title: True exogenous and endogenous nitrogen fractions in the human jejunum after ingestion of small amounts of 15N-labeled casein.
abstract: The purpose of this work was to determine exogenous and endogenous contributions to the overall nitrogen flux in the upper jejunum in humans. After the ingestion of water or 8 g of [15N]casein, the behavior of gastro-jejunal nitrogen and electrolyte (Na+, K+, Cl-) movements were studied in seven volunteers using the "slow marker" perfusion technique. The jejunal flow-rate of the chyme peaked during 0-20 min and 20-40 min periods following water and casein ingestion, respectively. Osmolarity, Cl- and Na+ concentrations decreased significantly (P < 0.05) during the first 20 min following meal ingestion and returned to the basal levels in the 20-60 min period. The gastric half-emptying times (min) of the liquid phase differed significantly (P < 0.05) for water (7.9 +/- 0.4) and casein (21.4 +/- 9.1). The basal flow rate of endogenous nitrogen was 9 +/- 3.3 mmol/h in the jejunum. After casein ingestion, the total nitrogen content reached maximum values in the 20-40 min period and then progressively returned to the initial level. The gastro-jejunal casein absorption was 58% and the remaining amount of casein in the jejunum was degraded more than 80% to alcohol-soluble compounds. After the ingestion of a low amount of casein no significant increase in the endogenous nitrogen fraction was observed. The 15N-dilution technique is an appropriate method in humans for the direct measurement of endogenous and exogenous contributions to the intestinal nitrogen fraction.
authors.affiliation: Unité INRA de Nutrition Humaine et de Physiologie Intestinale, Faculté des Sciences Pharmaceutiques et Biologiques, Paris, France.
authors.forename: S
authors.initials: S
authors.lastname: Mahé
authors.forename: N
authors.initials: N
authors.lastname: Roos
authors.forename: R
authors.initials: R
authors.lastname: Benamouzig
authors.forename: H
authors.initials: H
authors.lastname: Sick
authors.forename: A
authors.initials: A
authors.lastname: Baglieri
authors.forename: J F
authors.initials: JF
authors.lastname: Huneau
authors.forename: D
authors.initials: D
authors.lastname: Tomé
mesh_terms: D000328:Adult; D002364:Caseins / Q000008:administration & dosage / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D005260:Female; D005746:Gastric Emptying; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption; D007583:Jejunum / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
chemical_list: D002364:Caseins; D002712:Chlorides; D009587:Nitrogen Isotopes; D012964:Sodium; D009584:Nitrogen; D011188:Potassium