Effect of protein supplementation on expression and distribution of urea transporter-B in lambs fed low-quality forage1

Ludden, P. A.; Stohrer, R. M.; Austin, Kathy J.; Atkinson, Rowland; Belden, E. L.; Harlow, Henry J.

doi:10.2527/jas.2008-1399

Cited by 33 publications

(31 citation statements)

References 32 publications

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“…Previous studies have shown that UT-B protein is present all along the gastrointestinal tract of both cows (Dix et al 2013) and sheep (Ludden et al 2009), in contrast to observations in rats (Collins et al 2011). In agreement with predictions based on the known regulators of urea transport, the observed ruminant UT-B abundance pattern appeared to be rumen [ small intestine & colon (Dix et al 2013).…”

Section: Introductionsupporting

confidence: 81%

“…UT-B transporter proteins have previously been reported in the parotid salivary gland of both sheep and cows (Ludden et al 2009;Dix et al 2013). Furthermore, two distinct UT-B urea transporter isoforms, UT-B1 and UT-B2, are known to be expressed in the rumen of these species (Stewart et al 2005;Lu et al 2014).…”

Section: Introductionmentioning

confidence: 97%

“…In agreement with predictions based on the known regulators of urea transport, the observed ruminant UT-B abundance pattern appeared to be rumen [ small intestine & colon (Dix et al 2013). In addition, UT-B protein is known to be present in both dorsal and ventral rumen sacs (Ludden et al 2009). However, there has been minimal information reported regarding the precise location of UT-B transporters in these ruminant gastrointestinal tissues.…”

Section: Introductionmentioning

confidence: 98%

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UT-B Urea Transporter Localization in the Bovine Gastrointestinal Tract

et al. 2015

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Facilitative UT-B urea transporters play an important role in the urea nitrogen salvaging process that occurs in the gastrointestinal tract of mammals, particularly ruminants. Gastrointestinal UT-B transporters have previously been reported in various ruminant species-including cow, sheep and goat. In this present study, UT-B transporter localization was investigated in tissues throughout the bovine gastrointestinal tract. RT-PCR analysis showed that UT-B2 was the predominant UT-B mRNA transcript expressed in dorsal, ventral and cranial ruminal sacs, while alternative UT-B transcripts were present in other gastrointestinal tissues. Immunoblotting analysis detected a strong, glycosylated ~50 kDa UT-B2 protein in all three ruminal sacs. Immunolocalization studies showed that UT-B2 protein was predominantly localized to the plasma membrane of cells in the stratum basale layer of all ruminal sac papillae. In contrast, other UT-B protein staining was detected in the basolateral membranes of the surface epithelial cells lining the abomasum, colon and rectum. Overall, these findings confirm that UT-B2 cellular localization is similar in all ruminal sacs and that other UT-B proteins are located in epithelial cells lining various tissues in the bovine gastrointestinal tract.

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Section: Introductionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 98%

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UT-B Urea Transporter Localization in the Bovine Gastrointestinal Tract

et al. 2015

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“…Instead, an increase in UT-B expression has been found in the rumen epithelium of concentrate-fed steers, which was associated with higher concentrations of SCFA and a lower pH in the rumen (49). The same trend has also been observed in lambs and heifers that received a diet rich in easily fermentable substrata (35,40), and in calves received low-protein solid feed (7). These findings suggest that microbial metabolites play a role in regulating UT-B.…”

supporting

confidence: 59%

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

Gui

Yao

et al. 2015

American Journal of Physiology-Regulatory, Integrative and Comp

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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 NH 4Cl 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 NH 3-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 proteincoupled receptor (GPR) 41 and GPR4, in their rumen epithelium. The ruminal concentrations of SCFA and NH 3-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.SCFA and pH; UT-B expression; GPR41; GPR4; rumen epithelial cells; diet RECYCLING OF UREA TO THE MAMMALIAN gut accounts for 20 -30% of liver-synthesized urea that is present in humans (17). In contrast, these levels vary from 10 to 90% in ruminants (21) with feeding strategy (21) and intake of fermentable carbohydrates (22). These characteristics make the ruminant forestomach, especially the rumen, an excellent model for studies of urea entry and regulation in the gut. Urea transport across the rumen epithelium is generally accepted to occur down a concentration gradient from blood to lumen by diffusion through transport proteins, such as urea transporter B (UT-B), or possibly aquaporins. In our laboratory's recent studies, rumen fermentation products, including short-chain fatty acids (SCFA) and ammonia, as well as pH, were found to rapidly modulate UT-B activity (1, 34). It is possible that multiple mechanisms mediate regulation of urea transport, although these mechanisms are not fully characterized. UT-B has been found in many tissues and species, including human and rodent colon tissues, in erythrocytes and kidney tissue, as well as in ovine and bovine rumen (52). In bovine tissues, the UT-B protein exists as a multimer (30). Previous studies (21, 39, 41) have shown that changes in dietary nitrogen (N) content causes significant changes in serum urea-N (BUN) concentrations and the entry of urea into the gut. However, a correlation between N ...

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“…The future will show whether long-term effects of butyrate on urea transport are indeed related to a higher density of urea transporters in the ruminal tissue or whether concomitant increases in ruminal surface area are sufficient to explain these effects (24,90). In general, however, the demonstration of an effect of dietary changes on the expression of gastrointestinal urea transporters in ruminants has been challenging (18,48,51,61,80).…”

mentioning

confidence: 99%

Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO₂

Abdoun

Stumpff

Rabbani

et al. 2010

American Journal of Physiology-Gastrointestinal and Liver Physi

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Urea transport across the gastrointestinal tract involves transporters of the urea transporter-B group, the regulation of which is poorly understood. The classical stimulatory effect of CO2 and the effect of short-chain fatty acids (SCFA) on the ruminal recycling of urea were investigated by using Ussing chamber and microelectrode techniques with isolated ruminal epithelium of sheep. The flux of urea was found to be phloretin sensitive and passive. At a luminal pH of 6.4, but not at 7.4, the addition of SCFA (40 mmol/l) or CO2/HCO 3 Ϫ (10% and 25 mmol/l) led to a fourfold increase in urea flux. The stepwise reduction of luminal pH in the presence of SCFA from 7.4 to 5.4 led to a bell-shaped modification of urea transport, with a maximum at pH 6.2. Lowering the pH in the absence of SCFA or CO2 had no effect. Inhibition of Na ϩ /H ϩ exchange increased urea flux at pH 7.4, with a decrease being seen at pH 6.4. In experiments with double-barreled, pH-sensitive microelectrodes, we confirmed the presence of an apical pH microclimate and demonstrated the acidifying effects of SCFA on the underlying epithelium. We confirm that the permeability of the ruminal epithelium to urea involves a phloretin-sensitive pathway. We present clear evidence for the regulation of urea transport by strategies that alter intracellular pH, with permeability being highest after a moderate decrease. The well-known postprandial stimulation of urea transport to the rumen in vivo may involve acute pH-dependent effects of intraruminal SCFA and CO2 on the function of existing urea transporters. pH i; urea transporter-B; short-chain fatty acids; microclimate; volatile fatty acid UREA, POSSIBLY BECAUSE OF its small size, was long thought to move passively across epithelia, depending only on the rate of delivery via blood. The urea permeability of cellular membranes has now been established to be several orders of magnitude above that of lipid membranes (11,92) and is coupled to the expression of specific urea-transporting proteins with channel-like kinetics (7,46,71,81,82,95). Whereas the role that these proteins play in the elegant renal concentrating mechanism has received much attention, their function and regulation in other parts of the body, such as the gut (39), continues to be poorly understood.In contrast to the paucity of our knowledge concerning extrarenal urea transport in humans, we have long known of the ability of camels, cows, or sheep to shift the excretion of urea from the kidney (62, 72) to the gastrointestinal tract (79). The transport of urea through the rumen epithelium was first demonstrated many years ago in vivo and in vitro (16,29,79,89) and the physiological significance is clear: in the rumen, dietary cellulose is broken down by bacteria that utilize ureanitrogen for the synthesis of microbial proteins. After passage into the duodenum, the amino acids of these proteins are absorbed and reach the liver, where new urea for secretion into the rumen can be formed. Recycling of nitrogen via urea secretion into the rumen thus ...

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Effect of protein supplementation on expression and distribution of urea transporter-B in lambs fed low-quality forage1

Cited by 33 publications

References 32 publications

UT-B Urea Transporter Localization in the Bovine Gastrointestinal Tract

UT-B Urea Transporter Localization in the Bovine Gastrointestinal Tract

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

Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO₂

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Effect of protein supplementation on expression and distribution of urea transporter-B in lambs fed low-quality forage1

Cited by 33 publications

References 32 publications

UT-B Urea Transporter Localization in the Bovine Gastrointestinal Tract

UT-B Urea Transporter Localization in the Bovine Gastrointestinal Tract

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

Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO2

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Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO₂