DETERMINATION OF HUMAN PLATELET SURVIVAL UTILIZING C14-LABELED SEROTONIN*

Abstract

Blood (250cc) from 11 normal subiects was drawn into plastic bags and incubated with 1 to 2 [mu]c of C14-labeled 5-hydroxytryptamine. About 90% of the C14 activity was determined to be in the blood platelets following 30 minutes incubation. The whole blood was reinfused and determination of residual C14 radioactivity in circulating blood platelets of the recipient followed over 15 day periods. Platelet radioactivity declined in an exponential manner with a half time of 5 days. Approximately 55 to 60% of the infused radioactivity in platelets was estimated to be circulating in the recipient 24 hours after infusion. Platelet tagging could be accomplished by intravenous infusion of C14 5-hydroxytryptamine with subsequent decline in platelet radioactivity comparable to the in vitro labeling experiments. Radioactivity infused in homologous platelets gave results comparable to autologous platelet infusions. Decline of platelet activity following infusion again was similar. Less than 10% of the C14 activity infused bound to platelets appeared in the urine in the first 24 hours. In patients with thrombocytopenia due to platelet destruction in vivo (idiopathic thrombocytopenic purpura), as much as 90% of the C14 activity was in urine at the end of the first 24 hours. No radioactivity was present in the blood of the recipient. The results compare well with other methods of measurement of platelet survival.