Functional and ultrastructural studies on In-111-Merc labeled concentrated human platelets in plasma

Human platelets (1 billion) labeled with 200 μCi In-111-oxine in non-plasma medium have been reported to have impaired ultrastructure and function. The ultrastructure and function of platelets labeled in plasma with In-111-Merc was examined. Human platelets (2 billion) suspended in 0.5 ml plasma were incubated with 2 μg Merc and then labeled with 390-1170 μCi In-111. Unlabeled platelets and those incubated with Merc and decayed In-111 solution served as controls. Radiation dose received by platelets in each preparation was estimated. Aggregability studies were performed and platelets were prepared for transmission electron microscopy. Three samples from each pellet were thin sectioned and examined at 4000 to 11,000 magnification. Electron micrographs were obtained from fields containing at least 10 platelets. Assuming uniform labeling and complete decay of In-111, radiation dose per platelet ranged from 367 Gy to 1100 Gy. The aggregability of labeled platelets was unaffected (93.5 +- 3.8%) and the velocity averaged 75.5 +- 3.9% of control. Electron micrographs revealed no change in morphology of mitochondria, alpha granules, dense granules, canalicular system, microtubules and particulate glycogen; these demonstrated normal distribution. The authors conclude that despite the high radiation dose, the function and ultrastructure of platelets labeled in plasma with In-111-Merc remain unaltered