Functional alterations of human platelets following indium-111 labelling using different incubation media and labelling agents.

Human platelets were labelled in the absence or presence of plasma using indium-111 labelled oxine sulphate, tropolone or 2-mercaptopyridine-N-oxide (MPO). Under in vitro and in vivo conditions, platelet functions were evaluated by measuring their aggregability, survival, recovery and early distribution. High labelling efficiency was achieved in saline labelling, whereas with plasma labelling, it was necessary to concentrate the platelet-rich plasma to 4.8 x 10(6) platelets/microliters. The aggregation of platelets labelled in plasma or saline was compared with that of controls; platelets labelled in saline showed lower aggregability in 2 microM ADP but not in 5 microM ADP nor with collagen. No significant differences in platelet survival and recovery were noted between platelets labelled in plasma and those labelled in saline. Our results indicate that partial loss of ADP aggregability in vitro does not influence the in vivo viability of platelets labelled in saline. Scintigraphic studies showed that platelets labelled in a saline medium were temporarily sequestrated in the liver but not in the spleen or heart. Thus, platelet labelling in saline does not affect platelet function adversely, but platelets labelled in plasma are more desirable for assessing the early distribution of platelets in the reticuloendothelial system.