[Lotus]

Here's the information on E2 / BO I shared sometime ago. I have also copy of the PDF. 

The interaction of estradiol-17b with mature bovine endometrial tissue, and with isolated nuclei has been studied. The hormone binds to an insoluble nuclear fraction. This fraction contains membranes and evidence is presented to show that estradiol is bound to the nuclear membrane. Incubation of isolated nuclei and microsome fractions with estradial-17b shows that the hormone binds essentially instantaneously to microsomes and nuclei. Such binding is nonsaturable up to estradiol-17b concentrations as great as 2.5 x 10m6 moles per mg of membrane protein and it is likely that this interaction is not biologically significant. A second form of binding is observed in nuclei which is of higher affinity and saturable, with 507 •t 47 sites per nucleus. This class of binding sites is found to be blocked in cattle that are maintained in artificially induced estrus by feeding with diethylstilbesterol. The high affinity binding site is present only in the mature endometrium and is absent in nuclei from the mature myometrium (the muscular tissue surrounding the endometrium in the uterus) and the immature uterus. Potent estrogenic agents compete effectively with estradiol-17b for binding to this site, whereas weak estrogenic steroids (such as progesterone and testosterone) are inefficient competitors. The sensitivity of the high affinity site to pH and hydrolytic enzymes has been studied and compared with the effect of such agents on the low affinity, nonspecific, membrane site. Such a comparison underscores the inherent differences between these two sites of interaction. The thermodynamic parameters of the high affinity binding site have been measured and compared to reported values for the specific cytoplasmic receptor binding site. The nuclear high affinity binding site possesses a favorable free energy of interaction as a result of entropic forces (AS0 = +36.4 cal deg-l mole-‘, AH0 = - 0.66 Cal mole-‘). The number of high affinity nuclear sites varies dramatically during the estrous cycle in a bicyclic fashion. Sites are available during estrus and diestrus, whereas they are blocked in later metestrus and proestrus. * This work was supported by United States Public Health Service Grant CA-10871 and by the American Cancer (Iowa Division) Grant P451. $ Research Career Development Awardee of the National tutes of Health, Grant GM-48410. Society InstiEstradiol-17b causes cell proliferation in endometrial tissue approximately 48 hours after blood levels of the steroid rise during the estrous cycle (1). Prior to cell division there is an initial increase in ribosomal RNA synthesis (2) and 24 hours later an increase in DNA synthesis (3). It has been proposed that the hormone itself mediates at least part of this response by interacting directly with the genome (4-6). Following injection of the hormone in the rat, or direct incubation of the uterus with the hormone, a portion of the estradiol becomes associated with the uterine nuclear fraction in a specific manner (7-9). Although the nuclear fraction has not been analyzed in great detail, some evidence has been presented that estradiol binds to the chromatin fraction (7). We will present data which support the proposal that in vivo, estradiol binds to the nuclear membrane, which appears to be an integral part of chromatin as isolated. During in vitro incubation using isolated nuclei, the hormone binds nuclei both at a nonsaturable low affinity site (in a rapid reaction, which resembles its binding to isolated microsomal material) and also at a saturable high affinity site (with a measurable rate) which we propose is the same site as that involved in incubations with intact tissue. We also report on the thermodynamic parameters of hormone binding and on the sensitivity of the high affinity site to various hydrolytic enzymes and to pH. In several of these properties, the high affinity sites on the nucleus are clearly different from the cytoplasmic receptors and we will argue that the high affinity nuclear binding site which is present in endometrial tissue is a discrete entity in itself and is distinct and separate from the cytoplasmic receptor site. Finally, we have found that the availability of the nuclear high affinity sites varies during the estrous cycle, though this variation is not reflected in the concentration of cytoplasmic receptors in the cell, which remains relatively constant. MATERIALS 

Finally, we note that the in vitro high affinity site is absent in immature calves and also in mature heifers during the late metestrus and the proestrus stages of the estrous cycle. During diestrus the blood level of estradiol is low (42) and the tissue is prepared to respond, and thus the availability of open sites 011 the nucleus seems reasonable. During proestrus the blood level of estradiol is rising rapidly, the tissue is visibly responding and presumably the sites are unavailable because they are blocked by the bound endogenous hormone. As expected the number of sites increases through estrus where the hormone has completed its stimulation of endometrial proliferation, and the blood level of estrogen is declining. However, during early metestrus and late metestrus when the blood level of estradiol is quite low, the number of nuclear sites become vanishingly small, even though it is unlikely that at this stage of the cycle that the sites would be blocked by endogenous hormone. However, it is known that animals in late metestrus cannot reinitiate an appro21. 

The Binding of Estradiol-17β to the Bovine Endometrial Nuclear Membrane
https://www.sciencedirect.com/science/ar...5819429256