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Do forestomach epithelia exhibit a Mg2+/2H(+)-exchanger?
1Department of Physiology, School of Veterinary Medicine, Hannover, Germany. leomarek@physiology.tiho-hannover.de
Magnesium Research
|July 29, 1999
Summary
Dietary carbohydrates boost magnesium absorption in ruminants by altering rumen fluid. This pre-intestinal effect, linked to short-chain fatty acids and CO2, may involve proton exchange in the rumen epithelium.
Area of Science:
- Ruminant nutrition
- Gastrointestinal physiology
- Mineral absorption
Background:
- The forestomachs are the primary sites of magnesium (Mg) absorption in ruminants.
- Readily fermentable carbohydrates improve Mg availability in vivo.
- Carbohydrate addition influences rumen fluid parameters like SCFA, pH, and CO2.
Purpose of the Study:
- To investigate the pre-intestinal mechanisms by which carbohydrates enhance Mg absorption in ruminants.
- To explore the roles of short-chain fatty acids (SCFA) and bicarbonate/carbon dioxide (HCO3-/CO2) in stimulating Mg absorption.
- To evaluate the potential involvement of Mg/H exchange in the rumen epithelium.
Main Methods:
- In vivo studies using isolated reticulorumen to measure Mg efflux.
- In vitro studies measuring 28Mg flux across rumen epithelium.
- Analysis of rumen fluid composition and its correlation with Mg absorption.
Main Results:
- SCFA and HCO3-/CO2 significantly increase Mg efflux and flux across the rumen epithelium.
- The stimulatory effect of SCFA is dependent on their absorption and metabolism.
- HCO3-/CO2 effects are mediated by carbonic anhydrase, suggesting proton involvement.
Conclusions:
- Carbohydrate-enhanced Mg absorption in ruminants is a pre-intestinal process.
- Apical Mg/H exchange is a plausible mechanism explaining observed Mg absorption stimulation.
- Further research is needed to confirm the direct link between Mg2+ uptake and proton efflux.