Radiolabeled fibronectin for the scintigraphic detection of pulmonary emboli in dogs

Plasma fibronectin, a glycoprotein that is a component of blood thrombi, was evaluated for the in vivo scintigraphic detection of pulmonary emboli in dogs. Fibronectin (canine or human) was labeled with either ¹³¹I or with ¹¹¹In and diethylenetriaminepentaacetic acid (DTPA) as the bifunctional chelating agent using a modification of the mixed anhydride method. The radiolabeled proteins were administered intravenously 20 to 30 minutes after the embolization of a ^99mTc-labeled thrombus. The uptake of radioactivity by the embolus was monitored scintigraphically up to 24 hours. At the end of each experiment, the animal was killed and in vitro tissue counting of radioactivity was performed. Comparative study of the ¹³¹I- and ¹¹¹In-labeled agent is presented with particular reference to their pharmacokinetics. The in vivo uptake of radioactivity by the emboli was limited, indicating that radiolabeled fibronectin is not a good scintigraphic agent for the detection of pulmonary emboli.