Prenatal vitamin E improves lung and heart hypoplasia in experimental diaphragmatic [correction of diaphragamatic] hernia

Nitrofen induces in rats diaphragmatic hernia (CDH) with heart and lung hypoplasia by a mechanism involving oxidation. The aim of this study was to examine if prenatal administration of the anti-oxidant agent vitamin E (VitE) prevents to some extent heart and lung hypoplasia. Pregnant rats received on E9.5 either 100 mg of nitrofen alone or followed by 150 IU of VitE on E16.5-E20.5. Control animals received either vehicle or VitE alone. The fetuses were recovered on E21. The hearts and lungs were weighed and DNA and proteins were measured. Sections of the heart and lung were immunohistochemically stained for ki-67, Tunel and TTF-1, and the proportions of proliferating, apoptotic and TTF-1-expressing cells were determined. Cultured human pneumocytes were exposed to the same agents and similarly processed. TTF-1 expression and the proportion of proliferating cells were quantitated. The ANOVA or Kruskall-Wallis tests were used for comparison with p<0.05 as threshold of significance. Nitrofen-exposed rats had decreased lung and heart weight/body weight ratios, lung and heart DNA and protein, lung TTF-1 expression and proportion of proliferating cells in lung and heart. Additional treatment with VitE ameliorated these decreases except for lung TTF-1 and heart weight. In cultured pneumocytes, TTF-1 expression was decreased by nitrofen and rescued by VitE. Cell proliferation followed the same pattern. Antioxidant VitE partially reverses the effects of nitrofen on the heart and lungs of exposed rats. The same effects are observed in cultured human pneumocytes. These results further substantiate the oxidative nature of the effects of nitrofen and suggest that anti-oxidant agents could have a potential clinical application.

The adrenal cortex in experimental congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Adrenal cortical malfunction was found recently in patients with severe congenital diaphragmatic hernia (CDH). The current study tests the hypothesis that the development and function of the adrenal cortex could be abnormal in an experimental model of CDH.

METHODS

Pregnant rats were exposed on day 9.5 of gestation to 100 mg of 2-4-dichlorophenyl-p-nitrophenyl ether (nitrofen) diluted in olive oil. The sham group was treated only with oil. Fetuses were recovered on the 21st day, bled, and examined for the presence or absence of CDH. Adrenal glands from sham and CDH animals were dissected, weighed, and prepared for histologic, biochemical, and immunohistochemical studies (ki-67) aimed at measuring total DNA, total protein, and the proportion of proliferating cells. Serum corticosterone levels were assayed. The results in both groups were compared with parametric tests with a significance level of P <.05.

RESULTS

The adrenal weight was not different in CDH animals versus controls (0.049 +/- 0.014 v 0.052 +/- 0.012% of body weight; not significant). Total DNA was reduced significantly (1.180 +/- 0.481 v 1.909 +/- 0.893 microgram P <.05) with unchanged DNA to protein ratio. Proliferation index in both groups was 20.1 +/- 3.1% and 26.5 +/- 7.5%, respectively (not significant), and the proliferating cells were mainly located in the glomerular areas of the glands. Corticosterone levels were similar in both groups.

CONCLUSIONS

Nitrofen induces very slight changes in the development of adrenal glands of fetal rats, expressed by reduced cell proliferation especially in glomerular areas, reduced total DNA with preservation of cell sizes (constant DNA to protein ratio), with no change in function because corticosterone levels remained unchanged. It is doubtful that primary adrenal malformation/malfunction contributes to the severity of CDH in this model.

Neural crest-derived defects in experimental congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is often associated with other malformations. This study tests the hypothesis that the heart and great vessels, thymus, parathyroids, and thyroid might be abnormal in the rat model of CDH as a result of disturbed neural-crest development. Time-mated pregnant rats were fed either 100 mg 2-4-dichlorophenyl-p-nitrophenyl ether (nitrofen) or vehicle on gestational day 9.5. Diaphragm, lung, heart, and thymic malformations were sought after dissection and the parathyroids and thyroid were histologically investigated in term fetuses. Ten control fetuses had no malformations, whereas 22 of 32 nitrofen fetuses had CDH and 20 had cardiovascular defects like narrow pulmonary outflow tract (n = 7), aberrant right subclavian artery (n = 7), ventricular septal defect (n = 4), atrial septal defect (n = 4), tetralogy of Fallot (n = 2), double-outflow right ventricle (n = 2), right ductus arteriosus (n = 2), and others. The thymus was present but was significantly hypoplastic in all nitrofen fetuses and was ectopic or single-lobed in 28% of them while the parathyroid glands were unilaterally absent or ectopic in 50%. The thyroid was only minimally malformed or ectopic. In conclusion, malformations of structures derived from the pharyngeal arches are likely neural-crest related in rats exposed to nitrofen.

Prenatal dexamethasone rescues heart hypoplasia in fetal rats with congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Patients and rats with congenital diaphragmatic hernia (CDH) have lung and heart hypoplasia. Prenatal steroids improve lung hypoplasia in CDH rats. The current study tests the hypothesis that prenatal dexamethasone could rescue heart hypoplasia in rats with CDH.

METHODS

Timed pregnant rats received intragastrically either 100 mg nitrofen or oil on day 9.5, and other animals had the same treatment with, in addition, either 0.25 mg/kg dexamethasone intraperitoneally or no treatment on days 19 and 20. Fetuses were recovered on day 21, and heart weight to body weight ratios, heart DNA, protein, and glycogen were measured in fresh specimens. Left-to-right ventricular diameter and aortic-to-pulmonary diameter ratios were measured after formalin fixation.

RESULTS

Wet heart weight to body weight, left-to-right ventricular diameter, and aortic-to-pulmonary root diameter ratios, which were lower in fetuses exposed only to nitrofen than in their oil controls, were similar in those exposed to nitrofen plus dexamethasone than in their corresponding oil plus dexamethasone controls. Total heart DNA, which was decreased in fetuses exposed to nitrofen with CDH in comparison with their controls, was increased in those receiving nitrofen and dexamethasone in comparison with theirs. Protein to DNA ratio was decreased in all rats with CDH irrespective of their exposure or not to dexamethasone. Glycogen to DNA ratio was higher in all dexamethasone-treated fetuses than in those without this treatment. No gross histologic differences were seen among groups.

CONCLUSIONS

Heart hypoplasia in rats with CDH is in part rescued by prenatal dexamethasone treatment as expressed by increased number of smaller myocytes with higher glycogen content. Prenatal steroids could modify heart involvement in human fetuses with CDH as well.

Down-regulation of thyroid transcription factor-1 gene expression in fetal lung hypoplasia is restored by glucocorticoids

The thyroid transcription factor (TTF)-1 has an essential role in lung morphogenesis and development. It is involved in the transcription of surfactant proteins (SP), which are critical in respiratory function. Neonates with congenital diaphragmatic hernia die of respiratory failure caused by pulmonary hypoplasia with associated biochemical immaturity. To gain new insights into the causes of this disorder and the effect of prenatal hormonal treatment on reducing mortality in these infants, we evaluated the expression of TTF-1 as marker of lung morphogenesis and SP-B as marker of lung maturity. Using a rat model of lung immaturity, we show that TTF-1 and SP-B messenger RNA (mRNA) levels are drastically reduced in congenital lung hypoplasia. Interestingly, prenatal dexamethasone (Dex) treatment increased both TTF-1 and SP-B mRNAs over control levels when administered to rats with lung hypoplasia, but it had no effect on TTF-1 or a moderate effect on SP-B mRNA when administered to control rats. TRH alone also increases TTF-1 and SP-B mRNA levels but to a lesser extent than Dex. When administered together with Dex, TRH counteracts the induction observed with the glucocorticoid. The decrease in TTF-1 mRNA levels in lung hypoplasia is paralleled by a down-regulation of TTF-1 protein levels, as well as by a decrease in the TTF-1/DNA complex when the TTF-1-binding site of the SP-B promoter was used as a probe. Both parameters were reestablished after glucocorticoid treatment. Moreover, the regulation of TTF-1 gene expression described in this report is accompanied by the same regulation in its promoter activity, as demonstrated in transfection experiments performed in H-441 human lung-derived adenocarcinoma cells. In conclusion, our data demonstrate, for the first time, that lung hypoplasia and the associated respiratory dysfunction caused by SP-B deficiency are caused, in part, by down-regulation of TTF-1 gene expression. The observations that prenatal glucocorticoid treatment induces the expression of TTF-1 supports routine in utero glucocorticoid treatment of patients expected to have lung hypoplasia.

Neural crest-derived defects in experimental esophageal atresia

Esophageal atresia (EA) is often associated with cardiovascular and other malformations that are likely neural crest derived. The present study tests the hypothesis that the heart and great vessels and the thymus and parathyroids may be abnormal in the rat model of EA as a result of disturbed neural crest development. Time-mated pregnant rats received intraperitoneally on d 8 and 9 of gestation either 2 mg/kg adriamycin or vehicle. Esophageal, heart, and thymic malformations were sought under the microscope in term fetuses. The parathyroids were histologically investigated. Control fetuses had no malformations, whereas 69 of 109 fetuses exposed to adriamycin had EA and 45 of 69 had 15 right aortic arches, nine aberrant right subclavia, eight ventricular septal defects, six narrow pulmonary outflow tracts, five tetralogies of Fallot, three double outflow right ventricles, three double aortic arches, three atrial septal defects, three right ductus arteriosus, and two truncus. The thymus was absent in 19, hypoplastic in 12, and ectopic in five out of 36 fetuses with EA in which it was studied, whereas the parathyroid glands were absent in 16, single in four, and ectopic in one of the 23 fetuses with EA in which they were studied. In conclusion, the nature of the cardiovascular, thymic, and parathyroid malformations associated with EA in rats is consistent with the hypothesis of neural crest participation in their pathogenesis. Mechanisms simultaneously disturbing foregut septation, somitic segmentation, and neural crest development should be sought to explain the combined occurrence of malformations in EA.

Muscular architecture and manometric image of gastroesophageal barrier in the rat

The two components of the gastroesophageal barrier, the sphincter and the crural sling, closely overlap in humans, whereas they are widely separated in the rat. This investigation correlates the anatomical components of the barrier and their manometric counterparts in this animal. Sphincteric and crural sling pressures were measured in four quadrants in 23 rats. Muscle thickness was measured at nine levels of the gastroesophageal junction in the same quadrants in 12 rats and the muscular architecture of the region was studied in 10 fresh specimens. The manometric sphincteric component is stronger on the right side where the thickest muscle fibers anchor to the anterior and posterior borders of a mucosal ridge that almost surround the cardia. Conversely, the sling pressure is highest towards the left where the muscular bundles straddle the esophagus. In conclusion, there is a close correspondence between the manometric image and the muscular architecture of the components of the gastroesophageal barrier in the rat. The anatomical arrangement of U-shaped muscular bundles oriented in opposite directions creates a particularly powerful antireflux mechanism.

Gastroesophageal reflux after combined lower esophageal sphincter and diaphragmatic crural sling inactivation in the rat

This study tests the hypothesis that either selective or combined destruction of the lower esophageal sphincter and the diaphragmatic crural sling should induce reflux in the rat. Pull-through perfusion manometry was performed before and after lower esophageal myectomy, crural myotomy, or both. pH monitoring was used to detect reflux. Unmanipulated rats served as controls. Paired t tests were used for comparison of pre- and postoperative pressure values and contingency tables with Fisher's tests for examining the association between the interventions and the appearance of reflux. Esophageal myectomy decreased only sphincteric pressure from 25.9+/-15.5 to 9+/-6 mm Hg (P < 0.01), whereas crural myotomy decreased only sling pressure from 26.2+/-13.3 to 7.3+/-3.9 mm Hg (P < 0.01). Simultaneous performance of both procedures decreased sphincteric and crural pressures from 20.4+/-7.5 to 7.6+/-4.3 mm Hg (P < 0.01) and from 45.9+/-20.6 to 18.2+/-7.4 mm Hg (P < 0.01), respectively. None of the control, myectomy, or myotomy animals showed reflux upon pH-metry but 5/8 rats in which both procedures were performed had prolonged acid exposure. No esophagitis was seen. In conclusion, normal rats do not have reflux. Selective destruction of either the sphincter or the crural sling does not induce reflux, despite causing flattening of their respective manometric profiles. Conversely, combined inactivation of both components is significantly associated with reflux.

Skeletal malformations associated with congenital diaphragmatic hernia: experimental and human studies

BACKGROUND/PURPOSE

Skeletal malformations are seen occasionally in infants with congenital diaphragmatic hernia (CDH). This study examines whether nitrofen, able to produce CDH in fetal rats, also induces skeletal anomalies and, if so, whether these are similar to those seen in CDH patients.

METHODS

Pregnant rats received either nitrofen (100 mg, n = 7) or no treatment (n = 2) on gestational day 9.5. Skeletal anatomy was studied in fetuses recovered on day 21 after alcian blue-alizarin red staining. The charts and postmortem records of 117 stillborns or newborns who died of CDH were investigated retrospectively for skeletal defects. The proportions of anomalies found in the different groups were compared.

RESULTS

The 15 control rat fetuses were normal, whereas 57 of 90 nitrofen-exposed animals (63%) had CDH accompanied by other malformations. Skeletal defects limited to vertebral segmentation or identity anomalies (split vertebra or absent, hypoplastic, or fused ribs) were seen at low thoracic and high lumbar levels in 68% of animals with CDH and in 57% of those without. Delayed ossification of limbs was seen in treated animals. There were skeletal malformations in 31.6% of the 117 human patients with CDH. Costovertebral defects (malformed, extra or defective vertebral bodies or ribs and spina bifida) were comparably frequent in infants with syndromes and in those without them (31.2% v 17.8%, not significant), whereas limb defects were significantly more frequent in those with syndromes (56.2% v 13.9%, P<.05).

CONCLUSION

The nature and location of costovertebral malformations found in both CDH patients and nitrofen-exposed rats suggest that the diaphragmatic defect and the associated organ malformations might be caused by the same early embryonal disturbance involving axial and para-axial mesoderm.

Cardiovascular malformations in congenital diaphragmatic hernia: human and experimental studies

BACKGROUND/PURPOSE

Cardiovascular malformations (CVM) associated with congenital diaphragmatic hernia (CDH) account in part for the high mortality caused by this defect. The aim of this study is to examine the nature of these malformations in a large series of autopsies and to assess if similar defects are also present in rat fetuses with experimental CDH.

METHODS

The incidence of CVM and their nature were examined in the autopsy records of 136 stillborns and neonates with CDH admitted to our institution in the last 30 years. Experimental CDH was induced in rat fetuses by giving 100 mg of nitrofen to their mothers on gestational day 9.5, and the fetuses were harvested on day 21 (near full term). The presence of CDH and the anatomy of the heart and great vessels were studied under dissecting microscope after formalin fixation. Unexposed fetuses were used as controls.

RESULTS

Thirty-three newborns with CDH (24%) had CVM, either isolated or associated with other defects, and 7 had heart hypoplasia. Most CVM (ventricular septal defect, tetralogy of Fallot, transposition of the great vessels, double-outlet right ventricle) involved the outflow tract. In our animal experiments, no malformations were found in 21 control pups. Conversely, 80 of 130 nitrofen-exposed fetuses (61%) had CDH, and 59 of them (74%) had CVM. A significant association (Fisher's Exact test, P<.01) was found between CDH and CVM because only 25 of the 50 exposed animals without CDH (50%) had CVM. Again, most defects involved the outflow tract and were similar to those seen in human CDH (tetralogy of Fallot, persistent truncus, ventricular septal defect, double-outlet right ventricle, aberrant right subclavian artery, agenetic ductus, and interrupted aortic arch). Animals with CDH had significantly decreased heart weight to fetal weight ratio in comparison with controls and with those without CDH.

CONCLUSIONS

The similar nature of the cardiovascular defects found in babies succumbing to CDH and in nitrofen-exposed rats suggests that a similar disturbance of the regional organogenesis related to the neural crest might be involved in both settings, and further validates the use of this animal model for clarifying the cellular and molecular pathogenetic mechanisms.

Skeletal malformations associated with esophageal atresia: clinical and experimental studies

BACKGROUND/PURPOSE

Patients with esophageal atresia (EA) often have skeletal malformations. The purpose of this study is to examine if similar defects occur in rat fetuses prenatally exposed to Adriamycin, a chemical capable of causing EA in these animals.

METHODS

The charts of 443 babies with EA were reviewed to assess the incidence and nature of these defects in them. Time-mated female rats were given either 2 mg/kg intraperitoneal Adriamycin (experimental group, n = 16) or no treatment (control group, n = 4) on gestational days 8 and 9, and the fetuses were removed near term. Skeletal anatomy was studied after alcian blue and alizarin red staining.

RESULTS

A total of 528 skeletal malformations, mainly abnormal segmentation and vertebral identity (extra or defective bodies or ribs), mishaped vertebral bodies, and limb malformations like radial aplasia or hypoplasia were found in 245 babies (55%). Costal fusion and sternal anomalies were present in 17 and 4 babies, respectively. In the animal study, all control fetuses were normal, whereas 83 of 134 experimental fetuses (62%) had EA accompanied by other malformations. No segmentation or vertebral identity anomalies were seen, but butterfly, wedged, and asymmetric vertebral bodies were found at various levels in all animals with EA and in about half of those without it. Three fetuses had rib anomalies, and 3 more had sternal malformations. Ossification of limbs was delayed in treated fetuses and short, thick, and crooked bones were seen in 4 of 31 fetuses with EA and in none of the Adriamycin-exposed ones without EA.

CONCLUSIONS

Adriamycin exposure induces in fetal rats, in addition to esophageal, duodenal, and anorectal atresias, high proportions of vertebral malformations and some limb defects of nature not identical but quite similar to that of babies with EA. This further validates this model for investigating the nature of the processes leading to EA and its associated malformations.

Heart hypoplasia in experimental congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Heart hypoplasia is associated with congenital diaphragmatic hernia (CDH) and decisively influences survival rate. This study examines whether nitrofen-exposed fetal rats have heart hypoplasia.

METHODS

Pregnant rats received either 100 mg nitrofen or vehicle on gestational day 9.5. The hearts recovered near full term were either formalin fixed for anatomic studies or snap-frozen for biochemical studies. Heart weight, ventricular chamber diameters and aortic-to-pulmonary root diameter ratios were measured in fixed hearts. Protein and DNA were determined in frozen hearts. Analysis of variance (ANOVA) and correlation-regression studies were used for statistical assessment.

RESULTS

All control fetuses were normal, whereas 61% of those exposed to nitrofen had CDH. Cardiovascular malformations were found in 73% of CDH and in 50% of non-CDH animals. Wet and fixed heart weights in percent of fetal weight, left-to-right ventricular diameter ratio, and aortic-to-pulmonary root diameter ratio were significantly decreased in fetuses with CDH in comparison with controls. Only wet heart was significantly decreased in nitrofen-treated fetuses without CDH, although all other variables showed a trend in the same direction. Protein to DNA ratios were similar in the three groups. The structure of the myocytes was histologically similar in all groups.

CONCLUSIONS

The spectrum of lesions in the nitrofen model of CDH encompasses heart hypoplasia, further validating its use for research on this condition. Heart hypoplasia is related to cardiopulmonary compression, but its presence in treated animals without CDH demonstrates that the teratogen itself participate directly in its pathogenesis, and this finding invites further research on this line.

Tracheobronchial malformations in experimental esophageal atresia

BACKGROUND

Malformations of the tracheobronchial tree may account for postoperative respiratory symptoms in patients with esophageal atresia (EA). This study examines the respiratory tract in fetal rats with EA induced by Adriamycin.

METHODS

Time-mated female rats were given either 2 mg/kg intraperitoneal Adriamycin on gestational days 8 and 9 (adria group, n = 6) or no treatment (control group, n = 2), and the fetuses were recovered on day 21. Laryngo-tracheo bronchial tree was studied after transparentation and alcian blue-alizarin red staining that depicts the cartilage in blue and make the surrounding tissues transparent.

RESULTS

There were no malformations in any of the 1 1 control animals studied. Conversely, 31 of 46 (67%) Adriamycin fetuses had EA with distal TEF. These had more tracheal rings than controls (32+/-2 v 26+/-1.5, P < .05) at the expense of those of the mainstem bronchi (3.2+/-1 v 6.6+/-1.1 in the right, P< .05 and 6.2+/-2.1 v 11+/-1.1 in the left, P < .05). There were tracheal stenoses in 16 pups with EA (some severe and five double), and all these had fragmented rings in the trachea or bronchi. In six cases there was an ectopic upper right bronchus, and 1 had a grossly abnormal larynx. The malformations in the 15 Adriamycin-exposed fetuses without EA were limited to some fragmented or mishaped rings.

CONCLUSIONS

Laryngo-tracheobronchial malformations entailing the whole length of the tract are very constant and severe in rats with EA and tracheoesophageal fistula and correspond to an abnormal development of the tracheobronchial anlage from the ventral foregut. Their nature and extent invite a careful investigation of the respiratory tracts in EA babies in whom they could be underscored.

Effects of esophageal shortening on the gastroesophageal barrier: an experimental study on the causes of reflux in esophageal atresia

BACKGROUND/PURPOSE

Gastroesophageal reflux (GER) is frequently recognized after surgical repair of esophageal atresia. The aim of this study was to test the hypothesis that one or more components of the gastroesophageal pressure barrier are weakened by esophageal anastomosis under tension.

METHODS

Lower esophageal sphincter pressure (LESP), crural sling pressure (CSP), and the length of the intraabdominal segment of the esophagus (LIAE) were measured by pull-through perfusion manometry in 20 rats before and after resection of 15 mm of the cervical esophagus, and in eight rats before and after esophageal transection (control group).

RESULTS

This manouver decreased the LESP from 44.9+/-17.4 to 30.9+/-12.3 mm Hg and the LIAE from 17.9+/-2.8 to 15.8+/-2.4 mm (P < .05) in experimental animals, whereas they did not significantly change in controls. CSP did not change significantly.

CONCLUSIONS

Anastomosis of the esophagus under tension in this model decreases significantly the lower esophageal sphincter tone and length of the intraabdominal esophagus, but it does not change the crural sling pressure. Postoperative reflux in patients operated on for esophageal atresia might be in part, caused by this mechanism.

Notochord involvement in experimental esophageal atresia

Esophageal atresia (EA) is often accompanied by vertebral defects and other anomalies. The adriamycin rat model of EA has disclosed the embryology of the malformation and shown that the vertebrae and notochord are also abnormal. This study describes the nature of notochord malformations in rat embryos exposed to adriamycin. Time-mated rats received either 1.75 mg/kg adriamycin or vehicle i.p. on gestational days (E) 6 to 9; E-12, E-12.5, and E-13 embryos were harvested, embedded in paraffin, and serially sectioned at 3 microm in transverse plane from the head to the stomach for subsequent PAS staining. The findings in both groups were compared at the three endpoints. Control embryos had neither tracheoesophageal nor notochord malformations. On day 12, only 11/36 adriamycin embryos were normal; 7/36 had abnormal notochords, 11/36 had EA, and 7/36 had both. The corresponding figures for 12.5 days were 12/27, 0/27, 7/27, and 8/27 and those for the day 13 7/23, 5/23, 3/23, and 8/23. The malformed notochords were thickened, bifurcated, or trifurcated in the sagittal plane. The simultaneous presence of notochord and esophageal malformations suggests a direct link between both defects, but our observation of isolated occurrence of both shows that they reflect two expressions of the profound disturbance of embryonic para-axial organization responsible for the cluster of malformations rather than a cause-effect association.

Lung hypoplasia caused by nitrofen is mediated by down-regulation of thyroid transcription factor TTF-1

Prenatal exposure to nitrofen induces lung hypoplasia and diaphragmatic hernias very similar to those in human disease, but the mechanisms are still unknown. Thyroid transcription factor 1 (TTF-1) is involved in lung ontogeny and regulation of the expression of surfactant proteins, and is likely abnormally expressed in nitrofen-induced lung hypoplasia. This study examines the effect of nitrofen on TTF-1 messenger RNA (mRNA) expression in the lungs of prenatal rat fetuses and a human lung-cell line (NCI-H441) that expresses both TTF-1 and surfactant proteins in vivo. Lungs from preterm fetuses harvested from rats with 100 mg nitrofen on gestational day 9.5 and NCI-H441 cells maintained in RPMI medium containing 10% fetal bovine serum and exposed to nitrofen for different times and concentrations were assayed for TTF-1 mRNA by northern blot analysis. mRNA for TTF-1 was decreased in nitrofen-exposed pups in comparison with controls, and exposure to nitrofen caused a dose- and time-related decrease in TTF-1 expression in H441 cell cultures. These results indicate that nitrofen downregulates TTF-1 both in vivo and in vitro. Since this interferes with lung development, it is reasonable to accept that lung hypoplasia in this model is in part due to the direct effect of the teratogen rather than to compression by the abdominal viscera herniated into the thorax. This mechanism should be explored in the clinical setting.

The tracheobronchial tree is abnormal in experimental congenital diaphragmatic hernia

Neonates with congenital diaphragmatic hernia (CDH) have other malformations that contribute to the high mortality. The nitrofen rat model allows experimental study of these anomalies. This study examines whether the tracheobronchial tree is also abnormal in this model. Time-mated rats received 100 mg nitrofen on gestational day 9. 5; 90 fetuses were harvested on day 21 (near full term) and dissected. The trachea and bronchi were stained with alcian blue-alizarin red and their anatomy was examined by transillumination under a microscope. The findings were compared with those of 11 suitable controls. Control pups had no malformations. Those with CDH (n = 57) had significantly decreased numbers of tracheal rings in comparison with controls (22.9 +/- 1.9 vs 26 +/- 1.9, P < 0.05) and 40/57 had fragmented rings (0 in controls). Twelve CDH animals had, in addition, tracheal stenoses of variable severity, sometimes related to vascular rings. Nitrofen fetuses without CDH (n = 33) had only short tracheas and 4 had mild stenoses. Nitrofen-exposed fetuses have, in addition to lung hypoplasia and sometimes CDH, severe tracheobronchial anomalies that suggest the involvement of pathogenetic mechanisms capable of acting on various tissue components. The genetic control of organogenesis is most probably disturbed by the teratogen.

Embryology of esophageal atresia in the adriamycin rat model

PURPOSE

The aim of this study was to describe the dysmorphogenetic process leading to esophageal atresia and tracheoesophageal fistula (EA + TEF) in the recently developed Adriamycin model of the malformation.

METHODS

Time-mated pregnant rats were given either Adriamycin (1.75 mg/kg intraperitoneally) or saline on days 6 to 9 of gestation, and their embryos recovered on days 12, 12.5, and 13 were serially sectioned in the transversal plane and studied microscopically after H&E and PAS staining. The findings were compared with those of age-matched untreated embryos.

RESULTS

All untreated and saline embryos were normal, whereas 49% of Adriamycin embryos had foregut malformations. Tracheoesophageal separation was complete on day 12 in control embryos, whereas 9 of 10 Adriamycin-exposed embryos had a common esophagotrachea with low emergence of the bronchi at that stage. This pattern had evolved into that of a regular EA + TEF in all nine malformed embryos by day 13. On day 12.5, esophagotrachea was found in 6 of 13 and EA + TEF in 5 of 13 embryos. Two had less well-defined malformations.

CONCLUSIONS

Esophagotrachea equivalent to complete tracheoesophageal cleft is the first step leading to EA + TEF in this model. The full-blown malformation is finally acquired by partial loss of the posterior wall of the foregut, which tapers-off in the mediastinal mesenchyme and respiratory differentiation of the anterior wall down to the level of bronchial bifurcation, where it constitutes the fistula and the distal esophagus.

Identification of diaphragmatic crural component of gastroesophageal barrier in the rat

Manometric assessment of the diaphragmatic contribution to the human gastroesophageal barrier is difficult because it overlaps with that of the lower esophageal sphincter. Our aim was to investigate the barrier components in the rat in which the gastroesophageal junction is widely separated from the hiatus. Rats under anesthesia (N = 119) and after muscle relaxation (N = 14) underwent stationary and pull-through perfusion manometry. Inspiratory transdiaphragmatic pressure gradient was 5.79 +/- 1.69 mm Hg and lower esophageal sphincter pressure was 14.76 +/- 8.63 mm Hg. A 13.78 +/- 3.13-mm intraabdominal segment of the esophagus was interposed cranially between the sphincter and a group of phasic oscillations with frequency identical to the respiratory rate and pressure of 13.81 +/- 6.54 mm Hg, which disappeared after muscle relaxation. Both components of the gastroesophageal barrier in the rat are widely separated by a long intraabdominal esophagus. This arrangement allows investigation of the behavior of both components under challenging conditions.

Thyroid hormones in the pathogenesis of lung hypoplasia and immaturity induced in fetal rats by prenatal exposure to nitrofen

BACKGROUND/PURPOSE

Nitrofen is believed to act on prenatally exposed fetuses by changing maternal or fetal thyroid hormone physiology. The aim of this study was to determine whether the amounts of circulating and lung tissue T3 and T4 are decreased in rat fetuses with nitrofen-induced pulmonary hypoplasia and diaphragmatic hernia.

METHODS

Timed-pregnant rats were given 100 mg of nitrofen in oil on gestational day 9.5, and their fetuses were recovered on the 21st day. Lung weight to body weight ratio was determined. Hormonal studies consisted in measurement of plasma T3, T4, and TSH, and of T3, T4, and DNA in lung tissue. Suitable groups of control fetuses prenatally exposed to oil were used for comparison.

RESULTS

The lungs of nitrofen-treated fetuses were hypoplastic and those who had congenital diaphagmatic hernia were even more so. Nitrofen treatment led to decreased plasma T3 and T4 levels without TSH changes. T3 and T4 in lung tissue were apparently decreased in treated fetuses when expressed by weight, but these differences disappeared when expressed by DNA (cell content).

CONCLUSIONS

Lung hypoplasia and immaturity induced by nitrofen treatment are not related to decreased levels of thyroid hormones in tissue near term. This should be kept in mind when proposing hormonal treatment for prenatal induction of lung maturation.

An experimental study on the pathogenesis of gastroesophageal reflux after repair of diaphragmatic hernia

BACKGROUND/PURPOSE

Gastroesophageal reflux (GER) is increasingly reported after surgical repair of congenital diaphragmatic hernia (CDH) and eventration. The aim of this study was to test the hypothesis that transdiaphragmatic pressure gradients are increased and that the antireflux barrier is weakened after plication of a previously paralyzed diaphragm.

METHODS

Abdominal and esophageal pressures as well as lower esophageal sphincter pressures (LESP) and diaphragmatic pinchcock pressure (DPP) were measured before and after diaphragmatic plication in 16 rats in which the diaphragm had been previously eventrated by phrenic nerve section.

RESULTS

This maneuver increased the transdiaphragmatic inspiratory pressure gradient from 2.75 +/- 0.54 to 4.51 +/- 0.86 mm Hg (P < .05) by rising both the inspiratory (-2.02 +/- 0.39 v -3.11 +/- 0.92 mm Hg, P < .05) and the expiratory (1.47 +/- 0.87 v 0.51 +/- 0.41 mm Hg, P < .05) intrathoracic pressures. At the same time, the antireflux barrier was weakened because LESP decreased from 17.5 +/- 5.59 to 10.59 +/- 5.74 mm Hg (P < .05) and DPP tended to decrease from 13.57 +/- 8.67 to 6.07 +/- 1.72 mm Hg (ns).

CONCLUSIONS

Plication of the previously paralyzed diaphragm in the rat reinforces the GER driving forces while weakening the antireflux barrier. This may explain why reflux is frequent in children surviving repair of diaphragmatic hernia and eventration.

Transdiaphragmatic pressure gradients and the lower esophageal sphincter after tight abdominal wall plication in the rat

BACKGROUND

Gastroesophageal reflux (GER) is increasingly recognized as a complication of surgical closure of gastroschisis and omphalocele.

AIM

This study tests the hypothesis that forceful abdominal wall closure reinforces the transdiaphragmatic pressure gradients that constitute the main GER-driving force and challenges the antireflux barrier.

MATERIALS AND METHODS

Abdominal and esophageal pressures as well as lower esophageal sphincter pressures (LESP) and length (LESL) were measured in 17 adult rats before tight abdominal wall plication, after it, and 1 week later.

RESULTS

This maneuver increased the transdiaphragmatic expiratory gradient from 0.67 +/- 1.31 to 6.97 +/- 2.68 mm Hg (P < .01) and the inspiratory gradient from 4.36 +/- 1.13 to 10.79 +/- 2.31 mm Hg (P < .01) by markedly increasing both the expiratory (from 1.47 +/- 0.74 to 9.44 +/- 1.85 mm Hg; P < .01) and inspiratory (from 0.98 +/- 0.69 to 6.83 +/- 1.55 mm Hg; P < .01) intraabdominal pressures. These changes were transient, and all pressures became normal after 1 week. The antireflux barrier functioned properly under these new conditions because both LESP and the diaphragmatic pinch-cock pressure (DPP) increased, from 20.3 +/- 3.63 to 26.5 +/- 4.31 mm Hg (P < .01) and from 16.4 +/- 7.25 to 22.5 +/- 4.36 mm Hg (P < .01), respectively, while LESL remained unchanged.

CONCLUSION

Tight abdominal wall plication in the rat generates high intraabdominal pressures and thus reinforces the transdiaphragmatic pressure gradients, but these conditions elicit a healthy barrier response with sphincteric reinforcement. In addition, these changes are transient and fade out some time after operation. These facts should be taken into account for understanding the pathogenesis of GER after repair of abdominal wall defects in human babies.

Experimental ureterohydronephrosis in fetal rats

This study tests the hypothesis that prenatal exposure to 2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen), an herbicide known to induce pulmonary hypoplasia and other malformations in fetal rats, also may induce ureterohydronephrosis (UHN) and oligohydramnios. Time-dated pregnant Wistar rats were given 100 mg of the chemical on day 9 or 11 of gestation, and the findings in their fetuses were compared with those of suitable controls. Marked bilateral UHN was found in the majority of exposed fetuses, but without evidence of either mechanical obstruction or dysplastic parenchymal lesions. These animals had various degrees of lung hypoplasia. The amount of fluid in their amniotic sacs was increased rather than decreased and it was independent of lung weight but correlated to some extent with UHN grade. Urinary tract dilatation and polyhydramnios in this model most likely are attributable to polyuria caused by nitrofen-induced impairment of renal concentrating capacity. This relatively simple animal model might facilitate research into some aspects of the physiology of nonobstructive, prenatally dilated urinary tracts.

Narrowing the embryologic window of the adriamycin-induced fetal rat model of esophageal atresia and tracheoesophageal fistula

We recently reported on a new fetal rat model of esophageal atresia (EA) with tracheoesophageal fistula (TEF) induced by prenatal exposure to adriamycin (1.75 mg/kg i. p. injected daily to the pregnant dam from the 6th to 9th gestational days). With this treatment regime, many fetuses were resorbed and the number of associated malformations was very high. The present study demonstrates that similar doses of the drug administered only on the 8th and 9th gestational days allow higher fetal survival (9.7 ∓ 3.9 vs. 6.8 ∓ 4.7 fetuses per litter, P < 0.01) with a similar incidence of EA-TEF (41.2% vs. 56.4%, n. s.) and decreased occurence of associated anorectal and genitourinary malformations. Since this model is an instrument for further investigation of the disturbed cellular and morphogenetic events leading to EA and TEF, the narrowing of the embryologic window obtained by the present study will allow better focusing of the research on the critical period of time involved.

Testicular maldescent and maldevelopment in fetal rats prenatally exposed to nitrofen

In the rat model of nitrofen-induced congenital diaphragmatic hernia, we found the testicles in a high abdominal position in many male animals, and undertook to investigate whether the teratogen interferes with testicular descent and development. Male fetuses from time-mated Wistar rats treated intragastrically with 100 mg nitrofen dissolved in oil on day 9.5 of gestation were compared with control fetuses from mothers receiving only vehicle. The litters were recovered by cesarean section on days 17, 19, and 21 of gestation; the position of the testicles in male animals was recorded, and their volume was measured prior to histological assessment of mean tubular diameter, number of germ cells per tubule, and degree of collagenization of the tunica albuginea. Testicular maldescent was present in 100% of nitrofen-exposed fetuses on the 17th gestational day, 77% of those recovered on day 19, and 41% of those near term (21st day), whereas all control animals but 1 had "descended" gonads on all three days. Testicular volume was significantly decreased in treated fetuses on the 21st gestational day, and the mean tubular diameter was significantly decreased in all three age groups. Experimental and control animals had similar numbers of germ cells per tubule. The albuginea layer had apparently normal collagen content in all groups. These findings suggest that prenatal exposure to nitrofen interferes with both transabdominal descent of the testicle (transinguinal descent is postnatal in the rodent) and its normal development. Previous evidence and the present results authorize speculation on the possible role of nitrofen-induced prenatal thyroid hypofunction in the pathogenesis of maldescent and maldevelopment in this model, since thyroid hormones act directly on Sertoli cells, which secrete müllerian inhibiting substance, which is likely responsible for transabdominal descent.

A new rodent experimental model of esophageal atresia and tracheoesophageal fistula: preliminary report

In spite of the interest paid by pediatric surgeons to esophageal atresia (EA) with tracheoesophageal fistula (TEF), no animal experimental model has been available for investigation. This preliminary report describes a reproducible fetal model of these malformations. Time-mated pregnant rats were given 1.5, 1.75, or 2 mg/kg of Adriamycin intraperitoneally on days 6 to 9 of gestation, and the litters were recovered on day 21 (near full-term). The amount of amniotic fluid was measured, and the fetuses were dissected and studied histologically. The findings were compared with those of suitable control fetuses. Adriamycin-exposed fetuses weighed less than controls. EA with TEF (Gross' type C) was found in 28%, 45%, and 41% of animals in the three dose groups (respectively). The malformation was anatomically identical to that of the human neonate, and the amount of amniotic fluid in affected fetuses increased significantly. In one instance, an H-type fistula was observed. In addition to esophageal interruption, many other malformations fitting within the human VATER association were found: duodenal atresia (41%, 50%, and 47%, respectively), anorectal (28%, 50%, and 41%), renal (81%, 100%, and 100%), and limb malformations (0%, 2.3%, and 13.8%). This new, easily reproducible and relatively inexpensive experimental model of one of the most interesting pediatric surgical malformations permits new research into both its embryogenesis and the biology of the malformed fetus.

Lung hypoplasia and surfactant system immaturity induced in the fetal rat by prenatal exposure to nitrofen

We studied the biochemical maturity of the lungs of fetuses born to rats exposed to nitrofen on day 9.5 of gestation. In comparison with controls, nitrofen-treated fetuses had pulmonary hypoplasia (decreased lung/body weight), lung hypocellularity (low DNA content) and cellular atrophy (low protein/DNA and phospholipid/DNA) on gestational days 19 and 21. Treated animals with congenital diaphragmatic hernia (CDH) also had cell atrophy and surfactant immaturity (decreased disaturated phosphatidylcholine/DNA) near term. Our data demonstrate that nitrofen causes lung hypoplasia and some degree of surfactant system immaturity that is particularly prominent in fetuses with CDH.

Intestinal rotation in experimental congenital diaphragmatic hernia

This study examines whether experimental congenital diaphragmatic hernia (CDH) induced by nitrofen in rats is accompanied by intestinal malrotation similar to that observed in the human condition. Time-dated pregnant rats were fed 100 mg of nitrofen on day 9.5 gestation, and fetuses were examined on days 17, 19, and 21. Body weight, lung weight, grade of bowel herniation into the umbilical cord and grade of intestinal malrotation were compared with those of age-matched controls. Body and lung weights were significantly lower in nitrofen-exposed on days 17, 19, and 21. The umbilical hernia persisted on day 17 in 100% of experimental animals and 66% of controls (P < .01). Intestinal malrotation was more severe in experimental rats than in controls on days 19 (63% v 17% grade 2; P < .01) and 21 (27% v 0% grade 1; P < .01). Finally, 52% of nitrofen-fed fetuses with CDH had malrotation at term, whereas only 18.2% of those without it did (P < .05). There was a significant (P < .001) negative correlation between the lung weight/body weight ratio and the degree of malrotation in nitrofen-treated fetuses. In conclusion, maternal nitrofen exposure on gestational day 9.5 induces intestinal malrotation in fetal rats by (1) delaying fetal growth and maturation; (2) causing CDH, which permits displacement of the liver and the gut into the thorax during the critical period of reintegration and fixation; and (3) inducing lung hypoplasia and reducing thoracic volume during this period.

Neural tube defects: an experimental model in the foetal rat

We report on our experience in the experimental induction of Neural Tube Defects (NTD) in the foetal rat by maternal administration of retinoic acid. The teratogen diluted in olive oil was administered in a single intragastric dose (125 mg/kg body weight) to pregnant rats (n = 31) on the 10th day of gestation. Pure olive oil was given to control rats (n = 9). The foetuses were recovered by caesarian section on the 20th day and prepared for morphological investigation. We have studied 201 experimental and 82 control animals. There were NTD in 36.3% of experimental foetuses and none in the control ones. Sacral dysraphism was the most frequent defect but we also observed Arnold Chiari malformations and crowding of the bony limits by an enlarged neural axis. Other associated malformations found were: craneofacial (78.1%), caudal (80%), anorectal (31.4%), and limb defects (89.5%). This simple and inexpensive model may allow us to gain a better knowledge of the biology in the foetus with NTD.

Electrophysiologic changes during acute rejection of heterotopically transplanted rat hearts

Noninvasive monitoring of heart allograft rejection was performed by electrophysiologic techniques using an implanted electrode located on the epicardial surface of the heterotopic transplanted heart of rats. R wave and slew rate determinations were performed daily in 30 syngeneic and 66 allogeneic transplants. These determinations were later compared with histopathologic studies of the transplanted hearts. R wave and slew rate values of allogeneic or rejecting hearts were found to decrease significantly compared with syngeneic or nonrejecting hearts on the days studied. This noninvasive electrophysiologic method may be a promising method for monitoring heart allograft rejection.

Electrophysiological and anatomical findings in heart transplantation: experimental study

The diagnosis of acute rejection by electrophysiological methods is based on the fact that signs of rejection such as inflammatory infiltrate, interstitial edema, and mostly myocyte necrosis lead to obligated alterations in electrophysiological properties of the myocardium. In a total of 276 heterotopic abdominal transplants in rats, a noninvasive monitoring of heart allograft rejection by conventional ECG and electrophysiological techniques was performed. The correlation of these findings with pathological studies, including histologic determination of the degree of acute rejection, analysis of weight and cardiac perimeter, and volumetric cell density were also evaluated in 96 of them, 66 were allogeneic and 30 syngeneic. Sensitivity and specificity of the R wave and slew rate was also determined with respect to the Billingham classification. Results of the correlation analysis showed that electrophysiological variations in R wave and slew rate correlated more intensely with changes in volumetric cell density. The greatest sensitivity and specificity was observed in R wave changes in relation to the Billingham classification.

Partial splenic embolization in hypersplenism

Four patients with portal hypertension, oesophageal varices and severe hypersplenism were treated by partial splenic embolization. All showed improvement of blood and platelet counts early in the postoperative period. Three months after embolization IgA and C3 levels increased significantly. All patients had a decrease in the incidence of variceal bleeding and this procedure provides an acceptable alternative to splenectomy.