Two-generation reproduction toxicity study in rats with 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDT)

DDT, an organochlorine pesticide, has been cited as a representative chemical suspected of having endocrine disrupting effects. In this study, the potential endocrine disrupting activities of p,p'-DDT, a major component of DDT, were investigated in rats in a 2-generation reproduction toxicity study in accordance with the most current test guidelines of the Ministry of Agriculture, Forestry and Fisheries in Japan, Organization for Economic Cooperation and Development (OECD) and United States Environmental Protection Agency (USEPA) with some modifications and additions. p,p'-DDT was given to parental rats at dietary levels of 0, 5, 50 or 350 ppm. Systemic toxicities in the parental animals consisted of tremors and subsequent deaths (females only) and/or pathological alterations of the liver (both sexes of animals) of the 2 higher dose groups. Reproductive and postnatal developmental toxicities were not evident up to the highest dose level except for the decreased pup viability index on postnatal day 21 in the 350 ppm group. Changes in serum estradiol and progesterone levels and/or a delay in male sexual maturation were noted in the 2 higher dose groups in a dose-dependent fashion, suggesting alterations of endogenous endocrine functions. However, these changes never resulted in substantial reproductive disorders.

Pathogenetic transition in the morphology of abnormal sperm in the testes and the caput, corpus, and cauda epididymides of male rats after treatment with 4,6-dinitro-o-cresol

In order to elucidate the pathogenesis of tailless sperm, 4,6-dinitro-o-cresol (DNOC) was administered to Jcl:SD male rats at daily oral doses of 0, 10 or 15mg/kg for 5 days. Sperm were collected from the caput, corpus, and cauda epididymides on days 1, 7 and 14 after the last dosing (D1, D7 and D14, respectively), counted and examined morphologically by phase-contrast and scanning electron microscopy. The incidence of abnormal sperm was significantly increased in the DNOC 15mg/kg group. On D1, peeled sperm (loss of mitochondrial sheath at the proximal end of the middle piece) was frequently observed in the caput epididymides, whereas sperm in the corpus and cauda epididymides had normal morphology. Distribution of the peeled sperm changed as time passed and the corpus epididymides showed a peak incidence on D7. On D14, the highest incidence of abnormal sperm was observed in the cauda epididymides, where the major abnormality was tailless. Similar effects were also found in the 10mg/kg group but were less potent. Transmission electron microscopy of testicular sperm on D1 revealed the presence of elongated spermatids that lacked the mitochondrial sheath at the proximal end of the middle piece, although the round and elongating spermatids looked normal. These results suggest that DNOC exposure of male rats primarily causes partial loss of the mitochondrial sheath in the testicular elongated spermatids, and that the affected sperm become tailless by D14 after reaching the cauda epididymides.

Reassessment of ecotoxicities of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane in Japanese quail under the OECD draft new avian one-generation reproduction test guideline

Ecotoxicological hazards of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDT) were investigated by a one-generation reproduction study using Japanese quail (Coturnix coturnix japonica) under an Organization for Economic Co-operation and Development (OECD) draft new test guideline 206 following acute and subchronic toxicity studies. In the subchronic feeding toxicity study, tremors, convulsions, and deaths were observed with a clear sex difference, males being more susceptible than females. The estimated total number of sperm tended to decrease in a dose-dependent manner at the end of 6-week treatment. In the one-generation reproduction study conducted at dose levels of 0, 6, 30, and 150 ppm, the estimated total number of sperm tended to decrease in a dose-dependent manner with a significant difference at 150 ppm. Tremors were observed in the majority of hatchlings in the 150 ppm group and at lower incidences in the 30 ppm group. Significantly high mortality rate in chicks persisted from treatment week 3-6 in the 150 ppm group and at treatment weeks 4 and 5 in the 30 ppm group. Despite of these severe adverse effects of p,p'-DDT on hatchlings and chicks, fertilization, egg laying, eggshell thickness or embryonic development was hardly impaired by p,p'-DDT or its metabolites. From these results, it appears that the OECD draft new avian one-generation reproduction test guideline is effective for ecological hazard assessment of chemicals.

A TWO-GENERATION REPRODUCTIVE TOXICITY STUDY OF 2,4-DICHLOROPHENOL IN RATS

A two-generation reproductive toxicity study was conducted with 2,4-dichlorophenol (2,4-DCP), an agent suspected of exerting endocrine disrupting effects. Wistar-Hannover rats, 24/sex/group, were given diet containing 2,4-DCP at dose levels of 0, 500, 2000 or 8000 ppm to examine the potential effects of the test substance on parental animals and their offspring over 2 successive generations. Neither clear systemic nor reproductive toxicity of 2,4-DCP was apparent in the 500 ppm group. In the 2000 ppm group, mean body weight gain and food consumption of females were lowered significantly during the treatment period. Effects on body weights and food consumption were more serious in the 8000 ppm group, both males and females being significantly affected. Reproductive effects of the test substance were also observed in the 2000 and 8000 ppm groups dose-dependently. Observations included significantly increased uterine weights of F1 and/or F2 female weanlings and reduced numbers of implantation sites and live births of F1 parental females. These results suggest that 2,4-DCP has weak reproductive toxicity, possibly based on endocrine activity. However, the basic mechanisms for apparent estrogenic effects of 2,4-DCP remain to be elucidated.

A two-generation reproduction study to assess the effects of cows' milk on reproductive development in male and female rats

OBJECTIVE

To examine whether the considerable quantities of increased female sex hormone levels found in modern milk as a result of modern dairy farming practices are safe for human consumption.

DESIGN

Males and females of the P generation were maintained on a diet containing milk for 10 weeks before mating. Exposure to milk was continued up to the end of weaning of the F2b offspring.

SETTING

Two-generation reproduction study.

ANIMAL(S)

Male and female Wistar Galas rats.

INTERVENTION(S)

P- and F1-generation rats were mated.

MAIN OUTCOME MEASURE(S)

Fertility, fecundity, and morphology and function of reproductive organs.

RESULT(S)

Although milk had growth-promoting effects in both parents and offspring, it caused no impairments in fertility, fecundity, or reproductive organ development in either generation. However, a whole litter from a dam of the P generation was born dead, three litters in total had a pup with skeletal abnormalities, and the AGD of F2a female pups was reduced. These events occurred only in the milk-treated rats. It is unknown whether these issues had any relevance to milk or only happened by chance.

CONCLUSION(S)

Further study is required to determine whether milk from pregnant cows is completely free from adverse effects on reproductive health.

Comparative studies on the spermatotoxic effects of dinoseb and its structurally related chemicals

Three dinitrophenolic compounds, dinoseb (DNBP; 7.5 mg/kg b.w.), 4,6-dinitro-o-cresol (DNOC; 4, 7.5, 15 mg/kg b.w.), and 2,4-dinitrophenol (DNP; 7.5, 15, 30 mg/kg b.w.) were administered orally to sexually matured Jcl:SD male rats for 5 consecutive days. Half of the males in each group were necropsied at 3 (D3) and 14 (D14) days after the last dosing, respectively, and examined for the effects of dinitrophenols on spermato-/spermiogenesis. DNBP (7.5 mg/kg), DNOC (15 mg/kg), and DNP (30 mg/kg) caused 1, 5, and 0 deaths, respectively, as well as a decreased body weights during the treatment. Although examinations on D3 revealed no treatment-related alterations, DNBP and DNOC resulted in reduced sperm motility and increased incidence of tailless sperm in the cauda epididymis on D14. DNP also caused slightly increased incidence of tailless sperm on D14. These results demonstrate that DNBP, DNOC, and DNP manifest similar spermatotoxic effects at or around a lethal dose in rats.

Effects of p27Kip1 on cell cycle status and viability in A549 lung adenocarcinoma cells

p27Kip1 is a cyclin-dependent kinase inhibitor, it negatively regulates G1 progression and is reported to modulate apoptosis. Phosphorylation of this protein is thought to regulate its intracellular localisation and affect its stability. The aim of this study was to regulate p27Kip1 expression levels, and to examine how this protein affects cell cycle status and modulates viability in A549 lung adenocarcinoma cells. In addition, the association between phosphorylation status of p27Kip1 and its intracellular localisation was investigated, using expression vectors with cDNA of p27Kip1 or mutants in which the phosphorylation sites had been mutated. Although overexpression of p27Kip1 reduced cell cycle progression, its removal did not change cell cycle status. Modest induction of p27Kip1 rescued adenovector-induced apoptosis and its removal with short interfering RNA increased spontaneous cell death. It was also observed that p27Kip1 localised mainly in the cytoplasm, and forced expression of p27Kip1 cDNA with the substitution of serine (S) 10, threonine (T) 157 and T198 to glutamate (phosphor-mimetic) induced its cytoplasmic localisation. In conclusion, p27Kip1, when expressed physiologically, exists mainly in the cytoplasm, has little effect on cell cycle status and contributes viability in A549 lung adenocarcinoma cells. It was also surmised that intracellular localisation of p27Kip1 dominates its function and that its localisation was partly determined by its phosphorylation.

Effects of dinoseb, 4,6-dinitro-o-cresol, and 2,4-dinitrophenol on rat Sertoli-germ cell co-cultures

The effects of dinoseb (DNBP), a known testicular toxicant in the rat, on germ cells were investigated in Sertoli-germ cell co-cultures. Two DNBP-related dinitrophenolic compounds, 4,6-dinitro-o-cresol (DNOC) and 2,4-dinitrophenol (DNP), were also examined, as testicular toxicity of these compounds had not been elucidated. Cultures were exposed to each compound (10(-7)-10(-4)M) for 24h and examined for the number and viability of detached cells and morphologic alterations under a light microscope. DNBP significantly increased the number of detached cells (10(-5) and 10(-4)M) and suppressed their viability (10(-6)-10(-4)M). Morphologic observations revealed degenerative alterations in the germ cells and Sertoli cells. Similar effects as observed after DNBP exposure were evident at 10(-4)M DNOC and 10(-4)M DNP. These results demonstrate that DNBP, DNOC, and DNP have in vitro toxicity to these cell populations at high concentration, and suggest the possibility that DNOC and DNP also cause testicular damage in experimental animals and humans.

Curly vibrissae, a new mutation in the Wistar-derived rat

A new mutation was identified in the PD (Preaxial Duplication) strain of rats, the main manifestations of which were curly and sparse vibrissae with retarded outer hair growth. As the main characteristic of this mutant rat is abnormally curled appearance of the vibrissae, "curly vibrissae" is proposed as the name of this mutant gene, and "cv" as its symbol. Genetic analyses reveal that the mutant characteristics are inherited as autosomal recessive traits and the cv gene is independent from the pd gene that carried by the original PD colony. The cv/cv homozygous rats have a small number of short and/or curly vibrissae around the nose. The vibrissae on the cheek and/or above the eyes are also short and curled; however, no vibrissa appears on the lower mandible. Although hair growth seems to be retarded, the outer hairs showed nearly normal length by 10 weeks of age. The outer hairs of matured cv/cv rats appear silky and translucent. The adult mutant rats often exhibit loss of hair on the head and/or back. Lactating females usually lose their abdominal hair. Both sexes of cv/cv homozygotes have normal reproductive ability. No internal malformations accompany vibrissa and hair abnormalities.

Observation of X-Y chromosomal configuration in spermatocytes of infertile PD strain male rats

PD strain male rats that carry an autosomal recessive gene, preaxial duplication (gene symbol: pd), are sterile in the homozygous condition (pd/pd) due to a spermatogenic breakdown in the process of spermatogenesis at the spermatocyte and/or spermatid stage(s), although heterozygotes (pd/+) are normal. In this study, pd/pd males were examined for the presence of abnormal association of the sex chromosomes that might lead to spermatogenic breakdown. Light and electron microscopic observations of the chromosomes at meiotic prophase and metaphase in primary spermatocytes revealed several types of abnormal X-Y association and configurations in pd/pd males. However, the incidences of the abnormal configuration were comparable to those in pd/+ males. These results suggest that abnormal X-Y chromosome association in the germ cells is not a significant cause of spermatogenic breakdown in pd/pd males.

Thymic atrophy induced by methoxychlor in rat pups

The effect of Methoxychlor (MXC) on the thymus was examined in rat pups that were delivered from dams receiving MXC at a dietary concentration of 0 or 1500 ppm for a period from pregnancy to lactation. The pups of both sexes were euthanized on postnatal days (PNDs) 7, 14, and 21. Histologically, the thymus showed marked depletion of cortical lymphocytes on PND 7 and also had an increase in lymphophagocytosis in the cortical area on PNDs 14 and 21. Morphometrical analysis disclosed that both cortex and medulla of the thymus from treated pups were reduced in size, but the reduction was more evident in the cortex. A significant increase in transferase-mediated dUTP nick end labeling-positive cells was detected in the cortex area, corresponding to the presence of lymphophagocytosis. Flow cytometric analysis revealed a significant decrease in the double positive (CD3(int)CD4(+)CD8(+)) immature cells on PND 21. These results have suggested that MXC may impair maturation of thymic lymphocytes in rat pups, which results in enhancement of apoptosis leading to thymic atrophy during the postnatal period.

Historical control data on reproductive abilities and incidences of spontaneous fetal malformations in Wistar Hannover GALAS rats

Wistar Hannover rats, which have recently been introduced into Japan, are expected to be used in reproductive and developmental toxicity studies, yet the accumulation of background data is insufficient. This paper describes our historical data on the reproductive ability of this strain of rat. Three lots of sexually matured females (40 each) were received from CLEA JAPAN, Inc. with males of the same strain (30 or 36 each) and mated. A total of 47 dams were killed on gestation day 20 to examine their fetuses. The remaining 71 pregnant females were allowed to deliver spontaneously and observed for common reproductive parameters. The mating and fertility indices of females were both 99.2%. Overall mean numbers of implants and live fetuses at cesarean sectioning were 12.5 and 11.5, respectively. Fetal resorptions and deaths occurred at an incidence of 8.6%. Morphological examinations of fetuses revealed low incidences of spontaneous malformations (each one case of double aortic arch and absent cervical vertebral arch) and a variety of common variations. The followings are overall means of major reproductive parameters obtained from females with live birth: no. of implants, 12.5; no. of pups delivered, 11.8; viability index of pups at birth, 99.8%; and days of age at sexual maturation (vaginal opening and preputial separation), 30.3 and 42.8, respectively. Our present observations confirmed a minimal deviation among 3 lots of animals in terms of reproductive abilities. These results suggest that this strain of rat can be used in reproductive and developmental toxicity studies, although the sensitivity to toxicants remains to be elucidated.

Relationship between swallowing function and gas exchange during day and night in patients with obstructive sleep apnea syndrome

Patients with obstructive sleep apnea syndrome (OSAS) are likely to exhibit an impaired swallowing reflex. However, mechanisms of disturbed swallowing reflex have not been determined. Because the upper-airway function is inhibited by hypoxia and hypercapnia, we examined the relationship between the swallowing function and gas exchange during day and night in patients with OSAS. Twenty-four patients with OSAS and 24 age-matched controls were studied. OSAS was diagnosed from overnight polysomnography. The swallowing reflex was judged by the latent time (LT) for swallowing following bolus injection of distilled water at the suprapharynx, the inspiratory suppression time (IST) from swallowing termination to the next onset of inspiration, and the threshold for evoking the swallowing response in terms of a volume of water (TV). Whereas the LT values are positively correlated with PaCO2 but not with PaO2 during the day, the values of IST and TV were not associated with daytime PaCO2 or PaO2. Nocturnal nadir SaO2 was correlated with LT, IST, and TV. These results indicate that oxyhemoglobin desaturation and hypercapnia may be associated with one of the mechanisms of the impaired swallowing function in patients with OSAS.

An in vitro screening system for characterizing the cleft palate-inducing potential of chemicals and underlying mechanisms

An in vitro organ culture system with developing mouse palates was improved to characterize the cleft palate (CP)-inducing potential of chemicals and underlying mechanisms. Palatal explants collected from gestation day 12 mouse fetuses were cultured with various concentrations of teratogens and examined for palatal development after 48 and 72 h of culture to assess effects of the chemicals on growth and/or fusion of palatal shelves. When the explants were exposed to diphenylhydantoin or 5-fluorouracil, palatal growth was inhibited in a concentration-dependent manner at 48 h. Suppression of the expression of proliferative cell nuclear antigen revealed poor cell proliferation. At 72 h, the incidence of explants with CP was significantly increased in the high-dose groups, suggesting that CP induction is mainly attributable to inhibition of palatal growth. By contrast, retinoic acid and hydrocortisone significantly lowered the rates of fused palates at 72 h in all treated groups, while they exhibited no effects on palatal growth at 48 h even at the highest concentration. Because no apoptosis was found in the epithelial cells at the tip of these palates, these chemicals are suggested to inhibit palatal fusion process by preventing apoptosis.