Aggregation fo blood platelets and increased hydraulic conductivity of pulmonary exchange vessels.

Pulmonary microembolization secondary to platelet aggregation has been suggested to be a pathogenetic component of the shock lung syndrome. In vitro experiments have also shown that platelets can release factors with a permeability-enhancing activity. We studied the effect of collagen-induced platelet aggregation on the hydraulic conductivity of thexchange vessels in isolated, blood-perfused rabbit lungs. The net rate of fluid filtration in each pair of lungs was determined during standardized elevations of left atrial pressure before and after platelet aggregation induced by intraarterial collagen infusions. Such infusions were followed by a significant, but transient increase in the net rate of fluid filtration. These lungs were papaverinized so that collagen infusions caused only minor increases in inflow pressure. Separate experiments indicated that the observed increase in pulmonary arterial pressure could not explain the increase in net filtration rate after collagen infusion. When platelet-poor plasma was used as a perfusate no change in the net rate of fluid filtration was observed after collagen infusion. The conclusion from these experiments is then that intravascular platelet aggregation induced by collagen infusion caused a transient increase in the permeability of the pulmonary exchange vessels.