Regulation of estrogen receptor alpha by estradiol in pregnant and estradiol treated rats

Estrogens play an important role in tissue metabolism through specific regulation of several intracellular pathways. We studied ERalpha regulation in muscle and adipose tissue from pregnant and estradiol treated rats. In both groups, we identified three different ERalpha inmunoreactive proteins (80, 67 and 46 kDa) using total protein extracts. Because it has been showed that estrogens are able to promote rapid effects in several cellular models, we looked for three ERalpha-related proteins at plasma membrane. In skeletal muscle of both groups, we positively identified the three ERalpha-related isoforms in plasma membrane, but in adipose tissue from pregnant we were not able to identify ERalpha67, and in estradiol treated animals ERalpha80 was absent. Taking together, our results showed a tissue-specific regulation of whole-cell ERalpha-related proteins and ERalpha located at plasma membrane, which should be involved in non-genomic actions of 17beta-estradiol. The role of the three ERalpha inmunoreactive proteins is unknown, however, seems probably related to rapid activation of signalling pathways.     

Effects of estradiol and estradiol sulfamate on the uterus of ovariectomized or ovariectomized and hypophysectomized rats

Estradiol sulfamate (J995), estradiol-17beta with a substituted sulfamate group in position 3, has much higher systemic estrogenic activity after oral administration than 17beta-estradiol (E2) due to reduced hepatic metabolism of the drug. The lower dose necessary for achievement of adequate systemic estrogenic effects results in a substantial reduction of otherwise commonly observed hepatic side-effects. This makes J995 a strong candidate as an estrogen suitable for oral administration. The present study was performed to examine and compare the effects of J995 and E2 on the uterus after oral or subcutaneous administration to ovariectomized or ovariectomized+hypophysectomized female rats, in particular on the levels of the estrogen receptor (ER) (alpha+beta), ERalpha mRNA and insulin-like growth factor-I (IGF-I) mRNA. The ER levels were determined using a ligand binding assay and the mRNA levels using solution hybridization. The doses of J995 or E2 were chosen to achieve comparable uterotrophic activity. The rats were treated with hormones for 7 days and the treatment was initiated 14 days after surgery. We conclude that there are no major differences in the uterine response to treatment with J995 or E2 with respect to the effects on ER and ERalpha mRNA levels. The IGF-I mRNA level though, is more affected by J995 than by E2 after 7 days of treatment, indicating a prolonged effect of J995.     

Effects of estradiol and estradiol sulfamate on the liver of ovariectomized or ovariectomized and hypophysectomized rats

This study was performed to evaluate and compare the effects of estradiol sulfamate (J995) and estradiol (E2) on the hepatic levels of the estrogen receptor (ER) and its mRNA, in ovariectomized (OVX) and OVX+hypophysectomized (OVXHX) female rats and to study the effects on the liver-derived serum compounds angiotensin I, triglycerides, high-density lipoprotein (HDL) and cholesterol. ER concentrations were determined using ligand-binding assay (LBA) and enzyme immuno assay (EIA), and the mRNA levels using solution hybridization.

The rats were treated orally (p.o.) or subcutaneously (s.c.) for 7 days, with treatments initiated 14 days after surgery.

No differences were found in ER mRNA levels between J995 and E2 treated rats.

The s.c. administered estrogens increased ER levels in OVX rats. Addition of GH+DEX to OVXHX rats restored the ER to levels above those seen in intact rats, whereas simultaneous oral treatment with E2 significantly decreased ER levels again. The s.c. treatment with either J995 or E2 limited the increase caused by addition of GH+DEX.

After oral treatment angiotensin I levels were increased by E2, but not by J995, while triglycerides, HDL and cholesterol levels were decreased by oral E2, J995 showing a similar pattern but was less effective.

In summary, these results on hepatic ER levels and estrogen dependent compounds produced by the liver showed that J995 has a lower impact on the normal liver functions after oral treatment than E2. Thus, J995 is a very promising substance for development of oral estrogen treatment with reduced hepatic side effects.     

Copper and the estradiol receptor

Copper is an essential element in living organisms and it appears to be involved in estrogen action. This study bears on the manner in which the metal may be linked to the mechanism of this action. Divalent copper was found to induce at 37 degrees C a several fold increase in estradiol binding to the receptors in rat uterine cytosols. An endogenous substance present in the uterine cytosol and separated from it by fractionation on a hydroxylapatite column was found to function as a potent inhibitor of the copper effect. This substance has been found so far also in human breast tissue and in some human breast tumors.     

Exogenous estradiol reduces inhibition of luteinizing hormone by estradiol in prepubertal heifers

The hypothesis that high levels of exogenous estradiol administered to heifers during the prepubertal period would decrease subsequent negative feedback of estradiol on luteinizing hormone (LH) secretion was tested. Fourteen prepubertal heifers were ovariectomized on Day 0. Ovariectomized heifers received either no further treatment (OVX, n = 4), a single estradiol implant on Day 0 (OVXE, n = 5), or the single implant on Day 0 and two additional implants between Days 16 and 30 (OVXE+ E, n = 5). Ten ovary-intact heifers received either no treatment (INT, n = 5) or were administered the two estradiol implants between Days 16 and 30 (INT+ 5, n = 5). Comparison of LH secretion in OVXE to OVXE+E, and in INT to INT+E resulted in significant time-by-treatment interactions (p less than 0.05 for both). As pubertal age approached, mean concentration of LH (p less than 0.05) and pulse frequency (p less than 0.05) increased more rapidly in OVXE+E and INT+E than in OVXE and INT, respectively. Amplitude of LH pulses was unaffected by treatment. When data were standardized to day of puberty in INT and INT+E heifers, mean LH concentration and LH pulse frequency increased as puberty approached in both groups. These data confirm earlier reports indicating that secretion of LH increases gradually as puberty approaches in heifers. It was concluded that administration of estradiol during the prepubertal period hastened the decline in the subsequent negative feedback of estradiol. Precocious puberty was not induced in ovary-intact females.     

Metabolism of estradiol by true and pseudoperoxidases

The activation of 14C-labeled estradiol by "true" and "pseudo" peroxidases to form conjugates and other products was compared in four model systems using H2O2, glutathione, Mn2+ or irradiated riboflavin. Albumin was used as acceptor except in the glutathione system. The binding of estradiol to glutathione in the presence of the true peroxidases, lacto- or uterine peroxidase (no H2O2 added), was also examined and the conditions shown to differ from those required with the pseudoperoxidases, microperoxidase or trypsin-digested cytochrome c. The conjugates were purified by chromatography after elution from Amberlite XAD-2 and the relative amounts of these products assessed by autoradiography. The ratio of steroid to glutathione in the main water-soluble metabolite formed with lactoperoxidase was found to be approx 1:1 in a double label experiment with [14C]estradiol and [3H]glutathione. It was also shown, using estradiol labeled with 3H in different positions of the steroid molecule, that lactoperoxidase acts non-specifically in catalyzing the formation of glutathionyl conjugates as indicated by the release of 3H2O. The possible role of peroxidase and glutathione in the metabolism of estrogens and in the formation of artifactual products is discussed.     

Organometallic derivatives of estradiol as bioligands: targetted binding of the estradiol receptor

The complexation of estrogens by transitional metal units e.g. (alkyne)Co2(CO)6 and (alkyne)Mo2Cp2(CO)4, at the 17 alpha-position brings about a dramatic change in the chemical behavior of these compounds with respect to that of the free ligands. The 17 beta-OH function becomes particularly labile, even in weakly acidic medium, giving rise to carbenium ion-like species, from which, depending on the metal and the nucleophile, substitution, elimination and rearrangement take place. This situation provides the basis for a new type of active site directed-reagent for estradiol receptor. The hypothesis of vicinal space positioning of an acidic and a nucleophilic group in the estradiol receptor cavity is examined in the light of the amino-acid composition of the steroid binding domain. The requirement of the sulfhydryl group of a cysteine residue is suspected in the first step of the receptor inactivation process.     

Copper and endogenous mediators of estradiol action

Divalent copper increases by severalfold specific estradiol binding in rat uterine cytosol at 37 degrees C. Two endogenous substances have now been isolated from the cytosol one of which sharply inhibits the copper effect while the other sharply promotes it. The inhibitor is thermostable, it is adsorbed by dextran coated charcoal and elutes from Sephadex columns with water. The promoter is thermolabile at 60 degrees C, it is not readily adsorbed by the charcoal and elutes from Sephadex columns with KCl. The two substances are thought to be mediators of estradiol action.     

Estrogen and osteoarthritis: a study of synovial estradiol and estradiol receptor binding in human osteoarthritic knees.

Estrogen appears to be a risk factor in knee osteoarthritis (OA). Results from 21 patients revealed that synovial estradiol level was highly related to the severity of OA. Increased estradiol receptor bindings in the medial compartment of the femoral condylar and tibia plateau cartilages were observed; the increase was significantly higher in the medial than in the lateral compartment (p less than 0.05). Although the synovial estradiol level was significantly lower in women with OA than in men with OA (p less than 0.01), postmenopausal women were hypothesized to be more susceptible to OA, since the possible existence of synovial testosterone might counteract the high estradiol synovial level in men, which results in a lower incidence of knee OA in men than in postmenopausal women. We suggest that excessive synovial estradiol and higher estradiol receptor bindings may be involved in the development of knee OA, particularly in postmenopausal women.     

Acute, nongenomic vasodilatory action of estradiol is attenuated by chronic estradiol treatment

Deficiency of estradiol or chronic estrogen treatment may alter the responses to this hormone in many tissues. A possible interaction between the acute nongenomic and the chronic effects of estradiol on microvessels have not been investigated yet. In the present study we have investigated whether acute in vitro vasodilatory action of estradiol on a small artery is altered by chronic estradiol pretreatment. Female rats were surgically ovariectomized and subjected to either estradiol replacement therapy (estradiol propionate, 450 micrograms/kg/week) or vehicle administration for 5 weeks. Cylindrical segments of the saphenous artery were studied using videocomputerized microarteriography in vitro. Estradiol, in concentrations of 10(-6) to 10(-4) M relaxed norepinephrine precontracted vessel segments in a dose-dependent manner. Magnitude of relaxation observed in arteries of estradiol replaced animals was significantly smaller at all concentrations than that of nonreplaced ovariectomized rats; maximal relaxation in the control ovariectomized group was 64.5% +/- 3.6%, while it was 34.3% +/- 4.2% only in the ovariectomized and estradiol replaced group (P < 0.001). Comparison of acute relaxations in response to papaverine and nifedipine failed to prove a reduced activity of the general relaxation machinery in estradiol replaced animals. We conclude that chronic estradiol replacement can downregulate the acute nongenomic vasorelaxation effect of this hormone in small arteries of ovariectomized rats.     

Partial purification of estradiol receptor from Xenopus laevis liver and levels of receptor in relation to estradiol concentration

We have used ammonium sulphate precipitation followed by affinity chromatography to partially purify the estrogen receptor from Xenopus laevis liver which may control the genes for vitellogenin, the precursor of the egg yolk proteins. The rate at which receptor binds estradiol explains the kinetics of the induction of vitellogenin synthesis by estradiol, and the dissociation constant (0.5 X 10(-9) M) explains the concentration dependence of the response, which has a threshold of 10(-9) M estradiol, when 67% of the receptor is bound to estradiol. The estradiol concentration in male liver, which does not make vitellogenin, is 0.18 X 10(-9) M, sufficient to saturate 26% of the receptor, while in female liver, which makes vitellogenin continuously, the estradiol concentration is 3.5 X 10(-9) M, giving 88% saturation of receptor, suggesting that the proportion of occupied receptor decides whether or not the vitellogenin genes are active. In the physiological concentration range, estradiol modulates the level of receptor, which varies between 100 binding sites per nucleus in males and 440 in females, but artificially high concentrations of estradiol raise the level to approximately 1000 sites per nucleus. This suggests that the small increase in vitellogenin mRNA induced by physiological concentrations of estradiol is due to pre-existing receptor and that the much larger increases induced by very high concentrations depends on newly-synthesized receptor.