Effect of platelet depletion on lung vascular permeability after microemboli in sheep

To test whether platelets are necessary for the increased vascular permeability associated with microemboli, we used 16 anesthetized sheep in which we measured lung lymph flow, pulmonary arterial and left atrial pressures, thermodilution cardiac output, and lymph/plasma protein concentration. Injecting glass bead microemboli (200 micrometers diam) until pulmonary vascular resistance increased to three times base-line values caused lung lymph flow to increase at nearly constant lymph-to-plasma protein concentration ratio that is characteristic of increased microvascular permeability. Antiplatelet serum alone caused transient increases in pulmonary vascular resitance and lung lymph flow, but produced no change in steady-state lung fluid balance. After depleting platelets by greater than 97%, tripling pulmonary vascular resistance with emboli resulted in increases in lung lymph and protein flow comparable to that seen in untreated sheep. We injected twice the amount of beads in thrombocytopenic sheep compared to untreated sheep. We conclude that, although platelets do augment the pulmonary hypertension after emboli, they are not essential for the microemboli vascular injury.