Labeling plasmin with technetium-99m for scintigraphic localization of thrombi

• A detailed study has been made of the method for labeling plasmin (NOVO Indstri A/S Denmark) with 99mTc in order to prepare a radioactive indicator for early scintigraphic visualization of thrombi and tumors. The best method found for preparing 99mTc-plasmic involved the reduction of 2.5 ml 99mTc-pertechnetate solution with 0.5 ml of 4 mM SnCl2, 2 M NaCl and 70 mM HCl. This mixture was then added to 5 mg of plasmin to give a final pH of about 2. After 60 min of reaction the labeling efficiency was 80-90% as determined by gel chromatography column-scanning. The labeling kinetics and influence of pH, concentration of SnCl2, NaCl, plasmin and lysine were studied. The enzymatic activity of plasmin was reduced by less than 15% by the labeling process. Preliminary experiments in rabbits with artificially induced thrombi indicate accumulation of 99mTc activity in the same areas as 125I-fibrinogen after the administration of 99mTc-plasmin.

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