90-DAY FEEDING AND ONE-GENERATION REPRODUCTION STUDY IN CRL-CD BR RATS WITH 17-BETA-ESTRADIOL

Over the past several years, there has been increasing concern that ch emicals and pesticides found in the environment may mimic endogenous e strogens, potentially producing adverse effects in wildlife and human populations. Because estrogenicity is one of the primary concerns, a 9 0-day/one-generation reproduction study with 17 beta-estradiol was des igned to set dose levels for future multigenerational reproduction and combined chronic toxicity/oncogenicity studies. The purpose of these studies is to evaluate the significance of a range of responses as wel l as to provide benchmark data for a risk assessment for chemicals wit h estrogen-like activities. This 90-day/one-generation reproduction st udy was conducted in male and female Crl:CD BR rats using dietary conc entrations of 0, 0.05, 2.5, 10, and 50 ppm 17 beta-estradiol. Endpoint s were chosen in order to evaluate both subchronic and reproductive to xicity. In addition, several mechanistic/biochemical endpoints were ev aluated for their usefulness in follow-up studies. In the P-1 generati on, dietary administration of 2.5, 10, and 50 ppm 17 beta-estradiol pr oduced dose-dependent decreases in body weight, body weight gain, food consumption, and food efficiency. At 10 and 50 ppm 17 beta-estradiol, minimal to mild nonregenerative anemia, lymphopenia, decreased serum cholesterol (50 ppm only), and altered splenic lymphocyte subtypes wer e also observed in the P-1 generation. Additionally, at these concentr ations, there were changes in the weights of several organs. Evidence of ovarian malfunction, characterized by reduced numbers of corpora lu tea and large antral follicles, was observed at 2.5 ppm 17 beta-estrad iol and above. Other pathologic changes in males and females fed 10 an d 50 ppm 17 beta-estradiol included centrilobular hepatocellular hyper trophy; diffuse hyperplasia of the pituitary gland; feminization of th e male mammary glands; mammary gland hyperplasia in females; increased number of cystic follicles in the ovary; hypertrophy of the endometri um and endometrial glands in the uterus; degeneration of seminiferous epithelium; and atrophy of the testes and the accessory sex glands. In the reproduction portion of this study, rats fed 10 or 50 ppm 17 beta -estradiol did not produce litters. While there was no evidence that t he 50 ppm treated rats mated, 33.3% of the rats fed 10 ppm mated but d id not produce litters. No effects on mating and fertility indices wer e observed in rats fed 0.05 and 2.5 ppm 17 beta-estradiol. Pup weights at birth were statistically decreased relative to control in the grou ps fed 0.05 and 2.5 ppm 17 beta-estradiol. Weights of the rats in the 0.05 ppm group recovered by postnatal day 4 and remained similar to co ntrol throughout the remainder of the study. The mean gestation length of the 0.05 ppm group was slightly, albeit not statistically signific antly, shorter (0.5 days) than that of the control group, which may ha ve contributed to the decrease in birth weight of the 0.05 ppm group. In contrast, the weights of the F-1 generation rats fed 2.5 ppm 17 bet a-estradiol remained decreased relative to the control group throughou t the study. Parental administration of 17 beta-estradiol did not alte r anogenital distance in male or female pups. The onset of sexual matu ration, as measured by day of preputial separation in males and day of vaginal opening in females, was delayed in male rats fed 2.5 ppm (by 8.2 days) and was hastened in female rats fed 0.05 and 2.5 ppm (by 1.6 and 8.8 days, respectively). The age at vaginal opening ranged from 2 6 to 37, 26 to 35, and 21 to 25 days for rats fed 0, 0.05, and 2.5 ppm 17 beta-estradiol, respectively. Hence, the range of age at vaginal o pening was similar between the control and 0.05 ppm group. The organ w eight and pathologic alterations observed in the adult F-1 generation rats were similar to those observed in the P-1 generation rats. Howeve r, in some instances the observed effects, such as histopathological f indings in the female reproductive organs, were more severe in the F-1 generation than in the P-1 generation. Apparent differences in sensit ivity between the P-1 and F-1 generations may be explained by the incr eased daily intake of 17 beta-estradiol by the young F-1 generation ra ts, in utero exposure, or a combination of both. Dietary administratio n of 10 and 50 ppm 17 beta-estradiol clearly exceeded a maximum tolera ted dose. Future studies are needed to define the dose-response curve at dietary concentrations below 10 ppm. (C) 1998 Society of Toxicology .