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D Attaix

Publications and source records attributed to D Attaix.

45 records · Page 3Linked to original sources
PubMed1989

Influences of age and weaning on in vivo pancreatic protein synthesis in the lamb.

In vivo pancreatic protein synthesis rates were obtained from the uptake of L-[3,4(n)-3H]valine co-injected with a flooding dose of unlabeled valine into 1-, 5-, and 8-wk-old suckling lambs, and 8-wk-old weaned animals. Protein fractional synthesis rate was 184%/d at 1 wk of age and 153%/d in 5-wk-old animals (P greater than 0.05). This lack of developmental change resulted from constant (P greater than 0.05) ribosomal capacities (total RNA/protein ratios) and efficiencies of protein synthesis (synthetic rates relative to RNA). No further alteration for protein fractional synthesis rate (144%/d) occurred in 8-wk-old suckling animals (P greater than 0.05). In contrast, 8-wk-old ruminants exhibited higher protein fractional synthesis rate (244%/d) than 8-wk-old suckling animals, although ribosomal capacity was markedly higher in both 8-wk-old groups than in youngest animals (P less than 0.05). The present findings clearly indicate that in vivo protein synthesis in the developing ovine pancreas depends primarily on age. Potentialities for increased rates of pancreatic protein synthesis, i.e., increases in total RNA content and ribosomal capacity appear between 5 and 8 wk of age in this species. At 8 wk of age, however, when lambs are generally weaned, solid food ingestion resulted in a rise for both fractional and absolute rates of protein synthesis, essentially because ruminants maintained a higher efficiency of protein synthesis than milk-fed animals (P less than 0.005). Finally, there was a relationship between pancreatic protein synthesis and protein intake in only ruminant lambs.

Age Factors↗
PubMed1988

Respective influences of age and weaning on skeletal and visceral muscle protein synthesis in the lamb.

1. The influences of age and weaning on muscle protein synthesis were studied in vivo, by injecting a large dose of [3H]valine into 1-, 5- and 8-week-old suckling or 8-week-old weaned lambs. 2. The fractional rates of protein synthesis, in red- and white-fibre-type skeletal muscles or striated and smooth visceral muscles, were in 8-week-old suckling animals 24-37% of their values at 1 week of age. This developmental decline was related to decreased capacities for protein synthesis, i.e. RNA/protein ratios. 3. At 8 weeks of age, suckling and weaned lambs had similar fractional synthesis rates, capacities for protein synthesis and efficiencies of protein synthesis (i.e. rates of protein synthesis relative to RNA) in skeletal muscles. 4. In contrast, visceral-muscle fractional synthesis rates were lower in 8-week-old suckling lambs than in weaned animals, owing to decreased efficiencies of protein synthesis. It was concluded that developmental factors and the change to a solid diet, or weaning in itself, or both, affect differently skeletal and visceral muscle protein synthesis in the immature lamb.

Aging↗
PubMed1988

Contribution of liver, skin and skeletal muscle to whole-body protein synthesis in the young lamb.

1. Protein fractional synthesis rate (FSR) was measured in some major tissues and in the whole body of six 1-week-old sucking lambs by a large injection of L-[3H]valine. 2. Upper estimates of tissue protein FSR (%/d), assuming that the tissue-homogenate free-valine specific radioactivity defined that of valyl tRNA, were 115.0 in liver, 24.1 in skin, 22.9 in the white M. tensor fasciae latae, 21.6 in the red M. diaphragma and 19.6 in the remainder (exsanguinated whole body without liver and gastrointestinal tract) of lambs. 3. Absolute synthesis rates (ASR) of tissue protein were 17, 19 and 42 g/d in the liver, skin and skeletal muscle respectively, and 112 g/d in the remainder. The ASR of whole-body protein, derived from the tissue values, was 146 g/d, i.e. 33 g/d per kg body-weight. The calculated whole-body protein FSR was 23.9%/d. 4. The relative percentage contribution of liver, skin and skeletal muscle to whole-body protein synthesis was 11.7, 13.1, and 29.0. 5. We concluded that tissue protein FSR in lambs were in exactly the same decreasing order, from visceral tissues to skeletal muscles, as observed in rats. The ovine FSR estimates and the partitioning of protein synthesis between tissues were in the same range as values recently obtained by flooding-dose experiments in immature rats, piglets, and even in chicks. These findings suggest that inter-species differences are rather limited.

Animals↗
PubMed1988

[Findings and hormonal coordination of protein metabolism in ruminants].

Protein metabolism roughly exhibits the same characteristics in ruminants and non-ruminant species. Changes in whole-body protein mass are the result of the balance between the simultaneous protein synthesis and breakdown. Essential amino acids are either incorporated into protein or degraded. Insulin, growth hormone and glucagon have been shown to regulate those metabolic pathways in ruminants. Alteration of food intake both decreases protein synthesis and protein breakdown. Protein synthesis is affected to a greater extent than protein breakdown. So protein synthesis is the main factor controlling N balance in response to alteration of food intake. The decrease in protein synthesis may be related to an impairment of plasma insulin. Protein synthesis and breakdown both decrease throughout development. Protein deposition decreases throughout development because protein synthesis declines more rapidly than protein breakdown. The hormonal coordination of those changes depends on the age of the animals. For example the decrease in protein synthesis in the postnatal growth period may be due to either the decrease in plasma growth hormone or to the impairment in cellular insulin receptors. Due to milk protein synthesis in the mammary gland, lactating animals exhibit a large increase in whole-body protein synthesis. Surprisingly, protein synthesis decreases in some non-mammary tissues. This represents a mechanism for a greater partitioning of amino acids towards milk at the expense of body proteins. We recently demonstrated that insulin could be involved in that adaptative process.

Amino Acids↗
PubMed1987

Protein synthesis and growth in the gastrointestinal tract of the young preruminant lamb.

1. In Expt 1, fractional synthesis rates (FSR) of tissue protein were measured along the gastrointestinal tract (GIT) of six 1-week-old, milk-fed lambs by using a large amount of L-[3,4(n)-3H]valine. 2. In Expt 2, eighteen lambs were used to determine the fractional growth rate (FGR) of gastrointestinal tissue protein. 3. FSRMinimum (Min) and FSRMaximum (Max) were calculated assuming plasma or tissue homogenate free valine specific radioactivity was representative of the valine precursor pool for protein synthesis. There were no significant differences between FSRMin and FSRMax in any gastrointestinal tissue of lambs used in Expt 1 (P greater than 0.05). FSR gradually and significantly (P less than 0.05) increased from the oesophagus (FSRMax 26.5%/d), reticulo-rumen (30.1%/d), omasum (41.0%/d) and abomasum (56.1%/d) to small intestine (87.5%/d), and then declined significantly (P less than 0.05) towards the caecum (45.2%/d) and the colon (38.4%/d). No significant differences were observed between FSR in the duodenum, jejunum or ileum (P greater than 0.05). 4. FGR ranged from 2.6%/d in the oesophagus to 8.7%/d in the omasum. The ratio, FGR:FSR, which reflected the efficiency of protein deposition, was at a maximum in the stomachs and caecum and at a minimum in the small intestine. 5. The relative contribution of the oesophagus, stomachs, small intestine and large intestine to GIT protein synthesis was 1, 13, 76 and 10% respectively. The GIT accounted for approximately 11.5% of whole-body protein synthesis.

Animals↗
PubMed1986

Assessment of in vivo protein synthesis in lamb tissues with [3H]valine flooding doses.

Week-old lambs received an intravenous injection of 4.3, 8.5, 12.8 or 17.1 mmol [3H]valine/5 kg body weight, i.e., 3.6-14.4-times the whole-body free valine content. To ensure that protein synthesis measurements in lambs are reliable within a 30-min period, these large amounts of valine must account for at least around 11-times the total free pool of valine. This amounted to 12.8 mmol valine/5 kg body weight. There were no significant variations in plasma insulin and plasma glucagon levels 5, 13 and 30 min after the injection of so much valine. The fractional rates of protein synthesis were determined in tissues of animals receiving either 12.8 or 17.1 mmol valine/5 kg body weight. The rates of protein synthesis in the jejunum (87.5%/day), liver (106.6%/day) and tensor fasciae latae muscle (18.8%/day) of lambs injected with the 12.8 mmol [3H]valine flooding dose, were in the range of data obtained in immature rats. Increasing the flooding amount of valine up to 17.1 mmol/5 kg body weight did not significantly alter protein synthesis rates in the jejunum, liver or skeletal muscle. This suggested that both the flooding-dose method in itself and valine had no effect on in vivo protein synthesis.

Animals↗
PubMedDate not supplied

Ubiquitin-proteasome-dependent proteolysis in skeletal muscle.

The ubiquitin-proteasome proteolytic pathway has recently been reported to be of major importance in the breakdown of skeletal muscle proteins. The first step in this pathway is the covalent attachment of polyubiquitin chains to the targeted protein. Polyubiquitylated proteins are then recognized and degraded by the 26S proteasome complex. In this review, we critically analyse recent findings in the regulation of this pathway, both in animal models of muscle wasting and in some human diseases. The identification of regulatory steps of ubiquitin conjugation to protein substrates and/or of the proteolytic activities of the proteasome should lead to new concepts that can be used to manipulate muscle protein mass. Such concepts are essential for the development of anti-cachectic therapies for many clinical situations.

Animals↗
PubMedDate not supplied

Dietary control of protein turnover.

The balance between protein synthesis and breakdown (protein turnover) regulates whole-body protein mass. The relationships between dietary changes (amount and composition of food) and protein synthesis, protein breakdown and amino acid oxidation have been explored in order to better understand adaptations of protein and amino acid metabolism. Methods for measuring protein synthesis, especially whole-body protein synthesis, can be divided into two groups: the 15N end-product method (urea and/or ammonia), and the incorporation of labelled amino acid(s) into proteins. Assumptions and limitations of the widely used two-pool model (free amino acid and protein pools) are discussed. Results obtained with different methods and for amino acids have been compared, to assess their ability to detect changes in protein synthesis rates. Methods of measuring protein breakdown have also been described briefly. Food intake affects whole-body and tissue protein turnover throughout development of animals and humans in different ways. Protein metabolism fluctuates during the 24-hour period in response to intermittent food intake. During the post-prandial period, a net whole-body protein deposition occurs. This is essentially due to increased protein synthesis. The free amino acid pool and amino acid oxidation rates also increase. Consequently, amino acids are used to a great extent as energy substrates. In contrast, a decrease in protein breakdown could enhance protein deposition. During fasting, the rates of whole-body protein synthesis are lower than those of protein breakdown. This results in protein loss, essentially because the drop in protein synthesis rate in muscle is pronounced. N balance is controlled by the amounts and composition of the diet and by changes in protein synthesis and breakdown. Increasing food intake above levels of energy equilibrium can produce growth by enhancing both the whole-body protein synthesis and breakdown rates. Below energy equilibrium, whole-body protein loss occurs because of decreased protein synthesis which becomes lower than protein breakdown. Protein synthesis rate is the main factor controlling N balance in response to alterations in food intake. Increasing dietary protein, especially the essential amino acids, involves increased rates of whole-body protein synthesis and breakdown. The improved N balance obtained by enhancing dietary non-protein energy (carbohydrate, fat) can be brought on by reducing amino acid oxidation and slightly increasing protein synthesis. The effects of dietary protein and energy on protein turnover are apparently additive.

Animals↗