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Selective stimulation of brush border glutamine transport in the tumor-bearing rat.

Abstract
Intestinal extraction of circulating glutamine across the basolateral membrane is diminished in the tumor-bearing rat (TBR). This study was designed to investigate the effects of progressive malignant growth on brush border glutamine transport in order to gain further insight into the adaptive/regulatory changes in intestinal glutamine metabolism that occur in the tumor-bearing rat. Fischer 344 rats (225 +/- 5 g) were implanted with fibrosarcoma cells and were studied at various time points after implantation when the tumors comprised 7%, 20%, and 29% of total body weight. Control and tumor-bearing rats were pair-fed throughout the study. Jejunal brush border membrane vesicles (BBMVs) were prepared by magnesium aggregation/differential centrifugation and transport of radioactively labeled L-glutamine, L-leucine, L-alanine, and D-glucose by BBMVs was measured using a Millipore filtration technique. BBMVs were enriched 15-fold in alkaline phosphatase, indicating brush border vesicle purity. Uptake of all substrates occurred into an osmotically active space, exhibited overshoots, and had similar 1-hr equilibrium values. The rate of glutamine uptake by BBMVs from all tumor-bearing rats was significantly greater than controls, regardless of tumor size. The increase in transport activity was not due to a change in carrier affinity but rather to an increase in maximal transport velocity. In rats with small tumors (7% of body weight), the Vmax was 431 +/- 40 pmole/mg protein/10 sec compared to 259 +/- 30 in control animals (P less than 0.01). In marked contrast, the mean transport of alanine was diminished in BBMVs from TBR (31 +/- 3 pmole/mg protein/10 sec in TBR vs 23 +/- 2 in controls, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
AuthorsR M Salloum, E M Copeland 3rd, K I Bland, W W Souba
JournalThe Journal of surgical research (J Surg Res) Vol. 50 Issue 4 Pg. 391-7 (Apr 1991) ISSN: 0022-4804 [Print] United States
PMID2020190 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S., Research Support, U.S. Gov't, P.H.S.)
Chemical References
  • Carrier Proteins
  • glutamine transport proteins
  • Glutamine
Topics
  • Animals
  • Biological Transport
  • Carrier Proteins (metabolism)
  • Glutamine (metabolism)
  • In Vitro Techniques
  • Intestinal Absorption
  • Kinetics
  • Microvilli (metabolism)
  • Neoplasms, Experimental (metabolism, pathology)
  • Rats
  • Rats, Inbred F344

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