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Journal of animal science2022; 100(4); skac077; doi: 10.1093/jas/skac077

Equine enterocytes actively oxidize l-glutamine, but do not synthesize l-citrulline or l-arginine from l-glutamine or l-proline in vitro.

Abstract: In livestock species, the enterocytes of the small intestine are responsible for the synthesis of citrulline and arginine from glutamine and proline. At present, little is known about de novo synthesis of citrulline and arginine in horses. To test the hypothesis that horses of different age groups can utilize glutamine and proline for the de novo synthesis of citrulline and arginine, jejunal enterocytes from 19 horses of three different age groups: neonates (n = 4; 7.54 ± 2.36 d of age), adults (n = 9; 6.4 ± 0.35 yr), and aged (n = 6; 22.9 ± 1.0 yr) with healthy gastrointestinal tracts were used in the present study. Enterocytes were isolated from the jejunum and incubated at 37 °C for 30 min in oxygenated (95% O2/5% CO2) Krebs bicarbonate buffer (pH 7.4) containing 5 mM D-glucose and 0 mM, 2-mM L-[U-14C]glutamine, or 2 mM L-[U-14C]proline plus 2 mM L-glutamine. Concentrations of arginine, citrulline, and ornithine in cells plus medium were determined using high-performance liquid chromatography. Results indicate that the rate of oxidation of glutamine to CO2 was high in enterocytes from neonatal horses, but low in cells from adult and aged horses. Enterocytes from all age groups of horses did not degrade proline into CO2. Regardless of age, equine enterocytes formed ornithine from glutamine and proline, but failed to convert ornithine into citrulline and arginine. Because arginine is an essential substrate for the synthesis of not only proteins, but also nitrogenous metabolites (e.g., nitric oxide, polyamines, and creatine), our novel findings have important implications for the nutrition, performance, and health of horses. The amino acid arginine (Arg) is a precursor for the synthesis of multiple biological molecules including nitric oxide, polyamines, and creatine that are involved in cell proliferation, cellular remodeling, dilation of blood vessels, and phosphocreatine production for a readily available source of energy. Multipurpose capabilities of Arg have increased the interest in its effects in other species and must be evaluated in the horse. Levels of Arg are deficient in the milk of mammals such as humans, cows, sheep, and pigs, but their neonates are capable of synthesizing citrulline and Arg from glutamine and proline in the small intestine. High concentrations of Arg in milk have been observed in the horse, warranting investigation in case that the foal cannot synthesize Arg to support growth and thus rely on milk as the sole source of Arg. To date, no research has determined the endogenous production of Arg in horses to support metabolic and physiological processes; therefore, our experiment quantifies the synthesis of Arg in enterocytes of the small intestine of neonatal, adult, and aged horses. Data collected from this study serve as the necessary first step to determine the Arg requirement in the horse that has over-reaching implications to improve the growth, performance, reproductive efficiency, and to enhance longevity of the horse.
© The Author(s) 2022. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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Publication Date: 2022-03-12 PubMed ID: 35275603PubMed Central: PMC9030134DOI: 10.1093/jas/skac077Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research investigates how equine intestine cells, also known as enterocytes, use glutamine, an amino acid, but do not create citrulline or arginine, two other types of amino acids, from glutamine or proline in a laboratory setting.

Study Purpose and Methodology

  • The aim of this study was to examine the assumption that horses of varying ages can use the amino acids glutamine and proline to create the other two amino acids, citrulline and arginine. This is something that other livestock species have shown to do. Yet, it is not well-understood in relation to horses.
  • The authors studied enterocytes sourced from the small intestines of 19 horses of various age groups. These included neonates (newborn horses), adults, and aged horses, all of which were verified to have healthy gastrointestinal tracts.
  • The enterocytes were subjected to an oxygenated environment at 37 °C for half an hour. In this environment, they were exposed to glucose along with either a carbon-labelled version of glutamine or proline (plus glutamine).
  • The researchers then used high-performance liquid chromatography to measure levels of arginine, citrulline, and another amino acid known as ornithine in both the cells and the medium.

Results and Implications

  • The study found that neonatal horses’ enterocytes oxidize glutamine to CO2 at a high rate, whereas enterocytes from adult and aged horses showed lower rates. None of the enterocytes from any horse age group degraded proline into CO2.
  • All age groups’ enterocytes produced ornithine from glutamine and proline, but failed to convert ornithine into the amino acids citrulline and arginine.
  • These findings challenge the general understanding of arginine synthesis in the equine digestive system. Arginine is crucial for the synthesis of proteins and other nitrogenous metabolites such as nitric oxide, polyamines, and creatine, which have extensive roles in cellular activities.
  • The study implies repercussions for the optimal nutrition, performance, and health of horses. Therefore, these results warrant further investigation of arginine in horses, especially due to its significant functions in cell proliferation, cellular remodeling, blood vessel dilation, and phosphocreatine production for immediate energy provision.
  • Future efforts should focus on determining the required levels of arginine in horses to support metabolic and physiological processes. This could provide crucial insights on how to improve growth, performance, reproductive efficiency, and enhance the overall lifespan of horses.

Cite This Article

APA
Martinez RE, Leatherwood JL, Bradbery AN, Silvers BL, Fridley J, Arnold CE, Posey EA, He W, Bazer FW, Wu G. (2022). Equine enterocytes actively oxidize l-glutamine, but do not synthesize l-citrulline or l-arginine from l-glutamine or l-proline in vitro. J Anim Sci, 100(4), skac077. https://doi.org/10.1093/jas/skac077

Publication

Journal of animal science
ISSN: 1525-3163
NlmUniqueID: 8003002
Country: United States
Language: English
Volume: 100
Issue: 4
PII: skac077

Researcher Affiliations

Martinez, Rafael E
  • Department of Animal Science, Texas A&M University and Texas A&M AgriLife Research, College Station, TX 77843, USA.
Leatherwood, Jessica L
  • Department of Animal Science, Texas A&M University and Texas A&M AgriLife Research, College Station, TX 77843, USA.
  • Department of Large Animal Clinical Sciences, Texas A&M University, College Station, TX 77843, USA.
Bradbery, Amanda N
  • Department of Animal and Range Sciences, Montana State University, Bozeman, MT 59717, USA.
Silvers, Brittany L
  • Department of Animal Science, Texas A&M University and Texas A&M AgriLife Research, College Station, TX 77843, USA.
Fridley, Jennifer
  • Department of Large Animal Clinical Sciences, Texas A&M University, College Station, TX 77843, USA.
Arnold, Carolyn E
  • Department of Large Animal Clinical Sciences, Texas A&M University, College Station, TX 77843, USA.
Posey, Erin A
  • Department of Animal Science, Texas A&M University and Texas A&M AgriLife Research, College Station, TX 77843, USA.
He, Wenliang
  • Department of Animal Science, Texas A&M University and Texas A&M AgriLife Research, College Station, TX 77843, USA.
Bazer, Fuller W
  • Department of Animal Science, Texas A&M University and Texas A&M AgriLife Research, College Station, TX 77843, USA.
Wu, Guoyao
  • Department of Animal Science, Texas A&M University and Texas A&M AgriLife Research, College Station, TX 77843, USA.

MeSH Terms

  • Animals
  • Arginine / metabolism
  • Carbon Dioxide / metabolism
  • Citrulline / metabolism
  • Enterocytes
  • Glutamine / metabolism
  • Horses
  • Ornithine / metabolism
  • Proline / metabolism

Grant Funding

  • American Quarter Horse Foundation

References

This article includes 36 references
  1. Assaad HI, Zhou L, Carroll RJ, Wu G. Rapid publication-ready MS-Word tables for one-way ANOVA.. Springerplus 2014;3:474.
    doi: 10.1186/2193-1801-3-474pmc: PMC4153873pubmed: 25191639google scholar: lookup
  2. Aurich J, Köhne M, Wulf M, Nagel C, Beythien E, Gautier C, Zentek J, Aurich C. Effects of dietary L-arginine supplementation to early pregnant mares on conceptus diameter-Preliminary findings.. Reprod Domest Anim 2019 May;54(5):772-778.
    doi: 10.1111/rda.13422pmc: PMC6850369pubmed: 30809848google scholar: lookup
  3. Baldwin RL 6th, McLeod KR. Effects of diet forage:concentrate ratio and metabolizable energy intake on isolated rumen epithelial cell metabolism in vitro.. J Anim Sci 2000 Mar;78(3):771-83.
    doi: 10.2527/2000.783771xpubmed: 10764086google scholar: lookup
  4. Bertolo RF, Burrin DG. Comparative aspects of tissue glutamine and proline metabolism.. J Nutr 2008 Oct;138(10):2032S-2039S.
    doi: 10.1093/jn/138.10.2032Spubmed: 18806120google scholar: lookup
  5. Davis TA, Nguyen HV, Garcia-Bravo R, Fiorotto ML, Jackson EM, Lewis DS, Lee DR, Reeds PJ. Amino acid composition of human milk is not unique.. J Nutr 1994 Jul;124(7):1126-32.
    doi: 10.1093/jn/124.7.1126pubmed: 8027865google scholar: lookup
  6. Davis TA, Nguyen HV, Garcia-Bravo R, Fiorotto ML, Jackson EM, Reeds PJ. Amino acid composition of the milk of some mammalian species changes with stage of lactation.. Br J Nutr 1994 Dec;72(6):845-53.
    doi: 10.1079/bjn19940089pubmed: 7827005google scholar: lookup
  7. Dillon EL, Wu G. Cortisol enhances citrulline synthesis from proline in enterocytes of suckling piglets.. Amino Acids 2021 Dec;53(12):1957-1966.
    doi: 10.1007/s00726-021-03039-ypubmed: 34244859google scholar: lookup
  8. Flynn NE, Wu G. Enhanced metabolism of arginine and glutamine in enterocytes of cortisol-treated pigs.. Am J Physiol 1997 Mar;272(3 Pt 1):G474-80.
    doi: 10.1152/ajpgi.1997pubmed: 9124567google scholar: lookup
  9. Gilbreath KR, Bazer FW, Satterfield MC, Wu G. Amino Acid Nutrition and Reproductive Performance in Ruminants.. Adv Exp Med Biol 2021;1285:43-61.
    doi: 10.1007/978-3-030-54462-1_4pubmed: 33770402google scholar: lookup
  10. Henneke DR, Potter GD, Kreider JL, Yeates BF. Relationship between condition score, physical measurements and body fat percentage in mares.. Equine Vet J 1983 Oct;15(4):371-2.
    doi: 10.1111/j.2042-3306.1983.tb01826.xpubmed: 6641685google scholar: lookup
  11. Hou Y, Hu S, Jia S, Nawaratna G, Che D, Wang F, Bazer FW, Wu G. Whole-body synthesis of L-homoarginine in pigs and rats supplemented with L-arginine.. Amino Acids 2016 Apr;48(4):993-1001.
    doi: 10.1007/s00726-015-2145-4pubmed: 26676627google scholar: lookup
  12. Jobgen W, Meininger CJ, Jobgen SC, Li P, Lee MJ, Smith SB, Spencer TE, Fried SK, Wu G. Dietary L-arginine supplementation reduces white fat gain and enhances skeletal muscle and brown fat masses in diet-induced obese rats.. J Nutr 2009 Feb;139(2):230-7.
    doi: 10.3945/jn.108.096362pmc: PMC3151442pubmed: 19106310google scholar: lookup
  13. Aurich J, Köhne M, Wulf M, Nagel C, Beythien E, Gautier C, Zentek J, Aurich C. Effects of dietary L-arginine supplementation to early pregnant mares on conceptus diameter-Preliminary findings.. Reprod Domest Anim 2019 May;54(5):772-778.
    doi: 10.1016/j.jevs.2018.05.090pmc: PMC6850369pubmed: 30809848google scholar: lookup
  14. Hunka MM, da Silva ERR, Kutschenko M, Nogueira ET, da Costa Cordeiro Manso HEC, Manso Filho HC. Effects of l-arginine supplementation on lactating mares and the development of foals. Acta Sci. Vet. 44:1352.
    doi: 10.22456/1679-9216.80904google scholar: lookup
  15. Lee U, Garcia TP, Carroll RJ, Gilbreath KR, Wu G. Analysis of repeated measures data in nutrition research.. Front Biosci (Landmark Ed) 2019 Jun 1;24(8):1377-1389.
    doi: 10.2741/4785pmc: PMC6556387pubmed: 31136985google scholar: lookup
  16. Mateo RD, Wu G, Bazer FW, Park JC, Shinzato I, Kim SW. Dietary L-arginine supplementation enhances the reproductive performance of gilts.. J Nutr 2007 Mar;137(3):652-6.
    doi: 10.1093/jn/137.3.652pubmed: 17311955google scholar: lookup
  17. NRC. 2007. Nutrient requirements of horses. 6th rev. ed. Natl. Acad. Press, Washington, DC.
  18. Oba M, Baldwin RL 4th, Bequette BJ. Oxidation of glucose, glutamate, and glutamine by isolated ovine enterocytes in vitro is decreased by the presence of other metabolic fuels.. J Anim Sci 2004 Feb;82(2):479-86.
    doi: 10.2527/2004.822479xpubmed: 14974546google scholar: lookup
  19. Rogers QR, Phang JM. Deficiency of pyrroline-5-carboxylate synthase in the intestinal mucosa of the cat.. J Nutr 1985 Jan;115(1):146-50.
    doi: 10.1093/jn/115.1.146pubmed: 3965666google scholar: lookup
  20. Vosatka RJ, Hassoun PM, Harvey-Wilkes KB. Dietary L-arginine prevents fetal growth restriction in rats.. Am J Obstet Gynecol 1998 Feb;178(2):242-6.
    doi: 10.1016/s0002-9378(98)80007-0pubmed: 9500481google scholar: lookup
  21. Wakabayashi, Y. 1995. The glutamate crossway. In: Amino Acid Metabolism and Therapy in Health and Nutritional Disease (Cynober, L.A. ed.) pp. 88–98. CRC Press, New York, NY.
  22. Wu G. Determination of proline by reversed-phase high-performance liquid chromatography with automated pre-column o-phthaldialdehyde derivatization. J. Chromatogr. A 641:168–175.
    doi: 10.1016/s0021-9673(01)90673-9google scholar: lookup
  23. Wu G. Synthesis of citrulline and arginine from proline in enterocytes of postnatal pigs.. Am J Physiol 1997 Jun;272(6 Pt 1):G1382-90.
    doi: 10.1152/ajpgi.1997.272.6.G1382pubmed: 9227473google scholar: lookup
  24. Wu, G. 2022. Amino Acids: Biochemistry and Nutrition, 2nd ed. CRC Press, Boca Raton, FL.
  25. Wu G, Bazer FW, Davis TA, Kim SW, Li P, Marc Rhoads J, Carey Satterfield M, Smith SB, Spencer TE, Yin Y. Arginine metabolism and nutrition in growth, health and disease.. Amino Acids 2009 May;37(1):153-68.
    doi: 10.1007/s00726-008-0210-ypmc: PMC2677116pubmed: 19030957google scholar: lookup
  26. Wu G, Bazer FW, Johnson GA, Hou Y. BOARD-INVITED REVIEW: Arginine nutrition and metabolism in growing, gestating, and lactating swine.. J Anim Sci 2018 Dec 3;96(12):5035-5051.
    doi: 10.1093/jas/sky377pmc: PMC6276552pubmed: 30445424google scholar: lookup
  27. Wu G, Bazer FW, Satterfield MC, Gilbreath KR, Posey EA, Sun Y. L-Arginine Nutrition and Metabolism in Ruminants.. Adv Exp Med Biol 2022;1354:177-206.
    doi: 10.1007/978-3-030-85686-1_10pubmed: 34807443google scholar: lookup
  28. Wu G, Bazer FW, Satterfield MC, Li X, Wang X, Johnson GA, Burghardt RC, Dai Z, Wang J, Wu Z. Impacts of arginine nutrition on embryonic and fetal development in mammals.. Amino Acids 2013 Aug;45(2):241-56.
    doi: 10.1007/s00726-013-1515-zpubmed: 23732998google scholar: lookup
  29. Wu G, Davis PK, Flynn NE, Knabe DA, Davidson JT. Endogenous synthesis of arginine plays an important role in maintaining arginine homeostasis in postweaning growing pigs.. J Nutr 1997 Dec;127(12):2342-9.
    doi: 10.1093/jn/127.12.2342pubmed: 9405584google scholar: lookup
  30. Wu G, Knabe DA. Free and protein-bound amino acids in sow's colostrum and milk.. J Nutr 1994 Mar;124(3):415-24.
    doi: 10.1093/jn/124.3.415pubmed: 8120661google scholar: lookup
  31. Wu G, Knabe DA, Flynn NE. Synthesis of citrulline from glutamine in pig enterocytes.. Biochem J 1994 Apr 1;299 ( Pt 1)(Pt 1):115-21.
    doi: 10.1042/bj2990115pmc: PMC1138029pubmed: 8166628google scholar: lookup
  32. Wu G, Knabe DA, Yan W, Flynn NE. Glutamine and glucose metabolism in enterocytes of the neonatal pig.. Am J Physiol 1995 Feb;268(2 Pt 2):R334-42.
    doi: 10.1152/ajpregu.1995.268.2.R334pubmed: 7864226google scholar: lookup
  33. Wu G, Meininger CJ. Analysis of citrulline, arginine, and methylarginines using high-performance liquid chromatography.. Methods Enzymol 2008;440:177-89.
    doi: 10.1016/S0076-6879(07)00810-5pubmed: 18423217google scholar: lookup
  34. Wu G, Meininger CJ, McNeal CJ, Bazer FW, Rhoads JM. Role of L-Arginine in Nitric Oxide Synthesis and Health in Humans.. Adv Exp Med Biol 2021;1332:167-187.
    doi: 10.1007/978-3-030-74180-8_10pubmed: 34251644google scholar: lookup
  35. Wu G, Morris SM Jr. Arginine metabolism: nitric oxide and beyond.. Biochem J 1998 Nov 15;336 ( Pt 1)(Pt 1):1-17.
    doi: 10.1042/bj3360001pmc: PMC1219836pubmed: 9806879google scholar: lookup
  36. Zhu C, Li X, Bazer FW, Johnson GA, Burghardt RC, Jiang Z, Wu G. Dietary L-arginine supplementation during days 14-25 of gestation enhances aquaporin expression in the placentae and endometria of gestating gilts.. Amino Acids 2021 Aug;53(8):1287-1295.
    doi: 10.1007/s00726-021-03038-zpubmed: 34241695google scholar: lookup

Citations

This article has been cited 3 times.
  1. Martinez RE, Leatherwood JL, Bradbery AN, Paris BL, Hammer CJ, Kelley D, Bazer FW, Wu G. Evaluation of dietary arginine supplementation to increase placental nutrient transporters in aged mares. Transl Anim Sci 2023 Jan;7(1):txad058.
    doi: 10.1093/tas/txad058pubmed: 37593152google scholar: lookup
  2. Ohrt MM, Ing NH. Supplementary L-arginine can enhance reproductive parameters and outcomes in large mammals. Front Vet Sci 2025;12:1740399.
    doi: 10.3389/fvets.2025.1740399pubmed: 41602621google scholar: lookup
  3. Li P, Sun S, Zhang W, Ouyang W, Li X, Yang K. The Effects of L-citrulline Supplementation on the Athletic Performance, Physiological and Biochemical Parameters, Antioxidant Capacity, and Blood Amino Acid and Polyamine Levels in Speed-Racing Yili Horses. Animals (Basel) 2024 Aug 22;14(16).
    doi: 10.3390/ani14162438pubmed: 39199970google scholar: lookup
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