Objective: To study fat metabolism and evaluate lipid deposition in hepatocytes and Kupffer cells during parenteral nutrition (PN) with or without fat.
Design: 20 male Sprague-Dawley rats, divided into four groups, were investigated. Rats fed orally were used as a reference group and compared to three groups of rats receiving PN either without fat or with 33% of non-protein energy as fat or with 66% of non-protein energy as fat. The PN regimens were equicaloric and administered continuously via a jugular catheter for 7 days.
Interventions: After suffocation, blood was collected for determination of serum lipids. Epididymal fat and heart were collected for analysis of lipoprotein lipase activities, and pieces of liver were saved for analyses of liver triglyceride concentration and hepatic lipase activity. Light and electron microscopy were used for examination of lipid deposition in Kupffer cells.
Results: Directly after termination of parenteral feeding, the serum levels of triglycerides were similar in all PN groups, while the levels of non-high-density lipoprotein (HDL) cholesterol and non-HDL phospholipids were significantly increased in parallel with increased doses of fat. Lipid-free PN resulted in significantly less liver steatosis than high-fat PN. Lipid PN also resulted in downregulated hepatic lipase activity, signs of lipid accumulation in Kupffer cells and hepatocytes and an increased number of phagosomes in Kupffer cells.
Conclusions: Fat vacuoles were found in Kupffer cells after lipid PN, although serum levels of triglycerides were not elevated and lipoprotein lipase activity were not depressed. The cells were distended by fat vacuoles after administration of PN solutions with a high fat concentration. Morphological signs of increased Kupffer cell activity were also found, suggesting that intravenous fat emulsions may activate macrophages.