Salt and water excretion by birds: the lower intestine as an integrator of renal and intestinal excretion

Characterization of Cecal Smooth Muscle Contraction in Laying Hens

The ceca play an important role in the physiology of the gastrointestinal tract in chickens. Nevertheless, there is a gap of knowledge regarding the functionality of the ceca in poultry, especially with respect to physiological cecal smooth muscle contraction. The aim of the current study is the ex vivo characterization of cecal smooth muscle contraction in laying hens. Muscle strips of circular cecal smooth muscle from eleven hens are prepared to investigate their contraction ex vivo. Contraction is detected using an isometric force transducer, determining its frequency, height and intensity. Spontaneous contraction of the chicken cecal smooth muscle and the influence of buffers (calcium-free buffer and potassium-enriched buffer) and drugs (carbachol, nitroprusside, isoprenaline and Verapamil) affecting smooth muscle contraction at different levels are characterized. A decrease in smooth muscle contraction is observed when a calcium-free buffer is used. Carbachol causes an increase in smooth muscle contraction, whereas atropine inhibits contraction. Nitroprusside, isoprenaline and Verapamil result in a depression of smooth muscle contraction. In conclusion, the present results confirm a similar contraction behavior of cecal smooth muscles in laying hens as shown previously in other species.

Morphological Characteristics of the Developing Cecum of Japanese Quail (Coturnix coturnix japonica)

The current investigation was carried out to record the final stages of the development of both middle and distal parts of quail ceca, Coturnix coturnix japonica to understand the role of ceca in digestion, immune system, and absorption. The cellular and subcellular structures, including epithelial cell height, microvillus surface area, the proportion of goblet cells, the thickness of muscle layer, and cecum diameter showed great variations during the development. An undeveloped smooth muscularis mucosa was observed for the first time on the ED5. Primordia of glands were observed on the ED7. On the ED15, the middle part exhibited two shapes of mucosal villi: tongue-shaped villi and U-shaped. The plicae and crypts of Lieberkühn were demonstrated on the hatching day. The lymphatic tissues appeared in the wall of both parts of the ceca at the 4 weeks of age. Scanning electron microscopy revealed a great difference in the mucosal surface between different regions. Telocytes were observed in-between the muscle fibers and formed a network during the post-hatching period. Because of fermentation and other bacterial or chemical processes that have been shown to occur in the ceca, this study supports two hypotheses: the cecal development is related to diet and the cecal epithelium act as a site for primary absorption of nutrients or for re-absorption of electrolytes or amino acids derived from the urine.

Phylogeny and herbivory are related to avian cecal size

Avian ceca, a pair of blind sacs arising from the junction of the ileum and colon, are homologous to the cecum in mammals. Cecal size is hypothesized to depend on dietary proclivities and pressures, with faunivorous species having short ceca, whereas herbivorous species have long ceca. Previous tests of this hypothesis, however, did not account for phylogenetic pseudoreplication among closely related taxa. We collated published data on cecal length, dietary category, flying ability, and body mass from 155 avian taxa. Character states were mapped onto a phylogenetic framework, and the permutation tail probability test was used to detect phylogenetic signal in each character. Phylogenetic signal is significant among the characters. As with the cecoappendicular complex in mammals, closely-related birds tend to have similar cecal length. To account for phylogenetic pseudoreplication, we performed phylogenetic generalized least squares regression on cecal length and body mass with dietary category, superordinal-level clade, and flying ability as cofactors. The best-fitting regression model supports the dietary hypothesis for the avian cecum. Among sampled birds of comparable body mass, mean cecal length is significantly longer in herbivorous species than in carnivorous ones (p = 0.008), presumably allowing the extraction of nutrients without the burden of fermenting bulky masses of dietary fiber. Exceptions to this trend, however, suggest that avian ceca are functionally complex and may have additional roles in water balance and nitrogen recycling.

Transport characteristics and morphology of the colon and coprodeum in two wild birds of different habitats, the rock ptarmigan (Lagopus mutus) and the common murre (Uria aalge)

Dietary salt intake in domestic fowl affects epithelial transport and morphology of the lower intestine (colon and coprodeum). This study investigated lower intestinal morphology and transport activity in two wild bird species with natural diets containing either low or high salt. Tissues from rock ptarmigan (Lagopus mutus) and common murres (Uria aalge) were sampled for histology and electrophysiological analyses. The ptarmigan exists on a low salt diet, while the murre lives on a high protein and high salt diet. The ptarmigan colon and coprodeum had villi/folds and crypts and the epithelium contained absorptive epithelial cells, mitochondria-rich cells and goblet cells. The colon had significant amiloride-inhibitable Isc, 5-15 μA/cm(2), with no glucose-stimulated Isc, and no significant phloridzin inhibition. The coprodeum also had high amiloride-inhibitable Isc. This transport pattern corresponded to that of chickens on low-salt diets. However, the ptarmigan colon also had a significant lysine/leucine-stimulated Isc of 3±1.0 μA/cm(2). The short U. aalge colon was similar to that of ptarmigans, but with no villi. It demonstrated a significant lysine/leucine-stimulated Isc (11±3.5 μA/cm(2)) with no amiloride-inhibitable Isc, similar to the high-salt chicken colon, but with no Na(+)-glucose cotransport. The murre coprodeum was inert to all substances and showed high resistance (1000 Ω·cm(2)), with a multilayered squamous epithelium. Despite some variations possibly associated with dietary protein intake, we conclude that natural high and low salt diets in different avian species are associated with different lower intestinal transport patterns, providing for post-renal adjustments in ion and water excretion.

Adaptive strategies for post-renal handling of urine in birds

Birds are a diverse vertebrate class in terms of diet and habitat, but they share several common physiological features, including the use of uric acid as the major nitrogenous waste product and the lack of a urinary bladder. Instead, ureteral urine refluxes from the urodeum into the more proximal coprodeum and portions of the hindgut (colon or rectum and ceca). This presents a potential problem in that hyperosmotic ureteral urine in contact with the permeable epithelia of these tissues would counteract renal osmotic work. This review describes and provides examples of different strategies used by avian species to balance renal and post-renal changes in urine composition. The strategies described include: 1. a "reptilian" mode, with moderate renal concentrating ability, but high rates of post-renal salt and water resorption; 2. the "mammalian" strategy, in which the coprodeum effectively functions like a mammalian urinary bladder, preserving the osmotic concentrating work of the kidney; 3. an interaction strategy, in which post-renal transport processes are hormonally regulated in order to optimize renal function under varying conditions of salt or water stress; 4. the salt gland strategy seen in marine or estuarine birds with functional salt glands, in which post-renal transport mechanisms are used to conserve urinary water and to recycle excess NaCl to the nasal salt glands. Finally, we also describe some features of an as-yet unstudied group of birds, the birds of prey. At least some species in this group are relatively good renal concentrators, and would be predicted to have post-renal mechanisms to preserve this work. This new synthesis illustrates the marked diversity of adaptive mechanisms used by avian species to maintain osmotic homeostasis.

Expression and localization of an aquaporin-1 homologue in the avian kidney and lower intestinal tract

In birds, the kidneys and lower intestine function in osmoregulation. A 271-amino acid homologue to aquaporin-1 (AQP-1) was isolated from the kidneys, cecae, proximal and distal rectum, and coprodeum of the lower intestine in the house sparrow (Passer domesticus). This protein has six transmembrane domains connected by two cytoplasmic loops and three extracellular loops. It exhibits 94%, 88%, and 78% homology to AQP-1 sequences of chicken, human and toad, respectively. Many of the highly conserved amino acids that are characteristic of AQP-1 are found in the sparrow sequence. RT-PCR was performed and the presence of AQP-1 mRNA was detected in the kidney and all four regions of the lower intestine. Immunoblots of total protein identified a 28-kDa non-glycosylated AQP-1 band and a 56-kDa glycosylated AQP-1 band in the kidney and all four regions of the lower intestine. Immunohistochemistry demonstrated the presence of the AQP-1 protein within both the renal cortex and medulla. In the lower intestine, the protein was present in the proximal rectum, distal rectum, and in the coprodeum. As AQP-1 functions to allow water movement across mammalian cell membranes, its presence in water-permeable cells in a bird suggests it may have a similar function.

Endocrine regulation of ion transport in the avian lower intestine

The lower intestine (colon and coprodeum) of the domestic fowl maintains a very active, transporting epithelium, with a microvillus brush border, columnar epithelial cells, and a variety of transport systems. The colon of normal or high salt-acclimated hens expresses sodium-linked glucose and amino acid cotransporters, while the coprodeum is relatively inactive. Following acclimation to low salt diets, however, both colon and coprodeum shift to a pattern of high expression of electrogenic sodium channels, and the colonic cotransporter activity is simultaneously downregulated. These changes in the transport patterns seem to be regulated, at least in part, by aldosterone. Our recent work with this tissue has focused on whether aldosterone alone can account for the low salt pattern of transport. Other work has looked at the changes in morphology and in proportions of cell types that occur during chronic acclimation to high or low salt diets, and on a cAMP-activated chloride secretion pathway. Recent findings suggesting effects of other hormones on lower intestinal transport are also presented.

Location of the ureteral openings in the cloacas of tinamous, some ratite birds, and crocodilians: a primitive character

Cloacas of 67 avian species, of both sexes, from various habitats and differing dietary habits, were examined macro- and microscopically to investigate possible variation in the location of the ureteral openings. Differing from most birds studied, in adult male Rhea americana and several tinamous species the ureters were found to open into the coprodeum. In these species the urodeum receives only the vas deferens or oviduct. Similarly, in crocodiles Caiman crocodilus yacare, but not in lizards Tropidurus montanus and snakes Crotalus durissus terrificus, the ureters empty into the coprodeum. This similarity between ancient birds (ratites and tinamous) and crocodiles may indicate a primitive character linking reptiles and birds. This unusual position of the ureteral orifice can represent an adaptation to facilitate urine collection into the coprodeum and large intestine. Another possibility is that this variation in ureter position is a male reproductive strategy to avoid the mixture of urine and semen in the cloaca. There were no evident correlations between the location of the ureteral openings and the birds' habitat, diet, or histology of the coprodeal mucosa. The occurrence of a phallus in eight species of birds was detected, as well as a peculiar vascularization related to the coprodeal epithelium of anseriformes. Together, these data add to the scarce information about the morphophysiology of the avian cloaca, and also contribute to clarify avian phylogenetic linkages.

Dietary intake effects on arginine vasotocin and aldosterone in cloacal fluid of whitebellied sunbirds (Nectarinia talatala)

The main objective of this study was to determine whether or not the renal outputs of the osmoregulatory hormones arginine vasotocin (AVT) and aldosterone (ALDO) reflect the osmotic status of whitebellied sunbirds (Nectarinia talatala). The birds were fed a range of sucrose concentrations (from 0.07 to 2.5 mol/l, with osmolalities of 70 to approximately 5,800 mosM/kg), and adjusted their intakes so that they drank large volumes of dilute diets and small volumes of concentrated diets. Renal fluid outputs were appropriately regulated so that large volumes of cloacal fluid (CF) were voided on the dilute diets and small volumes on the concentrated diets. Accordingly, plasma AVT concentrations increased with increasing sugar concentration; however, AVT outputs in CF did not change in a similar manner, rather they decreased as dietary concentration increased. It was not possible to measure plasma ALDO concentrations in the small sunbirds because of insufficient blood samples available; however, ALDO outputs in CF did vary with the sucrose diets and renal function, being highest on the most concentrated diet. In addition ALDO output in CF fell markedly when sodium was added to the 0.5 mol/l sucrose diet. We conclude that in sunbirds fed increasingly concentrated sucrose solutions, changes in CF outputs of ALDO, but not AVT, appear to reflect the water flux and hydration state of these birds.

Effects of saline intake, sex, and season on Pekin duck osmoregulatory organ masses and comparison with wild Mallards

Osmoregulatory organ masses of freshwater Mallards (Anas platyrhynchos) do not differ between the sexes, but drinking saline induces changes that are sexually disparate in some organs. We examined relative size of organ masses of male and female Pekin ducks (that were domesticated from Mallards) and compared their responses to saline intake with those of Mallards. Organ masses of male and female Mallards do not differ in size. The liver and kidneys are heavier in female Pekin ducks and their digestive tract (except for the proventriculus and duodenum) is longer and heavier; male Pekin ducks have heavier salt glands. Mallards acclimated to saline drinking water have enlarged salt glands but not kidneys, adrenal glands, or Harderian glands, their proventriculus tends to be shorter and lighter, the jejunum longer in males, and the ileum longer and heavier in both sexes. In Pekin ducks that drink saline, the salt and Harderian glands are larger and their kidneys (but not adrenal glands) tend to be larger; the proventriculus is unaffected, but the small intestine is lighter, but not shorter, in females. Body, salt gland, Harderian gland, ventriculus, and duodenum masses vary seasonally in Pekin ducks. Discussion considers the effects of season and sex on relative organ masses and how saline-induced changes in them reflect domestication and may influence salt tolerance.

Regulation of salt gland, gut and kidney interactions

Marine birds can drink seawater because their cephalic 'salt' glands secrete a sodium chloride (NaCl) solution more concentrated than seawater. Salt gland secretion generates osmotically free water that sustains their other physiological processes. Acclimation to saline induces interstitial water and Na move into cells. When the bird drinks seawater, Na enters the plasma from the gut and plasma osmolality (Osm(pl)) increases. This induces water to move out cells expanding the extracellular fluid volume (ECFV). Both increases in Osm(pl) and ECFV stimulate salt gland secretion. The augmented intracellular fluid content should allow more rapid expansion of ECFV in response to elevated Osm(pl) and facilitate activation of salt gland secretion. To fully utilize the potential of the salt glands, intestinally absorbed NaCl must be reabsorbed by the kidneys. Thus, Na uptake at gut and renal levels may constrain extrarenal NaCl secretion. High NaCl intake elevates plasma aldosterone concentration of Pekin ducks and aldosterone stimulates intestinal and renal water and sodium uptake. High NaCl intake induces lengthening of the small intestine of adult Mallards, especially males. High NaCl intake has little effect on glomerular filtration rate or tubular sodium Na uptake of birds with competent salt glands. Relative to body mass, kidney mass and glomerular filtration rate (GFR) are greater in birds with salt glands than in birds that do not have them. Birds with salt glands do not change GFR, when they drink saline. Thus, their renal filtrate contains excess Na that is, in some species, almost completely renally reabsorbed and excreted in a more concentrated salt gland secretion. Na reabsorption by kidneys of other species, like mallards is less complete and their salt glands make less concentrated secretion. Such species may reflux urine into the hindgut, where additional Na may also be reabsorbed for extrarenal secretion. During exposure to saline, marine birds maintain elevated aldosterone levels despite high Na intake. Marine birds are excellent examples of physiological plasticity.

Do mammals, birds, reptiles and fish have similar nitrogen conserving systems?

Comparative physiological studies are a powerful tool for revealing common animal adaptations. Amino acid catabolism produces ammonia which is detoxified through the synthesis of urea (mammals, some fish), uric acid (birds), or urea and uric acid (reptiles). In mammalian herbivores and omnivores, urea nitrogen is salvaged by a series of steps involving urea transfer into the intestine, microbial mediated urea hydrolysis with synthesis of amino acids utilizing the liberated ammonia and transfer of the amino acids back to the host. A similar series of steps occur in omnivorous/granivorous and herbivorous birds, although in this case urine, containing uric acid, is refluxed directly into the intestine where microbes degrade the uric acid and utilize the liberated ammonia for amino acid synthesis. These amino acids are transferred back to the host. In reptiles and ureotelic fish not all of these steps have been experimentally confirmed. Reptiles like birds, reflux urine into the intestine where it is exposed to the microflora. However, the capacity of these microbes to breakdown the uric acid and urea and utilize ammonia for amino acid synthesis has not been documented. Ureotelic fish transfer urea into the intestine where urease (presumably of bacterial origin) hydrolyzes the urea. However, the amino acid synthesizing capacity of the intestinal microflora has not been studied. The series of steps, as outlined, would define the prevailing nitrogen conservation system for herbivores and omnivores at least. However, it would appear that some animals, in particular the fruit-eating bat and perhaps the fruit-eating bird, may have evolved alternative, as yet uncharacterized, adaptations to a very limited nitrogen intake.

Aldosterone suppresses expression of an avian colonic sodium-glucose cotransporter

Transport in the colon of the domestic fowl switches from sodium-linked hexose and amino acid cotransport on high-salt intake to amiloride-sensitive sodium channel expression on low-salt (LS) diets. The present experiments were designed to investigate the role of aldosterone in suppression of the colonic sodium-glucose luminal cotransporter (SGLT). LS-adapted hens were resalinated with or without simultaneous aldosterone treatment. Changes in the electrophysiological responses and SGLT protein expression levels were examined at 1, 3, and 7 days of treatment. Serum aldosterone levels fell from approximately 400 pmol/l in LS-adapted hens to values below the detection limit (<44 pmol/l) after 1 day of resalination. At the same time, glucose-stimulated short circuit current (I(SC)) increased from 20.9 +/- 8.7 to 56.3 +/- 15.5 microA/cm(2), whereas amiloride-sensitive I(SC) decreased from -68.9 +/- 12.7 microA/cm(2) on LS to +0.6 +/- 12.0 microA/cm(2). Glucose-stimulated I(SC) increased further at 3 and 7 days of resalination, whereas amiloride-sensitive I(SC) remained suppressed. When resalinated birds were simultaneously treated with aldosterone, the LS pattern of high amiloride-sensitive I(SC) and low glucose-stimulated I(SC) was maintained. Immunoblotting results from the same tissues demonstrated that SGLT-like protein expression increased following resalination. Aldosterone treatment completely blocked this effect. These results demonstrate that aldosterone suppresses both activity and protein expression of hen colonic SGLT. Resalination either through decreased aldosterone or other factors may be able to activate SGLT activity independently of increases in protein expression.

Luminal morphology of the avian lower intestine: evidence supporting the importance of retrograde peristalsis for water conservation

Tissue from the lower intestine of two species of sparrow, the house sparrow Passer domesticus and savannah sparrow Passerculus sandwichensis was sectioned in an unbiased manner and examined quantitatively using stereology. The tissue was processed for light microscopy, and scanning and transmission electron microscopy to examine the extent to which microvilli enhanced the epithelial surface area of the cecae, rectum, and coprodeum. Parameters measured included individual microvillus surface area, microvilli packing density, and absolute surface area. In both species, the average surface area, packing density, and absolute surface area of microvilli decreased distally along the rectum and coprodeum. All three measured variables were not statistically significant (P > 0.05) between species. Surface area amplification on the cecae due to microvilli was low, and approximated values equivalent to distal regions of the rectum and coprodeum. In the cecae, microvilli within the savannah sparrow had a significantly higher (P < 0.05) individual surface area, packing density, and absolute surface area than in the house sparrow. The functional implications of a change in microvilli population are discussed in relation to retrograde peristalsis within the lower intestine of birds.

The membrane-bound intestinal enzymes of waxwings and thrushes: adaptive and functional implications of patterns of enzyme activity

Cedar waxwings (Bombycilla cedrorum) feed predominantly on fruits that are rich in simple sugars and low in nitrogen, supplementing this diet with arthropod prey during the summer months as well as flowers and tree sap in springtime. In contrast, thrushes feed extensively on fatty, protein-rich invertebrate prey, supplemented with sugary and lipid-rich fruits. Simple sugars and fats are digested and/or absorbed by distinctly different physiological mechanisms, which suggests the possibility of contrasting digestive strategies in animals specialized to diets containing one of these two energy sources. In this study, we quantified enzymatic activity of three membrane-bound intestinal enzymes of cedar waxwings and five species of thrushes to explore this aspect of their digestive physiology. These enzymes catalyze the final steps in the digestion of carbohydrates (sucrase-isomaltase and maltase-glucoamylase) and protein (aminopeptidase-N). The two carbohydrases are homologous enzymes with overlapping functions; both enzymes catalyze the hydrolysis of maltase and isomaltase. The membrane-bound digestive enzyme systems that we described for cedar waxwings and thrushes can be explained by the particular nutrients contained within their respective natural diets. Consistent with previous work, cedar waxwings displayed intestinal sucrase activity, whereas thrushes did not. Correspondingly, cedar waxwings eat some foods containing sucrose, whereas thrushes do not. Sucrase-isomaltase conferred all maltase and isomaltase activity in cedar waxwings. In contrast, all maltase and isomaltase activity in thrushes was necessarily sucrase independent, which indicated the presence of maltase-glucoamylase. The absence of sucrase-independent maltase activity in cedar waxwings suggests that sucrase-isomaltase obviates the need for maltase-glucoamylase. Indeed, total maltase and isomaltase activities were much higher in cedar waxwings than in thrushes. Neither waxwings nor thrushes eat starchy foods; sucrase-isomaltase in waxwings and maltaseglucoamylase in thrushes probably function in digesting glycogen in animal foods. We suggest that digestive traits associated with specialization to monosaccharide-rich fruits (lack of a grinding gizzard) by frugivorous waxwings and thrushes may prevent utilization of starchy seeds. Total aminopeptidase-N activity in cedar waxwings was indistinguishable from the allometric pattern among thrush species, but the distribution of this enzyme along the intestines of waxwings and thrushes was distinctly different, which demonstrates that total enzyme activity can be insufficient as a descriptor of the functional activity of brush border enzymes. Aminopeptidase-N activity peaked in the anterior part of the intestines of thrushes and in the terminal portion of the intestines of waxwings, which suggests contrasting strategies for protein digestion from fatty versus sugary diets, respectively.

Effects of caecal ligation and colostomy on water intake and excretion in chickens

1. The effect of caecal ligation and colostomy on water intake and excretion were examined in chickens fed a low-protein diet or a low-protein diet supplemented with urea. 2. When fed a low-protein diet, the water intake and the ratio of water intake to food intake were increased by colostomy (P < 0.05) but not changed further by caecal ligation of colostomised chickens. 3. When fed a low-protein diet supplemented with urea, the amount of water intake and the ratio of water intake to food intake were not changed by either treatment. 4. Total water excretion was much higher in the colostomised plus caeca-ligated chickens than in other 3 groups fed both types of diet (P < 0.05). 5. The amount of faecal water excretion was increased by cecal ligation in colostomised chickens fed either diet (P < 0.01). 6. No effect of any treatment on water balance was observed in chickens fed either diet. 7. It is concluded that the lower intestine plays a useful role in the water economy of chickens fed a low-protein diet or a low-protein diet supplemented with urea.

Retrograde movement of urine into the gut of salt water acclimated Mallards (Anas platyrhynchos)

The influence of sex and salt-water intake on retrograde movement of urine into the hindgut was examined in captive adult wild Mallards (Anas platyrhynchos). Ducks were given intravenous injections of tritiated polyethylene glycol (3H-PEG) and killed 3 h later. The fluid content of each gut segment and its concentrations of 3H-PEG, sodium, and potassium were determined. Retrograde movement of urine into each gut segment was estimated from the quantity of 3H-PEG recovered there. In both ducks that drank tap water and those that drank saline, about 20% of the urine was moved into the hindgut, two-thirds of this into the ceca. Males deposited more urine in the ceca and reabsorbed more water from this urine than did females (P < 0.01). We conclude that retrograde movement of urine into the hindgut was unaffected by the salinity of drinking water and was greater in males than in females. Reabsorption of urinary sodium and water in the hindgut, particularly the ceca, may play an important role in osmoregulation in birds with salt glands.

Na+-H+ exchange and intracellular pH regulation in colonocytes from the chick

The involvement of Na(+)-H+ exchange in chicken colonocyte homeostasis was investigated. Colonocyte pH (pH(i)) was measured with 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF). The proton ionophore FCCP reduced basal pH(i), indicating that cytosolic [H+] is not at electrochemical equilibrium across the membrane. External Na+ removal decreased pH(i) and subsequent addition of Na+ returns pH(i) towards its control value. The rate of pH(i) recovery from an acid load was Na(+)-dependent (K(m) for Na+, 24 mM) and inhibited by EIPA (IC50, 0.18 microM). The initial rate of Na(+)-dependent cell alkalization increased as the pH(i) decreased from 7.2 to 6.6 (Hill coefficient, 1.88). Radioisotope flux studies revealed that an outwardly directed proton gradient transiently stimulated Na+ uptake into BBMV isolated from the chick colon. EIPA and amiloride inhibited pH gradient-driven Na+ uptake (IC50 of 4 microM and 32 microM, respectively). The K(m) for Na+ of pH gradient-driven Na+ uptake was 6.8 mM. The Hill coefficient of the relationship between the initial rate of pH-driven Na+ uptake and the intravesicular pH was 0.70. It is concluded that a Na(+)-H+ exchanger is involved in pH(i) homeostasis in chicken colonocytes and that these cells possess at least two types of Na(+)-H+ antiporters with different sensitivity to EIPA and different kinetic parameters.

Fermentation and growth response of a primary poultry isolate of Salmonella typhimurium grown under strict anaerobic conditions in continuous culture and amino acid-limited batch culture

Salmonella typhimurium is a significant hazard to consumer health that is carried asymptomatically in poultry gastrointestinal tracts. Nurmi cultures may prevent Salmonella colonization in young chicks, but the mechanism of competitive exclusion is unclear. Modeling Salmonella's metabolism in pure culture may allow for greater definition in choosing strains for Nurmi cultures. The growth rates and affinity constants of S. typhimurium growing in amino acid-limited conditions were determined in batch culture and compared to primary poultry isolates of cecal strains. Serine and NH4Cl were the best N sources for growth of all organisms tested in this study. The fermentation response of S. typhimurium was also monitored in continuous culture at a slow dilution rate of 0.021 h-1. S. typhimurium was found to adapt to VL media, with trends in protein disappearance, Yglucose, and Yprotein. This may show that amino acid or protein concentrations may be an integral component of the initial establishment of S. typhimurium in the cecum.

Sodium balance in ruffed grouse as influenced by sodium levels and plant secondary metabolites in quaking aspen

Forages in boreal ecosystems are often deficient in sodium for mammalian herbivores. Moreover, consumption of various plant secondary metabolites has been associated with negative sodium balance in mammals. Neither of these issues has been investigated in birds, which differ from mammals in their ion-exchange processes and postrenal absorption of urine. Our objectives were to determine if ruffed grouse (Bonasa umbellus) can maintain sodium balance on quaking aspen (Populus tremuloides) flower buds, an important winter food, and to determine if the buds' primary plant secondary metabolite (coniferyl benzoate) further compromises a bird's sodium balance. Captive ruffed grouse were fed either aspen buds (0.063 mg∙g−1 sodium) or a formulated diet having different concentrations of coniferyl benzoate in no-choice feeding trials. Sodium excretion did not change in response to coniferyl benzoate intake or acid load from detoxication processes; however, birds were marginally in negative sodium balance (P = 0.035; −5.06 ± 2.05 mg∙kg−1∙d−1) when feeding on aspen buds. Sodium levels in the feces from free-ranging grouse (0.050 ± 0.0 mg∙g−1) and in their winter foods (0.065 mg∙g−1) indicated that these birds likely maintained sodium balance. We estimated that free-ranging ruffed grouse may need as little as 7 mg∙kg−1∙d−1 of sodium to maintain sodium balance, which is lower than the minimum sodium requirements for poultry and mammals.

Intracellular pH regulation in cecal epithelial cells from the chick

Intracellular pH (pHi) regulation has been investigated in cells isolated from the proximal ceca of the chicken. pHi was measured with the pH-sensitive dye, 2',7'-bis(carboxyethyl)-5 (6)-carboxyfluorescein in nominally HCO(3-)-free solutions. Under resting conditions the pHi was 7.08. Removal of extracellular Na+ decreased pHi by approx. 0.24 pH units and the subsequent addition of Na+ increased pHi towards the control value. This Na(+)-dependent pHi recovery was inhibited by 5-(N-ethyl-N-isopropyl)amiloride (EIPA). Following an intracellular acidification, by abrupt withdrawal of NH4Cl, pHi alkalinized in the nominally absence of Na+. Rotenone, N-ethylmaleimide, N,N'-dicyclohexylcarbodiimide, 4-chloro-7-nitrobenz-2-oxa-1,3-diazole, iodoacetic acid and SCH 28080 inhibited the Na(+)-independent pHi recovery rate by 82, 82, 67, 74, 77 and 50% respectively. Bafilomycin A1 was without effect. Na(+)-independent cell alkalization was stimulated by external K+. In the presence of N-ethylmaleimide addition of Na+ induced a rapid pHi recovery. The initial rate of this recovery exhibited first-order dependence on Na+ concentration and it was inhibited by EIPA. The initial rate of Na(+)-dependent cell alkalization increased with a Hill coefficient greater than one when pHi was reduced from 7.2 to 6.2. The 'set point' for the exchanger is approx. 7.5. These studies demonstrate that in cecal epithelial cells exist at least two mechanisms for proton secretion: a Na(+)-H+ exchanger and a Na(+)-independent proton transport system.

Effect of a soluble polysaccharide (carboxy methyl cellulose) on the physico-chemical conditions in the gastrointestinal tract of broilers

1. The effects of an indigestible soluble polysaccharide (carboxy methyl cellulose: CMC) on broiler performance (body weight gain, food and water intake) and on chyme characteristics (moisture content, viscosity, pH, osmolality and retention time) in broilers were studied. 2. In semi-synthetic diets 0, 5.0 and 10.0 g/kg of cellulose was replaced by CMC on weight basis. These diets were fed to male broilers from 3 to 5 weeks of age. 3. When 10.0 g/kg CMC was included in the diet, food intake and body weight gain were reduced, compared to the 0, and 5.0 g/kg CMC diets. Food:gain ratio and water intake were increased at each CMC concentration. The significant quadratic response showed an increased response per 5.0 g/kg dietary CMC at the higher CMC concentration. 4. The viscosity in the supernatant of the chyme was linearly increased in all intestinal segments by CMC. A quadratic increase was observed in the crop. In the lower ileum, differences between the 5.0 and 10.0 g/kg CMC diets were not significant. 5. CMC increased the mean retention time of chromium in the duodenum and in the upper jejunum, and reduced the maximal rate of marker excretion. The transit time (first appearance of the marker in the excreta), however, was significantly reduced at the highest CMC concentration. 6. The osmolality of the intestinal fluid decreased less as the chyme moved from the duodenum into the lower ileum, with increasing concentrations of CMC. 7. The ileal pH was reduced linearly by the CMC content of the diet. 8. Based on a higher moisture content of the chyme in the CMC-fed birds, and the higher jejunal and ileal osmolarities in those birds, it was concluded that the efficiency of both digestion and absorption was reduced by CMC inclusion in broiler diets.

Effect of a soluble polysaccharide (carboxy methyl cellulose) on the absorption of minerals from the gastrointestinal tract of broilers

1. The effect of an indigestible soluble polysaccharide (carboxy methyl cellulose: CMC) on the absorption of some macro-elements (sodium, potassium, calcium, phosphorus and magnesium) from different segments of the small intestine of broilers was determined. 2. In semi-synthetic diets 0, 5.0 and 10 g/kg cellulose was replaced by CMC on weight basis. These diets were fed to male broilers from 3 to 5 weeks of age. 3. CMC inclusion reduced the rate of mineral absorption throughout the small intestine. The effect of CMC on sodium absorption was more pronounced than the effects on the absorption of the other minerals. 4. The cumulative absorption of all minerals up to the lower jejunum was reduced by dietary CMC. This negative effect of CMC on the absorption of minerals was alleviated in the lower ileum, except for potassium. 5. The concentrations of sodium and magnesium in the chyme supernatant were clearly decreased, while those of calcium and phosphorus were increased by dietary CMC inclusion. Taking the mineral concentrations in the total chyme into account, the solubilities of calcium, phosphorus and magnesium in the ileum were increased by dietary CMC. The solubilities of sodium and potassium were not increased. 6. The reduced cumulative absorption of minerals from the gastrointestinal tract with increasing dietary concentrations of CMC, was probably caused by the higher intraluminal viscosities in the small intestine. It is not likely that either the intestinal pH, or the time food was retained in successive gastrointestinal segments, will have affected mineral absorption negatively in any segment.

Steroid C-20 oxidoreductase activity of duck intestinal mucosa: the interrelations of the enzymatic activity with steroid binding

The binding of corticosterone and aldosterone to domestic duck (Anas platyrhynchos)-dispersed colonic mucosal cells at 37 degrees was investigated. It was found that in contrast to experiments using cell-free intestinal preparations, corticosterone was extensively metabolized and it was the metabolite, not the native steroid that became receptor bound and all the bound ligand was in the nuclear fraction. The metabolite turned out to be identical with 4-pregnene-11 beta,20 beta, 21-triol-3-one (20 beta-dihydrocorticosterone, 20 beta-DHB). Binding experiments with [3H]corticosterone yielded the following kinetic parameters: Kd = 87.6 nM, Nmax = 337,900 sites/cell. When synthetic [3H]20 beta-DHB was used as the ligand a curvilinear-binding isotherm was obtained. This could be resolved into a high affinity-low capacity (HA) and a low affinity-high capacity (LA) component with the following binding parameters: Kd,HA = 91 nM, Nmax,HA = 130,800 sites/cell; Kd,LA = 5.4 x 10(-6) M, Nmax, LA = 3.7 x 10(6) sites/cell. Binding of the metabolite to cell-free preparations, at 0 degree, gave the following results: for cytosol, linear-binding isotherm, Kd = 14.0 nM, Nmax = 26.5 fmol/mg protein; and for crude nuclei, curvilinear-binding isotherm, Kd,HA = 45.0 nM, Nmax, HA = 5.33 pmol/mg DNA; Kd,LA = 2.2 x 10(-6) M, Nmax,LA = 286.6 pmol/mg DNA. [3H]Aldosterone was also bound by the dispersed whole cells and again, this binding was only nuclear (Kd = 9.3 nM, Nmax = 10,042 sites/cell). The bound ligand was unchanged aldosterone. Competition experiments have shown that aldosterone did not compete with 20 beta-DHB for binding sites and vice versa. The intracellular 20 beta-hydroxysteroid oxidoreductase responsible for the transformation of corticosterone was found mostly in the cytoplasm. Kinetic studies with the enzyme yielded classical Michaelis-Menten kinetics (Km = 15.7 microM, Vmax = 2.6 nmol/min/mg protein). The enzyme had an apparent Mr of 35 kDa and a Rs of 25.5 A. It is believed that our results might explain the binding of aldosterone to mineralocorticoid-binding sites in the presence of overwhelming concentrations of corticosterone and that experiments with cell-free tissue preparations, performed at 0 degree, do not reflect the true cellular-binding events.

Absorption by the cecum of wild birds: is there interspecific variation

The major functions proposed for the avian cecum--energy balance and osmoregulation--involve absorption of material from the cecum, yet little is known of these absorptive processes in wild birds. The magnitude of transport of compounds from the ceca depends on the concentrations of compounds in the ceca, the presence of transport pathways for those compounds, and the size of the reabsorptive surface. Interspecific variation in size of avian ceca is well documented, but the other two determinants of absorption are much less well studied. All ceca examined contained acetic, propionic, and butyric acid; water content varies from less than 70 to greater than 90%. Most other constituents have been quantified in just one or two species. A model for cecal transport, derived from studies of mammalian ceca but consistent with observations on birds, is described. A luminal (mucosal) Na+/H+ exchanger couples the absorption of Na+ to that of volatile fatty acids, which are absorbed in their uncharged (protonated) form; these two compounds are thereby mutually stimulatory in their absorption. The cecum also absorbs water, sodium, carbon dioxide, and probably some nitrogenous compounds (e.g., ammonia). Too few data exist to analyze interspecific variation in cecal transport in birds. However, variations in the following characteristics do exist: cecal contents, cecal absorptive surface area, transport characteristics of other regions of avian intestine (e.g., rectum), cecal transport among mammalian species, and histology of avian ceca. Studies of the physiological consequences of these variation should yield insight into the function and contributions of the avian cecum.

Function and regulation of the avian caecal bulb: influence of dietary NaCl and aldosterone on water and electrolyte fluxes in the hen (Gallus domesticus) perfused in vivo

The function of the caecal bulb, and its adaptation to chronic high- or low-Na+ intake, was investigated by in vivo perfusion of anaesthetised birds. Effects of acute aldosterone injection (125 micrograms.kg-1 body mass) were also measured. Evidence was found for primary active net absorption of Na+, inducing parallel Na-linked absorption of water and Cl- and secretion of K+. Around 20-35% of total Cl- absorption and K+ secretion were independent of Na+ fluxes, and these components appear to be driven by passive processes with apparent conductances of 6.3 X 10(-3) (GCl) and 1.1 X 10(-3) (GK) S.cm-2. Acetate (40 mM) stimulated Na+ fluxes (8.5-9.9 microEq.cm-2.h-1) and Na-linked water fluxes (27-44 microliters.cm-2.h-1). Increased coupling ratios (2.9-4.6 microliters.microEq-1) and other data indicate that these effects may be due to increased osmotic permeabilities of barriers involved in the Na-linked water transfer pathway. Low-Na+ maintenance enhanced EPD (49-69 mV, serosa positive) and all net fluxes: JNa (6.8-11.6); JK (-3.2--4.3); JCl (4.3-5.6 microEq.cm serosal area-2.h-1); Jv (28-43 microliters.cm-2.h-1) (mucosal-serosal fluxes positive). Acute aldosterone enhanced JNa (10.8-14.0 microEq.cm-2.h-1) and EPD (54-66 mV) by 3 h after injection, but had no effect on the Na-linked components of JK or JCl.

Effect of cecectomy on water and nutrient absorption of birds

The effect of the removal of the avian digestive ceca on osmoregulation and on absorption of certain nutrients is reviewed. While data indicate that the ceca have the potential for absorption of a significant quantity of water, several studies have demonstrated that effects of cecectomy on water intake and output are transitory and that compensatory adjustments made within 2 to 3 weeks postsurgery allow cecectomized birds to eat and gain weight normally. However, cecectomized great horned owls exposed to 27 degrees C turned over their body water 1.6 times faster than intact owls under the same conditions, suggesting that the ceca do have a vital role in water balance of thermally stressed horned owls. Cecectomy resulted in slightly lower metabolizability of food, lower digestibility of crude fiber in low fiber diets, and greater loss of certain amino acids in cecectomized birds that were fasted or fed a protein-free diet. The latter suggests that the ceca are important in recovery of amino acids endogenous protein degradation. Loss of cecal function also resulted in higher energy intake and excretion in Japanese quail, amounting to 5.7% of the total daily energy requirement.

Sodium and potassium concentrations in the intestinal fluids of the fowl, Gallus domesticus

1. Na and K concentrations in the luminal fluids on the jejunum, ileum and colon were measured in domestic fowl on diets containing different amounts of Na and K. 2. Physiological adjustments of the Na and K content of these fluids were observed to occur in all three intestinal segments. 3. Regulation of gastrointestinal losses of Na and K appears to be initiated in the anterior regions of the intestines of the domestic fowl and is maintained or amplified as the ingesta moves posteriorly.

Water and electrolyte transport by the avian ceca

In galliform birds with well developed ceca, these are functionally important components of the lower intestinal complex, which is capable as a whole of substantial, hormone-regulated homeostatic modification of mixed urine and intestinal luminal fluid before final excretion. Active Na+ transport drives Na-linked absorption of water and Cl- and secretion of K+; there are also lesser Na-independent components of the latter fluxes. These transport processes are appropriately enhanced by dehydration, Na depletion, or exogenous aldosterone.

Transport function and control in bird caeca

1. The paired caeca at the junction of the ileum and rectum help determine the ionic composition of the voided excreta. 2. The caeca play a role in the transport of water, sodium, potassium, and chloride, the dominant effect being that of sodium transport.

Electrical PD, short-circuit current and fluxes of Na and Cl across avian intestine

In vitro measurements were made of transmural potential difference (PD), short-circuit current (Isc), resistance and unidirectional fluxes of 22Na and 36Cl across the duodenum, jejunum, ileum and colon of normal sodium-replete domestic fowl (Gallus domesticus). The PD ranged from about 1 mV across the duodenum to 8 mV across the colon while the Isc was, respectively, 2.8 and 64 microA X cm-2. The jejunum and ileum exhibited values between these extremes. Unidirectional fluxes (under short-circuit conditions) of Na and Cl were lowest across the duodenum where there was no evidence of active transport of these ions. Unidirectional fluxes of Na and Cl were less across the jejunum than across the ileum or colon. A net active transport of Na (but not Cl) was observed in the ileum (= 106% of the Isc) and colon (= 50% of Isc). The possible physiological significance of these observations in the domestic fowl are discussed and are compared to that of a mammal, the rabbit.

Urates and allantoic regulation in embryonic Japanese quail, Coturnix coturnix japonica

During embryonic development, allantoic fluid represents the shifting balance between renal excretion and reabsorption by chorioallantoic membranes. Allantoic contents of Na+, K+, Cl-, urate, pH, and water were followed over days 10-15 of the 16 day incubation. Water volume remained near 0.9 ml until day 13, then declined very rapidly. The pH declined more steadily, from 8 to 5.5. Contents of Na+ and Cl- fell regularly to final values 80-88% below day 10. The K+ content changed differently and nearly doubled by day 13 but returned to day 10 values at the end. Urate content rose until day 13, then fell suddenly to low levels. This was due to the abrupt precipitation of most urate into masses not sampled by our method, so that after day 13, urate was underestimated (probably by 90-96%). Ion binding by urates was low (about 3% of Na+ and Cl-, 10% of K+) and appeared to be nonspecific. The underestimate of urate contents means, however, that in late incubation about one third of allantoic Na+ and 65-70% of K+ and Cl- are bound to precipitated urate and do not appear in balance sheets of allantoic ions. These precipitated ions account for the significant amounts of Na+ and K+ that remain in the allantoic remnant, left in the eggshell after hatching, but whose presence is not predicted by analysis of allantoic fluid.

Independence of salt gland function and adrenocortical activity in ducks (Anas platyrhynchos)

In immature ducklings injected with hypertonic saline the volume of extrarenal salt gland secretion was unaffected by prior treatment (immediately or 4 hr before salt loading) with long-lasting adrenocorticotrophin (ACTH 100 iu/kg, im) or exogenous corticosterone (1.0 mg/kg, im). Pretreatment with metyrapone, an 11-beta-hydroxylase blocker, (80 mg/kg, im) 4 hr before salt loading did not effect the volume of salt gland secretion but delayed the onset of extrarenal excretion. Salt gland function was suppressed in birds pretreated with metyrapone immediately prior to salt loading. The intravenous administration of metyrapone after salt loading immediately reduced salt gland activity, which remained suppressed for at least 40-50 min thereafter. The inhibitory effect of metyrapone on salt gland activity was not counteracted by the subsequent or simultaneous administration of exogenous corticosterone to salt-loaded ducks. These results suggest that acute alterations in adrenocortical activity are not causally responsible for changes in salt gland function.

Control of plasma angiotensin II in a bird with salt glands (Anas platyrhynchos)

A radioimmunoassay was developed for the measurement of avian angiotensin II (1Asp-5Val-AII) in the blood plasma. This assay was used to investigate the relationship between body fluid parameters and plasma levels of AII in the Pekin duck, an avian species employing salt glands, besides the kidneys, for NaCl excretion in case of chronic salt stress. A plasma AII concentration of 35.3 +/- 3.9 pg X ml-1 (mean +/- SE) was found in normally hydrated, freshwater-adapted (FW) ducks with a plasma osmolality of 294.9 +/- 0.9 milliosmoles (mOsm) X kg-1. In saltwater-adapted (SW) ducks with a plasma osmolality of 312 +/- 1.5 mOsm X kg-1 and functioning salt glands, a plasma AII level of 102.6 +/- 9.3 pg X ml-1 was found and plasma AII was positively correlated with plasma osmolality (r = 0.601; n = 47; 2P less than 0.001). Intravenous infusion of AII at different rates resulted in a strictly linear relationship between the log values of the AII plasma concentrations and the infusion rates, indicating a plasma clearance rate for AII of 119 ml X min-1 X kg-1 when taking into consideration endogenous AII formation. Experiments designed to produce physiological changes in body fluid and plasma volume and tonicity in FW and SW ducks by appropriate salt and/or water loading indicate that although both parameters may contribute to the control of plasma AII, volume is the dominant stimulus.