Platelet removal from the circulation by the liver and spleen

Previous studies on the clearance of intravenously administered platelets have focused primarily on the long-term survival of platelets rather than the mechanisms responsible for the rapid removal of altered platelets from the blood. In the present study the short-term blood clearance and organ localization of circulating labeled platelets were evaluated in rats during particle induced reticuloendothelial (RE) blockage and after intravenous injection of increasing platelet loads in normal rats. Platelet disappearance conformed to a two-compartment exponential clearance with quantifiable rapid (K1) and slow (K2) rate constants. As platelet load increased, the rapid rate constant decreased. This clearance alteration was associated with a decrease in the percent of the injected platelet load localized in the liver and an increase in lung localization. During RE blockade, a decrease was observed in the clearance rates of both the rapid and slow compartments. Such clearance alterations were associated with decreased hepatic platelet localization and increased pulmonary and splenic platelet localization. Thus, the hepatic reticuloendothelial system may represent a rapid cellular clearance system for altered platelets. When this cellular system is impaired or overloaded, the consequences are decreased hepatic and increased extrahepatic platelet localization.