Significance of leukocytes in endotoxic shock

Peripheral blood leukopenia and the sequestration of large numbers of polymorphonuclear leukocytes in pulmonary capillaries have been observed in experimental shock. It has been suggested that the lysosomal enzymes released from these damaged and sequestered leukocytes may contribute to systemic hypotension and pulmonary capillary damage. This study was undertaken to evaluate the role of leukocytes in endotoxic shock. Six rhesus monkeys rendered leukopenic by total body irradiation (mean white blood count, 358/cu mm) were compared with six normal nonleukopenic monkeys (mean white blood count, 10,550/cu mm) for two hours after injection of E. coli endotoxin. The effects of irradiation alone were evaluated in three additional animals which did not receive endotoxin. Following the injection of endotoxin, the mean cardiac output and systemic pressure decreased more than 50% in both the leukopenic and normal groups. Metabolic acidosis developed in both groups. The mean arterial PO₂ was unchanged, but the alveolar-arterial O₂ gradients increased. Differences between the two injected groups were not significant in these parameters. Light and electron microscopy demonstrated sequestered polymorphonuclear leukocytes and platelets in pulmonary capillaries in the nonirradiated group, but leukocytes were virtually absent in sections from lungs of the leukopenic animals. In spite of this difference, significant endothelial swelling and perivascular edema were demonstrable in both groups. No significant histologic abnormalities were noted in the three irradiated leukopenic control animals who did not receive endotoxin. Leukopenia provided no protection from the hemodynamic effects or the histological damage in pulmonary capillaries observed after administration of endotoxin.