Mesenteric Venous Hypertension Research Articles

Mechanosensitive Ion Channels in the Development of Ileus

IntroductionApproximately 30% of trauma patients develop ileus, a decrease or cessation of intestinal motility resulting in pathological distension of the intestinal wall. Mechanosensitive ion channels play a role in both the physiological and pathological response to mechanical stimuli.ObjectiveThe objective of this study was to determine if mechanosensitive ion channels play a role in the development of ileus and the response of the intestine to pathological stretch.MethodsIn a rodent model, we induced ileus by a combination of hemodilution and mesenteric venous hypertension. We measured intestinal function using an ex vivo organ bath system. We also measured smooth muscle myosin light chain phosphorylation and intestinal wall fluid content. We collected tissue for microarray analysis.ResultsIntestinal wall fluid content increased significantly, indicating the development of intestinal edema. Edema development resulted in distension of the intestinal wall, decreased intestinal smooth muscle contractile activity, and decreased smooth muscle myosin light chain phosphorylation. We used microarray analysis to compare normal (unstretched) intestinal smooth muscle to edematous (stretched) intestinal smooth muscle to characterize changes in ion channel expression. We identified hyperpolarization‐activated cyclic nucleotide‐gated 2 (HCN2), a cyclic nucleotide gated ion channel, which is also stretch‐activated. HCN2 gene expression decreased in edematous intestinal tissue. In the ex vivo organ bath system, we tested the effects of HCN2 inhibitors on intestinal function. In preliminary experiments, HCN2 inhibition with ZD7288 resulted in decreased response to carbachol, with little change in spontaneous contractile activity or frequency.ConclusionsOur data suggest that HCN2 downregulation/inhibition can suppress intestinal contractile activity. Thus, HCN2 is a potential therapeutic target for improving intestinal motility. In future experiments, we will determine the role of HCN2 in the intestinal response to stretch.Support or Funding InformationHungarian National Research Development and Innovation Office (K120669, EFOP‐3.6.2‐16‐2017‐00006)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

04:03 PM Abstract No. 80 Technical success, efficacy, and safety of portomesenteric venous intervention following non-transplant hepatobiliary or pancreatic surgery

To assess the technical success, efficacy and safety of portomesenteric venous (PMV) intervention for PMV stenosis or occlusion following hepatobiliary or pancreatic (HPB) surgery. A retrospective review identified 42 patients with PMV occlusion (21%) or stenosis (79%) who underwent attempted PMV balloon venoplasty and/or stenting following HPB surgery between 6/2011 and 4/2018. Mean patient age was 60.1 years and 21 (50%) patients were female. Indications for intervention included mesenteric (43%) or portal venous (28%) hypertension or to maintain patency (24%). 70% received post-intervention anticoagulation. Main outcome parameters were technical success, primary patency rates and complications. Technical success was compared by venous pathology and primary patency by anticoagulation status using Fischer’s exact test. Rates of primary patency by stent group were estimated using Kaplan-Meier method. Technical success was 91% and significantly higher in patients with stenosis (100%) versus occlusion (56%) (p=0.001). Interventions included balloon venoplasty (2.6%), venoplasty/stenting (94.8%) and endovascular mechanical thrombectomy plus venoplasty/stenting (2.6%), with uncovered, covered and both stent types placed in 65%, 16% and 19%, respectively. Immediate venous collateral decompression was seen in 77% of patients as well as eventual resolution of ascites (64%), gastrointestinal bleeding (100%) and intestinal angina (93%). At an average imaging follow-up of 8.6±8.8 months, primary stent patency was 76% with 9 patients developing in-stent stenosis (n=3), non-occlusive thrombus (n=3) or occlusive thrombus (n=3), 5 of whom underwent re-stenting. 6- and 12-month primary patency rates for uncovered, covered and both stent groups were 72% and 50%, 100% and 100% and 83% and 83%, respectively. There was no significant difference in primary stent patency by anticoagulation status (p=1.0). There were two peri-procedural complications (4.8%). Portomesenteric venoplasty/stenting following HPB surgery is safe with a high rate of technical success if patients are intervened upon before chronic occlusion. 12-month primary stent patency may be better with covered stents.

Hepatic encephalopathy: Sometimes more portal than hepatic.

Hepatic encephalopathy is a severe complication of both chronic and acute liver diseases. The term hepatic encephalopathy stems from the belief that hepatic insufficiency is its fundamental etiopathogenic factor. However, most clinical cases show liver failure along with mesenteric venous portal hypertension. This portal hypertension would explain the abnormal mechanical forces suffered by the digestive tract in the early stages of the disorder. These forces could regulate some gut biochemical pathological pathways in a process known as mechanotransduction. Thus, portal hypertension would begin with the establishment of a mechanotransduced afferent or sensory inflammatory gut-brain pathway, resulting in functional and structural changes in the central nervous system. In this review, we will revisit the term "hepatic encephalopathy" in light of new results where portal hypertension occurs before liver failure and is accompanied by brain changes. Moreover, we will point out cellular links that can explain the microbiota, immune, gut, and brain axis disturbances found in this disorder.

Mesenteric lymphatic vessels adapt to mesenteric venous hypertension by becoming weaker pumps.

Lymphangions, the segments of lymphatic vessels between two adjacent lymphatic valves, actively pump lymph. Acute changes in transmural pressure and lymph flow have profound effects on lymphatic pump function in vitro. Chronic changes in pressure and flow in vivo have also been reported to lead to significant changes in lymphangion function. Because changes in pressure and flow are both cause and effect of adaptive processes, characterizing adaptation requires a more fundamental analysis of lymphatic muscle properties. Therefore, the purpose of the present work was to use an intact lymphangion isovolumetric preparation to evaluate changes in mesenteric lymphatic muscle mechanical properties and the intracellular Ca(2+) in response to sustained mesenteric venous hypertension. Bovine mesenteric veins were surgically occluded to create mesenteric venous hypertension. Postnodal mesenteric lymphatic vessels from mesenteric venous hypertension (MVH; n = 6) and sham surgery (Sham; n = 6) animals were isolated and evaluated 3 days after the surgery. Spontaneously contracting MVH vessels generated end-systolic active tension and end-diastolic active tension lower than the Sham vessels. Furthermore, steady-state active tension and intracellular Ca(2+) concentration levels in response to KCl stimulation were also significantly lower in MVH vessels compared with those of the Sham vessels. There was no significant difference in passive tension in lymphatic vessels from the two groups. Taken together, these results suggest that following 3 days of mesenteric venous hypertension, postnodal mesenteric lymphatic vessels adapt to become weaker pumps with decreased cytosolic Ca(2+) concentration.

Functional adaptation of bovine mesenteric lymphatic vessels to mesenteric venous hypertension

Lymph flow is the primary mechanism for returning interstitial fluid to the blood circulation. Currently, the adaptive response of lymphatic vessels to mesenteric venous hypertension is not known. This study sought to determine the functional responses of postnodal mesenteric lymphatic vessels. We surgically occluded bovine mesenteric veins to create mesenteric venous hypertension to elevate mesenteric lymph flow. Three days after surgery, postnodal mesenteric lymphatic vessels from mesenteric venous hypertension (MVH; n = 7) and sham surgery (Sham; n = 6) group animals were evaluated and compared. Contraction frequency (MVH: 2.98 ± 0.75 min(-1); Sham: 5.42 ± 0.81 min(-1)) and fractional pump flow (MVH: 1.14 ± 0.30 min(-1); Sham: 2.39 ± 0.32 min(-1)) were significantly lower in the venous occlusion group. These results indicate that postnodal mesenteric lymphatic vessels adapt to mesenteric venous hypertension by reducing intrinsic contractile activity.

Post‐nodal lymphatic vessels adapt to sustained high flow conditions by becoming weaker pumps

Edemagenic challenges can make passive lymph flow so high that active lymphatic vessel pumping may not be necessary to propel lymph. Indeed, an acute increase in lymph flow is reported to decrease lymphatic contraction frequency and strength in vitro. However, the lymphatic response to a chronic increase in flow in vivo is unknown. We hypothesized that lymphatic vessels become weaker pumps when exposed to a sustained increase in lymph flow. We surgically occluded bovine mesenteric veins to create mesenteric venous hypertension and high lymph flow conditions. Three days after surgery, post‐nodal mesenteric lymphatic vessels (MVH) were isolated and compared to vessels from sham surgery animals (SHAM) to quantify changes in function, biomechanics, calcium homeostasis and gene expression. Compared to SHAM, MVH vessels exhibited a lower pump index, active tension, K+ induced cytosolic [Ca2+], as well as a lower expression of SERCA type 3, voltage‐dependent Ca2+ channel, and voltage‐gated K+ channel regulatory genes. In short, post‐nodal lymphatic vessels adapt to high flow conditions by becoming weaker pumps. The present work is the first to integrate experimental approaches at the tissue, cellular, and molecular levels to relate the mechanisms of adaptation to biomechanical and functional responses to clinically‐relevant edemagenic stimuli. (Supported by NIH and AHA)

Decreased myosin phosphatase target subunit 1(MYPT1) phosphorylation via attenuated rho kinase and zipper‐interacting kinase activities in edematous intestinal smooth muscle

Intestinal edema development after trauma resuscitation inhibits intestinal motility which results in ileus, preventing enteral feeding and compromising patient outcome. We have shown previously that decreased intestinal motility is associated with decreased smooth muscle myosin light chain (MLC) phosphorylation. The purpose of the present study was to investigate the mechanism of edema-induced decreases in MLC in a rodent model of intestinal edema. Intestinal edema was induced by a combination of resuscitation fluid administration and mesenteric venous hypertension. Sham operated animals served as controls. Contractile activity and alterations in the regulation of MLC including the regulation of MLC kinase (MLCK) and MLC phosphatase (MLCP) were measured. Contraction amplitude and basal tone were significantly decreased in edematous intestinal smooth muscle compared with non-edematous tissue. Calcium sensitivity was also decreased in edematous tissue compared with non-edematous intestinal smooth muscle. Although inhibition of MLCK decreased contractile activity significantly less in edematous tissue compared with non-edematous tissue, MLCK activity in tissue lysates was not significantly different. Phosphorylation of MYPT was significantly lower in edematous tissue compared with non-edematous tissue. In addition, activities of both rho kinase and zipper-interacting kinase were significantly lower in edematous tissue. We conclude from these data that interstitial intestinal edema inhibits MLC phosphorylation predominantly by decreasing inhibitory phosphorylation of the MLC targeting subunit (MYPT1) of MLC phosphatase via decreased ROCK and ZIPK activities, resulting in more MLC phosphatase activity.

A murine model for the study of edema induced intestinal contractile dysfunction

We have published extensively regarding the effects of edema on intestinal contractile function. However, we have found the need to expand our model to mice to take advantage of the much larger arsenal of research support, especially in terms of transgenic mouse availability and development. To that end, we have developed and validated a hydrostatic intestinal edema model in mice. Male C57 Black 6 mice were subjected to a combination of high volume crystalloid resuscitation and mesenteric venous hypertension in an effort to induce hydrostatic intestinal edema. Wet to dry ratios, myeloperoxidase activity, mucosal injury scoring, STAT-3 nuclear activation, phosphorylated STAT-3 levels, NF-κB nuclear activation, myosin light chain phosphorylation, intestinal contractile activity, and intestinal transit were measured to evaluate the effects of the model. High volume crystalloid resuscitation and mesenteric venous hypertension resulted in the development of significant intestinal edema without an increase in myeloperoxidase activity or mucosal injury. Edema development was associated with increases in STAT-3 and NF-κB nuclear activation as well as phosphorylated STAT-3. There was a decrease in myosin light chain phosphorylation, basal and maximally stimulated intestinal contractile activity, and intestinal transit. Hydrostatic edema in mice results in activation of a signal transduction profile that culminates in intestinal contractile dysfunction. This novel model allows for advanced studies into the pathogenesis of hydrostatic edema induced intestinal contractile dysfunction.

Edema‐induced alterations in the regulation of myosin light chain phosphorylation in intestinal smooth muscle.

We have shown that edema decreases intestinal contractile activity via decreased intestinal smooth muscle myosin light chain (MLC) phosphorylation. The objective of this study was to determine the mechanism by which edema decreases MLC phosphorylation. Thus, regulation of MLC phosphorylation was studied in a rodent model of intestinal edema. Edema was induced by a combination of resuscitative fluid administration and induction of mesenteric venous hypertension. Edema‐induced changes in MLC kinase (MLCK) activity and phosphorylation of MYPT1 subunit of MLC phosphatase (MLCP) were measured in intestinal smooth muscle. Phosphorylation of the MYPT1 subunit in the presence of rho kinase (ROK), zipper interacting protein kinase (ZIPK), and p21 activated kinase (PAK) inhibitors, Y‐27632, SM‐1 peptide, and IPA‐3 respectively, was also measured. No significant changes in MLCK activity were observed in the edematous intestinal smooth muscle. In contrast, phosphorylation of the MYPT1 subunit of MLCP was significantly decreased in edematous intestinal smooth muscle compared to controls. Data suggest that both ROK and ZIPK were involved in edema‐induced decreases in MYPT1 phosphorylation. We conclude from these data that edema‐induced decreases in the inhibitory phosphorylation of MYPT1 subunit of MLCP via regulation of ROK and ZIPK result in decreased MLC phosphorylation in edematous intestinal smooth muscle.

Evaluating the Potential Role of Nitric Oxide as a Mediator of Hydrostatic Edema Mediated Intestinal Contractile Dysfunction

Administration of L-nil, a selective inhibitor of inducible nitric oxide synthase (iNOS), improves ileus in an animal model of resuscitation induced intestinal edema. The purpose of this study was to elucidate the iNOS/nitric oxide (NO) signal transduction pathway in intestinal edema. Male Sprague Dawley rats were divided into two groups; CONTROL and RESUS+VH (edema, 80 cc/kg normal saline (resuscitation) with mesenteric venous hypertension). iNOS mRNA and protein, iNOS activity, NO tissue levels, soluble guanylyl cyclase (sGC) expression, and cyclic guanosine monophosphate (cGMP) levels were measured. As a functional endpoint, we evaluated intestinal contractile strength and frequency in L-nil treated animals. Edema was associated with increased iNOS mRNA and protein expression without subsequent increases in iNOS activity or tissue NO levels. There was no significant change in sGC expression or increase in cGMP induced by edema. Administration of L-nil did not decrease edema development or preserve contractile strength, but increased contractile frequency. Hydrostatic intestinal edema is not associated with increased iNOS activity or tissue NO levels. Administration of L-nil in edema increases intestinal contractile frequency. This may represent a potential mechanism for the amelioration of ileus seen with the administration of L-nil.

A Novel Physiologic Model for the Study of Abdominal Compartment Syndrome (ACS)

: Current abdominal compartment syndrome (ACS) models rely on intraperitoneal instillation of fluid, air, and other space-occupying substances. Although this allows for the study of the effects of increased abdominal pressure, it poorly mimics its pathogenesis. We have developed the first reported large animal model of ACS incorporating hemorrhagic shock/resuscitation. : Hemorrhagic shock was induced and maintained (1 hour) in 12 Yorkshire swine by bleeding to a mean arterial pressure (MAP) of 50 mm Hg. The collected blood plus two additional volumes of crystalloid was then reinfused. Mesenteric venous hypertension was induced by tightening a previously placed portal vein snare in a nonocclusive manner to mimic the effects of abdominal packing. Crystalloids were infused to maintain MAP. Hemodynamic measurements, abdominal pressure, peak inspiratory pressures, urine output, and blood chemistries were measured sequentially. Animals were studied for 36 hours after decompression. : ACS (intra-abdominal pressure of > or =20 mm Hg with new organ dysfunction) developed in all animals. There were significant increases in peak inspiratory pressure, central venous pressure, and pulmonary artery pressure and decreases in MAP upon development of ACS. Urine output was significantly decreased before decompression. Mean blood lactate decreased and base excess increased significantly after decompression. : We have created the first reported physiologic animal ACS model incorporating hemorrhagic shock/resuscitation and the effects of damage control surgery.

Nuclear factor-κB activation by edema inhibits intestinal contractile activity

To investigate the molecular mechanisms leading to edema-induced decreases in intestinal smooth muscle myosin light-chain phosphorylation. Intestinal interstitial edema often develops during abdominal surgery and after fluid resuscitation in trauma patients. Intestinal edema causes decreased intestinal contractile activity via decreased intestinal smooth muscle myosin light-chain phosphorylation, leading to slower intestinal transit. Interstitial edema development is a complex phenomenon, resulting in many changes to the interstitial environment surrounding intestinal smooth muscle cells. Thus, the mechanism(s) by which intestinal edema development causes intestinal dysfunction are likely to be multifactorial. Randomized animal study. University laboratory. Male Sprague-Dawley rats, weighing 250-350 g. Studies were performed in a rat model in which a combination of mesenteric venous hypertension and administration of resuscitative fluids induces intestinal edema, mimicking the clinical setting of damage control resuscitation. Microarray analysis of edematous intestinal smooth muscle combined with an in silico search for overrepresented transcription factor binding sites revealed the involvement of nuclear factor-kappaB in edema-induced intestinal dysfunction. Nuclear factor-kappaB deoxyribonucleic acid binding activity was significantly increased in edematous intestinal smooth muscle compared with controls. Inhibition of nuclear factor-kappaB activation blocked edema-induced decreases in basal intestinal contractile activity. Inhibition of nuclear factor-kappaB activation also attenuated edema-induced decreases in myosin light-chain phosphorylation. We conclude that intestinal edema activates nuclear factor-kappaB, which, in turn, triggers a gene regulation program that eventually leads to decreased myosin light-chain phosphorylation and, thus, decreased intestinal contractile activity.

Hypertonic saline alters hydraulic conductivity and up-regulates mucosal/submucosal aquaporin 4 in resuscitation-induced intestinal edema

To characterize membrane conductivity by applying mathematical modeling techniques and immunohistochemistry and to localize and predict areas of the bowel where aquaporins may be associated with edema resolution/prevention associated with hypertonic saline. Intestinal edema induced by resuscitation and mesenteric venous hypertension impairs intestinal transit/contractility. Hypertonic saline decreases intestinal edema and improves transit. Aquaporins are water transport membrane proteins that may be up-regulated with edema and/or hypertonic saline. Laboratory study. University research laboratory. Male Sprague Dawley rats, weighing 270 to 330 g. Rats were randomized to control (with and without hypertonic saline) and mesenteric venous hypertension with either 80 mL/kg normal saline (RESUS + VH + VEH) or 80 mL/kg normal saline with hypertonic saline (RESUS + VH + HTS). After 6 hrs, intestinal wet/dry ratios, urine output, peritoneal fluid, and intraluminal fluid were measured. Hydraulic conductivity was calculated from our previously known and published pressure-flow data. The cDNA microarray, Western blot, polymerase chain reaction, and immunohistochemistry studies were conducted for candidate aquaporins and distribution in intestinal edema resolution. Hypertonic saline decreased edema and increased urine, intraluminal, and peritoneal fluid volume. RESUS + VH favors fluid flux into the interstitium. Hypertonic saline causes increased hydraulic conductivity at the seromuscular and mucosal surfaces at the same time limiting flow into the interstitium. This is associated with increased aquaporin 4 expression in the intestinal mucosa and submucosa. Hypertonic saline mitigates intestinal edema development and promotes fluid redistribution secondary to increased membrane conductivity at the mucosal and seromuscular surfaces. This is associated with up-regulation of aquaporin 4 gene expression and protein. Aquaporin 4 may be a useful therapeutic target for strategies to enhance edema resolution.

HYPERTONIC SALINE MODULATION OF INTESTINAL TISSUE STRESS AND FLUID BALANCE

Crystalloid-based resuscitation of severely injured trauma patients leads to intestinal edema. A potential mechanism of intestinal edema-induced ileus is a reduction of myosin light chain phosphorylation in intestinal smooth muscle. We sought to determine if the onset of edema initiated a measurable, early mechanotransductive signal and if hypertonic saline (HS) can modulate this early signal by changing intestinal fluid balance. An anesthetized rat model of acute interstitial intestinal edema was used. At laparotomy, the mesenteric lymphatic was cannulated to measure lymph flow and pressure, and a fluid-filled micropipette was placed in the intestinal submucosa to measure interstitial pressure. Rats were randomized into four groups (n=6 per group): sham, mesenteric venous hypertension+80 mL/kg 0.9% isotonic sodium chloride solution (ISCS 80), mesenteric venous hypertension+80 mL/kg 0.9% ISCS+4 mL/kg 7.5% saline (ISCS 80+HS), or 4 mL/kg 7.5% saline (HS alone) to receive the aforementioned intravenous fluid administered over 5 min. Measurements were made 30 min after completion of the preparation. Tissue water, lymph flow, and interstitial pressure were measured. Resultant applied volume induced stress on the smooth muscle (sigmaravi-muscularis) was calculated. Mesenteric venous hypertension and crystalloid resuscitation caused intestinal edema that was prevented by HS. Intestinal edema caused an early increase in intestinal interstitial pressure that was prevented by HS. Hypertonic saline did not augment lymphatic removal of intestinal edema. sigmaravi-muscularis was increased with onset of edema and prevented by HS, paralleling the interstitial pressure data. Intestinal edema causes an early increase in interstitial pressure that is prevented by HS. Prevention of the edema-induced increase in interstitial pressure serves to blunt the mechanotransductive signal of sigmaravi-muscularis.

Functional and Molecular Adaptation of Lymphatic Vessels

We developed a bovine model of mesenteric venous hypertension (MVH)by surgically occluding mesenteric veins for 3 days to investigate the functional and molecular adaptations of the mesenteric lymphatic vessels. The MVH model was characterized by an increase in mesenteric vein pressure from 10 to 30 mm Hg, a decrease in lymph protein concentration from 6 to 5 g/dL and an increase in intestinal water content from 72 to 78%. After 3‐days of MVH, isolated mesenteric lymphatic vessels demonstrated decreased contraction frequency, decreased ejection fraction and decreased stroke volume at each transmural pressure tested. Microarray analysis revealed that 117 genes were upregulated and 79 genes were down regulated in MVH lymphatics. A large number of the regulated genes are muscle contractile proteins, consistent with the changes in function. We further characterized changes in the mRNA of actin isoforms expressed in lymphatic muscle in response to venous hypertension. The smooth muscle actins (alpha and gamma) and skeletal actin were increased and cardiac actin decreased in lymphatics from the MHV model. Actin protein levels were analyzed by western blot analysis and revealed similar directional changes in response to MHV. These data suggest that lymphatic vessels undergo functional and molecular adaptation in response to changes in lymphdynamics in a time frame that may be important in resolution of edema. This work was supported by a LSI grant from Texas A&M University and CDC grant 623086.

EDEMA-INDUCED INTESTINAL DYSFUNCTION IS MEDIATED BY STAT3 ACTIVATION

Increased signal transducer and activator of transcription 3 (STAT3) activation has been shown to be associated with intestinal dysfunction. The purpose of this study was to investigate the role of STAT3 in edema-induced intestinal dysfunction. Intestinal edema was induced in male Sprague-Dawley rats by a combination of mesenteric venous hypertension and fluid resuscitation (RESUS + VH). Resuscitation fluid alone (RESUS), venous hypertension alone (VH), and sham-operated rats (CONTROL) were used as controls. Edema development, STAT3 DNA binding activity, nuclear translocation, and phosphorylation were measured in rat distal small intestinal muscularis. A significant amount of edema development was measured in the RESUS + VH rats compared with CONTROL and VH from 30 min to 6 h after surgery. Edema developed in the RESUS group at 30 min postsurgery but resolved before 2 h postsurgery. A significant increase in STAT3 DNA binding activity was observed from 30 min to 6 h after surgery in the edematous RESUS + VH group compared with nonedematous CONTROL. In addition, a significant increase in STAT3 nuclear translocation and phosphorylation was measured in the RESUS + VH group 2 and 6 h after surgery. No significant increases in STAT3 activation were observed in either the RESUS or VH groups compared with CONTROL. Rats in both the RESUS + VH and CONTROL groups were pretreated with AG490 (5 mg/kg, i.p.) to block STAT3 activation. Signal transducer and activator of transcription 3 inhibition attenuated edema-induced decrease in intestinal contractile activity and myosin light chain phosphorylation. We conclude from these data that edema-induced decreases in intestinal contractile activity are mediated, at least in part, by STAT3 activation.

Hypertonic saline reverses stiffness in a Sprague–Dawley rat model of acute intestinal edema, leading to improved intestinal function

Acute edema induced by resuscitation and mesenteric venous hypertension impairs intestinal transit and contractility and reduces intestinal stiffness. Pretreatment with hypertonic saline (HS) can prevent these changes. Changes in tissue stiffness have been shown to trigger signaling cascades via stress fiber formation. We proposed that acute intestinal edema leads to a decrease in intestinal transit that may be mediated by changes in stiffness, leading to stress fiber formation and decreased intestinal transit. Furthermore, HS administration will abolish these detrimental effects of edema. Intestinal edema causes a significant increase in tissue water and a significant decrease in intestinal transit and stiffness compared with sham. HS reversed these changes to sham levels. In addition, tissue edema led to significant stress fiber formation and decreased numbers of focal contacts. HS preserved tissue stiffness, prevented stress fiber formation, and was associated with improved intestinal function. HS eliminates intestinal tissue edema formation and improves intestinal transit. In addition, the action of HS may be mediated through its preservation of tissue stiffness, which leads to prevention of signaling via stress fiber formation, leading to preserved intestinal function. Finally, intestinal edema may provide a novel physiologic model for examining stiffness and stress fiber signaling.

Intestinal edema decreases intestinal contractile activity via decreased myosin light chain phosphorylation

The purpose of this study was to investigate the effects of interstitial edema on intestinal contractile activity. Randomized animal study. University laboratory. Male Sprague-Dawley rats. Intestinal edema was induced in rats by a combination of fluid infusion and mesenteric venous hypertension. Rats were divided into four groups: CONTROL, sham; RESUS, saline infusion only; RESUS+VH, saline infusion and venous hypertension; and VH, venous hypertension only. Edema development, basal contractile activity, maximum agonist-induced contractile response (measured as total force generation during the first 2 mins after carbachol treatment), and myosin light chain phosphorylation were measured in the distal small intestine. The amount of interstitial fluid, indicated by the wet-to-dry ratio, increased significantly in both the RESUS and RESUS+VH groups as early as 30 mins after surgery compared with the CONTROL group. Whereas the tissue fluid remained significantly elevated in the RESUS+VH group up to 6 hrs after surgery, the RESUS group wet-to-dry ratios returned to CONTROL group levels by 2 hrs after surgery. Basal contractile activity was significantly less in the RESUS+VH group compared with either the RESUS group or the CONTROL group 6 hrs after surgery. Maximum contractile response decreased significantly in the RESUS+VH group compared with the RESUS group. Basal contractile activity and maximum contractile response did not change significantly in the VH group compared with the CONTROL group. The phosphorylated fraction of myosin light chain was significantly lower in the RESUS+VH group compared with the CONTROL group at 0.5, 2, and 6 hrs after surgery. We conclude that edema decreases myosin light chain phosphorylation, leading to decreased intestinal contractile activity.

Hypertonic saline resuscitation prevents hydrostatically induced intestinal edema and ileus

We have shown that acute edema induced by mesenteric venous hypertension (MV-HTN) impairs intestinal transit and reduces the standardized engineering measures of intestinal stiffness (elastic modulus) and residual stress (opening angle). We hypothesized that hypertonic saline (7.5%) would reverse these detrimental effects of acute edema. Laboratory study. University laboratory. Male Sprague Dawley rats (270-330 g). Rats were randomized to five groups: sham, MV-HTN alone, MV-HTN with 4 mL/kg normal saline resuscitation (equal volume), MV-HTN with 33 mL/kg normal saline resuscitation (equal salt), and MV-HTN with 4 mL/kg hypertonic saline. Intestinal edema was measured by wet to dry tissue weight ratio. A duodenal catheter was placed and, 30 mins before death, fluorescein isothiocyanate Dextran was injected. At death, dye concentrations were measured to determine intestinal transit. Segments of distal ileum were hung to a fixed point in a tissue bath and to a force displacement transducer and stretched in increments of 1 mm; we recorded the new length and the corresponding force from the force displacement transducer to determine elastic modulus. Next, two transverse cuts were made yielding a 1- to 2-mm thick ring-shaped segment of tissue which was then cut radially to open the ring. Then the opening angle was measured. MV-HTN, MV-HTN with 4 mL/kg normal saline, and MV-HTN with 33 mL/kg normal saline caused a significant increase in tissue edema and a significant decrease in intestinal transit, stiffness, and residual stress compared with sham. Hypertonic saline significantly lessened the effect of edema on intestinal transit and prevented the changes in stiffness and residual stress. Hypertonic saline prevented intestinal tissue edema. In addition, hypertonic saline improved intestinal transit, possibly through more efficient transmission of muscle force through stiffer intestinal tissue.

Hypertonic saline reverses acute intestinal edema and improves transit through changes in cytoskeletal composition

Introduction: We have shown that acute edema induced by resuscitation and mesenteric venous hypertension (MV-HTN) impairs intestinal transit and contractility and reduces the standardized engineering measures of intestinal stiffness[elastic modulus (EM)] and residual stress[opening angle (OA)]. In addition, we have shown that pretreatment with hypertonic saline (7.5% HS) preserves intestinal transit, stiffness, and residual stress. We proposed that acute intestinal edema decreases force transmission through the more elastic tissue, leading to decreased transit. Furthermore, recent bioengineering literature has demonstrated that intermediate filaments, such as Vimentin, determine tissue stiffness. We hypothesized that hypertonic saline given after acute intestinal edema will reverse these detrimental effects of acute edema. In addition, this change in intestinal properties is mediated by a change in intermediate filaments and the composition of the intestinal cytoskeleton. Methods: Rats were randomized to four groups: sham, MV-HTN with 80 cc/kg NS (NS 80), HS alone, and NS 80 with HS administration after 30 minutes. Intestinal edema was measured by wet to dry tissue weight ratio (W/D). A duodenal catheter was placed and, 30 minutes prior to sacrifice, FITC Dextran was injected. At sacrifice, dye concentrations were measured to determine intestinal transit. Segments of distal ileum were hung to a fixed point in a tissue bath and to a tensiometer and stretched in increments of 1 mm, recording the new length and the corresponding force from the tensiometer to determine EM. Next, two transverse cuts were made yielding a 1-2 mm thick ring shaped segment of tissue and then cut radially to open the ring. Then, the OA was measured. Finally, using deconvolution microscopy, frozen tissue samples of distal ileum were stained for the cytoskeletal components filamentous (F) actin and Vimentin (Vim). Relative concentrations and locations of each cytoskeletal component were determined through pixel counts from Corel Photo-Paint 10. NS 80 cause a significant increase in tissue edema and a significant decrease in intestinal transit, stiffness, and residual stress compared to sham. HS reverses these changes to sham levels. In addition, hypertonic saline caused significant alterations to the mucosal and submucosal intestinal cytoskeleton. Conclusion: HS prevents intestinal tissue edema formation and improves intestinal transit, possibly through more efficient transmission of muscle force through stiffer intestinal tissue. HS may increase tissue stiffness by increasing tissue levels of Vimentin. In addition, HS causes a significant increase in smooth muscle F actin that may allow for improved muscle function and increased transit.