Studies on the Ultrastructure of Pseudopod Formation in Human Blood Platelets.

A method for quantitative evaluation of blood platelet pseudopod formation is presented. Pseudopod formation was studied in whole blood incubated for 0, 5, 10, 20 and 40 minutes at + 4°, + 15° or + 37° C. Samples were anticoagulated with EDTA or sodium citrate, or incubated without anticoagulant. In instantly fixed blood, platelets showed a pseudopod index of about 0.5. In samples incubated at + 4° C., the pseudopod index rose to about 3 after 20 minutes. After 40 minutes there was no further increase. At + 37° C. the pseudopod index did not increase during the first 20 minutes of incubation, but after 40 minutes it had risen to levels almost similar to those of the + 4° samples. EDTA and sodium citrate exerted no influence upon pseudopod formation at any temperature level tested. Mechanical forces operating during the preparation of platelet rich plasma caused pseudopod formation and enhanced temperature induced pseudopod formation. These results support the theory of Bull & Zucker (1965) that blood platelets maintain their lenticular shape by energy requiring processes.