The influence of intravenous nutrition on protein dynamics following surgery

Rates of whole body protein turnover were measured in 13 adult patients one day following abdominal surgery. A constant intravenous infusion of L-(1-14C)-leucine was used to estimate rates of whole body protein flux, synthesis, breakdown and fractional synthesis rates of albumin and mixed globulins. After a baseline measurement when saline was infused, patients were assigned to one of three groups in order to assess the relative effects of three hypocaloric intravenous nutrition regimens upon these rates. Group A (n = 5) was given 108 g/day of crystalline L-amino acids. Group D (n = 4) received 216 g/day of glucose and 22 units of insulin/day. Group AD (n = 4) received a combination of the two regimens (108 g/day amino acids, 216 g/day glucose and 22 units insulin/day). The two isotope infusion studies lasted 20 hr after which the specific intravenous diet was continued for a total of three days. The amino acid infusion increased whole body protein flux from 3.07 g/kg ideal body weight · day to 4.56 g/kg ideal body weight · day (p < 0.05), amino acid oxidation from 0.59 g/kg ideal body weight · day to 1.82 g/kg ideal body weight · day (p < 0.05) and improved protein balance from -0.59 g/kg ideal body weight · day to -0.12 g/kg ideal body weight · day (p < 0.05). Plasma globulin synthesis was also increased from 19.2%/day to 36.0%/day (p < 0.05). In contrast, glucose and insulin infusions reduced amino acid oxidation from 0.54 g/kg ideal body weight · day to 0.35 g/kg ideal body weight · day (p < 0.05) by decreasing the rate of protein breakdown (from 3.09 g/kg ideal body weight · day to 2.55 g/kg ideal body weight · day). Both globulin and albumin synthesis were also reduced from 26.1%/day to 18.8%/day (p < 0.05) and 7.5%/day to 4.2%/day (p < 0.05), respectively. The combined regimen of amino acids, glucose and insulin produced the greatest improvement in protein balance from -0.42 g/kg ideal body weight · day to +0.83 g/kg ideal body weight · day (p < 0.05) through a reduction in protein breakdown and an increase in protein synthesis. However, plasma protein synthesis was not significantly affected. Amino acid oxidation rates were positively correlated to the rate of nitrogen excretion in the urine when dietary intake was constant (r = 0.84, p < 0.01). Further significant correlations were observed between whole body protein flux and body weight (r = 0.70), amino acid intake and whole body protein synthesis (r = 0.82), flux and amino acid oxidation (r = 0.60), flux and globulin (r = 0.65) and albumin synthesis (r = 0.54) and finally, oxidation and globulin synthesis (r = 0.69). The positive correlations observed between protein flux and whole body and plasma protein synthesis suggest that increased amino acid availability promotes whole body and plasma protein synthesis. Protein synthesis is supported in postoperative patients by amino acid containing infusions and suppressed by solutions containing only glucose and insulin. © 1981.