Myofibrillar protein turnover and urinary N-tau-methylhistidine output. Response to dietary supply of protein and energy

Beef cows housed in mud during late gestation have greater net energy requirements compared with cows housed on wood chip bedding

Mud increases net energy requirements for cattle because mud and precipitation compromise the ability of the hair coat to insulate and maintain core body temperature of the cow. The increase in energy required for a gestating cow to compensate for a muddy environment is unknown. The objective of this study was to evaluate effects of muddy conditions on cow body weight (BW) and fetal growth during late gestation. Sixteen multiparous Angus cows (n = 8/treatment) were paired based on initial BW and one cow from each pair was randomly allocated to either the mud (MUD) or control (CON) treatment on day 213 of gestation. Pens in the CON group were bedded with wood chips, while pens in the MUD group were designed to create a muddy lot (average depth of 23.6 ± 5.8 cm). Cows were housed outdoors individually and fed the same diet that consisted of a limit-fed total mixed ration. Each pair was fed to meet energy and protein requirements for maintenance and gestation. From day 213 to 269 of gestation, cows were weighed and sampled for blood metabolites weekly. Data were analyzed as a randomized complete block design with repeated measurements (SAS 9.4). Though cows consumed the same amount of dry matter, cows in the MUD treatment weighed 37.4 kg less than cows in the CON treatment (P < 0.01) by day 269 of gestation. Cows in the MUD treatment decreased approximately half a body condition score (BCS), while cows in the CON treatment gained approximately 1 BCS during the treatment period (P < 0.01). There was no evidence of a treatment × day of gestation effect for 12th rib back fat (P = 0.85), rump fat (P = 0.48), total plasma protein concentrations (P = 0.85), or plasma 3-methylhistidine (P = 0.84); however, there was a marginally significant treatment × day of gestation effect for plasma non-esterified fatty acid concentration (P = 0.09). Despite differences in cow BW at the end of the treatment period, calf birth weight (P = 0.66) and calf total plasma protein (P = 0.27) were not different; however, the divergence in cow BW remained marginally significant at parturition (P = 0.06). These results indicate that mud increased net energy requirements for cows in the MUD treatment, as calf birth weight was not different but maternal BW was decreased compared with cows in the CON treatment.

Neuromuscular electrical stimulation may attenuate muscle proteolysis after cardiovascular surgery: A preliminary study

OBJECTIVE

To explore the efficacy of postoperative neuromuscular electrical stimulation (NMES) on muscle protein degradation and muscle weakness in patients after cardiovascular surgery.

METHODS

Sixty-one patients underwent NMES daily from postoperative days (PODs) 1 to 5 in addition to postoperative mobilization program (NMES group), and 41 patients underwent postoperative mobilization program only (non-NMES group). The primary outcome was the concentration of 3-methylhistidine (3-MH) in 24-hour urine corrected for urinary creatinine content (3-MH/Cre) from PODs 1 to 5. The secondary outcomes were knee extensor isometric strength (KEIS) and handgrip strength at POD 7.

RESULTS

Baseline characteristics such as age, sex, preoperative body mass index, hemoglobin, handgrip strength, KEIS, surgery type, cardiopulmonary bypass time, and immediate postoperative interleukin-6 were not different between the groups. Urinary 3-MH/Cre was increased significantly in both groups; however, urinary 3-MH/Cre in the NMES group peaked earlier compared with that in the non-NMES group. KEIS at POD 7 was significantly greater in the NMES group (median [interquartile range], 0.40 kg/weight [0.33-0.45] in the NMES group vs 0.23 kg/weight [0.15-0.36] in the non-NMES group; P < .01). Handgrip strength at POD 7 was also significantly greater in the NMES group (median [interquartile range], 32 kg [24.5-35.3] in the NMES group vs 24 kg [16.0-30.0] in the non-NMES group; P < .01).

CONCLUSIONS

This study demonstrated that NMES might attenuate skeletal muscle protein degradation and muscle weakness after cardiovascular surgery. A cause-effect relationship between NMES and functional preservation would be a future challenging issue.

Identification of 1- and 3-methylhistidine as biomarkers of skeletal muscle toxicity by nuclear magnetic resonance-based metabolic profiling

Nuclear magnetic resonance (NMR)-based metabolomic profiling identified urinary 1- and 3-methylhistidine (1- and 3-MH) as potential biomarkers of skeletal muscle toxicity in Sprague-Dawley rats following 7 and 14 daily doses of 0.5 or 1mg/kg cerivastatin. These metabolites were highly correlated to sex-, dose- and time-dependent development of cerivastatin-induced myotoxicity. Subsequently, the distribution and concentration of 1- and 3-MH were quantified in 18 tissues by gas chromatography-mass spectrometry. The methylhistidine isomers were most abundant in skeletal muscle with no fiber or sex differences observed; however, 3-MH was also present in cardiac and smooth muscle. In a second study, rats receiving 14 daily doses of 1mg/kg cerivastatin (a myotoxic dose) had 6- and 2-fold elevations in 1- and 3-MH in urine and had 11- and 3-fold increases in 1- and 3-MH in serum, respectively. Selectivity of these potential biomarkers was tested by dosing rats with the cardiotoxicant isoproterenol (0.5mg/kg), and a 2-fold decrease in urinary 1- and 3-MH was observed and attributed to the anabolic effect on skeletal muscle. These findings indicate that 1- and 3-MH may be useful urine and serum biomarkers of drug-induced skeletal muscle toxicity and hypertrophy in the rat, and further investigation into their use and limitations is warranted.

Regulation of muscle protein degradation, not synthesis, by dietary leucine in rats fed a protein-deficient diet

The aim of this study was to elucidate the effects of long-term intake of leucine in dietary protein malnutrition on muscle protein synthesis and degradation. A reduction in muscle mass was suppressed by leucine-supplementation (1.5% leucine) in rats fed protein-free diet for 7 days. Furthermore, the rate of muscle protein degradation was decreased without an increase in muscle protein synthesis. In addition, to elucidate the mechanism involved in the suppressive effect of leucine, we measured the activities of degradation systems in muscle. Proteinase activity (calpain and proteasome) and ubiquitin ligase mRNA (Atrogin-1 and MuRF1) expression were not suppressed in animals fed a leucine-supplemented diet, whereas the autophagy marker, protein light chain 3 active form (LC3-II), expression was significantly decreased. These results suggest that the protein-free diet supplemented with leucine suppresses muscle protein degradation through inhibition of autophagy rather than protein synthesis.

Cats are able to adapt protein oxidation to protein intake provided their requirement for dietary protein is met

Cats require more dietary protein than noncarnivorous species. Earlier work showed that cats lack the ability to regulate hepatic urea cycle enzymes in response to dietary protein concentration. We thus hypothesized that cats are unable to fully adapt protein oxidation to protein intake, particularly at low-protein concentrations. We used indirect respiration calorimetry to assess cats' ability to adapt substrate oxidation to diets containing different concentrations of protein, including 1 below their protein requirement. Nine cats (5 males and 4 females; 2.7 +/- 0.5 y; 4.49 +/- 0.19 kg) consumed each of 4 semipurified diets containing 7.5% [low protein (LP(3))], 14.2% [adequate protein (AP)], 27.1% [moderate protein (MP)], and 49.6% [high protein (HP)] of metabolizable energy from protein in a modified crossover design, beginning with the MP diet and then consuming the remaining diets in random order. After adaptation to each diet, cats completed a 5-d nitrogen balance trial and at least 2 12-h indirect calorimetry measurements. There was a significant effect of diet on protein oxidation (P < 0.0001), which measured 10.4 +/- 0.5, 14.1 +/- 1.0, 25.0 +/- 1.7, and 53.2 +/- 1.7% of total energy expenditure for the LP, AP, M,P and HP diets, respectively. The ratio of protein oxidation:protein intake was higher with the LP diet (1.39 +/- 0.07) than the other 3 diets (AP, 1.00 +/- 0.07; MP, 0.93 +/- 0.06; HP, 1.07 +/- 0.03; P < 0.0001), indicating a net loss of protein with the LP diet. Thus, cats are able to adapt protein oxidation to a wide range of dietary protein concentrations, provided their minimum protein requirement is met.

Stimulation of myofibrillar protein degradation and expression of mRNA encoding the ubiquitin-proteasome system in C(2)C(12) myotubes by dexamethasone: effect of the proteasome inhibitor MG-132

Addition of the synthetic glucocorticoid, dexamethasone (Dex) to serum-deprived C(2)C(12) myotubes elicited time- and concentration-dependent changes in N(tau)-methylhistidine (3-MH), a marker of myofibrillar protein degradation. Within 24 h, 100 nM Dex significantly decreased the cell content of 3-MH and increased release into the medium. Both of these responses had increased in magnitude by 48 h and then declined toward basal values by 72 h. The increase in the release of 3-MH closely paralleled its loss from the cell protein. Furthermore, Dex also decreased the 3-MH:total cell protein ratio, suggesting that myofibrillar proteins were being preferentially degraded. Incubation of myotubes with the peptide aldehyde, MG-132, an inhibitor of proteolysis by the (ATP)-ubiquitin (Ub)-dependent proteasome, prevented both the basal release of 3-MH (>95%) and the increased release of 3-MH into the medium in response to Dex (>95%). Northern hybridization studies demonstrated that Dex also elicited similar time- and concentration-dependent increases in the expression of mRNA encoding two components (14 kDa E(2) Ub-conjugating enzyme and Ub) of the ATP-Ub-dependent pathway. The data demonstrate that Dex stimulates preferential hydrolysis of myofibrillar proteins in C(2)C(12) myotubes and suggests that the ATP-Ub-dependent pathway is involved in this response.

Cellular adaptations in the diaphragm in chronic obstructive pulmonary disease

BACKGROUND

In patients with severe chronic obstructive pulmonary disease, the diaphragm undergoes physiologic adaptations characterized by an increase in energy expenditure and relative resistance to fatigue. We hypothesized that these physiologic characteristics would be associated with structural adaptations consisting of an increased proportion of less-fatigable slow-twitch muscle fibers and slow isoforms of myofibrillar proteins.

METHODS

We obtained biopsy specimens of the diaphragm from 6 patients with severe chronic obstructive pulmonary disease (mean [+/-SE] forced expiratory volume in one second, 33+/-4 percent of the predicted value; residual volume, 259+/-25 percent of the predicted value) and 10 control subjects. The proportions of the various isoforms of myosin heavy chains, myosin light chains, troponin, and tropomyosin were determined by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis. We also used immunocytochemical techniques to determine the proportions of the various types of muscle fibers.

RESULTS

The diaphragm-biopsy specimens from the patients had higher percentages of slow myosin heavy chain I (64+/-3 vs. 45+/-2 percent, P<0.001), and lower percentages of fast myosin heavy chains IIa (29+/-3 vs. 39+/-2 percent, P=0.01) and IIb (8+/-1 vs. 17+/-1 percent, P<0.001) than the diaphragms of the controls. Similar differences were noted when immunohistochemical techniques were used to compare the percentages of these fiber types in the two groups. In addition, the patients had higher percentages of the slow isoforms of myosin light chains, troponins, and tropomyosin, whereas the controls had higher percentages of the fast isoforms of these proteins.

CONCLUSIONS

Severe chronic obstructive pulmonary disease increases the slow-twitch characteristics of the muscle fibers in the diaphragm, an adaptation that increases resistance to fatigue.

Measurement of muscle protein degradation in live mice by accumulation of bestatin-induced peptides

Bestatin, an aminopeptidase inhibitor, permits the degradation of cellular proteins to di- and tripeptides but interferes with the further breakdown of these peptides to amino acids. We propose to measure instant rates of protein degradation in skeletal muscles of intact mice by the accumulation of bestatin-induced intermediates. Muscle protein was labeled by injection of L-[guanidino-14C]arginine; 3 days later, maximum accumulation of intermediates was measured in abdominal wall muscles 10 min after the intravenous injection of 5 mg of bestatin. The peptides were partially purified and hydrolyzed in 6 N HCl, and the radioactivity in peptide-derived arginine was determined, after conversion to 14CO2 by treatment with arginase and urease. The measurement of bestatin-induced intermediates provides a unique tool for studying acute changes in muscle protein turnover in live mice. We observed a 62% increase in muscle protein breakdown after a 16-h fast, which was reversed by refeeding for 3.5 h, and a 38% increase after 3 days of protein depletion.

[Methods for isotopic exploration of protein metabolism. Effects of anesthetics and surgical stress]

Techniques using stable isotopes, the only ones authorized in France, allow a new insight into protein metabolism. These methods use an amino acid labelled with nitrogen 15, carbon 13 or deuterium, making it possible to measure the synthesis and overall breakdown of the body, as well as the speed of tissue synthesis and specific protein synthesis. Analytically, the techniques using nitrogen 15 are based on measurements of the enrichment in terminal urinary products: total nitrogen, urea or ammonia. Methods using carbon 13 have become preferred, even though they are more invasive, as they require sampling of blood and expired air. In hypercatabolic states, particularly in intensive care, reaching a steady state while measuring the flux of an amino acid entails the use of a short perfusion preceded by priming, to reduce the risk of recycling. The flooding dose method, consisting of the simultaneous injection of a labelled amino acid and a large quantity of unlabelled amino acid, seems to be of particular interest for measuring specific protein synthesis. Whole body breakdown is easily calculated from flux of labelled amino acid. The combination of isotopic infusion with the net forearm balance for amino acid allows to measure changes in muscle protein synthesis and breakdown. In contrast, measurement of breakdown is more difficult. For example, fractional breakdown rate and tissue sites of catabolism of plasma protein cannot be determined in humans. These isotopic techniques have contributed to improving our understanding of protein metabolism as far as synthetic and catabolic processes are concerned. The effect of food intake on protein turnover is different in muscle and liver. The immediate responses of food intake is an increase of muscular protein synthesis with a decrease of it's breakdown, while liver protein synthesis does not change. In contrast, liver breakdown increases during post absorptive state. Insulin plays a major role in regulation of protein synthesis and inhibits proteolysis. Surgical stress is characterized by an increase of whole body protein synthesis and breakdown and a net protein catabolism. Uncomplicated surgery, but not general anaesthesia, induces change in protein turnover. The protein synthesis rate is unaffected by general anaesthesia while a decrease is seen after surgery. The effect of anaesthetic agents is not well characterized. In rats, lung protein synthesis is reduced by halothane, pentobarbitone and midazolam combined with fentanyl while liver protein synthesis is depressed by all these agents, excepted by midazolam/fentanyl. The effects of anaesthetic agents on skeletal muscle and heart are minor.

Postsurgical muscle protein turnover in perfused hindquarters of the rat

Skeletal muscle protein synthesis and degradation were measured simultaneously in perfused hindquarters of adult female rats 0, 2, and 4 days after surgical trauma. In order to explore the role of decreased postoperative nutrient intake on muscle protein turnover, a group of rats were pair-fed to the level of food consumed by surgical traumatized animals. Protein synthesis was measured by the incorporation of 3H-L-phenylalanine into the myofibrillar (contractile) and sarcoplasmic (soluble) proteins of gastrocnemius muscle. Protein degradation rates were calculated from the release of myofibrillar 3-methyl histidine (3MH) during the perfusion. Surgical trauma significantly depressed myofibrillar and sarcoplasmic protein synthetic rates by 33 and 29%, respectively. Protein degradation, as assessed by 3MH release into perfusate, increased 25% on the second postoperative day but returned to control levels by the 4th day after surgery. Food restriction of the pair-fed control rats did not alter protein synthesis, however, protein degradation decreased significantly. In conclusion, the effect of trauma on protein turnover appears not to be due to decreased nutrient consumption.

Prostaglandin synthetase inhibitors are not beneficial in the hypercatabolic state of acute uremia in rats

In rats the effect of prostaglandin synthetase inhibition on the enhanced protein degradation in acute uremia was investigated. After 48 h of bilateral nephrectomy the urea nitrogen appearance, an indicator of net protein degradation, was calculated, and N tau-methylhistidine (N tau-MH) serum concentration was measured for judging myofibrillar breakdown. Also serum urea nitrogen, creatinine, and potassium serum concentrations were followed up. All bilateral nephrectomized rats showed severe uremic disturbances with increased (P less than 0.01) concentrations of serum urea nitrogen, creatinine, and potassium. Moreover, the urea nitrogen appearance and N tau-MH serum concentration increased (P less than 0.05) significantly. Administration of indomethacin (4 mg.kg-1b.wt./12 hi.p.) in bilateral nephrectomized rats did not influence the analyzed parameters significantly. Thus, we could not demonstrate a positive influence on the increased skeletal muscle degradation in acutely uremic rats by prostaglandin synthetase inhibition. These data suggest that in our model of acute uremia prostaglandins do not play a major role in the degradation of striated muscle.

The retention and metabolism of N tau-methylhistidine by cockerels: implications for the measurement of muscle protein breakdown determined from the excretion of N tau-methylhistidine in excreta

Excreta were collected for four consecutive days from 4- to 18-week-old cockerels following subcutaneous injection of N tau-[14CH3]methylhistidine. The recoveries of radioactivity in excreta were incomplete and progressively decreased with increasing age. Most of the radioactivity not recovered in excreta after 4 d was found in skeletal muscle where greater than 55% of the radioactivity present was in the N tau-methylhistidine-containing dipeptide, balenine. This peptide appeared to be relatively stable so that most of the labelled N tau-methylhistidine incorporated was not released during the period of the recovery measurements. The total pool of non-protein bound N tau-methylhistidine (free (free N tau-methylhistidine + balenine) in pectoral and mixed thigh muscles increased with age and relative to the daily excretion of N tau-methylhistidine. At 18 weeks the pool was 3.3 times the daily excretion of N tau-methylhistidine. These observations account for the decreasing recoveries of radioactivity in excreta described previously, due to progressive dilution of labelled N tau-methylhistidine in an expanding pool of non-protein-bound N tau-methylhistidine, part of which was relatively stable. It is concluded that excretion of N tau-methylhistidine by 4- to 18-week-old cockerels cannot be used as a reliable index of muscle protein breakdown in vivo.

Sensitivity of myofibrillar proteins to glucocorticoid-induced muscle proteolysis

Previous studies have reported that prolonged administration of pharmacological doses of glucocorticoids in young rats results in a rise in urinary 3-methyl-L-histidine (3-MH) excretion followed by a fall to initial levels by 8 days. To determine whether this response reflects events in skeletal muscle, protein breakdown in this tissue was evaluated using the perfused hindquarter preparation with rats treated with corticosterone (10 mg X 100 g-1 X day-1) for 2, 4, or 8 days. Myofibrillar and total cell proteolysis were evaluated by measuring the release of 3-MH and tyrosine, respectively, after inhibition of protein synthesis with cycloheximide. Corticosterone treatment resulted in an early increase (1-4 days) followed by a fall (4-8 days) in 3-MH excretion. 3-MH release by the perfused hindquarter of treated rats responded in a similar manner, in that its release increased at days 2 and 4 and decreased to control levels by day 8. On the other hand, corticosterone treatment did not affect the release of tyrosine by the perfused hindquarter. Corticosterone treatment diminished protein synthesis in muscle by 30-50% (P less than 0.01), which unlike 3-MH release by perfused muscle persisted throughout the treatment period. The data indicate that glucocorticoids specifically augment the breakdown of myofibrillar proteins in skeletal muscle. This response is attenuated with prolonged treatment and is unrelated to a loss of metabolic effectiveness of the steroid. Also our findings suggest that the breakdown of myofibrillar and nonmyofibrillar proteins might be regulated independently.

Protective adaptation of low serum triiodothyronine in patients with chronic renal failure

Low serum triiodothyronine (T3) concentration is frequently found in patients with chronic renal failure (CRF). To test the hypothesis that this may serve to minimize protein catabolism in these patients, we measured nitrogen balance (Nb) in seven CRF and four control subjects in the basal state and when serum T3 concentration was elevated by L-triiodothyronine (LT3) and suppressed by sodium ipodate administration. In the basal state, both the controls and the CRF patients were in positive Nb, 0.02 +/- 0.51 and 0.58 +/- 0.34 g/day, respectively. During LT3 administration, Nb decreased to -0.80 +/- 0.39 g/day in the CRF patients (P less than 0.01), but remained positive, 0.22 +/- 0.67 g/day, in the controls. There was a significant negative correlation between serum T3 concentration and Nb in the CRF patients (r = -0.63, P less than 0.005), but not in the controls. Furthermore, urea nitrogen generation rate, calculated from urea kinetics, increased from a baseline of 4.6 +/- 0.55 to 6.0 +/- 0.50 mg/min during LT3 administration in the CRF patients (P less than 0.01). Sodium ipodate, which significantly lowered serum T3 concentrations, had little effect on nitrogen metabolism in the controls and the CRF patients. These data support the concept that low serum T3 concentrations may confer a protective effect on CRF patients regarding protein-nitrogen conservation and provide a rationale for not correcting such deficiency.

Analysis of 1- and 3-methylhistidines, aromatic and basic amino acids in rat and human urine

A procedure based on automated amino acid analysis has been developed to simultaneously quantify 1-methylhistidine (1-MH), 3-methylhistidine (3-MH), tyrosine, phenylalanine, tryptophan, lysine, histidine and arginine levels in human and rat urines. Deproteinized urine samples containing amino acids in the range 1-10 nmol were analyzed using single-column methodology with ninhydrin detection. Standard curves produced correlation coefficients greater than or equal to 0.99 with duplicate analyses agreeing to within +/- 1.9%. Quantitative recovery was ensured by using L-alpha-amino-beta-guanidinopropionic acid as an internal standard. Elution was accomplished in less than 90 min at pH 5.7 with sodium citrate buffers at 45 degrees C and 65 degrees C. Since 3-MH in the rat is acetylated at the alpha-amino group, rat, but not human, urine ultrafiltrates required acid hydrolysis prior to analysis. The utility of the technique of analysis of 1-MH and 3-MH in human urine was demonstrated for an adult male on a meat-free diet for 21 days; urinary excretion rates for 3-MH and 1-MH were determined to be 3.06 +/- 0.10 and 0.72 +/- 0.07 mumol/kg body mass/day, respectively. The technique was also used to measure the effect of disuse atrophy of rat skeletal muscle which induced a 40-60% increase in 3-MH. The procedure is also highly suited for measurement of urinary aromatic and/or basic amino acids.

Determination of 3 methyl-L-histidine in human urine by ion exchange high performance liquid chromatography. Applications to patients in post-operative surgical care

A new chromatographic procedure is proposed for measuring 3 methyl-L-histidine (3 MH) in human urine. The sample was purified on a cation-exchange resin (AGR 50W-X4) and analysed by ion exchange high performance liquid chromatography on a PARTISIL 10 SCX Whatman column in UV light at 210 nm within 16 min. This procedure gave similar outputs of 3 MH to those described in human normal urine (mean +/- SEM = 213 +/- 15 mumol X 24 h-1, n = 19). It was used to measure the urinary outputs of 3 MH of five patients admitted to an intensive surgical care unit, for 48, 28, 25, 15 and 10 days, respectively. The urinary outputs of 3 MH were normal or lower than normal. The 10(3) urinary 3 MH/creatinine molar ratios were also calculated; this new 3 MH analysis could help the reanimator to prescribe an adequate nutritional assessment.

Variation among chicken stocks in the fractional rates of muscle protein synthesis and degradation

Fractional rates (% X day-1) of synthesis and degradation were determined by measuring the output of N tau-methylhistidine (MeHis) in the excreta at 4 and 8 weeks of age in the chicken. At 4 weeks of age, the fractional rate of synthesis of the meat-type stock was twice that of the egg-type stock (White Leghorn), but the fractional rates of synthesis at 8 weeks of age were similar (4.1-5.1% X day-1) among stocks. The fractional rate of degradation (1.3-1.5% X day-1) of the meat-type stock at 8 weeks of age was less than half the rate of the egg-type stock (2.9% X day-1). The fractional rates of synthesis and degradation at 4 weeks of age in the Satsuma native fowl were relatively high compared with those in the other stocks. In particular, the rate of degradation (8.6% X day-1) at 4 weeks of age was approximately twice that of other stocks. These results show that fractional rates of synthesis and degradation of muscle protein in the chicken differ among genetically diverse groups. The effect of changes in rates of synthesis and degradation on the change in fractional growth rate also differed. From regression coefficients (bks . FGR and bKd . FGR) of these rates in skeletal muscle protein on the fractional growth rate, it was recognized that the change in growth rate accompanies the changes in both synthesis and degradation in White Leghorn and commercial broilers but only the change in synthesis in White Plymouth Rock (dw) and Satsuma native fowl.

Effect of parenteral nutrition on muscle amino acid output and 3-methylhistidine excretion in septic patients

The effects of adequate total parenteral nutrition (TPN) on nitrogen excretion, urea N percentage, 3-methylhistidine excretion, and leg amino acid output, were studied during the ten-day period following abdominal surgery for generalized peritonitis in nine patients. The first two postoperative days were without nutritional intake, TPN was started on the third postoperative day (57 cal/KgBW--40% as Intralipid--0.30 g of N/KgBW). Leg amino acid outputs were done before TPN (DO), then two days (D2) and eight days (D8) after TPN. Total nitrogen and urea N percentage did not significantly differ before and after TPN. Between DO and D2 there was a significant reduction of urinary 3-methylhistidine (467 +/- 37 to 280 +/- 29 mumol/24 h-P less than 0.001) and leg amino acid release (604 +/- 103 to 254 +/- 87 nmol/mn/100 g of calf muscle--P less than 0.01) reflecting reduction in muscle hypercatabolism despite the persistence of the septic state. Between D2 and D8, 3-methylhistidine remained stable while leg amino acid release continued to decrease (254 +/- 87 to 68 +/- 40 nmol/mn/100 g--P less than 0.05). This association suggests an increased muscle protein synthesis. A closer examination of the clinical evolution of these patients, especially concerning their septic evolution, shows that only improved patients with recovery from sepsis increased their muscle protein synthesis. Thus, in septic hypercatabolic patients TPN seems to be able to reduce muscle catabolism while the increase in protein synthesis is mainly the consequence of recovery from the septic state. In such patients TPN should be used as a preventive therapeutic measure.

Effect of a protein-free diet on muscle protein turnover and nitrogen conservation in euthyroid and hyperthyroid rats

Although protein turnover in skeletal muscle is increased in hyperthyroidism and decreased in hypothyroidism, a deficient protein intake tends to increase serum T3 (tri-iodothyronine) while decreasing muscle protein turnover. To determine whether this diet-induced decrease in protein turnover can occur independent of thyroid status, we have examined muscle protein turnover and nitrogen conservation in hyperthyroid rats fed on a protein-free diet. After inducing hyperthyroidism by giving 20 micrograms of T3/100g body wt. daily for 7 days, groups of euthyroid and hyperthyroid animals were divided into subgroups fed on basal and protein-free diets. Muscle protein turnover was measured by N tau-methylhistidine excretion and [14C]tyrosine infusion. Urinary nitrogen output of euthyroid and hyperthyroid animals fed on the protein-free diet was also measured. Although hyperthyroidism increased the baseline rates of muscle protein synthesis and degradation, it did not prevent a decrease in these values in response to protein depletion. Furthermore, hyperthyroid rats showed greatly decreased nitrogen excretion in response to the protein-free diet, although not to values for euthyroid rats. These findings suggest that protein depletion made the experimental animals less responsive to the protein-catabolic effects of T3.

Thyroid status and muscle protein breakdown as assessed by urinary 3-methylhistidine excretion: study in thyrotoxic patients before and after treatment

Urinary 3-methylhistidine (3MH) excretion was studied in nine thyrotoxic patients before and after treatment. Urinary creatinine (Cr) output was also measured and was low in the thyrotoxic subjects before treatment. Thus, although urinary output of 3MH was not greater than among the control population when expressed per subject, it was significantly elevated when expressed as the ratio of 3MH to Cr; this ratio fell significantly, reaching normal control values after a euthyroid state was obtained. In one patient who became hypothyroid, the 3MH/Cr ratio fell under the control value. There was a significant linear correlation between the 3MH/Cr ratio and the hormonal variables (T3, T4, FT4l); moreover, variations in the 3MH/Cr ratio and variations in the T3 level were closely correlated. 3-Methylhistidine appears to be a reliable index of muscular breakdown in thyrotoxicosis. From our results, it can be concluded, first of all, that hyperthyroidism is accompanied by an increased muscular catabolism, and, second, that the return to a euthyroid state results in an immediate normalization of muscular breakdown.

[Effect of orally-administered triglycerides on muscle proteolysis in the rat]

Earlier studies in man could demonstrate that intravenous lipids decreased the concentration of amino acids in plasma (to 50%). In short- and long-term experiments in rat the effect of orally applied olive-oil on the concentration of amino acids in blood, on the excretion of 3-methylhistidine and of total nitrogen into urine was measured. Two control groups were used: rats with total restriction of food and rats which were fed ad libitum. 2 ml olive-oil given to rats within 12 hours decreased the concentration of alanine, valine, leucine, isoleucine. Whereas food restriction increased the excretion of 3-methylhistidine into urine and the blood concentration of leucine, isoleucine, valine, tyrosine, phenylalanine, threonine, and glutamine, the oil-fed rats showed no increase of amino acid levels in plasma and no increase of 3-methylhistidine excretion into urine. These experiments suggest that lipid application inhibits proteolysis in muscle, and thus diminishes the amino acid levels in blood.

3-Methylhistidine turnover in the whole body, and the contribution of skeletal muscle and intestine to urinary 3-methylhistidine excretion in the adult rat

The tissue origin of 3-methylhistidine (N tau-methylhistidine) was investigated in adult female rats. The decay of labelling of urinary 3-methylhistidine was compared with the labelling of protein-bound 3-methylhistidine in skeletal muscle and intestine after the injection of [methyl-14C]methionine. The decay curve for urinary 3-methylhistidine was much steeper than that in muscle or intestine, falling to values lower than those in either tissue after 30 days. The lack of decay of labelling in muscle during the first 30 days is shown to result from the persistence of label in the precursor S-adenosylmethionine. The relative labelling of urinary, skeletal-muscle and intestinal 3-methylhistidine cannot be explained in terms of skeletal muscle accounting for a major proportion of urinary 3-methylhistidine. Measurements were also made of the steady-state synthesis rate of protein-bound 3-methylhistidine in intestinal smooth muscle in vivo in adult female rats. This involved measurement of the overall rate of protein synthesis and measurement of the relative rates of synthesis of 3-methylhistidine and of mixed protein. The synthesis rate of 3-methylhistidine was 29.1%/day, compared with the overall rate of 77.1%/day for mixed, non-mucosal intestinal protein. Measurement of the amount of 3-methylhistidine in skeletal muscle (0.632 +/- 0.024 mumol/g) and in the whole body (0.332 +/- 0.013 mumol/g) indicate that, although the muscle pool is 86% of the total, because of its slow turnover rate of 1.1-1.6%/day, it only accounts for 38-52% of the observed excretion. Measurements of the mass of the intestine (9.95 g/250 g body wt.) and protein-bound 3-methylhistidine content (0.160 mumol/g of tissue) indicate a pool size of 1.59 mumol/250 micrograms rat. Thus 463 nmol of the urinary excretion/day would originate from the intestine, 22% of the total. The tissue source of the remaining urinary excretion is not identified, but other non-muscle sources constituting about 10% of the whole-body pool could account for this with turnover rates of only 6%/day, a much lower value than the turnover rate in the intestine.

Leukocyte endogenous mediator alters protein dynamics in rats

Leukocyte endogenous mediator (LEM), a low-molecular-weight peptide synthesized by monocytic cells during phagocytosis, has been implicated as the host's initiator of the protein metabolic response to infection and inflammation. To determine whether administration of LEM would alter protein kinetics, appearance and oxidation of plasma tyrosine as well as the rates of protein synthesis in liver and skeletal muscle were determined in fasted rats that received a 30-hour continuous infusion of either physiologic saline, LEM, or heat-inactivated LEM. The LEM was obtained from rabbit peritoneal exudate and the treatment solutions supplied 2.8 X 10(8) cell equivalents/100 g of body weight (BW) per day. Endogenous tyrosine oxidation increased from 4.0 +/- 0.4 mumol/100 g BW/h to 5.4 +/- 0.7 mumol/100 g BW/h in animals infused with heat-inactivated LEM and to 7.5 +/- 1.5 mumol/100 g BW/h in rats receiving LEM (P less than 0.01). Nonsecretory protein synthesis in the liver was greatest in rats administered LEM (2239 +/- 325 mg/d) when compared with control groups receiving physiologic saline (1122 +/- 195 mg/d) or heat-inactivated LEM (1374 +/- 62 mg/d; P less than 0.01), whereas skeletal protein synthetic rates were unchanged. Rates of muscle and collagen protein breakdown were estimated from the urinary excretion rate of Nt-methylhistidine and hydroxyproline, respectively, and their excretion rose by 30% (P less than 0.05) and 42% (P less than 0.05) with LEM administration. These results suggest that administration of LEM stimulates a mobilization of amino acids from peripheral tissues to support increased visceral protein anabolism while whole body amino acid oxidation is also enhanced. Since similar effects follow fever and infection, these results suggest that LEM may play an underlying role in the protein metabolic response to infection and inflammation.

Content of methylhistidines in normal and pathological human skeletal muscles

The content of 3-methylhistidine (3-MH) and 1-methylhistidine (1-MH) was measured in muscle biopsy specimens from 13 normal controls, 19 patients with Duchenne muscular dystrophy, 8 limb-girdle disease patients, and 23 disease controls with different forms of muscular pathology. 3-MH and 1-MH concentrations in normal human muscle did not appear to be influenced by sex, body weight, and age, at least for subjects in the 10--60 year age group examined. Skeletal muscle 1-MH levels did not significantly differ from mean control values in any of the pathologies investigated. In the patient population examined, the mean 3-MH level per unit of noncollagen protein (NCP) was significantly lower than normal in Duchenne dystrophy only, the reduction being related to disease severity. The significantly lower concentrations of 3-MH in muscle of Duchenne patients indicate the importance of measuring 3-MH in diseased muscle to obtain reliable estimates of the myofibrillar protein catabolic rate.

Vitamin D Deficiency, hypocalcemia, and increased skeletal muscle degradation in rats

The myopathy associated with vitamin D deficiency was examined in vitamin D-deficient and vitamin D-supplemented rats. When compared with either vitamin D-supplemented ad lib. or pair-fed rats, weight gain and muscle mass were decreased in vitamin D-deficient hypocalcemic animals. With the exception of a modest decrease in muscle creatine phosphate levels, muscle composition was unchanged by vitamin D deficiency. Muscle protein turnover rates were determined in both in vivo and in vitro studies and demonstrated that myofibrillar protein degradation was increased in vitamin D deficiency. Normal growth rates could be maintained be feeding the rats vitamin D-deficient diets containing 1.6% calcium, which maintained plasma calcium within the normal range. In addition to its role in maintaining plasma calcium, vitamin D-supplemented rats had significantly higher levels of the anabolic hormone insulin. Vitamin D supplementation may affect muscle protein turnover by preventing hypocalcemia, as well as directly stimulating insulin secretion, rather than by a direct effect within skeletal muscle.

Corticosteroid myopathy: a clinical and pathological study

In six patients with Cushing's syndrome and three with steroid myopathy, the clinical, functional, biochemical and structural characteristics of myopathy are described. Proximal muscle weakness occurred in all the patients, preferentially affected the lower limbs and was accompanied by muscle wasting in all but one patient. Force measurements confirmed quadriceps weakness in every patient. Vastus lateralis muscle biopsies showed light microscopic abnormalities in two of three patients with steroid myopathy and one of five patients with Cushing's syndrome. Type II fibre atrophy was the commonest abnormality. Reduced type II mean fibre areas occurred in all the patients with steroid myopathy and were common in Cushing's syndrome patients. Type I mean fibre areas were also reduced in two of the former group and one of the latter group and two further patients in this group had areas at the lower end of the normal range. Abnormalities in electron microscopy, mitochondrial function tests and chemical content of skeletal muscle were frequent and are described and discussed. A plasma creatine kinase activity (CK) at the lower end of the normal range, a myopathic electromyogram (EMG) and a raised 24-h urinary 3-methylhistidine/creatinine ratio on a creatine free diet were other characteristic findings in both groups of patients.

Effect of testosterone on the rate of myofibrillar protein breakdown in castrated and adrenalectomized male rats measured by the urinary excretion of 3-methylhistidine

Urinary output in N tau-methylhistidine (3-MeHis) was used to evaluate changes in myofibrillar protein breakdown rate in the skeletal muscles of castrated and adrenalectomized-castrated young male rats, and the response of breakdown to testosterone and corticosterone replacement. The castrated rats grew less well than intact control rats and excreted significantly less 3-MeHis. Administration of low and high doses of testosterone restored the weight of the levator ani of the castrated animals but failed to affect growth rate or 3-MeHis output. Although this might suggest that testosterone has an indirect effect on muscle turnover through changes in growth rate, this parallelism was not confirmed by studies on adrenalectomized-castrated rats. Adrenalectomy of castrated rats caused a further reduction in growth rate and in output of 3-MeHis, but administration of testosterone now reduced 3-MeHis output still further while stimulating growth. Treatment of the adrenalectomized-castrated rats with low doses of corticosterone increased growth modestly, while depressing 3-MeHis output, and again output of this metabolite was further reduced when testosterone was added to the treatment, although growth rate was unaffected. Finally, large doses of testosterone given to adrenalectomized-castrated rats receiving excessive amounts of corticosterone did not prevent the growth failure or the increased output of 3-MeHis due to the corticosteroid, though it appeared to reduce the magnitude of the response to corticosterone alone. It is concluded that the effects of testosterone on growth and on 3-MeHis output are not necessarily associated and that the functional status of the adrenal cortex modifies the response of myofibrillar breakdown rate to testosterone treatment.

N tau-methylhistidine release: contributions of rat skeletal muscle, GI tract, and skin

The relative contributions of skeletal muscle, gastrointestinal tract, and skin to urinary N tau-methylhistidine (MH) excretion were estimated during in vitro studies using the rat hemicorpus preparation. After 0.5 h of perfusion, MH release into the perfusate was linear for 3 h and averaged 29.8 nmol . h-1 . 100 g hemicorpus-1. In vivo, 24-h urinary MH excretion averaged 37.3 nmol . h-1 . 100 g body wt-1. The ratio of soft tissue to skin weight is equal (3.2:1) in the whole rat and in the hemicorpus. The gastrointestinal tract released 16.0 nmol . h-1 . 100 g body wt-1 or approximately 41% of the total urinary MH excretion. Preparations perfused with or without skin showed modest differences in the rate of MH release that were not statistically significant. Skeletal muscle contains 89.8% of total body MH content, whereas gastrointestinal tract and skin contain 3.8 and 6.4%, respectively. Gastrointestinal tract actomyosin turns over rapidly with a fractional catabolic rate of 24%/day versus 1.4%/day for skeletal muscle actomyosin.

Urinary 3-methylhistidine/creatinine ratio as a clinical tool: correlation between 3-methylhistidine excretion and metabolic and clinical states in healthy and stressed premature infants

We have investigated the role of the urinary 3-methylhistidine (3MH) excretion, a measure of protein catabolism, in the evaluation of the metabolic state of premature infants. Two-hundred and twenty-two 24 hr urine collections and 3MH/Cr ratio determinations (expressed as mumoles of 3MH per mg creatinine) were carried out in 36 infants (average gestational age 32.7 +/- 0.7 wk, weight 1640 +/- 120 grams) and the relationship between the 3MH/Cr ratios and the metabolic and clinical state has been investigated. Five or more 3MH/Cr measurements were carried out on each of 19 infants and serial determinations on four of those babies are presented. The urinary 3MH/Cr ratio of healthy infants with adequate caloric intake and normal growth curve was .148 +/- .039 (S.D.) mumol/mg, about 35% higher than the 3MH/Cr ratio in healthy adults. As long as the premature infants were healthy the degree of prematurity had no effect on the 3MH/Cr ratio. The relationship between 3MH/Cr ratio and nitrogen balance was highly significant (p less than .001). 3MH/Cr ratio also correlates very well with the metabolic status of the infants: in the group with normal 3MH/Cr ratios less than or equal to .175 (.148 + 1 S.D., n = 90) there were four clinically stressed infants (4.4% false negative rate) while in the group with elevated 3MH/Cr ratios greater than .225 (.148 + 2 S.D.; n = 79) there were only three clinically well infants (3.8% false positive rate). In comparing the clinical status and 3MH/Cr ratios, we found that in the group of infants who could not be clearly defined as clinically well or stressed (n = 108) the 3MH/Cr ratio was more useful than clinical judgment in the prediction of metabolic status. It can be concluded that 3MH/Cr ratio is a potentially useful clinical tool which describes with high accuracy the clinical and metabolic status of premature infants. This conclusion is further supported by the data of serial 3MH/Cr determinations.

Muscle degradation in uremia: 3-methylhistidine release in fed and fasted rats

The rate of myofibrillar protein degradation was measured by 3-methylhistidine (3MH) release in moderately uremic and sham-operated control rats. The rats were studied in the fed state or after 24 and 48 hours of fasting. When fed, both uremic and control rats gained weight at the same rate. During 48 hours of fasting, the uremic animals lost more weight (17.1%) than the shams (13.2%). The ratio of gastrocnemius muscle protein per gram of wet weight was not significantly different under any conditions. When fed and 48-hour fasted animals are compared, urinary excretion of 3MH rose from 0.81 to 1.32 moles per 24 hr per 100 g of initial body wt shams and from 0.90 to 1.30 moles per 24 hr per 100 g of initial body wt in the uremics. When ratio of 3MH to creatinine excretion in the urine was compared, there was no change in 3MH excretion between 0 and 24 hours, but there was an increase between 24 and 48 hours. Analysis of serum and muscle samples from fed and 48-hours fasted animals revealed that the concentrations of 3MH increased in both groups during fasting, with the uremic rats having a large increase in the total body 3MH pool. Myofibrillar degradation rates calculated from the sum of urinary excretion plus the changes in body 3MH pool size revealed that with moderate fasting, degradation rates increased in both sham and uremic rats with a larger increase being seen in the uremic group. After 48 hours of fasting, the increased amount of 3MH released from muscle of uremic rats was comparable to their larger percentage weight loss.