Gastrointestinal processing of Na+, Cl-, and K+ during digestion: implications for homeostatic balance in freshwater rainbow trout

The role of the gastrointestinal tract in maintaining ionic homeostasis during digestion, as well as the relative contribution of the diet for providing electrolytes, has been generally overlooked in many aquatic species. An experimental diet that contained an inert reference marker (lead-glass beads) was used to quantify the net transport of Na(+), K(+), and Cl(-) during the digestion and absorption of a single meal (3% ration) by freshwater rainbow trout (Oncorhynchus mykiss). Secretion of Cl(-) into the stomach peaked at 8 and 12 h following feeding at a rate of 1.1 mmol.kg(-1).h(-1), corresponding to a theoretical pH of 0.6 in the secreted fluid (i.e., 240 mmol/l HCl). The majority ( approximately 90%) of dietary Na(+) and K(+) was absorbed in the stomach, whereas subsequent large fluxes of Na(+) and Cl(-) into the anterior intestine corresponded to a large flux of water previously observed. The estimated concentration of Na(+) in fluids secreted into the anterior intestine was approximately 155 mmol/l, equivalent to reported hepatic bile values, whereas the estimated concentration of Cl(-) ( approximately 285 mmol/l) suggested seepage of HCl acid from the stomach in advance of the chyme front. Net absorption of K(+) in the stomach occurred following the cessation of Cl(-) secretion, providing indirect evidence of K(+) involvement with HCl acid production. Overall, 80-90% of the K(+) and Cl(-) contents of the meal were absorbed on a net basis, whereas net Na(+) absorption was negligible. Chyme-to-plasma ion concentration gradients were often opposed to the direction of ion transport, especially for Na(+) and Cl(-).     

Cation and ATP content of ferret red cells

Ferret red cells were shown to have the following properties: 1. They have a high sodium (96 mmol/l cell) and low potassium (3.9 mmol/l cell) content. 2. The majority do not appear to have an active sodium pump in their membranes. 3. Their membranes are highly permeable to rubidium indicating that they are probably also highly permeable to potassium. 4. Their magnesium (3.01 mmol/l cell) and calcium (0.01 mmol/l cell) contents are similar to those of red cells from other species. 5. Their ATP content (0.6 mmol/l cell) is similar to that of cat and dog red cells and is sufficiently high to activate known ion transport systems.     

Differences in the range of faecal dry matter content between feeding types of captive wild ruminants

Mammal Research - The dry matter content of 245 faecal samples of 81 species of captive wild ruminants was investigated. Samples were taken from 10 different zoos from temperate climate during the...     

Estimation of short-chain fatty acid production from protein by human intestinal bacteria based on branched-chain fatty acid measurements

Abstract The importance of protein breakdown and amino acid fermentation in the overall economy of the large intestine has not been quantitated. We have therefore measured the production of branched chain-fatty acids (BCFA) both in vitro and in vivo in order to estimate the contribution of protein to fermentation.
In vitro batch-culture studies using human faecal inocula showed that short-chain fatty acids (SCFA) were the principal end products formed during the degradation of protein by human colonic bacteria. Approximately 30% of the protein broken down was converted to SCFA. Branched-chain fatty acids (BCFA) constituted 16% of the SCFA produced from bovine serum albumin and 21% of the SCFA generated when casein was the substrate. BCFA concentrations in gut contents taken from the human proximal and distal colons were on average, 4.6 and 6.3 mmol kg⁻¹ respectively, corresponding to 3.4% and 7.5% of the total SCFA. These results suggest that protein fermentation could potentially account for about 17% of the SCFA found in the caecum, and 38% of the SCFA produced in the sigmoid/rectum. Measurements of BCFA in portal and arterial blood taken from individuals undergoing emergency surgery indicated that net production of BCFA by the gut microflora was in the region of 11.1 mmol day⁻¹, which would require the breakdown of about 12 g of protein. These data highlight the role of protein in the colon and may explain why many colonic diseases affect mainly the distal bowel.     

Estimation of short-chain fatty acid production from protein by human intestinal bacteria based on branched-chain fatty acid measurements

Abstract The importance of protein breakdown and amino acid fermentation in the overall economy of the large intestine has not been quantitated. We have therefore measured the production of branched chain-fatty acids (BCFA) both in vitro and in vivo in order to estimate the contribution of protein to fermentation.
In vitro batch-culture studies using human faecal inocula showed that short-chain fatty acids (SCFA) were the principal end products formed during the degradation of protein by human colonic bacteria. Approximately 30% of the protein broken down was converted to SCFA. Branched-chain fatty acids (BCFA) constituted 16% of the SCFA produced from bovine serum albumin and 21% of the SCFA generated when casein was the substrate. BCFA concentrations in gut contents taken from the human proximal and distal colons were on average, 4.6 and 6.3 mmol kg⁻¹ respectively, corresponding to 3.4% and 7.5% of the total SCFA. These results suggest that protein fermentation could potentially account for about 17% of the SCFA found in the caecum, and 38% of the SCFA produced in the sigmoid/rectum. Measurements of BCFA in portal and arterial blood taken from individuals undergoing emergency surgery indicated that net production of BCFA by the gut microflora was in the region of 11.1 mmol day⁻¹, which would require the breakdown of about 12 g of protein. These data highlight the role of protein in the colon and may explain why many colonic diseases affect mainly the distal bowel.     

Dietary protein reduction in sheep and goats: different effects on <Emphasis Type="SmallCaps">l</Emphasis>-alanine and <Emphasis Type="SmallCaps">l</Emphasis>-leucine transport across the brush-border membrane of jejunal enterocytes

It was the aim of this study to examine the potential regulatory effects of a long-term low dietary protein supply on the transport capacity of the jejunal brush-border membrane for amino acids. For this purpose, we used the neutral amino acids L-alanine (representative for nonessential amino acids) and L-leucine (representative for essential amino acids) as model substances. Ten sheep lambs, 8 weeks of age and 19-27 kg body weight, were allotted to two dietary regimes with either adequate or reduced protein supply which was achieved by 17.9% and 9.7% of crude protein in the concentrated feed, respectively. The feeding periods were 4-6 weeks in length. Similarly, eight goat kids of 5-7 weeks of age and 8-14 kg body weight were allotted to either adequate (crude protein 20.1%, feeding period 9-12 weeks) or reduced protein supply (10.1%, feeding period 17-18 weeks). Dietary protein reduction in lambs caused a significant body weight loss of 0.6 +/- 0.7 kg, whereas the body weight in control animals increased by 1.9 +/- 0.7 kg (P<0.05). Plasma urea concentrations decreased significantly by 60% (low protein 2.3 +/- 0.1 versus control 5.7 +/- 0.2 mmol l(-1), P<0.001). In kids, reduction of dietary protein intake led to significant decreases of the daily weight gain by 48% from 181 +/- 8 g to 94 +/- 3 g (P<0.001) and daily dry matter intake by 27% from 568 +/- 13 g to 417 +/- 6 g (P<0.01). Respective urea concentrations in plasma were reduced by 77% from 5.2 +/- 0.4 to 1.2 +/- 0.2 mmol l(-1) (P<0.01). Kinetic analyses of the initial rates of alanine uptake into isolated jejunal brush-border membrane vesicles from sheep and goats as affected by low dietary protein supply yielded that the apparent Km was neither significantly different between the species nor significantly affected by the feeding regime thus ranging between 0.12 and 0.16 mmol.l(-1). Reduction of dietary protein, however, resulted in significantly decreased Vmax values of the transport system by 25-30%, irrespective of the species. Kinetic analyses of the initial rates of leucine uptake into jejunal brush-border membrane vesicles from sheep and goats yielded that leucine uptake was mediated by Na+-dependent as well as Na+-independent processes. Similar to alanine, apparent Km values of leucine uptake were neither different between the species nor affected due to low dietary protein and ranged between 0.08 and 0.15 mmol l(-1). In contrast to the alanine transport mechanism, dietary protein reduction resulted in increased Vmax values of Na+-dependent leucine transport by 53% in sheep and 230% in goats. Similarly, Na+-independent leucine uptake was stimulated by 85% and 200% in sheep and in goats, respectively. This study shows adaptation of amino acid absorption at the brush-border membrane level of jejunal enterocytes of small ruminants due to dietary protein reduction. Whereas the transport capacity for the nonessential amino acid alanine was reduced due to low dietary protein, the transport capacity for the essential amino acid leucine was markedly stimulated. From this, the involvement of rather different feedback mechanisms in adaptation of intestinal amino acid transport mechanisms has to be discussed.     

Water balance and osmoregulation in Stenocara gracilipes,a wax-blooming tenebrionid beetle from the Namib Desert

Dehydration (10 days at 27 degrees C) of the Namib tenebrionid Stenocara gracilipes resulted in a rapid weight loss (17.5%), and a substantial decline in haemolymph volume (72%). Although the lipid content decreased significantly, metabolic water production was insufficient to maintain total body water (TBW). Rehydration (no food) resulted in increases in haemolymph volume, body weight (sub-normal), and TBW to normality. Haemolymph osmolality, sodium, potassium, chloride, amino acids, and sugars (trehalose and glucose), were all subject to osmoregulatory control during both dehydration and rehydration. Major osmolar effectors in this species are sodium, chloride, and amino acids, with most of the contribution to regulation of haemolymph osmolality coming from changes in the levels of these constituents. Changes in amino acid levels are not the result of interchange with soluble protein during dehydration (the possibility exists during extended rehydration, however). Despite faecal losses of sodium being low (8.2% of that removed from the haemolymph during dehydration), sodium concentrations do not return to normal during rehydration. Chloride concentrations increase supra-normally when access to water is allowed, and remain elevated throughout the rehydration period. Although faecal loss of potassium greatly exceeded the amount removed from the haemolymph (by approximately 1.8 times), haemolymph potassium levels were strongly regulated during rehydration. S. gracilipes demonstrates an exquisite capacity to regulate haemolymph osmolality under conditions of both acute water-shortage and -abundance. Together with an efficient water economy (drinking when fog-water is available, and a superb water conservation mechanism in the form of wax-bloom production), this must serve to contribute to long-term survival of this species in an otherwise harsh abode.     

Properties of Na+-dependent nucleoside transport in the proximal and distal small intestine of cows

Large amounts of nucleic acids associated with rumen microorganisms are digested in the proximal part of the small intestine of ruminants. We studied how the proximal-distal gradient in nucleic acid digestion is related to activity of Na(+)-nucleoside transporters in brush border membrane vesicles isolated from the proximal and distal small intestine of cows. Two Na(+)-dependent nucleoside transporters with overlapping substrate specificity were shown to be present at the two intestinal sites, one for pyrimidine nucleosides and one for purine nucleosides. Affinity constants (K(m)-values) for both thymidine and guanosine transport were similar at the two intestinal sites, while transport capacity (V(max)) was 2-3 times higher in the proximal than in the distal small intestine. Glucose and alpha-methyl-D-glucoside (0.1 mmol/l or 2 mmol/l) inhibited transport of thymidine and guanosine markedly only in the proximal small intestine. It is concluded that absorption of nucleosides by the two Na(+)-nucleoside transporters reflects the proximal-distal gradient in nucleic acid digestion.     

Competition for hydrogen between sulphate-reducing bacteria and methanogenic bacteria from the human large intestine

Sulphate-reducing activity in human faecal slurries was followed by measuring sulphide production. Sulphate-reducing bacteria (SRB) were found to outcompete methanogenic bacteria (MB) for the mutual substrate hydrogen in faecal slurries from methane- and non-methane-producing individuals mixed together. When molybdate (20 mmol/l) was added to these slurries, sulphate reduction was inhibited and methanogenesis became the major route of electron disposal. Sulphide production was stimulated by the addition of 20 mmol/l sulphate in non-methanogenic but not in methanogenic slurries. In methanogenic slurries that contained the methanogen inhibitor 2-bromoethanesulphonic acid (BES), hydrogen accumulated whilst sulphide levels were unaffected, confirming the absence of SRB in methanogenic faeces. The addition of nitrate (10 mmol/l) to faecal slurries completely inhibited methanogenesis but only slightly reduced sulphate reduction. The sulphated mucopolysaccharides, chondroitin sulphate and mucin, strongly stimulated sulphide production in non-methanogenic faecal slurries only, suggesting that these substances may be a potential source of sulphate in the large gut.     

Lactate is mainly fermented to butyrate by human intestinal microfloras but inter-individual variation is evident

AIM: To assess the role of lactate as a precursor for butyrate biosynthesis in human colonic microflora. METHODS AND RESULTS: Three human faecal microfloras were incubated in vitro with media supplemented with 30 mmol l(-1) unenriched or 13C-enriched lactate. Lactate metabolism and short-chain fatty acid (SCFA) production were quantified. Lactate conversion to butyrate was investigated by gas chromatography-mass spectrometry and the pathways involved were identified by 13C nuclear magnetic resonance spectroscopy. All human faecal microfloras rapidly and completely fermented lactate, yielding approx. 19 mmol l(-1) total SCFAs. However, the SCFA composition varied markedly between microfloras. Butyrate was the main end-product for two microfloras but not for the third (60 and 61%vs 27% of the net concentration of SCFA produced respectively). The latter was typified by its ability to produce propionate as a major product (37%), and valerate (3%). 13C-Labelling showed that butyrate was produced through the acetyl-CoA pathway and that the three microfloras possessed significant differences in their metabolic pathways for lactate consumption. CONCLUSIONS: In contrast to the ruminal microflora, the human intestinal microflora can utilize both d- and l-lactate as precursors for butyrate synthesis. Inter-individual variation is found. SIGNIFICANCE AND IMPACT OF THE STUDY: This study suggests that the butyrogenic capability of colonic prebiotics could be related to lactate availability. These findings will direct the development of selection strategies for the isolation of new butyrate-producing bacteria among the lactate-utilizing bacteria present in the human intestinal microfloras.     

Nutrient concentrations in murine follicular fluid and the female reproductive tract

The culture of murine oocytes and preimplantation embryos in vitro has been used successfully for many years. However, this practice can result in cellular stress and reduced viability. Since this phenomenon is partly attributable to differences in nutrient composition between culture media and maternal tract fluids, we determined the concentrations of glucose, pyruvate, lactate and 19 amino acids in murine preovulatory follicles and oestrous oviductal and uterine fluids. Follicular fluids were aspirated from hyperstimulated ovaries, whereas oviductal fluids (with/without oocyte-cumulus complexes) and uterine fluids were collected from naturally cycling animals. Glucose, pyruvate and lactate concentrations were analysed using ultramicrofluorometric methods, whilst amino acid profiles were determined by reverse-phase high performance liquid chromatography. Mean glucose concentrations in follicular, oviduct (with/without cumulus cells) and uterine fluids were 0.46, 1.09/1.65 and 0.61 mmol l(-1), respectively. Pyruvate concentrations were 0.38, 0.37/0.17 and 0.25 mmol l(-1), respectively, and lactate concentrations were 17.34, 10.92/11.68 and 9.41 mmol l(-1), respectively. Oviductal pyruvate concentration was significantly higher, and glucose significantly lower, in the presence of cumulus cells. Taurine, glycine, alanine, glutamine and glutamate were the major amino acids detected. Concentrations of amino acids differed among fluids, with highest levels being found in the oviduct. The follicular fluid and tract nutrient profiles differed from those of murine maturation, fertilisation and embryo culture media. These data extend our understanding of cellular metabolism and of nutritional environments of the oocyte and early embryo as they progress along the reproductive tract in vivo. These results may also contribute to the formulation of nutritionally more physiological media for mouse oocyte maturation and embryo culture.     

Competition for hydrogen between sulphate-reducing bacteria and methanogenic bacteria from the human large intestine

Sulphate-reducing activity in human faecal slurries was followed by measuring sulphide production. Sulphate-reducing bacteria (SRB) were found to outcompete methanogenic bacteria (MB) for the mutual substrate hydrogen in faecal slurries from methane- and non-methane-producing individuals mixed together. When molybdate (20mmol/l) was added to these slurries, sulphate reduction was inhibited and methanogenesis became the major route of electron disposal. Sulphide production was stimulated by the addition of 20 mmol/1 sulphate in non-methanogenic but not in methanogenic slurries. In methanogenic slurries that contained the methanogen inhibitor 2-bromoethanesulphonic acid (BES), hydrogen accumulated whilst sulphide levels were unaffected, confirming the absence of SRB in methanogenic faeces. The addition of nitrate (10 mmol/l) to faecal slurries completely inhibited methanogenesis but only slightly reduced sulphate reduction. The sulphated mucopolysaccharides, chondroitin sulphate and mucin, strongly stimulated sulphide production in non-methanogenic faecal slurries only, suggesting that these substances may be a potential source of sulphate in the large gut.     

Cationic hydrogen exchanges in the reticulo-rumen and their significance in ruminants

Up-to-date experimental results on mechanisms and physiological significance of mineral cations absorption in the reticulo-rumen of ruminants are observed in the review. Up to 90% of sodium, 100% of potassium and calcium and about 30-60% of magnesium pass across epithelium of the reticulo-rumen of domestic ruminants by electroneitral way through cation per hydrogen exchanges. In wild ruminant (reindeer) the item for sodium is up to 100%. Intracellular hydrogen ions are available due to carbonic anhydrase I function. The exchanges have great significance for the animals. The first, their organisms get cations mainly by metabolic products using. The second, hydrogen ions excretion is necessary for reticulo-rumen epithelial cells successful proliferation. The third, hydrogen ions excretion may be considered as a excretory mechanism of metabolic acidosis compensation in the digestive tract of ruminants. These moments may be observed as physiological mechanisms of adaptation of wild ruminants to seasonal dynamic of nutrition.     

Protein-losing enteropathy and malabsorption in acute measles enteritis.

Gastrointestinal protein loss and xylose and lactose absorption were both abnormal in underweight children with acute measles and diarrhoea. The protein loss was equivalent to a mean absolute albumin loss of 1.68 plus or minus 0.21 g/day, while the mean one-hour blood xylose level was 0.93 plus or minus 0.38 mmol/l (14.0 plus or minus 5.7 mg/100 ml) in the acute stage and 1.71 plus or minus 0.43 mmol/l (25.6 plus or minus 6.5 mg/100 ml) after recovery (P less than 0.01). Lactose intolerance was found in four children out of 17 tested. Thus faecal protein loss and malabsorption may contribute significantly to the development of malnutrition after measles.     

Potassium conductance in straight proximal tubule cells of the mouse. Effect of barium, verapamil and quinidine

The present study has been performed to test for the influence of verapamil and quinidine on the potential difference across the basolateral cell membrane (PDbl) and on the basolateral potassium conductance of isolated perfused segments of the mouse proximal tubule. PDbl was recorded continuously with conventional microelectrodes during rapid alterations of bath or luminal perfusate composition. The contribution of the basolateral potassium conductance to the conductance of both cell membranes (tk) was estimated from the effects of altered bath potassium concentration on PDbl. Under control conditions tk approaches 0.8, i.e. the basolateral cell membrane is mainly conductive to potassium. Neither quinidine nor verapamil affect PDbl at concentrations below 10 mumol/l. At higher concentrations both substances depolarize the basolateral cell membrane mimicking the effect of 1 mmol/l barium. In the presence of 0.1 mmol/l verapamil tk is virtually abolished at 5 to 10 mmol/l bath potassium concentration but is almost unaffected at bath potassium concentrations between 20 and 40 mmol/l. 1 mumol/l ionophore A-23187 does not change the depolarizing effect of 0.1 mmol/l verapamil on cell membrane potential. In the presence of 0.1 mmol/l quinidine, tk is reduced to some 50%, irrespective of the bath potassium concentration. It is concluded that the potassium conductance in straight proximal tubules is inhibited not only by barium but as well by high concentrations of verapamil and quinidine. The effect is probably direct and not related to alterations in the intracellular calcium activity.     

Elaphostrongylus cervi in a population of red deer (Cervus elaphus) and evidence of cerebrospinal nematodiasis in small ruminants in the province of Varese, Italy

Thirty-one faecal samples were collected from red deer in the northern area of Varese, in the Italian region of Lombardy, between August and October 2008. The animals had either been hunted or accidently killed. Examination for internal parasites showed a prevalence of 45.2% for Elaphostrongylus cervi larvae and species identification was confirmed by polymerase chain reaction (PCR). Ninety-seven faecal samples were also collected from two goat flocks grazing in the same area between December 2007 and May 2008. These showed a prevalence of 74.7% for lungworms. Furthermore, the central nervous systems from five goats and one sheep from this area with a history of neurologically related lameness were examined. Histopathology confirmed E. cervi cerebro-spinal nematodiasis in five cases out of six. This study demonstrates E. cervi transmission from wild to domestic ruminants when the animals graze in the same area, and the possible occurrence of clinical disease in infected goats and sheep associated with high prevalence in deer.     

Faecal particle size in free-ranging primates supports a ‘rumination’ strategy in the proboscis monkey (<Emphasis Type="Italic">Nasalis larvatus</Emphasis>)

In mammalian herbivores, faecal particle size indicates chewing efficiency. Proboscis monkeys (Nasalis larvatus) are foregut fermenters in which regurgitation and remastication (i.e. rumination) was observed in the wild, but not with the same consistency as found in ruminants and camelids. To test whether this species has exceptional chewing efficiency among primates, as ruminants have among mammals, we compared faecal particle size in free-ranging specimens with those of 12 other primate species. The discrete mean faecal particle size (dMEAN) increased with body mass (M) as dMEAN (mm) = 0.65 (95 % confidence interval 0.49–0.87) M ^{0.33 (0.23–0.43)} in simple-stomached species. At 0.53 ± 0.09 mm, dMEAN of proboscis monkeys was particularly small for their average M (15 kg) and significantly smaller than values of two other foregut fermenting primate species. While we cannot exclude other reasons for the exceptional chewing efficiency in proboscis monkeys, this represents circumstantial evidence for regular use of rumination in this species. Thus, proboscis monkeys might be a model for convergent evolution towards rumination in a non-ungulate taxon.     

Seroepidemiology of chlamydial infections of wild ruminants in Spain

Chlamydial infections were determined serologically among wild ruminants in the Nature Park of the Sierras de Cazorla, Segura y Las Villas (CNP; Spain). Sampling was done during the period from 1990-95. There were 1,244 blood samples collected, consisting of 490 from fallow deer (Dama dama), 343 from mouflon (Ovis mussimon), 283 from red deer (Cervus elaphus) and 128 from Spanish ibex (Capra pyrenaica). Specific complement-fixing antibodies of Chlamydia spp. were detected by means of microtechnique, using lipopolysaccharide antigen. The relationship of biological (species, sex, age), temporal (year) and territorial (central and peripheral areas) factors to seropositive prevalence was examined, and preliminary data were collected on whether or not sheep and goat herds grazing in the peripheral areas of the park also were infected with Chlamydia spp. Chlamydiosis was common in the four species of wild ruminants in the CNP in all the years studied. The prevalence of Chlamydia sp. in mouflon (37%) was significantly greater than in fallow deer (30%), and both had a significantly higher prevalence rate than Spanish ibex and red deer (both 24%). The four species of wild ruminants were similar in that they act as reservoirs of Chlamydia spp., although their receptivity may be different, and the infection can certainly be maintained among these animals by intra-group transmission. The differences in prevalences and geometric mean titers (GMT), both between the sexes (male versus female) and between different ages (adult versus juvenile), were insignificant in all four species. For all species of wild ruminants both prevalence rates and GMTs were greater in populations occupying the peripheral areas of the park than in those inhabiting the central area. Herds of sheep and goats had a high prevalence of chlamydiosis. Intertransmission of Chlamydia sp. between wild and domestic ruminants occurred through grazing on the same pastures. The highest mean prevalence (44%) of patent infections (CFT titers of > or =1:80) was detected in red deer, although this frequency was not significantly different from those observed in mouflon (39%), Spanish ibex (38%), and fallow deer (37%). The proportion of patent infection was higher in females than in males, and none of the juveniles (<2-yr-old) showed patent infections. The prevalence of predicted patent chlamydial infections was always higher in the peripheral areas of the park, although only among mouflon and fallow deer were the differences statistically significant.