Effects of dissolved carbon dioxide on the integrity of the rumen epithelium: An agent in the development of ruminal acidosis

The carbon dioxide released and dissolved in rumen fluid may easily permeate across the epithelial cell membrane. Thus, we hypothesized that CO₂ may act as proton carrier and induce epithelial damage under acidotic conditions. Ovine ruminal epithelia were mounted in Ussing chambers under short-circuit conditions. The serosal buffer solution had a constant pH of 7.4 and was gassed either with 100% oxygen or with carbogen (95% O₂ /5% CO₂ ). The mucosal solution was gassed with either 100% oxygen or 100% carbon dioxide. The mucosal pH was lowered stepwise from 6.6 to 5.0 in the presence or absence of short-chain fatty acids (SCFA). The transepithelial conductance (G_t ) as an indicator of epithelial integrity and the short-circuit current (I_sc ) as an indicator of active electrogenic ion transfer were continuously monitored. At an initial mucosal pH of 6.6, there was no significant difference in G_t between the treatment groups. In the absence of both SCFA and CO₂ , G_t remained constant when the mucosal solution was acidified to pH 5.0. In the presence of SCFA, mucosal acidification induced a significant rise in G_t when the solutions were gassed with oxygen. A small increase in G_t was observed in the mucosal presence of CO₂ . However, no difference in final G_t was observed between SCFA-containing and SCFA-free conditions under carbon dioxide gassing during stepwise mucosal acidification. The SCFA+proton-induced increase in G_t could also be minimized by serosal gassing with carbogen. Because of the SCFA+proton-induced changes in G_t and their attenuation by CO₂ , a protective role for mucosally available carbon dioxide may be assumed. We suggest that this effect may be due to the intraepithelial conversion of carbon dioxide to bicarbonate. However, the serosal presence of CO₂ at a physiological concentration may be sufficient to protect the epithelia from SCFA+proton-induced damage for a certain period of time.

Gamma-aminobutyric acid (GABA) permeates ovine ruminal and jejunal epithelia, mainly by passive diffusion

Gamma-aminobutyric acid (GABA) represents the most abundant inhibitory neurotransmitter in the mammalian brain. GABA is also produced in plants and/or by the microbial conversion of amino acids. Thus, ruminants may be forced to take up significant amounts of GABA from their diet. However, it is not known whether exogenously acquired GABA might permeate the gastrointestinal barrier in such quantities as to induce systemic alterations. Thus, this study pursues the question of where within the ruminant's GI tract and by which pathways GABA may be taken up from the ingesta. The jejunal and ruminal epithelia of sheep were mounted in Ussing chambers under short-circuit conditions. The flux rates of radiolabelled GABA from the mucosal to the serosal side (J_ms ) and vice versa (J_sm ) were measured. GABA was applied in various concentrations with adjustment of the mucosal pH to 6.1 or 7.4. Furthermore, beta-alanine or glycine was used as a competitive inhibitor for GABA transport. In both the jejunal and ruminal epithelium, the J_ms of GABA was linearly correlated to the mucosal GABA concentration. However, J_ms across the jejunal epithelium was approximately 10-fold higher than J_ms across the ruminal epithelium. When 0.5 mmol/l GABA was applied on both sides of the epithelium, no net flux could be observed in the jejunal epithelia. Additionally, there was no effect of decreased mucosal pH or the application of glycine or beta-alanine under these conditions. The J_ms and J_sm of GABA were linearly correlated to the transepithelial conductance. Our results suggest that GABA is taken up from the small intestine rather than from the rumen. Due to the lack of influence of pH and competitive inhibitors, this uptake seems to occur primarily via passive diffusion.

Conjugated linoleic acids influence fatty acid metabolism in ovine ruminal epithelial cells

Conjugated linoleic acids (CLA), particularly cis-9,trans-11 (c9t11) and trans-10,cis-12 (t10c12), are used as feed additives to adapt to constantly increasing demands on the performance of lactating cows. Under these feeding conditions, the rumen wall, and the rumen epithelial cells (REC) in particular, are directly exposed to high amounts of CLA. This study determined the effect of CLA on the fatty acid (FA) metabolism of REC and expression of genes known to be modulated by FA. Cultured REC were incubated with c9t11, t10c12, and the structurally similar FA linoleic acid (LA), oleic acid (OA), and trans-vaccenic acid (TVA) for 48 h at a concentration of 100 µM. Cellular FA levels were determined by gas chromatography. Messenger RNA expression levels of stearoyl-CoA desaturase (SCD) and monocarboxylate transporter (MCT) 1 and 4 were quantified by reverse transcription-quantitative PCR. Fatty acid evaluation revealed significant effects of CLA, LA, OA, and TVA on the amount of FA metabolites of β-oxidation and elongation and of metabolites related to desaturation by SCD. The observed changes in FA content point (among others) to the ability of REC to synthesize c9t11 from TVA endogenously. The mRNA expression levels of SCD identified a decrease after CLA, LA, OA, or TVA treatment. In line with the changes in mRNA expression, we found reduced amounts of C16:1n-7 cis-9 and C18:1n-9 cis-9, the main products of SCD. The expression of MCT1 mRNA increased after c9t11 and t10c12 treatment, and CLA c9t11 induced an upregulation of MCT4. Application of peroxisome proliferator-activated receptor (PPAR) α antagonist suggested that activation of PPARα is involved in the changes of MCT1, MCT4, and SCD mRNA expression induced by c9t11. Participation of PPARγ in the changes of MCT1 and SCD mRNA expression was shown by the application of the respective antagonist. The study demonstrates that exposure to CLA affects both FA metabolism and regulatory pathways within REC.

Both butyrate incubation and hypoxia upregulate genes involved in the ruminal transport of SCFA and their metabolites

Butyrate modulates the differentiation, proliferation and gene expression profiles of various cell types. Ruminal epithelium is exposed to a high intraluminal concentration and inflow of n-butyrate. We aimed to investigate the influence of n-butyrate on the mRNA expression of proteins involved in the transmembranal transfer of n-butyrate metabolites and short-chain fatty acids in ruminal epithelium. N-butyrate-induced changes were compared with the effects of hypoxia because metabolite accumulation after O2 depletion is at least partly comparable to the accumulation of metabolites after n-butyrate exposure. Furthermore, in various tissues, O2 depletion modulates the expression of transport proteins that are also involved in the extrusion of metabolites derived from n-butyrate breakdown in ruminal epithelium. Sheep ruminal epithelia mounted in Ussing chambers were exposed to 50 mM n-butyrate or incubated under hypoxic conditions for 6 h. Electrophysiological measurements showed hypoxia-induced damage in the epithelia. The mRNA expression levels of monocarboxylate transporters (MCT) 1 and 4, anion exchanger (AE) 2, downregulated in adenoma (DRA), putative anion transporter (PAT) 1 and glucose transporter (GLUT) 1 were assessed by RT-qPCR. We also examined the mRNA expression of nuclear factor (NF) κB, cyclooxygenase (COX) 2, hypoxia-inducible factor (HIF) 1α and acyl-CoA oxidase (ACO) to elucidate the possible signalling pathways involved in the modulation of gene expression. The mRNA expression levels of MCT 1, MCT 4, GLUT 1, HIF 1α and COX 2 were upregulated after both n-butyrate exposure and hypoxia. ACO and PAT 1 were upregulated only after n-butyrate incubation. Upregulation of both MCT isoforms and NFκB after n-butyrate incubation could be detected on protein level as well. Our study suggests key roles for MCT 1 and 4 in the adaptation to an increased intracellular load of metabolites, whereas an involvement of PAT 1 in the transport of n-butyrate also seems possible.

Bicarbonate-dependent transport of acetate and butyrate across the basolateral membrane of sheep rumen epithelium

AIM

This study aimed to assess the role of HCO₃⁻ in the transport of acetate and butyrate across the basolateral membrane of rumen epithelium and to identify transport proteins involved.

METHODS

The effects of basolateral variation in HCO₃⁻ concentrations on acetate and butyrate efflux out of the epithelium and the transepithelial flux of these short-chain fatty acids were tested in Ussing chamber experiments using (14)C-labelled substrates. HCO₃⁻-dependent transport mechanisms were characterized by adding specific inhibitors of candidate proteins to the serosal side.

RESULTS

Effluxes of acetate and butyrate out of the epithelium were higher to the serosal side than to the mucosal side. Acetate and butyrate effluxes to both sides of rumen epithelium consisted of HCO₃⁻-independent and -dependent parts. HCO₃⁻-dependent transport across the basolateral membrane was confirmed in studies of transepithelial fluxes. Mucosal to serosal fluxes of acetate and butyrate decreased with lowering serosal HCO₃⁻ concentrations. In the presence of 25 mm HCO₃⁻, transepithelial flux of acetate was inhibited effectively by p-hydroxymercuribenzoic acid or α-cyano-4-hydroxycinnamic acid, while butyrate flux was unaffected by the blockers. Fluxes of both acetate and butyrate from the serosal to the mucosal side were diminished largely by the addition of NO₃⁻ to the serosal side, with this effect being more pronounced for acetate.

CONCLUSION

Our results indicate the existence of a basolateral short-chain fatty acid/HCO₃⁻ exchanger, with monocarboxylate transporter 1 as a primary candidate for acetate transfer.

Post-natal changes in MCT1 expression in the forestomach of calves

The monocarboxylate transporter 1 (MCT1) has been demonstrated to be involved in the transfer of short-chain fatty acids (SCFA) and/or their intraepithelial metabolites from the rumen to the blood. As MCT1 plays a role in SCFA transfer, it is assumed that SCFA are the main substrates influencing its expression. However, there are hints that MCT1 may also be expressed during the early life of the animal when SCFA are not released in the forestomach. To figure out whether MCT1 expression in the forestomach is influenced independently of SCFA during that period, we studied post-natal MCT1 expression immunohistochemically in the epithelia of omasum, atrium ruminis, saccus dorsalis ruminis, saccus ventralis ruminis and reticulum of calves born preterm and at term. The calves were nourished by colostrum or by milk-based formula diet. MCT1 could be found in all the forestomach compartments tested, even in preterm calves. The protein was mainly oriented to the luminal side in the immature epithelium 24 h after birth. Orientation to the blood side of the cells developed during the first 4 days after birth. In the rumen epithelia (but not in the other forestomach compartments tested), orientation of MCT1 to the blood side of the cells was paralleled by an increase in the overall expression rate during the first 4 days after birth. As lactate levels were very high directly after birth, a lactate-dependent substrate induction may have been the underlying mechanism. However, non-specific changes due to general differential processes might also be the cause. Both early upregulation of MCT1 and high blood lactate levels may provide the epithelia with lactate as energy source.

[Antithrombotic therapy after peripheral vascular treatment: what is evidence-based?]

Peripheral arterial occlusive disease is one manifestation of the systemic disease atherosclerosis. The initial therapy for every arteriosclerotic disease is aimed at reducing cardiovascular risk factors by lifestyle modification and medication. Patients who require surgical revascularisation need long-term antiplatelet therapy or anticoagulation. This therapy has to be differentiated according to the vascular territory involved and the method used for revascularisation. After local thrombendarterectomy, alloplastic bypass graft surgery of the aortic, aorto-iliac, aorto-femoral or femoro-popliteal region above the knee, long-term ASA 100 mg/d or clopidogrel 75 mg/d should be initiated. After alloplastic bypass grafting below the knee the combination of ASA 100 mg/d and clopidogrel 75 mg/d should be used. In contrast, after venous grafts the patency rate is improved by anticoagulation with vitamin K antagonists (INR 2-3), if there is a low risk of bleeding. If there is a contraindication to vitamin K antagonists, ASA 100 mg/d should be used. After revascularisation, a structured surveillance programme should be implemented aiming at controlling cardiovascular risk factors and monitoring the vascular state, as well as the anticoagulation and the antiplatelet therapy.

Presence of Borrelia burgdorferi sensu lato antibodies in the serum of patients with abdominal aortic aneurysms

Infectious agents are likely to play a role in the pathogenesis of chronic inflammatory diseases, including abdominal aortic aneurysms (AAAs). The goal of this study was to determine if Borrelia burgdorferi sensu lato (sl), a microorganism responsible for Lyme disease, is involved in the etiology of AAAs. The presence of serum antibodies against B. burgdorferi sl was measured with enzyme-linked immunosorbent assay (ELISA) and confirmed by Western blotting in 96 AAA and 108 peripheral artery disease (PAD) patients. Polymerase chain reaction (PCR) was used for the detection of Borrelia-specific DNA in the aneurysm wall. Among AAA patients 34% and among PAD patients 16% were seropositive for B. burgdorferi sl antibodies (Fisher's exact test, p = 0.003; odds ratio [OR] 2.79; 95% confidence interval [CI] 1.37-5.85). In the German general population, 3-17% are seropositive for Borrelia antibodies. No Borrelia DNA was detected in the aneurysm wall. Our findings suggest a relationship between AAAs and B. burgdorferi sl. We hypothesize that the underlying mechanism for B. burgdorferi sl in AAA formation is similar to that by the spirochete Treponema pallidum; alternatively, AAAs could develop due to induced autoimmunity via molecular mimicry due to similarities between some of the B. burgdorferi sl proteins and aortic proteins.

Modulation of electrogenic transport processes in the porcine proximal colon by enteric neurotransmitters

The aim of our study was to evaluate the involvement of essential pro- and antisecretory neurotransmitters in regulation of secretion in porcine proximal colon. Choline acetyltransferase (ChAT), nitric oxide synthase (NOS), vasoactive intestinal peptide (VIP), substance P (SP), somatostatin (SOM) and neuropeptide Y (NPY) were located immunohistochemically in the epithelium and subepithelial layer. Modulation of epithelial secretion was studied in Ussing chambers. Application of carbachol (CA), sodium nitroprussid (SNP), VIP and SP but not of NPY or SOM resulted in a chloride dependent increase in short circuit current (I(sc) ). I(sc) increase induced by CA, VIP or SNP was not altered by preincubation with tetrodotoxin or indomethacin. In contrast, SP-induced I(sc) increase was diminished by preincubation with tetrodotoxin, indomethacin, L-nitro-arginin-methyl-ester, and atropine but not hexamethonium. Simultaneous application of CA and VIP, or CA and SNP increased the I(sc) stronger as expected. Applying SP/CA led to a smaller increase in I(sc) as calculated. It is concluded that mainly prosecretory neurotransmitters are involved in regulation of colonic secretion. Cross-potentiations of acetylcholine and nitric oxide and acetylcholine and VIP suggest activation of different intracellular cascades. Similar intracellular pathways may be stimulated by acetylcholine and SP, thus preventing an additive effect of the transmitters.

A single mild episode of subacute ruminal acidosis does not affect ruminal barrier function in the short term

Twenty-four German Merino sheep (72.3±10.1 kg of body weight) were fed an all-hay diet and assigned to either the subacute ruminal acidosis (SARA) treatment (n=17) or sham treatment (n=7). The SARA sheep were orally dosed with a 2.2 M glucose solution to supply 5 g of glucose/kg of body weight, whereas sham sheep received an equal volume of water. Ruminal pH was measured for 48 h before and 3 h after the oral dose. Sheep were then killed and ruminal epithelia from the ventral sac were mounted in Ussing chambers. The serosal-to-mucosal flux rate of partially (3)H-labeled mannitol (J(mannitol-SM)), an indicator of barrier function, was measured while epithelia were exposed to 3 sequential in vitro measurement periods lasting 1 h each. The measurement periods consisted of baseline, challenge, and recovery periods and were interspersed by 30-min periods for treatment equilibration. Baseline conditions were pH 6.1 (mucosal solution) and pH 7.4 (serosal solution) with a bilateral osmolarity of 293 mOsm/L. During the challenge period, the mucosal side of the epithelia was exposed to either an acidotic challenge (pH 5.2, osmolarity 293 mOsm/L) or an osmotic challenge (pH 6.1, osmolarity 450 mOsm/L); a third group served as control (pH 6.1, osmolarity 293 mOsm/L). The mucosal buffer solution was replaced for the recovery period. In vivo, sheep on the SARA treatment had lower mean (5.77 vs. 6.67) and nadir (5.48 vs. 6.47) ruminal pH for the 3h following the oral drench compared with sham sheep, indicating the successful induction of SARA with the oral glucose dose. Despite the marked reduction in pH in vivo, induction of SARA had no detectable effects on the baseline measurements of J(mannitol-SM), tissue conductance (G(t)), and short-circuit current (I(sc)) in vitro. However, reducing mucosal pH to 5.2 in vitro had negative effects on epithelial barrier function in the recovery period, including increased J(mannitol-SM), increased G(t), and decreased I(sc). The osmotic challenge increased J(mannitol-SM) and G(t) and decreased I(sc) during the challenge period, which was reversible in the recovery period except for slight reduction in I(sc). Interactions between the in vitro treatment and measurement period were detected for J(mannitol-SM), G(t), and I(sc). These data indicate that a mild episode of SARA (nadir pH, 5.48; duration ruminal pH <5.8, 111 min relative to the 180-min measurement period) does not affect ruminal epithelial barrier function immediately after the episode but that a rapid and more severe acidification (pH 5.2) in vitro increases epithelial permeability following the insult.

Ruminant Nutrition Symposium: Role of fermentation acid absorption in the regulation of ruminal pH

Highly fermentable diets are rapidly converted to organic acids [i.e., short-chain fatty acids (SCFA) and lactic acid] within the rumen. The resulting release of protons can constitute a challenge to the ruminal ecosystem and animal health. Health disturbances, resulting from acidogenic diets, are classified as subacute and acute acidosis based on the degree of ruminal pH depression. Although increased acid production is a nutritionally desired effect of increased concentrate feeding, the accumulation of protons in the rumen is not. Consequently, mechanisms of proton removal and their quantitative importance are of major interest. Saliva buffers (i.e., bicarbonate, phosphate) have long been identified as important mechanisms for ruminal proton removal. An even larger proportion of protons appears to be removed from the rumen by SCFA absorption across the ruminal epithelium, making efficiency of SCFA absorption a key determinant for the individual susceptibility to subacute ruminal acidosis. Proceeding initially from a model of exclusively diffusional absorption of fermentation acids, several protein-dependent mechanisms have been discovered over the last 2 decades. Although the molecular identity of these proteins is mostly uncertain, apical acetate absorption is mediated, to a major degree, via acetate-bicarbonate exchange in addition to another nitrate-sensitive, bicarbonate-independent transport mechanism and lipophilic diffusion. Propionate and butyrate also show partially bicarbonate-dependent transport modes. Basolateral efflux of SCFA and their metabolites has to be mediated primarily by proteins and probably involves the monocarboxylate transporter (MCT1) and anion channels. Although the ruminal epithelium removes a large fraction of protons from the rumen, it also recycles protons to the rumen via apical sodium-proton exchanger, NHE. The latter is stimulated by ruminal SCFA absorption and salivary Na(+) secretion and protects epithelial integrity. Finally, SCFA absorption also accelerates urea transport into the rumen, which via ammonium recycling, may remove protons from rumen to the blood. Ammonium absorption into the blood is also stimulated by luminal SCFA. It is suggested that the interacting transport processes for SCFA, urea, and ammonia represent evolutionary adaptations of ruminants to actively coordinate energy fermentation, protein assimilation, and pH regulation in the rumen.

Expression and activity of key hepatic gluconeogenesis enzymes in response to increasing intravenous infusions of glucose in dairy cows

The present study aimed at investigating whether increasing concentrations of glucose supply have a depressive effect on the mRNA abundance and activity of key gluconeogenic enzymes in dairy cows. Twelve Holstein-Friesian dairy cows in mid-lactation were intravenously infused with saline (SI; n = 6) or a 40% glucose solution (GI; n = 6). For GI cows, the infusion dose increased by 1.25%/d relative to the initial NE(l) requirement until a maximum dose equating to surplus 30% NE(l) was reached on d 24. Cows receiving SI received an equivalent volume of 0.9% saline solution. Blood samples were taken every 2 d, and liver biopsies were collected every 8 d. A treatment x quadratic dose interaction (P < 0.01) was observed for the concentration of plasma glucose and serum insulin. The interactions were due to positive quadratic responses of the concentrations of glucose and insulin for GI cows, whereas the concentrations of glucose and insulin did not change over time for SI cows. The concentration of beta-hydroxybutyric acid (BHBA) and serum urea nitrogen (BUN) responded in a treatment x quadratic dose manner, such that greater decreases (P < 0.01) in BHBA and BUN concentrations were observed for cows receiving GI than SI as the dosage increased. Serum NEFA concentration tended to follow a similar pattern as serum BHBA and BUN; however, the interaction was not significant (P = 0.07). The mRNA abundance of gluconeogenesis enzymes followed a linear treatment x dose interaction (P < 0.05) for only pyruvate carboxylase (PC), which was paralleled by a trend for a linear treatment x dose interaction (P = 0.13) for PC enzyme activity. The least PC expression and activity were observed at the largest glucose dosage. The activity, but not mRNA abundance, of fructose 1,6-bisphosphatase (FBPase) showed treatment x quadratic dose interactions (P < 0.05) with decreasing activity at increasing glucose dose. Activities and expression of phosphoenolpyruvate carboxykinase and glucose 6-phosphatase were not affected (P > 0.25) by treatment. In conclusion, hepatic gluconeogenic enzymes are only moderately affected by slowly increasing glucose supply, including a translational or posttranslational downregulation of FBPase activity and a decrease in the mRNA abundance of PC with possible consequences for PC enzyme activity.

Expression of mRNA for glucose transport proteins in jejunum, liver, kidney and skeletal muscle of pigs

Although pigs are adapted to starch-rich diets and have high turnover rates of glucose, very scarce information is available on the molecular basis of glucose transport. Therefore, the present study attempted a systematic screening for the presence of mRNA of glucose transport proteins in main organs of glucose absorption, production and conservation. From the members of the solute carrier family SLC5A (sodium glucose cotransporter), the porcine jejunum was positive for SGLT1 and SGLT3, but also contained detectable levels of SGLT5. Liver contained SGLT1, SGLT5, traces of SGLT3 and, in one of five pigs, SGLT2. Kidney contained SGLT1, SGLT2, SGLT3, SGLT5 and hardly detectable levels of SGLT4. Skeletal muscle showed weak signals for SGLT3 and SGLT5. Screening for members of the SLC2A family (facilitated glucose transporter) in intestine revealed the presence of mRNA for GLUT1, GLUT2, GLUT5, GLUT7 and GLUT8, while GLUT3, GLUT4, GLUT10 and GLUT11 were also detectable. The liver contained GLUT1, GLUT2 and GLUT8 mRNA, while GLUT3, GLUT4, GLUT5, GLUT10 and GLUT11 were poorly detectable. The kidney was positive for GLUT1, GLUT2, GLUT5, GLUT8 and GLUT11, but traces of GLUT3, GLUT4 and GLUT10 could also be detected. Skeletal muscle had the strongest signal for GLUT4, while GLUT1, GLUT3, GLUT5, GLUT8, GLUT10 and GLUT11 showed weak signals. A total of 12 unique partial cDNA sequences were submitted to GenBank. In conclusion, this study provides molecular insight into the organ-specific expression of glucose transporters in pigs and thus sheds light on the way of glucose handling in this omnivorous species.

Expression of ABC-transport proteins in canine mammary cancer: consequences for chemotherapy

Intrinsic or acquired drug resistance is a major barrier for chemotherapy of cancer. Importantly, the presence of ATP-binding cassette, ABC-transport proteins in tumour cells circumvents an intracellular accumulation of chemotherapeutic drugs. In this study, 103 canine mammary tumour probes were investigated for mRNA expression of seven ABC-transporters by RT-PCR. All tumour samples expressed multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP). MRP7 was detected in 97.1% of tumour probes, MRP3 in 96.1%, Pgp in 92.2%, MRP5 in 85.4% and MRP6 in 64.1%. More of the half of tumour samples (56.1%) expressed all of the examined ABC-transport proteins. Approximately one-third of the tumour samples (32.7%) were lacking in one transporter and only 11.2% possessed from three to five transporters. The canine transporter cBCRP was functionally analysed in stable transfected Madin-Darby canine kidney-II cells using an MTT viability test. cBCRP transfected cells showed a 5.4-fold resistance to 10 microm doxorubicin. Cell survival in the presence of methotrexate was not affected by cBCRP. In conclusion, absence of efficiency of chemotherapy of canine mammary cancer can be caused by expression of seven various ABC-transport proteins. Because cBCRP is expressed in all examined tumour probes and induces resistance to doxorubicin, the application of doxorubicin for treatment of canine mammary is inappropriate.

[Arterial injuries combined with open fractures--management and therapy]

Vascular injuries are an uncommon finding. In times of peace vascular injuries occur in approximately 1-4 % during traffic accidents. Especially challenging is the treatment of open fractures combined with arterial lesions. These fractures are usually accompanied with severe soft tissue damage and injuries to neurological structures. The overall prognosis of these trauma patients is dependent on fast and sufficient diagnostics and therapy. In particular, for unstable patients time-consuming diagnostics can be dispensed and a primarily operative therapy should be targeted. Vascular reconstruction by direct suture is sometimes only possible with interposition and should be the primary goal. Interposition should be performed with autologous vein material because of the high risk of infection. Here we demonstrate on the basis of our patients the interdisciplinary -management of such trauma patients in our hospital.

Release and permeation of histamine in isolated caecum epithelia of pigs

OBJECTIVE

The objective was to investigate the role of histamine in the porcine caecum with special regard to its release and permeation.

MATERIAL AND METHODS

Caecal epithelia were mounted in Ussing chambers. Mast cells were stimulated by A23187 (1 micromol/l). Permeation and changes in short-circuit current (Isc) were assessed after unilateral application of 3H-labelled histamine (100 micromol/l). Mucosal-to-serosal (ms) and serosal- to-mucosal (sm) flux rates were calculated based on the contralateral appearance of radioactive histamine label (hist-rad; representing histamine plus catabolites) as well as histamine. 14C-mannitol fluxes were measured to assess paracellular permeability.

RESULTS

Both A23187 and serosal addition of histamine increased Isc of caecal epithelia. The Isc increase due to A23187 was associated with an elevated histamine release from epithelia. A discrepancy between hist-rad and histamine fluxes (P<0.05) indicated efficient histamine catabolism (ca. 85%), which was decreased by blockage of diamine oxidase through aminoguanidine. Fluxes of histamine were correlated to 14C-mannitol fluxes. Fluxes of hist-rad and histamine were higher in the sm direction.

CONCLUSIONS

Histamine can be released from endogenous stores and acts on the epithelium. The absorption of luminal histamine is predominantly restricted by paracellular permeability and catabolism. The latter is only partially catalysed by diamine oxidase.

[Utilization of glucose and long-chain fatty acids in lactating dairy cows fed a fat-enriched diet]

The fate of carbon from long-chain fatty acids and glucose in dairy cows which were fed with protected fat was studied using stable isotope technique. The experiment was carried out on two groups of dairy cows (n=16 in each group) during the first 15 weeks of the lactation period. The cows were fed isoenergetic and isoproteinogenous diets based on corn silage. About 1.8 kg of tapioca starch in the diet of the starch group was substituted by about 0.7 kg of rumen protected fat (Ca salts of palm oil and soybean oil) in the diet of the fat group. The carbon atoms of dietary fat were naturally depleted in 13C as compared to carbon atoms of starch. Daily milk performance and lactose output were significantly (P < 0.05) higher among the cows fed with fat diet. In comparison to the starch group, the enrichment of milk fat with 13C was significantly lower, while that of breath CO2 was significantly higher in the fat group (P < 0.05). This means the fatty acids were incorporated into milk fat in preference to metabolic oxidation. Further studies showed that blood glucose is oxidized to a lower extent and is used for the synthesis of lactose to a higher proportion if the cows were fed with the fat diet. The glucose entry rate into the body glucose pool was not different between the diets. In conclusion, the dietary fatty acids perform a glucose sparing effect and improve the glucose supply for the mammary gland.

Bicarbonate exporting transporters in the ovine ruminal epithelium

In order to stabilize the intraruminal pH, bicarbonate secretion by the ruminal epithelium seems to be an important prerequisite. The present study therefore focussed on the characterization of bicarbonate exporting systems in ruminal epithelial cells. Intracellular pH (pH(i)) was measured spectrofluorometrically in primary cultured ruminal epithelial cells loaded with the pH-sensitive fluorescent dye, 2,7-bis(carboxyethyl)-5(6')-carboxyfluorescein acetomethyl ester. Switching from CO2/HCO3- -buffered to HEPES-buffered solution caused a rapid intracellular alkalinization followed by a counter-regulation towards initial pH(i). The recovery of pH(i) was dependent upon extracellular chloride, but independent of extracellular sodium. Adding 500 microM H2DIDS significantly reduced the increase of pH(i). For further characterization of the bicarbonate exporting systems, we tested the ability to reverse the direction from HCO3- export to import in the absence of sodium and chloride. Under sodium and chloride-free conditions, counter-regulation after CO2-induced pH(i) decrease did not differ from pH(i) recovery in the presence of sodium and chloride. Existence of bicarbonate exporting systems in cultured ruminal epithelial cells and intact ruminal epithelium was verified by reverse transcription polymerase chain reaction (RT-PCR). Using RT-PCR and subsequent sequencing, expression of mRNA encoding for AE2, DRA and PAT1 could be found. Bicarbonate exporting systems could therefore be detected both on the functional and structural level.

Adrenoceptor heterogeneity in the ruminal epithelium of sheep

The pre-gastric rumen of sheep plays a crucial role in the fermentation of nutrients and in the absorption of nutrients and minerals. Adrenaline has been shown previously to increase ruminal absorption of glucose and water. The present study was intended to elucidate whether ruminal ion transport is also altered by adrenaline. In Ussing chambers, changes of I(sc) were recorded in isolated ovine ruminal epithelia after the serosal additions of adrenoceptor agonists or antagonists. I(sc) increased after the addition of adrenaline (10(-4) M) or clonidine (alpha2-agonist, 10(-4) M), but decreased after the addition of isoproterenol (beta-agonist, 10(-4) M) or terbutaline (beta2-agonist, 10(-5) M). The effect of adrenaline on I(sc) was augmented by the adrenoceptor antagonists prazosin (alpha(1), 10(-4) M) and bupranolol (beta, 10(-6) M), but inversed by yohimbine (alpha(2), 10(-5) M). Adrenaline induced an increase in Na+ net flux across the epithelium that was larger than the increase in equivalent current flow. It is concluded that adrenaline differentially regulates ion transport across the ruminal epithelium via alpha1-, alpha2-, and beta2-receptors. The main effect is a stimulation of electroneutral and electrogenic Na+ absorption. This stimulated Na+ absorption might be causative of increased water absorption from the rumen as described previously.

Luminal salmonella endotoxin affects epithelial and mast cell function in the proximal colon of pigs

BACKGROUND

Salmonellosis and systemic endotoxaemia affect intestinal function. However, little is known about the functional importance of luminal Salmonella (S.) endotoxin during intestinal infection.

METHODS

Pigs were either given or not given lipopolysaccharide (LPS, 30 mg day(-1)) of S. Typhimurium DT-104 orally for 14 days. Blood samples were taken weekly. After slaughter (day 14), epithelia of the proximal colon were investigated in Ussing chambers. Bacterial translocations to lung, liver, spleen and several lymph nodes were determined by culture.

RESULTS

Endotoxin feeding increased plasma C-reactive protein (CRP) and histamine levels without evoking clinical signs. Postmortem, proximal colonic epithelia of LPS-treated animals showed both a decreased histamine release after mast cell stimulation with A23187 and a smaller increase in short-circuit current after A23187 application. Addition of the nitric oxide donor, sodium nitroprusside (SNP), also elicited lower increases in short-circuit current in the proximal colon of endotoxin-treated pigs. Endotoxin pre-feeding decreased colonic ion conductance, although mannitol and histamine fluxes were high in some epithelia of this group. Luminal Salmonella endotoxin increased bacterial translocation to proximal jejunal lymph nodes. LPS applied to colonic epithelia in vitro had no electrophysiological effects.

CONCLUSIONS

Luminal endotoxin elicits an acute phase response and affects intestinal electrolyte transport and mast cell function. Furthermore, LPS induces epithelial spots of increased mannitol permeability that could be identical to spots of enhanced bacterial translocation.

Molecular and functional evidence for a Na(+)-HCO3(-)-cotransporter in sheep ruminal epithelium

The present study aimed to identify the HCO3(-)-dependent mechanisms contributing to the homeostasis of the intracellular pH (pHi) in ruminal epithelial cells of sheep. Therefore, pHi was measured spectrofluorometrically in primary cultured ruminal epithelial cells loaded with the pH-sensitive fluorescent dye, 2',7'-bis(carboxyethyl)-5(6')-carboxyfluorescein acetoxymethyl ester. Switching from a HEPES-buffered to a CO2/HCO3(-)-buffered solution caused a rapid intracellular acidification followed by a counter-regulation towards alkaline levels. The counter-regulation was totally dependent upon extracellular Na+, but independent of intracellular Cl-. Adding 30 microM EIPA to the solutions did not affect the pHi counter-regulation following the acidification. Presence of 500 M H2DIDS inhibited the counter-regulation of pHi by 67%. These results pointed to a Na(+)-HCO3(-)-cotransporter (NBC) as the main pHi regulatory mechanism in the presence of HCO3-. Existence of an NBC in both cultured ruminal epithelial cells and intact ruminal epithelium was verified by reverse transcription polymerase chain reaction (RT-PCR) studies. RT-PCR yielded a band of the expected molecular size of 333 bp in both cultured cells and intact epithelium. The mRNA sequences were identical and shared a homology of 62% with human kidney NBC (Genebank accession number AF007216), of 66% with rat kidney NBC (AF004017) and of 65% with mouse duodenal NBC (AF141934).

Effect of nitric oxide on electrolyte transport across the porcine proximal colon

The effect of nitric oxide (NO) on ion transport in the porcine proximal colon was investigated in slide-stripped epithelia mounted in Ussing chambers. The serosal addition of the NO-donors sodium nitroprusside (SNP, 0.5 mM) or S-nitroso-N-acetylpenicillamine (SNAP, 0.5 mM) induced a steep increase of short-circuit current ( I(sc)). The stimulatory effect of SNP on I(sc) could not be blocked by piroxicam or tetrodotoxin. Potassium channel inhibitors (quinidine, tetraethylammonium or barium) added serosally reduced the SNP- or SNAP-induced increases of I(sc). In chloride-free solutions, the SNP-induced increase of I(sc) was smaller than in chloride-containing solutions. Cl(- )and Na(+) flux measurements demonstrated that SNP diminished Cl(-) and Na(+) net absorption. Pre-treatment with barium was able to block the inhibitory effect of SNP on NaCl net absorption totally. NO effects on paracellular pathways were assessed by measuring flux rates of [(14)C]-D-mannitol. SNP did not change unidirectional D-mannitol flux rates. In conclusion, NO inhibits NaCl net absorption in the proximal colon of pigs by acting directly on the enterocyte. The antiabsorptive (and/or prosecretory) effect of NO depends on a functional basolateral potassium conductance.

Histamine-induced chloride secretion is mediated via H2-receptors in the pig proximal colon

OBJECTIVE

The aim of this study was to investigate the action of histamine on function of epithelia in the pig proximal colon.

MATERIAL AND METHODS

Isolated epithelia of the pig proximal colon were prepared by slide-stripping and mounted in Ussing chambers. Short-circuit current (Isc) was measured after serosal addition of histamine (20 micromol/l) with or without pretreatment with histamine receptor antagonists (H1: chlorpyramine, 10 micromol/l; H2: famotidine, 100 micromol/l; H3: thioperamide, 10 micromol/l), a cyclooxygenase inhibitor (indomethacin, 10 micromol/l), or a neuronal conduction blocker (tetrodotoxin, 1 micromol/l). Alternatively, histamine receptor agonists (H1: 2-pyridylethylamine; H2: dimaprit; H3: R-alpha-methylhistamine, each 100 micromol/l) were added to the serosal side. Flux studies using 14C-mannitol, 22Na+ and 36Cl- were performed in the presence of 100 micromol/l histamine on the serosal side.

RESULTS

Serosal application of histamine induced a rapid rise in Isc with a maximum 3 min after addition, followed by a slow decrease. Only pretreatment with famotidine decreased the epithelial response to histamine. Pretreatments with chlorpyramine, thioperamide, indomethacin or tetrodotoxin did not change histamine-induced increases in Isc. Action of histamine could be simulated by dimaprit, but not by 2-pyridylethylamine or R-alpha-methylhistamine. Histamine induced an increase in serosal-to-mucosal chloride flux leading to a decrease of chloride net absorption. Fluxes of sodium and mannitol were not affected by histamine.

CONCLUSIONS

In contrast to the importance of H1-receptors in other gut epithelia, histamine acts directly via H2-receptors in the porcine proximal colon. Changes in Isc after histamine addition are primarily due to chloride secretion. The paracellular permeability is not influenced by histamine.

Sodium glucose-linked transport in the ruminal epithelium of fallow deer -- comparison to sheep

A higher expression of the sodium glucose-linked transporter, SGLT-1, has been previously demonstrated in the intestine of adult fallow deer compared to sheep. The functional presence of SGLT-1 in the rumen of both species was investigated in the present study. Isolated ruminal epithelia were incubated in Ussing chambers. D-Glucose or 3-O-methyl-alpha-D-glucose (3-OMG) were applied at 10 mmol x l-1 to the mucosal side of tissues and the changes in short-circuit current (Delta I(sc)) were recorded. Alternatively, apical uptake of [14C]-D-glucose (200 micro mol x l-1) was determined in the presence or absence of phlorizin (100 micro mol x l-1) or Na+ (115 mmol x l-1). In both species, mucosal D-glucose addition induced a larger ( P<0.05) Delta I(sc) than the mucosal addition of 3-OMG. When comparing the effects of D-glucose or 3-OMG between species, the Delta I(sc) was two-fold larger ( P<0.01) in sheep compared to fallow deer. Accordingly, phlorizin-sensitive D-glucose uptake was approximately 50% smaller ( P<0.05) in fallow deer. It is concluded that D-glucose can be absorbed via SGLT-1 from the forestomachs of both species. However, the intermediate-mixed feeding habit of fallow deer does not seem to coincide with a higher activity of the ruminal SGLT-1.

Influence of food deprivation on the transport of 3-O-methyl-alpha-D-glucose across the isolated ruminal epithelium of sheep

Recent studies provided evidence that the ruminal epithelium is able to absorb D-glucose even at physiologically low intraruminal concentrations. To elucidate whether ruminal D-glucose transport shows adaptive responses during food deprivation, transport of 3-0-methyl-alpha-D-glucose (3-OMG), a hardly metabolizable D-glucose analogue, was measured in isolated ruminal epithelia obtained from hay-fed or food-deprived adult sheep. In both groups, a significant net absorption of 3-OMG to the serosal side (in vivo: blood side oriented) could be detected at 3-OMG concentrations between 0.25 mM and 5 mM. Net absorption of 3-OMG was abolished by mucosal (in vivo: lumen side oriented) addition of phlorizin, an inhibitor of the sodium glucose-linked transporter 1 (SGLT-1). Net absorption of 3-OMG followed Michaelis-Menten kinetics, but apparent affinity and maximal transport capacity were lower in epithelia obtained from food-deprived sheep. In contrast to the decrease of the (secondary) active 3-OMG transport, serosal-to-mucosal permeation of 3-OMG increased after food deprivation, suggesting an elevated passive 3-OMG transfer. It is concluded that the altered transport characteristics are either part of a global energy-sparing process during food deprivation (i.e., a lowered activity of the Na+/K+-ATPase) or result from specific down-regulation of SGLT-1.

Na+/H+ exchange in primary, secondary and n-butyrate-treated cultures of ruminal epithelial cells: short communication

Rate of amiloride-sensitive Na+ uptake into cultured rumen epithelial cells was studied in order to clarify the influence of culture conditions on Na+/H+ exchange (NHE). Cell cultures were exposed to Na-n-butyrate or not for seven days or subcultured. On the 14th day of culturing, primary cell cultures without butyrate exposure showed both non-stratified and stratified growth. Na-n-butyrate treated 14-day-old cultures and 3-day-old subcultures contained mostly non-stratified, i.e. non-keratinised cells. Both n-butyrate treatment and subculturing increased total and amiloride-sensitive Na+ uptake. Our results indicate that Na+ uptake via NHE is determined by the amount and the ratio of non-stratified (non-keratinised) cells.

Transfer of energy substrates across the ruminal epithelium: implications and limitations

The ruminal epithelium has an enormous capacity for the absorption of short-chain fatty acids (SCFAs). This not only delivers metabolic energy to the animal but is also an essential regulatory mechanism that stabilizes the intraruminal milieu. The epithelium itself, however, is endangered by the influx of SCFAs because the intracellular pH (pHi) may drop to a lethal level. To prevent severe cytosolic acidosis, the ruminal epithelium is able to extrude (or buffer) protons by various mechanisms: (i) a Na+/H+ exchanger, (ii) a bicarbonate importing system and (iii) an H+/monocarboxylate cotransporter (MCT). Besides pHi regulation, the MCT also provides the animal with ketone bodies derived from the intraepithelial breakdown of SCFAs. Ketone bodies, in turn, can serve as an energy source for extrahepatic tissues. In addition to SCFA uptake, glucose absorption has recently been identified as a potential way of eliminating acidogenic substrates from the rumen. At least with respect to SCFAs, absorption rates can be elevated when adapting animals to energy-rich diets. Although they are very effective under physiological conditions, the absorptive and regulatory mechanisms of the ruminal epithelium also have their limits. An increased number of protons during the state of ruminal acidosis can be eliminated neither from the lumen nor the cytosol, thus worsening dysfermentation and finally leading to functional and morphological alterations of the epithelial lining.

Influence of isoform and DNP on butyrate transport across the sheep ruminal epithelium

Short-chain fatty acids are absorbed in considerable amounts from the rumen. During transit through the epithelial layer, they are intensively metabolised. Interaction between intraepithelial metabolism and absorption, however, is hardly understood. The present study therefore compared the transepithelial transport of the easily metabolised n-butyrate with that of the more metabolism-resistant iso-butyrate both under in vivo conditions (isolated and washed reticulorumen) and in vitro conditions (Ussing chamber). Under in vivo conditions, net absorption of n-butyrate was significantly higher than that of iso-butyrate. The in vitro experiments showed that the higher net flux of n-butyrate was solely due to a higher mucosal-to-serosal flux, whereas the serosal-to-mucosal flux of butyrate was independent from the isoform. Blocking intraepithelial ATP delivery by 2,4-dinitrophenol abolished the net flux of n-butyrate. The study indicates that metabolism and/ or ATP availability stimulates n-butyrate net absorption. By this, the metabolic activity of the epithelium may have a regulatory influence on absorption of n-butyrate.

Glucose is absorbed in a sodium-dependent manner from forestomach contents of sheep

Intraruminal glucose is thought to be completely converted to short-chain fatty acids (SCFA) by symbiotic microorganisms. Nevertheless, earlier in vitro studies evidenced the expression of the sodium glucose-linked transporter (SGLT)-1, in the ovine ruminal epithelium. The present study aimed to determine whether the ruminal SGLT-1 is functionally important in vivo. In a first experimental series using the emptied, washed, and isolated reticulorumen of sheep, 6.3% of glucose was absorbed from an intraruminal buffer solution (2 L, 128 mmol/L Na(+), 0.5 mmol/L glucose, 0 mmol/L galactose) within 30 min (P < 0.001). Reducing Na(+) concentration to 10 mmol/L resulted in complete inhibition of glucose absorption, and the addition of 10 mmol/L galactose (at 128 mmol/L Na(+)) induced a small but insignificant inhibition. In a second experimental series, the addition of 12 mmol/L glucose to an initially glucose-free buffer led to an increase in the transruminal potential difference from 34.4 to 37.1 mV within 4 min (P < 0.001). From the 12 mmol/L glucose-containing buffer, 11.0% of glucose was absorbed within 30 min (P < 0.05). In all experiments, microbial glucose degradation in the reticulorumen was prevented by adding cefuroxime (100 mg/L) and colistin methanesulfonate (25 mg/L) to the buffer solution. The effectiveness of antimicrobial treatment was verified by ex vivo incubations of buffer samples drawn from the reticulorumen. We conclude that glucose is absorbed in a sodium-dependent manner from the reticulorumen at low and high glucose concentrations. Absorption at high glucose concentrations is of nutritional importance because it counteracts the genesis of ruminal lactic acidosis.

Portal recovery of short-chain fatty acids infused into the temporarily-isolated and washed reticulo-rumen of sheep

The present study was undertaken to study the metabolism of short-chain fatty acids (SCFA) by the reticulo-ruminal epithelium and the portal-drained viscera (PDV) under in vivo conditions with no interference from the metabolism of the rumen microbes. The technique of temporary isolation of the reticulo-rumen was applied to wethers implanted with catheters in a mesenteric artery, the hepatic portal vein and the right ruminal vein. Portal blood flow was measured by downstream dilution of p-aminohippuric acid; the PDV uptake of arterial acetate, as well as the whole-body irreversible loss rate (ILR) of acetate, was estimated by [2-(13)C]acetate infusion into the right ruminal vein. The sheep were maintained with a bicarbonate-buffered solution of SCFA in the reticulo-rumen along with continuous intraruminal infusion of SCFA for 4 h. The portal appearance of SCFA of non-reticulo-ruminal origin was estimated before and after the infusion protocol. Of the acetate absorbed by the sheep, 89 (SE 5), 109 (SE 7) and 101 (SE 7)% was recovered as portal net appearance of acetate, portal net appearance of acetate corrected for PDV uptake of arterial acetate and increase in the ILR of acetate respectively. Of the propionate, isobutyrate, butyrate, isovalerate and valerate absorbed by the sheep, 95 (SE 7), 102 (SE 9), 23 (SE 3), 48 (SE 5) and 32 (SE 4)% respectively was recovered as portal net appearance. In contrast to current concepts, the present study showed that the reticulo-ruminal epithelium metabolizes none (or only a small proportion) of the acetate and propionate absorbed from the rumen. This observation could lead to the more efficient use of results obtained with multi-catheterized animals to quantify the net metabolite output of the rumen microbes.

Functional and molecular biological evidence of SGLT-1 in the ruminal epithelium of sheep

Because of the effective catabolism of D-glucose to short-chain fatty acids by intraruminal microorganisms, the absorption of D-glucose from the rumen was thought to be of minor importance. However, clinical studies suggested that significant quantities of D-glucose are transported from the ruminal contents to the blood. We therefore tested the ruminal epithelium of sheep for the presence of Na(+)-glucose cotransporter 1 (SGLT-1) on both the functional and mRNA levels. In the absence of an electrochemical gradient, 3-O-methylglucose (3-OMG) was net absorbed across isolated ruminal epithelia mounted in Ussing chambers. The net transport of 3-OMG followed Michaelis-Menten kinetics and was sensitive to phlorizin or decreasing Na(+) concentrations. The mucosal addition of 10 mM D-glucose induced an immediate, phlorizin-sensitive increase in short-circuit current (I(sc)). I(sc) could also be increased by serosal addition of D-glucose or D-mannose, but electrogenic uptake of D-glucose or 3-OMG added on the mucosal side was still detectable after serosal stimulation of I(sc). RT-PCR using primers specific for the ovine intestinal SGLT-1 with subsequent TA cloning and sequencing revealed 100% identity between the cloned cDNA and mRNA fragment 187-621 of ovine intestinal SGLT-1. In conclusion, the ruminal epithelium has a high-affinity SGLT-1, which indicates that it maintains the capacity for D-glucose absorption.

Role of Na+/H+ exchange and HCO3- transport in pHi recovery from intracellular acid load in cultured epithelial cells of sheep rumen

This study sought to investigate effects of short-chain fatty acids and CO2 on intracellular pH (pHi) and mechanisms that mediate pHi recovery from intracellular acidification in cultured ruminal epithelial cells of sheep. pHi was studied by spectrofluorometry using the pH-sensitive fluorescent indicator 2',7'-bis (carboxyethyl)-5(6')-carboxyfluorescein acetoxymethyl ester (BCECF/AM). The resting pHi in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered solution was 7.37 +/- 0.03. In HEPES-buffered solution, a NH4+/NH3-prepulse (20 mM) or addition of butyrate (20 mM) led to a rapid intracellular acidification (P < 0.05). Addition of 5-(N-ethyl-N-isopropyl)-amiloride (EIPA: 10 microM) or HOE-694 (200 microM) inhibited pHi recovery from an NH4+/NH3-induced acid load by 58% and 70%, respectively. pHi recovery from acidification by butyrate was reduced by 62% and 69% in the presence of EIPA (10 microM) and HOE-694 (200 microM), respectively. Changing from HEPES-(20 mM) to CO2/HCO3(-)-buffered (5%/20 mM) solution caused a rapid decrease of pHi (P < 0.01), followed by an effective counter-regulation. 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS; 100 microM) blocked the pHi recovery by 88%. The results indicate that intracellular acidification by butyrate and CO2 is effectively counter-regulated by an Na+/H+ exchanger and by DIDS-sensitive, HCO3(-)-dependent mechanism(s). Considering the large amount of intraruminal weak acids in vivo, both mechanisms are of major importance for maintaining the pHi homeostasis of ruminal epithelial cells.

Transport, catabolism and release of histamine in the ruminal epithelium of sheep

Whereas intraruminal histamine does not affect healthy ruminants, histaminosis is apparent during ruminal acidosis. We therefore investigated the factors that, under physiological circumstances, prevent intoxication by intraruminal histamine and the disturbances occurring during acidotic or hypoxic epithelial damage. After mucosal (m) or serosal (s) application of 80 microM histamine, its flux across the isolated epithelia of the sheep rumen was determined radioactively (hist-rad flux) in Ussing chambers. The non-catabolized component of the hist-rad fluxes was determined by high-pressure liquid chromatography (HPLC) (histamine flux). The difference between hist-rad and histamine fluxes indicated efficient intraepithelial catabolism of histamine at pH 7.4 (m-s direction, 98.7%; s-m direction, 93.3%). Both 0.1 mM 2,4-dinitrophenol (DNP) and mucosal acidification to pH 5.1 increased hist-rad fluxes and decreased catabolic efficiency. pH-dependent secretion of histamine was indicated by differences between m-s and s-m fluxes of histamine and/or hist-rad. Epithelial permeability to hist-rad and mannitol was similar and their fluxes correlated partly. Epithelial release of endogenous histamine was 1.5 pmol x cm(-2) x h(-1) and was not increased by the mast cell stimulator, compound 48/80 (10 ng x ml(-1)). We conclude that histamine absorption across the intact epithelium is efficiently restricted by a low permeability to histamine in combination with catabolic and secretory processes. Especially increases in paracellular permeability and/or inhibition of catabolism enhance histamine absorption.

Effect and absorption of histamine in sheep rumen: significance of acidotic epithelial damage

The significance of ruminal histamine for the induction of epithelial damage and systemic histaminosis during the ruminal lactic acidosis syndrome was investigated using the Ussing chamber technique. Histamine did not affect the electrophysiological characteristics of ovine ruminal epithelia under shortcircuit conditions. In contrast, mucosal acidification to pH 5.1 induced pronounced effects on tissue conductance (Gt) and short-circuit current (Isc). Using [3H]histamine for flux determination (hist-rad fluxes), significant net absorption of hist-rad (.40+/-.07 nmol x cm(-2) x h(-1); n = 6) was evident under short-circuit conditions in the presence of a mucosal-to-serosal (ms) histamine gradient (80 microM:12 microM). In comparison to hist-rad, absorption of native histamine (ms histamine gradient 80 microM:0 microM) measured with HPLC under open circuit conditions was smaller (.010+/-.003 nmol x cm(-2) x h(-1); n = 10). Mucosal acidification to pH 5.1 led to an increase (P<.05) in net absorption of hist-rad (to .67+/-.06 nmol x cm(-2) x h(-1); n = 6) and a dramatic increase (P<.01) in the absorption of native histamine (to .27+/-.04 nmol x cm(-2) x h(-1); n = 10). Absorption of ruminal histamine should be considered an important cause of systemic histaminosis in acidotic ruminants. Histamine absorption is linked to ruminal epithelial damage, which is primarily induced by luminal acidity and not by histamine.