title: Nitrogen in dietary glutamate is utilized exclusively for the synthesis of amino acids in the rat intestine.
abstract: Although previous studies have shown that virtually the entire carbon skeleton of dietary glutamate (glutamate-C) is metabolized in the gut for energy production and amino acid synthesis, little is known regarding the fate of dietary glutamate nitrogen (glutamate-N). In this study, we hypothesized that dietary glutamate-N is an effective nitrogen source for amino acid synthesis and investigated the fate of dietary glutamate-N using [(15)N]glutamate. Fischer male rats were given hourly meals containing [U-(13)C]- or [(15)N]glutamate. The concentration and isotopic enrichment of several amino acids were measured after 0-9 h of feeding, and the net release of each amino acid into the portal vein was calculated. Most of the dietary glutamate-C was metabolized into CO(2), lactate, or alanine (56, 13, and 12% of the dietary input, respectively) in the portal drained viscera (PDV). Most of the glutamate-N was utilized for the synthesis of other amino acids such as alanine and citrulline (75 and 3% of dietary input, respectively) in the PDV, and only minor amounts were released into the portal vein in the form of ammonia and glutamate (2 and 3% of the dietary input, respectively). Substantial incorporation of (15)N into systemic amino acids such as alanine, glutamine, and proline, amino acids of the urea cycle, and branched-chain amino acids was also evident. These results provide quantitative evidence that dietary glutamate-N distributes extensively to amino acids synthesized in the PDV and, consequently, to circulating amino acids.
authors.affiliation: Institute for Innovation, Ajinomoto Co. Inc., Kawasaki, Japan. hidehiro_nakamura@ajinomoto.com
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Nakamura
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Kawamata
authors.forename: Tomomi
authors.initials: T
authors.lastname: Kuwahara
authors.forename: Kunio
authors.initials: K
authors.lastname: Torii
authors.forename: Ryosei
authors.initials: R
authors.lastname: Sakai
mesh_terms: D000596:Amino Acids / Q000032:analysis / Q000096:biosynthesis*; D000818:Animals; D001158:Arteries / Q000737:chemistry / Q000378:metabolism; D002244:Carbon / Q000737:chemistry / Q000493:pharmacokinetics; D004032:Diet; D004435:Eating / Q000502:physiology; D018698:Glutamic Acid / Q000737:chemistry* / Q000493:pharmacokinetics*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000737:chemistry; D008297:Male; D009584:Nitrogen / Q000493:pharmacokinetics*; D009994:Osmolar Concentration; D011169:Portal Vein / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
chemical_list: D000596:Amino Acids; D018698:Glutamic Acid; D002244:Carbon; D009584:Nitrogen