Effect of acute and chronic vanadate administration on sugar transport in rat jejunum.
Vanadate is known to have an insulin-like action which stimulates sugar transport in some systems like adipocytes and muscle cells, but in other systems it inhibits sugar transport by decreasing the activity of (Na+ +K+)-ATPase. To evaluate whether these two opposing actions may influence sugar transport across the intestine, we studied the effects of acute and chronic vanadate administration on the uptake of glucose, galactose, and 3-O-methylglucose in isolated rat intestinal cells. The sugar uptake measurements were also coupled by determinations of rubidium-86 uptake as a measure of the activity of the Na-K pump. Both acute and chronic vanadate administration reduced rubidium uptake by the cells but the reduction did not uniformly influence the uptake of the three sugars in question which were stimulated by the acute exposure of the cells to vanadate. Glucose uptake was also stimulated by chronic vanadate administration, but the uptakes of galactose and 3-O-methylglucose were respectively unaffected or inhibited by chronic vanadate. The findings suggest that the effect of vanadate on sugar transport is dependent on the net difference between two actions of vanadate: (i) stimulation of a receptor site (possibly an insulin receptor site) in the intestinal cell membrane and (ii) inhibition of the Na-K pump. During acute vanadate exposure, the stimulation of the receptor site was very likely a dominant feature which overwhelms the inhibition of the pump. Chronic exposure to vanadate led, on the other hand, to only a limited degree of stimulation of the receptor site and the inhibition of the Na-K pump became evident in the uptake measurements of galactose and 3-O-methyl-glucose. Glucose uptake, however, was stimulated by chronic vanadate ingestion due, very likely, to an increase in the metabolism of this sugar which occurred only with prolonged exposure of the rat intestine to vanadate.
Hajjar
J J
JJ
Department of Medicine, Veterans Administration Medical Center, Newington, Connecticut 06111.
Dobish
M P
MP
Tomicic
T K
TK
D019325:3-O-Methylglucose; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005690:Galactose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006019:Glycolysis / Q000187:drug effects; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008757:Methylglucosides / Q000378:metabolism*; D008759:Methylglycosides / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012413:Rubidium / Q000378:metabolism; D014638:Vanadates / Q000008:administration & dosage / Q000494:pharmacology*
D008757:Methylglucosides; D008759:Methylglycosides; D019325:3-O-Methylglucose; D014638:Vanadates; D005947:Glucose; D012413:Rubidium; D005690:Galactose