The arterial depressor response to chronic low-dose angiotensin II infusion in female rats is estrogen dependent

The complex role of the renin-angiotensin-system (RAS) in arterial pressure regulation has been well documented. Recently, we demonstrated that chronic low-dose angiotensin II (ANG II) infusion decreases arterial pressure in female rats via an AT(2)R-mediated mechanism. Estrogen can differentially regulate components of the RAS and is known to influence arterial pressure regulation. We hypothesized that AT(2)R-mediated depressor effects evident in females were estrogen dependent and thus would be abolished by ovariectomy and restored by estrogen replacement. Female Sprague-Dawley rats underwent ovariectomy or sham surgery and were treated with 17β-estradiol or placebo. Mean arterial pressure (MAP) was measured via telemetry in response to a 2-wk infusion of ANG II (50 ng·kg(-1)·min(-1) sc) or saline. MAP significantly decreased in females treated with ANG II (-10 ± 2 mmHg), a response that was abolished by ovariectomy (+4 ± 2 mmHg) and restored with estrogen replacement (-6 ± 2 mmHg). Cardiac and renal gene expression of components of the RAS was differentially regulated by estrogen, such that overall, estrogen shifted the balance of the RAS toward the vasodilatory axis. In conclusion, estrogen-dependent mechanisms offset the vasopressor actions of ANG II by enhancing RAS vasodilator pathways in females. This highlights the potential for these vasodilator pathways as therapeutic targets, particularly in women.     

Specific binding of estrogen receptor to the estrogen response element.

Gene transfer studies have shown that estrogen regulation of specific genes is mediated by estrogen response elements (ERE). We report that binding of the estrogen receptor to the ERE can be detected by a gel retardation (band shift) assay. This binding interaction was highly sequence and receptor specific. Methylation interference analysis showed that the ERE contact sites of estrogen receptor displayed a perfect twofold rotational symmetry. This is compatible with estrogen receptor binding to the ERE as a head-to-head dimer.     

Endocrine steroid sulfotransferases: porcine endometrial estrogen sulfotransferase

Porcine endometrial estrogen sulfotransferase has been isolated and its properties examined. This enzyme only appeared in uteri from ovariectomized gilts which had been primed with estrogen and treated with progesterone. The most stable form of the enzyme was obtained via chromatofocusing of the 100,000 g supernatant from secretory endometrium. A molecular weight of 31 KDa was determined for this sulfotransferase by molecular sieve (Sephadex G-200 Superfine) and disk-gel electrophoresis. The active protein displayed a pI of 6.1, pH optimum of 7.6-7.8 and a requirement of 10 mM Mg2+ for maximum transfer of sulfate from 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to estrone (E1). Km of the reaction was 24 +/- 4.7 microM for PAPS and 24 +/- 9.8 nM for E1 as substrate. Porcine endometrial sulfotransferase thus displayed a much greater affinity for E1 than a similar enzyme previously isolated from bovine adrenals. As has been observed of sulfotransferases from other tissues, an endogenous substrate (presumed to be E1) accompanies the enzyme throughout its purification.     

Role of porcine endometrial estrogen sulfotransferase in progesterone mediated downregulation of estrogen receptor

Estrogen sulfotransferase (EST) is a progesterone (Pg) induced secretory endometrial enzyme which may effect estrogen receptor levels by esterifying estradiol-17 beta (E2) to an inactive, sulfate form. The effects of this enzyme were studied using specific inhibitors of EST that do not bind to estrogen receptor (ER): 4-nitroestrone 3-methyl ether and 4-fluoroestrone 3-methyl ether. A 1 h pulse with 4 nM E2 caused ERn (i.e. E2-bound, chromatin-bound receptor) to increase 40% in incubations of proliferative gilt endometrium (no EST activity), while the same E2 treatment of secretory endometrium (high EST activity) caused no increase in ERn. ERn accumulation was completely restored in these experiments by preincubating secretory endometrium with 4 microM 4-fluoroestrone 3-methyl ether. Gilt endometrial explants cultured 7 days with 1 nM E2 plus 1 microM Pg (which induced EST activity) possessed half the ERn as explants devoid of EST activity which were cultured in E2 alone. The addition of 10 microM 4-nitroestrone 3-methyl ester to the cultures of secretory endometrium restored ERn to the levels seen in minces cultured with E2 alone. Furthermore, ovariectomized gilts injected daily with 250 micrograms E2 plus 25 mg Pg had much lower ERn (0.06 fmol/micrograms DNA) than gilts injected with E2 only (0.21 fmol/microgram DNA). ERn was restored completely by supplementing the E2 plus Pg injections with 0.5 g 4-nitroestrone 3-methyl ether administered by vaginal suppositories.(ABSTRACT TRUNCATED AT 250 WORDS)     

Polymorphisms of estrogen receptor alpha gene in endometrial cancer

It is hypothesized that polymorphisms of estrogen receptor-alpha (ERalpha) gene are involved in endometrial cancer. To test this hypothesis, the genotype distributions of six different loci (codon 10 T-->C, codon 87 G-->C, codon 243 C-->T, codon 325 C-->G, codon 594 G-->A, and intron 1 C-->G) of the ERalpha gene were investigated and their association with endometrial cancer was determined. The DNA from 113 cases of human endometrial cancer was analyzed by sequence-specific polymerase chain reaction. The relative risk of variant genotype was calculated by comparison with 200 healthy controls. The frequency of variant genotype on codon 10 was significantly lower in endometrial cancer patients as compared to controls. Nine of 113 endometrial cancer patients (8.0%) showed genotype 10C/C compared to 27 of 200 healthy controls (13.5%). The relative risk of genotype 10C/C was calculated as 0.44, compared to wild-type. Forty-five of 113 endometrial cancer patients (39.8%) showed genotype T/C on codon 10 compared to 111 of 200 healthy controls (55.5%). The relative risk of genotype 10T/C was calculated as 0.67, compared to wild-type. The polymorphism on codon 87 was not detected both in endometrial cancer patients and in healthy control. Other loci, intron 1, and codons 243, 325, and 594, did not show a correlation with endometrial cancer. The frequency of alleles on codon 10 was also significantly lower in endometrial cancer patients as compared to controls. Sixty-three of 226 alleles (27.9%) of endometrial cancer patients showed allele C compared to 165 of 400 (41.2%) of healthy controls. The relative risk of allele 10C was calculated as 0.67, compared to wild-type. Other loci, intron 1, and codons 243, 325, and 594, did not show a difference between cancer patients and controls. All genotype and allelic distributions were in accordance with the Hardy-Weinberg equilibrium. The present study demonstrates for the first time a protective effect of 10C allele against endometrial cancer. Thus, inherited alterations in ERalpha may be associated with changes in estrogen metabolism and thereby may possibly explain inter-individual differences in disease incidences of endometrial cancer.     

Rat ovarian angiotensin II receptors. Characterization and coupling to estrogen secretion

Angiotensin II receptor agonist (125I-angiotensin II) and antagonist (125I-[Sar1,Ile8]angiotensin II) bind in a specific and saturable manner to rat ovarian membranes. Agonist and antagonist binding affinity (KD approximately 0.5 nM) and the number of sites estimated (Bmax approximately 60 fmol/mg of protein) were similar. Dissociation of receptor-bound agonist was more rapid than the dissociation of receptor-bound antagonist, and agonist, but not antagonist, dissociation from the receptor was accelerated by GTP gamma S. A 0-150 mM increase in Na+ produced a 27% increase in the KD of agonist binding. Antagonist binding was not modified by Na+. These studies suggest that both agonist and antagonist identify putative angiotensin II receptors in the ovary but that the properties of agonist and antagonist binding are distinct. Angiotensin II antagonist binding sites are present on the granulosa cell layer of rat ovarian follicles (Speth, R. C., Bumpus, F. M., and Husain, A. (1986) Eur. J. Pharmacol. 130, 351-352). To determine the role of angiotensin II in ovarian function, we examined angiotensin II receptors and function during the onset of puberty. High affinity and low capacity angiotensin II receptors were present in ovaries from immature rats. After pregnant mare's serum gonadotropin induced ovulation in immature rats, antagonist binding to total ovarian membranes increased over 3-fold. In vitro incubation of peripubertal ovaries with 1 microM angiotensin II produced a stimulation of estrogen, but not progesterone, secretion. This steroidogenic effect of angiotensin II was most pronounced in the luteal phase of the estrus cycle. These studies point toward the involvement of angiotensin II in the regulation of ovarian function, possibly through modulation of follicular estrogen levels.     

Plasma concentration and the depressor response to bradykinin infusion

To determine the relationship between vascular response and plasma levels of kinins, 10 anesthetized mongrel dogs received an intravenous infusion of bradykinin in graded doses (0.3 to 10.0 μg/kg/mm). Arterial pressure was recorded and plasma kinins determined by radioimmunoassay. There was a significant (p < 0.001) correlation between the increment in plasma kinins and the decrement in blood pressure which stabilized within five minutes. At the highest dose, arterial blood pressure fell by 37 ± 5 mmHg, and plasma kinins had risen by 1.5 ± 0.4 ng/ml. The magnitude of the change in plasma kinin levels observed in this study is similar to that acutely reported with administration of converting enzyme inhibitors. Thus, kinins may contribute to the hypotensive effect of these agents.     

Binding of the estrogen receptor DNA-binding domain to the estrogen response element induces DNA bending.

We have used circular permutation analysis to determine whether binding of purified Xenopus laevis estrogen receptor DNA-binding domain (DBD) to a DNA fragment containing an estrogen response element (ERE) causes the DNA to bend. Gel mobility shift assays showed that DBD-DNA complexes formed with fragments containing more centrally located EREs migrated more slowly than complexes formed with fragments containing EREs near the ends of the DNA. DNA bending standards were used to determine that the degree of bending induced by binding of the DBD to an ERE was approximately 34 degrees. A 1.55-fold increase in the degree of bending was observed when two EREs were present in the DNA fragment. These in vitro studies suggest that interaction of nuclear receptors with their hormone response elements in vivo may result in an altered DNA conformation.     

Ovarian steroid hormones and endometrial response

As a bioassay of the steroidogenic function of the corpus luteum, endometrial biopsy has been proposed as the most efficient way of diagnosing corpus luteum insufficiency. However, analysis of our data on luteal phase evaluation in infertility shows that most cases (86%) of endometrial luteal inadequacy are associated with normal hormone (progesterone, estradiol) stimulation. This apparent lack of endometrial progestational response may be explained by an end organ defect localized to the endometrial steroid receptors.     

Renal response to intravenous phosphate infusion in the sheep.

Renal clearance experiments were performed on six Merino ewes in which plasma phosphate concentrations were increased by the intravenous infusion of isohydric sodium phosphate. As the phosphate load to the kidney increased, the renal tubular reabsorptive capacity became saturated and a definite tubular maximum for phosphate reabsorption (Tmp) was demonstrated. The Tmp was directly related to the glomerular filtration rate and had a mean value of 333-1+/-27-0 (s.e.m.) mumol/min or 416-6+/-13-5 mumol/100 ml glomerular filtrate. Calcium infused concurrently with phosphate in order to maintain plasma total calcium levels did not alter the Tmp. Ultrafilterability of calcium and phosphate in the plasma decreased with phosphate infusion and this was accentuated by an accompanying calcium infusion. The Tmp in sheep's kidney is higher than in non-ruminant animals and the implications of this are discussed.     

Dehydroepiandrosterone stimulates the estrogen response element

Studies suggest that the steroid, dehydroepiandrosterone (DHEA) can exert effects directly, in addition to its indirect role serving as a precursor for other steroids such as androgens and estrogens. Because DHEA is one of the most abundant adrenal steroids secreted in man, we investigated the functional activity of DHEA on the classic estrogen response element (ERE) in the presence of the estrogen receptor (ER) in transiently transfected cells. GT1-7 hypothalamic neuronal cells, devoid of the estrogen receptor, were transiently transfected with the estrogen receptor expression plasmid (HEGO) and the estrogen response element luciferase (ERELUC) reporter vector. As expected, a dose-response stimulation of luciferase activity was observed in cells treated with estradiol. Concentrations of estradiol from 10⁻¹⁰–10⁻⁶ M resulted in a 136–195 percent increase in luciferase activity compared with control. A dose-response stimulation was also observed in the cells treated with DHEA. A maximum stimulation of 177 percent increase in luciferase activity compared with control was observed with DHEA at a concentration of 10⁻⁵ M. Both the estradiol and DHEA stimulation of ERE luciferase activity was inhibited by the estrogen receptor antagonist, ICI 182,780. The aromatase inhibitor, formestane in combination with estradiol or DHEA had no effect on luciferase activity, suggesting that the effect of DHEA is independent of its conversion to estadiol. Estradiol levels, as measured by ELISA, were appropriately elevated in the estradiol-treated cells but were not significantly different from the control cells in the DHEA-treated cells. These studies suggest a functional in vitro role of DHEA in activating the ERE in the presence of the classic ER.     

Diminished steroidogenic response of hamster granulosa cells to estrogen in vitro

Summary We have previously demonstrated that estrogen can exert inhibitory or atretogenic effects on the ovaries of both rats and rhesus monkeys in vivo. This study was designed to test whether the hamster (Mesocricetus auratus) is an appropriate model in which to test the effects of estrogens (diethylstilbestrol and estradiol-17) on steroid accumulation by ovarian granulosa cells in vitro, and whether the effects are similar to those demonstrated for other species in vivo. Immature female hamsters were injected with pregnant mare's serum gonadotropin at 28 to 30 days of age. Animals were sacrificed and follicular contents aspirated three days later. Granulosa cells were either left untreated or treated with diethylstilbestrol or estradiol (1×10^-7 M) in vitro for 72 h in the presence of androstenedione (1×10^-7 M), and in the presence or absence of serum (10%) or human follicle-stimulating hormone (20 ng/ml), and long-term accumulation of estrogen and progesterone was determined. Diethylstilbestrol inhibited accumulation of estrogen regardless of the presence or absence of follicle-stimulating hormone. In contrast, only estradiol plus follicle-stimulating hormone augmented accumulation of progesterone by granulosa cells. These findings that estrogen can be non-stimulatory or inhibitory to function of granulosa cells in vitro parallel those shown in vivo. Our experimental approach may therefore represent an appropriate model for study of the direct effects of estradiol on the function of granulosa cells.