Effect of adenosine 5'-diphosphate and shape change on 5-hydroxytryptamine uptake by human blood platelets.

Abstract

<h2>Abstract</h2> It has been reported that low concentrations of ADP, associated with platelet shape change, can block the uptake of 5-hydroxytryptamine (5-HT) by rat platelets. We sought to test the validity of this observation for human platelets, for which an inhibition of 5-HT uptake was recently reported following platelet activation leading to the release reaction. We found that the rate of uptake of 5-HT in human platelets measured in citrated platelet-rich plasma (PRP) is unaffected by shape change induced either by low temperature or low adenosine 5′-diphosphate (ADP, 0.5 μM) concentrations. Higher ADP concentrations (⩾5 μM) sufficient to cause aggregation and release, but added under non-aggregating conditions, did not generally cause inhibition of 5-HT uptake; minor inhibition (≲35%) was observed only for 10 μM ADP, where microaggregation occurred. Prostaglandin E₁ (1 μM), at a concentration blocking any ADP-induced platelet shape change and aggregation did not affect 5-HT uptake. The reversible blocking action of ADP on 5-HT uptake described for rats does not appear to occur in man. Activation of human platelets leading to complete shape change does not alter 5-HT uptake in the absence of aggregation and release.