Metabolic factors underlying high serum triglycerides in the normal hamster

Comparative lipid metabolism of rats and hamsters was investigated to determine the metabolic basis for the relatively high concentrations of serum triglycerides in the hamster. It was found that serum free fatty acids (FFA) in the hamster are higher than in the rat in the fed condition. In addition, a higher percentage of the fatty acids esterified in the liver of the hamster is utilized for triglyceride synthesis. These factors combine to elevate hepatic triglyceride synthesis in the hamster. However, triglyceride does not accumulate in the liver in these animals in the fed state. In fact, liver triglycerides are lower in the fed hamster than in the fed rat, and the hamster stores much less triglyceride in liver lipid droplets than does the rat in this nutritional state. Most of the liver triglyceride in fed hamsters is present in dense particles corresponding to vesicular lipoprotein triglyceride in the secretory pool. In isolated organ perfusion experiments hamsters livers exhibited greater net triglyceride secretion than did rat livers. Serum triglycerides in the hamster remain elevated in the fasting state. In this condition the high proportion of free fatty acids utilized for liver triglyceride synthesis, relative to that incorporated into hepatic phospholipids, persists in the hamster and marked liver triglyceride accumulation occurs. Lipid droplets are extremely abundant in these livers. The present study implicates increased conversion of free fatty acids to triglyceride in the liver and increased hepatic production of very low density lipoproteins (VLDL) in the hamster in the genesis of the hyperglyceridemia characteristic of this species.