Effect of exercise on postoperative nitrogen balance.

This study was designed to investigate whether exercise, when used as an adjunct to parenteral nutrition, has any influence on postoperative muscle catabolism, amino acid metabolism, and nitrogen balance. Twenty male Sprague-Dawley rats were divided into two groups of exercised and nonexercised animals. All animals underwent laparotomy and jugular vein cannulation, were placed in metabolic cages, and were infused with a dextrose-protein solution at 15 kcal and 0.56 g amino acids/100 g body wt per 24 h for a total of 96 h. The exercised animals were run on a treadmill for 15 min/day for a total of 3 days. There was no difference in nitrogen balance and body weight change between exercised and nonexercised animals, as well as no difference between animals who experienced different degrees of exercise. Total and individual plasma amino acids in the exercised group were 15% lower than in the nonexercised group; the total and individual free amino acids in muscle of the exercised group were 66% higher than in the nonexercised group. This pattern of high levels of amino acids in the muscle, coupled with decreased plasma concentrations, is suggestive of increased amino acid turnover in the muscle of the exercised animals. We suggest that, in the postoperative or postinjury period, exercise has a stimulating effect on amino acid turnover in the skeletal muscle resulting from 1) amino acid (mainly the branched-chain amino acids) consumption for energg metabolism and gluconeogenesis, and 2) protein synthesis. The net balance of both results in nitrogen equilibrium similar to that of a nonexercised control group.