Methionine transsulfuration is increased during sepsis in rats.

Methionine transsulfuration in plasma and liver, and plasma methionine and cysteine kinetics were investigated in vivo during the acute phase of sepsis in rats. Rats were infected with an intravenous injection of live Escherichia coli, and control pair-fed rats were injected with saline. Two days after injection, the rats were infused for 6 h with [(35)S]methionine and [(15)N]cysteine. Transsulfuration was measured from the transfer rate of (35)S from methionine to cysteine. Liver cystathionase activity was also measured. Infection significantly increased (P < 0.05) the contribution of transsulfuration to cysteine flux in both plasma and liver (by 80%) and the contribution of transsulfuration to plasma methionine flux (by 133%). Transsulfuration measured in plasma was significantly (P < 0.05) higher in infected rats than in pair-fed rats (0.68 and 0.25 micromol. h(-1). 100 g(-1), respectively). However, liver cystathionase specific activity was decreased by 17% by infection (P < 0.05). Infection increased methionine flux (16%, P < 0.05) less than cysteine flux (38%, P < 0.05). Therefore, the plasma cysteine flux was higher than that predicted from estimates of protein turnover based on methionine data, probably because of enhanced glutathione turnover. Taken together, these results suggest an increased cysteine requirement in infection.

Protein feeding pattern does not affect protein retention in young women.

This study was undertaken to determine whether a pulse protein feeding pattern was more efficient than a spread pattern to improve protein anabolism in young women as was already shown in elderly women. After a 15-d adaptive period [1.2 g protein/(kg fat-free mass. d)], 16 young women (age 26 +/- 1 y) were given a 14-d diet providing 1.7 g protein/(kg fat-free mass. d), using either a pulse pattern (protein consumed mainly in one meal, n = 8), or a spread pattern (spreading daily protein intake over four meals, n = 8). Nitrogen balance was determined at the end of both the 15-d adaptive and the 14-d experimental periods. Whole-body protein turnover was determined at the end of the 14-d experimental period using [(15)N]glycine as an oral tracer. Nitrogen balance was 17 +/- 5 mg N/(kg fat-free mass. d) during the adaptive period. It was higher during the experimental period, but not significantly different in the women fed the spread or the pulse patterns [59 +/- 12 and 36 +/- 8 mg N/(kg fat-free mass. d) respectively]. No significant effects of the protein feeding pattern were detected on either whole-body protein turnover [5.5 +/- 0.2 vs. 6.1 +/- 0.3 g protein/(kg fat-free mass. d) for spread and pulse pattern, respectively] or whole-body protein synthesis and protein breakdown. Thus, in young women, these protein feeding patterns did not have significantly different effects on protein retention.

Glutathione turnover is increased during the acute phase of sepsis in rats.

Glutathione metabolism during infection has been poorly documented. Glutathione concentrations and synthesis rates were studied in infected rats (2 d after infection) and in pair-fed controls. Glutathione synthesis rates were determined in liver, spleen, lung, small and large intestine, skeletal muscle, heart and blood by a 4-h or 6-h (15)N cysteine infusion. The activities of four hepatic enzymes involved in glutathione metabolism were also determined. Glutathione synthesis rates were significantly greater in liver (+465%), spleen (+388%), large intestine (+109%), lung (+100%), muscle (+91%) and heart (+80%) of infected rats compared with pair-fed controls. Glutathione concentrations were also greater in these tissues but were unaffected in small intestine and lower in blood. In keeping with the stimulation of liver glutathione synthesis, the activities of liver gamma-glutamyl-cysteine synthetase and glutathione reductase were significantly greater in liver of infected rats than of pair-fed rats. From the present study, we estimate that glutathione synthesis accounts for at least 40% of the enhanced cysteine utilization during infection. This increased utilization may be the primary cause of an enhanced cysteine requirement in infection.

Protein turnover modifications induced by the protein feeding pattern still persist after the end of the diets.

This study was undertaken to determine whether the protein feeding pattern could induce chronic adaptation of protein turnover. After a 15-day adaptive period, elderly (68 yr) and young (26 yr) women received, for 14 days, a diet providing 200 KJ x kg fat-free mass (FFM)(-1) x day(-1), where the daily protein intake (1.7 g protein x kg FFM(-1) x day(-1)) was either spread over 4 meals in the spread pattern or mainly (80%) consumed at noon in the pulse pattern. One day after the end of the dietary treatment, whole body leucine kinetics were measured by use of a continuous [(13)C]leucine infusion, both in the postabsorptive state and in the same fed state. The pulse pattern was able to induce, in young as in elderly women, a lower postabsorptive leucine oxidation and endogenous leucine flux than the spread pattern and improved the responsiveness of nonoxidative leucine disposal during 4-h oral feeding. Thus the pulse pattern was able to induce chronic regulation of protein metabolism in young as in elderly women.

Lower recovery of muscle protein lost during starvation in old rats despite a stimulation of protein synthesis.

Sarcopenia could result from the inability of an older individual to recover muscle lost during catabolic periods. To test this hypothesis, we compared the capacity of 5-day-refed 12- and 24-mo-old rats to recover muscle mass lost after 10 days without food. We measured gastrocnemius and liver protein synthesis with the flooding-dose method and also measured nitrogen balance, 3-methylhistidine excretion, and the gene expression of components of proteolytic pathways in muscle comparing fed, starved, and refed rats at each age. We show that 24-mo-old rats had an altered capacity to recover muscle proteins. Muscle protein synthesis, inhibited during starvation, returned to control values during refeeding in both age groups. The lower recovery in 24-mo-old rats was related to a lack of inhibition of muscle proteolysis during refeeding. The level of gene expression of components of the proteolytic pathways did not account for the variations in muscle proteolysis at both ages. In conclusion, this study highlights the role of muscle proteolysis in the lower recovery of muscle protein mass lost during catabolic periods.

Protein pulse feeding improves protein retention in elderly women.

BACKGROUND: Adequate protein nutrition could be used to limit gradual body protein loss and improve protein anabolism in the elderly. OBJECTIVE: We tested the hypothesis that an uneven protein feeding pattern was more efficient in improving protein anabolism than was an even pattern. DESIGN: After a controlled period, 15 elderly women (mean age: 68 y) were fed for 14 d either a pulse diet (n = 7), providing 80% of the daily protein intake at 1200, or a spread diet (n = 8), in which the same daily protein intake was spread over 4 meals. Both diets provided 1.7 g protein x kg fat-free mass (FFM)(-1) x d(-1). Protein accretion and daily protein turnover were determined by using the nitrogen balance method and the end product method (ammonia and urea) after an oral dose of [15N]glycine. RESULTS: Nitrogen balance was more positive with the pulse than with the spread diet (54 +/- 7 compared with 27 +/- 6 mg N x kg FFM(-1) x d(-1); P < 0.05). Protein turnover rates were also higher with the pulse than with the spread diet (5.58 +/- 0.22 compared with 4.98 +/- 0.17 g protein x kg FFM(-1) x d(-1); P < 0.05), mainly because of higher protein synthesis in the pulse group (4.48 +/- 0.19 g protein x kg FFM(-1) x d(-1)) than in the spread group (3.75 +/- 0.19 g protein x kg FFM(-1) x d(-1)) (P < 0.05). CONCLUSION: A protein pulse-feeding pattern was more efficient than was a protein spread-feeding pattern in improving, after 14 d, whole-body protein retention in elderly women.

Effect of glucocorticoid excess on skeletal muscle and heart protein synthesis in adult and old rats.

This study was carried out to analyse glucocorticoid-induced muscle wasting and subsequent recovery in adult (6-8 months) and old (18-24 months) rats because the increased incidence of various disease states results in hypersecretion of glucocorticoids in ageing. Adult and old rats received dexamethasone in their drinking water for 5 or 6 d and were then allowed to recover for 3 or 7 d. As dexamethasone decreased food intake, all groups were pair-fed to dexamethasone-treated old rats (i.e. the group that had the lowest food intake). At the end of the treatment, adult and old rats showed significant increases in blood glucose and plasma insulin concentrations. This increase disappeared during the recovery period. Protein synthesis of different muscles was assessed in vivo by a flooding dose of [13C]valine injected subcutaneously 50 min before slaughter. Dexamethasone induced a significant decrease in protein synthesis in fast-twitch glycolytic and oxidative glycolytic muscles (gastrocnemius, tibialis anterior, extensor digitorum longus). The treatment affected mostly ribosomal efficiency. Adult dexamethasone-treated rats showed an increase in protein synthesis compared with their pair-fed controls during the recovery period whereas old rats did not. Dexamethasone also significantly decreased protein synthesis in the predominantly oxidative soleus muscle but only in old rats, and increased protein synthesis in the heart of adult but not of old rats. Thus, in skeletal muscle, the catabolic effect of dexamethasone is maintained or amplified during ageing whereas the anabolic effect in heart is depressed. These results are consistent with muscle atrophy occurring with ageing.

Metabolism of cysteine is modified during the acute phase of sepsis in rats.

In vivo cysteine metabolism during the inflammatory state has been studied minimally. We investigated cysteine metabolism (i.e. taurine, sulfate and glutathione formation) using a single dose of [35S] cysteine in septic rats that had been injected with live Escherichia coli into the tail vein and in control, pair-fed rats. Cysteine metabolites were separated by ion exchange chromatography, and radioactivity was counted in the different fractions. Radioactivity incorporated in tissue proteins was also measured after protein precipitation. [35S]Sulfate production was significantly lower in septic rats than in pair-fed rats. [35S]Taurine contents were significantly lower only in kidneys, spleen and gastrointestinal tract of septic rats. The higher production of [35S] taurine in the livers (the major site of taurine production) of septic rats could have a protective effect against oxidation. Glutathione concentrations were also significantly greater in liver, spleen, kidneys and gastrocnemius muscle of septic rats, presumably in order to combat oxidative stress induced by sepsis. [35S]Cysteine incorporation in glutathione was significantly higher in spleen and kidneys but not in liver of septic rats compared to pair-fed rats. This could be explained by the fact that, in liver, a greater amount of labeled glutathione had been utilized for host defense, or by a high level in glutathione turnover. Finally, [35S]cysteine incorporation into protein, in septic rats, was significantly greater than in pair-fed rats in spleen, lung and particulary in whole plasma proteins other than albumin, which mainly represent the acute-phase proteins. These data suggest an increased requirement for cysteine during sepsis in rats.

Muscle and liver protein synthesis adapt efficiently to food deprivation and refeeding in 12-month-old rats.

Our aim was to analyze mechanisms involved in the adaptation of protein metabolism to food deprivation and refeeding in adult rats. Twelve-month-old rats, which had been food-deprived for 113 h and refed for 6 h, were injected subcutaneously with a flooding dose of valine (with 50% [1-13C]-L-valine) to measure in vivo protein synthesis in tibialis anterior, soleus and liver. Protein and RNA contents were also measured. In both muscles, protein mass was maintained during food deprivation. Due to a drop in protein synthetic capacity (Cs), total and myofibrillar protein synthesis rates were reduced in food-deprived rats and were not stimulated by a 6-h refeeding. In contrast, protein levels were maintained lower than RNA levels in liver during food deprivation, and Cs was higher than in fed rats. Protein synthesis rates and ribosomal efficiency were reduced in food-deprived rats. Due to maintenance of protein synthetic capacity, there was a rapid stimulation of liver protein synthesis with refeeding, which induced a significant rise in protein mass (also related to an inhibition of protein degradation). In conclusion, coordinated responses of liver and muscles allowed a sparing of muscle proteins during food deprivation and a rapid recovery of liver proteins during refeeding. Control of ribosome quantity could play a critical role in these adaptations in tissue protein synthesis in adult rats.

Altered response of protein synthesis to nutritional state and endurance training in old rats.

This study was undertaken to determine whether the loss of muscle protein mass during aging could be explained by a reduced sensitivity of muscle protein synthesis to feeding and exercise. Male Wistar rats aged 12 and 24 mo were exercised by treadmill running for 4 mo. Protein synthesis was measured by the flooding dose method in tibialis anterior, soleus, and liver of conscious rested, trained rats and age-matched controls in the postprandial or in the postabsorptive state. No marked change with age could be detected in basal muscle protein synthesis. In contrast, protein synthesis was stimulated in adult but not in old rats by feeding in tibialis anterior and by exercise in soleus. In liver, protein synthesis was not modified by age but was stimulated by feeding and by exercise, which improved the response to feeding. We conclude that the impact of nutrition on muscle protein synthesis is blunted in old age, which could contribute to the age-related loss of nutrition-sensitive muscle proteins.

Effect of amino acids alone or with insulin on muscle and liver protein synthesis in adult and old rats.

This study was carried out to analyze age-related changes on amino acid and insulin effects on muscle and liver protein synthesis. Conscious male rats, aged 12 (adult) and 24 (old) mo, were infused for 90 min with either saline, amino acids, or amino acids with insulin and glucose. Protein synthesis was measured during the last 15 min of infusion (flooding dose of valine with L-[2,3,4-3H]valine). Gastrocnemius protein mass was 29% lower in old rats than in adults. However, basal muscle absolute synthesis rates were unchanged with age, and fractional synthesis rates (FSR) were increased. Amino acids significantly stimulated muscle FSR to a similar extent (18-20%) in adult (P < 0.01) and old rats (P = 0.03 when variability introduced by muscle atrophy was taken into account by a variance-covariance analysis). Insulin did not elicit any additional effect. Liver protein synthesis did not change with age or in response to infusions. We conclude that, despite an age-related loss of muscle proteins, capacity of muscle protein synthesis to be stimulated is preserved with age.

Colostrum protein digestion in newborn lambs.

The efficiency of colostral protein digestion was studied in nine newborn lambs fed one meal of bovine colostrum 3 h after birth. The results were compared with those obtained in two unfed lambs and four lambs fed bovine milk. The protein and peptide composition [immunoglobulins G1 and (IgG1), beta-lactoglobulin, alpha-lactalbumin, caseins and peptides resulting from casein hydrolysis] of digesta, gastrointestinal tissues, blood and urine were determined in samples taken 0.75 or 4 h after feeding. The amounts of ingested proteins in lambs fed colostrum were much higher than in those fed the milk diet, and their abomasal emptying was faster. alpha-Lactalbumin was highly degraded by abomasal and intestinal proteases, whereas beta-lactoglobulin and in particular the immunoglobulins were less sensitive. The gastric emptying of caseins was delayed in and the kinetics of appearance of peptides originating from casein hydrolysis was comparable to that observed in lambs fed milk and in 1-mo-old preruminant calves. Thirty-five percent of dietary amino acids ingested as colostrum were available within 4 h for amino acid metabolism; this percentage was 54% in the milk-fed lambs. In the lambs fed colostrum, these amino acids were provided by beta-lactoglobulin, casein and IgG1 (0.52, 0.43 and 0.30 g/kg body wt, respectively), whereas in milk-fed animals casein and beta-lactoglobulin were the most important sources of these amino acids (0.40 and 0.20 g/kg, respectively).

Methionine flux and tissue protein synthesis in lactating and dry goats.

Whole-body methionine flux (rate of irreversible loss from plasma) and tissue protein synthesis were estimated in dry and early lactating goats (10-14 d postpartum) by intravenous infusion of L-[35S]methionine. Tissue protein mass was significantly (p less than 0.05) higher for mammary gland and liver but lower for carcass in lactating animals. The plasma methionine flux was higher during lactation (8.5 vs. 5.1 g/d). The fractional synthesis rates of tissue proteins (Ksp: %/d) were lower during lactation for some muscles, especially the masseter muscle (1.46 vs. 2.15), and for skin (0.59 vs. 1.22) and the pooled head plus feet fraction (1.64 vs. 2.31), but the rates were greatly increased in mammary gland (42 vs. 3). The non-mammary methionine flux (plasma flux minus the flux corresponding to milk methionine output and methionine utilization for mammary protein synthesis) was significantly (p less than 0.05) lower for the lactating goats than for the dry group (93 vs. 131 mg.d-1.kg empty body weight-1). This is in agreement with the lower rates of protein synthesis in carcass (542 vs. 948 mg.d-1.kg empty body weight-1) and skin (93 vs. 189) for lactating compared to dry goats. It can be inferred from these data that in early lactation, when nutrient requirements of animals are not adequately met, an adaptative mechanism occurs that allows amino acids to be available for the mammary gland by a decrease of their utilization in some extramammary tissues.