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  • Title: Absorption of short-chain fatty acids across ruminal epithelium of sheep.
    Author: Kramer T, Michelberger T, Gürtler H, Gäbel G.
    Journal: J Comp Physiol B; 1996; 166(4):262-9. PubMed ID: 8810066.
    Abstract:
    Investigations on the absorption of shortchain fatty acids across ruminal epithelium of sheep were performed both in vitro (Ussing chamber technique, using propionic acid representatively for short-chain fatty acids) and in vivo (washed, isolated reticulorumen). A pH-induced, nearly tenfold increase in the concentration of undissociated propionate led to an only twofold increase in mucosal-to-serosal flux of propionate (in vitro). Neither amiloride (1 mmol.l-1, in vitro) nor theophylline (10 mmol.l-1, in vivo), inhibitors of the ruminal Na+/H+ exchanger, exerted any significant influence on propionate fluxes or short-chain fatty acids absorption, respectively. Total replacement of luminal Na+ (by choline) did not alter short-chain fatty acids absorption (in vivo). Mucosal 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (0.1 mmol.l-1) or mucosal nitrate (40 mmol.l-1) markedly reduced propionate net flux (in vitro). Increasing mucosal Cl- concentration brought about a significant drop in mucosal-to-serosal flux of propionate (in vitro) and in short-chain fatty acids net absorption (in vivo), respectively. The results obtained suggest that short-chain fatty acids are absorbed both as anions and as undissociated acids across ruminal epithelium of sheep. It is concluded that short-chain fatty acids anions either compete with Cl- for binding sites at a common anion-exchange mechanism or that they are absorbed by an short-chain fatty acids anion/ HCO3- exchanger indirectly coupled to a Cl-/HCO3- exchanger via intracellular bicarbonate.
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