Evaluation of low dose anaphylatoxic peptides in the pathogenesis of the adult respiratory distress syndrome (ARDS). Monitoring of early C5a effects in a guinea-pig in vivo model after i.v. application.

A guinea-pig in vivo model is presented that allows the infusion of purified C5a via a central vein catheter and the monitoring of its effects on granulocytes and platelets, the most important cells in the pathogenesis of several lung disorders, e.g. shock lung. After the infusion of C5a, which was adjusted to a quantity that caused slight and transient alterations of lung physiology, granulocytes disappeared from circulation within 1 min. Simultaneously the granulocyte content of the lung increased about three-fold as judged by histological evaluations. Morphologic destructions were not observed. After the drop a rebound of circulating Polymorpho-nuclear leucocytes (PMN) occurred, which was significantly higher than control values and the appearance of banded cells indicated a mobilization from bone marrow stores. Studies with 51-chromium labelled PMNs revealed that most, but not all, of the granulocytes returned to circulation after transient sequestration. The number of platelets also decreased after C5a infusion, but the rebound was delayed compared with the PMNs and did not exceed control values. The changes in circulating cells, lung histology, and lung physiology are comparable to those occurring during the onset of shock lung and thus strengthen the supposed importance of C5a concerning the pathogenesis of that syndrome.