Concepció Amat

Role of vasopressin in rat distal colon function

The specific role of vasopressin in colonic crypt function and its possible synergistic action with aldosterone were studied. Sprague‐Dawley rats fed a high‐Na+ (HS; 150 mm NaCl) or a low‐Na+ (LS; 150 μm NaCl) diet were deprived of water or infused with vasopressin, and some animals were treated with specific vasopressin receptor subtype V1 and V2 antagonists. The expression of the epithelial Na+ channel (ENaC), α‐smooth muscle actin (α‐SMA) and aquaporin‐2 (AQP‐2) were determined by immunolocalization in distal colonic mucosa. The pericryptal Na+ concentration was determined by confocal microscopy, using a low‐affinity Na+‐sensitive fluorescent dye (sodium red) and crypt permeability was measured by the rate of escape of fluorescein isothiocyanate‐labelled dextran (10 kDa) from the crypt lumen into the pericryptal space in isolated rat distal colonic mucosa. A high plasma concentration of vasopressin raised α‐SMA expression in the pericryptal sheath (P < 0.05), increased the pericryptal Na+ accumulation in this space (P < 0.01) and caused a reduction of crypt wall permeability (P < 0.01). All these effects were reversed by selective blockade of V1 and V2 receptors. No synergistic effects with aldosterone were observed. Dehydration and vasopressin infusion increased AQP‐2 expression in distal colonic mucosa (P < 0.05). This action of vasopressin was prevented by tolvaptan, a specific V2 receptor antagonist (P < 0.05). It is concluded that vasopressin has trophic effects in the rat distal colon, increasing pericryptal myofibroblast growth which affects crypt absorption, and these effects are independent of the presence of aldosterone.

Aldosterone Reduces Crypt Colon Permeability during Low-Sodium Adaptation

Fluid and electrolyte absorption by colonic crypts depends on the transport properties of crypt cellular and paracellular routes and of the pericryptal sheath. As a low-Na+ diet increases aldosterone and angiotensin II secretion, either hormone could affect absorption. Control and adrenalectomized (ADX) Sprague-Dawley rats were kept at a high-NaCl (HS) diet and then switched to low-NaCl (LS) diet for 3 days. Aldosterone or angiotensin II plasma concentrations were maintained using implanted osmotic mini-pumps. The extracellular Na+ concentration in isolated rat distal colonic mucosa was determined by confocal microscopy using a low-affinity Na+-sensitive fluorescent dye (Sodium red, and Na+-insensitive BODIPY) bound to polystyrene beads. Crypt permeability to FITC-labelled dextran (10 kDa) was monitored by its rate of escape from the crypt lumen into the pericryptal space. Mucosal ion permeability was estimated by transepithelial electrical resistance (TER) and amiloride-sensitive short-circuit current (SCC). The epithelial Na+ channel, ENaC, was determined by immunolocalization. LS diet decreased crypt wall permeability to dextran by 10-fold and doubled TER. Following ADX, aldosterone decreased crypt wall dextran permeability, increased TER, increased Na+ accumulation in the pericryptal sheath and ENaC expression even in HS. Infusion of angiotensin II to ADX rats did not reverse the effects of aldosterone deprivation. These findings indicate that aldosterone alone is responsible for both the increase in Na+ absorption and the decreased paracellular and pericryptal sheath permeability.

Induction of colitis in young rats by dextran sulfate sodium

Models using dextran sulfate sodium (DSS) to induce experimental colitis in rodents have been performed mostly in adult animals. For this reason, we aimed to develop a model of colitis in young rats. DSS was administered to 30-day-old rats at concentrations ranging from 0.5 to 5% in drinking water. Young rats were remarkably sensitive to DSS since clinical symptoms rapidly rose with 5% DSS and most animals died after the fifth day. With 1 and 2% DSS, the severity of mucosal lesions was also high on day 7, the animals showing leukocytosis and anemia. At 0.5% DSS, leukocytosis and mild colonic lesions were induced. This concentration of DSS significantly increased myeloperoxidase activity and goblet cell number in the colon, indicating mucosal inflammation. Since food consumption was not reduced by 0.5% DSS, we suggest that this protocol can be used to study the effects of dietary supplements on intestinal inflammatory processes.

Pericryptal myofibroblast growth in rat descending colon induced by low-sodium diets is mediated by aldosterone and not by angiotensin II.

Pericryptal myofibroblast growth in descending colonic crypts correlates with the activation of the renin-angiotensin-aldosterone system. Earlier work showed that during the transition from a high-Na+ (HS) to low-Na+ (LS) diet there are changes in the colonic crypt wall and pericryptal sheath. As LS diet increases both aldosterone and angiotensin II, the aim here was to determine their individual contributions to the trophic changes in colonic crypts. Experiments were conducted on control and adrenalectomized Sprague-Dawley rats fed an HS diet and then switched to LS diet for 3 days and supplemented with aldosterone or angiotensin II. The actions of the angiotensin-converting enzyme inhibitor captopril, the angiotensin receptor antagonist losartan and the aldosterone antagonist spironolactone on extracellular matrix proteins, claudin 4 and E-cadherin myofibroblast proteins, α-smooth muscle actin (α-SMA) and OB-cadherin (cadherin 11), angiotensin type 1 and TGFβr1 membrane receptors were determined by immunolocalization in fixed distal colonic mucosa. The LS diet or aldosterone supplementation following ADX in HS or LS increased extracellular matrix, membrane receptors and myofibroblast proteins, but angiotensin alone had no trophic effect on α-SMA. These results show that aldosterone stimulates myofibroblast growth in the distal colon independently of dietary Na+ intake and of angiotensin levels. This stimulus could be a genomic response or secondary to stretch of the pericryptal sheath myofibroblasts accompanying enhanced rates of crypt fluid absorption.

Transmural potential difference and short circuit current of chicken cecum in vitro

The electrical parameters of the chicken cecum were studied in vitro, in birds fed a commercial NaCl-rich diet. The statistical analysis of data was carried out using a linear model-based method which enabled standardization of concomitant factors that could mask the interpretation of the results. Transmural potential difference (PD) decreased initially reaching stable values at 50 min between 7.9 and 9.0 mV. Short-circuit current (Isc) was stable during incubation, with lower values in the medial (41.8 microA/cm2) than in the distal (58.1 microA/cm2) region of the cecum. The reduction of Na+ concentration in the incubation medium produced a fall in PD and Isc and both were ouabain and amiloride sensitive. This indicates that the current is largely carried by the net Na+ transport.

Does chicken rectal adaptation to a low nac1 diet involve changes in paracellular permeability

Abstract 1. 1. The electrical parameters (PD and I sc ) of the chicken rectum were studied in vitro , in birds fed either a high or a low NaCl diet. 2. 2. Chickens fed a high NaCl diet showed serosa negative values of PD and I sc (− 2.6 mV and − 39.2 μA/cm 2 , respectively), being unaffected by the suppression of Na + in the incubation medium. 3. 3. Chickens fed a low NaCl diet had serosa positive values of PD and I sc (4.7 mV and 128.7 μA/cm 2 , respectively). In these animals, the reduction of Na + concentration in the incubation medium produced a significant fall in both PD and I sc supporting the view that the adapted rectum is capable of net sodium transport from the mucosal to the serosal compartment. 4. 4. In high-Nad fed chickens, 2,4,6-Triaminopyrimidine added to the mucosal solution resulted in a reverse PD and I sc , suggesting that changes in the paracellular permeability to cations play a role in the rectal adaptation to the sodium content of the diet.

The Anti-Inflammatory Effect of Spray-Dried Plasma Is Mediated by a Reduction in Mucosal Lymphocyte Activation and Infiltration in a Mouse Model of Intestinal Inflammation.

Spray-dried preparations from porcine and bovine plasma can alleviate mucosal inflammation in experimental models and improve symptoms in patients with enteropathy. In rodents, dietary supplementation with porcine spray-dried plasma (SDP) attenuates intestinal inflammation and improves the epithelial barrier function during intestinal inflammation induced by Staphylococcus aureus enterotoxin B (SEB). The aim of this study was to discern the molecular mechanisms involved in the anti-inflammatory effects of SDP. Male C57BL/6 mice were fed with 8% SDP or control diet (based on milk proteins) for two weeks, from weaning until day 33. On day 32, the mice were given a SEB dose (i.p., 25 µg/mouse) or vehicle. SEB administration increased cell recruitment to mesenteric lymph nodes and the percentage of activated Th lymphocytes and SDP prevented these effects). SDP supplementation increased the expression of interleukin 10 (IL-10) or transforming growth factor- β (TGF-β) compared to the SEB group. The SEB challenge increased six-fold the expression of mucosal addressin cell adhesion molecule 1 (MAdCAM-1) and intercellular adhesion molecule 1 (ICAM-1); and these effects were attenuated by SDP supplementation. SEB also augmented NF-κB phosphorylation, an effect that was prevented by dietary SDP. Our results indicate that the anti-inflammatory effects of SDP involve the regulation of transcription factors and adhesion molecules that reduce intestinal cell infiltration and the degree of the inflammatory response.

Dietary unsaturated long-chain Fatty acids modify D-glucose absorption in weaning rats.

Objective: The authors evaluated the effects of dietary long-chain polyunsaturated fatty acids on D-glucose absorption in weaning rats. Methods: Pups were born from control mothers fed a diet containing (per kg of total fatty acids) 280 g of saturated fatty acids, 496 g of monounsaturated fatty acids and 222 g of polyunsaturated fatty acids or from mothers fed a diet containing a high proportion of saturated fatty acids (920 g/kg) and a low proportion of unsaturated fatty acids (low-unsaturated fatty acid, 80 g/kg), initiated 2 weeks before mating and continued throughout pregnancy. When pups from low-unsaturated fatty acid mothers were 15 days old, they were subdivided into two groups: one control (low-unsaturated fatty acid-C) and one fed a long-chain polyunsaturated fatty acid supplement rich in arachidonic acid and docosahexaenoic acid (low-unsaturated fatty acid-S) until weaning. At day 21, the kinetics of D-glucose absorption was studied in brush-border membrane vesicles from the jejunoileal segment. Results: The maximal transport rate (Vmax) of glucose in the low-unsaturated fatty acid-C and low-unsaturated fatty acid-S groups was higher than in control rats: 160 and 130 versus 98 pmol/(mg protein·s), respectively (P < 0.05). Rats fed the low-unsaturated fatty acid diet had a lower diffusion constant (Kd) than control rats did: 21.6 and 29.2 nL/(mg protein·s), respectively (P < 0.05). However, rats receiving the long-chain polyunsaturated fatty acid supplement and control rats had similar Kd values. Conclusion: These results indicate that dietary long-chain polyunsaturated fatty acid supplementation can restore, in part, the kinetic characteristics of intestinal D-glucose absorption in pups from mothers maintained on a low-unsaturated fatty acid diet.

Dietary Animal Plasma Proteins Improve the Intestinal Immune Response in Senescent Mice

Increased life expectancy has promoted research on healthy aging. Aging is accompanied by increased non-specific immune activation (inflammaging) which favors the appearance of several disorders. Here, we study whether dietary supplementation with spray-dried animal plasma (SDP), which has been shown to reduce the activation of gut-associated lymphoid tissue (GALT) in rodents challenged by S. aureus enterotoxin B (SEB), and can also prevent the effects of aging on immune system homeostasis. We first characterized GALT in a mouse model of accelerated senescence (SAMP8) at different ages (compared to mice resistant to accelerated senescence; SAMR1). Second, we analyzed the SDP effects on GALT response to an SEB challenge in SAMP8 mice. In GALT characterization, aging increased the cell number and the percentage of activated Th lymphocytes in mesenteric lymph nodes and Peyer’s patches (all, p < 0.05), as well as the expression of IL-6 and TNF-α in intestinal mucosa (both, p < 0.05). With respect to GALT response to the SEB challenge, young mice showed increased expression of intestinal IL-6 and TNF-α, as well as lymphocyte recruitment and activation (all, p < 0.05). However, the immune response of senescent mice to the SEB challenge was weak, since SEB did not change cell recruitment or the percentage of activated Th lymphocytes. Mice supplemented with SDP showed improved capacity to respond to the SEB challenge, similar to the response of the young mice. These results indicate that senescent mice have an impaired mucosal immune response characterized by unspecific GALT activation and a weak specific immune response. SDP supplementation reduces non-specific basal immune activation, allowing for the generation of specific responses.