Appearance of Platelet-Clumping Substance after Acidification of Plasma

1. The pH values of heparinized plasma from ten normal rabbits were from 7.53 to 7.80. The average pH and standard error was 7.69 ± 0.03. These plasmas did not show platelet-clumping activity when exposed to the platelet-saline suspension from the same or other normal rabbits. The platelet-clumping substance was not observed in all ten cases after alkalinization of the plasma to pH values ranging from 8.32 to 9.40. On the contrary, immediately after acidification of the plasmas, the platelet-clumping substance appeared at pH values from 4.90 to 6.82 at room temperature. The range of the lower pH value, in which the platelet-clumping substance was observed, was 4.90-5.60 (5.15 ± 0.07 in average) and the upper range was 5.95-6.82 (6.27 ± 0.12 in average). The pH range at which the strongest clumping of platelets appeared was 5.22-5.95 (5.61 ± 0.07 in average). The platelet-clumping substance did not disappear after the pH of the acidified plasma was reneutralized to the original value.

2. No clumping was found after the addition of citrated, oxalated, EDTA-plasma or serum even when they were acidified. After the pH value of the citrated, oxalated or EDTA-plasma was changed from 4.85 ± 0.39 to 7.55 ± 0.03 and in the presence of calcium ions (10 mM.), platelet-clumping activity was observed. After the addition of citrate (0.38 percent in final concentration), oxalate (0.2 percent in final concentration), or EDTA (0.1 percent in final concentration) to the heparinized plasma the platelet-clumping substance did not disappear. In the case of serum, the platelet-clumping activity did not appear after the pH changes.

3. The platelet-clumping substance in the acidified plasma was heat-labile; it was detected after BaSO₄-adsorption and defibrination; it was stable in storage at 4 C., and it was not dialyzable against Ringer’s solution for 72 hours. It induced platelet clumping not only in citrated platelet-rich plasma but also in the platelet-saline suspension.

4. The properties of the platelet-clumping substance in the acidified plasma were compared with that of substances known to have platelet-clumping activity and the experimental evidences showing the differences to ADP, thrombin, ADP-cofactor and thrombocyte agglutinating factors have been detailed.