the absence of airway manipulation, the absolute number of neutrophils in bronchoalveolar lavage (BAL) samples increased significantly 24 and 48 h after injection. This represented nearly a 24-h delay from the time that maximal numbers of neutrophils were seen in lung tissue and approximately an 18-h delay from the time that maximal numbers appeared in peripheral blood. We also found that after infusion of endotoxin the number of pulmonary alveolar macrophages (PAM) recoverable in BAL samples fell dramatically within 2 h and remained suppressed for at least 12 h. We conclude that: (1) neutrophils are capable of migration into air spaces after aggregation in pulmonary capillaries in the absence of airway manipulative procedures or instillation of chemoattractants into air spaces and (2) endotoxemia affected surface parameters of PAM in vivo that determine recoverability by lavage.