Platelet Refractory State Induced by Heparin

Addition of heparin to whole blood caused marked platelet aggregation, followed by rapid deaggregation during subsequent tilting. Some platelets, however, were irreversibly aggregated. Heparin also induced aggregation in citrated platelet‐rich plasma (PRP), and enhanced aggregation by adrenaline and collagen in citrated PRP. These findings are interpreted as due to heparin‐induced release of platelet ADP. A marked inhibition of aggregation by adrenaline (second phase) and collagen was observed in heparinized PRP. As reversible aggregation due to exposure to ADP is known to induce refractory platelets, this may probably explain the inhibition of aggregation in heparinized PRP. The controversial reported effects of heparin are discussed in view of the present findings.