Oleic acid (18:1n-9, OA), docosahexaenoic acid (22:6n-3, DHA), or eicosapentaenoic acid (20:5n-3, EPA) was added to HepG2 cells at a concentration of 1 mM in a 5:1 or 2:1 molar complex with bovine serum albumin (BSA), and this was incubated for 3 hours. The incorporation of 3H-glycerol into cellular and medium triglyceride (TG), and the mass of TG were measured. The effects of these fatty acids on the secretion of very low density lipoprotein (VLDL) apolipoprotein B (apo B) were estimated from the incorporation of 3H-leucine into the medium apo B in comparison to cells incubated with fatty acid-poor albumin. The secretion of human albumin by the cells was also estimated by immunochemical precipitation of the labeled albumin. In addition, the intracellular levels of apo B messenger ribonucleic acid (mRNA) were measured by the dot-blot hybridization technique. Relative to control cells incubated with BSA, OA (complexed to BSA at a 5:1 molar ratio) stimulated TG synthesis and secretion sevenfold. Compared to OA, EPA was 24% less effective for both processes, whereas DHA inhibited only the secretion of TG (-43%). The secretion of VLDL apo B was not affected by OA, but was decreased 31% by EPA and 54% by DHA. When the molar ratio of fatty acid complexed to albumin was changed to 2:1, similar results were obtained with respect to TG production. The levels of apo B mRNA relative to actin mRNA were not significantly altered by any of the fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)