scholarly journals Effects of intraruminal propionate supplementation on nitrogen utilisation by the portal-drained viscera, the liver and the hindlimb in lambs fed frozen rye grass

2003 ◽  
Vol 90 (5) ◽  
pp. 939-952 ◽  
Author(s):  
Isabelle C. Savary-Auzeloux ◽  
Linda Majdoub ◽  
Nathalie LeFloc'h ◽  
Isabelle Ortigues-Marty
Keyword(s):  
Protein Synthesis ◽  
Muscle Growth ◽  
Latin Square ◽  
Urea Synthesis ◽  
Peripheral Tissues ◽  
Rye Grass ◽  
Metabolisable Energy ◽  
Branched Chain ◽  
N Compounds

The influence of propionate supplementation on the splanchnic metabolism of amino acids (AA) and other N compounds (urea-N and NH3-N) and the supply of AA and NH3-N to the hindlimb was investigated in growing lambs. Six rumen-cannulated and multicatheterised lambs (32·2kg) were fed frozen rye grass at 690kJ metabolisable energy intake/d per kg average metabolic body weight. They were infused intraruminally with a salt solution (control) or with propionate solutions at 0·23mol/l (P1) or 0·41mol/l (P2) infused at a maximal rate of 1·68 (sd 0·057) ml/min according to a repeated Latin square design. The propionate infusion did not increase the net portal appearance of total AA (TAA)-N but increased that of some branched-chain AA (valine and to a lesser extent isoleucine). Simultaneously, the propionate treatment (especially P2) induced an increased TAA utilisation by the liver. This was due mainly to an increased (+79%;P<0·07) utilisation of the essential AA and particularly the branched-chain AA. A stimulation of protein synthesis in the liver is hypothesised since (1) propionate stimulated insulin secretion and (2) utilisation of non-essential AA were less influenced by the propionate treatment in the liver (except for alanine), suggesting that the AA utilised by the liver were directed towards protein synthesis rather than towards oxidation or urea synthesis. At the splanchnic level, the propionate treatment did not have any effect on the TAA, non-essential AA and essential AA, except for a net splanchnic release that was decreased for leucine (P<0·02) and methionine (P<0·01) and increased for threonine (P<0·05). The propionate treatment did not have any effect on the hindlimb uptake of AA (essential and non-essential). As a consequence, even though the propionate treatment induced some major alterations in the splanchnic metabolism of AA, there were no changes in the net AA balance in the hindlimb (and hence probably on muscle growth). The role of the splanchnic tissues in the regulation of the AA supply to the peripheral tissues (such as muscle) therefore appears to be prominent in the regulation of muscle growth. Whether the peripheral tissues regulate their own supply by interacting with the splanchnic tissues (and especially the liver) or the liver is the only regulator of the AA supply to the muscle remains in doubt.

The route of absorbed nitrogen into milk protein

2005 ◽  
Vol 80 (1) ◽  
pp. 11-22 ◽  
Author(s):  
H. Lapierre ◽  
R. Berthiaume ◽  
G. Raggio ◽  
M. C. Thivierge ◽  
L. Doepel ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Portal Vein ◽  
Milk Protein ◽  
Whole Body ◽  
Biological Efficiency ◽  
Peripheral Tissues ◽  
New Information ◽  
Unpublished Studies ◽  
Branched Chain ◽  
N Compounds

AbstractA database reviewing the metabolism of nitrogen (N) compounds from absorption to milk has been compiled from 14 published and unpublished studies (33 treatments) that measured the net flux of N compounds across the splanchnic tissues in dairy cows. Apparent N digestibility averaged 0·65, with this then partitioned between 0·34 excreted in urine and 0·31 secreted as milk.Nitrogen metabolites are absorbed from the lumen of the gut into the portal vein, mainly as free amino acids (AA) and ammonia; these represented 0·58 and 0·57 of digested N, respectively. All of the ammonia absorbed was removed by the liver with, as a result, a net splanchnic flux of zero. Detoxification of ammonia by the liver and catabolism of AA results in production of urea as an end-product. Hepatic ureagenesis is a major cross-road in terms of whole body N exchange, being the equivalent of 0·81 of digested N. Therefore, salvage of a considerable part of this ureagenesis is needed to support milk protein synthesis. This salvage occurs via transfer of urea from the blood circulation into the lumen of the gut. On average, 0·47 of hepatic ureagenesis was returned to the gut via the portal-drained viscera (equivalent to 0·34 of digested N) with 0·56 of this then used for anabolic purposes e.g. as precursor N for microbial protein synthesis. On average, 0·65 of estimated digestible AA was recovered in the portal vein. This loss (0·35) is due to oxidation of certain AA across the gut wall and non-absorption of endogenous secretions. The magnitude of this loss is not uniform among AA and varies between less than 0·05 for histidine to more than 0·90 for some non-essential AA, such as glutamine.A second database (six studies, 14 treatments) was constructed to further examine the subsequent fate of absorbed essential AA. When all AA are aggregated, the liver removed, on average, 0·45 of portal absorption but this value hides the considerable variation between individual AA. Simplistically, the AA behave as two major groups: one group undergoes very little hepatic removal and includes the branched-chain AA and lysine. For the second group, removal varies between 0·35 and 0·50 of portal absorption, and includes histidine, methionine and phenylalanine. For both groups, however, the efficiency of transfer of absorbed AA into milk protein decreases with increasing supply of protein. This loss of efficiency is linked directly with increased hepatic removal of AA from the second group and, probably, increased catabolism by peripheral tissues, including the mammary gland, of AA from the first group. Therefore, we must stop using fixed factors of conversion of digestible AA to milk in our predictive schemes and acknowledge that metabolism of AA between delivery from the duodenum and conversion to milk protein will vary with nutrient supply. New information evolving from re-analysis of the literature and recent studies will allow better models to be devised for the prediction of nutrient-based responses by the lactating cow. Consideration of biological efficiency, rather than maximal milk yield, will lead to systems that are economically more sensible for the farmer and that have better environmental impacts.

scholarly journals Effect of feed intake on amino acid transfers across the ovine hindquarters

2003 ◽  
Vol 89 (2) ◽  
pp. 167-179 ◽  
Author(s):  
S. O. Hoskin ◽  
I. C. Savary-Auzeloux ◽  
A. G. Calder ◽  
G. Zuur ◽  
G. E. Lobley
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Feed Intake ◽  
Vastus Lateralis ◽  
Vena Cava ◽  
Latin Square ◽  
Live Weight ◽  
Isoleucine Leucine ◽  
Peripheral Tissues ◽  
Branched Chain

Responses in variables of amino acid (AA) metabolism across peripheral tissues to feed intake were studied in six sheep (mean live weight 32 kg) prepared with arterio–venous catheters across the hindquarters. Four intakes (0·5, 1·0, 1·5 and 2·5 × maintenance energy) were offered over 2-week periods to each sheep in a Latin square design with two animals replicated. Animals were infused intravenously with a mixture of U-13C-labelled AA for 10 h and integrated blood samples withdrawn from the aorta and vena cava hourly between 5 and 9 h of infusion. Biopsy samples were also taken from skin andm. vastus lateralis. Data from both essential (histidine, isoleucine, leucine, lysine, phenylalanine, threonine) and nonessential (glycine, proline, serine, tyrosine) AA were modelled to give rates of inward and outward transport, protein synthesis and degradation, plus the fraction of total vascular inflow that exchanged with the hindquarter tissues. Rates of inward transport varied more than 10-fold between AA. For all essential AA (plus serine), inward transport increased with food intake (P<0·04). There were corresponding increases in AA efflux (P<0·05) from the tissues for threonine and the branched-chain AA. Protein synthesis rates estimated from the kinetics of these AA also increased with intake (P<0·02). Rates of inward transport greatly exceeded the amount of AA necessary to support protein retention, but were more similar to rates of protein synthesis. Nutritional or other strategies to enhance AA transport into peripheral tissues are unlikely to increase anabolic responses.

scholarly journals Effects of Growth Hormone on Leptin Metabolism and Energy Expenditure in Hemodialysis Patients with Protein-Calorie Malnutrition

2000 ◽  
Vol 11 (11) ◽  
pp. 2106-2113
Author(s):  
GIACOMO GARIBOTTO ◽  
ANTONINA BARRECA ◽  
ANTONELLA SOFIA ◽  
RODOLFO RUSSO ◽  
FULVIO FIORINI ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Protein Synthesis ◽  
Energy Expenditure ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Resting Energy Expenditure ◽  
Hemodialysis Patients ◽  
Gh Treatment ◽  
Peripheral Tissues

Abstract. The relationships among growth hormone (GH), leptin, and resting energy expenditure (REE) are not understood. It has been reported that in malnourished hemodialysis patients, GH increases muscle protein synthesis, a process that requires energy. The present study evaluated the arterial levels and the forearm exchange of leptin, as well as the REE of the same patients during their participation in the same study, in four sequential 6-wk periods: I, baseline; II, GH treatment; III, washout; and IV, GH + intradialytic parenteral nutrition. During periods II and IV, patients received GH (5 mg three times per week). REE rose by 5% in period II, declined during period III, and rose by 7% during period IV. Basal leptin levels were low (2.0 ± 0.19 ng/L). Insulin and leptin levels, as well as leptin release from the forearm, were unchanged during periods I through III but rose (+ 36%; P < 0.05) during period IV. Changes in arterial leptin were directly related to changes in forearm leptin release (P < 0.002), indicating a role of leptin production by peripheral tissues on leptinemia. Changes in leptin release were directly related to insulin (P < 0.001) and, less consistently, to insulin-like growth factor-binding protein-1 levels (P < 0.02). Similarly, variations in leptin levels were directly related to insulin (P < 0.01). Variations in REE were not related to variations in leptin or insulin levels but to changes in muscle protein synthesis (P < 0.025). The data show that in malnourished hemodialysis patients, treatment with GH is not invariably associated with an increase in leptin production. An increase in leptin release by peripheral tissues and leptin levels occurs only in the setting of hyperinsulinemia. The increase in REE that is induced by treatment with GH is not dependent on changes in leptin but is largely accounted for by the energy cost of the stimulation of muscle protein synthesis.

Role of Leucine in Protein Metabolism During Exercise and Recovery

2002 ◽  
Vol 27 (6) ◽  
pp. 646-662 ◽  
Author(s):  
Donald K. Layman
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Branched Chain Amino Acids ◽  
New Findings ◽  
Branched Chain

Exercise produces changes in protein and amino acid metabolism. These changes include degradation of the branched-chain amino acids, production of alanine and glutamine, and changes in protein turnover. One of the amino acid most affected by exercise is the branched-chain amino acid leucine. Recently, there has been an increased understanding of the role of leucine in metabolic regulations and remarkable new findings about the role of leucine in intracellular signaling. Leucine appears to exert a synergistic role with insulin as a regulatory factor in the insulin/phosphatidylinositol-3 kinase (PI3-K) signal cascade. Insulin serves to activate the signal pathway, while leucine is essential to enhance or amplify the signal for protein synthesis at the level of peptide initiation. Studies feeding amino acids or leucine soon after exercise suggest that post-exercise consumption of amino acids stimulates recovery of muscle protein synthesis via translation regulations. This review focuses on the unique roles of leucine in amino acid metabolism in skeletal muscle during and after exercise. Key words: branched-chain amino acids, insulin, protein synthesis, skeletal muscle

Disposal of alpha-ketoisocaproate: roles of liver, gut, and kidneys

1982 ◽  
Vol 243 (2) ◽  
pp. E123-E131 ◽  
Author(s):  
N. N. Abumrad ◽  
K. L. Wise ◽  
P. E. Williams ◽  
N. A. Abumrad ◽  
W. W. Lacy
Keyword(s):  
Intact Animal ◽  
Ketone Bodies ◽  
Hepatic Uptake ◽  
Urea Synthesis ◽  
Renal Veins ◽  
Peripheral Tissues ◽  
Keto Acids ◽  
Portal Systemic Encephalopathy ◽  
Branched Chain ◽  
Keto Analogues

The alpha-keto analogues of the branched-chain amino acids, and particularly that of leucine, alpha-ketoisocaproate (KIC), have been found to reduce urea synthesis and as a result have been proposed for the treatment of uremia and portal systemic encephalopathy. Because little is known about the fate of these keto acids in the intact animal, we examined the disposal of a KIC load in five conscious overnight-fasted dogs with catheters previously implanted in an artery, and in the portal, hepatic, and renal veins. During the absorptive period (54 +/- 9 min; range, 20-75 min), 62 +/- 5% of the administered load (6,358 +/- 662 mumol) of the keto acid was absorbed as KIC and 23 +/- 3% was transaminated across the gut and entered as leucine. The hepatic uptake of KIC was equivalent to 35 +/- 5% (2.316 +/- 419 mumol) of the administered load, and of that, one-third was transaminated to leucine and two-thirds were converted to ketone bodies. The splanchnic output of KIC amounted to 1,732 +/- 256 mumol of 27 +/- 2% of the administered load, half of which was transaminated across the kidneys to leucine. As a result, the amount of KIC reaching the extrahepatic extrarenal tissues as KIC carbon amounted to 15% of the load administered. We conclude that the majority of an intragastrically administered KIC load reaches the (extrarenal) peripheral tissues in the form of leucine or ketone bodies. The study also underscores the importance of the "gut," the kidneys, and the liver in metabolism of the absorbed KIC load.

Protein turnover—what does it mean for animal production?

2003 ◽  
Vol 83 (3) ◽  
pp. 327-340 ◽  
Author(s):  
G. E. Lobley
Keyword(s):  
Protein Synthesis ◽  
Protein Turnover ◽  
Intestinal Tract ◽  
Essential Amino Acids ◽  
Animal Products ◽  
Peripheral Tissues ◽  
Vital Functions ◽  
Gastro Intestinal Tract ◽  
Synthesis And Degradation

The dynamics of protein turnover confer great advantages for homeothermy, plasticity and metabolic function in mammals. The different roles played by the various organs have led to aspects of protein synthesis and degradation that aid the various functions performed. The so-called “non-productive” organs such as the gastro-intestinal tract and liver produce large quantities of export proteins that perform vital functions. Not all these proteins are recovered, however, and thus function can result in lowered net conversion of plant protein to animal products. The splanchnic tissues also oxidize essential amino acids (AA). For example, the gut catabolizes leucine, lysine and methionine, but not threonine and phenylalanine, as part of a complex interaction between AA supply and tissue metabolic activity. Losses by oxidation and endogenous secretions can markedly alter the pattern of absorbed AA. The fractional rates of extraction of total AA inflow to the liver are low and this allows short-term flexibility in controlling supply to peripheral tissues. Recent evidence suggests that the role of the liver in AA catabolism is more a response to non-use by other tissues rather than an immediate regulation of supply to the periphery. Neither arterial supply of AA nor the rate of transport into peripheral tissues limits protein gain, except when supply is very limited. Rather, control is probably exerted via hormone-nutrient interactions. Key words: Protein synthesis, amino acid, gastro-intestinal tract, liver, muscle, mammary gland

scholarly journals Effect of feed intake on ovine hindlimb protein metabolism based on thirteen amino acids and arterio–venous techniques

2001 ◽  
Vol 86 (5) ◽  
pp. 577-585 ◽  
Author(s):  
Simone O. Hoskin ◽  
Isabelle C. Savary ◽  
Grietje Zuur ◽  
Gerald E. Lobley
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Plasma Flow ◽  
Feed Intake ◽  
Vena Cava ◽  
Protein Breakdown ◽  
Peripheral Tissues ◽  
Linear Effect ◽  
Wide Range ◽  
Branched Chain

It has been suggested that protein synthesis in peripheral tissues: (1) responds in a curvilinear manner to increasing feed intake over a wide range of feeding levels; and (2) has a greater sensitivity to intake than protein breakdown. The aim of the present experiment was to test these hypotheses across the ovine hindlimb. Six growing sheep (6–8 months, 30–35 kg), with catheters in the aorta (two), posterior vena cava and jugular vein, received each of four intakes of dried grass pellets (0·5, 1·0, 1·5 and 2·5×maintenance energy; M) for a minimum of 7 d. A U-13C-labelled algal hydrolysate was infused intravenously for 10 h and from 3–9 hpara-aminohippuric acid was infused to measure plasma flow. Arterial and venous plasma were obtained over the last 4 h and the concentrations and enrichments of thirteen13C-labelled amino acids (AA) were determined by GC–MS. As intake increased, a positive linear response was found for plasma flow, arterial concentrations of the aromatic and branched-chain AA, total flow of all AA into the hindquarters and net mass balance across the hindquarters (except glycine and alanine). Based on two separate statistical analyses, the data for protein synthesis showed a significant linear effect with intake (except for phenylalanine, glycine and alanine). No significant curvilinear effect was found, which tends not to support hypothesis 1. Nonetheless, protein synthesis was not significantly different between 0·5, 1·0 and 1·5×M and thus the 2·5×M intake level was largely responsible for the linear relationship found. There was no significant response in protein breakdown to intake, which supports hypothesis 2.

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