Platelets in rat anaphylaxis.

The number of circulating platelets dropped abruptly in the early phase of severe anaphylactic shock (AS) of the rat and could be inhibited by Persantin but not by heparin pretreatment. The results strongly suggest that an aggregating agent, perhaps "platelet aggregating factor", formed or released during anaphylaxis is responsible for the decrease of platelet number. The organ distribution of 51Cr labelled platelets showed that in AS the aggregated platelets were removed from the circulation mostly by the spleen and part of them were trapped in the lung and the small intestine. The remaining platelets retained their functional integrity. The loss of circulating platelets is manifested by the prolongation of rat tail bleeding time and is one of the factors participating in the haemostatic disturbances during anaphylaxis.