Effect of different energy sources on hepatic triglyceride secretion during parenteral nutrition

This study examines the effect of parenteral nutrition on hepatic triglyceride secretion in postoperative patients. Five patients received fluids and electrolytes only (D/S), 10 received a 2000-kcal total parenteral nutrition (TPN) formula with 25% of the nonprotein energy from lipid (LIPID-TPN), and 11 received a similar regimen with all of this energy from dextrose (CHO-TPN). After 7 days an intravenous bolus of 3H-glycerol was given and hepatic triglyceride secretion measured from the decay curve of plasma radiolabeled triglyceride content. Plasma triglyceride concentrations were similar in each group. Hepatic triglyceride secretion was 16.3 mg/kg/hr after D/S, 10.7 mg/kg/hr after LIPID-TPN, and 12.2 mg/kg/hr after CHO-TPN (NS). There was no correlation between the rate of hepatic secretion and dextrose intake. Both TPN regimens resulted in significant reductions in plasma concentrations of apoproteins A1 and B but this did not appear to be related to triglyceride secretion rates. Despite the similar rates of hepatic secretion the quantity of labeled glycerol secreted in triglyceride was significantly greater after CHO-TPN (17629 dpm/24 hr) than either D/S (10560 dpm/24 hr) or LIPID-TPN (7264 dpm/24 hr, p less than 0.05), indicating that recycling of exogenous lipid may have occurred after LIPID-TPN. This study indicates that hepatic triglyceride secretion is not suppressed by TPN, irrespective of the energy source, but suggests that the rate of secretion may have an upper limit.