Platelet inhibition of renal cortical fibrinolytic activity in the rabbit

A fibrin slide test was utilized to study the effect of platelets and endotoxin on renal cortical fibrinolysis in rabbits. Cortical lysis was absent in kidney from animals made markedly thrombocytopenic with goat antirabbit platelet serum or endotoxin; light microscopy was normal and immunofluorescent microscopy for fibrin was negative. No loss of lysis was detected in kidney of animals given goat anti-rabbit albumin or isotonic saline. Plasma from animals with endotoxin or antiplatelet antibody-induced thrombocytopenia demonstrated an increased capacity to inhibit cortical fibrinolytic activity of normal rabbit kidney. Antiplatelet antibody could be substituted for the preparatory injection of endotoxin in the generalized Shwartzman reaction; a parallel rise in lysis inhibitory titer was detected in plasma from animals prepared with antibody or endotoxin. Although lysis was absent following incubation of normal renal cortex with washed platelets, no inhibition of lysis was found after incubation of normal cortex with endotoxin, histamine, serotonin, platelet membranes, or granules. Using a modified fibrin slide technique, a diffusable platelet inhibitor of lysis could be demonstrated. These studies indicate that platelets contain an inhibitor to renal cortical fibrinolysis which is released into the circulation upon platelet destruction. The findings also suggest that platelet destruction is the mechanism through which endotoxin inhibits cortical lysis.