Jin Ando

Subcutaneous treatment of p-tert-octylphenol exerts estrogenic activity on the female reproductive tract in normal cycling rats of two different strains

Effects of p-tert-octylphenol (OP), an endocrine disrupting chemical (EDC), on the female reproductive tract of normal cycling Fischer 344 (F344) and Donryu rats were investigated. OP was subcutaneously injected at concentrations of 12.5, 25, 50 or 100 mg/kg for 28 days. The most notable changes were the disappearance of normal cyclicity in the 50 mg/kg or more OP-treated groups of both the strains, and the appearance of persistent estrus (PE) evident on examination of vaginal smears in the 100 mg/kg groups of both the strains, the effects being time- and dose-dependent. In PE rats of both the strains, the uterine morphology deviated from the normal for each estrous stage of the cycling rats, and proliferation in the endometrium was slightly increased. The data for uterine weights, luminal epithelial cell-heights and/or numbers of epithelial cells in the endometrium demonstrated equivocal alteration. In both the strains, the serum 17beta-estradiol (E2) levels were decreased with 50 mg/kg of OP or more. Serum concentrations of the administrated chemical were dose and duration-dependently increased in all the treated groups of both the strains. The results demonstrate that subcutaneous administration of OP at doses of 50 mg/kg or more exerts time- and dose-dependent estrogenic activity on the reproductive tract of normal cycling female Donryu and F344 rats, indicating similar qualitative sensitivity to the effects in both the strains. Vaginal cytology may be the most sensitive endpoint for the detection of estrogenic activity of potential EDCs using adult cycling rats.

Dose- and treatment duration-related effects of p-tert-octylphenol on female rats.

We conducted a study to investigate the relation between estrogenic effects of p-tert-octylphenol (OP) and serum concentration as well as treatment duration. Adult ovariectomized rats were given daily subcutaneous injections of OP for 2 and 14 days. 17beta-Estradiol was also administrated at a dose of 5 microg/kg. OP was detected in serum at doses of 25 mg/kg and above for 2 days and with multiple doses (14 days) of 12.5 mg/kg. Uterine weights and luminal epithelial height were increased although the effects were weak compared to 17beta-estradiol. Estrous conversion of the vaginal smear was detected only in 14-day-treated animals. OP-treatment for 2 days caused a dose-related increase in proliferation of uterine luminal, glandular, and stromal cells and vaginal epithelial cells. From the 14-day experiment, the minimum estrogenic dose level of OP was concluded to be 25 mg/kg/day and the serum level at the dose was determined to be about 80 ng/ml. These findings demonstrated that OP exerts estrogenic activity in the female reproductive tract of ovariectomized rats only at high levels of exposure and that the effects are fundamentally related to serum OP levels.

Transplacental administration of diethylstilbestrol (DES) causes lesions in female reproductive organs of Donryu rats, including endometrial neoplasia

The effects of transplacental administration of diethylstilbestrol (DES) on female reproductive organs were investigated using Donryu rats. The animals were given subcutaneous injections of DES dissolved in olive oil at doses of 0.01 or 0.1 mg/kg on days 17 and 19 of gestation. In female offspring, clinical signs, body weights and estrous cycles were continuously assessed until all survivors were killed at month 18. A low mean litter size and shortening of period of pregnancy were recognized in the 0.1 mg/kg group. Disorder and/or suspension of the estrous cycle (so called persistent estrus) also appeared very early in the 0.1 mg/kg group. Macroscopically, the incidences of hypoplasia of the oviduct, cystic dilatation of the uterus and small size of the uterine cervix were higher in the 0.1 mg/kg group than those in the control group. Histologically, in the ovary, the incidence and degree of atrophy were increased in both 0.01 and 0.1 mg/kg groups. In the uterus, total incidences of endometrial hyperplasias were about the same in all groups. However, endometrial adenocarcinomas were dose-dependently increased in the treated groups, the incidence in the 0.1 mg/kg group being significant, compared to that in the control. In the vagina, mucification was more prominent in the treated animals, especially at the higher dose, but no tumors were observed. The present results indicate that prenatal exposure to DES can produce uterine adenocarcinomas in rats, as reported earlier for mice, although its carcinogenic activity is not so strong. Increase of endometrial adenocarcinoma incidence might depend on hormonal imbalance resulting from the ovarian atrophy due to transplacental treatment of DES.

Possible mechanisms underlying mammary carcinogenesis in female Wistar rats by nitrofurazone

Mechanisms underlying mammary carcinogenesis in female rat given nitrofurazone (NF) were examined. Experiment I: female Wistar rats were divided into three groups, and given diets containing 0, 500 or 1000 ppm NF for 5 weeks. At terminal sacrifice, body and uterus weights were the same in all groups, although ovary weights in NF-treated animals were significantly higher than in control animals, the increase being dose-dependent. Serum prolactin (PRL) concentrations in NF-treated groups at 17:00 h on the day of proestrus were also dose-dependently higher than that in control group. Experiment II: a two-stage rat mammary carcinogenesis protocol was performed. Rats were divided into four groups, Groups 2 and 4 being treated by 9,10-dimethyl-1,2-benzanthracene (DMBA) at 7-weeks-old. Groups 3 and 4 were given diets containing 1000 ppm of NF between 8 and 27 weeks of age, when all surviving rats were autopsied. DMBA-treated animals demonstrated mammary tumors at high incidences, 91.1 and 90.5%, respectively, in Groups 2 and 4, no tumor development being observed without the initial carcinogen exposure (Groups 1 and 3). The mean tumor weights and the mean numbers of tumors per tumor-bearing rats in Group 4 were increased as compared with Group 2, albeit not significantly. Serum PRL (proestrus day at 17:00 h) and progesterone (PG) (diestrus day at 10:00 h) concentrations in NF-treated animals (Groups 3 and 4) were significantly higher than those in untreated rats (Groups 1 and 2). These results suggest that increases of serum PRL and PG concentrations by NF may be the most important factors regarding its promotion of mammary tumor growth and/or enhancement of mammary carcinogenesis in female rats.

Uterine Adenocarcinoma in N-Ethyl-N-nitro-N-nitrosoguanidine-treated Rats with High-dose Exposure to p-tert-Octylphenol during Adulthood

Since many risk factors are associated with the development of uterine adenocarcinomas in humans, the etiology is unclear in most cases, although it has been pointed out that estrogen may play essential roles. To clarify the effects of exposure to p‐tert‐octylphenol (OP), an environmental xenoestrogen, on uterine carcinogenesis, adult Donryu rats were initiated with a single intrauterine treatment of N‐ethyl‐N‐nitro‐N‐nitrosoguanidine (ENNG) at 11 weeks of age and exposed thereafter to 100 mg/kg OP by s.c. injection until 15 months of age. Adult ovariectomized (OVX) rats were also treated in a similar way. OP had no effect on occurrence of persistent estrus in middle age, although uterotrophic effects were obvious in OVX rats. At the termination, development of uterine adenocarcinomas was significantly increased in animals exposed to OP during adulthood. No tumors, but a few focal hyperplasias, developed in OVX rats. These findings suggest that OP has tumor‐promoting effects on ENNG‐treated endometrium of rats, possibly due to direct action on the uterus, as indicated by the uterotrophic effect when a high dose of OP was given. The results provide clues to the mechanisms of influence of hormonal disrupters on uterine carcinogenesis.

Thirteen-week subchronic toxicity study of thiamphenicol in F344 rats.

A 13-week subchronic toxicity study of thiamphenicol (TAP) was performed in F344 rats. The minimum lethal dose was estimated to be greater than 10 g/kg body weight, when a single dose of 4-10 g/kg of TAP was given orally. In the subchronic toxicity study, groups of 12 F344 rats of each sex were given solutions containing 0 (control), 125, 250 and 500 ppm of TAP as their drinking water ad libitum for 13 weeks. Body weight gain was significantly suppressed in both sexes of the 250 and 500 ppm groups. Slight suppression of erythropoiesis was observed in the highest-dose group along with slightly reduced spermatogenesis in the testes of the males. In addition, spermatogranulomas were found in the epididymis of both middle- and highest-dose groups. The no observed adverse effect level (NOAEL) was concluded to be 125 ppm (daily doses of 9.0 mg/kg in males and 11.6 mg/kg in females). From the above described results, doses of 250 and 125 ppm were selected as appropriate for a 2-year carcinogenicity study.

Time-dependent promotion activity of 17β-estradiol on uterine carcinogenesis in mice initiated with N-ethyl-N-nitrosourea

The time-dependent promotion activity of 17beta-estradiol (E2) by initiation with N-ethyl-N-nitrosourea (ENU) on induction of mouse uterine endometrial proliferative lesions was examined. Illumination-induced persistent estrous female CD-1 mice were divided into five groups at 9 weeks of age. At 10 weeks of age, mice in all groups (n=25) were given a single intra-uterine administration of ENU (50 mg/kg), dissolved in polyethylene glycol. Animals in Groups 2 to 5 were then implanted s.c. with an E2 pellet at 9, 11, 14 and 17 weeks of age. The implants were left in place for 8 weeks and then taken out. At the termination of the experiment (week 15 after the ENU-treatment), all surviving mice were killed and the development of uterine proliferative lesions were assessed. All groups demonstrated endometrial hyperplasias and adenocarcinomas and the incidences of the latter in ENU plus E2 treated animals (Groups 2 to 5; 36, 48, 35 and 36%, respectively) were significantly higher compared to 8% for Group 1, without any variation with the age at E2 treatment. However, the incidences of adenocarcinomas plus severe hyperplasias increased from Groups 1 to 5 (28, 40, 56; P<0.05, 61; P<0.05 and 80%; P<0.01, respectively), indicating that promotion effects of E2 on induction of uterine proliferative lesions in the uterine endometrium become more pronounced with the interval after ENU initiation.

Lack of carcinogenicity of thiamphenicol in F344 rats

The carcinogenicity of thiamphenicol (TAP), an antibiotic drug, was examined in Fischer 344 rats of both sexes. TAP was given ad lib. in drinking water at levels of 0 (control), 125 or 250 ppm to groups of 50 male and 50 female rats for 2 yr. The treatment did not affect mortality and no toxic lesions were specifically induced. Furthermore, the incidence of tumours in the treated groups did not show any significant dose-related increase as compared with the control group. The results thus indicate that TAP is neither toxic nor carcinogenic, for any organs or tissues of F344 rats when given continuously at levels of 125 or 250 ppm in drinking water for 2 yr.