Morphometric and biomechanical remodelling in the intestine after small bowel resection in the rat

Characterization of the layer, direction and time-dependent mechanical behaviour of the human oesophagus and the effects of formalin preservation

The mechanical characterization of the oesophagus is essential for applications such as medical device design, surgical simulations and tissue engineering, as well as for investigating the organ's pathophysiology. However, the material response of the oesophagus has not been established ex vivo in regard to the more complex aspects of its mechanical behaviour using fresh, human tissue: as of yet, in the literature, only the hyperelastic response of the intact wall has been studied. Therefore, in this study, the layer-dependent, anisotropic, visco-hyperelastic behaviour of the human oesophagus was investigated through various mechanical tests. For this, cyclic tests, with increasing stretch levels, were conducted on the layers of the human oesophagus in the longitudinal and circumferential directions and at two different strain rates. Additionally, stress-relaxation tests on the oesophageal layers were carried out in both directions. Overall, the results show discrete properties in each layer and direction, highlighting the importance of treating the oesophagus as a multi-layered composite material with direction-dependent behaviour. Previously, the authors conducted layer-dependent cyclic experimentation on formalin-embalmed human oesophagi. A comparison between the fresh and embalmed tissue response was carried out and revealed surprising similarities in terms of anisotropy, strain-rate dependency, stress-softening and hysteresis, with the main difference between the two preservation states being the magnitude of these properties. As formalin fixation is known to notably affect the formation of cross-links between the collagen of biological materials, the differences may reveal the influence of cross-links on the mechanical behaviour of soft tissues.

Mechanical experimentation of the gastrointestinal tract: a systematic review

The gastrointestinal (GI) organs of the human body are responsible for transporting and extracting nutrients from food and drink, as well as excreting solid waste. Biomechanical experimentation of the GI organs provides insight into the mechanisms involved in their normal physiological functions, as well as understanding of how diseases can cause disruption to these. Additionally, experimental findings form the basis of all finite element (FE) modelling of these organs, which have a wide array of applications within medicine and engineering. This systematic review summarises the experimental studies that are currently in the literature (n = 247) and outlines the areas in which experimentation is lacking, highlighting what is still required in order to more fully understand the mechanical behaviour of the GI organs. These include (i) more human data, allowing for more accurate modelling for applications within medicine, (ii) an increase in time-dependent studies, and (iii) more sophisticated in vivo testing methods which allow for both the layer- and direction-dependent characterisation of the GI organs. The findings of this review can also be used to identify experimental data for the readers' own constitutive or FE modelling as the experimental studies have been grouped in terms of organ (oesophagus, stomach, small intestine, large intestine or rectum), test condition (ex vivo or in vivo), number of directions studied (isotropic or anisotropic), species family (human, porcine, feline etc.), tissue condition (intact wall or layer-dependent) and the type of test performed (biaxial tension, inflation-extension, distension (pressure-diameter), etc.). Furthermore, the studies that investigated the time-dependent (viscoelastic) behaviour of the tissues have been presented.

In the Short-term, Milk Fat Globule Epidermal Growth Factor-8 Causes Site-specific Intestinal Growth in Resected Piglets

OBJECTIVES

Short bowel syndrome (SBS) remains the leading cause of neonatal intestinal failure. Milk fat globule epidermal growth factor-8 (MFG-E8), present in human milk, has homology with epidermal growth factor (EGF), known to enhance adaptation in SBS. In this pilot study, the role of oral MFG-E8 treatment in SBS was explored in neonatal piglets.

METHODS

Neonatal piglets underwent 75% intestinal resection, either distal (jejunal-colonic [JC] anastomosis) or mid-intestinal (jejunal-ileal [JI] anastomosis). Piglets were randomized to intragastric treatment with MFG-E8  (5 mg/kg per day) or saline and were maintained on parenteral nutrition and enteral nutrition for 7 days. Adaptation was assessed by intestinal length and weight, histopathology, fecal fat analysis and RT-qPCR analysis of mucosal transcripts, including growth factors.

RESULTS

JI piglets demonstrated intestinal lengthening (P < 0.001), 2-fold greater in ileum than jejunum (P = 0.02), where lengthening was increased by MFG-E8 treatment (P = 0.02). JC piglets did not exhibit jejunal lengthening, regardless of treatment. Fat absorption was greater for JI piglets (P = 0.02), unaffected by treatment. In JI piglets, expression of Egf was increased in the ileum (P < 0.01) and MFG-E8 treatment increased Egfr (receptor) expression (P = 0.02).

CONCLUSIONS

MF-EG8 demonstrated site-specific trophic effects, only with JI anatomy. This may limit the utility of this treatment for SBS, except for rare patients with retained ileum. The mechanisms of these site-specific effects, however, and the role of MFG-E8 in neonatal gut growth and in diseases, such as necrotizing enterocolitis that commonly target ileum, warrant further exploration.

Digestive enzyme expression in the large intestine of children with short bowel syndrome in a late stage of adaptation

BACKGROUND AND AIMS

Intestinal adaptation in short bowel syndrome (SBS) includes morphologic processes and functional mechanisms. This study investigated whether digestive enzyme expression in the duodenum and colon is upregulated in SBS patients.

METHOD

Sucrase-isomaltase (SI), lactase-phlorizin hydrolase (LPH), and neutral Aminopeptidase N (ApN) were analyzed in duodenal and colonic biopsies from nine SBS patients in a late stage of adaptation as well as healthy and disease controls by immunoelectron microscopy (IEM), Western blots, and enzyme activities. Furthermore, proliferation rates and intestinal microbiota were analyzed in the mucosal specimen.

RESULTS

We found significantly increased amounts of SI, LPH, and ApN in colonocytes in most SBS patients with large variation and strongest effect for SI and ApN. Digestive enzyme expression was only partially elevated in duodenal enterocytes due to a low proliferation level measured by Ki-67 staining. Microbiome analysis revealed high amounts of Lactobacillus resp. low amounts of Proteobacteria in SBS patients with preservation of colon and ileocecal valve. Colonic expression was associated with a better clinical course in single cases.

CONCLUSION

In SBS patients disaccharidases and peptidases can be upregulated in the colon. Stimulation of this colonic intestinalization process by drugs, nutrients, and pre- or probiotics might offer better therapeutic approaches.

To learn, to remember, to forget-How smart is the gut?

The enteric nervous system (ENS) resides within the gut wall and autonomously controls gut functions through coordinated activation of sensory, inter and motor neurons. Its activity is modulated by the enteric immune and endocrine system as well as by afferent and efferent nerves of the parasympathetic and sympathetic nervous system. The ENS is often referred to as the second brain and hence is able to perform sophisticated tasks. We review the evidence that the "smartness" of the ENS may even extend to its ability to learn and to memorize. Examples for habituation, sensitization, conditioned behaviour and long-term facilitation are evidence for various forms of implicit learning. Moreover, we discuss how this may change not only basic Neurogastroenterology but also our understanding of development of gut diseases and chronic disorders in gut functions. At the same time, we identify open questions and future challenges to confirm learning, memory and memory deficits in the gut. Despite some remaining experimental challenges, we are convinced that the gut is able to learn and are tempted to answer the question with: Yes, the gut is smart.

The effect of small intestine heterogeneity on irreversible electroporation treatment planning

Nonthermal irreversible electroporation (NTIRE) is an ablation modality that utilizes microsecond electric fields to produce nanoscale defects in the cell membrane. This results in selective cell death while preserving all other molecules, including the extracellular matrix. Here, finite element analysis and experimental results are utilized to examine the effect of NTIRE on the small intestine due to concern over collateral damage to this organ during NTIRE treatment of abdominal cancers. During previous studies, the electrical treatment parameters were chosen based on a simplified homogeneous tissue model. The small intestine, however, has very distinct layers, and a more realistic model is needed to further develop this technology for precise clinical applications. This study uses a two-dimensional finite element solution of the Laplace and heat conduction equations to investigate how small intestine heterogeneities affect the electric field and temperature distribution. Experimental results obtained by applying NTIRE to the rat small intestine in vivo support the heterogeneous effect of NTIRE on the tissue. The numerical modeling indicates that the electroporation parameters chosen for this study avoid thermal damage to the tissue. This is supported by histology obtained from the in vivo study, which showed preservation of extracellular structures. The finite element model also indicates that the heterogeneous structure of the small intestine has a significant effect on the electric field and volume of cell ablation during electroporation and could have a large impact on the extent of treatment. The heterogeneous nature of the tissue should be accounted for in clinical treatment planning.

Hypertrophy dependent doubling of L-cells in Roux-en-Y gastric bypass operated rats

Background and Aims

Roux-en-Y gastric bypass (RYGB) leads to a rapid remission of type 2 diabetes mellitus (T2DM), but the underlying mode of action remains incompletely understood. L-cell derived gut hormones such as glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are thought to play a central role in the anti-diabetic effects of RYGB; therefore, an improved understanding of intestinal endocrine L-cell adaptability is considered pivotal.

Methods

The full rostrocaudal extension of the gut was analyzed in rats after RYGB and in sham-operated controls ad libitum fed or food restricted to match the body weight of RYGB rats. Total number of L-cells, as well as regional numbers, densities and mucosa volumes were quantified using stereological methods. Preproglucagon and PYY mRNA transcripts were quantified by qPCR to reflect the total and relative hormone production capacity of the L-cells.

Results

RYGB surgery induced hypertrophy of the gut mucosa in the food exposed regions of the small intestine coupled with a doubling in the total number of L-cells. No changes in L-cell density were observed in any region regardless of surgery or food restriction. The total gene expression capacity of the entire gut revealed a near 200% increase in both PYY and preproglucagon mRNA levels in RYGB rats associated with both increased L-cell number as well as region-specific increased transcription per cell.

Conclusions

Collectively, these findings indicate that RYGB in rats is associated with gut hypertrophy, an increase in L-cell number, but not density, and increased PYY and preproglucagon gene expression. This could explain the enhanced gut hormone dynamics seen after RYGB.

Time- and segment-related changes of postresected intestine: a 4-dimensional model of intestinal adaptation

OBJECTIVES

The aim of the present study was to investigate the segment- and time-related changes in rat short bowel syndrome and construct a 4-dimensional (4D) geometrical model of intestinal adaptation.

METHODS

Sprague-Dawley rats were divided into 3 groups: 2-day, 7-day, and 15-day postresection groups in which 75% of the jejunoileum was removed. Histological and morphometrical parameters in the remaining proximal to distal intestinal segments, from the jejunum to the distal colon, were comparatively evaluated in the groups. The data were used to construct a 4D geometric model in which villi were considered as cylinders, and their surface area was expressed as cylinder lateral area.

RESULTS

Major adaptive changes were observed in the ileum consisting of an increase in both the diameter of base and the height of villi. A parallel reduction in their number/mm was observed. The resulting ileal architecture was characterized by a limited number of large villi. An opposite pattern was observed in the jejunum whose postresection structure consisted of an increased number of villi. No changes were observed in the colon. Postresection restructuring was early and faster in the ileum than in the jejunum resulting in an increase in absorptive area of 81.5% and 22.5% in the ileum and jejunum, respectively.

CONCLUSIONS

Postresection adaptation is intestinal segment-specific because all of the major changes occur in the ileum rather than in the jejunum. Sparing ileal segments during resection may improve the outcome of patients undergoing extensive intestinal resection. Our 4D model can be used to test interventions aimed at optimizing postresection intestinal adaptation.

A Quasi-Nonlinear Analysis of the Anisotropic Behaviour of Human Gallbladder Wall

Estimation of biomechanical parameters of soft tissues from noninvasive measurements has clinical significance in patient-specific modeling and disease diagnosis. In this work, we present a quasi-nonlinear method that is used to estimate the elastic moduli of the human gallbladder wall. A forward approach based on a transversely isotropic membrane material model is used, and an inverse iteration is carried out to determine the elastic moduli in the circumferential and longitudinal directions between two successive ultrasound images of gallbladder. The results demonstrate that the human gallbladder behaves in an anisotropic manner, and constitutive models need to incorporate this. The estimated moduli are also nonlinear and patient dependent. Importantly, the peak stress predicted here differs from the earlier estimate from linear membrane theory. As the peak stress inside the gallbladder wall has been found to strongly correlate with acalculous gallbladder pain, reliable mechanical modeling for gallbladder tissue is crucial if this information is to be used in clinical diagnosis.

Irreversible electroporation on the small intestine

BACKGROUND

Non-thermal irreversible electroporation (NTIRE) has recently been conceived as a new minimally invasive ablation method, using microsecond electric fields to produce nanoscale defects in the cell membrane bilayer and induce cell death while keeping all other molecules, including the extracellular matrix, intact. Here, we present the first in vivo study that examines the effects of NTIRE on the small intestine, an organ whose collateral damage is of particular concern in the anticipated use of NTIRE for treatment of abdominal cancers.

METHODS

A typical NTIRE electrical protocol was applied directly to the rat small intestine and histological analysis was used to examine the effect of NTIRE over time.

RESULTS

The application of NTIRE led to complete cell ablation in the targeted tissue, but the animal did not show any physiological effects of the procedure and the intestine showed signs of recovery, developing an epithelial layer 3 days post treatment and regenerating its distinct layers within a week.

CONCLUSION

Our results indicate that this novel procedure can be used for abdominal cancer treatment while minimising collateral damage to adjacent tissues because of the unique ability of the NTIRE ablation method to target the cell membrane.

Gastrointestinal tract modelling in health and disease

The gastrointestinal (GI) tract is the system of organs within multi-cellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste. The various patterns of GI tract function are generated by the integrated behaviour of multiple tissues and cell types. A thorough study of the GI tract requires understanding of the interactions between cells, tissues and gastrointestinal organs in health and disease. This depends on knowledge, not only of numerous cellular ionic current mechanisms and signal transduction pathways, but also of large scale GI tissue structures and the special distribution of the nervous network. A unique way of coping with this explosion in complexity is mathematical and computational modelling; providing a computational framework for the multilevel modelling and simulation of the human gastrointestinal anatomy and physiology. The aim of this review is to describe the current status of biomechanical modelling work of the GI tract in humans and animals, which can be further used to integrate the physiological, anatomical and medical knowledge of the GI system. Such modelling will aid research and ensure that medical professionals benefit, through the provision of relevant and precise information about the patient’s condition and GI remodelling in animal disease models. It will also improve the accuracy and efficiency of medical procedures, which could result in reduced cost for diagnosis and treatment.

Phasic and tonic stress-strain data obtained in intact intestinal segment in vitro

The function of the small intestine is to a large degree mechanical, and it has the capability of deforming its shape by generating phasic (short-lasting) and tonic (sustained) contraction of the smooth muscle layers. The aim of this study was to obtain phasic and tonic stress-strain (normalized force-length) curves during distension of isolated rat jejunum and ileum (somewhat similar to the isometric length-tension diagram known from in vitro studies of muscle strips). We hypothesized that the circumferential stress-strain data depend on longitudinal stretch of the intestine. Intestinal segments were isolated from ten Wistar rats and put into an organ bath containing 37 degrees C aerated Krebs solution. Ramp distension was done on active and passive intestinal segments at longitudinal stretch ratios of 0, 10, and 20%. Ramp pressures from 0 to 7.5 cmH(2)O were applied to the intestinal lumen at each longitudinal stretch ratio. Passive conditions were obtained by adding the calcium antagonist papaverine to the solution. Total and passive circumferential stress and strain were computed from the length, diameter and pressure data and from the zero-stress state geometry. The active stress was defined as the total stress minus the passive stress. The total and passive circumferential stresses increased exponentially as a function of the strain. The amplitude of both the total and passive stress was biggest in the jejunum. The total circumferential stress decreased whereas the passive circumferential stress increased when the intestine was stretched longitudinally. Consequently, longitudinal stretching caused the active circumferential stress to decrease. The passive circumferential stress during longitudinal stretching increased more in the jejunum than in the ileum. Therefore, the active circumferential stress decreased most in the jejunum. In conclusion, the circumferential active-passive stress and strain depend on the longitudinal stretch and differs between the jejunum and ileum.

The villi contribute to the mechanics in the guinea pig small intestine

Previous studies have shown that intestinal mucosa is compressed in vivo. The present study investigated the contribution of the mucosal villi to the biomechanical properties in circumferential direction in the guinea pig jejunum. Eight 20-cm-long jejunal segments were excised and each separated into two 10-cm-long segments. The mucosal villi were scraped off from half the segments. The segments were pressurized in vitro with Krebs solution from 0-10cmH(2)O using a ramp distension protocol with simultaneous diameter recordings. Circumferential stresses and strains were computed from the diameter, pressure and the zero-stress state data. Removing the villi resulted in small opening angles (139+/-16 degrees vs 189+/-27 degrees with villi) and small absolute values of residual strain (inner: -0.05+/-0.03 vs -0.33+/-0.06 with villi; outer: 0.11+/-0.04 vs 0.33+/-0.08 with villi) (P<0.001). The outer diameter as a function of the pressure did not differ between jejunal segments with villi and without villi. The average mid-wall stress-strain curve without villi was shifted to the left compared to the segment with villi, indicating the wall was stiffer without villi. However, if the stress-strain computation for the segments with villi was referenced to the zero-stress state of the segments without villi, the curve was only partly shifted to the left. In conclusion, this paper provides the first direct experimental evidence that the villi are important for the biomechanical properties of guinea pig small intestine in circumferential direction, because the villi not only affect the zero-stress state configuration but also partially affect the stress-strain distribution in the intestinal wall. Therefore, the villi should be taken into account in the analysis of biomechanical properties of the intestinal wall.

Biomechanical remodeling of the chronically obstructed Guinea pig small intestine

Small intestinal obstruction is a frequently encountered clinical problem. To understand the mechanisms behind obstruction and the clinical consequences, data are needed on the relation between the morphologic and biomechanical remodeling that takes place in the intestinal wall during chronic obstruction. We sought to determine the effect of partial obstruction on mechanical and morphologic properties of the guinea pig small intestine. Partial obstruction was created surgically in 2 groups of animals living for 2 and 4 weeks. Controls were sham operated and lived for 4 weeks. A combined impedance planimetry-high-frequency ultrasound system was designed to measure the luminal cross-sectional area and wall thickness. These measures were used to compute the circumferential stress and strain of the excised intestinal segments. The incremental elastic modulus was obtained by using nonlinear fitting of the stress-strain curve. Histologic analysis and the measurements of total wall collagen were also performed. The luminal cross-sectional area, wall thickness, and elastic modulus in circumferential direction increased in a time-dependent manner proximal to the obstruction site (P < 0.01), whereas no differences in these parameters were found distal to the obstruction site (P > 0.25). The circumferential stress-strain curves of the proximal segments in 2- and 4-week groups shifted to the left, indicating the intestinal wall became stiffer. Histologic examination revealed a massive increase in the thickness of the muscle layer especially the circular smooth muscle layer (P < 0.05). The collagen content proximal to the obstruction site was significantly larger in the partially obstructed animals compared to controls (P < 0.05). No difference was found distal to the obstruction site. Strong correlation was found between the collagen content and the elastic modulus at stress levels of 70 kPa stress (P < 0.01) and 10 kPa (P < 0.05) proximal to the obstruction site suggesting that the alteration of collagen has great impact on the mechanical remodeling. The morphologic and biomechanical remodeling likely influence the function of the intestine affected by partial obstructed intestine.

Biomechanical properties of the layered oesophagus and its remodelling in experimental type-1 diabetes

Passive biomechanical properties in term of the stress-strain relationship and the shear modulus were studied in separated muscle layer and mucosa-submucosa layer in the oesophagus of normal and STZ (streptozotocin)-induced diabetic rats. The mucosa-submucosa and muscle layers were separated using microsurgery and studied in vitro using a self-developed test machine. Stepwise elongation and inflation plus continuous twist were applied to the samples. A constitutive equation based on a strain energy function was used for the stress-strain analysis. Five material constants were obtained for both layers. The mucosa-submucosa layer was significantly stiffer than the muscle layer in longitudinal, circumferential and circumferential-longitudinal shear direction. The mechanical constants of the oesophagus show that the oesophageal wall was anisotropic, the stiffness in the longitudinal direction was higher than in the circumferential direction in the intact oesophagus (P < 0.001) and in the muscle layer (P < 0.05). Diabetes-induced pronounced increase in the outer perimeter, inner perimeter and lumen area in both the muscle and mucosa-submucosa layer. The growth of the mucosa-submucosa layer (P < 0.001) was more pronounced than the muscle layer (P < 0.05). Furthermore, the circumferential stiffness of the mucosa-submucosa layer increased 28 days after STZ treatment. In conclusion, the oesophagus is a non-homogeneous anisotropic tube. Thus, the mechanical properties differed between layers as well as in different directions. Morphological and biomechanical remodelling is prominent in the diabetic oesophagus.

Tension and stress in the rat and rabbit stomach are location- and direction-dependent

Distension studies in the stomach are very common. It is assumed in pressure-volume (barostat) studies of tone and tension in the gastric fundus that the fundus is a sphere, i.e. that the tension in all directions is identical. However, the complex geometry of the stomach indicates a more complex mechanical behaviour. The aim of this study was to determine uniaxial stress-strain properties of gastric strips obtained from rats (n=12) and rabbits (n=10). Furthermore, we aimed to study the gastric zero-stress state since the stomach is one of the remaining parts of the gastrointestinal tract where residual strain studies have not been conducted. Longitudinal strips (in parallel with the lesser curvature) and circumferential strips (perpendicular to the lesser curvature) were cut from the gastric fundus (glandular part) and forestomach (non-glandular part). The residual stress was evaluated as bending angles (unit: degree per unit length and negative when bending outwards). The residual strain was computed from the change in length between the zero-stress state and no-load state. The stress-strain test was performed using a tensile test machine. The thickness and width of each strip were measured from digital images. The strips data were compared with data obtained in the intact stomach in vitro. Most residual stresses and strains were bigger in the glandular part than in the forestomach, and in general the rat stomach had higher values than the rabbit stomach. The glandular strips were stiffer than the forestomach strips and the longitudinal glandular strips were stiffer than the circumferential glandular strips (P<0.05). The gastric strips were stiffer in rats than in rabbits (P<0.01). The data obtained in the intact rat stomach confirmed the strips data and indicated that those were obtained in the physiological range. In conclusion, the biomechanical properties of the gastric strips from the rat and rabbit are location-dependent, direction-dependent and species-dependent. The assumption in physiological pressure-volume studies that the stomach is a sphere with uniform tension is not valid. Three-dimensional geometric data obtained using imaging technology and mechanical data are needed for evaluation of the stomach function.

Morphologic and biomechanical changes of rat oesophagus in experimental diabetes

AIM: To study morphologic and biomechanical changes of oesophagus in diabetes rats.

METHODS: Diabetes was induced by a single injection of streptozotocin (STZ). The type of diabetes mellitus induced by parenteral STZ administration in rats was insulin-dependent (type I). The samples were excised and studied in vitro using a self-developed biomaterial test machine.

RESULTS: The body mass was decreased after 4 d with STZ treatment. The length of esophagus shortened after 4, 7, 14 d. The opening angle increased after 14 d. The shear, longitudinal and circumferential stiffness were obviously raised after 28 d of STZ treatment.

CONCLUSION: The changes of passive biomechanical properties reflect intra-structural alteration of tissue to a certain extent. This alteration will lead to some dysfunction of movement. For example, tension of esophageal wall will change due to some obstructive disease.

Biomechanical and morphometric intestinal remodelling during experimental diabetes in rats

AIMS/HYPOTHESIS

Morphometric and passive biomechanical properties were studied in the duodenum, jejunum and ileum in 10 non-diabetic and 40 streptozotocin-induced diabetic rats.

METHODS

The diabetic rats were divided into groups living 4 days, 1, 2, and 4 weeks after diabetes was induced ( n=10 for each groups). The mechanical test was done as a ramp distension experiment. The intestinal diameter and length were obtained from digitised images of the intestinal segments at pre-selected pressures and at no-load and zero-stress states. Circumferential and longitudinal stresses (force per area) and strains (deformation) were computed from the length, diameter and pressure data and from the zero-stress state geometry.

RESULTS

The blood glucose concentration increased four- to fivefold in the diabetic rats. Streptozotocin-induced diabetes generated pronounced increase in the weight per centimetre length, wall thickness and wall cross-sectional area in all intestinal segments during diabetes ( p<0.05). Histological analysis showed that the thickness of the intestinal layers was increased in all segments during diabetes ( p<0.05). In the duodenum the opening angle did not change in the first 2 weeks and decreased after 4 weeks ( p<0.05). In the jejunum and ileum the opening angle increased after 1 week in the diabetic group. The residual strain showed the same pattern as the opening angle. Furthermore, it was found that the circumferential and longitudinal stiffness of the intestinal wall increased with the duration of diabetes ( p<0.05 and p<0.01).

CONCLUSION/INTERPRETATION

Morphological and biomechanical remodelling of the small intestine occurred during the development of diabetes.

Biomechanical properties of ileum after systemic treatment with epithelial growth factor

AIM: Systemic treatment with epidermal growth factor (EGF) leads to growth of all parts of the small intestine in normal functioning rats. In this study, we investigated the effect of this growth process on morphometric and biomechanical parameters of ileum.

METHODS: Rats were treated with EGF (150 μg·kg^-1d^-1) or placebo via osmotic minipumps for 2, 4, 7, and 14 d. A segment of ileum was removed. The morphology at no-load state and zero-stress state was measured and passive biomechanical properties were assessed using a biaxial test machine (combined inflation and axial stretching).

RESULTS: The ileum weight increased after EGF administration. After 4 d’ EGF treatment, the wall thickness was increased. Significantly smaller inner perimeters were seen in 4 d and 7 d EGF treatment groups. The opening angle and residual strain began to increase after 7 d’ EGF treatment. Wall stiffness, evaluated from the stress-strain curves, showed a continuous decrease in circumferential direction during the first 7 d’ EGF treatment. The longitudinal stiffness increased during the first 7 d. The stress-strain curves for both circumferential and longitudinal direction tended to shift back to normal 14 d after starting EGF administration.

CONCLUSION: EGF can cause significant changes both in the morphology and in the passive mechanical properties of the rat ileum.