Crinophagy as a means for degrading excess secretory proteins in rat liver

A method is presented for isolating crinosomes from rat liver, a subclass of secondary lysosomes. To this end, vinblastine was given to rats. Vinblastine blocked exocytosis of secretory granules at the cell border. Later on, characteristic granules containing lipoprotein particles were present allover the hepatocytes. These organelles were designated crinosomes. Immunolabelling showed that they contained albumin. The crinosomes were isolated on a sucrose gradient. They contained marker enzymes for both the Golgi complex and lysosomes. The crinosomes were also histochemically positive for acid phosphatase. They were proteolytically and lipolytically active. It is concluded that crinosomes develop from fusion between lysosomes and secretory granules--when the synthesis of secretory proteins exceeds the exocytotic capacity of the hepatocyte--and that they are active in degrading the retained secretory material.