Effects of diet and osmotic pressure on Na⁺ transport and tissue conductance of sheep isolated rumen epithelium

Abstract

The intention of this study was to determine the effects of mucosal osmotic pressure on transport and barrier functions of the rumen epithelium of sheep, which were fed various diets: hay ad libitum, or 600, 1200 or 1800 g day -1 of a supplemented diet plus hay ad libitum. The experiments were conducted by using the conventional Ussing chamber technique. Mucosal osmolarity was adjusted to 300 (control), 375 or 450 mosmol l -1 . Feeding of a supplemented diet led to a significant increase of mucosal to serosal Na + transport and net Na + transport, probably because of an increase of apical Na + -H + exchange activity. An increase in mucosal osmotic pressure: (a) reduced net Na + transport in all feeding groups, the remaining net Na + transport being higher in tissues of sheep fed a supplemented diet; (b) increased transepithelial tissue conductance, this rise being smallest with a high intake of the supplemented diet; and (c) enhanced the serosal to mucosal Na + transport in tissues of hay-fed sheep and sheep fed with 600 g day -1 of the supplemented diet, while higher intakes of the supplemented diet (1200 and 1800 g) did not produce any effect. All these changes indicate a diet-dependent adaptation to luminal hypertonicity.

A high-grain diet causes massive disruption of ruminal epithelial tight junctions in goats

“…The similar morphological changes as in our current study were presented in the acid-treated RE in vitro study, and these morphological alterations were accompanied by an increase in tissue conductance and J ms Na, which indicates passive permeability (9). Evidence also exists that the high-concentrate diet feeding (grain as in the present study) increased the ruminal epithelial passive permeability in Ussing chamber experiments (19,20). These earlier findings are in a good agreement with the assumption of increased passive permeability during HG diet feeding in the present study.…”

“…Rapidly fermentable nonstructural carbohydrates increase the rate of fermentation acid production in the rumen, and the accumulation of the acids leads to a decrease in ruminal pH, hyperosmolarity, and an increase in ruminal toxin concentration (2,29). Previous studies have investigated the specific effect of low pH (9,26), hyperosmolarity (20,34), or an exposure to toxins (7) on ruminal epithelial barrier function in vitro. It should be acknowledged that any one or the combination of these factors may affect epithelial barrier function.…”

Effects of duration of moderate increases in grain feeding on endotoxins in the digestive tract and acute phase proteins in peripheral blood of yearling calves

“…Therefore, this effect may not be observed in a mild episode of SARA for a few hours or a few days (Khafipour et al, 2009b;Penner et al, 2010;Li et al, 2012b). In contrast, evidence suggests that prolonged increases in grain feeding may cause epithelia of the digestive tract of cattle to adapt, enhancing epithelial barrier function (Lodemann and Martens, 2006). Although the increase in LPS in the rumen Gozho et al, 2007) and in the hindgut (Li et al, 2012b) due to high-grain diets has been confirmed repeatedly, there is little information about such increases in other sites of the digestive tract, such as the jejunum and ileum.…”

Rumen microorganisms and fermentation

“…Immediately after feed intake, the osmotic pressure increases from 350 to 400 mOsm and then decreases gradually over a period of 8 to 10 hours. The osmotic pressure increases with the presence of VFAs produced by fermentation processes and has a direct relationship with the pH in diets rich in carbohydrates (Lodemann and Martens 2006).…”

“…This may be due to the imbalance of intracellular hydrogen ions (Russell and Wilson 1996). The osmotic pressure in the rumen depends on the presence of ions and molecules, which generate a gas tension (Lodemann and Martens 2006). The ruminal fluid osmolality is approximately 250 mOsm/kg.…”