Egg yolk-induced lipolysosome proliferation and fat infiltration of rat liver

The contribution of subcellular organelles in egg yolk-induced fatty liver was investigated in liver tissue sections and fractionated liver homogenates. When 2.0 ml. of 12.5 per cent egg yolk were administered to Wistar male rats (body weight, 250 to 350 gm.), a fatty change occurred in the liver after a 4-hour period. The acute fatty liver was characterized by intralysosomal accumulations of fat. The number of fat-containing lysosomes increased as early as 30 minutes after egg yolk administration. During this period, fat infiltration was not evident elsewhere in the cytoplasm. The increase of these lysosomes in tissue sections coincided with a selective proliferation of lipolysosomes in the heavy subfraction of floating lipids of liver homogenate. Neither Golgi-derived dense bodies of very low density lipoproteins nor vesicles of the endoplasmic reticulum increased in number throughout the experimental period. These observations indicate that hepatic lysosomes are involved in the degradation of exogenous cholesterol and that transformation of lysosomes to lipolysosomes is a direct result of cholesterol overload and not simply a manifestation of fatty liver.