Evidence for estradiol promotion of neoplastic lesions in the rat vagina after initiation with N-methyl-N-nitrosourea

The hypothesis that estrogens are tumor promoters was tested by tumor induction in the rat vagina. Ovariectomized rats were given a single dose of N-methyl-N-nitrosourea (MNU) by vaginal instillation, followed one week later by long-term release Silastic implants containing estradiol (E2). After 16 months, a significant incidence (4/9) of benign vaginal stromal polyps was found in the MNU-E2 group, but no vaginal polyps were seen in groups given either MNU or E2 alone. A number of non-neoplastic changes were also seen and were due to E2 treatment either with or without MNU. The incidence of stromal polyps and their restriction to animals receiving the initiator-promoter regimen alone suggests that estrogens promote tumorigenesis in the rat vagina.

Uterine responses to estradiol in the neonatal rat

Although single doses of estrogens are known to be ineffective in stimulating complete uterine responses in newborn rats, repeated doses elicit toxic responses that become evident in adulthood. In this study, neonates injected daily from birth with 10 micrograms 17 beta-estradiol (E2) demonstrated significant uterine wet weight gain by day 3 and near-maximum growth (230% of control) by day 5. Elevated uterine weight can be maintained by repeated daily injections at least through day 13. Other uterine growth responses after 5 days of E2 (as percent of control) are: dry weight, 163%; DNA content, 193%; protein content, 211%; and nuclear estrogen receptor, 890%. Ornithine decarboxylase activity increased to 520% of control when measured 6 h after a single E2 injection on day 5. Histological examination of uteri from animals treated for 5 days reveals an altered stroma with evidence of circular muscle differentiation, while the lumenal epithelium, which is cuboidal in controls, becomes columnar after E2 injections. These data suggest that estrogens act in fundamentally the same manner in the neonatal uterus as in the adult uterus, although the appearance of the complete response appears to e slower in the neonate. The estrogen-induced precocious development we describe suggests that an estrogen may be involved in the normal postnatal development of uterine estrogen responsiveness. Adult toxicity, resulting from repeated neonatal estrogen dosing, may partly be a consequence of continual hormone action inducing developmentally inappropriate responses.

Failure of rotenone to interfere with 17 beta-estradiol action in the rat uterus

The involvement of rotenone in rat mammary carcinogenesis has been suggested to occur through estrogenic effects. This hypothesis was tested by determining the extent of rotenone inhibition of 17 beta-estradiol binding to the estrogen receptor and of the 17 beta-estradiol-induced uterotrophic response in ovariectomized Sprague-Dawley rats. Estradiol binding to the uterine estrogen receptor in the presence of rotenone was determined by charcoal assay and Scatchard analysis. Additionally, 17 beta-estradiol-receptor interactions were assessed on sucrose density gradients. No inhibition of binding was observed in either assay with ratios of rotenone/17 beta-estradiol in excess of 10,000. Finally, an in vivo approach was used to extend the in vitro data. Silastic capsules containing rotenone or 17 beta-estradiol were implanted in various combinations into eight groups of ovariectomized Sprague-Dawley rats (four rats/group). After five days, uteri were removed and weighed. An analysis of variance revealed that rotenone neither interfered with 17 beta-estradiol-induced uterine weight gain nor displayed any uterotrophic properties by itself. Results from these three procedures demonstrate that rotenone does not act as an estrogen or as an estrogen antagonist. Additionally, there were no other effects attributable to rotenone.

Diethylstilbestrol and estradiol binding to serum albumin and pregnancy plasma of rat and human

The equilibrium binding of diethylstilbestrol (DES) and 17 beta-estradiol (E2) to plasma proteins has been characterized. DES exhibits a 10- to 20-fold greater binding affinity index for bovine serum albumin and rat plasma than E2. As expected, E2 gave high values for binding to plasma from pregnant mice or rats, reflecting the presence of alpha-fetoprotein. DES bound to these samples as it did to bovine albumin and rat plasma. These results suggested that DES ineracts weakly with alpha-fetoprotein. This was verified by Scatchard plots of DES and E2 binding to rat and human pregnancy plasma. High affinity, low capacity binding was demonstrated with E2 but not with DES. The significantly lower binding of DES suggests that increased delivery of DES to the fetus may be at least partially responsible for the transplacental toxicity and carcinogenicity of DES.

Effects of estrogen on gene expression in the chick oviduct. Isolation and fractionation of chromatin non-histone proteins

Non-histones isolated from hen oviduct chromatin have been fractionated by a variety of methods. Chromatin was dissociated in 2 M NaC1, 5 M Urea, 0.1% beta-mercaptoethanol and 0.01 M Tris - HC1, pH 8.3, and the DNA removed by ultracentrifugation. After desalting by gel filtration the chromatin proteins were separated into three distinct fractions by stepwise elution with 0.10 M NaC1, 0.25 M Na C1 and 15% guanidine - HC1 from Bio-Rex 70 columns. Fractions I and II contain only non-histones and Fraction III contains histones plus a small amount of non-histones. Further fractionation of the non-histones was achieved by ammonium sulfate precipitation and DEAE-cellulose chromatography for Fraction I and phosphocellulose chromatography and gel filtration on Bio-Gel A-15 m for Fraction II. The histone and non-histones present in Fraction III were separated by gel filtration on Bio-Gel A-0.5 m. All fractionation methods have been used preparatively with reasonable recoveries of protein (greater than or equal to 60%). The fractions have been characterized by acrylamide gel electrophoresis. The integrity of the histones was maintained during the fractionation procedure indicating that proteolytic degradation was unlikely to have occurred. There was no selective loss of chromatin proteins during the ultracentrifugation and desalting steps and the non-histones were separated into distinct fractions with enrichment of some species not apparent prior to fractionation of the chromatin proteins.