Indium-111 labeled platelets: Studies on preparation and evaluation of in vitro and in vivo functions

Platelets have been labeled with a lipid soluble complex of the radionuclide indium-111. The complex is formed with 8-hydroxyquinoline and extracted in chloroform which is then evaporated to dryness. The residue is dissolved in 50 μl of ethanol and diluted to 200 μl with normal saline. Platelets are separated by differential centrifugation, washed and suspended either in Tyrodes-albumin solution or in normal saline. The solution of ¹¹¹In-complex is added to separated platelets and more than 95% of the radioactivity is incorporated with the platelets. The function of the labeled platelets has been studied by their aggregability using adenosine diphosphate and collagen as the stimulating agents. No adverse effects have been observed. The survival of the indium-labeled platelets was similar to that observed with chromium-51 labeled platelets. Labeled canine platelets have been administered to dogs in whom venous thrombi had been induced by alteration of the intima by an electric current. The thrombi were detected by imaging 50 minutes after administration of the labeled platelets. Twenty-four hours later the thrombi were removed and had 20–50 times the radioactivity of an equal weight of blood. Accumulation of large amounts of radioactivity in surgical wounds has also been observed. Damage of the intima of carotid arteries in animals by a balloon catheter demonstrated 8 to 20 times more activity in the damaged artery than in the normal artery. Results indicate that In-111 labeled platelets have potential both for platelet survival studies and for evaluation of vascular damage.