Effect of exercise
on postoperative
HERBERT FREUND, NORMAN YOSHIMURA, Department of Surgery, Massachusetts General Harvard Medical School, Boston, Massachusetts
FREUND, HERBERT, NORMAN YOSHIMURA, AND JOSEF E. FISCHER. Effect of exercise on postoperative nitrogen balance. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 46(l): 141-145, 1979. -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/l00 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 energy metabolism and gluconeogenesis, and 2) protein synthesis. The net balance of both results in nitrogen equilibrium similar to that of a nonexercised control group. postoperative catabolism; nitrogen gen; amino acid turnover; amino sis; branched-chain amino acids
metabolism; acid pattern;
urinary nitrogluconeogene-
IS WIDELY ADVOCATED and used in patients undergoing nutritional repletion as a means of increasing nitrogen retention. Studies by Goldberg (9) demonstrated that the level of muscular activity was a major determinant of amino acid transport and subsequently of the rate of protein synthesis in skeletal muscle. However, there has been considerable controversy about whether protein catabolism in vivo is influenced by exercise. Though some authors describe increased nitrogen losses or increased urea and creatinine production (10, 16, 20) others report no change in nitrogen excretion (4, 12, 24), or even a decrease in urinary nitrogen excretion following exercise (2). The present study was designed to investigate whether exercise, when used as an adjunct to parenteral
EXERCISE
0161-7567/79/0000-0000$01.25
Copyright
0 1979 the American
AND Hospital, 02114
nitrogen JOSEF and
balance
E. FISCHER
nutrition, has any influence on postoperative muscle catabolism, amino acid metabolism, and nitrogen balance in rats immediately following major operative trauma. MATERIALS
AND
METHODS
Twenty male Sprague-Dawley rats weighing 300-370 g (mean 350 t 10 g) were divided into two groups of exercised and nonexercised animals. The exercised animals were further divided according to the amount of exercise performed. Under pentobarbital anesthesia, all animals underwent laparotomy and jugular vein cannulation with a 22-gauge medical-grade silicone tubing. Postoperatively, the animals were placed in metabolic cages and infused with an amino acid and dextrose solution at a mean dose of 15 kcal/lOO g body wt per 24 h and 0.56 g of crystalline amino acids/l00 g body wt per 24 h for a total of 96 h. Water was allowed ad libitum. A control group of 10 additional rats was treated with 5% dextrose alone. Urine was collected and analyzed for total nitrogen determined by a Kjeldahl method. The exercised animals were run on a self-operated treadmill at an average speed of 4.1-10.9 m/min and slope of 0” for 15 min/day for a total of 3 days. Five rats ran 100-200 laps/3 days and five rats ran 300-500 laps/3 days. The last bout of exercise took place 24.:h before the animals were killed. After 96 h of infusion, the animals were killed by decapitation and blood, liver, and the right gastrocnemius muscle immediately removed and frozen for amino acid determination performed by a Beckman amino acid analyzer 121-MB on the supernatant fraction of muscle, liver, or plasma deproteinized by the addition of 4% sulfosalicylic acid. Muscle or liver tissue were acid homogenized in 3 vol (3 x wt) 4% sulfosalicylic with a motor-driven, all-glass homogenizer. The precipitated protein was separated by centrifugation at 20,000 x g for 20 min. All values are expressed as the mean t SE and statistical significance of measured changes was examined by Student’s t test.
Physiological
RESULTS
Nitrogen balance and body weight change. Nonexercised animals subjected to laparotomy and jugular vein cannulation and treated by infusion of 5% dextrose alone, lost 21% of their body weight, and were in negative nitrogen balance of 200-300 mg N/24 h. The mean cumulative and day-to-day nitrogen balances for the experimental groups treated with parenteral nutriSociety
141
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142
FREUND,
tion are summarized in Figs. 1 and 2. Both groups were in positive nitrogen balance with no difference between exercised (40 t 12 mg N/day) and nonexercised (46 t 10 mg N/day) animals. When dividing the exercised group according to the amount of exercise performed, there was no difference in nitrogen balance between animals running 100-200 laps/3 days (41 t 12 mg N/day) and those running 300-500 laps/3 days (37 t 10 mg N/day) (Fig. 1). On a daily basis, nitrogen balances of the exercised and nonexercised groups varied from day to day and between the two groups, the differences being statistically nonsignificant (Fig. 2). If body weight is compared over the 4-day period, both groups exhibited a similar minimal weight loss, with the nonexercised group losing 2 t 1.8% and the exercised group 2.6 t 1.6% of their body weight. In the exercised, postoperative group, those animals who ran 100-200 laps and those who ran 300-500 laps/3 days lost 2.6% body wt/day each (Fig. 3). Amino acid patterns. The plasma amino acid pattern of the exercised and nonexercised groups differed markedly (Fig. 4). Mean total free plasma amino acid concentration in the exercised animals was 15% lower than in the nonexercised group (P < 0.05); total branched-chain amino acid concentration (valine, leucine, isoleucine) in the exercised group was 23% lower than in the nonexercised group (P < 0.05). When each amino acid is considered separately, all amino acid levels except aspartic acid, serine, glutamic acid, glycine, and citrulline were higher in the plasma of the nonexercised animals
YOSHIMURA,
AND
FISCHER
Control
T l-r
FIG. 2. Daily (days l-4) nitrogen balances in exercised exercised postoperative, hyperalimented rats. Differences two groups are statistically not significant.
and nonbetween
Exercised:
100 - 200 60
300-
500
Exercised: *:::. .::::. .::::.. Total .:.:.:.:.:. 0+:.:.:.:.:
laps laps
-
IOOl!zBl
200
300-500
FIG. 1. Mean cumulative 4-day nitrogen and exercised postoperative, hyperalimented riencing different degrees of exercise.
balance in nonexercised rats and in rats expe-
laps laps
FIG. 3. Body weight changes during a 4-day period in exercised and nonexercised postoperative, hyperalimented rats, and in rats experiencing different degrees of exercise.
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EXERCISE
AND
POSTOPERATIVE
NITROGEN
143
BALANCE
n mol/ml 1,000
900
800
0-0 o-4
Exercised Non-Exerctsed
n mol/gm 700
St p < 0.05
700
04 0-4
600
Exercised Non- Exert wd * p < 0.05 ** p < 0.02
600
500
400
300
200
100
LYS VAL ARG ILU PHE CIT ALA PRO LEU HIS MET TYR ORN FIG. 5. Muscle free amino acid patterns in exercised and nonexercised postoperative, hyperalimented rats. GLY
0 GLY LYS TAU TRE GLU ILU PHE ORN ASP ALA SER PRO VAL LEU ARG HIS TYR CIT FIG. 4. Plasma amino acid patterns postoperative, hyperalimented rats.
in exercised
and nonexercised
than in the plasma of the exercised animals, although only alanine, leucine, ornithine, proline, and arginine showed statistically significant differences. In contrast to the plasma amino acid pattern, the muscle free amino acid pattern showed all the amino acids without exception to be higher in the exercised group than in the nonexercised one (Fig. 5). Total amino acids and total branched-chain amino acid levels in the exercised group were 66% and 52% higher, respectively, compared to the nonexercised group. Glytine, alanine, lysine, proline, arginine, and the branched-chain amino acid levels were particularly elevated. The liver amino acid patterns in the exercised and nonexercised groups were very similar (Fig. 6). Total amino acids and total branched-chain amino acid levels in the various groups were similar. There was little difference in plasma, muscle, and liver amino acids in the two groups of exercised animals (those running lOO200 laps/day or 300-500 laps/day) and for statistical purposes these are considered as one group. DISCUSSION
Exercise is known to increase the consumption of oxygen and metabolic fuels to provide energy for the exercising muscle. Fuels contributing to the exercise induced energy needs are free fatty acids, muscle glycogen, and blood-borne glucose (1, 6, 22). Although glucose production from hepatic glycogen dominates total glucose output, the contribution of hepatic gluconeogen-
w 00-0
800
Exemsed Non -Exercised
\ 700
-
600
-
500
-
400
-
300
-
200
-
100 -
OGLY LYS LEU ILU PHE TYR ClT ALA HIS ORN MET VAL ARG FIG. 6. Liver amino acid patterns postoperative, hyperalimented rats.
in exercised
and nonexercised
esis rises progressively as exercise continues (1, 6). The increased glucose utilization is associated with a rise in muscle alanine output, which in turn is used by the liver for gluconeogenesis. One source of nitrogen for the
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FREUND,
144
increased alanine production is from oxidation of branched-chain amino acids by the muscle and transamination with pyruvate to form alanine (7). Thus augmented proteolysis initiated by exercise could be expected to result in negative nitrogen balance. In the present investigation, the effect of exercise on postinjury protein metabolism was tested. Laparotomy and jugular vein cannulation in rats treated postoperatively with 5% dextrose only, resulted in a mean negative nitrogen balance of ZOO-300 mg N/day. The administration of 15 kcal and 0.56 g amino acid/100 g body wt per 24 h resulted in marginal, positive nitrogen balance in both exercised and nonexercised groups. In this short-term, postoperative exercise experiment, no differences could be found in nitrogen balance, body weight change between exercised and nonexercised animals, or between animals who experienced different degrees of exercise. As operative trauma and nutritional support were exactly similar for both groups, one must conclude that running exercise in the immediate postoperative period had no effect on nitrogen balance. One possible explanation for the failure of graded exercise to affect detectable alterations in nitrogen balances could be the magnitude of the operative injury, i.e., that the operative trauma was such a severe catabolic stimulus that the effect of exercise was negligible in comparison and had little influence on nitrogen balance. Another explanation could be the adequacy of nutritional support offered to the injured animals, which would mask any marginal effects of exercise on nitrogen balance or weight change. Whether the lack of a gross effect of running can be applied to all other forms of exercise is a matter of some controversy. Holloszy (13) has shown that although running does not stimulate muscle growth it increases mitochondrial enzyme levels and activity. On the other hand, Rogozkin (21), McManus et al. (15), and others have also shown that running or swimming does affect protein metabolism. Furthermore, one may argue that increased mitochondrial enzyme levels are in fact alterations in nitrogen metabolism. It is possible that resistance exercises might have given a different experimental result. However, to parallel the clinical situation which these experiments are intended to do, resistance exercises are not often used, whereas walking and running are. However, though weight changes and nitrogen balances, rather gross metabolic parameters, were unaffected by exercise, exercise was not without effect as manifested by the profound alterations in muscle and plasma amino acid patterns. The total plasma amino acids in the exercised group were 15% lower than in the nonexercised group, but the total free amino acids in muscle of the exercised group were 66% higher than in the nonexercised group. Considering individual amino acids in the plasma, all amino acids in the exercised group were at lower concentrations as compared with the nonexercised animals, except for serine, glutamate, aspartic acid, and citrulline. All muscle free amino acids were at a higher concentration in the exercised groux). This nattern of high levels of amino acids in the
YOSHIMURA,
AND
FISCHER
muscle of the exercised animals with low levels in the plasma is suggestive of increased amino acid turnover in the muscle of the exercised animals. It can be postulated that in the postinjury state, which is characterized by increased muscle protein breakdown, most of the energy required for exercise results from oxidation of amino acids and gluconeogenesis from alanine, both of which are the result of branched-chain amino acid oxidation by the muscle. This assumption gains favor when we consider that the basic hormonal profile in exercise, namely low insulin levels (14, 19, 22, 23) and high glucagon (1, 3, 8L catecholamines, growth hormone , and cortisol levels (11), is even more accentuated by the metabolic response to injury occurring after surgery (17). Furthermore, insulin hyposecretion is characterized by an increased output of amino acids from the muscle (18), whereas glucagon secretion stimulates branched-chain amino acid release from the liver and their oxidation by muscle tissue (1). This state of amino acid utilization to satisfy energy needs of the exercised group should have resulted in negative nitrogen balance, demonstrated, in fact, by Dohm et al. (5). However, the fact that the exercised animals in our experiment showed the same mild positive nitrogen balance as did the nonexercised animals and decreased concentrations of most amino acids in the plasma suggests that a parallel anabolic process initiated by exercise took place. Evidence for protein synthesis during exercise was offered by Rogozkin (21), who found an increase in the concentration of all amino acids in the skeletal muscle of animals subjected to repeated training sessions, with an increase in [14C]leucine incorporation and an increase in both microsomal and ribosomal RNA synthesis. McManus et al. (15) reported a significantly greater degree of labeled leucine incorporation into both sarcoplasmic and myofibrillar fractions of the trained guinea pig. However, no muscle hypertrophy occurred despite the elevated leucine incorporation, implying an increased protein degradation coupled with the observed enhancement of leucine incorporation and suggesting increased muscle protein turnover in a situation analogous to this exneriment. Further evidence for protein anabolism is the muscle hypertrophy occurring after repeated periods of exercise, demonstrable even in starvation (9). The present study, though raising many new questions as to the role of exercise in protein metabolism, suggests however that in the postoperative or postinjury period exercise has a stimulating effect on amino acid turnover in the skeletal muscle. This increased turnover is the result of two components: 1) amino acid consumption for energy metabolism and gluconeogenesis; and 2) protein synthesis. The net balance of both results in nitrogen equilibrium similar to that of a nonexercised control group. This study was supported AM-15347 and AM-19124. Address reprint requests eral Hospital. Received
28 April
in part by Public to J. E. Fischer
Health
Service
at Massachusetts
1978; accepted in final form 8 August
Grants Gen-
1978.
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EXERCISE
AND
POSTOPERATIVE
NITROGEN
BALANCE
145
REFERENCES 1. AHLBORG, G., P. FELIG, L. HAGENFELDT, R. HENDLER, AND J. WARREN. Substrate turnover during prolonged exercise in man. J. Clin. Invest. 53: 1080-1090, 1974. 2. ASHWORTH, A., AND A. D. B. HARROWER. Protein requirements in tropical countries: nitrogen losses in sweat and their relation to nitrogen balance. Br. J. Nutr. 21: 833-843, 1967. 3. BOTTIGER, I., E. M. SCHLEIN, G. R. FALOONA, ET AL. The effect of exercise on glucagon secretion. J. CZin. EndocrinoZ. Metab. 35: 117-125, 1972. 4. CHRISTENSEN, E. H. Das Essen und Trinken des Sportlers. Sportmed. Schriftenr. 5. DOHM, G. L., A. L. HECKER, W. E. BROWN, G. J. KLAIN, F. R. PUENTE, E. W. ASKEW, AND G. R. BEECHER. Adaptation of protein metabolism to endurance training. Biochem. J. 164: 705708, 1977. 6. FELIG, P., AND J. WAHREN. Fuel homeostasis in exercise. N. EngZ. J. Med. 293: 1078-1084, 1975. 7. FELIG, P., AND J. WAHREN. Amino acid metabolism in exercising man. J. CZin. Inuest. 50: 2703-2714, 1971. 8. FELIG, P., J. WAHREN, R. HENDLER, ET AL. Plasma glucagon levels in exercising man. N. EngZ. J. Med. 287: 184-185, 1972. 9. GOLDBERG, A. L. Mechanism of growth and atrophy of skeletal muscle. In: MuscZe Biology. New York: Dekker, 1972, vol. I, p. 89-118. 10. GONTZEA, I., R. SUTZESCU, AND S. DUMITRACHE. The influence of muscular activity on nitrogen balance and on the need of man for proteins. Nutr. Rept. Int. 11: 231-236, 1975. 11. HARTLEY, L. H., J. W. MASON, R. P. HOGAN, L. G. JONES, T. A. KOTCHEN, E. H. MOUGEY, F. E. C. WHERRY, L. L. PENNINGTON, AND P. T. RICKETTS. Multiple hormonal responses to graded exercise in relation to physical training. J. AppZ. Physiol. 33: 602-606, 1972. 12. HEDMAN, R. The available glycogen in man and the connection between rate of oxygen intake and carbohydrate usage. Acta Physiol. Stand. 40: 305-321, 1957. 13. HOLLOSZY, J. 0. Biochemical adaptations in muscle. J. BioZ.
Chem. 242: 2278-2282, 1967. 14. HUNTER, W.M., AND M. Y. SUKKAR. Changes in plasma insulin levels during muscular exercise. J. Physiol. London 196: llO112, 1968. 15. MCMANUS, B. M., D. R. LAMB, J. J. JUDAS, AND J. SCALA. Skeletal muscle, leucine incorporation and testosterone uptake in exercised guinea pigs. Eur. J. AppZ. PhysioZ. 34: 149-156, 1975. 16. MOLE, P. A., AND R. E. JOHNSON. Disclosure by dietary modification of an exercise-induced protein catabolism in man. J. AppZ. Physiol. 31: 185-190, 1971. 17. MOORE, F. D. Metabolic Care of the Surgical Patient. Philadelphia, PA: Saunders, 1959. 18. POSEFSKY, T., P. FELIG, J. D. TOBIN, J. S. SOELDNER, AND G. F. CAHILL. Amino acid balance across tissues of the forearm in post-absorptive man: effect of insulin at two dose levels. J. CZin. Invest. 48: 2273-2282, 1969. 19. PRUETT, E. D. R. Plasma insulin levels during prolonged exercise. In: MuscZe MetaboZism During Exercise, edited by B. Pernow and B. Saltin. New York: Plenum, 1971, p. 165-175. 20. REFSUM, H. E., AND S. B. STROMME. Urea and creatinine production and excretion in urine during and after prolonged heavy exercise. Stand. J. CZin. Lab. Invest. 33: 247-291, 1974. 21. ROGOZKIN, V. A. The effect of the number of daily training sessions on skeletal muscle protein synthesis. Med. Sci. Sports 8: 223-225, 1976. 22. SCHALCH, D. S. The influence of physical stress and exercise on growth hormone and insulin secretion in man. J. Lab. CZin. Med. 69: 256-269, 1967. 23. WAHREN, J., P. FELIG, G. AHLBORG, AND L. JORFELDT. Glucose metabolism during leg exercise in man. J. CZin. Inuest. 50: 27152725, 1971. 24. WILSON, D. W., W-L. LONG, H. C. THOMPSON, AND S. THURLOW. Changes in the composition of the urine after muscle exercise. J. BioZ. Chem. 65: 755-771, 1925.
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on postoperative
HERBERT FREUND, NORMAN YOSHIMURA, Department of Surgery, Massachusetts General Harvard Medical School, Boston, Massachusetts
FREUND, HERBERT, NORMAN YOSHIMURA, AND JOSEF E. FISCHER. Effect of exercise on postoperative nitrogen balance. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 46(l): 141-145, 1979. -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/l00 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 energy metabolism and gluconeogenesis, and 2) protein synthesis. The net balance of both results in nitrogen equilibrium similar to that of a nonexercised control group. postoperative catabolism; nitrogen gen; amino acid turnover; amino sis; branched-chain amino acids
metabolism; acid pattern;
urinary nitrogluconeogene-
IS WIDELY ADVOCATED and used in patients undergoing nutritional repletion as a means of increasing nitrogen retention. Studies by Goldberg (9) demonstrated that the level of muscular activity was a major determinant of amino acid transport and subsequently of the rate of protein synthesis in skeletal muscle. However, there has been considerable controversy about whether protein catabolism in vivo is influenced by exercise. Though some authors describe increased nitrogen losses or increased urea and creatinine production (10, 16, 20) others report no change in nitrogen excretion (4, 12, 24), or even a decrease in urinary nitrogen excretion following exercise (2). The present study was designed to investigate whether exercise, when used as an adjunct to parenteral
EXERCISE
0161-7567/79/0000-0000$01.25
Copyright
0 1979 the American
AND Hospital, 02114
nitrogen JOSEF and
balance
E. FISCHER
nutrition, has any influence on postoperative muscle catabolism, amino acid metabolism, and nitrogen balance in rats immediately following major operative trauma. MATERIALS
AND
METHODS
Twenty male Sprague-Dawley rats weighing 300-370 g (mean 350 t 10 g) were divided into two groups of exercised and nonexercised animals. The exercised animals were further divided according to the amount of exercise performed. Under pentobarbital anesthesia, all animals underwent laparotomy and jugular vein cannulation with a 22-gauge medical-grade silicone tubing. Postoperatively, the animals were placed in metabolic cages and infused with an amino acid and dextrose solution at a mean dose of 15 kcal/lOO g body wt per 24 h and 0.56 g of crystalline amino acids/l00 g body wt per 24 h for a total of 96 h. Water was allowed ad libitum. A control group of 10 additional rats was treated with 5% dextrose alone. Urine was collected and analyzed for total nitrogen determined by a Kjeldahl method. The exercised animals were run on a self-operated treadmill at an average speed of 4.1-10.9 m/min and slope of 0” for 15 min/day for a total of 3 days. Five rats ran 100-200 laps/3 days and five rats ran 300-500 laps/3 days. The last bout of exercise took place 24.:h before the animals were killed. After 96 h of infusion, the animals were killed by decapitation and blood, liver, and the right gastrocnemius muscle immediately removed and frozen for amino acid determination performed by a Beckman amino acid analyzer 121-MB on the supernatant fraction of muscle, liver, or plasma deproteinized by the addition of 4% sulfosalicylic acid. Muscle or liver tissue were acid homogenized in 3 vol (3 x wt) 4% sulfosalicylic with a motor-driven, all-glass homogenizer. The precipitated protein was separated by centrifugation at 20,000 x g for 20 min. All values are expressed as the mean t SE and statistical significance of measured changes was examined by Student’s t test.
Physiological
RESULTS
Nitrogen balance and body weight change. Nonexercised animals subjected to laparotomy and jugular vein cannulation and treated by infusion of 5% dextrose alone, lost 21% of their body weight, and were in negative nitrogen balance of 200-300 mg N/24 h. The mean cumulative and day-to-day nitrogen balances for the experimental groups treated with parenteral nutriSociety
141
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 16, 2019.
142
FREUND,
tion are summarized in Figs. 1 and 2. Both groups were in positive nitrogen balance with no difference between exercised (40 t 12 mg N/day) and nonexercised (46 t 10 mg N/day) animals. When dividing the exercised group according to the amount of exercise performed, there was no difference in nitrogen balance between animals running 100-200 laps/3 days (41 t 12 mg N/day) and those running 300-500 laps/3 days (37 t 10 mg N/day) (Fig. 1). On a daily basis, nitrogen balances of the exercised and nonexercised groups varied from day to day and between the two groups, the differences being statistically nonsignificant (Fig. 2). If body weight is compared over the 4-day period, both groups exhibited a similar minimal weight loss, with the nonexercised group losing 2 t 1.8% and the exercised group 2.6 t 1.6% of their body weight. In the exercised, postoperative group, those animals who ran 100-200 laps and those who ran 300-500 laps/3 days lost 2.6% body wt/day each (Fig. 3). Amino acid patterns. The plasma amino acid pattern of the exercised and nonexercised groups differed markedly (Fig. 4). Mean total free plasma amino acid concentration in the exercised animals was 15% lower than in the nonexercised group (P < 0.05); total branched-chain amino acid concentration (valine, leucine, isoleucine) in the exercised group was 23% lower than in the nonexercised group (P < 0.05). When each amino acid is considered separately, all amino acid levels except aspartic acid, serine, glutamic acid, glycine, and citrulline were higher in the plasma of the nonexercised animals
YOSHIMURA,
AND
FISCHER
Control
T l-r
FIG. 2. Daily (days l-4) nitrogen balances in exercised exercised postoperative, hyperalimented rats. Differences two groups are statistically not significant.
and nonbetween
Exercised:
100 - 200 60
300-
500
Exercised: *:::. .::::. .::::.. Total .:.:.:.:.:. 0+:.:.:.:.:
laps laps
-
IOOl!zBl
200
300-500
FIG. 1. Mean cumulative 4-day nitrogen and exercised postoperative, hyperalimented riencing different degrees of exercise.
balance in nonexercised rats and in rats expe-
laps laps
FIG. 3. Body weight changes during a 4-day period in exercised and nonexercised postoperative, hyperalimented rats, and in rats experiencing different degrees of exercise.
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 16, 2019.
EXERCISE
AND
POSTOPERATIVE
NITROGEN
143
BALANCE
n mol/ml 1,000
900
800
0-0 o-4
Exercised Non-Exerctsed
n mol/gm 700
St p < 0.05
700
04 0-4
600
Exercised Non- Exert wd * p < 0.05 ** p < 0.02
600
500
400
300
200
100
LYS VAL ARG ILU PHE CIT ALA PRO LEU HIS MET TYR ORN FIG. 5. Muscle free amino acid patterns in exercised and nonexercised postoperative, hyperalimented rats. GLY
0 GLY LYS TAU TRE GLU ILU PHE ORN ASP ALA SER PRO VAL LEU ARG HIS TYR CIT FIG. 4. Plasma amino acid patterns postoperative, hyperalimented rats.
in exercised
and nonexercised
than in the plasma of the exercised animals, although only alanine, leucine, ornithine, proline, and arginine showed statistically significant differences. In contrast to the plasma amino acid pattern, the muscle free amino acid pattern showed all the amino acids without exception to be higher in the exercised group than in the nonexercised one (Fig. 5). Total amino acids and total branched-chain amino acid levels in the exercised group were 66% and 52% higher, respectively, compared to the nonexercised group. Glytine, alanine, lysine, proline, arginine, and the branched-chain amino acid levels were particularly elevated. The liver amino acid patterns in the exercised and nonexercised groups were very similar (Fig. 6). Total amino acids and total branched-chain amino acid levels in the various groups were similar. There was little difference in plasma, muscle, and liver amino acids in the two groups of exercised animals (those running lOO200 laps/day or 300-500 laps/day) and for statistical purposes these are considered as one group. DISCUSSION
Exercise is known to increase the consumption of oxygen and metabolic fuels to provide energy for the exercising muscle. Fuels contributing to the exercise induced energy needs are free fatty acids, muscle glycogen, and blood-borne glucose (1, 6, 22). Although glucose production from hepatic glycogen dominates total glucose output, the contribution of hepatic gluconeogen-
w 00-0
800
Exemsed Non -Exercised
\ 700
-
600
-
500
-
400
-
300
-
200
-
100 -
OGLY LYS LEU ILU PHE TYR ClT ALA HIS ORN MET VAL ARG FIG. 6. Liver amino acid patterns postoperative, hyperalimented rats.
in exercised
and nonexercised
esis rises progressively as exercise continues (1, 6). The increased glucose utilization is associated with a rise in muscle alanine output, which in turn is used by the liver for gluconeogenesis. One source of nitrogen for the
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 16, 2019.
FREUND,
144
increased alanine production is from oxidation of branched-chain amino acids by the muscle and transamination with pyruvate to form alanine (7). Thus augmented proteolysis initiated by exercise could be expected to result in negative nitrogen balance. In the present investigation, the effect of exercise on postinjury protein metabolism was tested. Laparotomy and jugular vein cannulation in rats treated postoperatively with 5% dextrose only, resulted in a mean negative nitrogen balance of ZOO-300 mg N/day. The administration of 15 kcal and 0.56 g amino acid/100 g body wt per 24 h resulted in marginal, positive nitrogen balance in both exercised and nonexercised groups. In this short-term, postoperative exercise experiment, no differences could be found in nitrogen balance, body weight change between exercised and nonexercised animals, or between animals who experienced different degrees of exercise. As operative trauma and nutritional support were exactly similar for both groups, one must conclude that running exercise in the immediate postoperative period had no effect on nitrogen balance. One possible explanation for the failure of graded exercise to affect detectable alterations in nitrogen balances could be the magnitude of the operative injury, i.e., that the operative trauma was such a severe catabolic stimulus that the effect of exercise was negligible in comparison and had little influence on nitrogen balance. Another explanation could be the adequacy of nutritional support offered to the injured animals, which would mask any marginal effects of exercise on nitrogen balance or weight change. Whether the lack of a gross effect of running can be applied to all other forms of exercise is a matter of some controversy. Holloszy (13) has shown that although running does not stimulate muscle growth it increases mitochondrial enzyme levels and activity. On the other hand, Rogozkin (21), McManus et al. (15), and others have also shown that running or swimming does affect protein metabolism. Furthermore, one may argue that increased mitochondrial enzyme levels are in fact alterations in nitrogen metabolism. It is possible that resistance exercises might have given a different experimental result. However, to parallel the clinical situation which these experiments are intended to do, resistance exercises are not often used, whereas walking and running are. However, though weight changes and nitrogen balances, rather gross metabolic parameters, were unaffected by exercise, exercise was not without effect as manifested by the profound alterations in muscle and plasma amino acid patterns. The total plasma amino acids in the exercised group were 15% lower than in the nonexercised group, but the total free amino acids in muscle of the exercised group were 66% higher than in the nonexercised group. Considering individual amino acids in the plasma, all amino acids in the exercised group were at lower concentrations as compared with the nonexercised animals, except for serine, glutamate, aspartic acid, and citrulline. All muscle free amino acids were at a higher concentration in the exercised groux). This nattern of high levels of amino acids in the
YOSHIMURA,
AND
FISCHER
muscle of the exercised animals with low levels in the plasma is suggestive of increased amino acid turnover in the muscle of the exercised animals. It can be postulated that in the postinjury state, which is characterized by increased muscle protein breakdown, most of the energy required for exercise results from oxidation of amino acids and gluconeogenesis from alanine, both of which are the result of branched-chain amino acid oxidation by the muscle. This assumption gains favor when we consider that the basic hormonal profile in exercise, namely low insulin levels (14, 19, 22, 23) and high glucagon (1, 3, 8L catecholamines, growth hormone , and cortisol levels (11), is even more accentuated by the metabolic response to injury occurring after surgery (17). Furthermore, insulin hyposecretion is characterized by an increased output of amino acids from the muscle (18), whereas glucagon secretion stimulates branched-chain amino acid release from the liver and their oxidation by muscle tissue (1). This state of amino acid utilization to satisfy energy needs of the exercised group should have resulted in negative nitrogen balance, demonstrated, in fact, by Dohm et al. (5). However, the fact that the exercised animals in our experiment showed the same mild positive nitrogen balance as did the nonexercised animals and decreased concentrations of most amino acids in the plasma suggests that a parallel anabolic process initiated by exercise took place. Evidence for protein synthesis during exercise was offered by Rogozkin (21), who found an increase in the concentration of all amino acids in the skeletal muscle of animals subjected to repeated training sessions, with an increase in [14C]leucine incorporation and an increase in both microsomal and ribosomal RNA synthesis. McManus et al. (15) reported a significantly greater degree of labeled leucine incorporation into both sarcoplasmic and myofibrillar fractions of the trained guinea pig. However, no muscle hypertrophy occurred despite the elevated leucine incorporation, implying an increased protein degradation coupled with the observed enhancement of leucine incorporation and suggesting increased muscle protein turnover in a situation analogous to this exneriment. Further evidence for protein anabolism is the muscle hypertrophy occurring after repeated periods of exercise, demonstrable even in starvation (9). The present study, though raising many new questions as to the role of exercise in protein metabolism, suggests however that in the postoperative or postinjury period exercise has a stimulating effect on amino acid turnover in the skeletal muscle. This increased turnover is the result of two components: 1) amino acid consumption for energy metabolism and gluconeogenesis; and 2) protein synthesis. The net balance of both results in nitrogen equilibrium similar to that of a nonexercised control group. This study was supported AM-15347 and AM-19124. Address reprint requests eral Hospital. Received
28 April
in part by Public to J. E. Fischer
Health
Service
at Massachusetts
1978; accepted in final form 8 August
Grants Gen-
1978.
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EXERCISE
AND
POSTOPERATIVE
NITROGEN
BALANCE
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