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In vitro studies on active calcium absorption from ovine rumen
B Schröder1, S Vössing, G Breves
1Physiologisches Institut der Tierärztlichen Hochschule Hannover, Germany. bschroed@physiology.tiho-hannover.de
Summary
The rumen actively absorbs calcium (Ca2+) in sheep, primarily through a mechanism involving short-chain fatty acids and a Ca2+/H+ exchange. This process is independent of calcitriol and unaffected by lactation.
Area of Science:
- Animal Physiology
- Gastrointestinal Physiology
- Mineral Metabolism
Background:
- The rumen is a known site for calcium (Ca2+) absorption in ruminants.
- Previous studies indicate significant Ca2+ absorption occurs in the rumen of sheep and goats.
Purpose of the Study:
- To elucidate the active transport mechanisms of Ca2+ across the rumen wall in sheep.
- To investigate the role of short-chain fatty acids (SCFAs) and other factors in regulating Ca2+ absorption.
Main Methods:
- In vitro Ussing-chamber technique to measure unidirectional Ca2+ flux rates across sheep rumen epithelia.
- Application of various substances including SCFAs, verapamil, amiloride, and vanadate.
- Assessment of Ca2+ absorption under conditions of dietary Ca depletion and early lactation.
Main Results:
- Significant active Ca2+ net flux (Jnet) was observed across the rumen wall.
- A mixture of SCFAs (acetate, propionate, butyrate) significantly stimulated Ca2+ Jnet, with butyrate showing the most pronounced effect.
- Amiloride enhanced SCFA-stimulated Ca2+ Jnet, suggesting a Na+/H+ exchange involvement, while verapamil and vanadate had no significant effect.
- Dietary Ca depletion and early lactation did not alter active Ca2+ absorption.
Conclusions:
- The rumen is a primary site for active Ca2+ absorption in sheep.
- A Ca2+/H+ exchange mechanism in the apical membrane of rumen epithelial cells, dependent on SCFA absorption, is proposed.
- Basolateral Ca2+ extrusion likely occurs via Na+/Ca2+ exchange, independent of Ca2+-pump activity and calcitriol control.