Effects of short chain fatty acids and carbon dioxide on magnesium transport across sheep rumen epithelium

Fatty acids added to a suspension of wheat stem rust uredospores (Puccinia graminis var. tritici, race 15B) stimulate respiration. When compared on the basis of equal molar concentration, the utilization of oxygen by spores from wheat grown in the field or in the greenhouse is stimulated by short-chain fatty acids as follows: acetate < propionate < butyrate < valerate. The order for butyrate and valerate is reversed with spores from plants grown under artificial light. Radiotracer experiments indicate that the amount of respired carbon dioxide derived from the carboxyl carbon of the fatty acid added increases markedly with increase in chain length. The addition of exogenous acetate stimulated conversion of spore carbon to carbon dioxide, whereas valerate replaces, in part, spore material as a source of respiratory carbon. Valerate-1-C14 is almost 4 times as effective as acetate-1-C14 for labelling spore material, but the ratio of carbon-14 respired to that incorporated is 2.6 for valerate-1-C14 as compared with 1.5 for acetate-1-C14.

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Short-chain fatty acids and acidic pH upregulate UT-B, GPR41, and GPR4 in rumen epithelial cells of goats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00323.2014 ◽

2015 ◽

Vol 308 (4) ◽

pp. R283-R293 ◽

Cited By ~ 21

Author(s):

Zhongyan Lu ◽

Hongbing Gui ◽

Lei Yao ◽

Lei Yan ◽

Holger Martens ◽

...

Keyword(s):

Fatty Acids ◽

Short Chain Fatty Acids ◽

Short Chain ◽

Acidic Ph ◽

Fermentation Products ◽

Plasma Urea ◽

Protein Levels ◽

Rumen Epithelium ◽

Chain Fatty Acids

Currently, the mechanism(s) responsible for the regulation of urea transporter B (UT-B) expression levels in the epithelium of the rumen remain unclear. We hypothesized that rumen fermentation products affect ruminal UT-B expression. Therefore, the effects of short-chain fatty acids (SCFA), pH, ammonia, and urea on mRNA and protein levels of UT-B were assayed in primary rumen epithelial cell cultures and in rumen epithelium obtained from intact goats. In vitro, SCFA and acidic pH were found to synergetically stimulate both mRNA and protein expression of UT-B, whereas NH4Cl decreased mRNA and protein levels of UT-B at pH 6.8. Treatment with urea increased both levels at pH 7.4. When goats received a diet rich in nitrogen (N) and nonfiber carbohydrates (NFC), their rumen epithelium had higher levels of UT-B, and the rumen contained higher concentrations of SCFA and NH3-N with a lower pH. An increase in plasma urea-N concentration was also observed compared with the plasma of the goats that received a diet low in N and NFC. In a second feeding trial, goats that received a NFC-rich, but isonitrogenous, diet had higher mRNA and protein levels of UT-B, and higher levels of G protein-coupled receptor (GPR) 41 and GPR4, in their rumen epithelium. The ruminal concentrations of SCFA and NH3-N also increased, while a lower pH was detected. In contrast, the serum urea-N concentrations remained unchanged. These data indicate that ruminal SCFA and pH are key factors, via GPR4 and GPR41, in the dietary regulation of UT-B expression, and they have priority over changes in plasma urea.

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