Effects of resalination on intestinal glucose transport in chickens adapted to low Na+ intakes.
In chickens, we have shown that intestinal absorption of glucose via apical SGLT1 and basolateral GLUT2 transport systems is affected by dietary Na+; low-Na+ adapted birds show a dramatic reduction of glucose transporters in both membranes in the rectum, an intermediate response in the ileum and no effects in the jejunum. We have now studied the effect of resalination of low-Na+ adapted chickens on glucose kinetics across SGLT1 (using -methyl-D-glucoside as substrate) and GLUT2 (using D-glucose) and on the specific binding of phlorizin and cytochalasin B, respectively. Twelve-week-old male Leghorn chickens were fed wheat and barley with drinking water containing either 150 mM NaCl (high-Na+ group) or 0. 015 mM (low-Na+ group) for 14 days (serum aldosterone: 242 +/- 6 pg ml-1 in the low-Na+ and 46 +/- 4 pg ml-1 in the high-Na+ group). On day 14, the low-Na+ group was either resalinated with an oral dose of NaCl (9 g (kg body wt)-1) or switched to the high-Na+ condition, for 1 week. Serum aldosterone measured 4 h, 1 day and 7 days after the change in NaCl intake fell to between 30 and 39 pg ml-1. The changes in apical -methyl-D-glucoside and basolateral D-glucose transport observed in the ileum and rectum of low-Na+ adapted animals were completely reversed by resalination within 4 h of NaCl administration to the level of values observed for high-Na+ adapted birds. The good correlation between the -methyl-D-glucoside and D-glucose Vmax and the SGLT1 and GLUT2 density, respectively, supports the view that the increase in apical and basolateral hexose transport found in the ileum and rectum of both groups of resalinated birds is due to an increase in the number of protein transporters. The rapid changes in the number of glucose transporters observed suggest that the target of the regulatory signal(s) involved are the mature enterocytes present in the villi rather than the developing enterocytes in the crypt.
Departament de Fisiologia-Divisio IV, Facultat de Farmàcia, Universitat de Barcelona, E-08028, Barcelona, Spain.
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Garriga
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Moretó
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Planas
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002645:Chickens / Q000378:metabolism*; D003571:Cytochalasin B / Q000378:metabolism; D004039:Diet, Sodium-Restricted; D005947:Glucose / Q000378:metabolism* / Q000493:pharmacokinetics; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D008757:Methylglucosides / Q000493:pharmacokinetics; D008871:Microvilli / Q000378:metabolism; D010695:Phlorhizin / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology*
D008757:Methylglucosides; D003571:Cytochalasin B; D012965:Sodium Chloride; C027020:methylglucoside; D010695:Phlorhizin; D005947:Glucose