title: Phenylalanine flux in adult men: estimates with different tracers and route of administration.
abstract: The kinetics of three different tracers of phenylalanine were studied when continuously infused together either by an intravenous (IV) or intragastric (IG) route in six young healthy men during a fasting state. During IV infusion, mean flux values were 39.2 +/- 1.8, 40 +/- 3, 41.8 +/- 3.6 mumol.kg-1.h-1 for L-[ring-2H5], [15N], and L-[1-13C]phenylalanine, respectively (differences not significant). Fluxes were higher (P less than .001) during IG than IV infusion, indicating a disappearance of tracer during the first pass through the splanchnic area. Also, higher fluxes were found for [ring-2H5]phenylalanine (74 +/- 6.23 mumol.kg-1.h-1) compared with [15N] and L-[1-13C]phenylalanine (54.24 +/- 4.7 and 61.15 +/- 5.3 mumol.kg-1.h-1) during IG infusion. Proton exchange might explain this difference, possibly limiting in vivo use of this label when the tracer is to be administered by the IG route.
authors.affiliation: Laboratory of Human Nutrition, Massachusetts Institute of Technology, Cambridge 02139.
authors.forename: M
authors.initials: M
authors.lastname: Krempf
authors.forename: R A
authors.initials: RA
authors.lastname: Hoerr
authors.forename: L
authors.initials: L
authors.lastname: Marks
authors.forename: V R
authors.initials: VR
authors.lastname: Young
mesh_terms: D000328:Adult; D002247:Carbon Isotopes; D003903:Deuterium; D006801:Humans; D007262:Infusions, Intravenous; D007441:Intubation, Gastrointestinal; D008297:Male; D009587:Nitrogen Isotopes; D010649:Phenylalanine / Q000008:administration & dosage / Q000097:blood*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D010649:Phenylalanine; D003903:Deuterium