Expression of EphB2 in the development of anorectal malformations in fetal rats

Purpose

The receptor tyrosine kinase of the Eph family is a large group of highly conserved molecules that function in diverse intercellular recognition events. It has been reported that EphB2 is related to caudal remodeling events. The aim of this study is to investigate EphB2 expression in anorectal development in normal and rat embryos with anorectal malformations (ARMs) and attempt to define its role in anorectal morphogenesis.

Methods

The ethylenethiourea (ETU) rat model of the ARMs was used in this study. Immunohistochemical analyses and real time quantitative polymerase chain reaction (PCR) were carried out to investigate EphB2 protein localizations and messenger RNA (mRNA) expression levels. (1) Rat embryos with ARMs were obtained by treating pregnant rats (n = 24) with administration of ETU on gestation day (Gd) 10. Normal rat embryos (n = 111) and embryos treated by ETU without ARMs (n = 90) were the control groups, and embryos with ARMs (n = 108) from Gd13 to Gd16 were divided according to the sections taken from specimens. (2) Embryos were sequentially sectioned in the sagittal and transversal planes before staining with a specific antibody to EphB2. Spatiotemporal study was carried out on EphB2 expression. (3) Individual frozen sections were used to manually microdissect the cloaca and anorectal specimens for total RNA extraction. EphB2 expression was evaluated by real time quantitative PCR.

Results

On the immunologic labeling study, EphB2 expression was confined to the cloaca in control groups, whereas EphB2 expression was mainly located at the urorectal septum (URS) and cloacal membrane on Gd13 and Gd14. The increased positive expression was observed in the fused tissue of the URS and cloacal membrane on Gd15. On Gd16, the anal membrane broke down, and the rectum was able to be in contact with the anus, and EphB2 expression was then noted in mucous membrane of rectum. EphB2 expression was seen in the cloacal and anorectal tissues of embryos with ARMs. By integrated optical density (IOD) measurement, IOD value of EphB2 protein was significantly lower in the ARM group than that in the control groups on Gd13 to Gd16 (P < .05), respectively. As shown by real time quantitative PCR, EphB2 expression was detected in 3 groups. EphB2 mRNA level increased on Gd13 to Gd16 but gradually decreased after Gd16. The expression level of EphB2 mRNA in the ARM embryos was lower on Gd13 to Gd16 than that in control groups (P < .05).

Conclusions

EphB2 expression decreased in the ARM embryos and was confined to URS and cloaca, whereas it was higher in control group. Our data thus indicated that EphB2 molecules possibly contributed to the anorectal morphogenesis and the decreased expression of EphB2 might be related to the development of ARMs.     

Clarification of the processes that lead to anorectal malformations in the ETU-induced rat model of imperforate anus

Background: Ethylenethiourea (ETU) administered to timed-pregnant rats can induce anorectal malformations (ARMs) in about 80% of rat fetuses, thus providing an ideal animal model to study the embryogenesis of ARMs. The current study was undertaken to investigate the embryogenetic events that may be responsible for the development of ARMs in rats. Methods: Time-mated pregnant rats were divided randomly into control and experimental groups. The experimental rats received 1% ETU (125 mg/kg) by gavage on gestational day 10, and control rats received only the vehicle. Their embryos were harvested by cesarean section on gestational days 13, 14, 15, and 16. They were fixed and embedded in paraffin and serially sectioned in either the sagittal or transverse plane. The sections were stained with H[amp ]E, examined, and photographed. The comparative morphogenesis of the hindgut, cloaca, and tailgut of age-matched embryos was studied. Results: The key abnormalities in the experimental embryos were: (1) maldevelopment of cloaca and urorectal septum with no sign of the fusion between the urorectal septum and the cloacal membrane, (2) delay of tailgut regression, (3) abnormal and massive apoptotic cell death involving the posterior cloacal wall, and (4) underdevelopment of the dorsal aspect of the cloaca and its membrane. The type of ARM that was developing was discernible by gestational day 15 and 16. Conclusions: ARMs induced by ETU in rat embryos seem to be caused by the cumulative effect of aberrations in the development of several components of the hindgut and cloaca. Variation in the extent of maldevelopment of these structures may result in a spectrum of ARMs. J Pediatr Surg 37:1305-1312.     

Clarification of the process of separation of the cloaca into rectum and urogenital sinus in the rat embryo

BACKGROUND/PURPOSE: The normal process of division of the cloaca into a rectum and urogenital tract is still not fully understood. The main controversies relate to how the urorectal septum (URS) divides the cloaca and whether the URS fuses with the cloacal membrane. This study used a 3-dimensional reconstruction technique, combined with histologic correlation, to observe the developmental and septational processes of the cloaca of the normal rat embryo from gestational days 11 to 16. METHODS: Normal rat embryos from gestational days 11 to 16 were sectioned serially both transversely and sagittally and stained with H&E. 3-dimensional reconstructions were performed on embryos younger than day 13.5. The relevant structures were examined in a temporo-spatial sequence. RESULTS: The tailgut started to regress by apoptosis on day 12 in a cranio-caudal direction. The URS, first evident in day-12.5 embryos, extended and fused with the cloacal membrane on day 15 of gestation, completing the separation of the cloaca into rectum and bladder. Regression of the tailgut and ventral protrusion of the urogenital sinus markedly changed the configuration of the cloaca. The cloacal membrane did not break down until after it had fused with the URS. CONCLUSIONS: These findings clarify the relative contributions made by active septation of the cloaca by the URS and configurational changes of the cloaca to produce a rectum and bladder. The URS fuses with the cloacal membrane before the anal and urogenital membranes break down.     

Septation and differentiation of the embryonic human cloaca.

BACKGROUND/PURPOSE: Limitations in methodologies have fostered controversy regarding the septation of the human embryonic cloaca. The aim of this study was to evaluate the septation of the human embryonic cloaca. METHODS: Using the Carnegie Embryological Collection and specimens at Johns Hopkins, Baltimore, MD, the authors studied 12 embryos and five fetuses. Embryo photomicrographs were reconstructed using three-dimensional modeling. RESULTS: In Carnegie stage 13 the authors observed a cloaca, distinct primitive urogenital sinus, and anorectum separated by the urorectal septum. The primitive urogenital sinus and anorectum enter the cloaca separated from the amniotic space by the cloacal membrane. As the embryo becomes a fetus it lengthens, grows, expands and rotates through a process called transformation. Transformation gives rise to a loss of caudal curvature and a decrease in distance between the septum and membrane, but these structures do not fuse. Disintegration of the cloacal membrane produces openings for the urogenital sinus and anorectum. CONCLUSIONS: The observations suggest that the urogenital sinus and anorectum form early and are separated by the urorectal septum as a passive structure. There does not appear to be septation or differentiation of the cloaca itself.     

Prophylactic glycopyrrolate prevents bradycardia after spinal anesthesia for Cesarean section: a randomized, double-blinded, placebo-controlled prospective trial with heart rate variability correlation

Study Objective

To determine if prophylactic glycopyrrolate prevents bradycardia after spinal anesthesia.

Design

Prospective, randomized, double-blinded, placebo-controlled study.

Setting

Large university-affiliated community hospital.

Patients

81 consecutive term parturients (not in active labor) who were scheduled for elective Cesarean section.

Interventions

Parturients received 1.0 to 1.5 L of intravenous Ringer's lactate and either glycopyrrolate 0.4 mg or an equal volume of saline, with caregivers blinded to the immediate sequelae of study drug. Each patient received intrathecal bupivacaine (12 to 14 mg) with morphine sulfate (0.1 to 0.2 mg).

Measurements

Continuous heart rate (HR) and blood pressure monitoring occurred for 20 minutes, with the minimum HR recorded for each 5-minute epoch. Heart rates < 60 beats per minute defined bradycardia. Heart rate variability (HRV) analysis occurred offline.

Main Results

None of 34 patients administered glycopyrrolate and 6 of 35 (17%) patients receiving saline experienced bradycardia (P = 0.02476). Time domain, frequency domain, and nonlinear and embedded spectrum entropy analyses all reflected the decrease in HRV accompanying administration of glycopyrrolate.

Conclusion

Bradycardia after spinal anesthesia occurs commonly. Prophylactic glycopyrrolate may prevent the bradycardia, but not necessarily the hypotension.     

Sonic hedgehog and bone morphogenetic protein 4 expressions in the hindgut region of murine embryo with anorectal malformations

Purpose

The aim of this study was to determine the possible role of the retinoid-mediated signaling pathway in the pathogenesis of anorectal malformations (ARM). The authors investigated whether all-trans retinoic acid (ATRA) affects the expression pattern of Sonic hedgehog (Shh) and Bone morphogenetic protein 4 (BMP4), which play important roles in anorectal morphogenesis in vertebrates.

Methods

Pregnant ICR strain mice were fed 100 mg/kg of ATRA on the ninth gestational day (E9). Embryos with or without administration of ATRA were obtained from the uteri between E12 and E16 and were fixed immediately in a 4% paraformaldehyde solution. Frozen sections were evaluated for concentric layers around the endodermal epithelium by H&E and immunohistochemistry using antibodies created specifically to act against Shh and BMP4.

Results

More than 95% of the embryos administered ATRA had ARM; rectoprostatic urethral fistula, rectocloacal fistula, and short tail were the most frequent anomalies in the mouse embryos. On E14, normal mouse embryos had normal rectum and anus in which the epithelium of the anorectum was positive for Shh, and the mesenchyme was positive for BMP4. In the ARM embryos, however, the epithelium of the anorectum was negative for Shh, and the mesenchyme was also negative for BMP4.

Conclusions

In normal hindgut development, Shh from the epithelium induces BMP4 expression in the mesenchyme, which differentiates into the lamina propria and the submucosa. In ARM embryos, expressions of Shh and BMP4 could not be found in those regions of the hindgut. Therefore, these findings indicate that Shh and BMP4, which appear to play a crucial role in organogenesis of the hindgut, were disturbed in the cell signaling pathway between the epithelium and the mesenchyme layers.     

The effect of vitamin A deficiency during pregnancy on anorectal malformations

Objective

The aim of this study was to study the effect of vitamin A deficiency (VAD) on the embryological development of anorectal malformations (ARMs) and the enteric nervous system.

Materials and Methods

Female Sprague-Dawley rats were divided into 3 groups: VAD group, normal group (negative control), and ethylene thiourea (ETU) group (positive control) with a normal diet. On day 20 of pregnancy, cesarean section was performed on all rats. The incidence of ARMs in the fetal rats and Protein gene product 9.5 (PGP9.5) and S-100 protein expression by immunohistochemistry were determined.

Results

The incidence of ARMs in VAD and ETU groups was 64.8% (59/91) and 45.9% (61/133), respectively (P > .05). Anorectal malformations were not found in the normal group. Protein gene product 9.5 and S-100 protein expression in the non-ARM rectums of the VAD group was lower than the ETU (P = .0156 vs P = .0105) and normal groups (P = .0091 vs P = .0024). There was no significant difference in PGP9.5 and S-100 protein expression between ETU and normal groups. In the ARM rectums, PGP9.5 and S-100 protein expression in the VAD group was lower than the ETU group (P < .0001). Protein gene product 9.5 and S-100 protein expression was also lower in ARM than non-ARM rectums in the VAD and ETU groups (P < .0001, P = .0203, and P = .0122, respectively).

Conclusion

Vitamin A deficiency during pregnancy may result in the embryological development of ARMs. Enteric nervous system development may be related to ARMs.     

Colonic motility and functional assessment of the patients with anorectal malformations according to Krickenbeck consensus

Background/Purpose

In this study, the patients operated on for anorectal malformations (ARM) were evaluated in terms of segmental (SCTT) and total colonic transit times (TCTT) and clinical status according to Krickenbeck consensus before and after treatments.

Methods

Forty-one patients with ARM (28 males/13 females) older than 3 years (median age, 7.7 years; range, 3-25) who had no therapy before were assessed for voluntary bowel movements (VBM), soiling (from 1 to 3), and constipation (from 1 to 3), retrospectively. Distribution of the patients were rectourethral fistula (17), perineal fistula (PF; 8), vestibular fistula (VF; 8), cloaca (3), rectovesical fistula (1), rectovaginal fistula (1), pouch colon with colovestibular fistula (1), no fistula (1), and unknown (1). The patients ingested daily 20 radiopaque markers for 3 days, followed by a single abdominal x-ray on days 4 and 7 if needed. The results were compared with the reference values in the literature.

Results

Mean follow-up period was 36 months (range, 1-108.5 months). All patients but 1 had soiling in different degrees. Twenty-one patients who had VBM were divided into group 1, with constipation (n = 9), and group 2, without constipation (n = 12). The other 19 patients who had no VBM were divided into group 3, with constipation (n = 14), and group 4, without constipation (n = 5). The longest TCTT and rectosigmoid SCTT were found in group 3 (69.5 and 35.2 hours, respectively). Group 1 had long SCTT in rectosigmoid but normal TCTT (27.8 and 47.4 hours, respectively). Groups 2 and 4 had normal SCTT and TCTT, and there was no significant difference between them. After the appropriate treatment, of the patients, 45% (18/40) had no soiling, and the soiling score decreased to grade 1 in 27.5% (11/40) and to grade 2 in 10% (4/40). Four had unchanged soiling score, and 3 were excluded from the study because of follow-up problems. Half of the patients in group 3 (4 VF, 2 rectourethral fistula, PF) gained VBM without soiling after laxative treatment. Only four of 23 patients had decreased constipation score (2 cloaca, PF, VF).

Conclusions

In this study, ARM patients complaining of constipation with or without VBM had prolonged SCTT in the rectosigmoid region. Percentage of the improvement in soiling scores was more conspicuous than that of constipation scores. The dismal figure observed at the first examination in the assessment of VBM was not associated with an unfavorable improvement with laxative treatment. So, it is suggested that assessment of VBM initially may be deceptive for clinical status.     

Bone health in patients with cloacal exstrophy and persistent cloaca after bladder augmentation

Purpose

In this study, the prevalence of osteoporosis was evaluated in patients operated on for cloacal exstrophy or persistent cloaca and who had undergone bladder augmentation.

Methods

Seven patients operated on because of cloacal exstrophy and 3 patients operated on because of persistent cloaca were evaluated. Patients were clinically assessed. Areal bone mineral density for the lumbar spine (L1-L4), femoral neck, and whole body was measured with dual-energy x-ray absorptiometry. Acid-base balance, plasma 25-hydroxyvitamin D (vitamin D), and gonadal function were determined and correlated with dual-energy x-ray absorptiometry results.

Results

The patients were small in height (median, −2.2 SD). According to areal bone mineral density measurements, 40% of the patients had significantly reduced BMD. When the values were adjusted for patient size, only 1 patient had slightly reduced bone mass. Half of the patients had low vitamin D values. The height-corrected bone mineral content values showed a positive correlation with vitamin D values (P = .0072) but were not different in patients with and without hypogonadism (P = .33).

Conclusions

Patients with cloacal exstrophy or complicated cloaca have many risk factors for osteoporosis. However, this study showed good overall bone health in affected adolescents.     

Penislike clitorises with megalourethras in nonvirilized female fetuses and a newborn. A histopathologic study and its bearing on their pathogenesis

Purpose

The aim of the study was to analyze the microstructure of penislike clitorises in female pseudohermaphroditism in relation to their pathogenesis.

Methods

Penislike clitorises from 2 fetuses and 1 newborn with anorectal malformations and multiple other caudal anomalies and 1 fetus with phallic urethra duplication were histologically examined in toto.

Results

The penislike clitorises revealed basically female features in the histogenesis of the corpora cavernosa and glans and in the absence of penile raphe, septum, fasciae, and periurethral glands. In 2 cases, the “phallic urethra” was completely surrounded by a single corpus cavernosum and in 3 cases by a circular glans. Labia minora and vestibular bulbs had not developed in 3 cases. The urethras had transformed into fusiform or scaphoid megalourethras with stenotic meatuses in 3 specimens and an extra orifice in the fourth specimen.

Conclusions

Penislike clitorises in female pseudohermaphroditism show a fundamental dysgenesis of major structural elements. The pattern favors the hypothesis of an early error in the formation of the cloacal membrane and adjacent cloaca in embryos between 26 and 29 days postovulation that may lead to dysregulation of molecular developmental interactions during the following formation of the genital tubercle.     

Establishment of a rescue program for anorectal malformations induced by retinoic acid in mice

Aims of Study

Retinoid-mediated signal transduction plays a crucial role in the embryogenesis of various organs. We previously reported the successful induction of anorectal malformations in mice using retinoic acid (RA). Retinoic acid controls the expression of essential target genes for cell differentiation, morphogenesis, and apoptosis through a complicated interaction in which RA receptors form heterodimers with retinoid X receptors. In the present study, we investigated whether the retinoid antagonist, LE135, could prevent the induction of anorectal malformations (ARMs) in mice.

Methods

Retinoic acid was intraperitoneally administered as 100 mg/kg of all-trans RA on E9; and then the retinoid antagonist, LE135, was intraperitoneally administered to pregnant ICR strain mice on the eighth gestational day (E8), 1 day before administration of RA (group B) or on E9, simultaneously (group C) with RA administration. All of the embryos were obtained from the uteri on E18. Frozen sections were evaluated for concentric layers around the endodermal epithelium by hematoxylin and eosin staining.

Results

In group A, all of the embryos demonstrated ARM with rectoprostatic urethral fistula, or rectocloacal fistula, and all of the embryos showed the absence of a tail. In group B, 36% of the embryos could be rescued from ARM. However, all of the rescued embryos had a short tail that was shorter than their hind limb. The ARM rescue rates in group B were significantly improved compared to those in group A (P < .01). In group C, 45% of the embryos were rescued from ARM, but all of the rescued embryos had short tail. The ARM rescue rate in group C was significantly improved compared to that in group A (P < .01). However, there was no significant difference in the ARM rescue rate between group B and Group C.

Conclusion

The present study provides evidence that in the hindgut region, RAR selective retinoid antagonist, LE135, could rescue embryos from ARM. However, the disturbance of all-trans RA acid was limited to the caudal region. Further study to establish an appropriate rescue program for ARM in a mouse model might suggest a step toward protection against human ARM in the future.     

Factors influencing early failure of central venous catheters in children with cancer

Background

The authors report the results of a prospective, multicenter, multidisciplinary study of central venous catheters (CVCs) in pediatric oncology patients analyzing factors involved in early failure.

Methods

Information was collected from parent-held records on the fate of 824 devices inserted over a 20-month period, 415 of which were no longer in situ.

Results

Within the first 7 weeks after insertion, there were 66 failures, all occurring in external lines. Accidental dislodgement was the principal reason for CVC failure (44 of 66, 67%). Detailed analysis of the reason for failure of this large subgroup showed 11 factors individually associated with early dislodgement, of which, 4 were independently associated with failure by multivariate analysis. These 4 variables were the use of multilumen catheters, the absence of a skin exit site suture, platelet transfusion at the time of insertion, and patient age less than 2 years.

Conclusions

This study confirms the multiple influences on successful CVC usage. Our analysis supports the principle of only using multilumen lines when clinically essential. The findings also support the inception of randomized studies of fixation, particularly in infants.     

Modified Spectrometry (O2C Device) of Intraoperative Microperfusion Predicts Organ Function After Kidney Transplantation: A Pilot Study

Background

Delayed graft function (DGF) is defined as posttransplantation dialysis within 1 week, which might be associated with impaired long-term graft survival. The aim of our pilot study was to establish the ability of intraoperative spectrometry of allograft microperfusion to predict DGF.

Methods

Twenty human kidney allografts transplanted from deceased donors were evaluated intraoperatively after reperfusion using modified organ spectrometry (O2C device). We examined hemoglobin oxygen saturation, intravascular amount of hemoglobin, and microperfusion flow/velocity.

Results

Retrospectively, 10/20 (50%) allografts with measurable impairment of cortical hemoglobin oxygen saturation and microperfusion flow/velocity developed DGF. Retrospectively, we found that if the intravascular amount of hemoglobin was increased upon intraoperative measurement, the kidney was prone to develop DGF.

Conclusions

Spectrometry data predicted DGF. Our results supported the thesis that impaired microperfusion is the key to DGF and might be related to postcapillary endothelial damage or intravascular sludge.     

Preliminary report on the International Conference for the Development of Standards for the Treatment of Anorectal Malformations

Background

Anorectal malformations (ARM) are common congenital anomalies seen throughout the world. Comparison of outcome data has been hindered because of confusion related to classification and asssessment systems.

Methods

The goals of the Krinkenbeck Conference on ARM was to develop standards for an International Classification of ARM based on a modification of fistula type and adding rare and regional variants, and design a system for comparable follow up studies.

Results

Lesions were classified into major clinical groups based on the fistula location (perineal, recto-urethral, recto-vesical, vestibular), cloacal lesions, those with no fistula and anal stenosis. Rare and regional variants included pouch colon, rectal atresia or stenosis, rectovaginal fistula, H-fistula and others. Groups would be analyzed according to the type of procedure performed stratified for confounding associated conditions such as sacral anomalies and tethered cord. A standard method for postoperative assessment of continence was determined.

Conclusions

A new International diagnostic classification system, operative groupings and a method of postoperative assessment of continence was developed by consensus of a large contingent of participants experienced in the management of patients with ARM. These methods should allow for a common standardization of diagnosis and comparing postoperative results.     

Embryonic development of the striated muscle complex in rats with anorectal malformations

Purpose

Many patients with anorectal malformations (ARMs) continue to have postoperative anal dysfunction. The striated muscle complex (SMC) is one of the most important factors that influence defecation function. To explore the development of SMC in ARMs, the authors investigated the pelvic muscle development in rat embryos affected with ARMs.

Methods

Anorectal malformation embryos were induced by ethylenethiourea on the 10th gestational day (E10). Normal rat embryos and embryos with ARMs from E13 to E21 were serial-sectioned in the sagittal, transverse, and coronal planes, stained with H&;E and immunohistochemistry staining using specific antibodies to myogenin. Temporal and spatial sequence was carried out on SMC.

Results

On E16, in normal group, SMC appeared fibroid structure in normal rats; SMC arose from bulbocavernosus muscle and ran backward, parallel to the perineal skin, and loosely surrounded the anal canal and urethra. Although in ARM rats the rectum was absent, the location and appearance of SMC were similar to the normal group. On E18, in normal group, SMC musculature became much thicker than on E16 and SMC gave off 2 branches outside anterior to the rectum. Striated muscle complex surrounded the rectum more tightly. However, in ARM rats, obvious changes of SMC could be noted. In detail, SMC in ARMs were characterized by abnormal location, appearance, and path. Striated muscle complex shifted obviously cephalad, ventrally, and medianward and converged inferior to the rectal terminus and posterior to the urethra. The distance between SMC musculature and the perineal skin increased. This structure surrounded the fiberlike tissue posterior to the urethra. Under high-power view, there was connective tissue among intermuscular bundles, and the structure was disordered. During the following gestational days, SMC in normal and ARM groups continued their own tendency, respectively.

Conclusions

This study illustrated the development of the SMC in normal and ARM rats. On E16, the location and appearance of SMC in ARM rats were similar to the normal rats, and at this time, the ectopic rectal orifice could be noted. From E18 on, the maldevelopment of SMC could be observed in ARM rats. These observations suggested that the morphological changes of SMC take place after the occurrence of abnormal anorectum.     

Embryonic development of the internal anal sphincter in rats with anorectal malformations

Background/Purpose

The embryogenesis of the internal anal sphincter (IAS) in anorectal malformations (ARMs) remains unclear. This study aimed to investigate the development of the smooth muscle in the terminus of the digestive tract in normal and abnormal rats.

Methods

Rat embryos with ARMs were generated by administration of ethylenethiourea to pregnant rats. The normal rat embryos and embryos with ARMs from E13.5 to E21 were serially sectioned in the sagittal plane and stained immunohistochemically using specific antibody to α-smooth muscle actin (SMA). Temporospatial study was carried out on circular muscle of the distal portion of the hindgut.

Results

α-Smooth muscle actin immunolabeling cells could not be observed in the hindgut on E13.5, E14, and E14.5. On E15, there were α-SMA immunolabeling circular muscle cells in the hindgut; and the distal portion of the circular muscle was not thickened in the normal and ARMs rats. From E16 onward, the smooth muscle with slight dilated terminus, which was characterized by the features of IAS, could be noted in the primitive anorectum. In the normal group, the circular muscle in the distal portion of the hindgut thickened slightly and became the musculature with shutter-like bundles. In the ARMs group, the α-SMA immunolabeling myogenic precursors of the smooth muscle could be observed in the primitive anorectum as well. The musculature was similar to that in the normal group. On E15 and E16, there was no significant difference in the development of the circular muscle in the 2 groups. Moreover, the terminus of the circular muscle in the hindgut did not reach the orificium fistulae in ARMs rats. From E17 onward, in ARMs rats, the funnel-shaped distal hindgut communicated the genitourinary tract with a narrow fistula; the dilated musculature at this portion thinned gradually and formed an acute angled extremity in the ARMs group rather than formed blunt extremity in the normal group; the terminus circular muscle in the dorsal hindgut reached the orificium fistulae. During the following gestational days, the circular muscle of the hindgut in both normal and ARMs rats continued its own tendency.

Conclusion

The IAS primordium started to appear at the terminus of the hindgut on E15 in the 2 groups. The IAS in the ARMs group failed to develop as well as that in the normal group. The IAS dysplasia occurred in the late embryonic development (E17-E21).