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PubMed2000

Analytical performance of the fully automated AxSYM estradiol assay.

The test performance of the fully automated AxSYM Estradiol available on the immunoassay analyser Abbott AxSYM was evaluated. Imprecision, sensitivity and linearity of dilution were examined. For assessment of accuracy, the assay results measured in 12 control pools and 9 patient samples were compared with the values obtained with isotope dilution - mass spectrometry (reference method). The correlation with the manual radioimmunoassay Estradiol MAIA was evaluated using 140 serum samples with estradiol concentrations ranging from 0 to 10 nmol/l. Imprecision studies revealed for the AxSYM Estradiol within-run coefficients of variation of 2.8-8.4% and day-to-day coefficients of variation of 3.4-9.5% (concentration range 0.3-2.8 nmol/l). The lower limit of quantification (lowest estradiol concentration with a day-to-day coefficient of variation <20%) was <0.11 nmol/l; the lower limit of detection was <0.05 nmol/l. The estradiol concentration recovered in patient samples after dilution did not differ by more than 10% from the expected values. The estradiol concentration measured with the AxSYM Estradiol in 12 commercial control pools in some cases grossly deviated from the reference method values; however, for 9 individual patient samples the AxSYM results deviated by not more than 22% (-11% - +22%). There was a good overall correlation (coefficient of correlation = 0.989) between the results measured with the AxSYM Estradiol and the Estradiol MAIA in patient samples. The AxSYM Estradiol assay exhibits a good precision and a sufficient degree of sensitivity for measurement of estradiol in serum of menstruating women. Although the AxSYM results measured in the control pools, in some cases did not meet the target values, the good correlation with the Estradiol MAIA indicates that the reliability of the AxSYM Estradiol for clinical practice is comparable with well established radioimmunoassays. Thus, the AxSYM Estradiol offers an alternative which is comparable with respect to clinical reliability but has great advantages in view of rapidity, flexibility and convenience of analysis.

Automation↗
PubMed1989

Influence of dexamethasone, progesterone, gonadotropin-releasing hormone, and testosterone on estrous behavior of estradiol-treated ovariectomized heifers.

In Experiment 1, 12 ovariectomized heifers were assigned to receive weekly hormone treatments in a replicated 6 x 6 Latin square design. Hormonal treatments were given as two simultaneous injections i.m. and consisted of: 1) 2 ml propylene glycol and 2 ml propylene glycol; 2) .5 mg estradiol benzoate and 2 ml propylene glycol; 3) .5 mg estradiol benzoate and 4 mg dexamethasone; 4) .5 mg estradiol benzoate and 10 mg progesterone; 5) .5 mg estradiol benzoate and .4 mg GnRH; and 6) .5 mg estradiol benzoate and 12.5 mg testosterone propionate. The .5 mg estradiol benzoate and 4 mg dexamethasone treatment reduced the percentage of heifers in estrus compared with the .5 mg estradiol benzoate and 2 ml propylene glycol treatment. In Experiment 2, 16 ovariectomized heifers were used in four replicates of a 4 x 4 Latin square design to determine if pretreatment with progesterone potentiated the actions of estradiol. Hormonal treatments i.m. consisted of: 1) 0 mg progesterone and .2 mg estradiol benzoate; 2) 50 mg progesterone and .2 mg estradiol benzoate; 3) 0 mg progesterone and .5 mg estradiol benzoate; and 4) 50 mg progesterone and .5 mg estradiol benzoate. Progesterone pretreatment, at either dosage of estradiol benzoate, did not increase the percentage of heifers in estrus. Based on these observations, we conclude that: 1) dexamethasone inhibited estrus in estradiol-treated ovariectomized heifers and 2) progesterone pretreatment did not potentiate the actions of estradiol in ovariectomized heifers.

Animals↗
PubMed2005

Short-term administration of 17-beta estradiol to outbred male CD-1 mice induces changes in the immune system, but not in reproductive organs.

The magnitude of an immune response to many foreign and/or self-antigens is known to be gender-dependent and influenced by sex hormones. While the immune consequences of long-term exposure (3 to 5 months) to natural 17-beta estradiol in an inbred mouse model (e.g., C57BL/6, Balb/c) are relatively well-documented, the immunological effects of shorter-term 17-beta estradiol exposure in an outbred mouse model (CD-1) have not been thoroughly evaluated. The male outbred-CD-1 mouse is considered to be less 17-beta estradiol-responsive (in terms of reproductive changes) compared to the inbred mouse. In the present study, CD-1 male mice were dosed with vehicle, or 17-beta estradiol at 2 or 4 micrg/100 g body weight on alternate days over a 7-day period. The immune changes in the developmental organ (thymus) and mature lymphoid organ (spleen) were determined. Thymic organ weight/body weight ratio and thymocyte cellularity decreased with increasing dose of 17-beta estradiol, reaching significance at the 4 microg dose. Although 17-beta estradiol decreased thymocyte numbers, no differences were noted in the relative percentages of major thymocyte subsets (CD4+CD8-, CD4-CD8+, CD4+CD8+, CD4- CD8-) and no evidence of enhanced apoptosis was found. In contrast to the diminished thymocyte numbers, 17-beta estradiol increased splenic lymphocyte cellularity, especially in mice given 4 microg 17-beta estradiol dose. The functionality of splenocytes from mice exposed to 17-beta estradiol was also altered. Supernatants from Con-A activated splenocytes from 17-beta estradiol-treated mice had increased IFN-gamma and decreased IL-4 levels (p < 0.05 at the 4 microg dose). This increase in IFN-gamma in 17-beta estradiol-treated mice was not due to an increase in the relative percentages of T cells, since they were comparable to relative percentages of T cells from oil-treated control mice. In addition, supernatants from cultured splenocytes (both Con A-activated and unstimulated) also had significantly higher levels of nitric oxide activity, especially at the 4 microg 17-beta estradiol dose. These results indicate that short-term 17-beta estradiol treatment in outbred mice, at relatively modest doses (2-4 microg/100 g body weight), altered both thymocytes and splenocytes. These 17-beta estradiol-induced immune changes are compelling, since in these mice, post-17-beta estradiol exposure did not demonstrate robust changes in the male reproductive system (testicular and seminal vesical weights to body weight ratios).

Animals↗
PubMed1977

Binding of [3-H]estradiol by brain cell nuclei and female rat sexual behavior: inhibition by antiestrogens.

The antiestrogens MER-25, CI-628, and nafoxidine inhibit the uptake of [3H]-estradiol in whole homogenates and isolated cell nuclei tissues and the pituitary, and inhibit estradiol-induced female sexual behavior. The antiestrogens were injected intraperitoneally 2 h prior to an intravenous injection of [3H]estradiol, and the animals were killed 2 h after the estradiol. CI-628 reduces radioactivity in whole homogenates and isolated cell nuclei of cerebral cortex, hypothalamus, preoptic area -septum and pituitary. Nafoxidine reduces uptake in cell nuclei of the hypothalamus, preoptic area-septum and pituitary. In this paradigm, MER-25 inhibited uptake only in the pituitary. In the analogous behavioral experiments, with antiestrogens injected 2 h prior to an intravenous injection of unesterified estradiol, CI-628 and nafoxidine totally inhibited lordosis responding. MER-25 shows no inhibition of behavior in this paradigm. However, when MER-25 is injected 12 h prior to the estradiol, it inhibits retention of [3H]estradiol at 2 h in brain and pituitary cell nuclei, and lordosis responding is also inhibited. Additionally, the antiestrogens can apparently displace previously bound [3H]estrdiol. When the antiestrogens are injected 2 h prior to an injection of [3H]estradiol, MER-25, CI-628 and nafoxidine all show greater inhibition of nuclear estradiol retention at 12 h after the [3H]estradiol injection than 2 h. Analogously, when CI-628 is injected 2 h after an intravenous injection of [3H]estradiol, it displaces most of the radioactivity present in hypothalamic-preoptic area nuclei at 12 h after the estradiol injection. These results indicate that antiestrogens can prevent or reverse the nuclear concentration of estradiol in brain cells and are consistent with a role of the cell nucleus in the induction of estrous behavior by estradiol.

Animals↗
PubMed1989

Concentration and turnover of estradiol in the rat uterus in vivo.

The concentrations and turnover of estradiol isolated from cytosolic and nuclear fractions of uteri from ovariectomized rats given estradiol, either in single injections or in continuous infusion, were analyzed by gas chromatography-mass spectrometry. The analytical method was validated for different organs and lower limits of analysis were established. After infusion of 20 ng x h-1 for 18-22 h, mean estradiol levels were 2.0-2.4 fmol x mg-1 uterine wet weight in the nuclear fraction, and 1.2-1.5 fmol x mg-1 in the cytosolic fraction. The concentrations were about five times higher after a single injection of one microgram estradiol but the distribution between nuclear and cytosolic fractions was almost the same. The concentrations of estradiol in nuclei from liver and spleen were 50-200 times lower than those in uterus. Taken together with previous knowledge, the results indicate that the distributions of estradiol and its receptor are not the same and that hormone response cannot be predicted from the concentration of receptors alone. The exchange of estradiol molecules in the uterus was followed after a change of the infusion from unlabelled to [11,12,12-2H3]-labelled estradiol, or vice versa. The uterine uptake of estradiol was calculated to be about 0.7 fmol x h-1 x mg-1 uterine wet weight. The half-life time was calculated to be at least 4 h for estradiol molecules isolated from the nuclear fraction and 3 h (significantly shorter) for those isolated from the cytosolic fraction. The results indicate an uptake of 40-90% of all estradiol passing through the uterus in proestrus with only about 10% of available receptors becoming occupied. When the infusion was changed from estradiol to ethynylestradiol, estradiol disappeared from the uterus at the same rate as in the experiments above. Ethynylestradiol was taken up at a rate of about 0.3-0.4 fmol x h-1 x mg-1 tissue. The percentage of total steroid found in the nuclear fraction was higher for ethynylestradiol, about 70%, than for estradiol, about 60%, indicative of a more stable association of receptor to nuclear binding sites when ethynylestradiol is the ligand.

Animals↗
PubMed2003

The effect of mid-luteal estradiol level on the outcome of ICSI-ET cycles.

METHODS: We investigated if mid-luteal estradiol levels could predict the outcome in intracytoplasmic sperm injection embryo transfer (ICSI-ET) cycles ( n=231). Pregnant and non-pregnant women were compared regarding their peak estradiol levels on human chorionic gonadotropin (hCG) injection day, and mid-luteal estradiol levels on the 7th day following oocyte recovery. Pregnancy rates of the groups that were designed according to the "peak/mid-luteal estradiol level" and the mid-luteal estradiol levels were also compared. RESULTS: Peak and mid-luteal estradiol levels in pregnant women were higher than in non-pregnant women in all patients, although the difference between peak and mid-luteal estradiol levels were similar in pregnant and non-pregnants. Pregnant women had higher mid-luteal estradiol levels in good responders, but the peak estradiol levels of pregnant and non-pregnant women were similar. In poor responders, pregnant and non-pregnant women were similar with respect to peak and mid-luteal estradiol levels. Both in all patients and good responders, women with mid-luteal estradiol levels <200 pg/ml had lower pregnancy rates than those with >2000 pg/ml. Peak/mid-luteal estradiol ratios of pregnant and non-pregnant women were not significantly different in all patients, good responders and poor responders; although a tendency for a lower ratio in pregnants was encountered in good responders. Pregnancy rates of the groups according to the "peak/mid-luteal estradiol ratio" were similar; in all patients, good responders and poor responders. CONCLUSION: A relation between the mid-luteal estradiol level and the outcome is encountered only in good responders.

Adult↗
PubMed1996

Effect of physiological concentrations of estradiol on PGI2 and NO in endothelial cells.

OBJECTIVES: To elucidate the mechanisms by which estrogens protect against occlusive vascular disorders, we studied the effect of 17 beta-estradiol on the production of prostacyclin (PGI2) and nitric oxide (NO) in primary cultures of human umbilical vein endothelial cells (HUVECs). METHODS: To study the effect of 17 beta-estradiol on PGI2 production, HUVECs were incubated in the absence and presence of 17 beta-estradiol (0.01-10 nmol/l) encapsulated within beta-cyclodextrin for 12 h in serum-free medium. To study the effect of 17 beta-estradiol (100 nmol/l) on maximal calcium-dependent NO production, we used different approaches. First, HUVECs were incubated with 2 mumol/l calcium ionophore A23187 with or without 17 beta-estradiol (100 nmol/l) for 24 h in serum-free medium. Second, HUVECs were preincubated with or without 17 beta-estradiol (100 nmol/l) for 12 h in medium supplemented with 2% fetal calf serum, and thereafter incubated in serum-free medium with 2 mumol/l of A23187 and with 100 nmol/l of 17 beta-estradiol (cells which contained 17 beta-estradiol during the preincubation period as well as cells which did not) or without it (only cells which did not contain 17 beta-estradiol during the preincubation period) for 6 h or 24 h. RESULTS: 17 beta-Estradiol (0.1 nmol/l) increased the concentration of 6-keto-prostaglandin F1 alpha, a stable metabolite of PGI2 in the incubation medium, by 16%, and no further increase occurred with higher 17 beta-estradiol concentrations. The stimulation was prevented by tamoxifen. 17 beta-Estradiol did not affect NO production in any of our experiments measured as accumulation of nitrate and nitrite in the experimental medium. CONCLUSIONS: The stimulatory effect on PGI2 production of physiological concentrations of 17 beta-estradiol, shown now for the first time, may provide one explanation for the ability of 17 beta-estradiol to protect against occlusive vascular disorders.

Culture Techniques↗
PubMed1999

Serum and tissue hormone levels of vaginally and orally administered estradiol.

OBJECTIVE: Our purpose was to determine serum and endometrial estradiol levels when micronized estradiol is administered vaginally and orally. STUDY DESIGN: Five subjects were given oral estradiol (2 mg twice daily), during an artificial luteal phase, and another group of 5 subjects were given the same dose of estradiol by the vaginal route. Endometrial biopsies and blood samples were obtained on day 21 of the cycle, 2 hours after the last dose was administered. Tissue and blood samples were assayed for estradiol. RESULTS: Serum estradiol levels were significantly higher with vaginally administered estradiol than with orally administered estradiol (2344 +/- 398 vs 279 +/- 76 pg/mL, P <.005). Endometrial estradiol concentrations were also significantly higher with vaginally administered estradiol than with the oral preparation (918 +/- 412 vs 13 +/- 2 pg/mg protein, P <.05). CONCLUSIONS: Vaginal administration of estradiol is more effective in increasing serum and endometrial levels of estradiol than the oral route and may represent the optimal route of administration for recipients of egg donation. If the vaginal route of estradiol administration is considered for menopausal replacement therapy, much lower doses of the standard oral quantities should be used. Furthermore, if the uterus is present, a progestin must be used to compensate for the high tissue levels of estradiol.

Administration, Intravaginal↗
PubMed2001

Estradiol esterification in the human preovulatory follicle.

In the preovulatory follicle, the LH surge stimulates progesterone production, reduces estradiol synthesis, and scales up the permeability of the blood-follicle barrier. The purpose of this study was to investigate whether the extent of these changes is correlated with the levels of estradiol, estradiol esters, and cholesteryl esters in the follicular fluid. The follicular levels of progesterone, estradiol, estradiol linoleate, cholesterol, and cholesteryl linoleate were measured by HPLC. The estradiol linoleate/estradiol ratio, which reflects the efficiency of in vivo estradiol esterification, and the cholesteryl linoleate/cholesterol ratio were calculated and found negatively correlated. The estradiol level was positively correlated with the cholesteryl linoleate/cholesterol ratio while negatively correlated with the estradiol linoleate/estradiol ratio. The in vitro activity of lecithin-cholesterol acyltransferase, the enzyme esterifying both cholesterol and estradiol, was assayed by incubating the fluid with labeled substrates. This activity was not correlated with either the estradiol linoleate/estradiol or the cholesteryl linoleate/cholesterol ratio. The enzyme K(m) and V(max) values were lower with estradiol than with cholesterol. Higher estradiol linoleate/estradiol ratios and lower cholesteryl linoleate/cholesterol ratios were associated with higher level of Haptoglobin penetration into the follicle. This level, which was determined by ELISA, was found increased with increased progesterone concentration and, therefore, used as a marker of the LH-stimulated permeability of the blood-follicle barrier. Our data suggest that early preovulatory follicles contain more cholesteryl esters and less estradiol esters than follicles closer to ovulation.

Cholesterol↗
PubMed2001

Estradiol is a protective factor in the adult and aging brain: understanding of mechanisms derived from in vivo and in vitro studies.

We have shown that 17beta-estradiol exerts profound protective effects against stroke-like ischemic injury in female rats. These effects are evident using physiological levels of estradiol replacement in ovariectomized rats and require hormone treatment prior to the time of injury. The protective actions of estradiol appear to be most prominent in the cerebral cortex, where cell death is not apparent until at least 4 h after the initiation of ischemic injury and where cell death is thought to be apoptotic in nature. Middle-aged rats remain equally responsive to the protective actions of estradiol. The maintenance of responsiveness of the cerebral cortex to the neuroprotective actions of estradiol was unexpected since responsiveness of the hypothalamus to estradiol decreases dramatically by the time animals are middle-aged. We believe that the protective actions of estradiol require the estrogen receptor-alpha, since estradiol does not protect in estrogen receptor-alpha knockout mice. We have also implemented a method of culturing cerebral cortical explants to assess the protective effects of estradiol in vitro. This model exhibits remarkable parallelisms with our in vivo model of brain injury. We have found that 17beta-estradiol decreases the extent of cell death and that this protective effect requires hormone pretreatment. Finally, 17alpha-estradiol, which does not interact effectively with the estrogen receptor, does not protect; and addition of ICI 182,780, an estrogen receptor antagonist, blocks the protective actions of estradiol. We have begun to explore the molecular and cellular mechanisms of estradiol-mediated protection. In summary, our findings demonstrate that estradiol exerts powerful protective effects both in vivo and in vitro and suggest that these actions are mediated by estrogen receptors.

Aging↗
PubMed1996

17 beta-estradiol metabolism by hamster hepatic microsomes: comparison of catechol estrogen O-methylation with catechol estrogen oxidation and glutathione conjugation.

Catechol estrogens, the cytochromes P450 mediated metabolites of 17 beta-estradiol, undergo further metabolism either via catechol O-methyltransferase (COMT) catalyzed methylation, or by oxidation and subsequent thioether formation with glutathione (GSH). Secondary metabolites of 17 beta-estradiol arising from both these metabolic pathways have been identified in vivo. However, the relative contribution of catechol O-methylation, and catechol oxidation followed by GSH conjugation, to the disposition of the catechol estrogens is unclear. We have therefore quantified both pathways of catechol estrogen disposition, generated in situ from 17 beta-estradiol, in hamster hepatic microsomes. 17 beta-Estradiol was readily converted to 2- and 4-hydroxy-17 beta-estradiol, both of which were effectively methylated in the presence of COMT (300 units/mL). Addition of GSH (50 microM-1 mM) to microsomal incubations resulted in the formation of four catechol estrogen-derived GSH conjugates. Three conjugates of 2-hydroxy-17 beta-estradiol were identified: 2-hydroxy-1,4-bis(glutathione-S-yl)-17 beta-estradiol, 2-hydroxy-1-glutathione-S-yl-17 beta-estradiol, and 2-hydroxy-4-glutathione-S-yl-27 beta-estradiol. In contrast, just one GSH conjugate of 4-hydroxy-17 beta-estradiol was identified: 4-hydroxy-1-glutathione-S-yl-17 beta-estradiol. When a combination of COMT and GSH were simultaneously added to microsomal incubations, both metabolic pathways competed for the same pool of catechol estrogens, and ascorbate dramatically influenced which of these two pathways predominate. In the presence of ascorbate, catechol estrogen methylation predominated over catechol estrogen oxidation and GSH conjugation. In the absence of ascorbic acid, catechol estrogen methylation, and catechol estrogen oxidation inked to GSH conjugation, contributed equally to the disposition of the catechol estrogens. 17 beta-Estradiol 2- and 4-hydroxylase activity was always higher in the absence of ascorbate, irrespective of whether GSH or COMT was used as the trapping agent. Thus, the usual method (COMT plus ascorbate) of determining 17 beta-estradiol 2- and 4-hydroxylase activity underestimates enzyme activity by approximately 50% when compared to the value obtained when GSH is used to trap the o-quinones in the absence of ascorbate. A reassessment of 17 beta-estradiol 2- and 4-hydroxylase activity in different species and tissues is required to permit a more informed evaluation of the role of catechol estrogens in estrogen-induced carcinogenesis.

Animals↗
PubMed1997

Formation of catechol estrogen glutathione conjugates and gamma-glutamyl transpeptidase-dependent nephrotoxicity of 17beta-estradiol in the golden Syrian hamster.

In an animal model of hormone-mediated carcinogenesis, male golden Syrian hamsters develop renal carcinoma following prolonged exposure to 17beta-estradiol. The basis for the species and tissue specificity is unclear. Detailed information on the disposition of 17beta-estradiol in this model is lacking. Because catechol estrogens have been implicated in this model of carcinogenesis, we investigated the metabolism and nephrotoxicity of 17beta-estradiol in golden Syrian hamsters, with emphasis on the formation of catechol estrogen thioethers. 17beta-Estradiol (50 micromol/kg, i.p.) is a mild nephrotoxicant, causing significant elevations in the urinary excretion of gamma-glutamyl transpeptidase (gamma-GT), alkaline phosphatase, glutathione S-transferase (GST) and glucose. Increases in renal protein carbonyls and lipid hydroperoxides, which are markers of oxidative damage, also occur after administration of 17beta-estradiol (50 micromol/kg, i.p.). 17beta-Estradiol-mediated nephrotoxicity is reduced by treating animals with acivicin, an inhibitor of gamma-GT, implying that toxicity is mediated by metabolites requiring metabolism by this enzyme. Following administration of 17beta-[14C]estradiol (100 micromol/kg) to hamsters, 9.7% of the dose is recovered in bile after 5 h, the majority (7.9%) representing aqueous metabolites. Seven catechol estrogen GSH conjugates were identified, 2-hydroxy-1,4-bis-(glutathion-S-yl)-17beta-estradiol, 2-hydroxy-4-(glutathion-S-yl)-17beta-estradiol, 2-hydroxy-4-(glutathion-S-yl)-estrone, 4-hydroxy-1-(glutathion-S-yl)-estrone, 2-hydroxy-1-(glutathion-S-yl)-estrone, 4-hydroxy-1-(glutathion-S-yl)-17beta-estradiol, and 2-hydroxy-1-(glutathion-S-yl)-17beta-estradiol. At 5.4 micromol/kg of 17beta-estradiol, a dose-reflective of daily exposure levels in the hamster model of nephrocarcinogenicity, 12% of the dose is recovered within 5 h as a combination of GSH conjugates of 2- and 4-hydroxy-17beta-estradiol and 2- and 4-hydroxyestrone. In summary, oxidation of catechol estrogens, followed by GSH conjugation, occurs in vivo and 17beta-estradiol is a mild nephrotoxicant in a manner dependent on the activity of gamma-GT.

Alkaline Phosphatase↗
PubMed1998

Estradiol-mediated suppression of apoptosis in the rabbit corpus luteum is associated with a shift in expression of bcl-2 family members favoring cellular survival.

In the rabbit, estradiol is the primary luteotropic hormone. Estradiol withdrawal results in a rapid decline in serum progesterone and eventually in corpus luteum (CL) regression. The objective of this study was to determine whether estradiol modulates luteal cell apoptosis. In the first experiment, rabbits were randomly assigned to one of five experimental groups. An empty capsule (control) or estradiol-filled Silastic capsule was inserted s.c. on Day 0 of pseudopregnancy (day of hCG administration). On Day 11 of pseudopregnancy, some of the group I (control) and group II (estradiol capsule) rabbits were subjected to laparotomy, and one ovary from each rabbit was perfused in vitro to determine progesterone secretion rates. The CL from the contralateral ovary were dissected, snap-frozen, and stored at -70 degrees C until analyzed for internucleosomal DNA cleavage (apoptosis). Estradiol-containing capsules were removed from some of the remaining rabbits on Days 8, 9, and 10 to initiate estradiol deprivation. Rabbits were then subjected to laparotomy 24, 48, or 72 h after capsule removal (groups III, IV, and V, respectively), and ovaries or CL were processed as described above. Deprivation of estradiol for 24 (group III), 48 (group IV), or 72 (group V) h in vivo reduced in vitro progesterone secretion rates by more than 90% as compared to that in ovaries collected from estradiol capsule-intact animals. After in vivo endogenous estradiol suppression, withdrawal of exogenous estradiol resulted in luteal cell apoptosis, which increased in a time-dependent manner. Northern blot analysis revealed an increase in bax mRNA levels and a decrease in bcl-x mRNA levels coincident with luteal cell apoptosis induced by estradiol withdrawal. These data demonstrate that changes in progesterone production caused by estradiol exposure and deprivation are in part related to luteal cell apoptosis, and alterations in the expression of bcl-2 gene family members may be one of the mechanisms by which estradiol exerts its luteotropic effect in the rabbit CL.

Animals↗
PubMed2000

Estradiol attenuates the forskolin-induced increase in hypothalamic tyrosine hydroxylase activity.

The purpose of this study was to evaluate interactions between estradiol and the 3',5' cyclic adenosine monophosphate (cAMP) signaling pathway to regulate tyrosine hydroxylase (TH) activity in hypothalamic dopaminergic neurons. The first experiment examined the ability of forskolin to activate TH in the tuberoinfundibular dopaminergic neurons of adult ovariectomized rats with or without estradiol treatment. Estradiol treatment reduced both basal and forskolin-stimulated TH activity in the median eminence. The second group of experiments examined the effect of estradiol on the forskolin-induced activation of TH in fetal hypothalamic cells cultures. Estradiol decreased basal TH activity in the hypothalamic cell cultures to 80% of control levels. Forskolin treatment for 1 h increased TH activity in a concentration-dependent manner in control and estradiol-treated cells, but estradiol attenuated the stimulatory response to 0.01-10 microM forskolin. The suppressive effect of estradiol on cAMP-dependent activation of TH was evident with 1-12 h of forskolin treatment. The responses to other activators of the cAMP- protein kinase A pathway, including dibutyryl cAMP and 8-bromo-cAMP, and to a depolarizing stimulus were blunted in estradiol-treated cultures. Forskolin treatment for 1 h increased radiolabeled phosphate incorporation into TH protein in control but not estradiol-treated cells, suggesting that estradiol interferes with the ability of the cAMP pathway to phosphorylate TH. Forskolin caused a time-dependent increase in TH mRNA signal levels in control cultures. The magnitude of the forskolin-induced increase in TH mRNA levels was less in the estradiol-treated cells after 6 h of forskolin treatment, indicating that estradiol hinders cAMP-regulated TH gene expression. These data indicate that estradiol attenuates the ability of hypothalamic dopaminergic neurons to respond to cAMP-dependent stimulation by interfering with phosphorylation mechanisms in the short term and control of TH mRNA levels in the long term.

Age Factors↗
PubMed2002

Role of methoxyestradiols in the growth inhibitory effects of estradiol on human glomerular mesangial cells.

Metabolism of locally applied 17beta-estradiol (estradiol) to methoxyestradiols contributes to the growth inhibiting effects of estradiol on vascular smooth muscle cells via an estrogen receptor (ER)-independent mechanism. Because vascular smooth muscle cells are phenotypically similar to glomerular mesangial cells, it is feasible that estradiol inhibits glomerular mesangial cell growth via a similar mechanism, and this possibility was investigated. In human glomerular mesangail cells, estradiol concentration dependently (1 to 100 nmol/L) inhibited serum-induced proliferation (cell number) and DNA ((3)[H]-thymidine incorporation) and collagen ((3)[H]-proline incorporation) synthesis. The inhibitory effects of estradiol were mimicked by 2-hydroxyestradiol and 2-methoxyestradiol, metabolites of estradiol with little affinity for ERs. 2-Hydroxyestradiol and 2-methoxyestradiol were more potent growth inhibitors than estradiol. The inhibitory effects of estradiol were enhanced by CYP450 inducers 3-methylcholanthrene (10 micromol/L) and phenobarbital (10 micromol/L) and blocked by the CYP450 inhibitor 1-aminobenzotriazole (10 micromol/L). The growth inhibitory effects of estradiol were also blocked by quercetin (10 micromol/L) and OR 486 (10 micromol/L) inhibitors of catechol-O-methyltransferase (converts catecholestradiols to methoxyestradiols). ICI182780 (ER antagonist with ER binding affinity similar to estradiol) blocked the growth inhibitory effects of estradiol (1 to 100 nmol/L) only at concentrations (>50 micromol/L) that inhibited estradiol metabolism to catecholestradiols. The growth inhibitory effects of 2-hydroxyestradiol were abrogated by quercetin and OR486 (two structurally dissimilar catechol-O-methyltransferase inhibitors), but not by ICI182780. However, the growth inhibitory effects of 2-methoxyestradiol were unaltered by catechol-O-methyltransferase inhibitors and ICI182780. In conclusion, our findings provide the first evidence that methoxyestradiols mediate the growth inhibitory effects of locally applied estradiol on glomerular mesangial cell growth via an ER-independent mechanism.

Catechol O-Methyltransferase Inhibitors↗
PubMed1990

Acute stimulation of prolactin release by estradiol: mediation by the posterior pituitary.

We have previously shown that the posterior pituitary contains a potent PRL-releasing factor (PRF). Estradiol stimulates PRL release by acting at three possible sites: the hypothalamus, the anterior pituitary, and the posterior pituitary. The objectives were 1) to document the profiles of PRL and LH release in response to an acute administration of estradiol, and 2) to identify the site of action of estradiol by employing two surgical approaches, pituitary stalk section (SS) and posterior pituitary lobectomy (LOBEX). Ovariectomized rats were used throughout. In Exp 1, rats were injected iv with 5 micrograms/kg 17 beta-estradiol, and blood was collected at 30-min intervals for 4 h. Estradiol induced a rapid and profound decline in plasma LH levels and a delayed, 5- to 6-fold rise in PRL. The purpose of the second experiment was to determine whether estradiol stimulates PRL release by acting at the anterior pituitary. Injection of estradiol to SS rats failed to stimulate a rise in PRL. We have previously reported that lactotrophs of SS rats are responsive to PRL secretagogues such as TRH. The objective of the third experiment was to differentiate between hypothalamic and posterior pituitary sites of estradiol action. Estradiol induced only a small rise in PRL when injected into LOBEX rats. However, LOBEX and control rats showed similar large rises in PRL in response to injection of alpha-methyl-para-tyrosine, an inhibitor of tyrosine hydroxylase. The latter indicates that the hypothalamic dopaminergic system as well as anterior pituitary lactotrophs are functionally intact in LOBEX rats. We conclude that estradiol administration to ovariectomized rats induces a rapid decline in LH and a delayed marked increase in PRL. The posterior pituitary, probably via PRF, is the primary site that mediates the acute effects of estradiol on PRL release. Estradiol does not stimulate PRL release directly from the anterior pituitary. The role of the hypothalamus is unclear. Estradiol could act directly on PRF-containing cells in the posterior pituitary or indirectly, via hypothalamic neurons terminating in the posterior pituitary. The hypothalamus also has a minor component that responds to estradiol and is independent of the posterior pituitary.

Animals↗
PubMed2002

Estradiol valerate/dienogest.

Estradiol valerate 2mg/dienogest 2mg is an oral estrogen/ progestogen formulation that has been approved throughout the European Union for the treatment of climacteric symptoms in postmenopausal women. Dienogest is a progestogen that combines the properties of both progesterone and 19-nortestosterone derivatives. It has moderate affinity for the progesterone receptor, significant antiproliferative and antiandrogenic activity, and produces secretory transformation of the endometrium. Estradiol valerate is an esterified form of natural 17beta-estradiol, the most potent endogenous human ovarian estrogen, and is hydrolysed to estradiol soon after oral administration. Results from a randomised, double-blind, multicentre trial showed that oral estradiol valerate 2mg/dienogest 2mg and estradiol valerate 2mg/dienogest 3mg once daily for 1 year were each as effective as estradiol 2mg/estriol 1mg/norethisterone acetate 1mg in the treatment of climacteric symptoms in 581 postmenopausal women; reductions from baseline in Kupperman Index scores were 78.5, 74.5 and 75.0%, respectively. The number of days without any type of bleeding was lowest in patients treated with estradiol valerate 2mg/dienogest 2mg (8.7 days), and highest in the estradiol valerate 2mg/ dienogest 3mg group (12.1 days). During the twelfth month of treatment with estradiol valerate 2mg/dienogest 2mg, the percentage of patients who reported bleeding was 14.5%. Endometrial biopsy results were similar in patients treated with estradiol valerate 2mg/dienogest 2mg, estradiol valerate 2mg/dienogest 3mg or estradiol 2mg/estriol 1mg/norethisterone acetate 1mg once daily for 1 year; 90.8, 87.4 and 87.5% of samples, respectively, contained atrophic material. Proliferative material was found in 4.2, 2.5 and 4.4% of the biopsies, respectively; there was no incidence of hyperplasia in any of the treatment groups. A noncomparative multicentre study in 1501 postmenopausal women demonstrated that adverse events associated with estradiol valerate 2mg/dienogest 2mg once daily for 48 weeks included breakthrough bleeding, mastalgia, headache, abdominal pain, hypertension, thrush, migraine, weight gain, increase in endometrial thickness and metrorrhagia.

Administration, Oral↗
PubMed1980

Estradiol regulation of the frequency and site of origin of uterine contractions in news.

Five experiments were conducted to study the action of estradiol in regulating the frequency and site of origin of contractions in ewes anesthetized with sodium pentobarbitol. Contractions were observed visually by means of midventral laparotomy. In Exp. 1, the percentage of posterior contractions (contractions originating caudal to external bifurcation) of uterine horns and RNA/DNA declined by 36 to 48 hr after the onset of estrus; estradiol posterior contractions and increased RNA/DNA. In Exp. 2, the frequency of contractions in ovariectomized ewes was maximal (53 +/- 5) at 12 hr after an injection of 45 microgram estradiol and was about double the control value (28 +/- 9). The percentage of posterior contractions was greatest at 18 hr (90 +/- 5) and was almost nine times as great as control values (12 +/- 7). RNA/DNA increased from .26 +/- .07 at 12 hr to .48 +/- .05 at 18 hours. In Exp. 3, estradiol increased the frequency of contractions in ovariectomized ewes (48 +/- 2 vs 32 +/- 3) within 6 hours. Neither phenoxybenzamine nor cycloheximide blocked this estradiol-induced increase. In Exp. 4, estradiol increased the percentage of posterior contractions in ovariectomized ewes at 24 hr (7 +/- 4 vs 78 +/- 12), but not the frequency (24 +/- 5 vs 24 +/- 4). Neither 6-OH dopamine nor reserpine altered the estradiol effect on posterior origination of contractions, although reserpine reduced myometrial concentration (nanogram/milligram DNA) of norepinephrine (205 +/- 31 vs 52 +/- 16 without estradiol and 127 +/- 30 vs 62 +/- 13 with estradiol). In Exp. 5, estradiol increased the percentage of posterior contractions in ovariectomized ewes at 24 hr (8 +/- 4 vs 86 +/- 7), and the increase was blocked by indomethacin. Estradiol increased prostaglandin F (PGF) in endometrium but not in myometrium. Indomethacin reduced PGF in both tissues and blocked the estradiol-induced increase. Anterior portions of the uterus had higher concentrations of PGF than did posterior portions. Estradiol induction of high-frequency uterine contractions is dissociable from estradiol induction of a posterior site of origin of contractions, i.e., time for the two effects to appear in ovariectomized ewes differs and the estrogenic regulation of the site of origin of uterine contractions requires protein synthesis.

Animals↗