8 alpha-Estra-1,3,5(10)-triene-1,3, 17 beta-triol as a special type of estrogen having a high vaginotrophic activity and a low uterotrophic activity in castrated mice

Environmentally relevant xenoestrogen tissue concentrations correlated to biological responses in mice

The effects of xenoestrogens have been extensively studied in rodents, generally under single, high-dose conditions. Using a continuous-release, low-dose system in ovariectomized mice, we correlated the estrogenic end points of uterine epithelial height (UEH) and vaginal epithelial thickness (VET) with concentrations of two organochlorine pesticide isomers in fat and blood. Silastic capsules containing a range of doses of either ss-hexachlorocyclohexane (ss-HCH) or o, p'-dichlorodiphenyltrichloroethane (o,p'-DDT) were implanted subcutaneously, and animals were killed after 1 week. Average blood levels achieved by the various doses were 4.2-620 ng/mL for o,p'-DDT and 5.0-300 ng/mL for ss-HCH. Fat concentrations of o,p'-DDT and ss-HCH correlated linearly to blood levels (o,p'-DDT, r(2) = 0.94; ss-HCH, r(2) = 0.83). Fat concentrations (nanograms per gram of tissue) were higher than blood concentrations (nanograms per milliliter) by 90 +/- 5- and 120 +/- 9-fold (mean +/- SE) for o, p'-DDT and ss-HCH, respectively. The VET ranged from 12 +/- 0.9 microm in controls to 114 +/- 8 microm in treated animals, and was correlated to blood levels of either treatment compound. The UEH ranged from an average of 7.7 +/- 0.3 microm in controls to 26 +/- 2 microm in high-dose o,p'-DDT-treated animals. The UEH was also correlated with ss-HCH concentration, but it plateaued at approximately 11 microm at the highest doses. The lowest blood concentrations that produced statistically significant increases in VET or UEH were 18 +/- 2 ng/mL o,p'-DDT and 42 +/- 4 ng/mL ss-HCH. These values are within the same order of magnitude of blood concentrations found in some human subjects from the general population, suggesting that human blood concentrations of these organochlorines may reach estrogenic levels.

A morphologist's approach to the vagina--age-related changes and estrogen sensitivity

This paper reviews basic facts on vagina histology and ultrastructure with respect to passage of different substances and drugs through the epithelium. Particular interest is devoted to the action mechanism of topically-applied vaginal estrogen, its binding to receptors in different vaginal cell types, and possible local metabolic routes. Differences in estrogen sensitivity between uterus and vagina are discussed as well as the background for the high vaginal sensitivity.

Effects of danazol and medroxyprogesterone acetate on estrogen-(estradiol and estriol) specific binding sites in rabbit uterus

In rabbit uterus, the presence of separate specific binding sites for not only estradiol but also estriol has been proposed. These sites may be correlated with an antiestradiol effect. Therefore, this study was designed to investigate the effect of antiestrogenic agents such as danazol and medroxyprogesterone acetate (MPA), especially on the estriol binding sites. Danazol and MPA in combination with estradiol were administered subcutaneously to immature female rabbits daily for 10 days, and resulted in a significant (p < 0.05) decrease in uterine weight and estradiol binding sites in the uterus. Treatment with MPA significantly (p < 0.05) decreased the level of estriol binding sites, but treatment with danazol resulted in this to a minimal extent in the uterus primed by estradiol. MPA did not bind to estradiol and estriol binding sites, while danazol at a high concentration bound to estriol binding sites with some affinity, but not to estradiol binding sites in the uterine cytosol of estrogen-primed rabbits. These results suggest that within the antiproliferative effect of danazol and MPA (an antiestrogenic action on estrogen-stimulated uterine growth) there are likely to be specific differences between some of the possible mechanisms of danazol and MPA in their action at the estriol binding site.

Binding of estradiol-17β and estriol in cytosolic and nuclear fractions from urogenital tissues

This report describes the measurement and partial characterization of the specific binding of estradiol (E2) and estriol (E3) in the cytosols and nuclear fractions from uterus, vagina, urethra and urinary bladder of the rabbit. Fractions from uterine and vaginal tissues showed the highest binding with both E2 and E3 approx 300 fmol/mg protein. The levels of specifically bound E3 were about 70% of the corresponding values for E2. In the sedimentation analysis the cytosolic receptors for both E2 and E3 exhibited 2 major forms, 3 S and 8 S, in addition to the heavy aggregates. Sephacryl S-200 chromatography showed major and minor components corresponding to mol. wt of 250.000 and 20.000-40.000 respectively. No noteworthy differences in the cytosolic receptors from different tissues could be observed in the above analyses. Whereas the uterine nuclear E2 receptor sedimented at 4.3 S the vaginal receptor distributed in two peaks, 2.5 S and 4.3 S. The receptor from both urethra and urinary bladder sedimented at 2.5 S. Nuclear E3 receptor, however, showed a major peak at 3.5 S in all cases. Some differences in tissue nuclear receptor were also observed in their chromatographic behaviour. The results confirm the existence of estrogen receptor in both urethra and urinary bladder, and the data of the limited physiochemical analysis indicate that the receptors in these tissues are essentially similar to those in the uterus or vagina.

The agonistic and antagonistic actions of estriol

Estriol is a short acting estrogen, and as such, displays both agonistic and antagonistic properties, when it is injected in saline solution. These are predictable attributes of any short acting agonist if one considers the basic pharmacology of receptor ligand binding interactions. That is, short acting hormones or drugs occupy receptor sites for protracted time periods and, although they stimulate responses, these are of short duration. However, when estriol is administered in continuous fashion the estrogen receptor is occupied for long periods of time and full estrogenic responses are observed, and there is no antagonism of estradiol action. The purpose of this paper is to review the work that leads to the above conclusion and to discuss our more recent work on the relationship between estrogen receptor binding and the stimulation of type II estrogen binding sites.