Impairment by Heparin of Primary Haemostasis and Platelet [14C]5‐Hydroxytryptamine Release

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Abstract
Heparin was administered to 34 normal subjects by intravenous injection (100 u/kg) and the template bleeding time was significantly increased both 10 min and 120 min following injection. Before heparin the bleeding time was 5.3±1.0 min (mean±1 SD); 10 min after injection it was 9.8±5.6 min (PP14C]5‐HT released from platelet‐rich plasma (PRP) in response to collagen, 0.41 mM epinephrine and 8 μM ADP, although in vitro addition of heparin (0.1 u/ml, 0.5 u/ml and 2.5 u/ml) to baseline PRP of three subjects did not depress [14C]5‐HT release. Our experiments suggest that intravenous administration of a therapeutic dose of heparin can cause a significant reversible impairment of platelet haemostatic properties, possibly by an indirect mechanism.