Arteriosclerosis and Thrombosis, Vol 14, 1014-1020, Copyright © 1994 by American Heart Association

ARTICLES

Chylomicron-induced prothrombin activation and platelet aggregation

N Xu, AK Ohlin and A Nilsson
Department of Medicine, University Hospital of Lund, Sweden.

The effects on platelet aggregation of native rat chyle chylomicrons, chylomicron remnants, and chylomicrons that had been preincubated with rat or human EDTA-plasma, serum, whole blood, or pure human prothrombin were examined. The native chyle chylomicrons did not induce platelet aggregation but decreased ADP- and thrombin-induced platelet aggregation and [14C]serotonin release. Chylomicron remnants also failed to induce platelet aggregation, but they potentiated the aggregation and the [14C]serotonin release induced by ADP and thrombin. Aggregation, after a lag phase of 15 to 20 minutes, was seen when platelets were incubated with chylomicrons that had been preincubated with plasma and then isolated as the top layer after a single centrifugation at d = 1.006. This aggregation was inhibited in a dose- dependent manner by an antiserum against prothrombin that also inhibited thrombin-induced platelet aggregation. After washing by centrifugation the plasma-preincubated chylomicrons did not induce platelet aggregation, but this effect could be restored by adding a small amount of prothrombin, which did not cause aggregation when added alone or together with native chyle chylomicrons. Addition of 2% (vol/vol) plasma, however, induced aggregation when added together with either native chyle chylomicrons or washed preincubated chylomicrons, but not when added alone. Binding of 125I-labeled prothrombin to native chyle chylomicrons was demonstrated by gradient ultracentrifugation. During incubation of washed plasma-preincubated chylomicrons with 125I- prothrombin and platelets, a significant conversion of 125I-prothrombin to 125I-prethrombin and 125I-thrombin occurred, as demonstrated by autoradiography after separation on sodium dodecyl sulfate- polyacrylamide gel electrophoresis. The interaction between chylomicrons and prothrombin, and possibly other coagulation proteins, thus enhances prothrombin activation in the presence of platelets.

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