Hibernation induces expression of moesin in intestinal epithelial cells

Identification of proteins that are differentially expressed in mammals that hibernate can provide insight into mechanisms that preserve cellular function at low temperatures. A candidate protein was identified in intestinal brush border membranes of 13-lined ground squirrels. Intestinal brush border membrane proteins were separated using SDS-PAGE and gels were stained with Coomassie blue. We observed a approximately 75-kDa band that was specifically increased in brush border membranes isolated from torpid squirrels compared with summer active squirrels. The 75-kDa band was cut from one-dimensional gels and sequenced. A 17 amino acid sequence was identified of which amino acids 2-17 matched exactly a portion of moesin, a membrane-cytoskeletal linking protein and member of the ERM (ezrin/radixin/moesin) family. The sequence results were confirmed using anti-moesin antibodies that detected strong bands at approximately 75 kDa on Western blots of brush border membranes in torpid squirrels (Tb approximately 7 degreesC) and only faint signals in summer squirrels (Tb approximately 37 degrees C) or aroused hibernators (Tb approximately 37 degrees C). In contrast, signals obtained using anti-ezrin antibodies were uniformly strong in all squirrels, regardless of activity state. Intestinal brush borders of mice and rats expressed ezrin but not moesin. These results provide evidence for the physiological induction of an ERM protein in intestinal epithelial cells of torpid hibernators and support the idea that hibernation involves differential expression of gene products that may facilitate viability of cells at low temperatures.

Regional differences in the effect of cholera toxin and enterotoxigenic Escherichia coli infection on electrolyte and fluid transport in the porcine small intestine

The regional differences in secretory and absorptive responses to cholera toxin (CT) and to infection by enterotoxigenic Escherichia coli (ETEC), producing heat-stable enterotoxins, were studied in the porcine small intestine. Proximal, mid and distal small intestine from newly weaned piglets were used. Na+ and Cl- fluxes and electrical parameters in CT-stimulated and ETEC-infected intestine were measured by the Ussing chamber technique. In addition, CT-induced fluid accumulation in ligated loops was measured. CT induced fluid accumulation, which was highest in the proximal segment and decreased in the aboral direction of the small intestine. In addition, CT induced a net Cl- secretion in the proximal and mid segments, while net Na+ absorption was reduced only in the proximal segment. The ETEC-infected intestine showed a net increase in Cl- secretion in the proximal part and abolished the net Na+ absorption in the distal segment. These results demonstrate segmental differences in the epithelial transport responses to enterotoxin from Vibrio cholerae and to ETEC infection. This needs to be taken into consideration in relation to oral rehydration studies.

Guinea pig 5-HT transporter: cloning, expression, distribution, and function in intestinal sensory reception

Studies of the guinea pig small intestine have suggested that serotonin (5-HT) may be a mucosal transmitter that stimulates sensory nerves and initiates peristaltic and secretory reflexes. We tested the hypothesis that guinea pig villus epithelial cells are able to inactivate 5-HT because they express the same 5-HT transporter as serotonergic neurons. A full-length cDNA, encoding a 630-amino acid protein (89.2% and 90% identical, respectively, to the rat and human 5-HT transporters) was cloned from the guinea pig intestinal mucosa. Evidence demonstrating that this cDNA encodes the guinea pig 5-HT transporter included 1) hybridization with a single species of mRNA ( approximately 3.7 kb) in Northern blots of the guinea pig brain stem and mucosa and 2) uptake of [3H]5-HT by transfected HeLa cells via a saturable, high-affinity (Michaelis constant 618 nM, maximum velocity 2.4 x 10(-17) mol . cell-1 . min-1), Na+-dependent mechanism that was inhibited by chlorimipramine > imipramine > fluoxetine > desipramine > zimelidine. Expression of the 5-HT transporter in guinea pig raphe and enteric neurons and the epithelium of the entire crypt-villus axis was demonstrated by in situ hybridization and immunocytochemistry. Inhibition of mucosal 5-HT uptake potentiates responses of submucosal neurons to mucosal stimulation. The epithelial reuptake of 5-HT thus appears to be responsible for terminating mucosal actions of 5-HT.

Migration of intestinal intraepithelial lymphocytes into a polarized epithelial monolayer

Intraepithelial lymphocytes (IEL) are a phenotypically distinct population of lymphocytes that reside in mucosal epithelia, below the intercellular tight junctions. Although adhesive functions of this population have been previously studied, relatively little is known about IEL migration from the microvasculature into the epithelium. We demonstrated that cultured human IEL were capable of migration into polarized epithelial cells in vitro, where they assumed a subjunctional position, identical to that observed in vivo. The migration was rapid and efficient and was directionally polarized, such that IEL migrated into epithelial monolayers from the basolateral, but not the apical, aspect. After a 4-h period of residence, up to one-half of the IEL then exited the monolayer basolaterally. Migration was partially inhibited by pertussis toxin, suggesting a potential mechanism for IEL migration by chemokine receptor-mediated signaling. The conditions and ligand pairs used in IEL migration were different from those for neutrophils, another cell type known to migrate through epithelia. This system may serve as a model for microenvironmental homing of IEL into the epithelium.

Conductive pathways for chloride and oxalate in rabbit ileal brush-border membrane vesicles

To evaluate the possibility that an apical membrane conductive pathway for oxalate is present in the rabbit distal ileum, we studied oxalate ([14C]oxalate) and chloride (36Cl) uptake into brush-border membrane vesicles enriched 15- to 18-fold in sucrase activity. Voltage-sensitive pathways for oxalate and chloride were identified by the stimulation of uptake provided by an inwardly directed potassium diffusion potential in the presence of valinomycin. Additionally, outwardly directed oxalate (or chloride) gradients stimulated [14C]oxalate (or 36Cl) uptake to a greater degree in the absence of valinomycin (when intracellular and extracellular potassium are equal) than in the presence of valinomycin. Voltage-dependent anion uptake was poorly saturable: apparent affinity constants were 141 +/- 17 and 126 +/- 8 mM for chloride and oxalate, respectively. Activation energies for the voltage-dependent uptake processes were low: 4.7 and 6.3 kcal/mol for chloride and oxalate, respectively. Sensitivity profiles of voltage-dependent chloride and oxalate uptake to anion transport inhibitors were similar. We conclude that an anion conductance is present in the apical membranes of ileal enterocytes and that this conductance is a candidate pathway for oxalate efflux from the enterocyte during transepithelial oxalate secretion.

Strain induces Caco-2 intestinal epithelial proliferation and differentiation via PKC and tyrosine kinase signals

Although the intestinal epithelium undergoes complex deformations during normal function, nutrient absorption, fasting, lactation, and disease, the effects of deformation on intestinal mucosal biology are poorly understood. We previously demonstrated that 24 h of cyclic deformation at an average 10% deformation every 6 s stimulates proliferation and modulates brush-border enzyme activity in human intestinal Caco-2 cell monolayers. In the present study we sought potential mechanisms for these effects. Protein kinase C (PKC) activity increased within 1 min after initiation of cyclic deformation, and the PKC-alpha and -zeta isoforms translocated from the soluble to the particulate fraction. Cyclic deformation also rapidly increased tyrosine kinase activity. Tyrosine phosphorylation of several proteins was increased in the soluble fraction but decreased in the particulate fraction by cyclic deformation for 30 min. Inhibition of PKC and tyrosine kinase signals by calphostin C, G-06967, and erbstatin attenuated or blocked cyclic deformation-mediated modulation of Caco-2 DNA synthesis and differentiation. These results suggest that cyclic deformation may modulate intestinal epithelial proliferation and brush-border enzyme activity by regulating PKC and tyrosine kinase signals.

Inhibition of prostaglandin-induced intestinal secretion by igmesine in healthy volunteers

BACKGROUND & AIMS

Igmesine, a final sigma ligand, has been shown to inhibit intestinal secretion and diarrhea in animal models. The purpose of this study was to measure the inhibitory effect of igmesine on basal and prostaglandin E2 (PGE2)-induced jejunal secretion in normal volunteers.

METHODS

Jejunal absorption of water and electrolytes was measured with a three-lumen open-segment perfusion method in 16 volunteers. A double-blind crossover study was performed involving intraluminal infusion of PGE2 after oral administration of placebo or igmesine at two doses.

RESULTS

PGE2 induced net secretion of water and electrolytes (P < 0.01 vs. basal conditions). The effect of PGE2 on water and electrolytes was not changed by 25 mg of igmesine but was suppressed by 200 mg of igmesine. This effect lasted at least 3 hours after a single oral dose. Igmesine at a dose of 200 mg also produced a significant decrease in basal rates of water and electrolyte absorption.

CONCLUSIONS

Igmesine, a final sigma ligand, inhibits PGE2-induced intestinal secretion in normal humans. Evaluating the drug in chronic diarrheas may be of interest.

Nitric oxide modulates T-lymphocyte migration in Peyer's patches and villous submucosa of rat small intestine

BACKGROUND & AIMS

Although nitric oxide (NO) is known to influence the recruitment of neutrophils in inflamed tissue, its role in lymphocyte-endothelial cell interactions remains poorly understood. The objectives of this study were to assess the effects of NO synthesis inhibition on T-lymphocyte migration in microvessels of rat small intestine and to define the role of adhesion molecules in this process.

METHODS

T lymphocytes collected from rat intestinal lymph were labeled with carboxyfluorescein diacetate succinimidyl ester and injected into the jugular vein of recipient rats. The migration of T lymphocytes into normal and NG-nitro-L-arginine methyl ester (L-NAME)-treated intestinal microvessels was monitored by using an intravital microscope.

RESULTS

L-NAME significantly increased rolling and adherence of lymphocytes in postcapillary venules of Peyer's patches and submucosal venules without significantly decreasing red blood cell velocity. The subsequent appearance of lymphocytes in the initial lymphatics was also accelerated by L-NAME. Anti-4-integrin antibody markedly inhibited the L-NAME-induced lymphocyte-endothelial cell interaction. Anti-P-selectin monoclonal antibody also significantly attenuated these adhesive interactions in both vascular regions.

CONCLUSIONS

These data suggest that NO is an important modulator of lymphocyte migration in Peyer's patches and in nonlymphoid regions of the intestine.

[Intestinal permeability in the first year of life. The effect of diarrhea]

OBJECTIVE

The permeability of the intestinal mucosa to lactulose and mannitol was explored longitudinally in infants at 1, 3-4 and 11-12 months of age. This was also evaluated during the episodes of diarrhea that they suffered during follow-up.

PATIENTS AND METHODS

Sugar excretion was measured by gas chromatography in five-hour urine samples.

RESULTS

A decrease in lactulose excretion was observed, which became significant at 11-12 months of age (p = 0.02). No changes were detected in mannitol excretion, although this showed a tendency to decrease. The lactulose/mannitol (L/M) ratio remained unchanged. During the 15 episodes of diarrhea observed in these infants during the 12 month follow-up, a considerable increase in this ratio was seen, due mainly to increased lactulose excretion.

CONCLUSIONS

It is hypothesized that the decrease in lactulose excretion between one and 11-12 months of age is part of the maturational process of the intestinal barrier, while diarrhea results in increased permeability due to damage to the absorptive epithelium.

Modulation of secretin release by neuropeptides in secretin-producing cells

Nerve fibers containing bombesin (BB)/gastrin-releasing polypeptide (GRP), pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP), or galanin are known to innervate the mucosa of the upper small intestine. Both BB/GRP and PACAP have been shown to elicit secretin secretion in vivo. We studied whether the above-mentioned neuropeptides can act directly on secretin-producing cells, including the murine neuroendocrine cell line STC-1 and a secretin cell-enriched preparation isolated from rat upper small intestinal mucosa. Secretin release from both cell types was stimulated by various agents known to elicit secretin release and by the neuropeptides BB, GRP, and PACAP, suggesting a comparable response between the two cell preparations. The effects of neuropeptides were further studied in STC-1 cells. BB, GRP, and PACAP stimulated secretin release time and concentration dependently. VIP also stimulated secretin release concentration dependently. Stimulation by BB/GRP or PACAP was accompanied by elevation of inositol-1,4,5-trisphosphate (IP3) or cAMP, respectively. The stimulatory effect of PACAP on secretin release was synergistically enhanced by BB without any synergistic increase in IP3 or cAMP production, suggesting cross talk between different signal transduction pathways downstream of the production of these two second messengers. The L-type Ca2+ channel blocker diltiazem (10 microM) and the Ca2+ chelator EGTA (1 mM) significantly inhibited BB-stimulated secretin release by 64% and 59%, respectively, and inhibited PACAP-stimulated release by 75% and 55%, respectively. The protein kinase A-specific inhibitor Rp-cAMPS (100 microM) also inhibited both BB- and PACAP-stimulated secretin release by 30% and 62%, respectively. Galanin inhibited BB- and PACAP-stimulated secretin release and production of second messengers in a concentration-dependent and pertussis toxin-sensitive manner. These results suggested that the neuropeptides BB/GRP, PACAP, VIP, and galanin can modulate secretin release in secretin-producing cells and that STC-1 cells can serve as a useful model for studying the cellular mechanism of secretin secretion elicited by luminal secretagogues and neuropeptides.

Postischemic inflammation: a role for mast cells in intestine but not in skeletal muscle

The objective of this study was to directly study a role for mast cells in ischemia-reperfusion (I/R)-induced mucosal and microvascular dysfunction. I/R was induced in the intestine and skeletal muscle (gastrocnemius and cremaster muscle) of wild-type mice and mast cell-deficient mice (W/Wv). Changes in mucosal permeability (blood-to-lumen clearance of 51Cr-EDTA), leukocyte infiltration (myeloperoxidase activity in the intestine and intravital microscopy in the cremaster muscle), and vascular permeability (tissue wet-to-dry weight ratio and FITC-albumin leakage) were measured as indexes of tissue dysfunction. In wild-type animals, intestinal I/R induced a significant increase in mucosal permeability, leukocyte infiltration, and vascular permeability. Mast cell-deficient animals were completely protected from I/R-induced mucosal dysfunction. However, skeletal muscle I/R induced a significant increase in leukocyte infiltration, FITC-albumin leakage, and edema formation to the same degree in both wild-type and mast cell-deficient animals. These data suggest that mast cells may be important mediators of I/R-induced mucosal and microvascular dysfunction in the intestine but not of microvascular dysfunction in skeletal muscle.

Glibenclamide blocks volume-sensitive Cl- channels by dual mechanisms

To study the mechanisms of glibenclamide actions on volume-sensitive Cl- channels, whole cell patch-clamp studies were performed at various pH levels in human epithelial Intestine 407 cells. Extracellular application of glibenclamide reversibly suppressed volume-sensitive Cl- currents in the entire range of voltage examined (-100 to +100 mV) and accelerated the depolarization-induced inactivation at pH 7.5. When glibenclamide was applied from the intracellular side, in contrast, no effect was observed. At acidic pH, at which the weak acid glibenclamide exists largely in the uncharged form, the instantaneous current was, in a voltage-independent manner, suppressed by the extracellular drug at micromolar concentrations without significantly affecting the depolarization-induced inactivation. At alkaline pH, at which almost all of the drug is in the charged form, glibenclamide speeded the inactivation time course and induced a leftward shift of the steady-state inactivation curve at much higher concentrations. Thus it is concluded that glibenclamide exerts inhibiting actions on swelling-activated Cl- channels from the extracellular side and that the uncharged form is mainly responsible for voltage-independent inhibition of instantaneous currents, whereas the anionic form facilitates voltage-dependent channel inactivation in human epithelial Intestine 407 cells.

Characterization of PKA isoforms and kinase-dependent activation of chloride secretion in T84 cells

Chloride exit across the apical membranes of secretory epithelial cells is acutely regulated by the cAMP-mediated second messenger cascade. To better understand the regulation of transepithelial chloride secretion, we have characterized the complement of cAMP-dependent protein kinase (PKA) isoforms present in the human colonic epithelial cell line T84. Our results show that both type I and type II PKA are present in T84 cells. Immunoprecipitation of 8-azido-[32P]cAMP-labeled cell lysates revealed that the major regulatory subunits of PKA were RIalpha and RIIalpha. In addition, immunogold electron microscopy showed that RIIalpha labeling was found on membranes of the trans Golgi network and on apical plasma membrane. In contrast, RIalpha was randomly distributed throughout the cytoplasm, with no discernible membrane association. Northern blot analysis of T84 RNA revealed that Calpha was the predominantly expressed catalytic subunit. Short-circuit current measurements were performed in the presence of combinations of site-selective cAMP analog pairs to preferentially activate either PKA type I or PKA type II in intact T84 cell monolayers. Maximal levels of chloride secretion (approximately 100 microA/cm2) were observed for both type I and type II PKA-selective analog pairs. Subsequent addition of forskolin was unable to further increase chloride secretion. Thus activation of either type I or type II PKA is able to maximally stimulate chloride secretion in T84 colonic epithelial cells.

Calcium signaling in cultured human and rat duodenal enterocytes

Vagal stimuli increase duodenal mucosal HCO-3 secretion and may provide anticipatory protection against acid injury, but duodenal enterocyte (duodenocyte) responses and cholinoceptor selectivity have not been defined. We therefore developed a stable primary culture model of duodenocytes from rats and humans. Brief digestion of scraped rat duodenal mucosa or human biopsies with collagenase/dispase yielded cells that attached to the extracellular matrix Matrigel within a few hours of plating. Columnar cells with villus enterocyte morphology that exhibited spontaneous active movement were evident between 1 and 3 days of culture. Rat duodenocytes loaded with fura 2 responded to carbachol with a transient increase in intracellular calcium concentration ([Ca2+]i), with an apparent EC50 of approximately 3 microM. In a first type of signaling pattern, [Ca2+]i returned to basal or near basal values within 3-5 min. In a second type, observed in cells with enlarged vacuoles characteristic of crypt cell morphology, the initial transient increase was followed by rhythmic oscillations. Human duodenocytes responded with a more sustained increase in [Ca2+]i, and oscillations were not observed. Rat as well as human duodenocytes also responded to CCK-octapeptide but not to vasoactive intestinal polypeptide. Equimolar concentrations (100 nM) of the subtype-independent muscarinic antagonist atropine and the M3 antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide prevented the response to 10 microM carbachol, whereas the M1 antagonist pirenzepine and the M2 antagonists methoctramine and AF-DX 116BS had no effect at similar concentrations. Responses in rat and human duodenocytes were similar. A new agonist-sensitive primary culture model for rat and human duodenocytes has thus been established and the presence of enterocyte CCK and muscarinic M3 receptors demonstrated.

Growth factors and gut function

Growth factors play a key role in maintaining gut integrity and in stimulating repair. By understanding their physiological function we can use this information to apply to the treatment of conditions in which mucosal homeostasis has broken down.

Regulation of jejunal sodium and water absorption by angiotensin subtype receptors

The purpose of this study was to determine the precise role of angiotensin subtype-1 (AT1) and -2 (AT2) receptors and the mechanisms by which they act to alter fluid transport in the rat jejunum. In rats on normal sodium intake, ANG II at low dose stimulated net jejunal fluid absorption, whereas at a high dose the peptide inhibited absorption. Low-dose ANG II-stimulated fluid absorption was blocked completely by the specific AT2 receptor antagonist PD-123319 (PD) but was unchanged by the AT1 receptor antagonist losartan (Los). The AT2 receptor agonist CGP-42112A, caused an inversely dose-dependent increase in fluid absorption, which also was totally prevented by PD but was unaltered by Los. Conversely, high-dose ANG II inhibition of absorption was blocked by Los but not by PD. In animals receiving normal sodium intake, neither Los nor PD alone altered fluid absorption. In sodium-restricted animals, however, Los alone increased absorption and PD alone inhibited absorption. In rats on normal sodium intake, low-dose ANG II increased jejunal interstitial and luminal (loop) fluid concentrations of cGMP. These increases in cGMP were blocked with PD but not with Los. 8-Bromoguanosine-3',5'-cyclic monophosphate administered via the mesenteric artery or the submucosal interstitial space markedly increased absorption, but it inhibited absorption when administered into the loop. High-dose ANG II decreased jejunal interstitial and loop fluid cAMP and increased PGE2. The increase in PGE2 was blocked by Los but not by PD. The data demonstrate that ANG II mediates jejunal sodium and water absorption by an action at the AT2 receptor involving cGMP formation. The data also show that ANG II inhibits absorption via the AT1 receptor by a mechanism that is both negatively coupled to cAMP and increases jejunal PGE2 production.

Mechanism of increased vessel wall nitric oxide concentrations during intestinal absorption

Vasoactive compounds, including nitric oxide (NO) and hypertonic sodium, may diffuse from venous endothelial cells and blood to the arterial wall during intestinal absorption. This hypothesis was tested by measuring the perivascular NO concentration ([NO]) for paired small arteries and veins with NO-sensitive microelectrodes. Resting arterial and venous wall concentrations for nine vessel pairs (5 rats) were 353 +/- 28 and 401 +/- 48 (SE) nM. During mucosal absorption of 100 and 300 mg/dl glucose, the artery dilated 12 +/- 1.5 and 17 +/- 2%, [NO] increased to 540 +/- 68 and 550 +/- 49 nM, and venous wall [NO] increased to 557 +/- 60 and 633 +/- 70 nM. During venous occlusion to block diffusion of materials from venous blood to the artery wall, the arterial and venous [NO] decreased by 70-80%, and one-half of the arterial dilation subsided. Superfusion with 320 and 360 mosmol/l hypertonic sodium medium to simulate the sodium hyperosmolarity during mucosal absorption of glucose increased the arterial [NO] by 20-30 and 40-50%; 360 mosmol/l saline made hypertonic with mannitol did not significantly increase the [NO]. Although venous to arterial diffusion of NO occurred, the increased arterial [NO] during mucosal glucose absorption was primarily generated by the arterial wall in response to materials that diffused from venous blood, such as hypertonic sodium.

Expression of the transforming growth factor-beta gene during growth inhibition following polyamine depletion

Polyamine depletion and cytokine transforming growth factor-beta (TGF-beta) inhibit cell proliferation. The current study tests the hypothesis that polyamine depletion results in growth inhibition by altering expression of the TGF-beta gene in intestinal epithelial cells. Studies were conducted in the IEC-6 cell line derived from rat small intestinal crypt cells. Cells were grown in DMEM in the presence or absence of alpha-difluoromethylornithine (DFMO), a specific inhibitor of polyamine biosynthesis, for 6 and 12 days. Administration of DFMO not only depleted intracellular polyamines but also significantly increased the mRNA levels of TGF-beta. Increased TGF-beta mRNA in DFMO-treated cells was paralleled by an increase in TGF-beta content. Depletion of intracellular polyamines by DFMO had no effect on the rate of TGF-beta gene transcription, as measured by nuclear run-on assay. The half-life of mRNA for TGF-beta in normal cells was approximately 65 min and increased to >16 h in cells treated with DFMO for 6 or 12 days. Exogenous polyamine, when given together with DFMO, prevented the increased half-life of TGF-beta mRNA in IEC-6 cells. TGF-beta added to the culture medium significantly decreased the rate of DNA synthesis and final cell number in normal and polyamine-deficient cells. Furthermore, growth inhibition caused by polyamine depletion was partially but significantly blocked by addition of immunoneutralizing anti-TGF-beta antibody. These results indicate that 1) depletion of intracellular polyamines induces the activation of the TGF-beta gene through posttranscriptional regulation and 2) increased expression of the TGF-beta gene plays an important role in the process of growth inhibition following polyamine depletion.

Duodenal Ca2+ absorption is not stimulated by calcitriol during early postnatal development of pigs

The role of calcitriol in stimulating intestinal active Ca2+ absorption during postnatal life was studied in newborn, suckling, and weaned control (Con) piglets and piglets suffering from inherited calcitriol deficiency (Def piglets). In addition, a group of Def piglets was treated with vitamin D3 (Def-D3 piglets), which normalized plasma calcitriol levels. Regardless of age, duodenal calbindin-D9k concentrations ranged between 1,839 and 2,846 microg/g mucosa in Con piglets, between 821 and 1,219 microg/g mucosa in Def piglets, and between 2,960 and 3,692 microg/g mucosa in Def-D3 animals. In weaned animals, active Ca2+ absorption as calculated from in vitro 45Ca2+ flux rate measurements in Ussing chambers could be related to calbindin-D9k levels. Thus active Ca2+ absorption was completely absent in Def animals but was reconstituted in Def-D3 animals. In contrast, in newborn Def piglets active Ca2+ absorption functioned normally despite the low plasma calcitriol and mucosal calbindin-D9k levels and could not be affected by treatment with vitamin D3. Similar results were obtained from suckling Def piglets. The microtubule-disrupting agent colchicine caused significant inhibition of transepithelial net Ca2+ absorption in duodenal epithelia from newborn piglets without exerting an effect in suckling and weaned animals. Colchicine had no effect on Ca2+ uptake across the brush border membrane of mucosal enterocytes or on glucose-dependent electrogenic net ion flux rates in duodenal preparations from newborn Con piglets. In conclusion, our findings reveal intestinal active Ca2+ absorption during early postnatal life of pigs that involves calcitriol-independent mechanisms and that may include intact microtubule actions.

Endothelins promote egg albumin-induced intestinal anaphylaxis in rats

BACKGROUND & AIMS

The basic mechanisms of food allergies are still unknown. The aims of this study were to investigate whether endothelins (ETs) in the intestinal mucosa are involved in the pathogenesis of intestinal anaphylaxis.

METHODS

Sprague-Dawley rats were sensitized to chicken egg albumin (EA) by intraperitoneal injection. Fourteen days after sensitization, EA was administered in the jejunal segments to induce intestinal anaphylaxis. Net water outflux and histamine release into loops and serum concentrations of rat mast cell protease II (RMCP-II) were determined. ET-1 and ET-3 concentrations in the jejunal mucosa were determined, and expression of the corresponding messenger RNAs was examined by competitive polymerase chain reaction.

RESULTS

In sensitized animals, challenge with intraluminal antigen caused a significant increase in net water outflux and histamine release together with an elevation of serum RMCP-II concentrations. Mucosal concentrations of ET-1 and ET-3 and expression of their messenger RNAs were significantly increased in sensitized animals after EA challenge. Treatment with an ETA-receptor antagonist, but not an ETB-receptor antagonist, attenuated the increase in net water outflux, histamine release, and serum RMCP-II concentrations in rats with EA-induced intestinal anaphylaxis.

CONCLUSIONS

Release of ETs in the intestinal mucosa increased in sensitized animals after EA challenge. ETs may play a significant role in the development of intestinal anaphylaxis via an ETA receptor.

The response of rat colonic mucosa to 5-hydroxytryptamine in health and following restraint stress

The present study characterized the rat colonic secretory response to 5-hydroxytryptamine (5-HT) and determined alterations in this response following stress. 5-HT stimulated rat colonic short-circuit current in a concentration-dependent fashion (pD2 = 5.19). This response was subject to desensitization and was mimicked by the indolealkylamines with a rank order potency of 5-HT approximately alpha-methyl-5-HT > 5-carboxytryptamine approximately 5-methoxytryptamine. 2-Methyl-5-HT was a partial agonist. The colonic response to 5-HT was unaltered by methysergide (10 microM), ritanserin (0.1 microM), ondansetron (1 microM) or clozapine (10 microM), but was antagonized by the 5-HT4 receptor antagonists SB204070 (pD'2 = 9.32), GR113808 (pKb = 8.56), DAU6285 (pKb = 6.07) and SDZ205557 (pKb = 6.80). The response of colonic epithelial and oesophageal tunica muscularis mucosae to 5-HT is therefore mediated by a similar 5-HT4 receptor. Following wrap restraint stress, the colonic response to 5-HT became bimodal. Half of the preparations were hyper-responsive, while the rest were hypo-responsive to 5-HT. This 5-HT4 receptor may therefore be involved in stress related changes in fluid transport.

Intestinal adaptation is enhanced by epidermal growth factor independent of increased ileal epidermal growth factor receptor expression

BACKGROUND/PURPOSE

Intestinal adaptation after massive small bowel resection (SBR) is augmented by epidermal growth factor (EGF) via an unknown mechanism. We recently have observed that EGF increases the expression of EGF receptor mRNA and protein content in the remnant ileum after SBR. The purpose of this study was to determine whether the magnitude of EGF-induced receptor expression correlates with intestinal adaptation.

METHODS

A 50% proximal SBR or sham operation (bowel transection with reanastomosis) was performed on male ICR mice. Animals from each group were then selected randomly to receive either human recombinant EGF (150 microg/kg/d) or saline by twice daily intraperitoneal injections. The remnant ileum was harvested at 1 week, and parameters of adaptation measured as changes in protein content. Ileal EGF receptor mRNA was quantitated using a ribonuclease protection assay. Changes in the expression ileal EGF receptor protein were determined by Western blot after immunoprecipitation. Comparisons of mean values between groups was performed using analysis of variance (ANOVA) and a P value of less than .05 was considered significant. Values are presented as mean +/- SEM.

RESULTS

EGF was mitogenic to the ileum after sham operation as monitored by increases in ileal protein content (2.21 +/- 0.002 mg/cm Sham v 2.97 +/- 0.25 mg/cm Sham +/- EGF; P < .05). After SBR, adaptation resulted in increased ileal protein content (4.45 +/- 0.27 mg/cm), which was substantially boosted by EGF (5.98 +/- 0.39 mg/cm; P < .05). No differences were detected in ileal EGF receptor mRNA or protein expression between Sham or SBR groups that did not receive EGF. However, EGF significantly enhanced the expression of ileal EGF receptor mRNA to an equal extent after both sham and SBR (approximately threefold). The magnitude of this increase in EGF receptor protein (four- to sixfold) was similar in both EGF groups as shown by Western blotting.

CONCLUSIONS

Changes in ileal EGF receptor expression are not mandatory for adaptation to occur. EGF upregulates the expression of mRNA and protein for its own intestinal receptor in vivo. Because EGF-induced receptor expression was comparable after both SBR and Sham operation, the beneficial effect of EGF during adaptation is likely caused by other factors in addition to increased receptor expression.

Effect of in vivo corticosteroids on Na+ transport across airway epithelia

We have investigated the role in vivo of mineralocorticoid and glucocorticoid hormones in regulating the rate of electrogenic amiloride-sensitive Na+ absorption across murine airway tissue studied in vivo (nasal potential difference) and in vitro (Ussing chambers). We found that elevating the plasma aldosterone concentration 10-fold (low-Na+ diet) had no significant effect on amiloride-sensitive Na+ absorption across tracheal or nasal epithelia. High doses of dexamethasone for 1 wk likewise did not change the rate of amiloride-sensitive Na+ absorption across airway epithelia. In contrast, both hormonal manipulations elevated the rate of colonic Na+ absorption. Furthermore, adrenalectomy (both normal and cystic fibrosis mice) also failed to alter Na+ absorption across airway epithelia. We conclude that, in vivo, neither the mineralocorticoid nor the glucocorticoid hormones significantly regulate the rates of amiloride-sensitive electrogenic Na+ absorption across airway epithelia in the adult mouse.