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The Interactive Effect of Dietary Glycerol and Corn Oil on Rat Liver Lipids, Serum Lipids and Serum Lipoproteins¹

Biochemistry and Nutrition Group, Food Sciences Laboratory, U.S. Army Natick Research and Development Command, Natick, Massachusetts 01760

The long-term effects of dietary glycerol in the absence and presence of dietary corn oil on rat tissue lipids and six density classes of serum lipoproteins were investigated in young male Holzman rats. Group A was fed a fat-free diet consisting by weight of 74.2% glucose. Group B was fed a 30% glycerol and 44.2% glucose diet. Groups C and D were fed diets identical to those for groups A and B, respectively, except for the addition of 4% corn oil at the expense of glucose. The diets for groups A (glucose, fat-free) and B (glycerol, fat-free) were approximately isoenergetic (3.7 kcal/g) and had only a slightly lower density of energy (0.2 kcal/g) than those for groups C (glucose, corn oil) and D (glycerol, corn oil). The food consumption was lower in the glycerol, corn oil group than in the glucose, corn oil group. The weight gain was substantially less in fat-free groups A (glucose) and B (glycerol) compared with corn oil-containing groups C (glucose) and D (glycerol), but the glycerol treatment (glycerol, fat-free and glycerol, corn oil) resulted in increased liver mass, irrespective of whether there was fat in the diet or not. After 21 weeks, liver cholesterol and triglycerides increased between 1- and 2-fold in group B (glycerol, fat-free) compared with group A (glucose, fat-free) and confirmed previous results with old rats from this laboratory. A small, but significant, increase in liver total lipids and cholesterol was observed in group D (glycerol, corn oil) when compared with group C (glucose, corn oil). Serum cholesterol, but not triglycerides, was higher in group B (glycerol, fat-free) than in group A (glucose, fat-free), while the reverse was true for group D (glycerol, corn oil) compared with group C (glucose corn oil). The serum chylomicra significantly increased in both glycerol groups but more so in group D (glycerol, corn oil) than in all other groups. The high density lipoproteins (HDL₂ and HDL₃) were significantly higher in group B (glycerol, fat-free) than in group A (glucose, fat free), but the difference between groups D (glycerol, corn oil) and C (glucose, corn oil) was not statistically significant. These results have generally indicated a beneficial interactive effect of corn oil in glycerol-containing diets, but the mechanism of accelerated induction of fatty livers in rats fed fat-free diets containing glycerol remains to be explored further. It was suggested that dietary glycerol might stimulate hepatic lipogenesis and speed up the induction of fatty acid desaturases resulting in changes in liver fatty acid composition and in altered membrane permeabilities.

KEY WORDS: • glycerol • lipoproteins • corn oil • serum lipids • chylomicra • high density lipoproteins • essential fatty acid deficiency • fatty acid desaturases • fatty livers

¹ Presented in part at the 62nd Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, New Jersey (1978) Federation Proc. 37, 258 (Abstr.).

Manuscript received 18 September 1978.