Changes in nitrogen metabolism in catabolic patients given three different parenteral nutrition regimens

Nitrogen metabolism was investigated in 24 catabolic patients (15 men and 9 women) given three different parenteral nutrition regimens for 10-12 days. Energy was supplied as either carbohydrates alone (glucose group) or as carbohydrates and fats (lipid group) and nitrogen as amino acids. In the third group (amino acid group) amino acids were given in excess and less energy was supplied as carbohydrate. Each patient served as his own control. On the basis of daily urinary urea excretion all infused amino acid was retained in the body in the glucose and lipid groups during parenteral nutrition, but in the amino acid group 54% of infused amino acids were metabolized in gluconeogenesis apparently for energy production. In the glucose and lipid groups nitrogen balance rose to a "plateau" within 2-4 days but in the amino acid group within 5-7 days. The increment of nitrogen balance, 0.169 +/- 0.030 g N/kg/day, in the glucose group was greater than that, 0.140 +/- 0.037 g N/kg/day, in the lipid group (p less than 0.05) and that, 0.122 +/- 0.044 g N/kg/day, in the amino acid group (p less than 0.01). The initially low values of serum and liver protein did not change in the glucose and lipid groups, but in the amino acid group serum protein rose from 53.7 +/- 6.5 g/l to 61.1 +/- 5.9 g/l (less than 0.01) and liver protein from 47.4 +/- 7.2 mg/mgDNA to 65.0 +/- 22.6 mg/mgDNA (p less than 0.05). It seems tht a parenteral nutrition program rich in amino acids stimulates the vital protein synthesis of the liver more than regimens with abundance of non-nitrogen energy sources and poorer in amino acids. Nitrogen balance does not reveal information about the important protein metabolism of the liver. The results of this study support the opinion that during parenteral nutrition carbohydrates improve nitrogen balance more than isocaloric amount of fat.