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Diurnal rhythmicity in intestinal SGLT-1 function, V(max), and mRNA expression topography.
A Tavakkolizadeh1, U V Berger, K R Shen
1Department of Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
American Journal of Physiology. Gastrointestinal and Liver Physiology
|February 24, 2001
Summary
Circadian rhythms in intestinal sugar absorption are driven by daily changes in the Na(+)-glucose cotransporter 1 (SGLT-1) maximal velocity (Vmax). This study reveals SGLT-1 activity is anticipatory, not food-driven.
Area of Science:
- Physiology
- Chronobiology
- Gastroenterology
Background:
- Circadian rhythmicity influences intestinal sugar absorption, but the underlying mechanisms are not fully understood.
- The role of the Na(+)-glucose cotransporter 1 (SGLT-1) in this rhythmicity requires elucidation.
Purpose of the Study:
- To investigate whether daily fluctuations in intestinal sugar absorption are mediated by changes in SGLT-1 function.
- To determine if SGLT-1 activity exhibits circadian variation.
Main Methods:
- Measured phloridzin-inhibitable sugar fluxes in rat jejunum mounted in Ussing chambers.
- Quantified 3-O-methylglucose (3-OMG) fluxes and short-circuit current.
- Analyzed SGLT-1 mRNA expression and localization using Northern blotting and in situ hybridization.
Main Results:
- Significant increases in 3-OMG flux and short-circuit current, indicative of SGLT-1 activity, were observed at CT9 compared to CT3.
- Kinetic analysis revealed a higher SGLT-1 maximal velocity (Vmax) at CT9.
- Increased SGLT-1 mRNA expression and labeling intensity along the villus axis were noted at CT9 and CT15.
- Observed changes in SGLT-1 activity were anticipatory, occurring before significant food intake.
Conclusions:
- Diurnicity in intestinal sugar absorption is primarily caused by circadian periodicity in SGLT-1 Vmax.
- SGLT-1 activity exhibits a daily rhythm, suggesting a regulated, anticipatory mechanism for nutrient absorption.