The effect of increasing heparin doses and of heparinoid on platelet factor 4 (PF4) release in normal subjects.

The effect of different heparin doses on PF4 release and the ability of a second dose of heparin to mobilize more PF4 was studied in normal subjects. A heparinoid was also administered to 2 normal subjects. The administred heparin dose seemed to be important in influencing the release of PF4 which correlated well with the prolongation of APTT. A second bolus of heparin given 2 hours after the first, failed to elicit a second peak of this platelet protein in spite of the fact that APTT showed a marked prolongation. The platelet concentration also seemed to play an important role in the relase of heparin-released PF4 (HR-PF4). The injection of the heparinoid induced a very small release of PF4, well correlated with the level of APTT.