Regulation of hepatic synthesis and secretion of cholesterol and glycerolipids in animals maintained in different nutritional states

The distribution of newly synthesized and exogenous fatty acids and of newly synthesized cholesterol between cellular and very-low-density lipoprotein (VLDL) lipids was studied in hepatocytes derived from animals fed on a normal diet or on diets supplemented with polyunsaturated fat or sucrose. Phospholipid synthesis from either exogenous or endogenous (biosynthetic) fatty acids was unaffected by nutritional state. Cholesterol synthesis was decreased in the fat-fed animals, but sucrose feeding had no significant effect. In all nutritional states, newly synthesized rather than exogenous fatty acids were better substrates for phospholipid synthesis. In all groups, compared with newly synthesized triacylglycerol, smaller proportions of newly synthesized phospholipid and cholesterol were secreted as VLDLs. This was confirmed in intact animals by using Triton WR-1339. Newly synthesized phospholipid formed a greater proportion of the VLDL glycerolipid in the fat-fed than in the normal or sucrose-fed animals. In all groups, phospholipids labelled from endogenous fatty acids were secreted in preference to those labelled from exogenous fatty acids.