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Ileal resection enhances jejunal absorptive adaptation for water and electrolytes to extrinsic denervation: Implications for segmental small bowel transplantation
Ileal Resection Enhances Jejunal Absorptive Adaptation for Water and Electrolytes to Extrinsic Denervation: Implications for Segmental Small Bowel Transplantation By Karen D. Libsch, Troy M. Duininck, and Michael G. Sarr Rochester, Minnesota
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.
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.
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.
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. J Pediatr Surg 38:502-507. Copyright 2003, Elsevier Science (USA). All rights reserved.
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⫺,
INDEX WORDS: Absorption, small intestinal resection, extrinsic denervation, small bowel transplantation, intestinal adaptation.
W
From the Gastroenterology Research Unit and Department of Surgery, Mayo Clinic and Mayo Foundation, Rochester, MN. Presented at the 33rd Annual Meeting of the American Pediatric Surgical Association, Phoenix, Arizona, May 19-23, 2002. This work was supported in part by a grant from the National Institutes of Health (NIH R01 39337-MGS) and the Department of Surgery, Mayo Clinic. Address reprint requests to to Michael G. Sarr, MD, Professor of Surgery, Gastroenterology Research Unit (AL 2-435), Mayo Clinic, 200 First St SW, Rochester, MN 55905. Copyright 2003, Elsevier Science (USA). All rights reserved. 0022-3468/03/3803-0043$35.00/0 doi:10.1053/jpsu.2003.50088
more thorough preoperative evaluation of both recipient and donor, decreased waiting time to receive the transplant (with less malnutrition) and, the opportunity for an elective, staged operative procedure with the attendant benefit of decreased warm and cold ischemic times. Thus, the interest in segmental SBT is intense. However, given the intestinal dysfunction observed after wholeorgan SBT, a potential limitation to the use of segmental SBT is posttransplant enteric dysfunction. Whereas experimental studies in highly controlled models of SBT in rats have shown the feasibility of segmental transplantation in supporting growth and maintaining nutrition,4 the physiology and regional adaptability of the transplanted segment has not been well studied in large animal models. For many years, our laboratory has been interested in the enteric physiology of SBT.5 Our canine model of complete in situ neural isolation of the jejunoileum6 has allowed us to study the physiology of the autotransplanted intestine devoid of immune considerations, ischemia/reperfusion injury, and systemic (versus portal) venous drainage of the gut. Our aim in the current study was to extend our previous model to examine the absorptive physiology and morphometry of the extrinsically denervated jejunum after ileectomy—a model of segmental SBT. Our previous work with this model examined the absorption of simple nutrients7; the current
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Journal of Pediatric Surgery, Vol 38, No 3 (March), 2003: pp 502-507
IDESPREAD USE of small bowel transplantation (SBT), although now a clinical reality,1,2 is limited by multiple factors, including issues of immune rejection, immune suppression, ischemia/reperfusion injury, organ availability and preservation, and posttransplant enteric graft dysfunction. Segmental SBT has been proposed as an option to address current limitations facing whole-organ SBT.3 Segmental SBT would decrease the total antigen load for the transplant recipient as well as potentially expand the cadaveric organ pool. Most significantly, however, the segmental transplant offers the potential for a living-related or even living nonrelated donor, which will not only markedly increase the available organ pool, but also will lead to the potential for HLA matching, preoperative immunomodulation,
EFFECT OF DENERVATION ON JEJUNAL ADAPTATION
Fig 1. Insertion site of infusion catheter system in the jejunum. Inerts detail the proximal infusion and proximal aspiration site and the distal cannula.
study was designed to evaluate changes in absorption of water and electrolytes and morphometric adaptation. Based on previous literature on segmental autotransplantation of the porcine ileum,8 our hypothesis was that extrinsic denervation would blunt the ability of the jejunum to adapt to ileectomy. MATERIALS AND METHODS
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ing 2 weeks for recovery, baseline absorption experiments (see below) were performed. Because all dogs at this stage had the complete length of neurally intact small intestine, both groups were comparable at this time point. Small bowel resection. After completion of baseline experiments, a second celiotomy was performed. All dogs underwent resection of the distal 50% of the jejunoileum (Fig 2A), maintaining the last 3 cm of ileum (and thereby preserving the ileocecal junction). Intestinal continuity was restored with end-to-end jejunal-terminal ileal anastomosis. This procedure creates a moderate short bowel syndrome with weight loss and diarrhea but without mortality.7,14-16 To control for effects of disrupting proximal continuity of the enteric nervous system in our model of complete extrinsic denervation (see below), CON dogs also underwent transection and reanastomosis of the proximal jejunum just distal to the ligament of Treitz (Fig 2B). All extrinsic neural innervation to the remaining jejunum was maintained carefully. EXT DEN dogs, in addition to undergoing distal 50% enterectomy, also underwent our model of in situ neural isolation of the remaining jejunum (Fig 2C), as described previously.5-7,9-13 This preparation involves a complete extrinsic denervation as well as disruption of intrinsic neural and lymphatic continuity to the jejunum without interruption or occlusion of the primary blood supply. In brief, all mesenteric, lymphatic, and neural tissues at the base of the small bowel mesentery were transected except for the superior mesenteric vessels, which were skeletonized carefully with the aid of optical magnification by stripping the investing adventitia and associated neural elements from the vessel walls. Just distal to the ligament of Treitz, the proximal jejunum was transected to complete intrinsic neural disruption. Intestinal continuity then was restored by end-to-end jejunojejunostomy.
Overall Design Two groups of 6 dogs each underwent baseline in vivo experiments of jejunal absorption of water and electrolytes. Thereafter, both groups underwent resection of the distal 50% of the small bowel (total ileectomy); one group (CON) remained neurally intact, whereas the other (EXT DEN) underwent complete extrinsic denervation of the remaining jejunum. Both groups were restudied 2 weeks and 12 weeks postoperatively with identical experiments of absorption in vivo. Intestinal morphology was quantitated at the time of resection with or without denervation and at the time of death.
Animal Preparation Surgical procedures, postoperative care, and subsequent conduct of experiments were performed with approval by the Animal Care and Use Committee of the Mayo Foundation in accordance with the guidelines of the National Institutes of Health and the Public Health Service policy on humane care and use of laboratory animals. All dogs fasted 12 hours before surgery. Catheter and cannula insertion. The 12 healthy female mongrel dogs (weight, 14 to 22 kg) were anesthetized with intravenous sodium methohexital induction (12.5 mg/kg) and maintained on inhaled halothane (Ayerst Laboratories, New York, NY). After preoperative randomization to one of 2 groups (CON or EXT DEN), dogs underwent a midline celiotomy and placement of a jejunal infusion catheter (internal diameter, 1.5 mm), a proximal jejunal aspiration catheter (internal diameter, 3.0 mm), and a modified Thomas cannula (internal diameter, 1 cm) at 25 cm, 40 cm, and 120 cm from the ligament of Treitz, respectively. The proximal ends of the catheters were cemented in a metal cannula; this cannula and the modified Thomas cannula were exteriorized through the abdominal wall (Fig 1). This configuration allowed for intrajejunal infusion of a test solution, a 15-cm mixing segment, and an 80-cm study segment similar in principle to our previous studies.7,9-13 For 3 days postoperatively, dogs were given intramuscular butorphanol for pain control and maintained on parenteral fluid and electrolytes before allowing ad lib feeding. After allow-
Absorption Experiments After an overnight fast, fully conscious dogs resting in a Pavlov sling were studied before (baseline, 0 wk) and at 2 weeks and 12 weeks after ileectomy using a modification of the triple-lumen perfusion technique.17 Each experiment began with gentle flushing of the jejunal test segment with warmed infusate to remove intraluminal particulate debris. The infusate, designed to reproduce the electrolytic milieu of the jejunal lumen, was a warmed (39°C), isosmolar, nonnutrient electrolyte solution (in millimoles/liter, sodium, 140; potassium, 5; chloride, 110; bicarbonate, 35) containing 5 g/L of the nonabsorbable volume marker polyethylene glycol (PEG, molecular weight, 3350 Daltons) labeled with 14C-PEG (5 uCi/L). After flushing, the test solution was infused via the proximal jejunal catheter at a continuous rate of 5 mL/min. Samples of intestinal content were aspirated from the second catheter (15 cm distally) at a constant rate of 1 mL/min using a withdrawal pump (Harvard Apparatus Co, Dover, MA). By measuring the flow rate and concentration of electrolytes at the aspiration site, the exact composition and flow rate of intestinal content entering the study segment (which includes infusate and intestinal content from the duodenum) could be determined. Effluent from the end of the 80-cm test segment was collected by gravity flow via the distal jejunal cannula. As based on previous experiments,7,9-13 a 1-hour equilibration period was allowed to establish steady state dynamics. Subsequently, samples from the proximal catheter and distal cannula were collected during 6 consecutive 30-minutes intervals for analysis. Experiments were repeated twice at each time-point (baseline, and 2 weeks and 12 weeks after ileal resection).
Analytic Methodology All samples were analyzed in duplicate and run within several days of the experiment. Concentrations of the nonabsorbable marker, 14CPEG, were measured by liquid scintillation techniques. Sodium and potassium concentrations were measured by flame photometry and chloride concentrations by chloridimeter.
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Fig 2. Experimental model. (A) At time of baseline studies, all dogs had complete length of neurally intact small intestine. The ileum between X1 and X2 is resected in the next operation. (B) After ileectomy, the remnant jejunum remains extrinsically innervated in the control group. Note that CON dogs underwent transection/reanastomosis of the proximal jejunum to control for proximal disruption of the enteric nervous system. (C) After resection of the ileum, the remnant jejunum (shaded) is extrinsically denervated in EXT DEN dogs.
Analysis of absorption data. Net absorptions of water, sodium, potassium, and chloride were determined using principles of the triplelumen perfusion technique as described previously.7,9-13 In brief, after allowing the first hour for establishment of steady state conditions (ie, the amount of nonabsorbable marker entering the study segment per unit time equaling the amount of marker leaving the distal end of the segment), net absorption of water for each experimental interval was calculated as net absorptive flux (microliters per centimeter per minute); this value was obtained from the difference in volume entering and leaving the 80-cm jejunal test segment as calculated by changes in concentrations of 14C-PEG between the proximal jejunal aspiration site and the distal jejunal diverting cannula using standard formulas for an 80-cm test segment.7,9-13 Positive values represent net absorption, whereas negative values represent net secretion. The individual values of net absorption for each of the 6 separate 30-minute intervals per experiment were meaned, and mean values for the 2 duplicate experiments in each dog also were meaned. Results of absorption were grouped into 3-hour periods. Grand means across dogs were calculated for the baseline, 2-week and 12-week absorptive experiments. Morphometry. A 1- ⫻ 2-cm sample of jejunum was excised from the most proximal end of the resected bowel at the time of the distal 50% enterectomy. A second sample was obtained just before death at least 10 cm proximal to the site of the prior anastomosis. Each sample was oriented carefully and pinned mucosa side up on Styrofoam. After fixation in formalin, intestinal samples were embedded in paraffin. Three strips were cut from 3 different areas of each tissue sample, and 3 measurements were made for each parameter per strip (for a total of 27 measurements per parameter at each time-point). Stained with H&E, tissue samples were evaluated for villus height, crypt depth, and widths of circular and longitudinal muscle layers by light microscopy using an optical reticule, as described previously.13,18 Samples from CON dogs served as baseline values for adapted “neurally intact” bowel and were compared with samples from EXT DEN dogs reflecting the adapted “neurally isolated” bowel. Morphometric variables were evaluated by comparing data within groups to baseline values.
Statistical Analysis. Experiments were evaluated by comparing data within the groups to baseline values (paired analysis) and values between the 2 groups (CON and EXT DEN) at each time-point (unpaired analysis). Mean net absorptive fluxes within the groups were compared for all dogs across the time-points (baseline, 2 weeks, and 12 weeks). Mean values for villus height, crypt depth, circular muscle width, and longitudinal muscle width were compared within groups and between groups for all dogs at baseline and at time of death. Data were analyzed using analysis of variance (ANOVA) and a subsequent Student’s t test for paired data with probability adjusted according to the Bonferroni correction for multiple related comparisons when appropriate. Data in the text are presented as mean values ⫾ SEM.
RESULTS
Health/General Characteristics of Dogs All dogs tolerated catheter and cannula placement and subsequent ileal resection well, maintained a good appetite, and remained active and healthy. As described before7 in this model of ileal resection, all dogs had a watery diarrhea, which resolved in all CON dogs at a mean of 10 weeks but persisted in all EXT DEN dogs throughout the study. All dogs initially lost weight after the distal 50% small bowel resection, but the maximum weight loss was greater in EXT DEN (2.3 ⫾ 0.5 kg v 3.8 ⫾ 0.3 kg; P ⬍ 0.05) despite subjectively similar appetites, activity level, and overall health in the 2 groups. Absorptive Function Table 1 shows net absorptive fluxes for water, Na⫹, K , and Cl⫺. Our analysis compared net absorptive flux ⫹
Table 1. Net Absorptive Fluxes of Water and Electrolytes Na⫹ (Eq/cm/min ⫻ 10⫺1)
Water (L/cm/min)
K⫹ (Eq/cm/min ⫻ 10⫺2)
Cl⫺ (Eq/cm/min ⫻ 10⫺1)
Period
CON
EXT DEN
CON
EXT DEN
CON
EXT DEN
CON
EXT DEN
0 wk 2 wk 12 wk
11.0 ⫾ 0.2 10.2 ⫾ 1.1 11.8 ⫾ 0.1
9.5 ⫾ 0.1 7.2 ⫾ 1.5 9.3 ⫾ 3.0
16 ⫾ 2 15 ⫾ 2 17 ⫾ 1
13 ⫾ 1 13 ⫾ 2 13 ⫾ 4
3.7 ⫾ 1.3 2.9 ⫾ 1.1 1.8 ⫾ 1.3
4.4 ⫾ 0.6 3.9 ⫾ 0.8 3.8 ⫾ 2.3
9.5 ⫾ 1.7 9.7 ⫾ 1.4 10.4 ⫾ 1.0
8.6 ⫾ 1.0 9.3 ⫾ 1.4 8.4 ⫾ 3.0
NOTE. N ⫽ 6 dogs per group, mean ⫾ SEM. No statistical differences noted within or between groups for any solute.
EFFECT OF DENERVATION ON JEJUNAL ADAPTATION
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Table 2. Morphometry Baseline
12 Weeks
Morphometric Parameter (mm)
CON
EXT DEN
CON
EXT DEN
Villus height Crypt depth Circular muscle width Longitudinal muscle width
1.93 ⫾ 0.13 0.99 ⫾ 0.04 1.06 ⫾ 0.03 0.39 ⫾ 0.03
1.95 ⫾ 0.10 1.02 ⫾ 0.02 1.25 ⫾ 0.18 0.47 ⫾ 0.11
1.97 ⫾ 0.13 1.24 ⫾ 0.07* 1.09 ⫾ 0.08 0.47 ⫾ 0.08
2.20 ⫾ 0.24 1.13 ⫾ 0.11† 1.23 ⫾ 0.08 0.48 ⫾ 0.03
NOTE. N ⫽ 6 dogs per group. *P ⫽ .02 compared with baseline CON. †P ⫽ .06 compared with baseline EXT DEN.
of water and electrolytes within groups at each timepoint and then between the 2 groups at each time-point. In the CON dogs, there were no differences in water absorption at 2 weeks or 12 weeks after ileectomy when compared with baseline (0 weeks). Although there appeared to be a decrease in water absorption from baseline at 2 weeks in the EXT DEN dogs (in microliters per centimeter per minute, 9.5 ⫾ 0.1 v 7.2 ⫾ 1.5; P ⫽ .25), this difference was not significant; water absorption also did not differ from baseline 12 weeks after denervation. Also, there were no differences in water absorption between the 2 groups at any time-point. Net absorptive fluxes of electrolytes followed a pattern similar to water absorption in both groups of dogs. Fluxes of sodium, potassium, and chloride were unchanged from baseline both 2 weeks and 12 weeks after operative intervention in both groups, and there were no differences between the 2 groups at any time-point. Morphometry Table 2 shows morphometric values of jejunal tissue. At baseline, as expected, there were no differences between the 2 groups in any parameter. In CON dogs 12 weeks after ileectomy, there were no alterations in villus height (in millimeters, 1.93 ⫾ 0.13 v 1.97 ⫾ 0.13), circular muscle width (in millimeters, 1.06 ⫾ 0.03 v 1.09 ⫾ 0.08), or in longitudinal muscle width (in millimeters, 0.39 ⫾ 0.03 v 0.47 ⫾ 0.08; P ⱖ 0.25 in each). However, crypt depth did increase (in millimeters, 0.99 ⫾ 0.04 v 1.24 ⫾ 0.07; P ⫽ .02). EXT DEN dogs showed a very similar pattern. Again, after ileectomy in the extrinsically denervated jejunum, there were no alterations in villus height (in millimeters, 1.95 ⫾ 0.10 v 2.20 ⫾ 0.24), in circular muscle width (in millimeters, 1.25 ⫾ 0.18 v 1.23 ⫾ 0.08), or in longitudinal muscle width (in millimeters, 0.47 ⫾ 0.11 v. 0.48 ⫾ 0.03; P ⱖ .39 in each). Crypt depth did, however, also increase after ileectomy in the denervated jejunum (in millimeters, 1.02 ⫾ 0.02 v 1.13 ⫾ 0.11; P ⫽ .06). There were, however, no differences between the 2 groups after operative intervention—increases in crypt depth in CON and EXT DEN (delta, in millimeters, 0.25 v 0.11; P ⫽
.33) and final crypt depth (1.02 ⫾ 0.02 v 1.13 ⫾ 0.11; P ⫽ .39) were similar. DISCUSSION
In this study, we showed that extrinsic denervation does not prevent the jejunal adaptive response to ileectomy. Distal 50% enterectomy induced a transient short gut syndrome in the dog with diarrhea and weight loss, which was worsened by extrinsic denervation. Net absorptive fluxes of water and electrolytes were not altered after resection or after extrinsic denervation. Resection induced an increase in jejunal crypt depth, which also occurred in extrinsically denervated jejunum. Thus, although distal 50% enterectomy results in a short gut syndrome of greater severity and of longer duration in extrinsically denervated dogs, extrinsic denervation does not appear to blunt the jejunal adaptive responses to ileectomy. When interpreted in the context of our previous related publication10 the most important implication of our study is that segmental autotransplantation actually may enhance the absorptive adaptation for water and electrolytes compared with total jejunoileal autotransplantation. Segmental SBT has several theoretic advantages over whole small bowel transplantation,3 but for this new method to be a feasible alternative to whole-bowel transplantation, some degree of adaptation must occur for the graft to provide enough absorptive capacity for the recipient to maintain a satisfactory nutritional state with oral intake. Adaptation in morphology and enteric function occurs in the small bowel mucosa after major small bowel resection or bypass. Structural adaptation begins within hours of injury with hyperproliferation of crypt cells and an increased rate of enterocyte migration, which results in deeper crypts and increased villus height. Absorptive adaptation is marked initially by a decrease in enterocyte absorptive function for several weeks after resection, attributed to immature enterocytes in the villus then a return to baseline or even increased levels of absorption.19 Factors important in this response include the presence of luminal nutrients, available enteric or plasma glutamine, pancreaticobiliary secretions,
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circulating humoral agents such as hormones, growth factors, and putative regulatory peptides, and the ability of specific anatomic regions of the remaining gut to express various transport proteins.20-25 The role of extrinsic innervation to the gut (sympathetic and vagal/ parasympathetic), which modulates absorptive function, may represent another factor important in the adaptive response that has not been well investigated. To examine the role of extrinsic innervation in modulating adaptation of a segment of small intestine, our goal was to extend our previous model of total jejunoileal extrinsic denervation to a model of extrinsic denervation of specific anatomic segments after subtotal small bowel resection (a model of segmental small intestinal (auto)transplantation). In previous work, we showed that when the entire jejunoileum was subjected to this model of in situ neural isolation (without concomitant small bowel resection), net jejunal10 and ileal11 absorption of water and electrolytes was notably decreased 2 weeks postoperatively; when morphology was evaluated 8 weeks postoperatively when absorption had returned to baseline, there was no measurable change in bowel wall morphology.18 In the current study, after total ileectomy, we found no decrease in net absorption of water and electrolytes in the extrinsically denervated jejunum at either 2 or 12 weeks postoperatively, and there was an identical increase in crypt depth. Tsiotos et al13 noted similar findings in the extrinsically denervated ileum after total jejunectomy. The differences between total jejunoileal denervation (and denervation with resection) might prove to be very important in the application of segmental SBT clinically. Our findings suggest not only that the neurally isolated jejunum can “adapt” to the stress of ileectomy, but also that resection may enhance adaptation to neural isolation. These observations differ from the work of Lauronen
et al8 who studied the effect of a model of complete autotransplantation of the porcine ileum. These investigators reported that adaptation in the autotransplanted ileum was significantly blunted. Our differing results may be secondary to species differences, regional anatomic differences, or the differences of our selective extrinsic denervation (which avoids any ischemia/reperfusion injury) from the preparation of Lauronen et al,8 which is a true autotransplantation, necessitating some degree of ischemia and reperfusion. However, despite similar absorptive capacities of water and electrolytes between CON and EXT DEN dogs, EXT DEN dogs had persistent diarrhea and weight loss. The reasons for this clinical difference remain unclear; however, in this study, experiments investigating absorption were performed in the fasting state. We hypothesize that there may be some difference in postprandial patterns of absorption between the 2 groups and currently are conducting studies to examine the role of extrinsic innervation in postprandial patterns of absorption. These results suggest that extrinsic denervation, as necessitated by SBT and by segmental SBT, does not blunt absorptive or morphometric adaptation. This observation, therefore, offers reassuring and possibly important implications for the concept of living-related or living nonrelated segmental SBT. Because our previous work showed that water an electrolyte absorption was decreased in a related model of whole SBT,10 the lack of any decrease in net absorption in this current study may suggest that resection enhances the early adaptation to extrinsic denervation. ACKNOWLEDGMENTS The authors thank Judy A. Duenes and Louis J. Kost for their assistance with electrolyte analysis and Deborah I. Frank for her help in preparing the manuscript.
REFERENCES 1. Nishida S, Kato T, Tector J, et al: Ninety-five cases of intestinal transplantation at the University of Miami. Gastroenterology 120:402, 2001 2. Abu-Elmagd K, Reyes J, Bond, G, et al: Clinical intestinal transplantation: A decade of a single center experience. Ann Surg 234:404-416, 2001 3. Cicalese L, Rastellini C, Sileri P, et al: Segmental living related small bowel transplantation in adults. J Gastrointest Surg 5:168-173, 2001 4. Rahman MS, Taguchi T, Nakao M, et al: Long-term results of short segmental syngeneic small intestinal transplantation: comparison of jejunal and ileal graft. J Pediatr Surg 31:908-911, 1996 5. Sarr MG, Duenes JA, Walters AM: Jejunal and ileal absorptive function after a model of canine jejunoileal autotransplantation. J Surg Res 51:223-229, 1991 6. Sarr MG, Duenes JA, Tanaka M: A model of jejunoileal in vivo neural isolation of the entire jejunoileum: Transplantation and the effect on intestinal motility. J Surg Res 47:66-272, 1989
7. Libsch KD, Zyromski NJ, Tanaka T, et al: Role of extrinsic innervation in jejunal absorptive adaptation to subtotal small bowel resection—A model of segmental small bowel transplantation. J Gastrointest Surg 6:240-247, 2002 8. Lauronen J, Pakarinen MP, Kuusanmaki P, et al: Synchronous ileal autotransplantation impairs adaptation of the remaining gut in pigs with proximal small bowel resection. Dig Dis Sci 44:2187-2195, 1999 9. Oishi AJ, Sarr MG: Intestinal transplantation: Effects on ileal enteric absorptive physiology. Surgery 117:545-553, 1995 10. Herkes SM, Smith CD, Sarr MG: Jejunal responses to absorptive and secretory stimuli in the neurally isolated jejunum in vivo. Surgery 116:576-586, 1994 11. Foley MK, Inoue Y, Souba WW, et al: Extrinsic innervation modulates canine jejunal transport of glutamine, alanine, leucine, and glucose. Surgery 123:321-329, 1998 12. Oishi AJ, Inoue Y, Souba WW, et al: Alterations in carrier-
EFFECT OF DENERVATION ON JEJUNAL ADAPTATION
mediated transport after a model of canine jejunal autotransplantation. Dig Dis Sci 41:1915-1924, 1996 13. Tsiotos GG, Kendrick ML, Libsch KD, et al: Ileal absorptive adaptation to jejunal resection and extrinsic denervation: Implications for living-related small bowel transplantation. J Gastrointest Surg 5:517-524, 2001 14. Yanoff SR, Willard MD, Boothe HW, et al: Short bowel syndrome in four dogs. Vet Surg 21:217-222, 1992 15. Quigley EM, Thompson JS: Effects of artificial ileocolonic sphincter on motility in intestinal remnant following subtotal small intestinal resection in the dog. Dig Dis Sci 39:1222-1228, 1994 16. Feldman EJ, Dowling RH, McNaughton J, et al: Effects of oral versus intravenous nutrition on intestinal adaptation after small bowel resection in the dog. Gastroenterology 70:712-719, 1976 17. Cooper H, Levitan R, Fordtran JS, et al: A method for studying absorption of water and solute from the human small intestine. Gastroenterology 54:783-787, 1968 (Suppl) 18. Sarr MG, Siadati MR, Bailey J, et al: Neural isolation of the
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jejunoileum. Effect on tissue morphometry, mucosal disaccharidase activity, and tissue peptide content. J Surg Res 61:416-424, 1996 19. Whang EE, Dunn JC, Joffe H, et al: Enterocyte functional adaptation following intestinal resection. J Surg Res 60:370-374, 1996 20. Jenkins AP, Thompson RP: Mechanisms of small intestinal adaptation. Dig Dis 12:15-27, 1994 21. Alison MR, Sarraf CE: The role of growth factors in gastrointestinal cell proliferation. Cell Biol Internat 18:1-10, 1994 22. Wang HT, Miller JH, Avissar N, et al: Small bowel adaptation is dependent on the site of massive enterectomy. J Surg Res 84:94-100, 1999 23. Grant D: Intestinal transplantation: 1997 report of the international registry. Transplantation 67:1061-1064, 1999 24. Jaffe BM, Beck R, Flint L, et al: Living-related small bowel transplantation in adults: A report of two patients. Transplant Proc 29:1851-1852, 1997 25. Jaffe BM, Burgos AA, Martinez-Noack M: The use of jejunal transplants to treat a genetic enzyme deficiency. Ann Surg 223:649656, 1996
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.
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.
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.
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. J Pediatr Surg 38:502-507. Copyright 2003, Elsevier Science (USA). All rights reserved.
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⫺,
INDEX WORDS: Absorption, small intestinal resection, extrinsic denervation, small bowel transplantation, intestinal adaptation.
W
From the Gastroenterology Research Unit and Department of Surgery, Mayo Clinic and Mayo Foundation, Rochester, MN. Presented at the 33rd Annual Meeting of the American Pediatric Surgical Association, Phoenix, Arizona, May 19-23, 2002. This work was supported in part by a grant from the National Institutes of Health (NIH R01 39337-MGS) and the Department of Surgery, Mayo Clinic. Address reprint requests to to Michael G. Sarr, MD, Professor of Surgery, Gastroenterology Research Unit (AL 2-435), Mayo Clinic, 200 First St SW, Rochester, MN 55905. Copyright 2003, Elsevier Science (USA). All rights reserved. 0022-3468/03/3803-0043$35.00/0 doi:10.1053/jpsu.2003.50088
more thorough preoperative evaluation of both recipient and donor, decreased waiting time to receive the transplant (with less malnutrition) and, the opportunity for an elective, staged operative procedure with the attendant benefit of decreased warm and cold ischemic times. Thus, the interest in segmental SBT is intense. However, given the intestinal dysfunction observed after wholeorgan SBT, a potential limitation to the use of segmental SBT is posttransplant enteric dysfunction. Whereas experimental studies in highly controlled models of SBT in rats have shown the feasibility of segmental transplantation in supporting growth and maintaining nutrition,4 the physiology and regional adaptability of the transplanted segment has not been well studied in large animal models. For many years, our laboratory has been interested in the enteric physiology of SBT.5 Our canine model of complete in situ neural isolation of the jejunoileum6 has allowed us to study the physiology of the autotransplanted intestine devoid of immune considerations, ischemia/reperfusion injury, and systemic (versus portal) venous drainage of the gut. Our aim in the current study was to extend our previous model to examine the absorptive physiology and morphometry of the extrinsically denervated jejunum after ileectomy—a model of segmental SBT. Our previous work with this model examined the absorption of simple nutrients7; the current
502
Journal of Pediatric Surgery, Vol 38, No 3 (March), 2003: pp 502-507
IDESPREAD USE of small bowel transplantation (SBT), although now a clinical reality,1,2 is limited by multiple factors, including issues of immune rejection, immune suppression, ischemia/reperfusion injury, organ availability and preservation, and posttransplant enteric graft dysfunction. Segmental SBT has been proposed as an option to address current limitations facing whole-organ SBT.3 Segmental SBT would decrease the total antigen load for the transplant recipient as well as potentially expand the cadaveric organ pool. Most significantly, however, the segmental transplant offers the potential for a living-related or even living nonrelated donor, which will not only markedly increase the available organ pool, but also will lead to the potential for HLA matching, preoperative immunomodulation,
EFFECT OF DENERVATION ON JEJUNAL ADAPTATION
Fig 1. Insertion site of infusion catheter system in the jejunum. Inerts detail the proximal infusion and proximal aspiration site and the distal cannula.
study was designed to evaluate changes in absorption of water and electrolytes and morphometric adaptation. Based on previous literature on segmental autotransplantation of the porcine ileum,8 our hypothesis was that extrinsic denervation would blunt the ability of the jejunum to adapt to ileectomy. MATERIALS AND METHODS
503
ing 2 weeks for recovery, baseline absorption experiments (see below) were performed. Because all dogs at this stage had the complete length of neurally intact small intestine, both groups were comparable at this time point. Small bowel resection. After completion of baseline experiments, a second celiotomy was performed. All dogs underwent resection of the distal 50% of the jejunoileum (Fig 2A), maintaining the last 3 cm of ileum (and thereby preserving the ileocecal junction). Intestinal continuity was restored with end-to-end jejunal-terminal ileal anastomosis. This procedure creates a moderate short bowel syndrome with weight loss and diarrhea but without mortality.7,14-16 To control for effects of disrupting proximal continuity of the enteric nervous system in our model of complete extrinsic denervation (see below), CON dogs also underwent transection and reanastomosis of the proximal jejunum just distal to the ligament of Treitz (Fig 2B). All extrinsic neural innervation to the remaining jejunum was maintained carefully. EXT DEN dogs, in addition to undergoing distal 50% enterectomy, also underwent our model of in situ neural isolation of the remaining jejunum (Fig 2C), as described previously.5-7,9-13 This preparation involves a complete extrinsic denervation as well as disruption of intrinsic neural and lymphatic continuity to the jejunum without interruption or occlusion of the primary blood supply. In brief, all mesenteric, lymphatic, and neural tissues at the base of the small bowel mesentery were transected except for the superior mesenteric vessels, which were skeletonized carefully with the aid of optical magnification by stripping the investing adventitia and associated neural elements from the vessel walls. Just distal to the ligament of Treitz, the proximal jejunum was transected to complete intrinsic neural disruption. Intestinal continuity then was restored by end-to-end jejunojejunostomy.
Overall Design Two groups of 6 dogs each underwent baseline in vivo experiments of jejunal absorption of water and electrolytes. Thereafter, both groups underwent resection of the distal 50% of the small bowel (total ileectomy); one group (CON) remained neurally intact, whereas the other (EXT DEN) underwent complete extrinsic denervation of the remaining jejunum. Both groups were restudied 2 weeks and 12 weeks postoperatively with identical experiments of absorption in vivo. Intestinal morphology was quantitated at the time of resection with or without denervation and at the time of death.
Animal Preparation Surgical procedures, postoperative care, and subsequent conduct of experiments were performed with approval by the Animal Care and Use Committee of the Mayo Foundation in accordance with the guidelines of the National Institutes of Health and the Public Health Service policy on humane care and use of laboratory animals. All dogs fasted 12 hours before surgery. Catheter and cannula insertion. The 12 healthy female mongrel dogs (weight, 14 to 22 kg) were anesthetized with intravenous sodium methohexital induction (12.5 mg/kg) and maintained on inhaled halothane (Ayerst Laboratories, New York, NY). After preoperative randomization to one of 2 groups (CON or EXT DEN), dogs underwent a midline celiotomy and placement of a jejunal infusion catheter (internal diameter, 1.5 mm), a proximal jejunal aspiration catheter (internal diameter, 3.0 mm), and a modified Thomas cannula (internal diameter, 1 cm) at 25 cm, 40 cm, and 120 cm from the ligament of Treitz, respectively. The proximal ends of the catheters were cemented in a metal cannula; this cannula and the modified Thomas cannula were exteriorized through the abdominal wall (Fig 1). This configuration allowed for intrajejunal infusion of a test solution, a 15-cm mixing segment, and an 80-cm study segment similar in principle to our previous studies.7,9-13 For 3 days postoperatively, dogs were given intramuscular butorphanol for pain control and maintained on parenteral fluid and electrolytes before allowing ad lib feeding. After allow-
Absorption Experiments After an overnight fast, fully conscious dogs resting in a Pavlov sling were studied before (baseline, 0 wk) and at 2 weeks and 12 weeks after ileectomy using a modification of the triple-lumen perfusion technique.17 Each experiment began with gentle flushing of the jejunal test segment with warmed infusate to remove intraluminal particulate debris. The infusate, designed to reproduce the electrolytic milieu of the jejunal lumen, was a warmed (39°C), isosmolar, nonnutrient electrolyte solution (in millimoles/liter, sodium, 140; potassium, 5; chloride, 110; bicarbonate, 35) containing 5 g/L of the nonabsorbable volume marker polyethylene glycol (PEG, molecular weight, 3350 Daltons) labeled with 14C-PEG (5 uCi/L). After flushing, the test solution was infused via the proximal jejunal catheter at a continuous rate of 5 mL/min. Samples of intestinal content were aspirated from the second catheter (15 cm distally) at a constant rate of 1 mL/min using a withdrawal pump (Harvard Apparatus Co, Dover, MA). By measuring the flow rate and concentration of electrolytes at the aspiration site, the exact composition and flow rate of intestinal content entering the study segment (which includes infusate and intestinal content from the duodenum) could be determined. Effluent from the end of the 80-cm test segment was collected by gravity flow via the distal jejunal cannula. As based on previous experiments,7,9-13 a 1-hour equilibration period was allowed to establish steady state dynamics. Subsequently, samples from the proximal catheter and distal cannula were collected during 6 consecutive 30-minutes intervals for analysis. Experiments were repeated twice at each time-point (baseline, and 2 weeks and 12 weeks after ileal resection).
Analytic Methodology All samples were analyzed in duplicate and run within several days of the experiment. Concentrations of the nonabsorbable marker, 14CPEG, were measured by liquid scintillation techniques. Sodium and potassium concentrations were measured by flame photometry and chloride concentrations by chloridimeter.
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Fig 2. Experimental model. (A) At time of baseline studies, all dogs had complete length of neurally intact small intestine. The ileum between X1 and X2 is resected in the next operation. (B) After ileectomy, the remnant jejunum remains extrinsically innervated in the control group. Note that CON dogs underwent transection/reanastomosis of the proximal jejunum to control for proximal disruption of the enteric nervous system. (C) After resection of the ileum, the remnant jejunum (shaded) is extrinsically denervated in EXT DEN dogs.
Analysis of absorption data. Net absorptions of water, sodium, potassium, and chloride were determined using principles of the triplelumen perfusion technique as described previously.7,9-13 In brief, after allowing the first hour for establishment of steady state conditions (ie, the amount of nonabsorbable marker entering the study segment per unit time equaling the amount of marker leaving the distal end of the segment), net absorption of water for each experimental interval was calculated as net absorptive flux (microliters per centimeter per minute); this value was obtained from the difference in volume entering and leaving the 80-cm jejunal test segment as calculated by changes in concentrations of 14C-PEG between the proximal jejunal aspiration site and the distal jejunal diverting cannula using standard formulas for an 80-cm test segment.7,9-13 Positive values represent net absorption, whereas negative values represent net secretion. The individual values of net absorption for each of the 6 separate 30-minute intervals per experiment were meaned, and mean values for the 2 duplicate experiments in each dog also were meaned. Results of absorption were grouped into 3-hour periods. Grand means across dogs were calculated for the baseline, 2-week and 12-week absorptive experiments. Morphometry. A 1- ⫻ 2-cm sample of jejunum was excised from the most proximal end of the resected bowel at the time of the distal 50% enterectomy. A second sample was obtained just before death at least 10 cm proximal to the site of the prior anastomosis. Each sample was oriented carefully and pinned mucosa side up on Styrofoam. After fixation in formalin, intestinal samples were embedded in paraffin. Three strips were cut from 3 different areas of each tissue sample, and 3 measurements were made for each parameter per strip (for a total of 27 measurements per parameter at each time-point). Stained with H&E, tissue samples were evaluated for villus height, crypt depth, and widths of circular and longitudinal muscle layers by light microscopy using an optical reticule, as described previously.13,18 Samples from CON dogs served as baseline values for adapted “neurally intact” bowel and were compared with samples from EXT DEN dogs reflecting the adapted “neurally isolated” bowel. Morphometric variables were evaluated by comparing data within groups to baseline values.
Statistical Analysis. Experiments were evaluated by comparing data within the groups to baseline values (paired analysis) and values between the 2 groups (CON and EXT DEN) at each time-point (unpaired analysis). Mean net absorptive fluxes within the groups were compared for all dogs across the time-points (baseline, 2 weeks, and 12 weeks). Mean values for villus height, crypt depth, circular muscle width, and longitudinal muscle width were compared within groups and between groups for all dogs at baseline and at time of death. Data were analyzed using analysis of variance (ANOVA) and a subsequent Student’s t test for paired data with probability adjusted according to the Bonferroni correction for multiple related comparisons when appropriate. Data in the text are presented as mean values ⫾ SEM.
RESULTS
Health/General Characteristics of Dogs All dogs tolerated catheter and cannula placement and subsequent ileal resection well, maintained a good appetite, and remained active and healthy. As described before7 in this model of ileal resection, all dogs had a watery diarrhea, which resolved in all CON dogs at a mean of 10 weeks but persisted in all EXT DEN dogs throughout the study. All dogs initially lost weight after the distal 50% small bowel resection, but the maximum weight loss was greater in EXT DEN (2.3 ⫾ 0.5 kg v 3.8 ⫾ 0.3 kg; P ⬍ 0.05) despite subjectively similar appetites, activity level, and overall health in the 2 groups. Absorptive Function Table 1 shows net absorptive fluxes for water, Na⫹, K , and Cl⫺. Our analysis compared net absorptive flux ⫹
Table 1. Net Absorptive Fluxes of Water and Electrolytes Na⫹ (Eq/cm/min ⫻ 10⫺1)
Water (L/cm/min)
K⫹ (Eq/cm/min ⫻ 10⫺2)
Cl⫺ (Eq/cm/min ⫻ 10⫺1)
Period
CON
EXT DEN
CON
EXT DEN
CON
EXT DEN
CON
EXT DEN
0 wk 2 wk 12 wk
11.0 ⫾ 0.2 10.2 ⫾ 1.1 11.8 ⫾ 0.1
9.5 ⫾ 0.1 7.2 ⫾ 1.5 9.3 ⫾ 3.0
16 ⫾ 2 15 ⫾ 2 17 ⫾ 1
13 ⫾ 1 13 ⫾ 2 13 ⫾ 4
3.7 ⫾ 1.3 2.9 ⫾ 1.1 1.8 ⫾ 1.3
4.4 ⫾ 0.6 3.9 ⫾ 0.8 3.8 ⫾ 2.3
9.5 ⫾ 1.7 9.7 ⫾ 1.4 10.4 ⫾ 1.0
8.6 ⫾ 1.0 9.3 ⫾ 1.4 8.4 ⫾ 3.0
NOTE. N ⫽ 6 dogs per group, mean ⫾ SEM. No statistical differences noted within or between groups for any solute.
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Table 2. Morphometry Baseline
12 Weeks
Morphometric Parameter (mm)
CON
EXT DEN
CON
EXT DEN
Villus height Crypt depth Circular muscle width Longitudinal muscle width
1.93 ⫾ 0.13 0.99 ⫾ 0.04 1.06 ⫾ 0.03 0.39 ⫾ 0.03
1.95 ⫾ 0.10 1.02 ⫾ 0.02 1.25 ⫾ 0.18 0.47 ⫾ 0.11
1.97 ⫾ 0.13 1.24 ⫾ 0.07* 1.09 ⫾ 0.08 0.47 ⫾ 0.08
2.20 ⫾ 0.24 1.13 ⫾ 0.11† 1.23 ⫾ 0.08 0.48 ⫾ 0.03
NOTE. N ⫽ 6 dogs per group. *P ⫽ .02 compared with baseline CON. †P ⫽ .06 compared with baseline EXT DEN.
of water and electrolytes within groups at each timepoint and then between the 2 groups at each time-point. In the CON dogs, there were no differences in water absorption at 2 weeks or 12 weeks after ileectomy when compared with baseline (0 weeks). Although there appeared to be a decrease in water absorption from baseline at 2 weeks in the EXT DEN dogs (in microliters per centimeter per minute, 9.5 ⫾ 0.1 v 7.2 ⫾ 1.5; P ⫽ .25), this difference was not significant; water absorption also did not differ from baseline 12 weeks after denervation. Also, there were no differences in water absorption between the 2 groups at any time-point. Net absorptive fluxes of electrolytes followed a pattern similar to water absorption in both groups of dogs. Fluxes of sodium, potassium, and chloride were unchanged from baseline both 2 weeks and 12 weeks after operative intervention in both groups, and there were no differences between the 2 groups at any time-point. Morphometry Table 2 shows morphometric values of jejunal tissue. At baseline, as expected, there were no differences between the 2 groups in any parameter. In CON dogs 12 weeks after ileectomy, there were no alterations in villus height (in millimeters, 1.93 ⫾ 0.13 v 1.97 ⫾ 0.13), circular muscle width (in millimeters, 1.06 ⫾ 0.03 v 1.09 ⫾ 0.08), or in longitudinal muscle width (in millimeters, 0.39 ⫾ 0.03 v 0.47 ⫾ 0.08; P ⱖ 0.25 in each). However, crypt depth did increase (in millimeters, 0.99 ⫾ 0.04 v 1.24 ⫾ 0.07; P ⫽ .02). EXT DEN dogs showed a very similar pattern. Again, after ileectomy in the extrinsically denervated jejunum, there were no alterations in villus height (in millimeters, 1.95 ⫾ 0.10 v 2.20 ⫾ 0.24), in circular muscle width (in millimeters, 1.25 ⫾ 0.18 v 1.23 ⫾ 0.08), or in longitudinal muscle width (in millimeters, 0.47 ⫾ 0.11 v. 0.48 ⫾ 0.03; P ⱖ .39 in each). Crypt depth did, however, also increase after ileectomy in the denervated jejunum (in millimeters, 1.02 ⫾ 0.02 v 1.13 ⫾ 0.11; P ⫽ .06). There were, however, no differences between the 2 groups after operative intervention—increases in crypt depth in CON and EXT DEN (delta, in millimeters, 0.25 v 0.11; P ⫽
.33) and final crypt depth (1.02 ⫾ 0.02 v 1.13 ⫾ 0.11; P ⫽ .39) were similar. DISCUSSION
In this study, we showed that extrinsic denervation does not prevent the jejunal adaptive response to ileectomy. Distal 50% enterectomy induced a transient short gut syndrome in the dog with diarrhea and weight loss, which was worsened by extrinsic denervation. Net absorptive fluxes of water and electrolytes were not altered after resection or after extrinsic denervation. Resection induced an increase in jejunal crypt depth, which also occurred in extrinsically denervated jejunum. Thus, although distal 50% enterectomy results in a short gut syndrome of greater severity and of longer duration in extrinsically denervated dogs, extrinsic denervation does not appear to blunt the jejunal adaptive responses to ileectomy. When interpreted in the context of our previous related publication10 the most important implication of our study is that segmental autotransplantation actually may enhance the absorptive adaptation for water and electrolytes compared with total jejunoileal autotransplantation. Segmental SBT has several theoretic advantages over whole small bowel transplantation,3 but for this new method to be a feasible alternative to whole-bowel transplantation, some degree of adaptation must occur for the graft to provide enough absorptive capacity for the recipient to maintain a satisfactory nutritional state with oral intake. Adaptation in morphology and enteric function occurs in the small bowel mucosa after major small bowel resection or bypass. Structural adaptation begins within hours of injury with hyperproliferation of crypt cells and an increased rate of enterocyte migration, which results in deeper crypts and increased villus height. Absorptive adaptation is marked initially by a decrease in enterocyte absorptive function for several weeks after resection, attributed to immature enterocytes in the villus then a return to baseline or even increased levels of absorption.19 Factors important in this response include the presence of luminal nutrients, available enteric or plasma glutamine, pancreaticobiliary secretions,
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circulating humoral agents such as hormones, growth factors, and putative regulatory peptides, and the ability of specific anatomic regions of the remaining gut to express various transport proteins.20-25 The role of extrinsic innervation to the gut (sympathetic and vagal/ parasympathetic), which modulates absorptive function, may represent another factor important in the adaptive response that has not been well investigated. To examine the role of extrinsic innervation in modulating adaptation of a segment of small intestine, our goal was to extend our previous model of total jejunoileal extrinsic denervation to a model of extrinsic denervation of specific anatomic segments after subtotal small bowel resection (a model of segmental small intestinal (auto)transplantation). In previous work, we showed that when the entire jejunoileum was subjected to this model of in situ neural isolation (without concomitant small bowel resection), net jejunal10 and ileal11 absorption of water and electrolytes was notably decreased 2 weeks postoperatively; when morphology was evaluated 8 weeks postoperatively when absorption had returned to baseline, there was no measurable change in bowel wall morphology.18 In the current study, after total ileectomy, we found no decrease in net absorption of water and electrolytes in the extrinsically denervated jejunum at either 2 or 12 weeks postoperatively, and there was an identical increase in crypt depth. Tsiotos et al13 noted similar findings in the extrinsically denervated ileum after total jejunectomy. The differences between total jejunoileal denervation (and denervation with resection) might prove to be very important in the application of segmental SBT clinically. Our findings suggest not only that the neurally isolated jejunum can “adapt” to the stress of ileectomy, but also that resection may enhance adaptation to neural isolation. These observations differ from the work of Lauronen
et al8 who studied the effect of a model of complete autotransplantation of the porcine ileum. These investigators reported that adaptation in the autotransplanted ileum was significantly blunted. Our differing results may be secondary to species differences, regional anatomic differences, or the differences of our selective extrinsic denervation (which avoids any ischemia/reperfusion injury) from the preparation of Lauronen et al,8 which is a true autotransplantation, necessitating some degree of ischemia and reperfusion. However, despite similar absorptive capacities of water and electrolytes between CON and EXT DEN dogs, EXT DEN dogs had persistent diarrhea and weight loss. The reasons for this clinical difference remain unclear; however, in this study, experiments investigating absorption were performed in the fasting state. We hypothesize that there may be some difference in postprandial patterns of absorption between the 2 groups and currently are conducting studies to examine the role of extrinsic innervation in postprandial patterns of absorption. These results suggest that extrinsic denervation, as necessitated by SBT and by segmental SBT, does not blunt absorptive or morphometric adaptation. This observation, therefore, offers reassuring and possibly important implications for the concept of living-related or living nonrelated segmental SBT. Because our previous work showed that water an electrolyte absorption was decreased in a related model of whole SBT,10 the lack of any decrease in net absorption in this current study may suggest that resection enhances the early adaptation to extrinsic denervation. ACKNOWLEDGMENTS The authors thank Judy A. Duenes and Louis J. Kost for their assistance with electrolyte analysis and Deborah I. Frank for her help in preparing the manuscript.
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