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Transfers of N metabolites across the ovine liver in response to short-term infusions of an amino acid mixture into the mesenteric vein

Published online by Cambridge University Press:  09 March 2007

G. E. Lobley ,
D. M. Bremner ,
R. Nieto ,
T. Obitsu ,
A. Hotston Moore  and
D. S. Brown
G. E. Lobley*
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, UK
D. M. Bremner
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, UK
R. Nieto
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, UK
T. Obitsu
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, UK
A. Hotston Moore
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, UK
D. S. Brown
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, UK
*
*Corresponding author: Dr G. E. Lobley, fax +44 (0) 1224 716629, email gel@rri.sari.ac.uk
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Abstract

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The effect of acute (4.5 h) infusions into the mesenteric vein of an amino acid (AA) mixture, which simulated the composition of rumen microbial protein, on net transfers of NH3, urea and total AA across the portal-drained viscera (PDV) and liver in the ovine has been examined. Four wether sheep were surgically prepared with vascular catheters across the PDV and liver (Lobley et al. 1995) and were offered a basal diet of 1000 g grass pellets/d (approximately 1.4 × energy maintenance). Each animal was infused at weekly intervals with one of four dilutions of the AA mixture. These dilutions provided 0.44, 0.88, 1.32 and 1.84mmol AA-N/min infused, the lowest of which approximately doubled the net absorption of AA-N from the basal diet. Animals were treated with heparin to allow continuous collection of blood by peristaltic pump for 2 h preceding, and between 0.5–2.5 and 2.5–4.5 h after, the start of the AA infusions. Blood flow in the hepatic artery increased (100 v. 208 g/min; P = 0.002) in response to AA infusion, while hepatic portal venous flow decreased (2090 v. 1854 g/min; P = 0.006). The AA infusion also stimulated O2 uptake by the PDV (P < 0.001) and liver (P = 0.016). Absorption across the PDV and hepatic removal of NH3 were unchanged between basal and amino acid infusion conditions. Urea-N removal across the PDV was unaltered, but hepatic production increased (P < 0.001) with level of AA infusion. During infusions, net appearance of AA across the PDV was below the theoretical level. This may have been due to inhibition of AA uptake from the small intestine, and/or increased removal by the digestive tract of AA from the systemic circulation associated with greater arterial concentrations. Hepatic extraction of AA increased with level of infusion, both for total AA and those included in the infusate. Total hepatic urea-N production tended towards a maximum (estimated as 2 μmol N/g liver wet weight per min). The AA removed by the liver and not used for ureagenesis remained similar (170 μmol AA-N/min) between basal and AA infusions. This was presumed available for anabolic purposes (mainly synthesis of export proteins). The proportion of net AA-N appearance (absorption plus infused) across the PDV removed by the liver declined from 0.71 to 0.53 between basal and AA infusions. In contrast to findings from cattle (Wray-Cahen et al. 1997), increased AA infusion did not alter the net removal of glutamine across the liver. This may reflect differences between the studies in NH3: AA-N absorbed. Further differences between the cattle study and the current findings may relate to the different physiological state (pregnancy v. growth), which may alter the partition of AA between anabolic and catabolic fates.

Keywords

Portal-drained visceraAmino acidsN metabolitesPlasma protein synthesis
Type
Research Article
Information
British Journal of Nutrition , Volume 80 , Issue 4 , October 1998 , pp. 371 - 379
Copyright
Copyright © The Nutrition Society 1998

References

Calder, AG & Smith, A (1988) Stable isotope ratio analysis of leucine and ketoisocaproic acid in blood plasma by gas chromatography/mass spectrometry. Rapid Communications in Mass Spectrometry 2, 14–16.CrossRefGoogle ScholarPubMed
Connell, A, Calder, AG, Anderson, SE & Lobley, GE (1997) Hepatic protein synthesis in the sheep: effect of intake as monitored by use of stable-isotope-labelled glycine, leucine and phenylala-nine. British Journal of Nutrition 77, 255–271.CrossRefGoogle Scholar
Goetsch, AL, Patil, AR, Galloway, DL, Kouakou, B, Wang, ZS, Park, KK & Rossi, JE (1997) Net flux of nutrients across splanchnic tissues in wethers consuming grasses of different sources and physical forms ad libitum. British Journal of Nutrition 77, 769–781.CrossRefGoogle ScholarPubMed
Hanigan, MD, Dijkstra, J, Gerrits, WJJ & France, J (1997) Modelling post-absorptive protein and amino acid metabolism in the ruminant. Proceedings of the Nutrition Society 56, 631–643.CrossRefGoogle ScholarPubMed
Häussinger, D, Lamers, WH & Moorman, AFM (1992) Hepatocyte heterogeneity in the metabolism of amino acids and ammonia. Enzyme 46, 72–93.CrossRefGoogle Scholar
Kuhara, T, Ikeda, S, Ohneda, A & Sasaki, Y (1991) Effects of intravenous infusion of 17 amino acids on the secretion of GH, glucagon and insulin in sheep. American Journal of Physiology 260, E21–E26.Google ScholarPubMed
Lindsay, DB (1993) Metabolism of the portal-drained viscera. In Quantitative Aspects of Ruminant Digestion and Metabolism, pp. 267–289 [Forbes, JM and France, J, editors]. Wallingford, Oxon: CAB International.Google Scholar
Lobley, GE, Connell, A, Lomax, MA, Brown, DS, Milne, E, Calder, AG & Farningham, DAH (1995) Hepatic detoxification of ammonia in the ovine liver; possible consequences for amino acid catabolism. British Journal of Nutrition 73, 667–685.CrossRefGoogle ScholarPubMed
Lobley, GE, Connell, A, Milne, E, Newman, AM & Ewing, AT (1994) Protein synthesis in splanchnic tissues of sheep offered two levels of intake. British Journal of Nutrition 71, 3–12.CrossRefGoogle ScholarPubMed
Lobley, GE & Milano, GD (1997) Regulation of hepatic nitrogen metabolism in ruminants. Proceedings of the Nutrition Society 56, 547–563.CrossRefGoogle ScholarPubMed
Lobley, GE, Weijs, PJM, Connell, A, Calder, AG, Brown, DS & Milne, E (1996) The fate of absorbed and exogenous ammonia as influenced by forage or forage–concentrate diets in growing sheep. British Journal of Nutrition 76, 231–248.CrossRefGoogle ScholarPubMed
MacRae, JC, Bruce, LA, Brown, DS & Calder, AG (1997) Amino acid use by the gastrointestinal tract of sheep given lucerne forage. American Journal of Physiology 273, G1158–G1165.Google ScholarPubMed
Meijer, AJ, Lof, C, Ramos, IC & Verhoeven, AJ (1985) Control of ureagenesis. European Journal of Biochemistry 148, 189–196.CrossRefGoogle Scholar
Milano, GD (1997) Liver nitrogen transactions in sheep (Ovis aries). PhD Thesis, University of Aberdeen.Google Scholar
Orzechowski, A, Motyl, T, Pierzynowski, G & Barej, W (1987) Hepatic capacity for ammonia removal in sheep. Journal of Veterinary Medicine 34A, 108–112.CrossRefGoogle Scholar
Reynolds, CK, Tyrrell, HF & Reynolds, PJ (1991) Effects of diet forage-to-concentrate ratio and intake on energy metabolism in growing beef heifers: net nutrient metabolism by visceral tissues. Journal of Nutrition 121, 1004–1015.CrossRefGoogle ScholarPubMed
Sarraseca, A, Milne, E, Metcalf, MJ & Lobley, GE (1998) Urea recycling in sheep: effect of intake. British Journal of Nutrition 79, 79–88.CrossRefGoogle ScholarPubMed
Storm, E & Ørskov, ER (1983) The nutritive value of rumen micro-organisms in ruminants. 1. Large-scale isolation and chemical composition of rumen micro-organisms. British Journal of Nutrition 50, 463–470.CrossRefGoogle ScholarPubMed
Summerskill, WHJ & Wolpert, E (1970) Ammonia metabolism in the gut. American Journal of Clinical Nutrition 23, 633–639.CrossRefGoogle ScholarPubMed
Symonds, H, Denise, W, Mather, L & Collins, KA (1981) The maximum capacity of the bovine liver to metabolize ammonia. Proceedings of the Nutrition Society 40, 63A.Google Scholar
Wray-Cahen, D, Roberts, S, Metcalf, JA, Backwell, FRC, Bequette, BJ, Brown, DS, Sutton, JD & Lobley, GE (1997) Hepatic response to increased exogenous supply of plasma amino acids by infusion into the mesenteric vein of Holstein-Friesian cows in late gestation. British Journal of Nutrition 78, 913–930.CrossRefGoogle ScholarPubMed