The effect of trauma on protein synthesis

Inter-organ protein and carbohydrate metabolic relationships during sepsis: necessary evils or uncanny coincidences?

Sepsis alters the dynamic flux of metabolic substrates between skeletal muscle and liver. Derangements in skeletal muscle glucose metabolism evoked by sepsis to a certain extent determine the rate of gluconeogenesis in the liver. In contrast, accelerated rates of gluconeogenesis do not drive net catabolism in skeletal muscle, nor does the upregulation of hepatic protein metabolism in sepsis or inflammation appear to be contingent or dependent upon the catabolism of muscle proteins during sepsis.

Protein metabolism after injury with turpentine: a rat model for clinical trauma

Subcutaneous injections of turpentine induced discrete aseptic abscesses in rats without detectable injury to other tissues. Hypoalbuminemia and high circulating concentrations of alpha 2-macroglobulin were present after 48 h. Liver size, protein content, and protein fractional synthetic rate (FSR) were all increased, whereas loss of muscle protein occurred together with similar (45-50%) reductions in both intramuscular glutamine concentrations ([Gln]i, mmol/l intracellular water) and FSR. The rats became anorexic, but pair feeding (50% ad libitum for 48 h) produced a 22% increase in muscle [Gln]i and only an 18% reduction in muscle FSR. Dietary restriction therefore did not demonstrate the positive relationship between muscle [Gln]i and FSR, which has been observed in animal trauma studies. It is concluded that subcutaneous injections of turpentine produce many of the features of the acute-phase response to injury, and therefore this technique is recommended as a convenient laboratory model for studying various aspects of the protein metabolic response to injury.

Muscle protein metabolism of rats in surgical trauma

The effects of decreased food intake and degree of surgical trauma on total, myofibrillar and sarcoplasmic muscle protein synthesis and degradation were assessed in two experiments (A and B). Trauma consisted of an abdominal incision with or without hysterectomy. The degree of trauma in experiment B was increased relative to that in experiment A by extending the length of the incision, operative manipulation and time required to perform the surgery. To account for postoperative diminutions in food intake on protein turnover, a group of nonoperated rats were pair-fed to the level of food consumed by hysterectomized rats. Traumatized rats in experiment B lost more weight, ate less, and had a lower muscle total protein concentration than corresponding rats in experiment A, confirming a more severe trauma in experiment B. In both experiments, trauma depressed total protein content of muscle. Synthesis was measured by the incorporation of L-[U-14C] tyrosine from a single meal into total, sarcoplasmic and myofibrillar proteins of gastrocnemius muscle. Degradation was calculated as the difference between the growth rate and the synthetic rate. Synthetic rate (ks) of total protein was depressed by surgical trauma; the more severe the trauma, the greater the depression. In mild trauma, the depression in ks was due only to a decrease in sarcoplasmic protein synthesis (ke), whereas with more severe trauma, synthetic rates of both sarcoplasmic (kes) and myofibrillar (kem) proteins were decreased. Protein degradation (kd,) was increased on day 2 in experiments A and B, had returned to control values on day 4 in experiment A and had decreased below control values in experiment B.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered protein kinetics in vivo after single-limb burn injury

Recovery from burn injury is associated with stimulated whole-body protein turnover. Since skeletal muscle and liver are the tissues most likely to influence whole-body measurements, we studied protein kinetics in soleus and plantaris muscles as well as liver 3 days after a 3 s burn on one hindlimb of the rat. Muscles from both the burned and unburned limbs of burned rats were compared with those of uninjured controls to distinguish between local and systemic factors involved. The following measurements were performed: (1) fractional growth rate of the tissue protein pool, determined from tissue protein content on days 2, 3 and 4; (2) fractional protein-synthetic rate, measured by [14C]tyrosine constant infusion on day 3; (3) fractional protein-degradation rate, calculated from the difference between the rates of protein synthesis and growth. Protein growth by soleus and plantaris muscles of control rats and unburned limb of burned rats was not paralleled by those in the burned limb, which showed progressive atrophy between 2 and 4 days post-burn (P less than 0.005). Protein synthesis by soleus but not plantaris muscle in the unburned limb of burned rats was enhanced by 62% (P less than 0.04) above control. Protein synthesis by burned-limb soleus and plantaris muscles was elevated by 114% (P less than 0.001) and 67% (P less than 0.02) respectively above control. Protein degradation by both soleus and plantaris muscles in the unburned limb of burned rats did not differ from control. In contrast, that of soleus and plantaris muscles in the burned limb was stimulated by 230% (P less than 0.001) and 164% (P less than 0.001) respectively compared with controls. Protein turnover of soleus muscles in both control and burned rats was more rapid than in corresponding plantaris muscles. Liver protein mass exhibited steady growth in control rats, but remained unchanged in burned animals between 2 and 4 days post-burn. Liver protein synthesis in burned rats was elevated by 56% (P less than 0.01) and protein breakdown was stimulated by 61% (P less than 0.002) above those of controls. The data indicate that both local and systemic factors influence tissue protein turnover in animals recovering from a single-hindlimb scald.

Metabolism of protein, amino acids, and glucose and their response to insulin in atria and cardiac myocytes of traumatized rats

Soft tissue injury to one hindlimb of rats was used to test the metabolic response of atrial and ventricular muscle to trauma. Effects of insulin on muscle metabolism were also studied. In myocytes and atria from normal animals, insulin increased protein synthesis and decreased protein degradation. For myocytes of rats at one and two days after trauma, this effect of insulin on proteolysis could not be detected. Over the next two days, the inhibitory effect returned to normal. Insulin also did not increase protein synthesis on day 1, but did thereafter. In atria, in contrast to heart cells, the inhibitory effect of insulin on proteolysis was enhanced at two and three days after trauma, and its stimulation of protein synthesis was unaltered. Insulin increased carbohydrate metabolism in both myocytes and atria of normal rats and traumatized rats after 2 days, and trauma did not alter this response. In myocytes, but not atria, trauma led to a faster oxidation of leucine and a significant rise in the production of alanine. Production of glutamine and glutamate was not affected in either tissue. These results show that the metabolic responses to trauma of atrial and ventricular muscle differ considerably.

Leupeptin's effect on organ weight, RNA, DNA, and protein content after long bone fracture in the rat

Long bone fracture in the rat is accompanied by enhanced urinary nitrogen loss reflecting changes in protein synthesis and breakdown. The effects of leupeptin, an inhibitor of lysosomal proteases, were assessed on organ weights, RNA, DNA, and protein content after injury in the rat. Two groups of 8-week-old rats were studied: The first group received left femoral fracture. Half of these received leupeptin (25 mumole ip/day), and the remainder received saline. The second group served as uninjured pair-fed controls, with half receiving leupeptin and half receiving saline. On Days 0, 1, 2, 4, and 7 after injury, animals were sacrificed and organs were removed for determination of weight, RNA, DNA, and protein content. All injured rats lost weight, with maximum loss occurring on Day 4. Food intake was also reduced. Pair-fed rats lost the same amount of weight as injured ones, and leupeptin could not prevent whole body weight loss. Expressed as percentage of total body weight, livers from leupeptin-treated injured rats weighed 10% greater than saline-treated ones on Days 2, 4, and 7 after injury (P less than 0.05). No differences occurred in RNA, DNA, or protein contents. Diaphragms similarly weighed 10, 20, and 30% greater on Days 2, 4, and 7 after injury, respectively, in leupeptin-treated rats (P less than 0.05). In addition, the RNA and DNA contents of diaphragms were 96 and 88% greater, respectively, in treated rats than in controls (P less than 0.05) on Day 4. It is concluded that leupeptin causes a relative increase in the weights of livers and diaphragms after injury, and causes a marked increase in the RNA and DNA contents of diaphragms.

Gluconeogenic response during glucose infusions in patients following skeletal trauma or during sepsis

In order to quantitate the effect of sepsis and skeletal trauma on gluconeogenesis, four septic and five skeletal trauma patients were evaluated for their ability to convert 14C-L-alanine to 14C-glucose while receiving 5% dextrose by peripheral vein. In the septic group, the mean glucose pool size increased by 35% and the glucose turnover rate increased by 85% over normal. The alanine conversion averaged 11.1% of the dose. The skeletal trauma group showed a glucose pool size increase of 61%, a 100% increase in glucose turnover rate and a 11.7% conversion of the alanine dose to glucose. The increased conversion of 14C-alanine to 14C-glucose in both sepsis and skeletal trauma in the face of an exogenous glucose infusion indicates an abnormal unsuppressible response. Each of the above parameters when compared to normal values was found to be significant at levels greater than 97.5%. The percentages of the dose expired as 14CO2 in three hours were not significantly different from the normals.

The effect of surgical trauma on muscle protein turnover in rats

The rate of synthesis and catabolism of sarcoplasmic- and myofibrillar-muscle protein was measured in operated, sham-operated and food-restricted rats by using Na2 14CO3. The food-restricted group underwent sham operations and were limited to the food intake of the operated animals. Protein synthesis and catabolism were increased in the sarcoplasmic-muscle fraction in operated rats compared with that in sham-operated or food-restricted rats. The rate of synthesis of the myofibrillar protein decreased in operated animals, but the rate of catabolism was not altered in the myofibrillar-muscle fraction of the operated animals compared with that in food-restricted and sham-operated animals. In the operated animals, there was a net loss of protein from the muscle. Thus the rats that underwent surgery lost muscle protein, primarily as a result of a decrease in synthesis of myofibrillar protein. The changes in protein turnover in operated animals were not due to decreases in food intake, since protein turnover in sham-operated animals that were restricted to the food intake of the operated rats was not different from that in sham-operated rats fed ad libitum.

Protein-sparing effect of intravenously administered branched chain amino acids in adult rats

Branched chain amino acids (BCAA) serve as intermediate energy substrates for peripheral tissues. Experiments were conducted to evaluate protein-sparing properties of BCAA at different doses without dextrose. Forty healthy male adult Wistar rats, weighing 437 +/- 34 gm, were randomly assigned to one of five groups. Four groups of eight rats were cannulated at the jugular vein and infused with 3% amino acid solutions containing 13, 23, 50 or 100% BCAA; an additional eight fasted rats served as controls. Results show that weight loss was not significantly different between groups, but was lower than in the fasted rats. Nitrogen balance (NB) was least negative in the 23% BCAA group, followed by 13, 50 and 100% BCAA. Protein-sparing index (PSI), defined as that portion of the infused nitrogen that is used for sparing body proteins, agreed with the calculated fat/protein ratios. Higher PSI and fat/protein ratios resulted from solutions containing balanced amino acid patterns (13 and 23%). No obvious imbalances in plasma amino acid patterns were observed. It is concluded that more protein conservation can be achieved with amino acid solutions containing a balanced amino acid pattern and that the effect of additional BCAA on protein conservation is limited in adult rats.

Changes in protein synthesis after trauma: importance of nutrition

The effect of trauma (femur fracture) on protein synthesis in rats given four different parenterally administered nutrient formulations ("diets") was investigated. Diet I was a maintenance formulation. It contained sufficient amino acids and glucose to keep the rats in nitrogen balance but was inadequate to support growth. Diet II was amino acids only, diet III was severely hypocaloric glucose, and diet IV was diet I minus the amino acids. The rats received parenterally all nutrients for the duration of the 4-5 day study. Twenty-four hours posttrauma, the fractional synthesis rates of liver, lung, heart, kidney, and muscle were estimated by infusing [15N]glycine for 17.5-19 h. (T.P. Stein, J.C. Oram-Smith, M.J. Leskiw, H.W. Wallace, L.C. Long, and J.M. Leonard. The effects of protein and calorie restriction on protein synthesis in the rat. Am. J. Physiol. 230: 1321-1326, 1976.) Two trends were found: i) on the amino acid-containing diets (I and II), most protein synthesis rates were increased posttrauma. Lung was the exception: no change was found; ii) rats on the amino acid deficient diets (III and IV) showed a decrease in the fractional muscle and lung synthesis rates posttrauma. We concluded that in this rat trauma model the requirement is mostly for amino acid nitrogen posttrauma.