A model of jejunoileal in vivo neural isolation of the entire jejunoileum: transplantation and the effects on intestinal motility

Effects of Calcitonin Gene-Related Peptide on Colonic Motility and Defecation in Conscious Dogs

BACKGROUND

Although intra-arterial infusion of calcitonin gene-related peptide (CGRP) reportedly stimulates giant migrating contractions (GMCs) of the small intestine in conscious dogs, the effect of intravenous CGRP administration on colonic motility remains unclear. In the present study, we investigated the effects of intravenous CGRP on colonic motility and defecation and determined the underlying mechanism of action in conscious dogs.

METHODS

Sixteen Beagle dogs weighing 11-13 kg were included. The effects of intravenous CGRP at doses of 3.33 (with various antagonists), 0.83, and 1.67 μg/kg on colonic motility and defecation were evaluated in neurally intact dogs (n = 6). For comparison, dogs with transection/re-anastomosis (T/R) between the proximal and middle segments of the colon (n = 5) and dogs with extrinsic denervation of the ileocolonic segments (n = 5) also received intravenous CGRP at 3.33 μg/kg. All dogs were equipped with strain gauge force transducers on the ileocolon for measurement of the colonic contractile activity.

RESULTS

Intravenous CGRP evoked GMCs and defecation in the neurally intact group; these stimulatory effects were inhibited by atropine and hexamethonium. Compared with the neurally intact group, the T/R group exhibited similar proximal colonic motility and decreased distal colonic motility after intravenous CGRP administration, whereas the extrinsic denervation group exhibited increased colonic motility overall.

CONCLUSIONS

Intravenous CGRP induces colonic motility and defecation through acetylcholine release in conscious dogs. The continuity of the enteric nerves plays an important role in CGRP-induced colonic contractions and defecation, while the extrinsic nerves suppress CGRP-induced colonic motility.

Intracolonic Administration of the TRPA1 Agonist Allyl Isothiocyanate Stimulates Colonic Motility and Defecation in Conscious Dogs

BACKGROUND

The aim of the present study was to investigate the effects of the intracolonic transient receptor potential (TRP) A1 agonist allyl isothiocyanate (AITC) on colonic motility and defecation.

METHODS

The effects of AITC administered into the proximal colonic lumen on colonic motility and defecation were studied in neurally intact dogs equipped with strain-gauge force transducers on the colon, with or without various antagonists. Effects of intracolonic AITC were also studied in dogs with either transection/re-anastomosis (T/R) between the proximal and middle colon and complete extrinsic denervation of an ileocolonic segment.

RESULTS

AITC increased colonic motility and induced giant migrating contractions (GMCs) with defecations in 75% of experiments in neurally intact dogs. These effects were inhibited by atropine, hexamethonium, ondansetron, and HC-030031 but unaltered by capsazepine. In dogs with T/R, the increase in colonic motility was inhibited in the middle-distal colon. In dogs with extrinsic denervation, the increase in colonic motility in the distal colon was decreased.

CONCLUSIONS

Intracolonic AITC stimulates colonic motility and defecation via cholinergic, serotonergic, and TRPA1 pathways. Continuity of colonic enteric neurons plays an essential role in the intracolonic AITC-induced colonic motor response, while extrinsic nerves are important in occurrence and propagation of GMCs.

The pig as a preclinical model for intestinal ischemia-reperfusion and transplantation studies

Small bowel transplantation has become an established procedure for treatment of irreversible intestinal failure. In this procedure, primary ischemia and reperfusion is inevitable and will lead to some level of tissue injury. Both clinical and experimental data demonstrate that events occurring at the time of transplantation, called ischemia reperfusion injury (IRI), may have deleterious short- and long-term effects, manifesting as increased episodes of acute rejection and chronic allograft dysfunction. Recently, the acute phase of IRI has been increasingly viewed as part of the innate immune response to the lack of vascular perfusion and oxygen. Research on intestinal IRI that aims to understand its mechanisms and the means to reduce its impact on morbidity and mortality related to intestinal transplantations is considered important because a link has been suggested between innate immunity, adaptive immune responses and organ regeneration, and thus long-term graft function. This article provides an overview of porcine models commonly used to study intestinal reperfusion injury and to evaluate intestinal transplant protocols. It also updates the current knowledge obtained from this model, establishing the pig as a reference standard in intestinal transplantation research.

Description of a new model of intestinal denervation and in situ ischemia-reperfusion injury using the cecal artery for perfusion

BACKGROUND

The main purpose of the present investigation was to describe a model of intestinal denervation and in situ intestinal ischemia-reperfusion injury in adult rats, with utilization of the distal branch of the superior mesenteric artery close to the cecum for perfusion.

METHODS

In the root of the mesentery, the mesenteric artery and vein were completely isolated. Close to the cecal valve, a lymphatic node served as the reference point for the localization of the cecal artery, which was cannulated for perfusion with cold lactated Ringer's solution. One hundred adult male rats were utilized in the study.

RESULTS

In a pilot study, we demonstrated that the cold ischemia time was sufficient to promote histopathologic intestinal changes characteristic of ischemia-reperfusion injury. Among 88 operated animals, 62 (70.5%) survived the procedure.

CONCLUSION

The experimental model described herein has the advantage of preserving the entire intestine, which makes it more suitable for studies of physiological and morphological alterations after intestinal transplantation.

Intracolonic capsaicin stimulates colonic motility and defecation in conscious dogs

BACKGROUND

The aim of this study was to investigate the effects of intracolonic capsaicin on colonic motility and defecation.

METHODS

The effects of capsaicin (1, 2, 5, and 10 mg) administrated into the proximal colon on ileocolonic motility and defecation were studied in neurally intact dogs with or without various antagonists (atropine, hexamethonium, ondansetron, propranolol, and FK224), dogs with extrinsic denervation of an ileocolonic segment, and dogs with enterically isolated ileocolonic loops equipped with strain gauge force transducers.

RESULTS

Capsaicin at 5 and 10 mg evoked giant migrating contractions in a dose-independent manner, and it induced defecations with more than 90% probability in neurally intact dogs. These effects of capsaicin were abolished by atropine and hexamethonium. Ondansetron inhibited the capsaicin-induced increase in colonic motility but did not affect the induction of defecation. The other antagonists had no effect. In dogs with extrinsic denervation, capsaicin did not evoke giant migrating contractions in the colon but still induced defecation in 30-40% of experiments. In dogs with ileocolonic loops, capsaicin did not stimulate colonic motility nor induce defecation.

CONCLUSION

These results indicate that intracolonic capsaicin causes giant migrating contractions and defecation. Intact extrinsic innervation, continuity of the colon, and intraluminal contents were considered necessary for this effect.

Role of alpha-2 adrenoceptors in regulation of giant migrating contractions and defecation in conscious dogs

The aim was to investigate the effects of alpha(2)-adrenoceptor antagonist yohimbine on colonic motility and defecation. The effects of yohimbine (0.5, 1.0, and 3.0 mg/kg) on colonic motility and defecation were studied in neurally intact dogs (N=6), dogs with extrinsic denervation of the ileocolon (N=4), and dogs with enterically isolated ileocolnic loops (N=5) equipped with strain gauge force transducers on the ileocolon. The effects of yohimbine on colonic motility and defecation were also studied in the presence of various antagonists (atropine, hexamethonium, ondansetron, FK224, and naloxone). Yohimbine evoked giant migrating contractions and defecation in a dose-independent manner in neurally intact dogs. These stimulatory effects of yohimbine were abolished by atropine and hexamethonium. In dogs with extrinsic denervation, yohimbine induced giant migrating contractions in the colon but did not stimulate defecation. In dogs with ileocolonic loops, yohimbine induced colonic motor complexes but not giant migrating contractions in the enterically isolated colon. These results indicate that alpha(2)-adrenoceptors in the peripheral nervous system regulate giant migrating contractions by controlling the release of acetylcholine, while those in the central nervous system must be important in the regulation of defecation.

Development of a simple model of extrinsic denervation of the small bowel in mouse

Small bowel transplantation (SBT) is associated with poorly understood enteric dysfunction. The study of SBT in mice is hindered by the technical difficulty of orthotopic SBT in the mouse. Our aim was to develop an easy preparation of extrinsic denervation of the entire jejunoileum in mice as a model of orthotopic SBT. All neurolymphatic tissues accompanying the superior mesenteric artery (SMA) and vein (SMV) were ligated just distal to the middle colic vessels. The SMA and SMV were then stripped of investing adventitia, and the mesentery to jejunum and colon were transected radially. Jejunum and colon were not transected and reanastomosed. To confirm extrinsic denervation 1, 3, and 6 months later, segments of small bowel were stained for protein gene product 9.5 (PGP9.5) and tyrosine hydroxylase (TH). Tyrosine hydroxylase immunoreactive intensity was then quantified using a semiquantitative analysis. Immunohistochemical fluorescence showed persistence of PGP9.5 immunoreactivity confirming enteric nerves in jejunoileum; however, there was no TH immunoreactivity in jejunoileum in denervated mice despite the expected preservation of TH immunoreactivity in the still-innervated duodenum at 1 month. At 3 months, sparse immunoreactivity for TH was present, and by 6 months, reinnervation of TH-containing nerves appeared similar to controls. Quantification of intensity at each time-point further confirmed this trend. This technique in the mouse accomplishes a complete extrinsic denervation of jejunoileum early postoperatively (1 and 3 months); reinnervation occurs by 6 months. This is an easily learned murine model of orthotopic SBT.

In Situ Intestinal Ischemia-Reperfusion Injury in the Pig: A Model Using the First Jejunal Artery for Flushing

BACKGROUND

We describe a new surgical technique of in situ intestinal ischemia-reperfusion injury in the pig, which includes transection of the small bowel, extrinsic autonomic denervation, lymphatic disruption, and finally in-situ cold ischemia of the graft by flushing through the first jejunal artery.

MATERIAL AND METHODS

Ten female pigs were used for the study. All neural and lymphatic connections to the jejunoileum were transected. The stripped superior mesenteric vessels remained as the only connections. The skeletonized mesenteric vessels were clamped and the superior mesenteric artery was cannulated through the first jejunal artery. The isolated jejunoileum was flushed with cold IGL-1 solution. A small incision on the superior mesenteric vein was made to allow outflow of the effluent. After the flushing process was complete, the small incision in the superior mesenteric vein was closed and the vascular clamps were removed. The proximal 70% of the graft was resected.

RESULTS

The mean preoperative weight of the animals was 25.8 +/-7.6 kg. The mean duration of the operation was 242.0 +/- 28.6 min. The mean cold ischemia time was 47.6 +/- 3.9 min. All animals survived the procedure and were sacrificed at day 8. At sacrifice, there were no adhesions. The small bowel appeared normal. On intestinal histology, there were no significant changes between specimens obtained from the animal immediately at the end of cold flushing (T0), 2 h after reperfusion (T1), and at sacrifice (T2).

CONCLUSIONS

This novel technique for intestinal ischemia-reperfusion injury in the pig provides an extremely useful model for experimental studies of immunological and cold ischemia-reperfusion injury of transplanted small bowels.

The diurnal periodicity of hexose transporter mRNA and protein levels in the rat jejunum: role of vagal innervation

BACKGROUND

Protein and messenger RNA (mRNA) levels of the hexose transporters sodium-dependent glucose transporter-1, glucose transporter 2, and glucose transporter 5 follow a (daily) diurnal rhythm in rat jejunum. Because vagal innervation mediates the diurnal activity of other proteins in the rat small bowel, we hypothesized that the diurnal variation of mRNA and protein levels of these hexose transport proteins are mediated by vagal innervation.

METHODS

Forty-eight rats kept in a strictly maintained, alternating 12-hour light-dark room underwent either sham laparotomy (n = 24) or bilateral total abdominal vagotomy (n = 24). Four weeks postoperatively, jejunal mucosa was harvested from 6 rats in each group at 3 am, 9 am, 3 pm and 9 pm; mRNA levels were determined by reverse transcription real-time polymerase chain reaction and protein levels by semiquantitative Western blot analysis. Transporter mRNA and protein levels were expressed as a ratio to the corresponding mRNA and protein levels of the stably expressed housekeeping gene glyceraldehyde-6-phosphate dehydrogenase.

RESULTS

mRNA and protein levels for all 3 hexose transporters showed diurnal variation in sham controls (P < or = .01 for all). After vagotomy, although mRNA levels of all 3 transporters showed diurnal variation (each P < .01), diurnal variation in all 3 hexose transporter protein levels was abolished (P > .10 for all).

CONCLUSIONS

Vagal innervation appears to differentially mediate the diurnal changes in hexose transporter mRNA and protein expression in the rat jejunum by posttranscriptional, and/or posttranslational processes.

Postprandial augmentation of absorption of water and electrolytes in jejunum is neurally modulated: implications for segmental small bowel transplantation

Postprandial augmentation of absorption of water and electrolytes is believed to occur in the jejunum. Neural mechanisms of control, however, have not been studied in the in situ jejunum or in the transplanted bowel. The aim of this study was to determine if postprandial augmentation of absorption occurs in the in situ jejunum and to evaluate neural mechanisms controlling postprandial jejunal absorption. Based on our previous work, we hypothesized that postprandial augmentation of absorption does not occur in the jejunum in situ and that extrinsic denervation of the jejunum is associated with decreased postprandial absorption. Absorption was studied in an 80 cm, in situ jejunal segment in six dogs by using an isosmolar electrolyte solution alone, or with 80 mmol/L glucose before and after jejunal transection to disrupt intrinsic neural continuity of the study segment with the remaining gut. Net absorptive fluxes of water and electrolytes were measured in the fasted state and after a 400-kcal meal. Another six dogs were studied 3 weeks after our validated model of extrinsic denervation of jejunoileum; identical fasting and postprandial absorptive states were evaluated. Postprandial augmentation of absorption of water and electrolytes did occur in the jejunum (P < 0.03) both in the absence and in the presence of intraluminal glucose. After intrinsic neural transection or extrinsic denervation, no postprandial augmentation of absorption occurred, with or without glucose. Postprandial augmentation of absorption of water and electrolytes occurs in the in situ jejunum. Disrupting intrinsic neural continuity or extrinsic denervation (as after intestinal transplantation) abolishes postprandial augmentation.

In Vivo Complete Neural Isolation of the Rat Jejunoileum: A Simple Model to Study Denervation Sequelae of Intestinal Transplantation

BACKGROUND

Our aim was to develop and validate a technically easy, reliable, and reproducible method of complete jejunoileal denervation in the rat to allow study of the physiologic effects of intestinal transplantation devoid of immunologic phenomena and ischemia/reperfusion injury.

MATERIALS AND METHODS

Six adult Sprague-Dawley rats underwent transection and reanastomosis of the proximal jejunum and proximal colon, transection of all neurolymphatic tissues at the base of the mesentery, stripping adventitia off the superior mesenteric artery and vein, and radial transection of the intervening mesenteries, thereby denervating the jejunoileum in situ without disrupting blood flow. Three rats each were sacrificed 1 and 6 months later. Intestinal smooth muscle from the still-innervated duodenum and the denervated jejunum, mid-small bowel, and ileum was compared to corresponding tissues from a normal rat for tyrosine hydroxylase immunohistochemistry, a marker of extrinsic innervation.

RESULTS

One and six months after denervation, all duodenal samples demonstrated normal tyrosine hydroxylase immunostaining. In contrast, tyrosine hydroxylase immunoreactivity was undetectable in jejunum, mid-small bowel, or ileum of rats at 1 month and 2 of the 3 rats at 6 months; 1 rat at 6 months had low levels of tyrosine hydroxylase immunoreactivity at the mesenteric border of jejunum and mid small bowel.

CONCLUSION

This simple technique of in situ neural isolation effectively and reproducibly achieves complete extrinsic denervation of the entire rat jejunoileum. Low levels of neural regeneration may be present 6 months after denervation.

Inhibition by nitric oxide and nonadrenergic, noncholinergic (NANC) nerves is preserved in a canine model of extrinsic denervation: Implications for small bowel transplantation

BACKGROUND

Small bowel transplantation (SBT) is complicated by changes in graft motility, especially in the early postoperative period. This dysmotility may be related in part to the extrinsic denervation necessitated by the procedure, but specific neurotransmitter response to SBT is incompletely understood. The aim of this study was to evaluate the role of nitric oxide and nonadrenergic, noncholinergic (NANC) enteric neural input in the nonimmunologic etiology of the dysmotility seen after SBT.

METHODS

A technique of jejunoileal extrinsic denervation (without disruption of mesenteric vascular supply) was used as a model of canine jejunoileal autotransplantation to avoid potential confounding factors such as ischemia-reperfusion and postallotransplant immunologic effects. Longitudinal smooth muscle strips from ileum and jejunum were studied with in vitro tissue chamber methodology at 0, 2, and 8 weeks after this experimental model to explore early and late effects of denervation. Effects of exogenous nitric oxide (NO) and electric field stimulation (EFS), which releases native, endogenous enteric neurotransmitters) were evaluated in neurally intact control dogs and those undergoing extrinsic denervation.

RESULTS

Exogenous NO caused a dose-dependent inhibition of spontaneous contractile activity and in some muscle strips a decrease in basal tone in both groups of dogs. These effects were unchanged by neural blockade with tetrodotoxin and preserved after extrinsic denervation. EFS produced inhibition of spontaneous contractile activity in ileum and a complex, inconsistent response in jejunum. The response to EFS in both ileum and jejunum was unchanged after extrinsic denervation.

CONCLUSIONS

Nitric oxide inhibits contractile activity in canine longitudinal muscle of small bowel. Motility changes seen after this large animal model of extrinsic denervation are not caused by changes in NO or NANC neural function. The variability observed between different segments of intestine is important to consider in the context of SBT.

Extrinsic denervation alters postprandial absorption of glucose and glutamine in the ileum: implications for small bowel transplantation

In the postprandial period, augmentation of absorption of water, electrolytes, and taurocholate is believed to occur in the ileum. The role of extrinsic innervation in this postprandial augmentation has not been well studied and may be an important concept in small bowel transplantation. Our aim was to investigate extrinsic neural mechanisms mediating postprandial absorptive patterns. The study hypothesis was that postprandial augmentation of absorption in the ileum is blunted in transplanted (extrinsically denervated) bowel. Ileal absorption was studied in six dogs with an 80-cm in situ ileal segment via a triple-lumen perfusion technique using an iso-osmolar, ileal-like electrolyte solution alone and containing either glucose 2.5 mM, glutamine 2.5 mM, oleic acid 5 mM, or taurocholate 5 mM. Net absorptive fluxes of each substrate, as well as water and electrolytes, were measured in both the fasted state and after a 400-Kcal mixed meal before and at 2 and 12 weeks after our validated model of complete extrinsic denervation of the jejunoileum. At baseline, there were no differences in absorption of water, electrolytes, or any nutrient postprandially compared with the fasted state. Two weeks after extrinsic denervation, absorption of glucose at both 1 and 2 hours postprandially was decreased compared with absorption during fasting. Glutamine absorption was also decreased at 2 hours postprandially. At 12 weeks after extrinsic denervation, net postprandial absorption of glucose and glutamine returned toward normal and was not different from fasting absorption. No differences were noted in postprandial absorption of oleic acid or taurocholate at any time point. Decreases in absorption of nutrients postprandially after extrinsic denervation (which is necessitated by small bowel transplantation) may play an important role in post-transplant enteric absorptive dysfunction. The previously described postprandial augmentation in net absorption may be a function of enterically isolated gut and does not appear to occur in the in situ ileum.

Growth hormone selectively improves intestinal cholesterol absorption after jejunoileal autotransplantation in pigs

BACKGROUND/PURPOSE

Small bowel transplantation impairs enteric function and causes malabsorption of cholesterol and bile acids. Growth hormone stimulates intestinal absorptive function. The authors hypothesized that long-term growth hormone therapy could improve absorption of bile acids and cholesterol after autotransplantation of the jejunoileum.

METHODS

Sixteen pigs with similar food, cholesterol, and fat intake underwent either sham laparotomy or a model of jejunoileal autotransplantation, including extrinsic autonomic denervation, lymphatic interruption, and in situ cold ischemia. Five randomly chosen autotransplanted animals received daily growth hormone treatment for 8 weeks. Serum lipids, absorption, and excretion of cholesterol, bile acids, and fat were determined after 8 weeks. Mucosal morphometrics, proliferation, and enzyme activities were determined. Plasma cholesterol precursors and plant sterols, respective markers of cholesterol synthesis and absorption, were measured after 2 and 8 weeks.

RESULTS

After jejunoileal autotransplantation, growth hormone treatment significantly increased body weight gain, cholesterol absorption efficiency from 45.1% to 62.1%, plasma campesterol to cholesterol proportions, and biliary secretion of cholesterol. With or without growth hormone treatment, autotransplantation significantly increased fecal bile acid excretion, plasma cholesterol precursors, fecal bacterially modified neutral sterols, mucosal thickness of the ileum (but not jejunum), and intestinal transit time when compared with sham-operated animals. Crypt cell proliferation, mucosal enzyme activities, and microvilli showed no differences between the groups.

CONCLUSIONS

These findings suggest that growth hormone treatment selectively improves cholesterol, but not bile acid absorption, after autotransplantation of the jejunoileum.

Chronic extrinsic denervation of the small bowel: effect on adrenergic and cholinergic contractile mechanisms in canine ileal circular muscle

BACKGROUND

Small bowel transplantation necessitates chronic extrinsic denervation and is often followed by enteric dysfunction. Our aim was to study canine ileal contractile activity after extrinsic denervation.

METHODS

In vitro dose responses to cholinergic and adrenergic agonists were evaluated in canine ileal muscle strips in control subjects and after jejunoileal extrinsic denervation (EX DEN) at 0, 2, and 8 weeks after operative preparation.

RESULTS

Spontaneous activity and the increased activity after tetrodotoxin (enteric nerve blockade) did not differ between groups. Response to acetylcholine and bethanechol did not differ at any time in the control or EX DEN group. In contrast, the EX DEN group demonstrated a procontractile hypersensitivity to norepinephrine at 2 and 8 weeks that was not seen in the control group. This adrenergic hypersensitivity in the EX DEN group was insensitive to intramural neural blockade with tetrodotoxin.

CONCLUSIONS

Extrinsic denervation does not affect basal contractile activity, augmented contractile activity to intramural neural blockade, nor response to cholinergic agonists. However, it induces a procontractile adrenergic hypersensitivity in canine ileal circular muscle mediated at the level of the smooth muscle and not at the enteric nervous system.

Effects of transection and extrinsic denervation and a model of autotransplantation of the porcine jejunoileum on cholesterol biodynamics

BACKGROUND/PURPOSE

Small bowel transplantation impairs enteric function, necessitating transection, extrinsic denervation, and ischemia-reperfusion of the small intestine. The authors investigated how each of these nonimmunologic insides of the transplantation procedure modulates biodynamics of cholesterol and absorption of lipids.

METHODS

Twenty-three pigs with similar food, cholesterol, and fat intake underwent sham laparotomy (group 1), transection (group 2), extrinsic jejunoileal denervation (group 3), or a model of autotransplantation, including extrinsic jejunoileal denervation with in situ ischemia-reperfusion (group 4). Serum lipids, absorption, and excretion of cholesterol, bile acids, and fat were determined after 8 weeks. Plasma cholesterol precursors and plant sterols, respective markers of cholesterol synthesis, and absorption, were measured after 2 and 8 weeks.

RESULTS

When compared with sham laparotomy and transection groups, denervation and autotransplantation significantly decreased weight gain and increased plasma cholesterol precursors and fecal excretion of bile acids. In relation to sham operated animals, transection alone modestly increased plasma plant sterols at 2 weeks and biliary secretion and mass absorption of cholesterol. The latter changes were not observed after denervation or autotransplantation, ie, fractional and total absorption of cholesterol were significantly decreased in autotransplanted pigs when compared with transected controls. As compared with all the other groups, autotransplantation significantly increased bacterial metabolites of neutral sterols in feces and net fecal elimination of cholesterol, mainly as bile acids.

CONCLUSIONS

Extrinsic autonomic denervation of the jejunoileum, with or without synchronous ischemia-reperfusion, results in increased cholesterol synthesis, bile acid malabsorption, and decreased weight gain. Cholesterol malabsorption may develop gradually after intestinal autotransplantation, and even a short period of ischemia further impairs absorptive function of the denervated jejunoileum, resulting in increased fecal elimination of cholesterol mainly as bile acids.

Methods for decreasing postoperative gut dysmotility

Postoperative disturbances of gastrointestinal function (postoperative ileus) are among the most significant side-effects of abdominal surgery for cancer. Without specific treatment, major abdominal surgery causes a predictable gastrointestinal dysfunction which endures for 4-5 days and results in an average hospital stay of 7-8 days. Ileus occurs because of initially absent and subsequently abnormal motor function of the stomach, small bowel, and colon. This disruption results in delayed transit of gastrointestinal content, intolerance of food, and gas retention. The aetiology of ileus is multifactorial, and includes autonomic neural dysfunction, inflammatory mediators, narcotics, gastrointestinal hormone disruptions, and anaesthetics. In the past, treatment has consisted of nasogastric suction, intravenous fluids, correction of electrolyte abnormalities, and observation. Currently, the most effective treatment is a multimodal approach. Median stays of 2-3 days after removal of all or part of the colon (colectomy) are now achievable. Recent discoveries have the potential to significantly reduce postoperative ileus in patients with cancer who have had abdominal surgery.

Neuronal adrenergic and muscular cholinergic contractile hypersensitivity in canine jejunum after extrinsic denervation

Extrinsic denervation may be responsible for motor dysfunction after small bowel transplantation. The aim of this study was to examine the role of extrinsic innervation of canine jejunum on contractile activity. An in vitro dose response of cholinergic and adrenergic agonists was evaluated in canine jejunal strips of circular muscle at 0, 2, and 8 weeks in a control group and after jejunoileal extrinsic denervation (EX DEN). Neurons in circular muscle were quantitated by means of immunohistochemical techniques. Adrenergic and cholinergic responses did not differ at any time in the control group. However, at 2 and 8 weeks, extrinsic denervation caused an increased sensitivity to the procontractile effects of the cholinergic agonist bethanechol at the level of the smooth muscle cells, and increased sensitivity to the inhibitory effects of the adrenergic agent norepinephrine mediated at the level of the enteric nervous system. Immunohistochemical analysis showed a reduction in all neurons and a complete lack of adrenergic fibers in the EX DEN group after 2 and 8 weeks. Extrinsic denervation induces enteric neuronal cholinergic and adrenergic smooth muscle hypersensitivity in canine jejunal circular muscle.

Ileal resection enhances jejunal absorptive adaptation for water and electrolytes to extrinsic denervation: implications for segmental small bowel transplantation

BACKGROUND/PURPOSE

Segmental small bowel transplantation (SBT) may be an alternative to whole jejunoileal SBT. The aim of this study was to evaluate adaptability of extrinsically denervated jejunum after ileectomy.

METHODS

Baseline absorption of an isomolar, nonnutrient electrolyte solution was measured in an 80-cm in situ jejunal segment. Control (CON) and extrinsically denervated dogs (EXT DEN) then underwent distal 50% enterectomy; EXT DEN dogs also underwent a complete extrinsic denervation of remnant jejunum. Absorption was remeasured 2 and 12 weeks later; jejunal biopsies at 12 weeks were compared with baseline.

RESULTS

All dogs experienced weight loss and diarrhea, which resolved by 10 weeks in CON but persisted in EXT DEN dogs. Net absorptive fluxes of water, Na+, K+, and Cl-, however, remained unchanged in both groups 2 weeks and 12 weeks after denervation. Morphometric evaluation showed an increase in crypt depth in both groups at the 12-week time-point.

CONCLUSIONS

Despite a clinical short bowel syndrome, more weight loss, and diarrhea in EXT DEN, there were no temporal differences in net absorptive fluxes of water and electrolytes within or between these 2 groups, and both developed increased crypt depth at 12 weeks. Extrinsic denervation does not blunt jejunal adaptive response to ileectomy.

Canine ileal motor activity after a model of jejunoileal autotransplantation

OBJECTIVE

To determine mechanisms by which extrinsic innervation to the jejunoileum controls ileal motility.

SUMMARY BACKGROUND DATA

Small bowel transplantation is complicated by diarrhea and delayed gastric emptying, possibly secondary to altered motility. Ileal motility after small bowel transplantation is poorly characterized.

METHODS

Motor activity was recorded from four dogs during fasting and after feeding small (64 Kcal) or large (256 Kcal) meals. Short-chain fatty acids known to induce unique ileal motor patterns were administered into the distal ileum during fasting. Dogs were studied before and after jejunoileal denervation simulating autotransplantation.

RESULTS

After jejunoileal denervation, the ileal migrating motor complex (MMC) persisted but was no longer temporally coordinated with duodenal MMCs. Spontaneous giant migrating contractions occurred more frequently after denervation and more commonly originated proximally in the jejunum, but the velocity of migration did not differ. In contrast, the incidence and characteristics of spontaneous discrete clustered contractions (DCCs) did not differ. Short-chain fatty acids reproducibly initiated giant migrating contractions and discrete clustered contractions in the distal ileum without differences before and after denervation. Large but not small meals inhibited the ileal MMC after denervation.

CONCLUSIONS

Extrinsic innervation and/or intrinsic neural continuity with the duodenum and/or colon control temporal coordination of ileal motility with the duodenum and modulate postprandial inhibition of fasting motility and presence of giant migrating contractions. These changes in motility patterns may prove important in mediating enteric dysfunction after small bowel transplantation.

Intraileal capsaicin inhibits gastrointestinal contractions via a neural reflex in conscious dogs

BACKGROUND & AIMS

The aim of the present study was to determine the effect of intraileal administration of capsaicin on gastrointestinal motility.

METHODS

Mongrel dogs equipped with strain gauge force transducers on the stomach, small intestine, and colon were used. We studied the effects of intraileal capsaicin on gastrointestinal contractions with or without pharmacologic antagonists. The effects of capsaicin administration into the lumen of innervated and extrinsically denervated ileal Thiry loops were also studied.

RESULTS

Intraileal capsaicin dose dependently inhibited postprandial contractions at all sites and interdigestive contractions in the upper gastrointestinal tract. Intraileal capsaicin-induced inhibition of gastrointestinal contractions was partially reversed by a nitric oxide (NO) synthase inhibitor, a 5 hydroxytryptamine-3 receptor antagonist (5-HT(3)), and an opiate antagonist. Administration of capsaicin into the innervated ileal Thiry loop had inhibitory effects on gastrointestinal contractions, but gastrointesinal motor activity was not affected by capsaicin administered into the extrinsically denervated Thiry loop.

CONCLUSIONS

Stimulation of ileal afferent fibers by capsaicin inhibits gastrointestinal contractions via an extrinsic neural reflex.

Differential adrenergic response to extrinsic denervation in canine longitudinal jejunal and ileal smooth muscle

Early postoperative complications after small bowel transplantation (SBT) are likely mediated, at least in part, by dysmotility caused by the obligate disruption of extrinsic and enteric nerves in the graft. Adrenergic hypersensitivity of gut smooth muscle has been observed in some (but not all) segments of intestine in various experimental models of SBT, highlighting regional and species variability in response to denervation. Little is known about changes in canine longitudinal muscle after extrinsic denervation. Six dogs each underwent either complete extrinsic denervation of the jejunoileum or a control operation (transection and reanastomosis of the proximal jejunum and distal ileum). In vitro contractile response of longitudinal muscle strips to norepinephrine was evaluated at the time of the operation, and 2 weeks and 8 weeks later. After extrinsic denervation, the jejunal response to norepinephrine was preserved at all time points; however, the ileum displayed a decreased sensitivity to norepinephrine, an effect unmasked after intramural neural blockade with tetrodotoxin. These data support a potential for neurally mediated dysmotility after SBT and reinforce the differences in responses to extrinsic denervation between species, as well as differences within different regions and between anatomic segments of small intestine in the same species.

Role of extrinsic innervation in jejunal absorptive adaptation to subtotal small bowel resection: a model of segmental small bowel transplantation

Segmental small bowel transplantation offers theoretic advantages over total jejunoileal transplantation, but the regional ability of the transplanted segment to adapt is unknown. Absorption was measured in an 80 cm jejunal segment via a triple-lumen perfusion technique. Separate experiments measuring absorption of four nutrients (glucose, glutamine, oleic acid, and taurocholic acid) were performed before and 2 and 12 weeks after operative intervention. Control dogs (CON, n = 6) underwent distal 50% enterectomy. Experimental dogs (EXT DEN, n = 6), in addition to resection, underwent complete extrinsic denervation of the remaining jejunum. All dogs developed diarrhea, which resolved in all CON dogs but persisted in all EXT DEN dogs. Maximal weight loss was greater in the EXT DEN group. Glucose and oleate absorption was decreased 2 weeks after ileal resection in both the CON and EXT DEN dogs; glutamine absorption was decreased at 2 weeks in EXT DEN dogs only. Taurocholate and water absorption remained unchanged in both groups. Absorption of all solutes returned to baseline at 12 weeks in both groups. Despite greater weight loss and persistent diarrhea in EXT DEN dogs, at 12 weeks there were no differences in net absorptive fluxes between the EXT DEN and the CON group after extrinsic denervation. The extrinsic denervation necessitated by small bowel transplantation does not appear to blunt the net jejunal adaptive response to total ileal resection, but may temporarily alter glutamine absorption.

Study of morbidity in orthotopic small intestine transplantation with Wistar rats. Experimental study

BACKGROUND

Transplantation of the small intestine is a surgical procedure currently under investigation for its possible application in the treatment of patients with short bowel syndrome, aiming at the reintroduction of an oral diet.

AIM

To define the morbidity and mortality of intestinal transplantation in small animals using microsurgery. Intra and postoperative morbidity and mortality were studied in Wistar rats submitted to orthotopic intestinal allotransplantation.

MATERIAL AND METHOD

The animals were divided into three groups: group A (37 donor animals), group B (37 recipient animals), and group C (10 control animals). Group B was divided into three subgroups according to survival time. Subgroup TI consisted of animals that died during surgery or due to causes directly related to surgical intervention, subgroup T2 consisted of animals that died between the 4th and 29th postoperative day, and subgroup T3 consisted of animals that survived after 30 days. Transplanted animals were evaluated in terms of surgical technique used (vascular and intestinal anastomosis), graft quality, surgical time, and clinical parameters. The animals that died by the 29th postoperative day were submitted to autopsy and the remaining ones were sacrificed after 30 days.

RESULT

There was a high rate of complication of a surgical nature. Early mortality rate, i.e., mortality up to the third postoperative day, was 54% with vascular anastomosis being the major cause of death. Surgical time was evaluated in a restricted and homogeneous group and showed a strong prognostic value in terms of successful transplantation. Clinical parameters such as weight loss, reduction of ingestion, reduction of motor activity and diarrhea were directly correlated with acute rejection.

CONCLUSION

The experimented intestinal transplant is a procedure companied by considerable morbidity and mortality due to surgical complications in postoperative period, vascular anastomosis and total surgical time.

Extrinsic neural innervation mediates absorption of water and electrolytes in canine proximal colon in vivo

INTRODUCTION

Extrinsic innervation mediates a proabsorptive effect in small intestine. Our aim was to determine whether extrinsic neural input modulates similar effects in the proximal colon in vivo.

METHODS

Ten adult dogs underwent enteric isolation of a 50-cm proximal colon loop; five each were randomized to undergo extrinsic denervation (Ext Den) of the isolated colonic segment or to serve as neurally innervated controls. After recovery, a 38 degrees C electrolyte solution (Na(+) 125 meq/L, K(+) 9 meq/L, Cl(-) 75 meq/L, HC03(-) 65 meq/L) was infused at 4 ml/min into the segment. Effluent was collected in 30-min intervals for 2 h after achieving steady state (determined by 14C nonabsorbable marker recovery); four studies were conducted at 1 and 12 weeks postoperatively. Net flux of H20, Na(+), K(+), and Cl(-) was determined. Colon morphometry was evaluated at 0 and 14 weeks. Data are presented as mean +/- SEM. Unpaired t test was applied for comparisons.

RESULTS

Net absorptive flux of H20 (microL/min/cm) was decreased in Ext Den vs controls at 1 week (4.40 +/- 0.63 vs 7.92 +/- 0.92, P = 0.03) but was not different at 12 weeks (4.70 +/- 1.20 vs 5.97 +/- 0.69; P > 0.05). Na(+) and Cl(-) followed the trends in H20 absorption (P < or = 0.05). Crypt depth (microm) decreased in controls at 14 weeks vs 0 week (915 +/- 20 vs 740 +/- 07, P = 0.01) but remained unchanged in Ext Den.

CONCLUSIONS

Loss of extrinsic neural input decreases colonic absorption. This observation suggests that extrinsic neural innervation provides net proabsorptive mechanisms for absorption of water and electrolytes in the proximal canine colon.

Effects of intestinal transplantation on postprandial motility and regulation of intestinal transit

BACKGROUND

The effects of intestinal transplantation on gut motility have not been completely defined. In this study we examine the effects of ileal transplantation on ileal smooth muscle contractility, together with gastroduodenal emptying, intestinal flow, and transit rates in a canine model of short-gut syndrome.

METHODS

Animals (n = 22) were instrumented with strain gauge transducers, collection cannulae, and infusion catheters to assess motility, intestinal flow and transit rates, and gastroduodenal emptying. Ten animals served to define normal parameters. Six animals underwent a 70% resection of the proximal small intestine to serve as short-gut controls. Six animals underwent removal of a 100-cm segment of the ileum, with cold storage, and autotransplantation the following day combined with a 70% resection of proximal bowel.

RESULTS

Transplant animals exhibited delayed gastroduodenal emptying, reduced intestinal flow rates, and postprandial phasic contractions that were similar to short-gut controls. However, transplant animals experienced rapid intestinal transit compared with short-gut controls (4.8 +/- 0.4 cm/min vs 2.0 +/- 0.3 cm/min; mean +/- SEM; P <.05).

CONCLUSIONS

The transplanted intestine, even with 18 hours of cold storage, exhibits a relatively normal postprandial motor response. However, adaptive responses of the transplanted intestine, such as regulation of intestine transit, may be impaired by neuromuscular injury associated with denervation or ischemia.

Role of extrinsic innervation in release of motilin and patterns of upper gut canine motility

The need for extrinsic neural input to the upper gut in regulation/control of cyclic interdigestive motility and release of motilin remains a topic of controversy. Our aim was to determine whether extrinsic denervation of the upper gut disrupts cyclic release of motilin in relation to the migrating motor complex. Ten dogs underwent transection of all extrinsic innervation and enteric neural input to the stomach, small intestine, colon, pancreas, and liver while enteric neural continuity within this multivisceral complex was maintained. A cyclic pattern of motility occurred during fasting in all dogs in the small bowel (period = 100 +/- 3 min, mean +/- standard error of the mean) and in 8 of 10 dogs in the stomach (period = 98 +/- 4 min). Gastric cycles were temporally coordinated with small bowel cycles. Plasma motilin concentrations cycled temporally with the motility pattern with the greatest concentrations occurring during gastroduodenal phase III-like activity. Exogenous motilin induced a burst of gastric contractions and a premature migrating motor complex in all dogs. Oral meals disrupted cyclic motility and cyclic changes in plasma motilin. Extrinsic innervation to the upper gut is not necessary for cyclic motor activity, for coordinated cyclic release of motilin, or to initiate a premature migrating motor complex-like response to motilin. Central nervous system input (afferent, efferent) is not necessary for cyclic interdigestive activity or cyclic release of motilin.

Canine small bowel motor patterns and contractions are not neurally regulated during enteric nutrient infusion

The aims of this study were to determine the effects of duodenal and jejunoileal nutrient infusions on small intestinal motor patterns and intestinal contractions in neurally intact and neurally isolated small bowel. Fifteen dogs were prepared with duodenal and jejunal infusion and manometry catheters and a diverting jejunal cannula. Ten of the dogs underwent in situ neural isolation of the jejunoileum. A mixed nutrient meal (0.5 kcal/ml) was infused into the duodenum or jejunum at 3 ml/min for 5 h. Control experiments involved infusion of a balanced salt solution. Manometric data collected on-line to a microcomputer were analyzed for direction, distance, and velocity of spread of single pressure waves (SPW) and clustered contractions. Isolated duodenal and jejunoileal nutrient infusions inhibited the fasting motor pattern in neurally intact and neurally isolated small bowel. Motor activity (motility index) increased slightly during nutrient infusion within groups, but there were few differences between groups. Neither neural isolation nor nutrient infusion had a consistent effect on spread of SPW or migration of clustered contractions. Isolated duodenal and jejunoileal nutrient infusions in the dog inhibit fasting motor patterns and increase motor activity slightly but have little effect on characteristics of individual and clustered contractions. Extrinsic innervation to the jejunoileum or intrinsic neural continuity of the jejunum with the duodenum had little effect on single or grouped contractions. Although the changes in motor activity demonstrated in this study appear small, alterations in intestinal transit and absorption may still occur and may be of importance physiologically.

Duodenal motility in fasting dogs: humoral and neural pathways mediating the colonic brake

We have previously described a negative feedback loop that inhibits duodenal motility when nutrients are infused into the ileum and colon. In the present study, we examined the role of extrinsic innervation and plasma levels of peptide YY (PYY) in mediating this phenomenon. We perfused neurally intact (n = 5 dogs) or extrinsically denervated (n = 6 dogs) isolated loops of proximal colon with isomolar NaCl or a mixed-nutrient solution at 2 and 6 ml/min for 4 h during fasting or for 2 h beginning 15 min after a meal. Both rates of infusion with NaCl prolonged the cycle length of the duodenal migrating motor complex (MMC) in the group with neurally intact loops but not in the group with extrinsically denervated loops. Nutrient infusions increased the MMC cycle length in both groups. Integrated plasma concentrations of PYY were increased by nutrients but not by NaCl in both groups. These data suggest that increased volumes and unabsorbed nutrients in the proximal colon alter proximal small bowel motility. Volume-induced effects are mediated via extrinsic nerves, whereas nutrient-induced effects may be mediated by humoral factors, such as plasma PYY.

In situ neural isolation of the entire canine upper gut: effects on fasting and fed motility patterns

BACKGROUND

Multiorgan upper gut transplantation is becoming clinically feasible; however, the effects of multivisceral transplantations on gastrointestinal motility are unknown. Our aim was to determine the neural and hormonal mechanisms controlling motility patterns after complete extrinsic denervation of the upper gut as a model of multivisceral upper gut autotransplantation.

METHODS

Seven dogs successfully underwent in situ neural isolation of the stomach, entire small intestine, proximal colon, liver, and pancreas by transecting all connections (distal esophagus, midcolon, all nerves, lymphatics) to this multivisceral complex except the celiac artery, superior mesenteric artery, and the suprahepatic and infrahepatic vena cava; these vessels were meticulously stripped of adventitia under optical magnification. Blood flow was not disrupted to prevent confounding effects of ischemia-reperfusion injury. After 1- to 2-week recovery, myoelectric and manometric recordings of stomach and myoelectric recordings of small bowel were obtained from conscious animals.

RESULTS

During fasting the characteristic cycling migrating motor complex (MMC) was observed in the stomach and small intestine. The gastric component of the MMC was absent in one of the seven dogs. Regular cycling of the MMC during fasting, however, was intermittently disrupted and replaced by a noncyclic pattern of intermittent contractions in two of seven dogs 43% of the recording time. A small meal (50 gm liver) did not abolish the MMC as occurs in normal dogs; in contrast, a large meal (500 gm liver) did abolish the MMC.

CONCLUSIONS

Extrinsic innervation to the upper gut modulates but is not requisite for interdigestive and postprandial motility of the stomach. Because relatively normal global motility patterns are preserved, multivisceral upper gut transplantation should be a viable option in selected patients.

Alterations in carrier-mediated glutamine transport after a model of canine jejunal autotransplantation

The effects of small bowel transplantation (SBTx) on absorptive function are unknown. Preliminary experiments showed a decrease in absorption of glutamine. Our aim was to determine mechanisms of decreased ileal transport of glutamine utilizing a model of intestinal autotransplantation. Seven dogs were studied before and after a model of jejunoileal autotransplantation. In vivo absorption experiments were performed before and two and eight weeks postoperatively with an electrolyte solution containing glutamine (20 mM). In vitro glutamine transport was studied using brush-border membrane vesicles (BBMV) prepared from ileal mucosa obtained from six other dogs and compared to a controls. In vivo net absorptive flux of glutamine decreased at two weeks but returned toward baseline by eight weeks (P = 0.06). Transport of glutamine into BBMVs was decreased at two weeks and remained decreased at eight weeks. KmaxNa+, a measure of carrier affinity was unchanged but VmaxNa+, a function of the number of transporter was decreased at two and eight weeks. Glucose transport was unchanged. It is concluded that jejunoileal autotransplantation decreases ileal absorption of glutamine by a decrease in carrier-mediated transport of glutamine.

Myoelectric activity and absorptive capacity of rat small intestinal isografts

The effect of transplantation on small intestinal absorption, digestive capacity, myoelectric activity, and morphology was assessed in inbred Lewis rats. Electrodes were sutured to the duodenum and isografted jejunoileum or to the native jejunoileum in controls. The frequency of migrating myoelectric complexes (MMCs) in the duodenum was 3.3 +/- 0.3/hr in controls and 1.8 +/- 0.4/hr in transplants (P < 0.05). MMC frequency in the jejunoileum was 5.1 +/- 1.3/hr in controls and 3.2 +/- 0.9/hr in transplants (P > 0.05). MMCs appeared to migrate from the duodenum to the jejunoileum 80 +/- 3% of the time in controls and 59 +/- 7% of the time in transplant rats (P < 0.05). Absorption in the transplanted jejunoileum demonstrated a 35-40% decrease in glucose and electrolytes absorption. Villus height and number of nuclei per villus was reduced. Intestinal length (dry) was 103 +/- 6 cm for controls and 51 +/- 3 cm for transplant rats (P < 0.05). Brush border sucrase activity was unchanged. We conclude that small intestinal isografts display similar myoelectric activity as controls, but the decreased absorptive capacity and villus height may require longer segments of intestine to be transplanted in order to support normal nutrition.

Ileal nutritional function after one-stage orthotopic ileum transplantation in the growing pig: reversal of lethal short bowel syndrome

Intestinal isolation is associated with hypoplasia of defunctioned mucosa and reduction in the segmental absorption, whereas the presence of luminal nutrition is essential for the expression of the ileal adaptive response after proximal small bowel resection. On the other hand, intensive postoperative graft monitoring is obligatory because of the disastrous consequences of small bowel graft rejection. Thus, the authors sought to develop an experimental ileum transplantation model that provided immediate graft placement in bowel continuity, together with readily available graft monitoring connection through a proximal Roux-en-Y enterostomy. Four groups of pigs were prepared: RESTX (n = 9), proximal 50% small bowel resection with simultaneous orthotopic ileum autotransplantation; RES (n = 7), proximal 50% small bowel resection; NONRES (n = 6), transection; and SB (n = 5), short bowel. Early (1 to 4 weeks) and long-term (5 to 12 weeks) studies of animal growth, nutritional status, disaccharide absorption, water and electrolyte balances, and liver function were performed after ileum autotransplantation (IAT) in relation to small intestine of variable length with undivided mesentery (intact neural and lymphatic connections). The perioperative transplantation mortality rate remained at about 10%. Reasons not related to the transplantation procedure accounted for the late complication rate of 38%. In the ileum autotransplantation (RESTX) group, weight gain was recovered 2 to 3 weeks after transplantation, and the mean weight reached the preoperative level at 5 weeks. The SB pigs underwent progressive weight loss. The transection (NONRES) and proximal resection (RES) animals gained weight at similar rates. IAT had no effect on the plasma protein concentrations. Proximal resection, with or without IAT, was associated with depressed plasma cholesterol contents in the early period. Plasma cholesterol levels amended long-term, after both IAT and proximal resection. IAT resulted in deficient intraluminal processing of maltose, whereas isolated proximal resection tended to enhance disaccharide absorption early after the surgery. The short bowel pigs were not able to preserve sufficient nutritional status, and demonstrated a marked decline in the hemoglobin, protein, and cholesterol levels. No biochemical signs suggestive of potential liver damage caused by portocaval graft vascularization were recognized. These findings suggest that one-stage ileum autotransplantation provides sufficent absoprtive capacity to reverse otherwise lethal short bowel syndrome in the growing pig. However, transplantation disturbs the in vivo absorptive function of the nonrejecting ileum. Long-term impairment in disaccharide absorption may be partially related to an altered intestinal adaptive response secondary to proximal resection when combined with simultaneous transplantation. The authors developed this ileal small bowel transplantation model using rapidly growing pigs, wherein body weight gain represents an objective parameter of intestinal absorptive function. Only this type of animal model can yield clinically relevant data in the evaluation of a transplant's ability to provide sufficient nutritional function in a growing recipient.

Jejunoileal transplantation. Effects on characteristics of canine jejunal motor activity in vivo

This study was designed to determine if extrinsic innervation and intrinsic neural continuity with the duodenum (neuroenteric physiologic pathways disrupted during intestinal transplantation) modulate the characteristics of interdigestive motor activity in the canine small bowel. Five dogs served as neurally intact controls (group 1) and 10 dogs (group 2) underwent a model of jejunal autotransplantation involving in situ neural isolation of the jejunoileum. Fasting duodenal and jejunal motor activity was recorded on-line to a microcomputer using closely spaced duodenal and jejunal manometry catheters. Characteristics of global motor patterns, the migrating motor complex (MMC), and local motor patterns, including individual contractions and grouped clustered contractions, were determined. Neural isolation of the jejunoileum disrupted coordination of duodenal and jejunal phase III activity, increased the variability of cycling of the MMC, decreased the period of the jejunal MMC, and increased motility indices in the neurally isolated jejunum. In contrast, single pressure waves and clustered contractions in the neurally isolated jejunum were not altered significantly in incidence or direction, distance, or velocity of spread. In situ neural isolation of the jejunoileum leads to temporal dissociation of the MMC between the transplanted segment (jejunum) and the duodenum but does not appear to alter markedly the characteristics of local contractile activity as measured by individual or grouped contractions. The occurrence of interdigestive jejunal motor patterns and the local organization of individual and grouped small intestinal contractions are not controlled by extrinsic innervation or intrinsic neural continuity with the duodenum.

Contractile properties of enteric smooth muscle after small bowel transplantation in rats

BACKGROUND

The effects of small bowel transplantation (SBTx) on the function of enteric smooth muscle are not understood.

PURPOSE

To study the contractile properties of enteric smooth muscle after SBTx in rats.

METHODS

Five groups of inbred Lewis rats (n > or = 8 each group) were studied: unoperated, naive controls; operated controls 1 week (OC1) and 8 weeks after intestinal transection/reanastomosis of the proximal jejunum and distal ileum; and 1 week (TX1) and 8 weeks (TX8) after syngeneic orthotopic SBTx. Contractile activity of circular muscle strips of jejunum was evaluated in tissue chambers. Spontaneous contractile activity (force per wet weight tissue) increased in TX1, TX8, and OC1 rats (P < or = 0.01). Frequency of contractions doubled in OC1 rats (P < or = 0.001) but was unchanged in the other groups. In the presence of nonadrenergic noncholinergic (NANC) blockade, spontaneous contractile activity increased in TX1 and OC1 (P < or = 0.005) without a change in frequency of contractions. Inhibition of neural activity with tetrodotoxoin increased amplitude and frequency in all groups. Bethanechol (3 x 10(-6) to 3 x 10(-4) mol/L) increased, and norepinephrine (1 x 10(-6) to 1 x 10(-4) mol/L) dose-dependently decreased the amplitude and frequency of contractions in all groups; equi-effective concentrations, however, did not differ among groups.

CONCLUSIONS

The increase in contractile activity after intestinal transection/reanastomosis is secondary to an increase in frequency of contractions and not amplitude. SBTx increases contractile amplitude of circular muscle due, in part, to downregulation of NANC nerves but not via muscarinic or adrenergic hypersensitivity. These alterations in enteric physiology of intestinal contractile activity may have important implications in clinical SBTx.

Immunohistochemical demonstration of enteric nervous distribution after syngeneic small bowel transplantation in rats

BACKGROUND

Small bowel transplantation causes a disturbance of the enteric neural networks after complete extrinsic denervation.

METHODS

The morphologic changes in the enteric nervous system after transplantation were immunohistochemically investigated in jejunal isografts at 10 days, 100 days, and 400 days after transplantation.

RESULTS

No remarkable differences were revealed concerning the antibodies for general neural markers, vasoactive intestinal polypeptide, substance P, somatostatin, or galanin between controls and isografts. Identical differences were detected in the distribution of nerve fibers containing calcitonin gene-related peptide and catecholamines. In the isografts a partial reduction of calcitonin gene-related peptide-immunopositive fibers was shown. A complete elimination of catecholaminergic nerves was seen in the isografts at 10 and 100 days; however, a sparse distribution of catecholaminergic nerves was observed in the 400-day isograft.

CONCLUSIONS

Most intrinsic neural elements are preserved; however, the extrinsic, sympathetic, and sensory nerves are completely disrupted as a consequence of transplantation. Reinnervation of extrinsic nerve fibers could occur in the transplanted small intestine.

Intestinal transplantation: effects on ileal enteric absorptive physiology

BACKGROUND

The effects of small intestine transplantation on enteric physiology are poorly understood. After orthotopic jejunoileal autotransplantation, dogs develop a severe watery diarrhea and lose up to 15% of their body weight. The cause of these changes has not been explained. Our aim was to determine the influence of jejunoileal autotransplantation on ileal absorption of water, electrolytes, and bile salts and the effects of proabsorptive and prosecretory agents on ileal transport.

METHODS

Seven dogs were studied before and at 2 and 8 weeks after in situ jejunoileal neural and lymphatic isolation (a model of small intestine autotransplantation). With a triple-lumen perfusion technique, net ileal fluxes of water, electrolytes, and bile salts were measured before and at 2 and 8 weeks after this model of jejunoileal autotransplantation. In addition, the effects of an intravenous infusion of vasoactive intestinal polypeptide (a prosecretory agent) and norepinephrine (a proabsorptive agent) on net transport were evaluated.

RESULTS

Dogs developed a profuse diarrhea after this model of autotransplantation. Ileal absorption of water and electrolytes decreased immediately (measured during operation), remained decreased for 2 weeks, and returned toward baseline by 8 weeks. A similar decrease in net flux of bile salts was shown at 2 weeks after transplantation and returned toward baseline by 8 weeks. The prosecretory response of vasoactive intestinal polypeptide on ileal fluxes of water and electrolytes was unchanged, whereas the proabsorptive response to norepinephrine increased after this model of autotransplantation.

CONCLUSIONS

Jejunoileal autotransplantation decreases ileal absorption of water, electrolytes, and bile salts. The profuse watery diarrhea observed in dogs after small intestine autotransplantation may be a secretory and/or a bile salt-induced diarrhea related to the effects of jejunoileal denervation.

The impact of jejunal transplant peristalsis on enteric flora

The importance of phase III of the migrating myoelectric complex (MMC) for homeostasis of enteric flora is well documented. The goal of this study was to evaluate in an isogeneic rat model the effect of MMC changes on the self-purging capacity of the jejunal graft. The proximal 25% of the entire jejunoileum of Lewis rats was transplanted orthotopically. Electrodes were then fixed to the graft. Native bowel of five rats and five rats with analogue jejunal segmentation served as controls. Myoelectric recordings were carried out until day 21, when animals were killed for bacteriologic analysis of the segments analyzed myoelectrically and the of neighboring gut. MMCs were observed in all animals during all recordings. Phase III was irregular in transplants because of long-lasting periods of phase III absence alternating with phase III occurring more frequently. The variation coefficient of phase III periodicity calculated for grafts was 48.74, for native bowel 14.79, and for segmented jejunum 22.9. Enteric flora found in all specimens consisted of colonic-like microorganisms. Titers of microorganisms in grafts did not differ from control segments. These findings show that phase III periodicity is severely altered in jejunal grafts. Homeostasis of enteric flora, however, is not influenced by the transplant procedure.

Effects of jejunoileal autotransplantation on gastrointestinal regulatory peptides

Plasma gastrointestinal hormones were measured before and during feeding in eight dogs, more than one year after total autotransplant of the entire jejunoileum, and in controls. At sacrifice, tissues were taken from the transplanted segment and intact bowel for measurement of hormone and enteric neuropeptide content. Gastrin levels were reduced in autotransplanted dogs (fasting 63% of control, incremental response 67% of control, both P < 0.05), reflecting the loss of acid inhibitory reflexes. Secretin and cholecystokinin responses were identical between the two groups. Postprandial levels of gastric inhibitory peptide (incremental response 175% of control, P < 0.005), insulin, and peptide YY (158% of control, P < 0.05) were elevated following denervation, the former suggesting more rapid gastric emptying while the latter may reflect malabsorption. The neurotensin meal response was obtunded by denervation (incremental response 43% of control, P < 0.05), providing evidence for a neural pathway for its release. Pancreatic polypeptide responses were identical between the groups, suggesting intact pancreatic innervation. Abnormal hormone secretion may contribute to the impaired fed motor responses seen following extrinsic denervation of the small bowel. In contrast, the neuropeptide content of the autotransplanted small intestine is normal, suggesting that extrinsic denervation has no long-term effects on peptide content of the enteric nervous system.

Myoelectric activity during small bowel allograft rejection

The effect of rejection on myoelectric activity of an orthotopically transplanted small intestinal segment (group I, N = 14) was studied. Electrodes were placed on grafts and recipient small bowel. Isografts (group II, N = 5) and native bowel (group III, N = 5) served as controls. The first morphological signs of rejection were seen on day 6 and steadily progressed until day 11, when the cellular infiltrate involved all layers of the bowel wall. Slow-wave frequencies remained unchanged throughout the observation period. No difference was detectable between grafts (group I: 31.9 +/- 1.65; group II: 31.36 +/- 0.7) and native bowel after transection (group I: 32.16 +/- 1.78; group II: 31.50 +/- 1.01), which was different (P = 0.0001) from intact bowel of group III animals (38.4 +/- 0.81). Irregular MMCs were detectable in grafts from day 5 on and replaced after food intake by random spiking activities. At day 8, spiking activities disappeared in allografts, which showed a still preserved mucosal architecture, while slow-wave activities continued. These findings demonstrate that intestinal allografts during rejection develop paralysis before mucosal destruction is established, which might be of clinical relevance.

Small bowel transplantation: an overview

Small bowel transplantation (SBT) would, in theory, be the treatment of choice for patients suffering from the short bowel syndrome. Although SBT has been done with a considerable degree of success in some centers [36, 145], it is by no means an established or widely applicable therapy for those with short bowel syndrome. The small bowel is unique among vascularized organ grafts because it not only elicits a vigorous rejection reaction but is also capable of inducing graft-versus-host disease (GVHD). Rejection of the graft does not only lead to loss of function but also to bacterial translocation. The risk of fatal sepsis is aggravated by the immunosuppression given to prevent rejection. Here, the history of SBT is described, and recent developments in experimental and clinical SBT, as well as future prospects for this theoretically optimal treatment modality for patients dependent on total parenteral nutrition (TPN) for life, are outlined.

Effect of a model of canine jejunoileal orthotopic autotransplantation on jejunal and ileal transport of water and electrolytes

Canine jejunoileal transplantation induces an early profuse watery diarrhea of uncertain etiology. Our aim was to determine the temporal effects of a canine model of jejunoileal autotransplantation (a model devoid of confounding effects of ischemia-reperfusion or immune rejection) on basal jejunal and ileal absorption of water and electrolytes to determine if impaired absorption is responsible for the diarrhea. Our hypothesis was that net absorption of water and electrolytes in an enterically isolated loop would decrease after jejunoileal transplantation. Four groups of dogs (N > or = 6) were prepared with 80-cm modified Thiry-Vella loops: group I, neurally intact jejunum; group II, autotransplanted jejunum; group III, neurally intact ileum; and group IV, autotransplanted ileum. The loops were perfused for 3 hr with 150 mM NaCl at 3 ml/min under fasted conditions; transit time through the loop was determined by bolus of a nonabsorbable marker. Dogs were studied on three separate days at one, two, eight, and nine weeks postoperatively. Net absorptive fluxes of water and electrolytes and transit times were similar (P > 0.05) between neurally intact and autotransplant groups (group I vs II and group III vs IV) at each time point. Ileal loops absorbed more than jejunal loops, and transit was slower in ileal loops (each P < 0.05). Our findings suggest that, despite the obligate disruption of extrinsic innervation, enteric (intrinsic) neural continuity, and lymphatic drainage that accompanies this canine model of jejunoileal autotransplantation, net basal absorptive function of water and electrolytes during the fasted state was not decreased nor was transit altered either in jejunum or ileum.(ABSTRACT TRUNCATED AT 250 WORDS)

Small bowel transplantation: an overview

Small bowel transplantation (SBT) would, in theory, be the treatment of choice for patients suffering from the short bowel syndrome. Although SBT has been done with a considerable degree of success in some centers [36, 145], it is by no means an established or widely applicable therapy for those with short bowel syndrome. The small bowel is unique among vascularized organ grafts because it not only elicits a vigorous rejection reaction but is also capable of inducing graft-versus-host disease (GVHD). Rejection of the graft does not only lead to loss of function but also to bacterial translocation. The risk of fatal sepsis is aggravated by the immunosuppression given to prevent rejection. Here, the history of SBT is described, and recent developments in experimental and clinical SBT, as well as future prospects for this theoretically optimal treatment modality for patients dependent on total parenteral nutrition (TPN) for life, are outlined.

Motor activity and transit in the autonomically denervated jejunum

The role of extrinsic (autonomic) innervation in postprandial contractile activity of the small intestine is unknown. Using a canine model, we investigated the effects of complete extrinsic denervation on the parameters of fasting and postprandial jejunal contractions and their relationship to intestinal transit. Individual contractions were recorded using strain gauge transducers. Spatial and temporal parameters of contractions were analyzed by computer methods. Bolus injection of 14C-polyethylene glycol was used to calculate intestinal transit rates. Statistical comparisons of control and denervated animals were made by nonparametric tests. Extrinsic denervation did not abolish fasting or fed motor activity, but the following effects were observed: (1) the frequency of migrating motor complexes (MMCs) increased; (2) the onset of fed motor activity was delayed, and the duration of fed activity was shortened; (3) frequency, mean amplitude, and mean area of postprandial contractions were decreased; (4) fewer contractions propagated distally, and mean propagation distance was shortened; and (5) intestinal transit was slower for solids, but not for liquids. In the small intestine, extrinsic nerves modulate motor activity, which is under primary control of the intrinsic (enteric) nervous system.

Pathophysiology of small intestinal motility

Only in the last few years have we begun to understand the effects of surgical procedures on contractile activity of the small intestine. Although most patients readily adapt to the procedures that are performed, operations such as small intestinal transplantation make it imperative that we pursue a more thorough understanding of the effects of surgery on the motility of the small intestine.

Enteroendocrine peptides in a canine model of orthotopic jejunoileal autotransplantation

The enteroendocrine cells of the small bowel provide a rich source of regulatory peptides involved in the modulation of gastrointestinal function. Recent work from our laboratory showed that in situ neural isolation (autotransplantation) of the jejunoileum produced marked changes in tissue expression of several neuropeptides. In the present study, we examined the influence of extrinsic innervation on the tissue expression of endocrine peptides localized to various regions of the gastrointestinal tract. Concentrations of immunoreactive gastric inhibitory polypeptide (GIP), neurotensin (NT) and peptide tyrosine tyrosine (PYY) in fasting plasma and regional tissue biopsies were determined before and at varying time points (2, 6, 12 weeks) after a model of canine orthotopic jejunoileal autotransplantation. GIP was not altered in plasma or tissue at any time point. Plasma concentrations of NT and PYY increased after autotransplantation. Following a decrease in tissue concentrations two weeks after autotransplantation, NT increased progressively from 2 to 6 to 12 weeks, reaching a maximal increase of 895% over baseline in proximal ileum. Tissue concentrations of PYY followed much the same pattern as NT, but these trends never achieved statistical significance. Chromatographic characterization of tissue biopsy extracts revealed molecular heterogeneity of NT-like immunoreactivity, while GIP and PYY immunoreactivity coeluted as single species with authentic standards. Taken together with our earlier observations, it appears that disruption of extrinsic and intrinsic neural continuity to the jejunoileum (autotransplantation) does not affect gut endocrine peptides such as GIP and PYY to the same extent as enteric neuropeptides. NT has been localized to neural as well as endocrine cells and is involved in the temporal adaptive response to autotransplantation.