Hepatic protein synthesis in the sheep: effect of intake as by use of stable-isotope-labelled glycine, leucine and phenylalanine

Connell, Alexmary; Calder, Andrew A.; Anderson, Susan E.; Lobley, G. E.

doi:10.1079/bjn19970028

Cited by 75 publications

(99 citation statements)

References 46 publications

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“…Furthermore, there seems to be a compartmentalization where proteins for export are synthesized on the rough endoplasmic reticulum while constitutive proteins are synthesized on polysomes within the cell cytosol (Connell et al, 1997). However, insulin was not involved in the stimulation of protein synthesis in the liver of neonatal pigs (Davis et al, 2001).…”

Section: I/g Ratiomentioning

confidence: 92%

Metabolic differences in hepatocytes of obese and lean pigs

González-Valero

Rodríguez-López

Lachica

et al. 2014

Animal

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There are important differences in terms of metabolic activity, energy utilization and capacity of protein and fat deposition when Iberian and modern pigs are compared. Primary culture of hepatocytes was used to evaluate hepatic function and sensitivity to hormones between breeds without the interference of circulating blood factors. Hepatocytes were isolated from pure Iberian (n = 10) and Landrace (n = 8) pigs of similar BW (24.5 ± 12.1 and 32.9 ± 6.1 kg BW, respectively), by collagenase perfusion. Monolayers were established in medium containing fetal bovine serum for 1 day and switched to serum-free medium for the remainder of the culture period. Hepatocytes were maintained in William's E supplemented with β-mercaptoethanol (0.1 mM), glutamine (2 mM), antibiotics (gentamicin, penicillin, streptomycin and amphotericin B), dimethyl sulfoxide (1 µg/ml), dexamethasone (10 −8 M), insulin (0.173 and 17.3 nM) and glucagon (0.287, 2.87 and 28.7 nM) for 24 to 48 h. Gluconeogenesis (GNG), glycogen degradation, triglycerides (TG) content and esterification, β-hydroxybutyrate (BHB) synthesis, IGF-1 synthesis, albumin and urea synthesis were determined. Iberian pigs had greater capacity of GNG than Landrace (24%, P < 0.05), although no difference in glycogen degradation was found (P > 0.10). TG content and esterification tended to be lower in hepatocytes from Iberian compared with Landrace pigs (12% and 31%, respectively; 0.10 < P < 0.05). Furthermore, addition of free fatty acids (CLA or linoleic acid, 0.2 mM) increased TG content (64%, P < 0.001) although no difference between fatty acids was found. When free fatty acids were compared, a trend toward increased esterification (41%, P = 0.078) was found for CLA. Although glucagon stimulated and insulin inhibited BHB synthesis, no difference between breeds was found (P > 0.10). IGF-1 synthesis was diminished in hepatocytes from Iberian compared with Landrace pigs (16%, P < 0.05). On the contrary, rate of albumin synthesis was greater in Iberian compared with Landrace pigs (58%, P < 0.05). Finally, the capacity of urea synthesis was lower in hepatocytes of Iberian compared with Landrace pigs (37%, P < 0.05). When ammonia was added to the media, urea concentration increased (648%, 1108% and 2791% when 0 mM was compared with 2.5, 5 and 10 mM, respectively). Urea synthesis increased on increasing ammonia content (55% and 325% when 0 mM was compared with 5 and 10 mM, respectively; P < 0.0001). In conclusion, the genetic background accounts for important differences in protein and energy metabolism pathways found in primary culture of hepatocytes from lean and obese pigs.Keywords: hepatocytes, metabolism, pig ImplicationsSeveral studies have shown the existence of numerous dissimilarities in metabolic activity between Iberian and modern pig breeds that might be explained by genotypic differences. Primary hepatocyte cultures are a valuable tool to study specific metabolic liver functions, without the interference of changing levels of metabolites and hormones found in vivo. These...

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Section: I/g Ratiomentioning

confidence: 92%

Metabolic differences in hepatocytes of obese and lean pigs

González-Valero

Rodríguez-López

Lachica

et al. 2014

Animal

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“…These are also sensitive to intake [12,48,49] and these values can increase by approximately 40% when intake is raised from 1 to 2 M [49]. Interestingly, these increases in absolute protein synthesis are associated with greater tissue mass, since the fractional rates of protein synthesis for the splanchnic tissues tend to be insensitive to intake [42,50]. What regulates such splanchnic utilisation is not known, nor do we know how much is used to support anabolic compared with catabolic processes.…”

Section: Discussionmentioning

confidence: 99%

“…Wolff et al [18]; Chung et al [24]). For sheep, although serine is converted to glycine [41], the converse does not occur ( [42] and unpublished results). This will lead to higher PrF for serine compared with glycine.…”

Section: Discussionmentioning

confidence: 99%

Effect of intake on whole body plasma amino acid kinetics in sheep

Savary-Auzeloux¹,

Hoskin

Lobley³

2003

Reprod. Nutr. Dev.

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-While both the quantity and quality of food ingested are potent regulators of whole body protein metabolism in ruminants, little data are available on responses across a wide range of intakes. The current study examined the responses in whole body protein flux (PrF) to such intake changes and compared these with the responses across the hind-quarters (in a companion study). Six growing sheep (6-8 months, 30-35 kg) received each of four intakes of dried grass pellets (0.5, 1.0, 1.5 and 2.5 times maintenance energy; M) for a minimum of 7 days. At each intake, a mixture of U-13 C amino-acids (AA) was infused intravenously for 10 h. Arterial plasma and blood were obtained over the last 4 h of infusion and the concentrations and the enrichments of thirteen 13 C labelled AA were determined. The absolute values for plasma Irreversible Loss Rate (ILR) but also converted PrF varied between the AA. PrF values were lower for histidine, methionine, aspartate, glycine and proline (range 68 to 174 g·d -1 at 1.5 M) than for isoleucine, leucine, valine and glutamate (range 275 to 400 g·d -1 at 1.5 M). These discrepancies may be explained by (1) the differential AA removal by the splanchnic tissues, (2) the de novo synthesis of the non-essential AA, (3) the transfer of AA from the erythrocytes or plasma to the tissues. The first two assumptions require further investigation whereas recent work has shown a minor role for AA transfers between erythrocytes and tissues. For most AA, ILR and PrF responded linearly to intake but curvilinear responses were observed for phenylalanine, lysine, leucine, isoleucine and tyrosine. These differences were not due to hind-quarter metabolism and may involve the digestive tract and liver.intake / whole body / kinetics / ovine / amino acid Reprod. Nutr. Dev. 43 (2003) 117-129 117

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“…However, the net hepatic uptake of NEAA was not different between C and LE, whereas it tended to decrease for EAA (0.80 of C). This alteration of net uptake and/or the extraction ratio observed may be explained by the various fates of AA within the liver, not only catabolism and ureagenesis but also protein synthesis (export and endogenous; Connell et al, 1997), protein breakdown (Attaix et al, 2005), gluconeogenesis (Reynolds, 1992) and synthesis of specific substances such as glutathione and hippurate.…”

Section: Discussionmentioning

confidence: 99%

Adaptations of hepatic amino acid uptake and net utilisation contributes to nitrogen economy or waste in lambs fed nitrogen- or energy-deficient diets

Kraft

Ortigues-Marty

Durand

et al. 2011

Animal

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We investigated the effect of relative changes in dietary nitrogen (N) and energy supply and the subsequent variations in net portal appearance (NPA) of nitrogenous and energy nutrients on the net amino acid (AA) uptake by the liver and net N supply to the peripheral tissues. Six lambs were catheterised across the splanchnic tissues and received, in a replicated Latin square, one of three dietary treatments. The diets were formulated to either match the requirements of N and energy (C), or supply only 0.8 of the N requirement (LN) or 0.8 of the energy requirement (LE). Net fluxes of AA and urea-N were measured across the portal-drained viscera, and estimation of arterial hepatic flow allowed the estimation of hepatic fluxes. Catheters were implanted into the portal and hepatic veins as well as in the abdominal aorta for the measurement of AA fluxes. Animals fed the LN diet showed more efficient N retention (0.59 of digested N) than did the C and LE diet (0.50 and 0.33, respectively;P< 0.001). The NPA of total AA-N for the LN diet was only 0.60 of the value measured for the control (C) diet (P< 0.01). Despite this, the total estimated AA-N net splanchnic fluxes were not significantly different across the three diets (3.3, 1.9 and 2.6 g total AA-N/day for C, LN and LE, respectively,P= 0.52). Thus, different metabolic regulations must have taken place across the liver between the three experimental diets. A combination of decreased net uptake of total AA-N by the liver of animals in the LN diet (0.61 of the C diet;P= 0.002) and reduced urinary urea-N production (0.52 of the C diet;P= 0.001) spared AA from catabolism in the LN diet relative to the other two diets. For the LE diet, the urinary urea-N output was 1.3 times the value of the C diet (P= 0.01). This may relate to an increased catabolism of AA by the muscle and/or, to a lesser extent, to an increased utilisation of AA for gluconeogenesis in the liver. These effects may explain the reduced whole body protein retention observed with the LE diet.

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Hepatic protein synthesis in the sheep: effect of intake as by use of stable-isotope-labelled glycine, leucine and phenylalanine

Cited by 75 publications

References 46 publications

Metabolic differences in hepatocytes of obese and lean pigs

Metabolic differences in hepatocytes of obese and lean pigs

Effect of intake on whole body plasma amino acid kinetics in sheep

Adaptations of hepatic amino acid uptake and net utilisation contributes to nitrogen economy or waste in lambs fed nitrogen- or energy-deficient diets

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