Ageing erythrocytes release vesicles the metabolism of which is unknown. 2. Human and rat erythrocytic vesicles labelled with 51Cr and injected into rats, disappear very rapidly from the circulation with half-lives from 2 to 8 min. 3. Their lifetime resembles that of liposomes encapsulating [51Cr]haemoglobin (Hb) and in both cases, liver and spleen take up considerable amounts of radioactivity. 4. These results indicate, for the first time, that vesicles released from erythrocytes are cleared at very fast rates from the circulation and suggest that this may be the reason for the absence of vesicles in the plasma in vivo.
