PubMed Health⌕ Search

Biomedical subjects

W von Engelhardt

Publications and source records attributed to W von Engelhardt.

At least 37 records · Page 2Linked to original sources
PubMed1995

Unidirectional fluxes of short-chain fatty acids across segments of the large intestine in pig, sheep and pony compared with guinea pig.

Unidirectional fluxes of short-chain fatty acids across pig, sheep and pony caecum, proximal and distal colon were studied under short-circuit current conditions in Ussing chambers. Findings are compared with results from guinea pig. Marked species differences are apparent; highest mucosal-to-serosal fluxes of acetate, propionate and butyrate were seen in guinea pig, lower values in pig and smallest fluxes in sheep and pony. Segmental differences between caecum, proximal and distal colon exist mainly in guinea pig and are less developed in pig, sheep and pony. Inhibition of Na+/H+ exchange by amiloride added to the mucosal solution decreased the mucosal-to-serosal fluxes of short-chain fatty acids clearly in guinea pig caecum and proximal colon, and very little in distal colon. This effect was somewhat less pronounced in pig caecum and distal colon, in caecum and distal colon of sheep and caecum of the pony. In pig, sheep and pony proximal colon and pony distal colon no significant inhibition was observed. Inhibition of the K(+)-H+ ATPase by addition of ouabain to the mucosal solution diminished mucosal-to-serosal fluxes of short-chain fatty acids in the guinea pig distal colon extensively. No comparable inhibition was seen in any of the other segments in the animals studied.

Amiloride↗
PubMed1995

Comparative views of electrophysiological parameters of large intestinal segments in pig, sheep, pony, guinea pig and rat.

Short circuit current (ISC) and transepithelial conductance (gt) across sheets of epithelia were measured in the caecum, the proximal and the distal colon of pig, sheep, pony, rat and guinea pig. The electrical parameters underline the basic segmental and species differences. The diversity of ISC demonstrates the different nature of electrogenic transport mechanisms, and data clearly show the heterogeneity with respect to transport mechanisms along the large intestine in the various species. The great differences in amiloride sensitive ISC indicate the variabilities in the electrogenic Na transport. Whereas in the pig, sheep and pony caecum, in the guinea pig proximal colon and in all segments of the rat hindgut no indications for a major electrogenic Na transport was seen, in all other segments amiloride caused a marked decrease in ISC. Electrogenic Na transport seems to be highest in sheep distal colon and in pig proximal and distal colon, somewhat less in guinea pig and in pony distal colon. The epithelium with the lowest Powest transepithelial conductance clearly is that of the pony caecum. Except in sheep, gt-values are not much different from those in pony and also pig and guinea pig. By far the epithelium with the highest conductance is that of the rat proximal colon. gt was similar in the proximal and the distal colon of pig, sheep and pony; in guinea pig values were slightly, in rat much lower.

Animals↗
PubMed1995

Regulation of intracellular pH in the colonic epithelial cell line HT29 clone 19A.

Intracellular pH (pHi) of the colonic tumor cell line HT29 cl. 19A was studied by microspectrofluorometry using the pH-sensitive dye BCECF. Single cells within a confluent monolayer grown in a polarized manner on permeable supports were examined. An amiloride-sensitive Na(+)-H+ exchange and a stilbene-insensitive Cl(-)-HCO3- exchange mechanism have been identified in the basolateral membrane. This Na(+)-H+ exchange mechanism in the basolateral membrane is an acid extruder, whereas the Cl(-)-HCO3- exchanger is an acid loader. Both of these in the basolateral membrane located mechanisms are important for the maintenance of intracellular pH in HT29 cl. 19A cells.

Antiporters↗
PubMed1994

Functional role of bicarbonate in propionate transport across guinea-pig isolated caecum and proximal colon.

1. Unidirectional fluxes of propionate across isolated epithelia from the guinea-pig caecum and proximal colon were measured under short-circuit current conditions. In the caecum and proximal colon the serosal-to-mucosal propionate flux (JPrsm) was higher than mucosal-to-serosal flux (JPrms), resulting in a net secretory flux of propionate. 2. HCO3(-)-CO2-free solution reduced JPrms in the caecum and proximal colon markedly; JPrsm was not (caecum) or little (proximal colon) affected. The subsequent addition of acetazolamide caused a further decrease in JPrms in the proximal colon, but not in the caecum. 3. In HCO3(-)-containing solutions acetazolamide or ethoxzolamide inhibited JPrms; JPrsm was not affected. A macromolecular carbonic anhydrase inhibitor, prontosil-dextran, had no effect on propionate fluxes, indicating that the intracellular carbonic anhydrase is of importance for short-chain fatty acid transport. 4. Subsequent to carbonic anhydrase inhibition, mucosal addition of amiloride caused a slight further decrease of JPrms in the caecum and proximal colon; JPrsm was not affected. 5. Results support the view that a considerable proportion of short-chain fatty acids (SCFAs) is absorbed via a SCFA(-)-HCO3- exchange.

Acetazolamide↗
PubMed1994

The gastrointestinal tract of the rock hyrax (Procavia habessinica). 1. Morphology and motility patterns of the tract.

The stomach of the rock hyrax (Procavia habessinica) is divided into a non glandular part with very slow movements, and a glandular part which rapidly mix the digesta. The large intestine has two fermentation chambers, the caecum, which rapidly mixes the digesta, and the colonic sac, which efficiently, but slowly, mixes digesta. Between these chambers runs the connecting colon. No retrograde transport is observed in any part of the large intestine.

Animals↗
PubMed1994

Absorption of short-chain fatty acids from the in-situ-perfused caecum and colon of the guinea pig.

BACKGROUND: Short-chain fatty acids (SCFA) originate from microbial fermentation of carbohydrates in the hindgut. Mechanisms involved in SCFA absorption are not fully understood. METHODS: The caecum and proximal and distal colon of the guinea pig were perfused in situ. RESULTS: SCFA absorption per gram mucosal dry weight was highest in the proximal colon and lowest in the caecum. Owing to the large surface, quantitatively SCFA absorption was highest from the caecum. In the distal colon clearance of SCFA increased with chain length (Ac < Pr < Bu); in the caecum and proximal colon only a comparatively small or no such influence was observed. Inhibition of the proton antiport systems in the apical membrane and inhibition of the carbonic anhydrase activity diminished SCFA absorption. The diffusive and carrier components of absorption were calculated for propionate at increasing propionate concentrations. CONCLUSIONS: Marked segmental differences in SCFA absorption are apparent in the large intestine of the guinea pig.

Animals↗
PubMed1993

Basolateral mechanisms of intracellular pH regulation in the colonic epithelial cell line HT29 clone 19A.

The intracellular pH (pHi) of the colonic tumour cell line HT29 cl.19A was studied by microspectrofluorometry using the pH-sensitive dye BCECF. Single cells within a confluent monolayer, grown in a polarized manner on permeable supports, were examined. An amiloride-sensitive Na+/H+ exchange and a stilbene-insensitive Cl-/HCO3- exchange mechanism have been identified in the basolateral membrane. Removal of Na+ from the basolateral solution caused a decrease of pHi by 0.50 +/- 0.09 unit (n = 4). Amiloride or Na(+)-free solution at the apical side had no effect on pHi. Cl- removal at the basolateral side led to an increase of pHi by 0.20 +/- 0.03 unit (n = 4) whereas apical removal had no influence on pHi. This effect was independent of Na+ and was insensitive to 0.2 mM 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulphonic acid. A basolateral Cl-/HCO3- exchanger is the most likely explanation for this observation. The Na+/H+ exchange mechanism in the basolateral membrane is an acid extruder, whereas the Cl-/HCO3- exchanger is an acid loader. Both of these mechanisms are important for the maintenance of intracellular pH in HT29 cl.19A cells.

Amiloride↗
PubMed1993

Effects of amiloride and ouabain on short-chain fatty acid transport in guinea-pig large intestine.

1. Effects of H+ secreting mechanisms on unidirectional passage of the short-chain fatty acids (SCFA) acetate, propionate and n-butyrate across isolated guinea-pig caecum, proximal and distal colon were studied under short-circuit current conditions in Ussing chamber isotope flux experiments. 2. In the caecum and the proximal colon the serosal-to-mucosal fluxes (Jsm) were higher than the mucosal-to-serosal fluxes (Jms). Thus a net secretion of SCFA was present in the caecum and proximal colon. The higher Jsm appears to be coupled to the Na+ gradient established by the basolateral membrane Na(+)-K(+)-ATPase, whereas Jms is related to the operation of an apical membrane Na(+)-H+ exchanger. Inhibition of Na(+)-H+ exchange by amiloride (1 mM) added to the mucosal solution decreased Jms of SCFA in caecum and in proximal colon, but had no major effect in distal colon. 3. In distal colon Jms exceeds Jsm and thus a net absorption of SCFA was observed. Jms is Na+ independent and coupled to the activity of the apical membrane K(+)-H(+)-ATPase. Inhibition of the K(+)-H(+)-ATPase by addition of ouabain (0.1 mM) to the mucosal solution diminished Jms in the distal colon; in the caecum and proximal colon ouabain had no effect on Jms. 4. Neither amiloride nor ouabain caused major changes in Jsm in any of the large intestinal segments. 5. In conclusion, absorption of SCFA, e.g. Jms, in all large intestinal segments is related to the presence and activity of H+ secreting systems located in the apical membrane of colonocytes. In the caecum and proximal colon the predominant system appears to be Na(+)-H+ exchange, and in the distal colon K(+)-H(+)-ATPase. Supply of H+ ions allows protonation of SCFA anions and subsequent permeation by non-ionic diffusion across the apical membrane. These mechanisms account for 35, 40-50 and 60-80% of SCFA transport in the caecum, the proximal and the distal colon of guinea-pig, respectively. The nature of the Na(+)-dependent secretory pathway in the caecum and proximal colon remains to be determined.

Acetates↗
PubMed1992

Segmental differences of short-chain fatty acid transport across guinea-pig large intestine.

Unidirectional fluxes of short-chain fatty acids (SCFAs) were measured under short-circuit current conditions across guinea-pig caecum, proximal and distal colon. Fluxes increased linearly with concentration. In the caecum with equal concentrations on both sides of the mucosa the serosal-to-mucosal (sm) fluxes were nearly twice the mucosal-to-serosal (ms) fluxes for all SCFAs; in the distal colon ms fluxes were always higher than sm fluxes. Thus, in the caecum the net effect was secretion while in the distal colon net absorption occurred. In caecum, ms fluxes decreased with chain length while sm fluxes were similar for the three fatty acids, acetic, propionic and butyric acid. In the distal colon both unidirectional fluxes increased with chain length. Fluxes across the mucosa of the proximal colon were intermediate to those in caecum and distal colon. A paracellular transport of short-chain fatty acids is not present. The results indicate that other processes are involved in transcellular transport of SCFA besides non-ionic diffusion.

Acetates↗
PubMed1992

[Physical performance--a comparison between horses and men].

During heavy exercise horses can increase oxygen uptake compared to resting conditions considerably more than man. Processes involved like respiration, heart size, cardiac output, oxygen transport capacity of the blood and oxygen release in the capillaries are discussed. Besides these advantages in the aerobic metabolism conditions for the anaerobic metabolism are also more advantageous in horses than in man. The portion of fast contracting muscle fibers with little fatigue-resistance and also some of the enzymes required for the anaerobic metabolism are higher in horses.

Animals↗
PubMed1990

The effect of size and density on mean retention time of particles in the gastrointestinal tract of sheep.

The selective retention of particles in the reticulo-rumen and in the gastrointestinal tract distal to the reticulo-rumen was studied in fistulated sheep maintained on a roughage diet. Polyethylene glycol and plastic particles of different lengths (1 and 10 mm) and densities (0.92, 1.03, 1.22 and 1.44 g/ml) were either fed or were introduced into the omasum. The mean retention time in the reticulo-rumen (MRTRR) of 1 mm long particles with a density of approximately 1.0 g/ml was about 67 h, that is eight times longer than the MRTRR of fluid; the heavier particles were retained only three times longer than fluid. Particles with a length of 10 mm were retained in the reticulo-rumen 19-28 h longer than 1 mm long particles of the same density. Particles with a length of 10 mm were reduced to smaller particles (0.5-4 mm) due to rumination. Multiple regression analysis indicated that particle density and particle size accounted for 59 and 28% of the total variation of MRTRR respectively. The mean retention time distal to the reticulo-rumen (MRTGut) of 1 and 10 mm long particles with a density near 1.0 g/ml was 18-19 h, similar to that of fluid (16 h). The heavier particles were retained about 3-8 h longer.

Animals↗
PubMed1990

Factors affecting the potassium concentration at the mucosal surface of the proximal and the distal colon of guinea pig.

K+ concentrations were measured in vitro with K+ sensitive microelectrodes in the microclimate at the luminal cell surface of the colon of guinea pigs. The serosal K+ concentration was mostly 5.4 mmol/1, the mucosal K+ concentrations were changed (0, 5, 50, or 70 mmol/l). Under control conditions K+ concentrations in the microclimate of the proximal colon were also low (6-9 mmol/l) and rather independent from K+ concentrations in the bulk luminal solution. In the distal colon K+ concentrations in the microclimate increased from 3.7 mmol/l when no K+ was in the luminal solution, up to 22 mmol/l when the mucosal K+ concentrations was 70 mmol/l. Attempts to decrease K+ conductance of the apical membrane with Ba++, to impair K+ transport with ouabain and to increase the paracellular shunt with deoxycholic acid did not affect K+ concentrations in the microclimate of the proximal colon but decreased K+ concentrations in the distal colon. When valinomycin or triaminopyrimidine were added to the mucosal solution at high K+ concentrations in the luminal solutions the K+ concentration in the microclimate was raised. At low luminal K+ concentrations valinomycin had no effect, triaminopyrimidine significantly diminished K+ concentrations at the cell surface. Regional differences in paracellular shunt conductance and in the preepithelial diffusion barrier are thought to be responsible for the observed differences between the proximal and the distal colon. Obviously, however, further unknown mechanisms have to be involved.

Animals↗
PubMed1989

Absorption of dissociated and undissociated short-chain fatty acids across the colonic epithelium of guinea-pig.

Diffusion potentials for Na+, Cl-, acetate (Ac-), propionate (Pr-) and butyrate (Bu-) across the isolated epithelium of the proximal and the distal colon of guinea-pig were measured with flowing electrodes in Ussing chambers. Permeabilities of the anions are expressed in relation to the permeability of sodium. Unidirectional fluxes of Na+ and short-chain fatty acids (SCFAs) were estimated. Fluxes of SCFA anions and of undissociated SCFAs were calculated from relative permeabilities and flux values. In the proximal colon of guinea-pig 50% of SCFAs were transported in the dissociated and 50% in the undissociated form; transport rates of the three SCFAs were similar. In the distal colon SCFA transport was based primarily on diffusion of the free acids; the ratios of fluxes were: HAc/Ac- = 2.4; HPr/Pr- = 6.9; HBu/Bu- = 9.3, and transport rates increased with chain length of the SCFA.

Animals↗
PubMed1989

Is gastro-intestinal mucus an ion-selective barrier?

The mucus layer at the epithelial surface seems to be responsible for the formation of a microclimate in which the concentrations of H+, K+, Na+, and Cl- are rather constant. It is possible that this is not due simply to an unstirred layer effect, but also to a higher diffusion resistance of mucus. Flux measurements revealed that sodium and potassium permeabilities in mucus are 50% lower than those in saline. Dilution and biionic diffusion potentials indicated a higher relative permeability of mucus for sodium and potassium than for chloride. Thus mucus represents a diffusion barrier, slightly more permeable for cations than for anions.

Animals↗
PubMed1988

Fermentation of polysaccharides and absorption of short chain fatty acids in the mammalian hindgut.

1. Hindgut volume varies considerably between carnivores, omnivores and herbivores. But a common feature in all mammals is an extensive microbial fermentation of polysaccharides in the hindgut. Large amounts of short chain fatty acids (SCFA) are produced. Total concentrations of SCFA are generally ca 100 mmol/l. SCFA metabolism contributes considerably to the energy metabolism of the animal. 2. In hindgut fermenting herbivores ileal outflow provides fluid and the buffering capacity essential for microbial metabolism. 3. SCFA are rapidly absorbed. Absorption is passive and, unexpectedly, nearly independent from luminal pH. This is attributed to the presence of a constant pH-microclimate at the epithelial surface. 4. The permeability of the proximal compared to the distal colon of guinea pig is higher for acetate, equal for propionate and lower for butyrate. This difference is due to partial absorption of SCFA in the dissociated form in the proximal segment. 5. Protons required for SCFA transport in the undissociated form may be partially explained by HCO3 accumulation or by Na-H exchange. Findings are controversial.

Animals↗
PubMed1988

Concentration- and pH-dependence of short-chain fatty acid absorption in the proximal and distal colon of guinea pig (Cavia porcellus).

1. Absorption of short-chain fatty acids (SCFA), acetate, propionate, and butyrate was studied in simultaneously perfused proximal and distal segments of the colon in anaesthetized guinea pigs. 2. Acetate absorption rates increased linearly with concentration in both segments, indicating passive transport. 3. SCFA-clearance was independent of bulk luminal pH between pH 6.2 and 8.1 in the proximal and distal colon. SCFA-clearance was slightly higher in both segments at pH values less than 6. 4. The unexpected pH-independence of SCFA-absorption is attributed to the existence of a constant pH-microclimate at the surface of the colonic epithelium. 5. Relative permeabilities to acetate:propionate:butyrate were estimated as 1:1.19 +/- 0.03:1.27 +/- 0.05 in the proximal colon and 1:2.31 +/- 0.39:3.50 +/- 0.61 in the distal colon. The significance of these findings with respect to the pH-partition hypothesis are discussed.

Acetates↗