Functional and ultrastructural alterations of autologous platelets labeled with 111In-oxine

High activity labeled platelets could be useful for the detection and observation of small foci of thrombosis by gamma-camera imaging. Therefore platelets were labeled with 111In-oxine containing increasing activities of 111In to determine the elimiting amount of this tracer that did not cause cell damage. A labeling procedure was employed so that all the chemical parameters remained constant except the amount of 111In. Platelet damage was studied by ADP-induced aggregability according to the Born procedure and by scanning and ultrastructural electron microscopy. Platelets labeled with the lowest activity 2.2 MBq/ml of platelet suspension (10(9) cells/ml) showed no alterations. With the highest activity studied, (22 MBq/ml) aggregability decreased by two-thirds and great changes in the shape of the platelets were seen by electron microscopy. These modifications were attributed to the decay of 111In predominantly located in the platelet cytosol. Labeling of platelets with an activity higher than 7.4 MBq/ml is unsuitable for detection of thrombosis since normal platelet functions are not retained.