Anabolic Effects of Insulin and Amino Acids in Promoting Nitrogen Accretion in Postoperative Patients

Abstract

The present study evaluates the effect of insulin and amino acids on nitrogen balance in the immediate postoperative period in moderately stressed patients who have undergone major abdominal surgical operations. Patients were randomly assigned into two large groups (n = 16 each) and four subgroups (n = 8 each). Groups I_CON and I_INS received an infusion of total parenteral nutrition solution containing 0.25 g of nitrogen per kilogram per day with a calorie:nitrogen (C:N) ratio of 150:1. Groups II_CON and II_INS received twice the load of nitrogen with a C:N ratio of 75:1. Groups I_INS and II_INS received an additional continuous infusion of insulin at a rate of 1.0 mU/kg per minute for 7 days. During the total parenteral nutrition period, the patients were kept NPO, and 24-hour urine output was collected for estimation of total nitrogen excretion and nitrogen balance. Net nitrogen excretion (grams per kilogram per day) averaged 0.143 ± 0.06 in I_INS and 0.23 ± 0.08 in I_CON (p < .05) and 0.178 ± 0.6 in II_INS and 0.25 ± 0.10 in II_CON (p < .05). Nitrogen balance (grams per day) was positive in the four groups: +0.65 ± 3.8 in I_INS and + 6.74 ± 2.94 in I_CON (p < .05), and +14.4 ± 2.61 in II_INS and + 11.63 ± 6.44 in II_CON (p = not significant). The average nitrogen incorporation (percent per day) was: 41.3 ± 6.2 in I_INS and 14.6 ± 20.1 in I_CON (p < .05), and 58.3 ± 4.5 in IIINS and 38.7 ± 26.2 in II_CON (p = not significant). The results indicate that nitrogen balance in modestly stressed subjects is achieved at nitrogen intakes of approximately 0.25 g/kg and a C:N ratio of 150:1. Doubling the nitrogen intake while decreasing the C:N ratio of 75:1 resulted in higher positive nitrogen balance. Insulin infusion, to achieve physiologic elevation in plasma insulin (55 to 70 μU/mL), resulted in further improvement in positive nitrogen balance in the group receiving lower nitrogen intake, suggesting that the effect of amino acids in improving nitrogen accretion is saturable. (Journal of Parenteral and Enteral Nutrition 18:214-218, 1994)

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