A sensitive new method of "ex vivo" platelet deposition

In 1978, an "in vivo" quantitative method of platelet aggregation based on the increment of weight of a rabbit tendon when superfused with flowing blood (3 ml/min) derived from a carotid artery of a cat and reentering the contralateral jugular vein was reported. To increase the sensitivity of the method, we labeled platelets with indium-111 and reinjected them after two hours; then, with a gamma counter, we quantitated the ¹¹¹In-labeled platelets deposited on the superfused rabbit tendon. Results of the radioactivity method and of the weight method were compared. We found that the ¹¹¹In-labeling of platelets was a more precise and reproducible method, rendering possible the use of a small amount of blood without need for reentry into the venous system.