Electron microscopic observations on the mouse liver after intravenous administration of fat emulsion.

A large volume of biochemical and physiological literature indicates that the liver plays a significant role in fat metabolism. The fats given to animals as a food stuff, after digestion and absorption in the alimentary canal, appear as chylomicra in the blood plasma and most of them are rapidly taken up by the fat tissue and the liver. Between 30 and 50% of the uptake occurs in the liver (ROBINSON, 1964). In the next step, it is suggested that the liver produces lipoproteins and discharges them into the circulation. An important problem, however, still remains as to the lipid uptake by the liver cells (FAWCETT, 1964). Some authors have inferred that the liver cells ingest the chylomicra directly by pinocytosis from their surface facing the sinusoid (ASHWORTH, STEMBRIDGE and SANDERS, 1960; PARKS, 1962; OLIVECRONA, 1962a), while others have held that the chylomicra are hydrolyzed into fatty acids and glycerols by the lipoprotein lipase present in the blood plasma and then diffusion into the liver cell occurs (BELFRAGE, 1966; STEIN and STEIN, 1967). Recently artificial fat emulsions have been used for patients to provide high caloric intake after surgery. It has been shown that fat particles are removed rapidly from the circulation after an intravenous administration of the emulsion and that low density lipoproteins appear in several minutes (KINSELL, MICHAELS and IMAICHI, 1965). However, the detailed mechanism of fat uptake by the liver after artificial fat administration has remained obscure. The present study was carried out to elucidate this problem by means of electron microscopy.