Serosal zinc attenuate serotonin and vasoactive intestinal peptide induced secretion in piglet small intestinal epithelium in vitro.

This study addressed the mechanisms by which dietary zinc affects diarrhoea and aimed to study possible interactions between zinc status and the presence of zinc in vitro on secretagogue-induced secretion from piglet intestinal epithelium in Ussing chambers. In addition, it was studied from which side of the epithelium zinc would perform an effect and if copper caused similar effects. Twenty-four piglets (28 days of age) were weaned and fed diets containing 100 or 2500 mg zinc/kg (as ZnO) for 5 or 6 days (12 piglets per group). Intestinal epithelium underwent the following 5 treatments: zinc at the mucosal side (M(Zn)), zinc at the serosal side (S(Zn)), zinc at both sides (MS(Zn)), copper at both sides (MS(Cu)) or water at both sides (control). Provoked secretion in terms of short circuit responses to serotonin (5-HT) and vasoactive intestinal peptide (VIP) were measured. Zinc at the serosal or both sides of the epithelium reduced the 5-HT induced secretion (P<0.001); however, due to interactions (P=0.05) the effect of zinc in vitro was only present in the ZnO(100) group. The secretion caused by VIP was not affected by the diet (P=0.33), but zinc at the serosal side or both sides reduced the response to VIP (P<0.001). Copper reduced the 5-HT and VIP induced secretion to a larger extent than zinc. However, copper also disturbed intestinal barrier function as demonstrated by increased transepithelial conductance and increased short circuit current, which was unaffected by zinc. In conclusion, zinc at the serosal side of piglet small intestinal epithelium attenuated 5-HT and VIP induced secretion in vitro. These in vitro studies indicate that in vivo there will be no positive acute effect of increasing luminal Zn concentration on secretagogue-induced chloride secretion and that zinc status at the serosal side of the epithelium has to be increased to reduce secretagogue-induced chloride secretion and thereby diarrhoea.     

Serosal zinc attenuate serotonin and vasoactive intestinal peptide induced secretion in piglet small intestinal epithelium in vitro

This study addressed the mechanisms by which dietary zinc affects diarrhoea and aimed to study possible interactions between zinc status and the presence of zinc in vitro on secretagogue-induced secretion from piglet intestinal epithelium in Ussing chambers. In addition, it was studied from which side of the epithelium zinc would perform an effect and if copper caused similar effects. Twenty-four piglets (28 days of age) were weaned and fed diets containing 100 or 2500 mg zinc/kg (as ZnO) for 5 or 6 days (12 piglets per group). Intestinal epithelium underwent the following 5 treatments: zinc at the mucosal side (M(Zn)), zinc at the serosal side (S(Zn)), zinc at both sides (MS(Zn)), copper at both sides (MS(Cu)) or water at both sides (control). Provoked secretion in terms of short circuit responses to serotonin (5-HT) and vasoactive intestinal peptide (VIP) were measured. Zinc at the serosal or both sides of the epithelium reduced the 5-HT induced secretion (P<0.001); however, due to interactions (P=0.05) the effect of zinc in vitro was only present in the ZnO(100) group. The secretion caused by VIP was not affected by the diet (P=0.33), but zinc at the serosal side or both sides reduced the response to VIP (P<0.001). Copper reduced the 5-HT and VIP induced secretion to a larger extent than zinc. However, copper also disturbed intestinal barrier function as demonstrated by increased transepithelial conductance and increased short circuit current, which was unaffected by zinc. In conclusion, zinc at the serosal side of piglet small intestinal epithelium attenuated 5-HT and VIP induced secretion in vitro. These in vitro studies indicate that in vivo there will be no positive acute effect of increasing luminal Zn concentration on secretagogue-induced chloride secretion and that zinc status at the serosal side of the epithelium has to be increased to reduce secretagogue-induced chloride secretion and thereby diarrhoea.     

Influence of weaning and effect of post weaning dietary zinc and copper on electrophysiological response to glucose, theophylline and 5-HT in piglet small intestinal mucosa

This study aimed to examine how weaning and how dietary zinc and/or copper fed post weaning may affect the electrophysiological response to glucose and to chloride secretagogues in piglet small intestine in vitro. Study 1 included 54 piglets (six litters of nine piglets). One piglet from every litter was killed 1 day before weaning. The remaining 48 piglets were allocated at weaning (28 d) to four dietary zinc treatments and subsequently killed 1-2, 5-6 or 14-15 days after weaning. Study 2 included 48 piglets (six litters of eight piglets) allocated to four dietary treatments, consisting of high or low dietary zinc with or without high dietary copper. All piglets in study 2 were killed 5-7 days after weaning. The in vitro studies in Ussing chambers showed that weaning resulted in increased ileal glucose absorption as well as increased neuroendocrine-regulated (activated by 5-HT) and cAMP-dependent (activated by theophylline) chloride secretion. High zinc supplementation reduced the responses to 5-HT and theophylline. The study did not reveal any influence of copper on these parameters. It is concluded that the positive effect of zinc supplementation on diarrhoea in weaned piglets may be due to zinc reducing the intestinal mucosal susceptibility to secretagogues that activate chloride secretion.     

Calcium-sensing receptor inhibits secretagogue-induced electrolyte secretion by intestine via the enteric nervous system

Bacterial toxins such as cholera toxin induce diarrhea by both direct epithelial cell generation of cyclic nucleotides as well as stimulation of the enteric nervous system (ENS). Agonists of the extracellular calcium-sensing receptor (CaSR) can reduce toxin-stimulated fluid secretion in ENS-absent colonic epithelial crypts by increasing phosphodiesterase-dependent cyclic-nucleotide degradation. Here we show that the CaSR is also highly expressed in tetrodotoxin (TTX)-sensitive neurons comprising the ENS, suggesting that CaSR agonists might also function through neuronal pathways. To test this hypothesis, rat colon segments containing intact ENS were isolated and mounted on Ussing chambers. Basal and cyclic nucleotide-stimulated electrolyte secretions were monitored by measuring changes in short-circuit current (I(sc)). CaSR was activated by R-568 and its effects were compared in the presence and absence of TTX. Consistent with active regulation of anion secretion by the ENS, a significant proportion of I(sc) in the proximal and distal colon was inhibited by serosal TTX, both at basal and under cyclic AMP-stimulated conditions. In the absence of TTX, activation of CaSR with R-568 significantly reduced basal I(sc) and cyclic AMP-stimulated I(sc); it also completely reversed the cAMP-stimulated secretory responses if the drug was applied after the forskolin stimulation. Such inhibitory effects of R-568 were either absent or significantly reduced when serosal TTX was present, suggesting that this agonist exerts its antisecretory effect on the intestine by inhibiting ENS. The present results suggest a new model for regulating intestinal fluid transport in which neuronal and nonneuronal secretagogue actions are modulated by the inhibitory effects of CaSR on the ENS. The ability of a CaSR agonist to reduce secretagogue-stimulated Cl(-) secretion might provide a new therapeutic approach for secretory and other ENS-mediated diarrheal conditions.     

Absorption of intact beta-casomorphins (beta-CM) in rabbit ileum in vitro

The functional significance of the presence of opioid peptides in enzymatic digestion of bovine milk beta-casein remains unclear. Opiates modify intestinal electrolyte transport by acting on receptors located on the serosal side of the intestine. The aim of the present study is to determine under which conditions beta-casomorphins could act from the luminal side of the intestine. The effect of natural morphiceptin (beta-CM4-NH2) and the non metabolized analogue beta-[DAla2,4, Try5]-CM5-NH2 were studied on isolated rabbit ileum mounted in Ussing chambers. Both peptides caused a naloxone-reversible reduction in short-circuit current (lsc) and stimulated Na and Cl absorption after addition to the serosal side of the tissue. After mucosal addition, only the analogue (10(-3) M) crossed the epithelium intact (Jm-s = 3.5 +/- 1.2 nmol.h-1.cm-2) and reduced lsc. Morphiceptin, under the same conditions, was degraded by the intestinal mucosa without opiate action on electrolyte transport. Pretreatment of the ileum by 10(-3)M diisopropylfluorophosphate that inhibited brush-border dipeptidylpeptidase IV, prevented mucosal degradation of morphiceptin. Under these conditions, the peptide (10(-3)M) crossed the epithelium intact (Jm-s = 1.8 +/- 0.16 nmol.h-1.cm-2) and stimulated electrolyte absorption by means of an opioid mechanism. These results show that both natural morphiceptin and the protected analogue have an opiate activity on intestinal electrolyte transport. Their action from the lumen depends on their transfer intact to the serosal side of the intestine where opiate receptors are located. The limiting step in this transfer is at the brush-border membrane where dipeptidylpeptidase IV in particular seems to play a major role.     

The effect of atrial natriuretic peptide on intestinal electrolyte transport.

The effect of atrial natriuretic peptide (ANP) on rat small intestinal electrolyte transport was examined. In vivo, intravenous administration of rat ANP(99-126) induced diuresis and natriuresis in conjunction with a significant decrease in intestinal water (basal, 37.1 +/- 5.7 versus ANP 28.5 +/- 6.0 microliters/cm per 20 min, P less than 0.05) and Na+ (4.0 +/- 0.7 versus 2.8 +/- 0.9 mumol/cm per 20 min, P less than 0.05) absorption (n = 9). In vitro, in Ussing chambers, in both jejunum and ileum, addition of 1.0 microM ANP to short circuited, stripped tissue produced a maximal increase in short circuit current and stimulated net Cl- secretion due to a significant increase in the unidirectional serosal to mucosal flux (JCl-sm: jejunum 17.4 +/- 1.3 versus 19.8 +/- 1.3 microEq/cm2 per h, P less than 0.01, n = 6; ileum 13.4 +/- 0.5 versus 17.2 +/- 0.6, P less than 0.01, n = 6) which was inhibited by the calcium channel antagonist verapamil (82 +/- 26%, P less than 0.05) and by the 5-HT2 receptor antagonist cinanserin (72 +/- 44%, P less than 0.05). Guanylate cyclase activity was stimulated by ANP in intact epithelium, but not in isolated crypt and villus enterocytes.     

Zinc reduces the electrophysiological responses in vitro to basolateral receptor mediated secretagogues in piglet small intestinal epithelium

Dietary zinc treatment has a preventive impact on diarrhoea in newly weaned piglets and in undernourished children. The mechanisms behind this effect of zinc are however, still not fully understood. The aim of the present study was to assess if zinc has a direct effect on porcine intestinal secretory responses to different secretagogues in vitro. The study included two Ussing chamber experiments, where the short circuit current responses to different secretagogues were measured in piglet small intestinal epithelium. Exp. 1 aimed to study the effect of increased zinc concentrations in the bathing media on the secretory responses to 5-HT and theophylline. The objective of exp. 2 was to study the effect of zinc in the bathing media on the secretory responses induced by vasoactive intestinal polypeptide (VIP), Substance P (SP), Carbachol, and theophylline. The results showed that there were significant decreasing effects of zinc on the secretion, stimulated by 5-HT, VIP and carbachol, from piglet intestinal epithelium in vitro, whereas the secretion caused by SP and theophylline was not significantly affected. The data indicate that the inhibitory mechanism of zinc ions may take place at the receptors situated at the basolateral membrane of the epithelial cells.     

Feeding Low or Pharmacological Concentrations of Zinc Oxide Changes the Hepatic Proteome Profiles in Weaned Piglets

Pharmacological levels of zinc oxide can promote growth and health of weaning piglets, but the underlying molecular mechanisms are yet not fully understood. The aim of this study was to determine changes in the global hepatic protein expression in response to dietary zinc oxide in weaned piglets. Nine half-sib piglets were allocated to three dietary zinc treatment groups (50, 150, 2500 mg/kg dry matter). After 14 d, pigs were euthanized and liver samples taken. The increase in hepatic zinc concentration following dietary supplementation of zinc was accompanied by up-regulation of metallothionein mRNA and protein expression. Global hepatic protein profiles were obtained by two-dimensional difference gel electrophoresis following matrix-assisted laser desorption ionization/time-of-flight mass spectrometry. A total of 15 proteins were differentially (P<0.05) expressed between groups receiving control (150 mg/kg) or pharmacological levels of zinc (2500 mg/kg) with 7 down- (e.g. arginase1, thiosulfate sulfurtransferase, HSP70) and 8 up-regulated (e.g. apolipoprotein AI, transferrin, C1-tetrahydrofolate synthase) proteins. Additionally, three proteins were differentially expressed with low zinc supply (50 mg/kg Zn) in comparison to the control diet. The identified proteins were mainly associated with functions related to cellular stress, transport, metabolism, and signal transduction. The differential regulation was evaluated at the mRNA level and a subset of three proteins of different functional groups was selected for confirmation by western blotting. The results of this proteomic study suggest that zinc affects important liver functions such as blood protein secretion, protein metabolism, detoxification and redox homeostasis, thus supporting the hypothesis of intermediary effects of pharmacological levels of zinc oxide fed to pigs.     

Zinc inhibits cAMP-stimulated Cl secretion via basolateral K-channel blockade in rat ileum

Zn, an essential micronutrient and second most abundant trace element in cell and tissues, reduces stool output when administered to children with acute diarrhea. The mechanism by which Zn improves diarrhea is not known but could result from stimulating Na absorption and/or inhibiting anion secretion. The aim of this study was to investigate the direct effect of Zn on intestinal epithelial ion absorption and secretion. Rat ileum was partially stripped of serosal and muscle layers, and the mucosa was mounted in lucite chambers. Potential difference and short-circuit current were measured by conventional current-voltage clamp method. 86Rb efflux and uptake were assessed for serosal K channel and Na-K-2Cl cotransport activity, respectively. Efflux experiments were performed in isolated cells preloaded with 86Rb in the presence of ouabain and bumetanide, whereas uptake experiments were performed in low-Cl isotonic buffer containing Ba and ouabain. Neither mucosal nor serosal Zn affected glucose-stimulated Na absorption. In contrast, forskolin-induced Cl secretion was markedly reduced by serosal but not mucosal addition of Zn. Zn also substantially reversed the increase in Cl secretion induced by 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) with half-maximal inhibitory concentration of 0.43 mM. In contrast, serosal Zn did not alter Cl secretion stimulated by carbachol, a Ca-dependent agonist. Zn inhibited 8-BrcAMP-stimulated 86Rb efflux but not carbachol-stimulated 86Rb efflux. Zn had no effect on bumetanide-sensitive 86Rb uptake, Na-K-ATPase, or CFTR. We conclude from these studies that Zn inhibits cAMP-induced Cl secretion by blocking basolateral membrane K channels.     

Zinc availability and digestive zinc solubility in piglets and broilers fed diets varying in their phytate contents, phytase activity and supplemented zinc source

The study was conducted to evaluate the effects of dietary zinc addition (0 or 15 mg/kg of Zn as inorganic or organic zinc) to three maize-soybean meal basal diets varying in their native Zn, phytic P contents and phytase activity (expressed in kg of feed: P- with 25 mg Zn and 1.3 g phytic P, P+ with 38 mg Zn and 2.3 g phytic P or P+/ENZ being P+ including 500 units (FTU) of microbial phytase per kg) in two monogastric species (piglets, broilers). Measured parameters were growth performance, zinc status (plasma, and bone zinc) and soluble zinc in digesta (stomach, gizzard and intestine). The nine experimental diets were fed for 20 days either to weaned piglets (six replicates per treatment) or to 1-day-old broilers (10 replicates per treatment). Animal performance was not affected by dietary treatments (P > 0.05) except that all P- diets improved body weight gain and feed conversion ratio in piglets (P < 0.05). Piglets fed P- diets had a better Zn status than those fed P+ diets (P < 0.05). In both species, Zn status was improved with supplemental Zn (P < 0.05), irrespective of Zn source. Phytase supplementation improved piglet Zn status to a higher extent than adding dietary Zn, whereas in broilers, phytase was less efficient than supplemental Zn. Digestive Zn concentrations reflected the quantity of ingested Zn. Soluble Zn (mg/kg dry matter) and Zn solubility (% of total Zn content) were highest in gizzard contents, which also presented lower pH values than stomach or intestines. The intestinal Zn solubility was higher in piglet fed organic Zn than those fed inorganic Zn (P < 0.01). Phytase increased soluble Zn in piglet stomach (P < 0.001) and intestine (P = 0.1), but not in broiler gizzard and intestinal contents. These results demonstrate (i) that dietary zinc was used more efficiently by broilers than by piglets, most probably due to the lower gizzard pH and its related higher zinc solubility; (ii) that zinc supplementation, irrespective of zinc source, was successful in improving animal's zinc status; and (iii) suggest that supplemented Zn availability was independent from the diet formulation. Finally, the present data confirm that phytase was efficient in increasing digestive soluble Zn and improving zinc status in piglets. However, the magnitude of these effects was lower in broilers probably due to the naturally higher Zn availability in poultry than in swine.     

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

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

Parathyroid hormone-related protein regulates intestinal calcium transport in sea bream (Sparus auratus)

Parathyroid hormone-related protein (PTHrP) is a factor associated with normal development and physiology of the nervous, cardiovascular, immune, reproductive, and musculoskeletal systems in higher vertebrates. It also stimulates whole body calcium uptake in sea bream (Sparus auratus) larvae with an estimated 60% coming from intestinal uptake in seawater. The present study investigated the role of PTHrP in the intestinal calcium transport in the sea bream in vitro. Unidirectional mucosal-to-serosal and serosal-to-mucosal 45Ca fluxes were measured in vitro in duodenum, hindgut, and rectum mounted in Ussing chambers. In symmetric conditions with the same saline, bathing apical and basolateral sides of the preparation addition of piscine PTHrP 1-34 (6 nM) to the serosal surface resulted in an increase in mucosal to serosal calcium fluxes in duodenum and hindgut and a reduction in serosal to mucosal in the rectum, indicating that different mechanisms are responsive to PTHrP along the intestine. In control asymmetric conditions, with serosal normal and mucosal bathed with a saline similar in composition to the intestinal fluid, there was a net increase in calcium uptake in all regions. The addition of 6 nM PTHrP 1-34 increased net calcium uptake two- to threefold in all regions. The stimulatory effect of PTHrP on net intestinal calcium absorption is consistent with a hypercalcemic role for the hormone. The results support the view that PTHrP, alone or in conjunction with recently identified PTH-like peptides, counteracts in vivo the hypocalcemic effects of stanniocalcin.     

Concentration and chemical form of dietary zinc shape the porcine colon microbiome,its functional capacity and antibiotic resistance gene repertoire

Despite a well-documented effect of high dietary zinc oxide on the pig intestinal microbiota composition less is it yet known about changes in microbial functional properties or the effect of organic zinc sources. Forty weaning piglets in four groups were fed diets supplemented with 40 or 110 ppm zinc as zinc oxide, 110 ppm as Zn-Lysinate, or 2500 ppm as zinc oxide. Host zinc homeostasis, intestinal zinc fractions, and ileal nutrient digestibility were determined as main nutritional and physiological factors putatively driving colon microbial ecology. Metagenomic sequencing of colon microbiota revealed only clear differences at genus level for the group receiving 2500 ppm zinc oxide. However, a clear group differentiation according to dietary zinc concentration and source was observed at species level. Functional analysis revealed significant differences in genes related to stress response, mineral, and carbohydrate metabolism. Taxonomic and functional gene differences were accompanied with clear effects in microbial metabolite concentration. Finally, a selection of certain antibiotic resistance genes by dietary zinc was observed. This study sheds further light onto the consequences of concentration and chemical form of dietary zinc on microbial ecology measures and the resistome in the porcine colon.Subject terms: Microbiome, Applied microbiology     

Absorption of intact morphiceptin by diisopropylfluorophosphate-treated rabbit ileum

The amidated beta-casomorphin morphiceptin Tyr-Pro-Phe-Pro-NH2 is an opioid peptide isolated from bovine milk beta-casein digests whose physiological significance remains unclear. Opiates are known to modify intestinal electrolyte transport by acting on receptors located on the serosal side of the intestine. The aim of the present study was to determine under what conditions morphiceptin can act from the luminal side. When added to the serosal side of untreated rabbit ileum in an Ussing chamber in vitro, 10(-3) M morphiceptin acted through an opiate mechanism to reduce simultaneously short-circuit current (delta Isc = 0.33 +/- 0.07 muEq.hr-1.cm-2) and stimulate net Na and Cl absorption (delta JnetNa = 1.62 +/- 0.11 and delta JnetCl = 2.07 +/- 0.08 muEg.hr-1.cm-2). After mucosal addition under the same conditions, morphiceptin was degraded without any opiate action on electrolyte transport. Pretreatment of the ileum by 10(-3) M diisopropylfluorophosphate, which inhibited brush-border dipeptidylpeptidase IV, prevented mucosal degradation of morphiceptin. Under these conditions, morphiceptin was able, when added mucosally, to cross the epithelium intact (Jm----s = 1.8 +/- 0.16 nmole.hr-1.cm-2) and to stimulate electrolyte absorption by means of an opioid mechanism (delta Isc = 0.22 +/- 0.02 muEq.hr-1.cm-2). These results showed that the action of morphiceptin from the lumen depends on its transfer intact to the serosal side of the intestine where the opiate receptors are located. The limiting step in this transfer is at the brush-border membrane, where dipeptidylpeptidase IV in particular seems to play a major role.     

Amylase transport across ileal epithelium in vitro

Amylase transport was measured across the rabbit ileum in vitro employing a modified Ussing chamber. Amylase was moved preferentially in the mucosal to serosal direction. Its rate of transfer was 2–3 orders of magnitude greater than that for inulin. Mucosal to serosal transport of exogenous amylase was completely inhibited in the absence of oxygen. There was also a constant release of endogenous amylase from intestinal tissue into both mucosal and serosal compartments in the absence of an exogenous source. An estimate of the rate of amylase absorption indicates that it may be of sufficient magnitude to account for the enteropancreatic circulation of amylase secreted by the pancreas during augmented secretion.     

Amylase transport across ileal epithelium in vitro.

Amylase transport was measured across the rabbit ileum in vitro employing a modified Ussing chamber. Amylase was moved preferentially in the mucosal to serosal direction. Its rate of transfer was 2--3 orders of magnitude greater than that for inulin. Mucosal to serosal transport of exogenous amylase was completely inhibited in the absence of oxygen. There was also a constant release of endogenous amylase from intestinal tissue into both mucosal and serosal compartments in the absence of an exogenous source. An estimate of the rate of amylase absorption indicates that it may be of sufficient magnitude to account for the enteropancreatic circulation of amylase secreted by the pancreas during augmented secretion.     

Neuropeptide modification of chloride secretion in guinea pig distal colon

This study examined the effects of electrically stimulating submucosal neurons in the guinea pig isolated distal colonic mucosa and determined the effects of several peptides that are present in these neurons. Electrical field stimulation of muscle-stripped segments of guinea pig distal colonic mucosa, set up in Ussing flux chambers, evoked an increase in short-circuit current (Isc), of 371 +/- 31 MicroA.cm-2. The response to electrical stimulation was abolished by tetrodotoxin and significantly reduced by serosal furosemide. Atropine reduced, but did not abolish, the neurally evoked response. Addition of neuropeptide Y and galanin to the serosal bath had no effect on baseline Isc, but both evoked a concentration-dependent decrease in the neurally evoked secretory response. Vasoactive intestinal polypeptide evoked a concentration-dependent increase in basal (unstimulated) Isc that was reduced by furosemide and unaltered by tetrodotoxin. Neuropeptide Y, but not galanin, significantly reduced the secretory responses to vasoactive intestinal polypeptide and bethanechol. Somatostatin 201-995 and human calcitonin gene-related peptide had no effect on basal Isc nor did either alter the neurally evoked response. These results suggest that acetylcholine and non-cholinergic neurotransmitter(s) stimulate chloride secretion in the guinea pig distal colonic mucosa. This neurosecretory response may be modulated by neuropeptide Y and galanin that are found within submucosal neurons.     

Effects of Enterococcus faecium NCIMB 10415 as probiotic supplement on intestinal transport and barrier function of piglets

Many studies report positive effects of probiotic supplementation on the performance and health of piglets. The intention of this study was to describe the effects of Enterococcus faecium NCIMB 10415 on the transport and barrier functions of pig small intestine to improve our understanding of the underlying mechanisms of this probiotic. Ussing chamber studies were conducted with isolated jejunal epithelia of piglets at the age of 14, 28, 35 and 56 days. Jejunal tissues of the control group were compared with epithelia of piglets that had received a diet supplemented with the probiotic Enterococcus faecium NCIMB 10415. Transport properties (absorption and secretion) of the epithelia were examined by mucosal addition of glucose or L-glutamine or by serosal addition of PGE2. Electrophysiology of the epithelia was continuously recorded and the change in short circuit current (Isc) was determined. Paracellular permeability was measured by measuring the flux rates of mannitol. The increase of Isc caused by mucosal addition of glucose was, at all glucose concentrations, higher in the probiotic group compared with the control group. However, the difference (up to 100% of the control) was not significant. The increase of Isc after the mucosal addition of L-glutamine (12mmol/l) was higher in the tissues of the probiotic group but did not reach significance. Serosal PGE2 induced a significantly higher increase of Isc in tissues of the probiotic group at the age of 28 days. No consistent differences were observed in mannitol transport rates between the feeding groups. Significant age-dependent alterations of absorptive and secretory properties of the jejunal epithelium were observed; these were independent of the treatment. A probiotic supplementation seems to influence transport properties of small intestine epithelium. The increased absorption of glucose could be interpreted as a positive effect for the animal.     

Basolateral Mg2+/Na+ exchange regulates apical nonselective cation channel in sheep rumen epithelium via cytosolic Mg2+

High potassium diets lead to an inverse regulation of sodium and magnesium absorption in ruminants, suggesting some form of cross talk. Previous Ussing chamber experiments have demonstrated a divalent sensitive Na(+) conductance in the apical membrane of ruminal epithelium. Using patch-clamped ruminal epithelial cells, we could observe a divalent sensitive, nonselective cation conductance (NSCC) with K(+) permeability > Cs(+) permeability > Na(+) permeability. Conductance increased and rectification decreased when either Mg(2+) or both Ca(2+) and Mg(2+) were removed from the internal or external solution or both. The conductance could be blocked by Ba(2+), but not by tetraethylammonium (TEA). Subsequently, we studied this conductance measured as short-circuit current (I(sc)) in Ussing chambers. Forskolin, IBMX, and theophylline are known to block both I(sc) and Na transport across ruminal epithelium in the presence of divalent cations. When the NSCC was stimulated by removing mucosal calcium, an initial decrease in I(sc) was followed by a subsequent increase. The cAMP-mediated increase in I(sc) was reduced by low serosal Na(+) and serosal addition of imipramine or serosal amiloride and depended on the availability of mucosal magnesium. Luminal amiloride had no effect. Flux studies showed that low serosal Na(+) reduced (28)Mg fluxes from mucosal to serosal. The data suggest that cAMP stimulates basolateral Na(+)/Mg(2+) exchange, reducing cytosolic Mg. This increases sodium uptake through a magnesium-sensitive NSCC in the apical membrane. Likewise, the reduction in magnesium uptake that follows ingestion of high potassium fodder may facilitate sodium absorption, as observed in studies of ruminal osmoregulation. Possibly, grass tetany (hypomagnesemia) is a side effect of this useful mechanism.