The significance of the dilated renal pelvis in the nitrofen-exposed rat fetus: effects on morphology and function

Postnatal fate of prenatal-induced fetal alterations in laboratory animals

Currently it is common practice to evaluate the developmental toxicity hazard of chemicals or pharmaceuticals by evaluation of fetuses after administration of the compound to pregnant animals. These studies are designed to provide possible compound-related fetal changes near term, which are usually classified into malformations or variations. Malformations, but not variations are expected to adversely affect the survival or health. Therefore, classification has striking different regulatory consequences. For categorization as variation reversibility is an important criterion, but it is usually not examined in a standard guideline study. Although this issue has already been recognized long time ago, data dealing with the postnatal reversibility of fetal alterations are still rare. In the current review, literature data, regulatory documents as well as in-house data were compiled. Beside skeletal alterations of skull, vertebral column, ribs, shoulder and pelvic girdle, and extremities, kidney and heart defects are discussed and assessed.

Kidney development in the nitrofen-induced pulmonary hypoplasia and congenital diaphragmatic hernia in rats

BACKGROUND/PURPOSE

The relationship of the developing lung and kidney is not completely understood. Renal enlargement has been reported in association with pulmonary hypoplasia in congenital diaphragmatic hernia (CDH). Recent studies suggest that retinoids may be involved in the pathogenesis of CDH. The aims of this study were to investigate the effects of pulmonary hypoplasia on renal development and to evaluate retinoids status of kidneys in the nitrofen model of CDH.

METHODS

Pregnant rats were exposed to either olive oil or 100 mg of nitrofen on day 9.5 of gestation. Fetuses were recovered at term and divided into 3 groups: 1, control (n = 69); 2, nitrofen without CDH (n = 25); and 3, nitrofen with CDH (n = 40). Kidneys were dissected, weighed, and processed for biochemical measurements of DNA, proteins, total retinol content, and for immunohistochemical staining of proliferating cells.

RESULTS

Kidneys were smaller in nitrofen-exposed animals vs control animals (group 3, 0.65 +/- 0.08; group 2, 0.62 +/- 0.09 vs group 1, 0.73 +/- 0.09% of body weight, P < .001), and there were no differences between right and left kidney weight in all the 3 groups. Regression of total kidney weight on body weight showed a linear direct correlation between them in all the groups. Total amount of DNA was significantly reduced in nitrofen-exposed animals vs controls (group 3, 80.58 +/- 35.65; group 2, 64.71 +/- 20.28 vs group 1, 110.34 +/- 42.15 microg, P < .01), but the DNA concentration remained the same in the 3 groups (group 3, 3.59 +/- 1.26; group 2, 3.06 +/- 1.19; group 1, 3.43 +/- 1.05 microg DNA/mg kidney). Total protein content (group 3, 1145.59 +/- 500.36; group 2, 993.2 +/- 276.62; group 1, 1287.48 +/- 312.52 microg), protein concentration (group 3, 49.76 +/- 11.12; group 2, 43.95 +/- 6.79; group 1, 47.38 +/- 6.93 microg protein/mg kidney), and protein-to-DNA ratio (group 3, 15.12 +/- 5.98; group 2, 16.22 +/- 6.85; group I, 16.16 +/- 7.02 microg/microg) were similar in all groups. Retinol concentration was significantly reduced in both nitrofen-exposed groups compared with the control group (group 3, 1.35 +/- 0.24; group 2, 1.28 +/- 0.11; group 1, 2.53+/-0.61 microg retinol/g kidney). Proliferation index was similar in all 3 groups (group 3, 50.43 +/- 8.81; group 2, 47.96 +/- 6.01; group 1, 47.64 +/- 5.76% of proliferating cells).

CONCLUSIONS

Our data clearly show that renal enlargement in association with pulmonary hypoplasia is not seen in the nitrofen-induced CDH. These results rule out any possible relationship between lung and kidney development. Moreover, kidneys are hypoplastic in both nitrofen-exposed groups and have reduced retinol content, suggesting that a retinoid pathway disruption could be the common mechanism in the pathogenesis of lung and kidney hypoplasia in the nitrofen model of CDH.

Nitrofen-induced congenital malformations of the heart and great vessels in rats: an animal model

BACKGROUND

Nitrofen (2,4-dichloro-4'-nitrodiphenyl ether), a diapheny ether herbicide, is known to induce in rat fetuses a variety of congenital cardiovascular anomalies, together with diaphragmatic hernia and hydronephrosis. The purpose of the current study was to produce congenital cardiovascular anomalies in rat fetuses by oral nitrofen administration at the indicated doses and days of gestation, and to determine the characteristics of resulting nitrofen-induced cardiovascular anomalies.

METHODS

All the observed fetuses were removed from pregnant Sprague-Dawley rats killed on the 21st day of gestation. They were preserved in 10% formalin, and dissection for examination was carried out under a dissecting microscope.

RESULTS

The following results were based on dissecting microscopic findings of 482 offspring: (1) The 11th day of gestation was the most sensitive for nitrofen induction of congenital cardiovascular anomalies. The incidence of these was dose related. (2) Ventricular septal defect was the most common single cardiovascular anomaly, representing more than half of all such irregularities. The next most common were aortic arch anomalies and tetralogy of Fallot. (3) Cardiac anomalies derived from infundibular maldevelopment such as tetralogy of Fallot and pulmonary atresia with ventricular septal defect were observed only in the group treated with nitrofen on the 11th gestational day. (4) Aortic arch anomalies were very frequent; the great majority were anomalous right subclavian artery with left aortic arch.

CONCLUSION

This animal model is suitable for further embryological investigation of the development of congenital cardiovascular anomalies.

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.

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.