Journal of Applied Physiology, Vol 65, Issue 4 1716-1722, Copyright © 1988 by American Physiological Society
Determinants of platelet kinetics: effects of pulmonary microembolism
B. K. McCandless, J. E. Kaplan, J. A. Cooper and A. B. Malik
Department of Radiology, Albany Medical College, Union University, New York 12208.
We examined the mechanisms of platelet uptake in the lungs after
alpha-thrombin-induced pulmonary microembolism. Platelets labeled with
111In-oxine were reinfused into chronically prepared sheep. Pulmonary
microembolism resulted in an increase in lung platelet radioactivity (95.5
+/- 15.3%; n = 4), which was followed by an exponential washout (half-life
= 115 +/- 4 min). Platelet uptake in the lungs was more sustained after
prior fibrinolytic inhibition with tranexamic acid (half-life = 178 +/- 11
min), although the initial increase was similar (90.7 +/- 9.6%; n = 7).
Prior depletion of fibrinogen with ancrod (Arvin), blunted the initial
increase in lung platelet uptake after alpha-thrombin challenge (31.7 +/-
11.3%, n = 5), indicating that the effect of thrombin was markedly
dependent on fibrinogen. We examined the role of circulating granulocytes,
since platelets may bind to subendothelial matrix exposed after
granulocyte-mediated lung vascular injury. Maximal pulmonary platelet
uptake after thrombin in granulocytopenic sheep was not different from
control (71.7 +/- 14.4%; n = 4). The results indicate that pulmonary
microembolism results in lung platelet sequestration. Platelet uptake is
not dependent on granulocyte-mediated vascular injury but requires fibrin
deposition and is sustained if fibrinolysis is inhibited.
