Radioisotopic model for investigating thromboembolism in the rabbit.

111Indium (111In)-oxine labeled platelets have been used in a variety of species to assess platelet behavior in vivo. We have shown that 111In-oxine is a suitable label for rabbit platelets and, using a noninvasive technique for the automated, continuous, external imaging of these radiolabeled platelets, we have shown that intravenous adenosine disphosphate (ADP), collagen, platelet activating factor (PAF), and thrombin all elicit dose-related accumulation of platelet-(but not erythrocyte-)associated radioactivity in the thoracic region and a concomitant fall in both the cranial and hindlimb regions of the anesthetized rabbit. Intracarotid (i.c.) ADP, collagen, PAF, and thrombin also produce dose-related increases in platelet-associated radioactivity in the thoracic and decreases in the cranial and hindlimb regions. However, the initial fall in cranial counts induced by i.c. thrombin was followed by a marked increase that was sustained for up to 3 hr. These results suggest this may be a useful model for investigating the mechanisms of platelet activation in the arterial and venous circulations in vivo and may provide a novel model for investigating thromboembolic events in the cerebral circulation.