Glycerol kinetics with parenteral lipid emulsions (long-chain triglycerides, medium-chain triglycerides, and structured lipids) in rats.
Several studies have reported that parenteral lipid emulsions containing medium-chain triglycerides (MCT) and structured lipids (SL) are better utilized than those containing long-chain triglycerides (LCT). The objective of this study was to test the hypothesis that parenteral LCT require more extensive modification via hydrolysis and reesterification (triglyceride-free fatty acid [TG-FFA] recycling) for effective utilization, whereas MCT and SL do not. As an index of TG-FFA cycling activity, we measured glycerol and palmitate kinetics in rats (204 to 243 g) fed parenterally one of three isocaloric (250 kcal/kg/d) isonitrogenous (1.5 g N/kg/d) diets with half of the nonprotein energy from glucose and the rest from either LCT, LCT plus MCT, or SL for 5 days. Two experiments were performed. On day 5, rats were given a 7-to 8-hour infusion of either 5H2 Glycerol and 1-14C Palmitate bound to albumin to measure palmitate and glycerol kinetics (experiment 1), or U-13C glucose to determine the proportion of endogenous glycerol production derived from glucose (experiment 2). Data are presented as means +/- SEM. Endogenous glycerol production was significantly higher with LCT (11.33 +/- 2.89 mmol/kg/h) than with SL (2.91 +/- 0.62 mmol/kg/h). The value for the physical mixture of LCT plus MCT (5.46 +/- 1.29 mmol/kg/h) fell midway between that for LCT and SL (P = NS). There were no significant differences in palmitate kinetics or oxidation. The increased glycerol production is due to the mobilization of endogenous triglyceride and is consistent with a higher rate of TG-FFA cycling being involved in the metabolism of LCT than of SL.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Surgery, School of Osteopathic Medicine, University of Medicine and Dentistry of New Jersey, Camden 08103.
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D000704:Analysis of Variance; D000818:Animals; D005217:Fat Emulsions, Intravenous / Q000493:pharmacokinetics*; D005260:Female; D005947:Glucose / Q000378:metabolism; D005990:Glycerol / Q000097:blood / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D010084:Oxidation-Reduction; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000493:pharmacokinetics*; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley
D005217:Fat Emulsions, Intravenous; D010169:Palmitic Acids; D019308:Palmitic Acid; D005947:Glucose; D005990:Glycerol