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Role of Bile in Intestinal Motility After Massive Liver Resection in Conscious Rats
Journal of Surgical Research 150, 131–136 (2008) doi:10.1016/j.jss.2008.02.011
Role of Bile in Intestinal Motility After Massive Liver Resection in Conscious Rats Chenghu Ma, M.D.,1 Tatsuo Shimura, M.D., Ph.D., Taketoshi Suehiro, M.D., Ph.D., Atsushi Takahashi, M.D., Ph.D., Erito Mochiki, M.D., Ph.D., Takayuki Asao, M.D., Ph.D., and Hiroyuki Kuwano, M.D., Ph.D. Department of General Surgical Science, Surgery 1, Gunma University, Graduate School of Medicine, Maebashi, Japan Submitted for publication August 28, 2007
Aim. To investigate the effect of 90% partial hepatectomy (90% PHx) and the involvement of bile on ileal motility in conscious rats. Methods. Two strain gauge force transducers were chronically implanted in the ileum of each of 20 rats. The rats were divided into four groups, three of which underwent 90% PHx. The experiments were performed with the rats in a conscious, fasted state. After ileal motility was recorded, bile or saline was perfused into the duodenum of each rat in two of the 90% PHx groups. The effects of the perfusion on ileal motility were observed and recorded using the motility index (MI), defined as the area under the contraction cues after surgery and expressed as the ratio to the MI in the preoperational motility. The time of the first passage of stool after surgery was recorded. Results. A typical migrating motor complex (MMC) pattern was observed in normal fasted rats. Increased MMC cycle lengths and a decreased MI at 1 day and 3 days after 90% PHx were observed. The MMC after 90% PHx was characterized by an increased duration of Phase 2-like activity. The MMC cycle length, the MI, and the time of the first passage of stool after 90% PHx were improved by perfusion of bile into the duodenum through the biliary cannula but were not influenced by perfusion of saline into the duodenum through the biliary cannula. Conclusion. The MMC cycle length and the MI were inhibited after 90% PHx, with the involvement of decreased bile flow into the gastrointestinal tract by liver resection. © 2008 Elsevier Inc. All rights reserved. 1 To whom correspondence and reprint requests should be addressed at Department of General Surgical Science, Surgery 1, Gunma University, Graduate School of Medicine, 3-39-22, Showamachi, Maebashi, Gunma 371-8511, Japan. E-mail: machenghu2002@ hotmail.com.
Key Words: bile; ileal motility; migrating motor complex; 90% partial hepatectomy; strain gauge force transducer. INTRODUCTION
Postoperative ileus, a poorly understood phenomenon occurring uniformly with all abdominal laparotomies, is generally accepted as a normal response to abdominal surgery [1]. In addition to causing significant discomfort for the patient because of respiratory compromise, abdominal distention, nausea, and emesis, it prolongs the patient’s hospital stay and delays early enteral nutrition [2]. After liver surgery, postoperative ileus cannot be disregarded. Systemic endotoxemia, which is related to a high incidence of liver failure through increased apoptosis and a diminished liver regeneration pathway [3], occurs because of inadequate clearance of endogenous endotoxins [4] and inhibited gastrointestinal motility. Gastrointestinal motility disturbances are clearly associated with small bowel bacterial overgrowth and its products (endotoxins) [5]. Postoperative ileus remains an area in which improved treatment could result in a decrease in complications after liver resection. Unfortunately, the physiological control mechanisms of gastrointestinal motility changes after massive liver resection are incompletely understood. To our knowledge, there have been no reports of changes in gastrointestinal motility using a strain gauge force transducer after massive partial hepatectomy in conscious rats. Previous studies have shown that enterohepatic bile circulation and interdigestive motility are related. The presence of bile in portohepatic circulation or the processing of bile in the liver provide important stimuli for the initiation of regular duodenal migrating motor
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complex (MMC) [6], and the absence of bile in the intestine induces gastrointestinal motility disturbances [7]. Because bile flow into the gastrointestinal tract after liver resection decreases and then gradually returns to the preoperative level [8], it is tempting to hypothesize that the decreased bile flow into the duodenum contributes to the gastrointestinal motility change after massive liver resection. The present study was performed to investigate the effect of 90% partial hepatectomy and the possible involvement of bile on ileal motility in conscious rats. MATERIALS AND METHODS Animals Male Wister rats weighing 250 to 300 g were used. The animals were housed in individual cages with free access to water and food. Housing conditions were kept constant, with the temperature at 22°C, the humidity at 40%, and a 12-h light/dark cycle. All animals were allowed to adjust to these conditions for 1 week before surgery. The experiments were conducted at the Institute of Experimental Animal Research, Gunma University School of Medicine, Gunma, Japan. The procedures used in this study were approved by the review committee for animal use at Gunma University, Maebashi, Japan.
Surgical Methods All surgical procedures were performed under general anesthesia with ether.
Implantation of Strain Gauge Force Transducer The gastrointestinal tract was exposed by a midline laparotomy. The strain gauge force transducer (F-041S/B; Star Medical, Tokyo, Japan) was sutured with 5-0 silk onto the serial surface of the ileum (10 cm and 5 cm proximal to the ileocecum, respectively) parallel to the circular muscle layer. The lead wires from the strain gauge force transducer, which were brought out of the abdominal cavity through a subcutaneous tunnel, exiting through a skin incision on top of the back, were protected with plastic tape, folded, and fixed inside a small plastic container sutured to the skin. After 6 days of recovery, rats were fasted with free access to water for 24 h before the experiments were conducted.
Gastrointestinal Motility Recordings Before the measurements were taken, rats were fasted with free access to water for 24 h. On the experiment days, the strain gauge force transducer wires were connected to an amplifier. The amplified signals were fed into a computer through an analogue/digital converter and a multi-channel data acquisition recorder (Star Medical Co., Ltd., Tokyo, Japan).
Experimental Procedures The rats, each implanted with a strain gauge force transducer 6 days earlier, were randomly divided into four groups of five rats each. The SO group underwent laparotomy and mobilization of the liver without liver removal; the 90% PHx group, only 90% liver resection; the 90% PHx ⫹ saline group, 90% PHx ⫹ biliary cannula ⫹ saline perfusion; and the 90% PHx ⫹ bile group, 90% PHx ⫹ biliary cannula ⫹ bile perfusion. All surgical procedures were carried out under sterile conditions. The preoperative motility was recorded for 2 h. For measurements of postoperative motility change, the ileal motility in each group was recorded for 4 h immediately after surgery and for more than 3 h at 1 day and 3 days after surgery. Administration of 2.4 mL/kg of saline or bile through the biliary cannula took place immediately after and again 12 h after surgery. Recording with the administration of 2.4 mL/kg of saline or bile took place 1 day and 3 days after surgery in the 90% PHx ⫹ saline and 90% PHx ⫹ bile groups. The procedures for the administration of bile or saline were carried out under sterile conditions.
Analysis of Gastrointestinal Motility The recording of intestinal contractions was modified by computer software (Star Medical Co., Ltd.) to exclude artifacts such as respiration and body movements. From the modified integrated recordings, the MMC cycle length and the motility index (MI) were visually evaluated and determined. The MMC cycle length measurement was made from the abrupt end of one Phase 3 complex to the abrupt end of the next complex. The MI was defined as the area under the contraction cues in each 1 h recording after surgery and was expressed as the ratio to the MI in the preoperational motility. A 2 h recording was analyzed in two 1 h segments, and the average of the two segments was taken as the preoperative motility, which was set at 100%, with each animal serving as its own control. The time of the first passage of stool after surgery was also recorded.
Statistical Analysis All values are expressed as the mean ⫾ the standard error of the mean (SEM). Statistical significance was determined by the unpaired Student’s t-test. A probability level of P ⬍ 0.05 was used to define statistical significance.
90% Partial Hepatectomy (PHx) and Biliary Cannula The 90% PHx was performed using the technique described by Morioka et al. [9]. In brief, the liver was detached from the surrounding connective tissue under a large midline incision. We isolated the portal pedicle and then ligatured it using 6-0 silk. Before the hepatic lobe was resected, three transfixing sutures were made with 4-0 polypropylene to encircle and ligature separately the hepatic vein near its root and on both sides of the neighboring hepatic parenchyma. The biliary cannula, made of silicone tubing, was inserted after 90% PHx was performed. Briefly, one silicone cannula was inserted into the right bile duct. The cannula was exteriorized through a subcutaneous tunnel exiting at the top of the head through a skin incision and was fixed inside a small plastic container that had been sutured to the skin. This cannula allowed bile or saline to be infused concurrently without any additional surgery or anesthesia.
RESULTS
In this study, we conducted the investigations only at 1 day and 3 days after surgery. The 90% PHx rats treated with the methods, described by either Morioka et al. [9] or Higgins and Anderson [10] if they survived for 72 h after surgery, lived out their life span with normal liver function. In the present study, all rats that underwent 90% PHx or 90% PHx ⫹ biliary cannula were still alive 7 days after the hepatectomy. There were no significant differences in body weight among rats in the 90% PHx, 90% PHx ⫹ saline, and 90% PHx ⫹ bile groups during the experiments.
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MA ET AL.: ROLE OF BILE IN INTESTINAL MOTILITY
TABLE 1 Effect of Bile Administration on MMC Cycle Length (min) After 90% PHx in Rats (n ⴝ 20, mean ⴞ SE) 90% PHx ⫹ Bile cannulae
FIG. 1. Typical pattern of MMC of the ileum of rats in the fasted, conscious state. (filled inverted triangle): Phase 3 of MMC. Ileum 1 and Ileum 2 (10 cm and 5 cm proximal to the ileocecum, respectively).
Normal Small Intestinal Motility
Under 24 h fasting conditions, the interdigestive ileal motility was characterized as a typical complex of MMC consisting of three phases: Phase 1, no detectable contractive activity; Phase 2, irregular contractive activity; and Phase 3, clearly distinguishable and intense contractive activity (Fig. 1). The average preoperative MMC cycle length in the ileum of the rats was 28.7 ⫾ 0.9 min. Effect of 90% PHx on Ileal Motility
There was a significant difference between the SO and 90% PHx groups in terms of the times of the first passage of stool after surgery (Fig. 2). In the latter groups, the MMC cycle length increased 1 day and 3 days after 90% PHx, which was significantly different from the cycle length of the SO group (Table 1, Fig. 3). The MMC after 90% PHx was characterized by an increased duration of Phase 2-like activity. The MI decreased 1 day and 3 days after 90% PHx, a result that was significantly different from that of the SO group (Fig. 4). The MMC cycle length and MI were not influenced by the insertion of the bile duct cannula.
FIG. 2. Time of the first passage of stool after surgery. There was a significant difference between the SO and 90% PHx groups. The time of the first passage of stool was earlier in the 90% PHx ⫹ bile group than in the 90% PHx ⫹ saline group. *P ⬍ 0.05 (n ⫽ 5 in each group, mean ⫾ SE).
Day
SO
90% PHx
Saline (0.6 mL/d)*
Bile (0.6 mL/d)*
Pre Day 1 Day 3
28.1 ⫾ 0.2 26.9 ⫾ 1.8 26.9 ⫾ 1.5
28.2 ⫾ 0.3 53.7 ⫾ 6.7** 42.8 ⫾ 2.3**
29.8 ⫾ 0.7 44.3 ⫾ 3.9 44.2 ⫾ 2.7
28.3 ⫾ 0.5 33.3 ⫾ 2.8†,‡ 32.2 ⫾ 2.1†,‡
Pre ⫽ preoperative day. * 1 h after bile or saline administration. ** P ⬍ 0.05 90% PHx versus SO. † P ⬍ 0.05 versus 90% PHx ⫹ saline. ‡ P ⬍ 0.05 versus 90% PHx.
Effect of Saline Administration on Ileal Motility Induced by 90% PHx
There was no significant difference between the 90% PHx ⫹ saline and 90% PHx groups in terms of the time of the first passage of stool after surgery (Fig. 2). With saline administration 1 h after recording on days 1 and 3 after surgery in the 90% PHx ⫹ saline group, there were no significant differences in MMC cycle length before and after saline administration in similar rats, although the MMC cycle length tended to decrease at 1 d after surgery (Fig. 5). The MMC cycle length and MI in the 90% PHx ⫹ saline group did not differ from those in the 90% PHx group, although the MMC cycle length tended to decrease at 1 day after surgery in the 90% PHx ⫹ saline group compared with the 90% PHx group, which may have been associated with systemic volume expansion and/or local stimulation of the gut by saline administration (Table 1, Fig. 4) [11].
FIG. 3. Typical pattern of MMC of the ileum at 1 and 3 days after 90% PHx in rats. The MMC cycle length at 1 day and 3 days after 90% PHx was significantly increased. (filled inverted triangle): Phase 3 of MMC. Ileum 1 and Ileum 2 (10 cm and 5 cm proximal to the ileocecum, respectively). POD ⫽ postoperative day.
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FIG. 4. Effect of administration of bile on MI 1 day and 3 days after 90% PHx in rats. There were significant differences between the MI of the 90% PHx ⫹ bile group and that of the 90% PHx ⫹ saline group. The MI at 1 day after surgery was higher than that at 3 days in the 90% PHx ⫹ bile group. †P ⬍ 0.05 (n ⫽ 5 in each group; mean ⫾ SE). *1 h after bile or saline administration. POD ⫽ postoperative day.
Effect of Bile Administration on Ileal Motility Induced by 90% PHx
Passage of stool occurred early after 90% PHx with bile administration, and there was a significant difference between the 90% PHx ⫹ saline group and the 90% PHx ⫹ bile group (Fig. 2). In the 90% PHx ⫹ bile group, with bile administration 1 h after recording at 1 day and 3 days, we observed a decreased MMC cycle length in similar rats (Fig. 6). There were significant differences in the MMC cycle length and MI in the 90% PHx ⫹ bile group compared with those in the 90% PHx ⫹ saline group. The MI at 1 day after surgery was higher than that at 3 days after surgery in the 90% PHx ⫹ bile group (Table 1, Fig. 4). DISCUSSION
In the present study, we investigated the ileal motility changes and the role of bile in gastrointestinal motility after 90% PHx in fasted, conscious rats. In our 90% PHx animal model, we used the technique described by Morioka et al. [9]. When we used this tech-
FIG. 5. Effects of saline administration (filled arrow) on ileum motility of rats 1 day and 3 days after 90% PHx. With saline administration 1 h after recording at 1 day and 3 days after 90% PHx, there were no significant differences in MMC cycle length before and after saline administration in similar rats, although the MMC cycle length tended to decrease at 1 day after surgery. (filled inverted triangle): Phase 3 of MMC. Ileum 1 and Ileum 2 (10 cm and 5 cm proximal to the ileocecum, respectively). POD ⫽ postoperative day.
FIG. 6. Effects of bile administration (black arrow) on ileum motility of rats 1 day and 3 days after 90% PHx. With bile administration 1 h after recording at 1 day and 3 days after 90% PHx, the MMC cycle length was decreased in similar rats. (filled Inverted triangle): Phase 3 of MMC. Ileum 1 and Ileum 2 (10 cm and 5 cm proximal to the ileocecum, respectively). POD ⫽ postoperative day.
nique to manipulate the area around the hepatic vein, all 90% PHx rats lived out their life span with normal liver function. The use of different methods, however, led to conflicting results [9, 12]. The model that we have developed seems suitable for studying the change in gastrointestinal motility after 90% PHx in conscious rats, and there are possible relationships among interdigestive small bowel motility, enterohepatic bile circulation, and liver regeneration. The surgical procedures were well tolerated by the animals implanted with the force transducer, and insertion of the bile cannula in the 90% PHx rats seemed to affect neither the MMC cycle length nor the MI. Wang et al. also studied gastrointestinal motility at 1 h and 2 h after 90% PHx using methods to record small intestinal transit [12]. In their study, the influence of ether anesthesia on small intestinal motility was disregarded. In addition, in the rats that had undergone 90% PHx by the technique previously described, the mortality rate was so high that it was difficult to determine the real influence of liver resection on gastrointestinal motility. The stenosis of the inferior vena cava leading to hepatic venous outflow insufficiency in the liver remnant, caused by the mass ligature used in the method of Higgins and Anderson, may have been associated with higher mortality after 90% PHx [10]. The ileal motility pattern in normal rats is characterized by cyclical Phase 3 contractions propagating aborally through the two recording segments and followed by a period of quiescence. The MMC cycle length was higher in the ileum than in the jejunum [13]. Compared with the SO rats, the 90% PHx rats showed a longer MMC cycle length, lower MI, and delayed passage of stool after surgery. The MMC after 90% PHx was characterized by an increased duration of Phase 2-like activity. Both quantitative and qualitative changes in contractions clearly induced changes in gastrointestinal transit [14]. These findings suggest
MA ET AL.: ROLE OF BILE IN INTESTINAL MOTILITY
that massive liver resection inhibited gastrointestinal transit, partly associated, perhaps, with an increased MMC cycle length and decreased MI in the ileum. However, from our data, it is impossible to determine the main cause of delayed gastrointestinal transit. The stomach, the small intestine, and the colon must be considered separately when gastrointestinal transit is investigated since the enteric nervous system and the extrinsic innervation of the different parts of the gastrointestinal tract display different neurochemical coding or receptors [15, 16]. Thus, further work is necessary to evaluate the influence of liver resection on stomach and colon motility and to identify the main cause of delayed gastrointestinal transit. The mechanisms by which partial hepatectomy resulted in altered ileal motility remain unclear. In general, it has been suggested that neural reflex, inflammatory changes, and hormonal changes are involved in mediating postoperative ileus [17]. After liver resection, however, decreased bile secretion into the gastrointestinal tract may be an important factor influencing ileum motility change. In previous studies, the presence of bile in portohepatic circulation or the processing of bile in the liver provided an important stimulus for the initiation of regular duodenal MMCs [6], and decreased bile secretion to the gastrointestinal tract inhibited small bowel motility, which was significantly correlated with an increased MMC cycle length [7]. Increased bile flow to the duodenum was correlated with small bowel motility [18]. In this study, we observed that the first passage of stool was earlier in the 90% PHx ⫹ bile group than in the 90% PHx and 90% PHx ⫹ saline groups. Furthermore, in the 90% PHx ⫹ bile group, with bile administered at 1 day and 3 days, we observed a decreased MMC cycle length and increased MI 1 h after the administration in similar rats. There was a significant improvement in the MMC cycle length and MI 1 h after bile administration. Based on these findings, we suggest that decreased bile flow into the gastrointestinal tract by liver resection is partly involved in ileal motility change by 90% PHx in conscious rats. The mechanism whereby decreased bile secretion contributes to ileum motility change could not be determined from our experiment. It is interesting to note that the MI at 1 day after surgery was higher than those at 3 days after surgery in 90% PHx ⫹ bile groups. Although the mechanism remains unclear, this result may be associated with decreased intestinal sensitivity to bile because of higher levels of glucagon, which is related to inhibited gastrointestinal motility [14] in blood at 3 days after 90% PHx than at 1 day after 90% PHx [19]. In addition to decreased bile flow into the duodenum, a possible factor is gastrointestinal motility change induced by liver resection. Although ileal motility change was induced by 95% liver resection in the rats, all of which survived at least 3 days after surgery, it
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was not completely improved by perfusion of bile through the biliary cannula (data not shown). After liver resection, portal pressure, inducing splanchnic venous congestion, rapidly increased [20], which may have influenced small intestinal motility. However, there was no relationship between portal pressures and changes in ileal motility after 70% partial hepatectomy (data not shown). It has been demonstrated that liver resection decreases the blood flow to the small intestine [21], and ischemia reperfusion induces intestinal motility change [22]. Bielefeldt and Conklin demonstrated that intestinal response decreased as a result of electrical field stimulation during ischemia and that there was a relationship between the duration of hypoxia and the change in intestinal motility [23]. The effect of hemodynamics on small intestinal motility change by massive liver resection requires further investigation. Liver failure after major partial hepatectomy remains a problem. Systemic endotoxemia, which is related to a high incidence of liver failure through increased apoptosis and a diminished liver regeneration pathway [3], occurs because of inadequate clearance of endogenous endotoxins [4] and inhibited gastrointestinal motility contributing to bacterial overgrowth and its products (endotoxins) [5]. There were positive relationships between MMC cycle length and bacterial overgrowth in the small intestine of rats with obstructive jaundice [24], and the absence of bile in the intestinal tract led to delayed liver regeneration in rats [25]. Bile is considered to be a protective factor in intestinal barrier function [26]. It has been reported that bile administration to the intestine decreased intestine MMC cycle length [7, 18] and inhibited bacterial overgrowth [26]. Unfortunately, the physiological control mechanisms of gastrointestinal motility changes after massive liver resection in rats or humans are incompletely understood. In our study, we first demonstrated an improved effect of bile on gastrointestinal motility change after 90% PHx in rats. This finding may provide a basis for investigating how to reduce complications after massive liver resection. In conclusion, we have confirmed that the MMC cycle length and MI in the ileum were inhibited after 90% PHx, which may have been associated with delayed intestinal transit time; furthermore, there was some involvement of decreased bile flow into the gastrointestinal tract.
ACKNOWLEDGMENTS
The authors thank Dr. Y. Kamiyama, Dr. S. Hashimoto, and Dr. K. Okada for technical assistance. This study was supported in part by a Grant-in-Aid for scientific research and the 21st century COE program from the Ministry of Education, Culture, Sports, Science, and Technology.
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REFERENCES 1.
Waldhausen JH, Shaffrey ME, Skenderis BS, et al. Gastrointestinal myoelectric and clinical patterns of recovery after laparotomy. Ann Surg 1990;211:777.
2.
Kalff JC, Schraut WH, Simmons RL, et al. Surgical manipulation of the gut elicits an intestinal muscularis inflammatory response resulting in postsurgical ileus. Ann Surg 1998;228: 652.
3.
Morita T, Togo S, Kubota T, et al. Mechanism of postoperative liver failure after excessive hepatectomy investigated using a cDNA microarray. J Hepatobiliary Pancreat Surg 2002;9:352.
4.
Boermeester MA, Straatsburg IH, Houdijk AP, et al. Endotoxin and interleukin-1 related hepatic inflammatory response promotes liver failure after partial hepatectomy. Hepatology 1995; 22:1499.
5.
Zhang SC, Wang W, Ren WY, et al. Effect of cisapride on intestinal bacterial and endotoxin translocation in cirrhosis. World J Gastroenterol 2003;9:534.
13.
Sagrada A, Fargeas MJ, Bueno L. Involvement of ␣-1 and -2 adrenoceptors in the postlaparotomy intestinal motor disturbances in the rat. Gut 1987;28:955.
14.
Scott LD, Summers RW. Correlation of contractions and transit in rat small intestine. Am J Physiol 1976;230:132.
15.
Furness JB, Bornstein JC, Murphy R, et al. Roles of peptides in transmission in the enteric nervous system. Trends Neurosci 1992;15:66.
16.
Burks TF. Neurotransmission and neurotransmitters. In Johnson LR, Ed. Physiology of the gastrointestinal tract, 3rd ed. New York: Raven Press, 1994:211–242.
17.
Andrew Luckey, Edward Livingston, Yvette Tache. Mechanisms and Treatment of Postoperative Ileus. Arch Surg 2003; 138:201.
18.
Fang P, Dong L, Zhang WJ, et al. Relationship between enterohepatic bile acid circulation and interdigestive migrating myoelectrical activity in rats. World J Gastroenterol 2005;11:5377.
19.
Gaub J, Iversen J. Rat liver regeneration after 90% partial hepatectomy. Hepatology 1984;4:902.
6.
Ozeki K, Sarna SK, Condon RE. Bile acts at a porto-hepatic circulation site to initiate duodenal MMCs. Gastroenterology 1991;100:A479. [Abstract].
20.
Lee SS, Hadengue A, Girod C, et al. Reduction of intrahepatic vascular space in the pathogenesis of portal hypertension. In vitro and in vivo studies in the rat. Gastroenterology 1987;93:157.
7.
Nieuwenhuijs VB, Luiking YC, Verheem A, et al. Disrupted bile flow affects interdigestive small bowel motility in rats. Surgery 1997;122:600.
21.
8.
Xu HS, Rosenlof LK, Jones RS. Bile secretion and liver regeneration in partially hepatectomized rats. Ann Surg 1993;218: 176.
Boermeester MA, Houdijk AP, Straatsburg IH, et al. Organ blood flow after partial hepatectomy in rats: Modification by endotoxin-neutralizing bactericidal/permeability-increasing protein (rBPI23). J Hepatol 1999;31:905.
22.
9.
Morioka D, Watanabe K, Makino H, et al. Safety limit of the extent of hepatectomy for rats with moderately fatty liver: Experimental study concerning living liver donor safety. J Gastroenterol Hepatol 2006;21:367.
Takahashi A, Tomomasa T, Kaneko H, et al. Intestinal motility in an in vivo rat model of intestinal ischemia-reperfusion with special reference to the effects of nitric oxide on the motility changes. J Pediatr Gastroenterol Nutr 2001;33:283.
23.
Bielefeldt K, Conklin JL. Intestinal motility during hypoxia and reoxygenation in vitro. Dig Dis Sci 1997;42:878.
24.
Nieuwenhuijs VB, van Dijk JE, Gooszen HG, et al. Obstructive jaundice, bacterial translocation, and interdigestive smallbowel motility in rats. Digestion 2000;62:255.
25.
Junji Ueda, Kazuo Chijiiwa, Kenji Nakano, et al. Lack of intestinal bile results in delayed liver regeneration of normal rat liver after hepatectomy accompanied by impaired cyclin E-associated kinase activity. Surgery 2002;131:564.
26.
Ogata Y, Nishi M, Nakayama H, et al. Role of bile in intestinal barrier function and its inhibitory effect on bacterial translocation in obstructive jaundice in rats. J Surg Res 2003;115:18.
10.
Higgins GM, Anderson RM. Experimental pathology of the liver. Arch Pathol 1931;12:186.
11.
Grossie VB Jr., Weisbrodt NW, Moore FA, et al. Ischemia/ reperfusion-induced disruption of rat small intestine transit is reversed by total enteral nutrition. Nutrition 2001;17:938.
12.
Wang XD, Guo WD, Wang Q, et al.The association between enteric bacterial overgrowth and gastrointestinal motility after subtotal liver resection or portal vein obstruction in rats. Eur J Surg 1994;160:153.
Role of Bile in Intestinal Motility After Massive Liver Resection in Conscious Rats Chenghu Ma, M.D.,1 Tatsuo Shimura, M.D., Ph.D., Taketoshi Suehiro, M.D., Ph.D., Atsushi Takahashi, M.D., Ph.D., Erito Mochiki, M.D., Ph.D., Takayuki Asao, M.D., Ph.D., and Hiroyuki Kuwano, M.D., Ph.D. Department of General Surgical Science, Surgery 1, Gunma University, Graduate School of Medicine, Maebashi, Japan Submitted for publication August 28, 2007
Aim. To investigate the effect of 90% partial hepatectomy (90% PHx) and the involvement of bile on ileal motility in conscious rats. Methods. Two strain gauge force transducers were chronically implanted in the ileum of each of 20 rats. The rats were divided into four groups, three of which underwent 90% PHx. The experiments were performed with the rats in a conscious, fasted state. After ileal motility was recorded, bile or saline was perfused into the duodenum of each rat in two of the 90% PHx groups. The effects of the perfusion on ileal motility were observed and recorded using the motility index (MI), defined as the area under the contraction cues after surgery and expressed as the ratio to the MI in the preoperational motility. The time of the first passage of stool after surgery was recorded. Results. A typical migrating motor complex (MMC) pattern was observed in normal fasted rats. Increased MMC cycle lengths and a decreased MI at 1 day and 3 days after 90% PHx were observed. The MMC after 90% PHx was characterized by an increased duration of Phase 2-like activity. The MMC cycle length, the MI, and the time of the first passage of stool after 90% PHx were improved by perfusion of bile into the duodenum through the biliary cannula but were not influenced by perfusion of saline into the duodenum through the biliary cannula. Conclusion. The MMC cycle length and the MI were inhibited after 90% PHx, with the involvement of decreased bile flow into the gastrointestinal tract by liver resection. © 2008 Elsevier Inc. All rights reserved. 1 To whom correspondence and reprint requests should be addressed at Department of General Surgical Science, Surgery 1, Gunma University, Graduate School of Medicine, 3-39-22, Showamachi, Maebashi, Gunma 371-8511, Japan. E-mail: machenghu2002@ hotmail.com.
Key Words: bile; ileal motility; migrating motor complex; 90% partial hepatectomy; strain gauge force transducer. INTRODUCTION
Postoperative ileus, a poorly understood phenomenon occurring uniformly with all abdominal laparotomies, is generally accepted as a normal response to abdominal surgery [1]. In addition to causing significant discomfort for the patient because of respiratory compromise, abdominal distention, nausea, and emesis, it prolongs the patient’s hospital stay and delays early enteral nutrition [2]. After liver surgery, postoperative ileus cannot be disregarded. Systemic endotoxemia, which is related to a high incidence of liver failure through increased apoptosis and a diminished liver regeneration pathway [3], occurs because of inadequate clearance of endogenous endotoxins [4] and inhibited gastrointestinal motility. Gastrointestinal motility disturbances are clearly associated with small bowel bacterial overgrowth and its products (endotoxins) [5]. Postoperative ileus remains an area in which improved treatment could result in a decrease in complications after liver resection. Unfortunately, the physiological control mechanisms of gastrointestinal motility changes after massive liver resection are incompletely understood. To our knowledge, there have been no reports of changes in gastrointestinal motility using a strain gauge force transducer after massive partial hepatectomy in conscious rats. Previous studies have shown that enterohepatic bile circulation and interdigestive motility are related. The presence of bile in portohepatic circulation or the processing of bile in the liver provide important stimuli for the initiation of regular duodenal migrating motor
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complex (MMC) [6], and the absence of bile in the intestine induces gastrointestinal motility disturbances [7]. Because bile flow into the gastrointestinal tract after liver resection decreases and then gradually returns to the preoperative level [8], it is tempting to hypothesize that the decreased bile flow into the duodenum contributes to the gastrointestinal motility change after massive liver resection. The present study was performed to investigate the effect of 90% partial hepatectomy and the possible involvement of bile on ileal motility in conscious rats. MATERIALS AND METHODS Animals Male Wister rats weighing 250 to 300 g were used. The animals were housed in individual cages with free access to water and food. Housing conditions were kept constant, with the temperature at 22°C, the humidity at 40%, and a 12-h light/dark cycle. All animals were allowed to adjust to these conditions for 1 week before surgery. The experiments were conducted at the Institute of Experimental Animal Research, Gunma University School of Medicine, Gunma, Japan. The procedures used in this study were approved by the review committee for animal use at Gunma University, Maebashi, Japan.
Surgical Methods All surgical procedures were performed under general anesthesia with ether.
Implantation of Strain Gauge Force Transducer The gastrointestinal tract was exposed by a midline laparotomy. The strain gauge force transducer (F-041S/B; Star Medical, Tokyo, Japan) was sutured with 5-0 silk onto the serial surface of the ileum (10 cm and 5 cm proximal to the ileocecum, respectively) parallel to the circular muscle layer. The lead wires from the strain gauge force transducer, which were brought out of the abdominal cavity through a subcutaneous tunnel, exiting through a skin incision on top of the back, were protected with plastic tape, folded, and fixed inside a small plastic container sutured to the skin. After 6 days of recovery, rats were fasted with free access to water for 24 h before the experiments were conducted.
Gastrointestinal Motility Recordings Before the measurements were taken, rats were fasted with free access to water for 24 h. On the experiment days, the strain gauge force transducer wires were connected to an amplifier. The amplified signals were fed into a computer through an analogue/digital converter and a multi-channel data acquisition recorder (Star Medical Co., Ltd., Tokyo, Japan).
Experimental Procedures The rats, each implanted with a strain gauge force transducer 6 days earlier, were randomly divided into four groups of five rats each. The SO group underwent laparotomy and mobilization of the liver without liver removal; the 90% PHx group, only 90% liver resection; the 90% PHx ⫹ saline group, 90% PHx ⫹ biliary cannula ⫹ saline perfusion; and the 90% PHx ⫹ bile group, 90% PHx ⫹ biliary cannula ⫹ bile perfusion. All surgical procedures were carried out under sterile conditions. The preoperative motility was recorded for 2 h. For measurements of postoperative motility change, the ileal motility in each group was recorded for 4 h immediately after surgery and for more than 3 h at 1 day and 3 days after surgery. Administration of 2.4 mL/kg of saline or bile through the biliary cannula took place immediately after and again 12 h after surgery. Recording with the administration of 2.4 mL/kg of saline or bile took place 1 day and 3 days after surgery in the 90% PHx ⫹ saline and 90% PHx ⫹ bile groups. The procedures for the administration of bile or saline were carried out under sterile conditions.
Analysis of Gastrointestinal Motility The recording of intestinal contractions was modified by computer software (Star Medical Co., Ltd.) to exclude artifacts such as respiration and body movements. From the modified integrated recordings, the MMC cycle length and the motility index (MI) were visually evaluated and determined. The MMC cycle length measurement was made from the abrupt end of one Phase 3 complex to the abrupt end of the next complex. The MI was defined as the area under the contraction cues in each 1 h recording after surgery and was expressed as the ratio to the MI in the preoperational motility. A 2 h recording was analyzed in two 1 h segments, and the average of the two segments was taken as the preoperative motility, which was set at 100%, with each animal serving as its own control. The time of the first passage of stool after surgery was also recorded.
Statistical Analysis All values are expressed as the mean ⫾ the standard error of the mean (SEM). Statistical significance was determined by the unpaired Student’s t-test. A probability level of P ⬍ 0.05 was used to define statistical significance.
90% Partial Hepatectomy (PHx) and Biliary Cannula The 90% PHx was performed using the technique described by Morioka et al. [9]. In brief, the liver was detached from the surrounding connective tissue under a large midline incision. We isolated the portal pedicle and then ligatured it using 6-0 silk. Before the hepatic lobe was resected, three transfixing sutures were made with 4-0 polypropylene to encircle and ligature separately the hepatic vein near its root and on both sides of the neighboring hepatic parenchyma. The biliary cannula, made of silicone tubing, was inserted after 90% PHx was performed. Briefly, one silicone cannula was inserted into the right bile duct. The cannula was exteriorized through a subcutaneous tunnel exiting at the top of the head through a skin incision and was fixed inside a small plastic container that had been sutured to the skin. This cannula allowed bile or saline to be infused concurrently without any additional surgery or anesthesia.
RESULTS
In this study, we conducted the investigations only at 1 day and 3 days after surgery. The 90% PHx rats treated with the methods, described by either Morioka et al. [9] or Higgins and Anderson [10] if they survived for 72 h after surgery, lived out their life span with normal liver function. In the present study, all rats that underwent 90% PHx or 90% PHx ⫹ biliary cannula were still alive 7 days after the hepatectomy. There were no significant differences in body weight among rats in the 90% PHx, 90% PHx ⫹ saline, and 90% PHx ⫹ bile groups during the experiments.
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TABLE 1 Effect of Bile Administration on MMC Cycle Length (min) After 90% PHx in Rats (n ⴝ 20, mean ⴞ SE) 90% PHx ⫹ Bile cannulae
FIG. 1. Typical pattern of MMC of the ileum of rats in the fasted, conscious state. (filled inverted triangle): Phase 3 of MMC. Ileum 1 and Ileum 2 (10 cm and 5 cm proximal to the ileocecum, respectively).
Normal Small Intestinal Motility
Under 24 h fasting conditions, the interdigestive ileal motility was characterized as a typical complex of MMC consisting of three phases: Phase 1, no detectable contractive activity; Phase 2, irregular contractive activity; and Phase 3, clearly distinguishable and intense contractive activity (Fig. 1). The average preoperative MMC cycle length in the ileum of the rats was 28.7 ⫾ 0.9 min. Effect of 90% PHx on Ileal Motility
There was a significant difference between the SO and 90% PHx groups in terms of the times of the first passage of stool after surgery (Fig. 2). In the latter groups, the MMC cycle length increased 1 day and 3 days after 90% PHx, which was significantly different from the cycle length of the SO group (Table 1, Fig. 3). The MMC after 90% PHx was characterized by an increased duration of Phase 2-like activity. The MI decreased 1 day and 3 days after 90% PHx, a result that was significantly different from that of the SO group (Fig. 4). The MMC cycle length and MI were not influenced by the insertion of the bile duct cannula.
FIG. 2. Time of the first passage of stool after surgery. There was a significant difference between the SO and 90% PHx groups. The time of the first passage of stool was earlier in the 90% PHx ⫹ bile group than in the 90% PHx ⫹ saline group. *P ⬍ 0.05 (n ⫽ 5 in each group, mean ⫾ SE).
Day
SO
90% PHx
Saline (0.6 mL/d)*
Bile (0.6 mL/d)*
Pre Day 1 Day 3
28.1 ⫾ 0.2 26.9 ⫾ 1.8 26.9 ⫾ 1.5
28.2 ⫾ 0.3 53.7 ⫾ 6.7** 42.8 ⫾ 2.3**
29.8 ⫾ 0.7 44.3 ⫾ 3.9 44.2 ⫾ 2.7
28.3 ⫾ 0.5 33.3 ⫾ 2.8†,‡ 32.2 ⫾ 2.1†,‡
Pre ⫽ preoperative day. * 1 h after bile or saline administration. ** P ⬍ 0.05 90% PHx versus SO. † P ⬍ 0.05 versus 90% PHx ⫹ saline. ‡ P ⬍ 0.05 versus 90% PHx.
Effect of Saline Administration on Ileal Motility Induced by 90% PHx
There was no significant difference between the 90% PHx ⫹ saline and 90% PHx groups in terms of the time of the first passage of stool after surgery (Fig. 2). With saline administration 1 h after recording on days 1 and 3 after surgery in the 90% PHx ⫹ saline group, there were no significant differences in MMC cycle length before and after saline administration in similar rats, although the MMC cycle length tended to decrease at 1 d after surgery (Fig. 5). The MMC cycle length and MI in the 90% PHx ⫹ saline group did not differ from those in the 90% PHx group, although the MMC cycle length tended to decrease at 1 day after surgery in the 90% PHx ⫹ saline group compared with the 90% PHx group, which may have been associated with systemic volume expansion and/or local stimulation of the gut by saline administration (Table 1, Fig. 4) [11].
FIG. 3. Typical pattern of MMC of the ileum at 1 and 3 days after 90% PHx in rats. The MMC cycle length at 1 day and 3 days after 90% PHx was significantly increased. (filled inverted triangle): Phase 3 of MMC. Ileum 1 and Ileum 2 (10 cm and 5 cm proximal to the ileocecum, respectively). POD ⫽ postoperative day.
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FIG. 4. Effect of administration of bile on MI 1 day and 3 days after 90% PHx in rats. There were significant differences between the MI of the 90% PHx ⫹ bile group and that of the 90% PHx ⫹ saline group. The MI at 1 day after surgery was higher than that at 3 days in the 90% PHx ⫹ bile group. †P ⬍ 0.05 (n ⫽ 5 in each group; mean ⫾ SE). *1 h after bile or saline administration. POD ⫽ postoperative day.
Effect of Bile Administration on Ileal Motility Induced by 90% PHx
Passage of stool occurred early after 90% PHx with bile administration, and there was a significant difference between the 90% PHx ⫹ saline group and the 90% PHx ⫹ bile group (Fig. 2). In the 90% PHx ⫹ bile group, with bile administration 1 h after recording at 1 day and 3 days, we observed a decreased MMC cycle length in similar rats (Fig. 6). There were significant differences in the MMC cycle length and MI in the 90% PHx ⫹ bile group compared with those in the 90% PHx ⫹ saline group. The MI at 1 day after surgery was higher than that at 3 days after surgery in the 90% PHx ⫹ bile group (Table 1, Fig. 4). DISCUSSION
In the present study, we investigated the ileal motility changes and the role of bile in gastrointestinal motility after 90% PHx in fasted, conscious rats. In our 90% PHx animal model, we used the technique described by Morioka et al. [9]. When we used this tech-
FIG. 5. Effects of saline administration (filled arrow) on ileum motility of rats 1 day and 3 days after 90% PHx. With saline administration 1 h after recording at 1 day and 3 days after 90% PHx, there were no significant differences in MMC cycle length before and after saline administration in similar rats, although the MMC cycle length tended to decrease at 1 day after surgery. (filled inverted triangle): Phase 3 of MMC. Ileum 1 and Ileum 2 (10 cm and 5 cm proximal to the ileocecum, respectively). POD ⫽ postoperative day.
FIG. 6. Effects of bile administration (black arrow) on ileum motility of rats 1 day and 3 days after 90% PHx. With bile administration 1 h after recording at 1 day and 3 days after 90% PHx, the MMC cycle length was decreased in similar rats. (filled Inverted triangle): Phase 3 of MMC. Ileum 1 and Ileum 2 (10 cm and 5 cm proximal to the ileocecum, respectively). POD ⫽ postoperative day.
nique to manipulate the area around the hepatic vein, all 90% PHx rats lived out their life span with normal liver function. The use of different methods, however, led to conflicting results [9, 12]. The model that we have developed seems suitable for studying the change in gastrointestinal motility after 90% PHx in conscious rats, and there are possible relationships among interdigestive small bowel motility, enterohepatic bile circulation, and liver regeneration. The surgical procedures were well tolerated by the animals implanted with the force transducer, and insertion of the bile cannula in the 90% PHx rats seemed to affect neither the MMC cycle length nor the MI. Wang et al. also studied gastrointestinal motility at 1 h and 2 h after 90% PHx using methods to record small intestinal transit [12]. In their study, the influence of ether anesthesia on small intestinal motility was disregarded. In addition, in the rats that had undergone 90% PHx by the technique previously described, the mortality rate was so high that it was difficult to determine the real influence of liver resection on gastrointestinal motility. The stenosis of the inferior vena cava leading to hepatic venous outflow insufficiency in the liver remnant, caused by the mass ligature used in the method of Higgins and Anderson, may have been associated with higher mortality after 90% PHx [10]. The ileal motility pattern in normal rats is characterized by cyclical Phase 3 contractions propagating aborally through the two recording segments and followed by a period of quiescence. The MMC cycle length was higher in the ileum than in the jejunum [13]. Compared with the SO rats, the 90% PHx rats showed a longer MMC cycle length, lower MI, and delayed passage of stool after surgery. The MMC after 90% PHx was characterized by an increased duration of Phase 2-like activity. Both quantitative and qualitative changes in contractions clearly induced changes in gastrointestinal transit [14]. These findings suggest
MA ET AL.: ROLE OF BILE IN INTESTINAL MOTILITY
that massive liver resection inhibited gastrointestinal transit, partly associated, perhaps, with an increased MMC cycle length and decreased MI in the ileum. However, from our data, it is impossible to determine the main cause of delayed gastrointestinal transit. The stomach, the small intestine, and the colon must be considered separately when gastrointestinal transit is investigated since the enteric nervous system and the extrinsic innervation of the different parts of the gastrointestinal tract display different neurochemical coding or receptors [15, 16]. Thus, further work is necessary to evaluate the influence of liver resection on stomach and colon motility and to identify the main cause of delayed gastrointestinal transit. The mechanisms by which partial hepatectomy resulted in altered ileal motility remain unclear. In general, it has been suggested that neural reflex, inflammatory changes, and hormonal changes are involved in mediating postoperative ileus [17]. After liver resection, however, decreased bile secretion into the gastrointestinal tract may be an important factor influencing ileum motility change. In previous studies, the presence of bile in portohepatic circulation or the processing of bile in the liver provided an important stimulus for the initiation of regular duodenal MMCs [6], and decreased bile secretion to the gastrointestinal tract inhibited small bowel motility, which was significantly correlated with an increased MMC cycle length [7]. Increased bile flow to the duodenum was correlated with small bowel motility [18]. In this study, we observed that the first passage of stool was earlier in the 90% PHx ⫹ bile group than in the 90% PHx and 90% PHx ⫹ saline groups. Furthermore, in the 90% PHx ⫹ bile group, with bile administered at 1 day and 3 days, we observed a decreased MMC cycle length and increased MI 1 h after the administration in similar rats. There was a significant improvement in the MMC cycle length and MI 1 h after bile administration. Based on these findings, we suggest that decreased bile flow into the gastrointestinal tract by liver resection is partly involved in ileal motility change by 90% PHx in conscious rats. The mechanism whereby decreased bile secretion contributes to ileum motility change could not be determined from our experiment. It is interesting to note that the MI at 1 day after surgery was higher than those at 3 days after surgery in 90% PHx ⫹ bile groups. Although the mechanism remains unclear, this result may be associated with decreased intestinal sensitivity to bile because of higher levels of glucagon, which is related to inhibited gastrointestinal motility [14] in blood at 3 days after 90% PHx than at 1 day after 90% PHx [19]. In addition to decreased bile flow into the duodenum, a possible factor is gastrointestinal motility change induced by liver resection. Although ileal motility change was induced by 95% liver resection in the rats, all of which survived at least 3 days after surgery, it
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was not completely improved by perfusion of bile through the biliary cannula (data not shown). After liver resection, portal pressure, inducing splanchnic venous congestion, rapidly increased [20], which may have influenced small intestinal motility. However, there was no relationship between portal pressures and changes in ileal motility after 70% partial hepatectomy (data not shown). It has been demonstrated that liver resection decreases the blood flow to the small intestine [21], and ischemia reperfusion induces intestinal motility change [22]. Bielefeldt and Conklin demonstrated that intestinal response decreased as a result of electrical field stimulation during ischemia and that there was a relationship between the duration of hypoxia and the change in intestinal motility [23]. The effect of hemodynamics on small intestinal motility change by massive liver resection requires further investigation. Liver failure after major partial hepatectomy remains a problem. Systemic endotoxemia, which is related to a high incidence of liver failure through increased apoptosis and a diminished liver regeneration pathway [3], occurs because of inadequate clearance of endogenous endotoxins [4] and inhibited gastrointestinal motility contributing to bacterial overgrowth and its products (endotoxins) [5]. There were positive relationships between MMC cycle length and bacterial overgrowth in the small intestine of rats with obstructive jaundice [24], and the absence of bile in the intestinal tract led to delayed liver regeneration in rats [25]. Bile is considered to be a protective factor in intestinal barrier function [26]. It has been reported that bile administration to the intestine decreased intestine MMC cycle length [7, 18] and inhibited bacterial overgrowth [26]. Unfortunately, the physiological control mechanisms of gastrointestinal motility changes after massive liver resection in rats or humans are incompletely understood. In our study, we first demonstrated an improved effect of bile on gastrointestinal motility change after 90% PHx in rats. This finding may provide a basis for investigating how to reduce complications after massive liver resection. In conclusion, we have confirmed that the MMC cycle length and MI in the ileum were inhibited after 90% PHx, which may have been associated with delayed intestinal transit time; furthermore, there was some involvement of decreased bile flow into the gastrointestinal tract.
ACKNOWLEDGMENTS
The authors thank Dr. Y. Kamiyama, Dr. S. Hashimoto, and Dr. K. Okada for technical assistance. This study was supported in part by a Grant-in-Aid for scientific research and the 21st century COE program from the Ministry of Education, Culture, Sports, Science, and Technology.
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REFERENCES 1.
Waldhausen JH, Shaffrey ME, Skenderis BS, et al. Gastrointestinal myoelectric and clinical patterns of recovery after laparotomy. Ann Surg 1990;211:777.
2.
Kalff JC, Schraut WH, Simmons RL, et al. Surgical manipulation of the gut elicits an intestinal muscularis inflammatory response resulting in postsurgical ileus. Ann Surg 1998;228: 652.
3.
Morita T, Togo S, Kubota T, et al. Mechanism of postoperative liver failure after excessive hepatectomy investigated using a cDNA microarray. J Hepatobiliary Pancreat Surg 2002;9:352.
4.
Boermeester MA, Straatsburg IH, Houdijk AP, et al. Endotoxin and interleukin-1 related hepatic inflammatory response promotes liver failure after partial hepatectomy. Hepatology 1995; 22:1499.
5.
Zhang SC, Wang W, Ren WY, et al. Effect of cisapride on intestinal bacterial and endotoxin translocation in cirrhosis. World J Gastroenterol 2003;9:534.
13.
Sagrada A, Fargeas MJ, Bueno L. Involvement of ␣-1 and -2 adrenoceptors in the postlaparotomy intestinal motor disturbances in the rat. Gut 1987;28:955.
14.
Scott LD, Summers RW. Correlation of contractions and transit in rat small intestine. Am J Physiol 1976;230:132.
15.
Furness JB, Bornstein JC, Murphy R, et al. Roles of peptides in transmission in the enteric nervous system. Trends Neurosci 1992;15:66.
16.
Burks TF. Neurotransmission and neurotransmitters. In Johnson LR, Ed. Physiology of the gastrointestinal tract, 3rd ed. New York: Raven Press, 1994:211–242.
17.
Andrew Luckey, Edward Livingston, Yvette Tache. Mechanisms and Treatment of Postoperative Ileus. Arch Surg 2003; 138:201.
18.
Fang P, Dong L, Zhang WJ, et al. Relationship between enterohepatic bile acid circulation and interdigestive migrating myoelectrical activity in rats. World J Gastroenterol 2005;11:5377.
19.
Gaub J, Iversen J. Rat liver regeneration after 90% partial hepatectomy. Hepatology 1984;4:902.
6.
Ozeki K, Sarna SK, Condon RE. Bile acts at a porto-hepatic circulation site to initiate duodenal MMCs. Gastroenterology 1991;100:A479. [Abstract].
20.
Lee SS, Hadengue A, Girod C, et al. Reduction of intrahepatic vascular space in the pathogenesis of portal hypertension. In vitro and in vivo studies in the rat. Gastroenterology 1987;93:157.
7.
Nieuwenhuijs VB, Luiking YC, Verheem A, et al. Disrupted bile flow affects interdigestive small bowel motility in rats. Surgery 1997;122:600.
21.
8.
Xu HS, Rosenlof LK, Jones RS. Bile secretion and liver regeneration in partially hepatectomized rats. Ann Surg 1993;218: 176.
Boermeester MA, Houdijk AP, Straatsburg IH, et al. Organ blood flow after partial hepatectomy in rats: Modification by endotoxin-neutralizing bactericidal/permeability-increasing protein (rBPI23). J Hepatol 1999;31:905.
22.
9.
Morioka D, Watanabe K, Makino H, et al. Safety limit of the extent of hepatectomy for rats with moderately fatty liver: Experimental study concerning living liver donor safety. J Gastroenterol Hepatol 2006;21:367.
Takahashi A, Tomomasa T, Kaneko H, et al. Intestinal motility in an in vivo rat model of intestinal ischemia-reperfusion with special reference to the effects of nitric oxide on the motility changes. J Pediatr Gastroenterol Nutr 2001;33:283.
23.
Bielefeldt K, Conklin JL. Intestinal motility during hypoxia and reoxygenation in vitro. Dig Dis Sci 1997;42:878.
24.
Nieuwenhuijs VB, van Dijk JE, Gooszen HG, et al. Obstructive jaundice, bacterial translocation, and interdigestive smallbowel motility in rats. Digestion 2000;62:255.
25.
Junji Ueda, Kazuo Chijiiwa, Kenji Nakano, et al. Lack of intestinal bile results in delayed liver regeneration of normal rat liver after hepatectomy accompanied by impaired cyclin E-associated kinase activity. Surgery 2002;131:564.
26.
Ogata Y, Nishi M, Nakayama H, et al. Role of bile in intestinal barrier function and its inhibitory effect on bacterial translocation in obstructive jaundice in rats. J Surg Res 2003;115:18.
10.
Higgins GM, Anderson RM. Experimental pathology of the liver. Arch Pathol 1931;12:186.
11.
Grossie VB Jr., Weisbrodt NW, Moore FA, et al. Ischemia/ reperfusion-induced disruption of rat small intestine transit is reversed by total enteral nutrition. Nutrition 2001;17:938.
12.
Wang XD, Guo WD, Wang Q, et al.The association between enteric bacterial overgrowth and gastrointestinal motility after subtotal liver resection or portal vein obstruction in rats. Eur J Surg 1994;160:153.