Functional aspects of blood platelets in irradiated burros.

In irradiated burros (Equus asinus), a delayed clinical syndrome characterized by a depletion of megakaryocytes and platelets has been observed. To clarify the cause of this syndrome, the functional abilities of platelets in 7 irradiated and 3 control burros were studied in vitro. The irradiated burros were survivors (greater than 18 years) of total-body exposures to near-lethal doses of gamma-radiation. Burro platelet aggregability induced with adenosine diphosphate and thrombin, and with a complex stimulator from burro aortas, was determined by means of a self-calibrating aggregometer. Data indicate that the aggregation responsiveness to adenosine diphosphate and thrombin of platelets from surviving irradiated and unirradiated burros is not defective. An extractible collagen-like stimulator of platelet aggregation was discovered in the aorta of a burro that had survived greater than 24 years after exposure to a total-body dose of 545 roentgens (R) of tantalum-182 gamma-radiation. The platelet-aggregating ability of this stimulator from the vessel wall of the irradiated burro was nearly fourfold greater than that from the aorta of an unirradiated control. Perhaps a delayed radiation effect could be the cause of this vascular agent's high platelet-aggregating ability and could lead to a clinical syndrome marked by depletion of megakaryocytes and platelets.