Masahito Yamazato

The isolated bowel segment (Iowa model II) created in functioning bowel

In experimental rats (n = 15), an isolated bowel segment (IBS) was created by (1) initial enteropexy between an 8-cm-long jejunal segment and the liver margin (hepatoenteropexy; Iowa model II) with its proximal and distal ends divided and immediately reanastomosed in an end-to-end fashion to reconstruct the bowel; and (2) secondary division of the IBS mesentery 5 weeks later. The IBS is then completely free of its mesentric and intramural nervous and vascular communications. The viability of the IBS is preserved by vascular collaterals developed at the hepatoenteropexy. Twelve rats proceeded to the second procedure, having tolerated regular rat chow with satisfactory weight gain. The Iowa model II created in functioning bowel was evaluated by contrast studies and myoelectrical activities. Contrast studies demonstrated peristalsis in the IBS. In the myoelectrical recordings, the frequency of slow wave was 32.5 +/- 1.0 in the IBS and 36.3 +/- 0.8 in the normal bowel (P less than .05). During fasting, the migrating motor complex (MMC) was observed to propagate aborally in the IBS in a coordinated fashion. The cyclic period of the MMC was 17.2 +/- 1.1 minutes in the IBS and 15.8 +/- 0.8 minutes in the normal bowel (P = .30). We conclude from this study that (1) the IBS (Iowa model II) retains motor function as demonstrated by successful feeding, as well as contrast studies and myoelectrical recordings that were essentially identical to those in the normal bowel; and (2) the IBS (Iowa model II) has significant research potential for studies of bowel physiology.

The isolated bowel segment (Iowa Model II): Absorption studies for glucose and leucine☆

A model of the isolated bowel segment (IBS, Iowa Model II) was successfully created in experimental animals using a new surgical technique we developed. The IBS is completely free of its mesenteric attachment, yet its viability is preserved. The technique consists of two staged procedures: (1) initial enteropexy between the anterior margin of the liver and the antimesenteric border of the IBS with its ends forming cutaneous stomas; and (2) division of the IBS mesentery 5 weeks later. The IBS is nourished by vascular collaterals that form at the hepatoenteropexy during the interval between these two procedures. Our previous studies demonstrated preserved viability and motility in the IBS. This study was undertaken to test absorption in the IBS. In 25 rats (experimental group), the IBS (Iowa Model II) was created using an 8-cm-long isolated segment of jejunum. In 15 rats (control group), an 8-cm-long segment of jejunum was arranged to form a Thiry-Vella loop. Five weeks later, the IBS mesentery was divided in the experimental group, and sham laparotomy was performed in the control group animals. Absorption of glucose and leucine was studied in 13 rats of the experimental group and 6 of the control group using a constant single perfusion technique at 3, 8, and 11 weeks after the initial operation. The results were compared between the two groups. There was a 25% to 35% reduction in absorption of glucose and leucine in both groups with the advance of time, but no significant difference was observed between the groups except in leucine absorption at 11 weeks after the initial operation. This study concludes that absorption of glucose and leucine is preserved in the IBS after its mesentery is divided, suggesting that the IBS can be used as a functioning bowel for bowel reconstruction.

Congenital true diverticula of the esophagus: A case report

Pseudodiverticulosis secondary to gastroesophageal reflux is a common disease in adults, but true esophageal diverticula are rare in infants and children. A 5-year-old boy was well until the age of 1 1/2 years when he started vomiting. An upper gastrointestinal series showed two diverticula bulging from the posterior right side of the middle esophagus associated with slight hiatal hernia and short esophagus. Diverticulectomy, the Collis-Nissen antireflux procedure, and pyloroplasty were performed simultaneously through a left thoracoabdominal incision. Histological examination of the diverticula showed that the wall of each diverticulum consisted of a full-thickness of esophageal wall. Because there was no tracheal remnant in the diverticula, this lesion is more likely to be a true diverticulum than a duplication.

Mucosal morphology in isolated bowel segments: importance of exposure to luminal contents

An isolated bowel segment (IBS) is a loop of intestine that has been freed from its mesenteric attachment after the development of vascular collaterals between the antimesenteric surface of the gut and the host organ. Surgical creation of such artificially vascularized isolated bowel segments is of interest to researchers for a variety of studies, and may be useful in the treatment of short bowel syndrome, allowing longitudinal division of the remaining small bowel to double its length. We created four surgical variants to study the ability of the collateral blood supply to maintain mucosal integrity in the presence or absence of normal luminal contents. In all groups, a collateral blood supply was created in a 5- to 7-cm segment of adult rat jejunum by hepatoenteropexy (Iowa model II). In Thiry-Vella (T-V) and isolated bowel segment (IBS) rats, this segment was exteriorized at both ends to exclude luminal contents. Control and IBS in continuity (IBS-C) loops were left in continuity. The mesentery of IBS and IBS-C rats was divided 5 weeks later, leaving the experimental segment entirely dependent on the collateral circulation. All animals were harvested at 7 weeks after the initial surgery. Tissues were analyzed for mucosal weight, protein content per centimeter of bowel, length of villi, depth of crypts, DNA content, and sucrase activity. We found that segments retaining luminal continuity had significantly higher mucosal weight and DNA content per centimeter of bowel compared with exteriorized loops.

Motility of isolated bowel segment Iowa model III.

The isolated bowel segment (IBS) is an amesenteric segment of bowel that is devoid of extrinsic nerves and yet is viable with motility and absorption preserved after its mesentery is completely severed. The IBS is created by initial coaptation of a loop of bowel to a host organ, such as muscle (Iowa model I), liver (Iowa model II), or intestine, and secondary severance of its mesentery several weeks later. In previous studies using Iowa models I and II, the viability, motility, and absorption of the IBS were preserved by vascular collaterals, which form across the coaptation. In rats, an IBS was created in the jejunum by initial enteroenteropexy (Iowa model III), followed by its mesenteric division five weeks later. At the second laparotomy, bipolar electrodes were implanted in the IBS and the adjacent jejunum. One week later, myoelectrical recording was performed during a fasting state. Coordinated aborad propagation of migrating motor complex (MMC) was observed in the IBS. The MMC period was 16.9 ± 1.7 and 19.3 ± 0.8 min in the intact bowel, and 22.8 ± 0.8 min in the IBS (P=0.1). After feeding, the MMC in the IBS was replaced by irregular spike burst activity similar to that observed in the intact bowel. This study concludes that the IBS Iowa model III can be used for studies of bowel physiology.

The isolated bowel segment (Iowa model II); Motility across the anastomosis with or without mesenteric division

In previous reports, anastomosis has been shown to disrupt the myoelectric activity of the bowel. However, these studies have failed to delineate the role of the extrinsic nerves. Using an isolated bowel segment (IBS) and an amesenteric bowel segment (ABS), motility was evaluated by myoelectric recording across a bowel anastomosis. Ten rats were divided equally into the experimental group with the IBS and the control group with the ABS. In the IBS group, an 8-cm segment of jejunum was divided, reanastomosed, and coapted to the liver margin (Iowa model II). In the ABS group, an 8-cm segment of jejunum was coapted to the liver margin without disruption of bowel continuity (Iowa model II variant). Two weeks later, bipolar electrodes were implanted in the IBS and ABS, and normal jejunum in both groups. Mesenteric division (MD) was performed 4 weeks later to eliminate extrinsic innervation. Myoelectrical recordings were taken 2 weeks before and after MD. In the control group with IBS, incoordination in the propagation of the migrating motor complex (MMC) and reduction in the frequency of slow waves (FSW) were observed across the anastomosis and were unchanged by MD. In the control group with the ABS, the MMC and FSW were identical to that in the normal jejunum and were unaffected by MD. In both groups postprandial inhibition of the MMC was the same as in the normal jejunum and was unaffected by MD. This study confirms that incoordination in propagation of the MMC and reduction in FSW occur across a bowel anastomosis, and elimination of extrinsic innervation does not affect the autonomy of these changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption in the isolated bowel segment

An isolated bowel segment (IBS) is a viable amesenteric segment of intestine. This study was undertaken to investigate the effects of mesenteric vascular and neural supply on intestinal absorption. Ten rats were used for leucine absorption and another 10 for glucose absorption experiments. L-leucine, 12 ml of 15.0 mM/L, or 3.0 mM/L of D-glucose solution were recirculated through the IBS (n = 5) and rat jejunum that underwent sham operation (n = 5) at 2.56 ml/min for 90 min. Absorption was expressed as millimoles of leucine or glucose per gram of mucosal protein. The Students t test was used for statistical analysis; a p ≤ 0.05 was considered significant. The net absorption of L-leucine was 36.20 ± 3.31 mM/g of mucosal protein in the IBS and 15.52 ± 1.48 mM/g of mucosal protein in the control group (p < 0.001). The net absorption of D-glucose was 3.82 ± 0.26 mM/g of mucosal protein in the experimental group and 4.34 ± 0.31 mM/g of mucosal protein in the control group (p = 0.02). This study concludes that absorption of leucine and glucose in the IBS is preserved after mesenteric division.

Bipolar Electrode Implantation for Myoelectrical Recordings of Rat Bowel

This report describes a technique to implant bipolar electrodes into the rat bowel. We implanted a total of 129 pairs of bipolar electrodes into the bowel of rats. 124 pairs of electrodes (96.3%) have continuously functioned allowing repeated myoelectrical readings. Of these, 69 electrodes functioned over 8 weeks. Only 5 electrodes (3.7%) failed. The advantage of our technique includes: (1) high success rate in implantation, (2) long term durability, and (3) less technical difficulty.