Effect of total parenteral nutrition on amino acid and glucose transport by the human small intestine.
OBJECTIVE
The effect of total parenteral nutrition (TPN) on small intestinal amino acid transport activity was studied in humans.


BACKGROUND
Studies in humans receiving TPN indicate that a decrease in the activities of the dissacharidase enzymes occurs, but morphologic changes are minimal with only a slight decrease in villous height.


METHODS
Surgical patients were randomized to receive TPN (n = 6) or a regular oral diet (controls, n = 7) for 1 week before abdominal surgery. Ileum (5 controls, 5 TPN) or jejunum (2 controls, 1 TPN) were obtained intraoperatively and brush-border membrane vesicles (BBMV) were prepared by magnesium aggregation/differential centrifugation. Transport of L-MeAlB (a selective system A substrate), L-glutamine, L-alanine, L-arginine, L-leucine, and D-glucose was assayed by a rapid mixing/filtration technique in the presence and absence of sodium.


RESULTS
Vesicles demonstrated approximately 18-fold enrichments of enzyme markers, classic overshoots, transport into an osmotically active space, and similar 1-hour equilibrium values. TPN resulted in a 26-44% decrease in the carrier-mediated transport velocity of all substrates except glutamine across ileal BBMVs. In the one patient receiving TPN from whom jejunum was obtained, there was also a generalized decrease in nutrient transport, although glutamine was least affected. Kinetic studies of the system A transporter demonstrated that the decrease in uptake was secondary to a reduction in carrier Vmax, consistent with a decrease in the number of functional carriers in the brush-border membrane.


CONCLUSIONS
TPN results in a decrease in brush-border amino acid and glucose transport activity. The observation that glutamine transport is not downregulated by 1 week of bowel rest may further emphasize the important metabolic role that glutamine plays as a gut fuel and in the body's response to catabolic stresses.
Inoue
Y
Y
Department of Surgery, University of Florida College of Medicine, Gainesville.
Espat
N J
NJ
Frohnapple
D J
DJ
Epstein
H
H
Copeland
E M
EM
Souba
W W
WW
D000328:Adult; D000409:Alanine / Q000493:pharmacokinetics; D000596:Amino Acids / Q000493:pharmacokinetics*; D001120:Arginine / Q000493:pharmacokinetics; D001693:Biological Transport, Active; D005947:Glucose / Q000493:pharmacokinetics*; D005973:Glutamine / Q000493:pharmacokinetics; D006801:Humans; D007082:Ileum / Q000378:metabolism* / Q000648:ultrastructure; D007413:Intestinal Mucosa / Q000378:metabolism / Q000648:ultrastructure; D007583:Jejunum / Q000378:metabolism / Q000648:ultrastructure; D007930:Leucine / Q000493:pharmacokinetics; D008871:Microvilli / Q000378:metabolism; D009994:Osmolar Concentration; D010289:Parenteral Nutrition, Total; D010539:Permeability; D012964:Sodium / Q000494:pharmacology; D014617:Vacuoles / Q000378:metabolism; D015091:beta-Alanine / Q000031:analogs & derivatives / Q000493:pharmacokinetics
D000596:Amino Acids; D005973:Glutamine; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; D001120:Arginine; D012964:Sodium; D007930:Leucine; D005947:Glucose; D000409:Alanine