Postnatal developmental alterations following prenatal exposure to the herbicide 2,4-dichlorophenyl-p-nitrophenyl ether: a dose response evaluation in the mouse

Teratological effects of pesticides in vertebrates: a review

In the last decades, the use and misuse of pesticides in the agriculture have increased, having a severe impact on ecosystems and their fauna. Although the various effects of pesticides on biodiversity have been already documented in several studies, to our knowledge no consistent overview of the impact of pesticides in vertebrates, both terrestrial and aquatic, is available. In this review, we try to present a concise compilation of the teratogenic effects of pesticides on the different classes of vertebrates - mammals, birds, reptiles, amphibians and fish.

In utero phthalate effects in the female rat: a model for MRKH syndrome

Mayer–Rokitansky–Kuster–Hauser (MRKH) syndrome is characterized by uterine and vaginal canal aplasia in normal karyotype human females and is a syndrome with poorly defined etiology. Reproductive toxicity of phthalate esters (PEs) occurs in rat offspring exposed in utero, a phenomenon that is better studied in male offspring than females. The current study reports female reproductive tract malformations in the Sprague–Dawley rat similar to those characteristic of MRKH syndrome, following in utero exposure to a mixture of 5 PEs. We determined that females are ~2-fold less sensitive to the effects of the 5-PE mixture than males for reproductive tract malformations. We were not fully successful in defining the critical exposure period for females; however, incidence of malformations was 88% following dosing from GD8 to 19 versus 22% and 0% for GD8–13 and GD14–19, respectively. Overall, this study provides valuable information regarding female vulnerability to in utero phthalate exposure and further characterizes a potential model for the human MRKH syndrome.

Vitamin A deficiency (VAD), teratogenic, and surgical models of congenital diaphragmatic hernia (CDH)

Congenital diaphragmatic hernia (CDH) is a congenital malformation that occurs with a frequency of 0.08 to 0.45 per 1,000 births. Children with CDH are born with the abdominal contents herniated through the diaphragm and exhibit an associated pulmonary hypoplasia which is frequently accompanied by severe morbidity and mortality. Although the etiology of CDH is largely unknown, considerable progress has been made in understanding its molecular mechanisms through the usage of genetic, teratogenic, and surgical models. The following review focuses on the teratogenic and surgical models of CDH and the possible molecular mechanisms of nitrofen (a diphenyl ether, formerly used as an herbicide) in both induction of CDH and pulmonary hypoplasia. In addition, the mechanisms of other compounds including several anti-inflammatory agents that have been linked to CDH will be discussed. Furthermore, this review will also explore the importance of vitamin A in lung and diaphragm development and the possible mechanisms of teratogen interference in vitamin A homeostasis. Continued exploration of these models will bring forth a clearer understanding of CDH and its molecular underpinnings, which will ultimately facilitate development of therapeutic strategies.

Toxicological characteristics of endocrine-disrupting chemicals: developmental toxicity, carcinogenicity, and mutagenicity

It is generally accepted that endocrine-disrupting chemicals (EDCs) play a role in a variety of adverse health effects in an intact organism or its progeny as a consequence of changes in the endocrine system. Primary toxic effects of EDCs were reported to be related to infertility, reduction in sperm count, and teratogenicity, but other important toxic effects of EDCs such as carcinogenicity and mutagenicity have also been demonstrated. The aim of the present study was to systematically analyze the toxicological characteristics of EDCs in pesticides, industrial chemicals, and metals. A comprehensive literature survey on the 48 EDCs classified by the Centers for Disease Control and Prevention (CDC) was conducted using a number of databases which included Medline, Toxline, and Toxnet. The survey results revealed that toxicological characteristics of EDCs were shown to produce developmental toxicity (81%), carcinogenicity (79%, when positive in at least one animal species; 48%, when classified based on IARC evaluation), mutagenicity (79%), immunotoxicity (52%), and neurotoxicity (50%). Regarding the hormone-modulating effects of the 48 EDCs, estrogenic effects were the most predominant in pesticides, while effects on thyroid hormone were found for heavy metals. EDCs showing estrogen-modulating effects were closely related to carcinogenicity or mutagenicity with a high degree of sensitivity. Systematic information on the toxicological characteristics of the EDCs will be useful for future research directions on EDCs, the development of new screening methods, legal regulation, and for investigations of their mechanism of action.

Altered gene level expression of thyroid hormone receptors alpha-1 and beta-1 in the lung of nitrofen-induced diaphragmatic hernia

PURPOSE

Thyroid receptor alpha-1 (TR-alpha1) and thyroid receptor beta-1 (TR-beta1) are thought to be essential for the fetal and postnatal development of the lung. The authors investigated gene level expression of TR-alpha1 and TR-beta1 in the lung of nitrofen-induced congenital diaphragmatic hernia (CDH) using reverse transcription polymerase chain reaction (RT-PCR).

METHODS

CDH was induced in pregnant rats after administration of 100 mg nitrofen on day 9.5 of gestation. Cesarean section was performed on day 21 of gestation. The fetuses were divided into 3 groups: normal controls (n = 16), nitrofen-induced CDH (n = 16), and nitrofen-treated without CDH (n = 16). mRNA was extracted from the left lung in each group. RT-PCR was performed to evaluate mRNA expressions of TR-alpha1 and TR-beta1. Levels of mRNA were expressed as a ratio of the band density divided by that of beta-actin, a house-keeping gene.

RESULTS

TR-alpha1 mRNA expression was decreased significantly in CDH lung (1.618 +/- 0.148) compared with controls (2.658 +/- 0.251; P <.01) and nitrofen-treated without CDH lung (2.232 +/- 0.193; (P <.05). TR-beta1 mRNA expression also was significantly decreased in CDH lung (2.223 +/- 0.270) compared with controls (3.569 +/- 0.262; P <.01) and nitrofen-treated without CDH lung (3.235 +/- 0.299; P <.05).

CONCLUSION

These data suggest that the downregulation of thyroid hormone signaling pathway through altered expression of TR-alpha1 and TR-beta1 during lung morphogenesis may be a contributory factor in the pathogenesis of pulmonary hypoplasia in nitrofen-induced CDH.

Prenatal exposure to nitrofen induces Fryns phenotype in mice

Prenatal exposure to nitrofen is known to cause multiple malformations in mice. The reported malformations include lung hypoplasia, diaphragmatic hernia, cardiovascular defects, skeletal malformations, cleft palate, and renal abnormalities. The authors present detailed findings of craniofacial defects after prenatal exposure to nitrofen, and propose that together with the previously reported malformations, nitrofen exposure induces a Fryns phenotype in mice. Fryns syndrome is a rare human genetic syndrome that is an autosomal recessive disorder characterized by lung hypoplasia, diaphragmatic hernia, craniofacial malformations, skeletal malformations, cardiovascular malformations, and genitourinary malformations. Timed-pregnant Swiss Webster mice were gavage-fed 25 mg of nitrofen on day 8 of gestation. Control animals received olive oil. Osteogenesis and chondrogenesis were studied in fetuses recovered on day 17 after Alcian blue-Alizarin red staining. Approximately 26% of the nitrofen-exposed embryos had severe craniofacial defects, and there was generalized delay in chondrogenesis and osteogenesis throughout the skeleton. No such defects were noted in the control group. The authors propose that prenatal exposure to nitrofen induces a Fryns phenotype in mice, and thus speculate that nitrofen may target similar molecular mechanisms to those that lead to Fryns syndrome.

Pulmonary hypoplasia induced by liquid paraffin injection into fetal thoracic cavity with special reference to renal development in rats

The present study was designed to clarify lung-kidney interrelation in fetal rats. On fetal day 20, liquid paraffin (LP) was injected into fetal thoracic cavity to produce pulmonary hypoplasia. No significant difference in body and renal weights were noted between the LP injected and control fetuses. The weight of lung, however, was significantly lower in the LP injected fetuses than in the control ones. Histological examinations on the lung and kidney of the LP injected fetuses revealed that the lung was hypoplastic characterized by rich interstitium and reduced air spaces. In the kidney, mature types of glomeruli and profiles of proximal tubules near them were increased in number. Furthermore, strong expression of EGF immunoreactivity was noted in the apical cytoplasm of epithelium of the proximal tubules in the LP injected fetuses. These findings indicate that lung-kidney interrelation exists in fetal rats during late gestational days, and suggest that interruption of the lung development induces accelerated growth of the kidney in fetal rats.

Maternal and developmental toxicity of halogenated 4'-nitrodiphenyl ethers in mice

In an ongoing effort to delineate structure-activity relationships in the developmental toxicity of diphenyl ethers, we evaluated the maternal and developmental toxicity of 10 diphenyl ethers related to the herbicide nitrofen. All possible trichlorophenyl 4'-nitrophenyl ethers were evaluated, as were the 2,4-difluorophenyl and 2,4-dibromophenyl 4'-nitrophenyl ethers. We also evaluated bifenox and chlomethoxyfen, which are 2,4-dichlorophenyl congeners with meta-substituents on the 4'-nitrophenyl ring. Nitrofen (2,4-dichlorophenyl 4'-nitrophenyl ether) was included for comparison. Identity of the halogen affected the postnatal (but not prenatal) mortality induced by 2,4-dihalogenated 4'-nitrophenyl ethers. The presence of 3'-substituents on the 4'-nitrophenyl ring reduced both pre- and postnatal toxicity of 2,4-dichlorinated congeners. Among chlorinated 4'-nitrophenyl congeners without meta-substituents on the nitrophenyl ring, the position of chlorine substituents strongly affected the congener's potential for inducing prenatal vs. postnatal syndromes. All congeners increased liver to body weight ratios in unmated females, but such increases were not well-correlated with either prenatal or postnatal embryotoxicity.

Maternal and developmental toxicity of polychlorinated diphenyl ethers (PCDEs) in Swiss-Webster mice and Sprague-Dawley rats

Polychlorinated diphenyl ethers (PCDEs) are industrial byproducts found in many ecosystems at low levels. PCDEs are not markedly toxic to adult rodents, but their developmental toxicity has not previously been examined. We evaluated the maternal and perinatal toxicity of nine PCDE congeners to outbred mice when compounds were administered from gestation day (GD) 6 through GD 15. 2,2',4,4',5,6'-hexaCDE and 2,3',4',6-tetraCDE decreased the number of pups born per female mated and the number of pups surviving per litter born. 2,2',4,4',5,5'-hexaCDE and 2,2',4,5,6'-pentaCDE decreased the number of litters born per female mated, without decreasing postnatal survival. The other PCDEs did not decrease survival either pre- or postnatally. None of the PCDEs caused absence of Harderian glands in surviving offspring at the doses administered. Neither induction of cytochromes P450 nor tissue residues of individual congeners correlated well with developmental toxicity. Three PCDEs were also evaluated in outbred (Sprague-Dawley) rats: 2,2',4,5,6'-pentaCDE and 2,3',4',6-tetraCDE, because of their toxicity to mice; 2,2',4,4',5,5'-hexaCDE, because it should exhibit PCB-like toxicity. Each congener was administered at three dose levels from GD 6 through GD 15. 2,2',4,5,6'-pentaCDE decreased the number of litters born at 100 mg/kg/day, and the survival of pups in litters carried to term, at both 50 and 100 mg/kg per day. Postnatal weight gain was also reduced. In contrast to its action in mice, 2,3',4',6-tetraCDE decreased neither the numbers of litters born nor postnatal survival of rat offspring, but did suppress postnatal weight gain at least through PD 5. As in mice, induction of cytochromes P450 was not well correlated with the developmental toxicity of individual congeners.

Pathogenesis of nitrofen-induced congenital diaphragmatic hernia in fetal rats

Congenital diaphragmatic hernia (CDH) is a developmental anomaly characterized by the malformation of the diaphragm and impaired lung development. In the present study, we tested several hypotheses regarding the pathogenesis of CDH, including those suggesting that the primary defect is due to abnormal 1) lung development, 2) phrenic nerve formation, 3) developmental processes underlying diaphragmatic myotube formation, 4) pleuroperitoneal canal closure, or 5) formation of the primordial diaphragm within the pleuroperitoneal fold. The 2,4-dichloro-phenyl-p-nitrophenyl ether (nitrofen)-induced CDH rat model was used for this study. The following parameters were compared between normal and herniated fetal rats at various stages of development: 1) weight, protein, and DNA content of lungs; 2) phrenic nerve diameter, axonal number, and motoneuron distribution; 3) formation of the phrenic nerve intramuscular branching pattern and diaphragmatic myotube formation; and 4) formation of the precursor of the diaphragmatic musculature, the pleuroperitoneal fold. We demonstrated that previously proposed theories regarding the primary role of the lung, phrenic nerve, myotube formation, and the closure of pleuroperitoneal canal in the pathogenesis of CDH are incorrect. Rather, the primary defect associated with CDH, at least in the nitrofen rat model, occurs at the earliest stage of diaphragm development, the formation of the pleuroperitoneal fold.

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.

Nitrofen-induced congenital diaphragmatic defects in CD1 mice

In previous clinical reports, we have documented the association of several morphologic changes with congenital diaphragmatic hernia or, perhaps more appropriately termed, congenital diaphragmatic defect (CDD). These anomalies include decreased cardiac mass with left ventricular hypoplasia in infants with left-sided CDDs (Siebert et al., '84), enlarged, asymmetric chests (Siebert and Benjamin, '87), and extrathoracic anomalies (Benjamin et al., '88), including urinary tract anomalies and elevated kidney weights in otherwise normal kidneys (Glick et al., '90; Siebert et al., '90). Hypoplastic lungs and hearts and enlarged chests are thought to result from the herniation of abdominal viscera into the thoracic cavity, but for the renal abnormalities, pathogenesis is unclear. The findings are intriguing, for they could mirror unrecognized developmental relationships between the diaphragm, lung, heart, and kidney. In order to further examine these issues and to test the applicability of experimentally produced CDDs to human disease, we administered nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether), an herbicide known to produce diaphragmatic defects in rodents, to time-mated CD1 mice by gavage feeding on gestational days 8 and 9. Dosages were 200 (low dose) or 500 (high dose) mg/kg body weight, and fetuses were studied on gestational day 18. Diaphragmatic defects occurred in a dose-response fashion: 0% (0/48) control or sham-fed, 5% (5/104) in the low-dose group, and 25% (19/75) in the high-dose group. Several fetuses with cleft palate, renal agenesis, exencephaly/encephalocele, and/or Di-George sequence were noted at the high dose, the latter a previously undescribed finding. Diaphragmatic defects were primarily right sided and only associated with herniation of abdominal viscera in animals exposed to 500 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

The kidney in the fetal rat model of congenital diaphragmatic hernia induced by nitrofen

This paper explores whether there is a correlation between kidney and lung growths in an experimental model of congenital diaphragmatic hernia (CDH) induced by intragastric administration of Nitrofen (115 mg/kg) in olive oil on time-dated pregnant Wistar rats at the 9th day of gestation. For comparison we used pregnant rats treated with olive oil alone. Twenty-nine normal fetuses from 3 control rats and 24 left CDH fetuses from 6 Nitrofen rats were studied. Fetal (3.6 +/- 0.8 v 4.9 +/- 0.4 g, P < .001) and total lung (2% +/- 0.5% v 2.6% +/- 0.3% of body weight, P < .001) weights were significantly decreased in animals with CDH. Kidneys were also smaller in CDH animals although not significantly (0.7% +/- 0.1% v 0.8% +/- 0.1% of body weight, P = .05) and were also histologically immature. Regression of kidney weight on body weight for both groups yielded regression lines that were identical at analysis of covariance and all data points from the CDH group were within the control group 95% confidence limits. After converting raw data into lung/body and kidney/body weight ratios, no inverse correlation suggesting a feedback mechanism of growth regulation between both organs could be found. Since nitrofen acts through modifications of the thyroid hormone status in both dam and fetus, altered maturation of several organs should be expected although some of them, like the lung, are the leading targets. The present CDH rodent model is probably different from the human malformation in spite of the striking anatomic similarities between them.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental toxicity of diphenyl ether herbicides in nestling American kestrels

Beginning the day after hatching, American kestrel (Falco sparverius) nestlings were orally dosed for 10 consecutive days with 5 microliters/g of corn oil (controls) or one of the diphenyl ether herbicides (nitrofen, bifenox, or oxyfluorfen) at concentrations of 10, 50, 250, or 500 mg/kg in corn oil. At 500 mg/kg, nitrofen resulted in complete nestling mortality, bifenox in high (66%) mortality, and oxyfluorfen in no mortality. Nitrofen at 250 mg/kg reduced nestling growth as reflected by decreased body weight, crown-rump length, and bone lengths including humerus, radius-ulna, femur, and tibiotarsus. Bifenox at 250 mg/kg had less effect on growth than nitrofen, but crown-rump, humerus, radius-ulna, and femur were significantly shorter than controls. Liver weight as a percent of body weight increased with 50 and 250 mg/kg nitrofen. Other manifestations of impending hepatotoxicity following nitrofen ingestion included increased hepatic GSH peroxidase activity in all nitrofen-treated groups, and increased plasma enzyme activities for ALT, AST, and LDH-L in the 250-mg/kg group. Bifenox ingestion resulted in increased hepatic GSH peroxidase activity in the 50- and 250-mg/kg groups. Nitrofen exposure also resulted in an increase in total plasma thyroxine (T4) concentration. These findings suggest that altricial nestlings are more sensitive to diphenyl ether herbicides than young or adult birds of precocial species.

Relative teratogenicity of nitrofen analogs in mice: unchlorinated, monochlorinated, and dichlorinated-phenyl ethers

To determine the role of number and position of chlorine substituents on the developmental toxicity of diphenyl ether analogs of nitrofen, we have evaluated one unchlorinated, three monochlorinated, and five dichlorinated-phenyl 4'-nitrophenyl ethers with respect to effects on liver weight and on maintenance of pregnancy in females, and with respect to postnatal survival and the occurrence of small or absent Harderian glands in offspring. None of the diphenyl ethers evaluated in these experiments was as active as nitrofen with respect to any parameter evaluated. Both the position and the number of chlorine substituents affected toxicity, but no simple relationship between number or position of chlorine substituents and either maternal or fetal endpoints was established.

Role of structure in diphenyl ether teratogenesis

The fetotoxicity of nitrofen and 5 analogous diphenyl ethers was compared in mice, using survival on postnatal day 5 to evaluate prenatal and perinatal toxicity. The effect of each chemical on the Harderian gland weight of surviving pups was also assessed, since decreased Harderian gland weight is seen in nitrofen-exposed pups at levels of treatment that do not cause mortality. All treatments were percutaneous. 2,4,5-Trichlorophenyl 4'-nitrophenyl ether was significantly more fetotoxic than nitrofen, but 2,4,6-trichlorophenyl 4'-nitrophenyl ether (CNP) was not fetotoxic at the doses used. Neither of the 2 monochlorinated 4'-nitrophenyl ethers nor the unchlorinated 4'-nitrophenyl ether were fetotoxic at the doses tested. Absent Harderian glands resulted only from exposure to nitrofen (71% of litters) or to 2,4,5-trichlorophenyl 4'-nitrophenyl ether (22% of litters), which were also the only compounds to decrease Harderian gland weight significantly.

Kidney morphology and function in the young of rats malnourished and exposed to nitrofen during pregnancy

The separate and combined effects of prenatal protein deficiency (6% casein) and prenatal nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) exposure (12.5 mg/kg on gestational d 7-21) on renal morphology in the 21-d fetal and postnatal rat were examined. Body weights and kidney weights were reduced in prenatally protein-deprived (PPD) pups at birth and on postnatal day (PND) 10. Numbers of mature glomeruli, creatinine clearance, water diuresis, and response of antidiuretic hormone (ADH), but not the concentrating ability, were lower in the PPD neonates. These changes suggest that prenatal protein deficiency delays renal development and possibly results in a decrease in glomerular clearance and in tubular response to a water load and to antidiuretic hormone. Prenatal nitrofen exposure reduced body weight and kidney size on PND 0 and 10. An increased incidence of hydronephrosis was indicated in the nitrofen-exposed fetus. Prenatal nitrofen exposure depressed the ability to excrete excess water, the response to ADH, and urine-concentrating ability. The functional deficits indicate tubular dysfunction, but little or no effect on glomerular function, as indicated by the absence of an effect on creatinine clearance. Postnatal survival was reduced to 22% by PND in the PPD plus nitrofen pups. Also, prenatal nitrofen exposure increased the susceptibility of the glomeruli in the gestational day (GD) 21 PPD fetus to the adverse effects of prenatal protein deficiency. By PND 10 the toxic effects were of the same order. Renal dysfunction may contribute to the increased mortality in PPD plus nitrofen pups by reducing the ability to respond to stress, but the effects are not sufficiently marked to be considered the primary cause of death.

Mutagenicity of N-arylacetohydroxamic acids and their O-glucosides derived from chlorinated 4-nitrobiphenyl ethers

The mutagenic activity of N-arylacetohydroxamic acids, their O-acetates, their O-glucosides, and N-arylhydroxylamines, derived from chlorinated 4-nitrobiphenyl ethers (CNBs), was tested in the Salmonella reversion assay. N-Arylhydroxylamines were mutagenic by themselves; however, other compounds containing an N-acetyl group showed mutagenic activity in the presence of guinea pig liver S9. The mutagenic activation of the glucosides of N-arylacetohydroxamic acids was caused by Ms but not by S10.5, whereas their aglycones, N-arylacetohydroxamic acids, were activated to mutagens by both the fractions. The mutagenic activation of these compounds was inhibited by bis(p-nitrophenyl)phosphate, which indicates that enzymatic deacetylation is a crucial step in the mutagenic activation. Analysis of metabolites of the O-glucosides of N-arylacetohydroxamic acids by h.p.l.c. indicates that the corresponding deacetylated O-glucosides are primary metabolites, which decomposed to amino and azoxy (via hydroxylamine) derivatives, and that the deacetylating activity of S9 locates exclusively in Ms.

Effects on the fetus of maternal nitrofen exposure in the protein-deprived rat

The separate and combined effects of protein deprivation and nitrofen exposure were studied in the pregnant rat. Animals were fed diets containing 24, 8, 6 or 4% casein throughout gestation. Within each diet group, subgroups were gavage-fed with 12.5 (lower dose) and 25 (higher dose) mg nitrofen/kg body weight or with oil carrier only on days 7-21 of gestation. Dams were weighed and food intake was measured daily. On day 21 of gestation, cesarean-derived pups were examined for congenital anomalies and dissected for determination of organ weights. Skeletons were alizarin-stained and examined for skeletal anomalies and developmental stage. No effects on the skeleton or gross congenital anomalies were seen. Fetal size and weights of liver, kidney, intestine, heart, lung and brain were reduced with decreasing casein content of the diet and as a result of the higher dose of nitrofen. An effect of interaction between diet and nitrofen exposure was shown in the kidney, intestine and lung weights. Specific toxicity affecting organ size was shown to occur in the intestine and lung. An interaction between diet and nitrofen specifically affected kidney and intestine. Brain size tended to be preserved, a possible protective mechanism negated by nitrofen exposure. The data suggest also that kidney, intestine and lung are particularly affected. Effects, however, occur primarily in young of severely malnourished dams receiving a relatively high dose of nitrofen.

Effects on the fetal rat intestine of maternal malnutrition and exposure to nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether)

The effects of maternal protein-energy malnutrition and exposure to nitrofen on selected aspects of intestinal morphology and function were studied in the fetal rat. Pregnant rats were fed, throughout gestation, diets containing 24% or 6% casein as the sole source of protein. Reduced total food intake produced protein-energy malnutrition (PEM). Each diet group was divided in half and gavaged with either 12.5 mg nitrofen in corn oil/kg/day or corn oil carrier only from days 7 to 21 of gestation. Body weight, intestinal weight, length, and diameter were measured as were villus length (VL), villus width (VW), and number of villi per length of intestine (VMM). Protein (horseradish peroxidase) and lipid absorption were studied histochemically. Lactase and dipeptidase activities were determined in proximal, medial, and distal thirds of the intestine. Results showed that the restricted maternal diet resulted in reduced fetal body weight (BW), intestinal weight (IW) and length (IL), reduced IW/BW and IW/IL ratios, VH, and VMM. The VW was reduced only in the distal third. Protein and lipid absorption were unaffected. Lactase and dipeptidase activities were reduced. Maternal nitrofen exposure resulted in reduced body weight, intestinal size, and lipid absorption, with some evidence of interaction with the diet effects on enzyme activities. It is concluded that effects of maternal malnutrition were extensive, but that nitrofen exposure, at this dosage level, is not likely to contribute to the postnatal fetal mortality rate in either adequately nourished or malnourished rats.

The postnatal effects of prenatal exposure to low doses of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) in Sprague-Dawley rats

Nitrofen was administered to pregnant Sprague-Dawley rats by gavage on days 8-16 of gestation at 5 different dose levels--0, 0.46, 1.39, 4.17 and 12.5 mg/kg/day. Diaphragmatic hernias were found in pups that died immediately after birth at the 3 highest dose levels. At the 1.39-mg/kg dose level 3 of the 4 pups examined had diaphragmatic hernias, at the 4.17-mg/kg dose level 2 out of 3 pups had diaphragmatic hernias, and at the 12.5-mg/kg dose level all 5 pups found dead had diaphragmatic hernias. Locomotor activity of the offspring was measured on postnatal days 17 and 24, and hyperactivity was evident at the 3 highest dose levels. However, when the rats were later tested at 45, 49 and 90 days of age they had apparently recovered from this earlier hyperactivity. In the female rat, nitrofen did not delay the onset of puberty as measured by the age of vaginal opening or the age at first estrus. At necropsy of the offspring which began on postnatal day 133, Harderian gland weight reduction and hydronephrosis were seen at the 4.17- and 12.5-mg/kg dose levels, while no effects were found in body, liver, testes, seminal vesicle, kidney, or lung weights. Results of the present study and earlier studies demonstrate that rats are more sensitive than mice to the teratogenic effect of nitrofen (Gray et al., Science, 215 (1982) 293 and Gray et al., Toxicol. Appl. Pharmacol., 67 (1983) 1). In general, nitrofen affects the same organ systems in rats as it does in mice, but the rank order of sensitivity of these effects differs from those described earlier in the mouse by Gray et al. (Toxicol. Appl. Pharmacol., 67 (1983) 1).

Teratogenicity of nitrofen (2,4-dichloro-4'-nitrodiphenyl ether) and its effects on thyroid function in the rat

Nitrofen is a herbicide with potent teratogenic activity in rodent species. Previous studies have indicated that this agent has a stereochemical structure similar to thyroid hormone, and that exposure of adult mice results in depression of thryoxine (T4) levels. The present study was undertaken to determine if teratogenic exposure to nitrofen alters pituitary-thyroid function in nonpregnant, pregnant, and fetal rats, and if these potential alterations could be related to induction of birth defects. In adult thyroparathyroidectomized (TPTX) female rats, nitrofen exposure for 2 weeks resulted in a significant suppression of thyrotropin-stimulating hormone (TSH) levels. When a single dose of nitrofen was administered to euthyroid female rats, a trend toward reduction (p = 0.058) in the release of TSH after a thyrotropin-releasing hormone (TRH) challenge was observed 4 and 5 hr after exposure. Pregnant euthryoid rats given a single dose of nitrofen on Day 11 of gestation had significantly depressed TSH and T4 levels, and fetal T4 levels were markedly depressed at term. Administration of T4 on Day 2 through 22 of pregnancy plus nitrofen on Day 9 through 11 to TPTX dams resulted in a 70% reduction in the frequency of malformed fetuses, especially in regard to the frequency of heart anomalies, compared to nitrofen exposure alone. Competitive displacement studies in radioimmunoassays for T4 and T3 indicated that a nitrofen metabolite (4-hydroxy-2,5-dichloro-4'-aminodiphenyl ether) competed with [125I]T3 for antibody binding, while the parent compound and six isolated metabolites failed to compete with [125I]T4 for antibody binding. These results have been interpreted to indicate that nitrofen teratogenicity is mediated at least in part by alterations in maternal and/or fetal thyroid hormone status, and may be due to a premature and pharmacologic exposure to the embryo to a nitrofen-derived, T3-active metabolite.

An extended evaluation of an in vivo teratology screen utilizing postnatal growth and viability in the mouse

A teratology test system proposed by Chernoff and Kavlock utilizes growth and viability for 3 days after birth to prioritize chemicals for standard teratology testing. The present study is an extended observation of the growth and viability of Chernoff and Kavlock's animals from 41 treatments for 250 days to determine if neonatal weight reductions persisted throughout life, if mortality occurred later in life or, if other serious abnormalities developed that could not be anticipated from the neonatal data. One chemical which was positive in the present study would be a false negative in the standard teratology test and the Chernoff/Kavlock Assay (CKA). Congo red did not cause frank malformations or mortality but it specifically altered reproductive function in the offspring. Two chemicals produced a variety of unusual abnormalities that were not apparent in the neonates, indicating that postnatal testing is necessary to determine the full teratogenic potential of some compounds. Mice exposed prenatally to cytosine arabinoside became hydrocephalic and 30% of them lacked lower incisors. Nitrofen caused hydrocephaly, the age of eye-opening was delayed, a few of the mice had no eyes, and most of the mice lacked Harderian glands. Eighteen of the 41 treatments caused mortality of 15%, or greater, by day 3, and four of these treatments resulted in additional mortality past the neonatal period. No compound caused a decrease in viability after the neonatal period without also reducing days 1 or 3 litter sizes, validating the use of this measurement in the CKA. Cytosine arabinoside was administered later in gestation than the CKA dosing regime and caused a marginally significant increase in mortality near birth but killed over 50% of the pups after weaning. Altering the duration or period of exposure in the CKA may necessitate a longer postnatal evaluation than presently recommended. Neonatal weight, the second parameter used in the CKA to prioritize chemicals for additional testing, appears to be less useful than viability. It was a poor predictor of subsequent growth, some early weight effects persisted, while most of those concurrent with maternal weight reductions were transient. A correlation analysis of the parameters measured in the CKA and in the present study, excluding the compounds that produce frank malformations, indicated that compounds that reduced maternal weight gain during dosing had fewer live pups and growth was transiently retarded.(ABSTRACT TRUNCATED AT 400 WORDS)

Nitrofen: a review and perspective

With the exception of occasional reports of skin irritation, 20 years of commercial nitrofen use has not produced indications of toxicity in man. In mature non-pregnant laboratory animals nitrofen is only slightly toxic after acute oral, dermal, or respiratory exposures, and it is not a sensitizer. However, absorption through skin occurs rapidly from solvent-based formulations. Chronic administration in the diet at doses of 20 mg/kg body wt/day and higher produced liver toxicity in mice, rats, and dogs with liver tumors developing in mice at dose levels at 470 mg/kg/day. In addition to liver tumors in mice, the National Cancer Institute's Carcinogen Bioassay Program also found a dose-related incidence of pancreatic tumors in females of 1 of 2 strains of rat after lifetime feeding at levels at and above 65 mg/kg/day. Single and repeated doses given during pregnancy to rats and mice produce neonatal lethality accompanied by signs of impaired breathing, diaphragmatic hernias, heart anomalies, hydronephrosis, and apparent eye anomalies which are due to effects on the Harderian gland. These anomalies were produced by both oral and dermal doses, but did not occur in the rabbit or when dosing was restricted to the male parent only. Neonatal deaths appear after repeated maternal doses of 3 mg/kg/day and higher; the overall no observed effect level for effects in the offspring was 0.17 mg/kg/day. Based on a 10(-6) level of tumorigenic risk the acceptable average daily intake for man is 1 microgram/kg/day; pregnant women should not be exposed to more than 1.7 micrograms/kg in any single 24-h period.