17 Beta-estradiol stimulates expression of endothelial and inducible NO synthase in rat myocardium in-vitro and in-vivo

OBJECTIVES: NO production has been attributed to play a major role in cardiac diseases such as cardiac hypertrophy and cardiac remodeling after myocardial infarction which display significant gender-based differences. Therefore we assessed the effect of 17 beta-estradiol (E2) on estrogen receptor (ER) alpha and beta and endothelial and inducible NO synthase in neonatal and adult rat cardiomyocytes. METHODS: The presence of ER alpha and ER beta was demonstrated by immunofluorescence and western blot analysis as well as the expression pattern of inducible NO synthase (iNOS) and endothelial NOS (eNOS) in isolated cardiomyocytes from neonatal and adult rats. Furthermore, regulation of myocardial iNOS and eNOS expression by estrogen was evaluated in the myocardium from ovariectomized or sham-operated adult Wistar-Kyoto rats. RESULTS: Incubation with E2 led to translocalization of the ER into the nucleus and increased receptor protein expression. E2 stimulated expression of iNOS and eNOS in both neonatal and adult cardiac myocytes. Coincubation with the pure anti-estrogen ICI 182,780 inhibited upregulation of ER and NOS expression. In ovariectomized rats myocardial iNOS and eNOS protein levels were significantly lower compared to sham-operated female animals. CONCLUSION: Taken together, these results show that E2 stimulates the expression of iNOS/eNOS in neonatal and adult cardiomyocytes in-vivo and in-vitro. These novel findings provide a potential mechanism of how estrogen may modulate NOS expression and NO formation in the myocardium.     

Difference in the responsiveness of old female rats to estrogen to secrete sex attractants as a function of different reproductive states

Two age groups of Long-Evans rats (young: 3.5-7 months of age and old: over 23 months of age) were ovariectomized and implanted subcutaneously with a 1:2 estradiol benzoate (E2)-cholestrol mixture-filled Silastic capsule. Olfactory preference of male partners to these female rats over ovariectomized young rats without E2 replacement was examined. Olfactory preference of adult male rats as indicated by investigation frequency and investigation time for old pseudopregnancy (PSP) rats and long-term ovariectomized rats was decreased but not that of prolonged-vaginal-cornification (PVC) rats when compared with young female rats. These results indicate that the responsiveness of old PVC rats to estrogen to secrete sex attractants is not decreased but that of PSP rats and long-term ovariectomized rats is decreased when compared with young female rats.     

Evidence against a role of physiological concentrations of estrogen in post-myocardial infarction remodeling.

OBJECTIVES: The purpose of this study was to examine whether endogenous estrogen deficiency induced by ovariectomy affects chronic left ventricular dysfunction post-myocardial infarction (MI). BACKGROUND: Epidemiologic findings suggest that mortality of postmenopausal women is increased after MI, but the underlying mechanisms are unknown. METHODS: Rats were either not ovariectomized (non-OVX), ovariectomized (OVX) or ovariectomized and treated with subcutaneous 17-beta-estradiol (E2) pellets (OVX + E2). Two weeks later, animals were sham-operated (Sham) or left coronary artery ligated (MI). Eight weeks later, in vivo echocardiographic and hemodynamic measurements were performed. Thereafter, hearts were isolated and perfused isovolumically. RESULTS: Mean infarct size was similar among the three MI groups. Ovariectomy decreased serum E2 levels (11 +/- 4 vs. 49 +/- 11 pg/ml in non-OVX, p < 0.01) and increased body weight. These changes were reversed by E2 replacement. The degree of cardiac hypertrophy was similar for all groups post-MI. Left ventricular diameters were increased post-MI (8.9 +/- 0.4 in non-OVX + MI vs. 6.7 +/- 0.2 mm in non-OVX + Sham hearts, p < 0.0001), but OVX or OVX + E2 replacement did not alter left ventricular diameters in post-MI and Sham hearts. Left ventricular fractional shortening was severely impaired post-MI (19 +/- 2% vs. 50 +/- 3 in non-OVX + Sham hearts, p < 0.0001) with no influence of hormonal status. Left ventricular end-diastolic pressure, measured in vivo, was increased in all MI groups without significant differences between groups. Pressure-volume curves, obtained in perfused hearts, demonstrated a right and downward shift with reduced maximum left ventricular developed pressure post-MI (75 +/- 6 vs. 108 +/- 3 mm Hg in non-OVX + Sham hearts, p < 0.001) and were also unaffected by either OVX or E2 replacement. CONCLUSIONS: Chronic endogenous estrogen deficiency does not have major effects on the development of cardiac hypertrophy, dysfunction and dilation post-MI.     

Estrogen replacement raises rat CRP without evidence of complement activation

Given current controversies regarding anti- and pro-inflammatory effects of estrogen, there is a need to explore relationships between gonadal hormones and inflammation using appropriate animal models. It has been proposed that rats are not appropriate for such research since, contrary to the effect of estrogen in humans, earlier animal studies had reported that estrogen downregulates serum C-reactive protein (rCRP) levels in the rat. With these considerations in mind, we re-examined the effects of estrogen withdrawal and replacement on CRP expression and complement activation in the rat. F-344 rats underwent bilateral ovariectomy or sham surgery at 9-10 months of age. Four months later, ovariectomized rats were treated with traditional high-dose 17beta-estradiol (Hi-E2) capsules, lower-dose (Lo-E2) 17beta-estradiol capsules, or placebo capsules for 7 days prior to sacrifice. Levels of plasma rat C-reactive protein (rCRP) were significantly lower in ovariectomized vs. sham-operated animals (415.5 +/- 10.6 vs. 626.6 +/- 23.0 mg/L, p < 0.001). Estrogen replacement significantly raised rCRP levels in ovariectomized animals (690.0 +/- 28.0 mg/L in Lo-E2 and 735.5 +/- 35.8 mg/L in Hi-E2, respectively, p < 0.001). Plasma rCRP levels correlated significantly with both hepatic rCRP (r = 0.79, p < 0.001) and serum estradiol (r = 0.70, p < 0.001) levels. However, no significant differences were observed in indices of complement activation (C4b/c) or CRP-complement complex generation (rCRP-C3 complex). In the mature female rat, ovariectomy reduces and estrogen replacement raises rCRP. Effects of estrogen on plasma rCRP induction are mediated, at least in part, through hepatic mechanisms and do not appear to require or be associated with complement activation.     

The effects of relaxin and estrogen deficiency on collagen deposition and hypertrophy of nonreproductive organs

In this study, we determined the effects of relaxin and estrogen deficiency and estrogen replacement therapy (ERT) on the cardiac, renal, and pulmonary phenotypes of female relaxin gene knockout (Rln1-/-) and age-matched wild-type (Rln1+/+) mice. One-month-old Rln1+/+ and Rln1-/- mice were bilaterally ovariectomized or sham-operated and aged until 9 or 12 months. A subgroup of ovariectomized mice received ERT from 9 to 12 months of age. At the appropriate time points, heart, kidney, and lung tissues from these mice were collected and analyzed for changes in organ fibrosis, hypertrophy, and airway thickening. Neither ovariectomy nor ERT had any effect on cardiac or renal collagen concentration in all groups studied. In contrast, total lung collagen concentration and airway subepithelial collagen deposition were significantly increased in ovariectomized Rln1+/+ mice (P<0.05 vs. sham) and to a greater extent in ovariectomized Rln1-/- mice (P<0.01 vs. sham). Ovariectomy of Rln1+/+ mice also led to a significant increase in airway smooth muscle (SM) (lung) thickening, which was further exaggerated in Rln1-/- mice. Cardiac hypertrophy, evidenced by increased heart weight and expression of hypertrophy-related genes (all P<0.05 vs. sham) was only observed in Rln1-/- mice. These findings demonstrated an increased pathology in mice that were deficient of both relaxin and estrogen. ERT significantly decreased airway fibrosis, airway SM thickening, and cardiac hypertrophy when administered to ovariectomized Rln1-/- mice (all P<0.05 vs. ovariectomy alone). These findings suggest that relaxin and estrogen appear to play protective roles against airway fibrosis, airway SM thickening, and cardiac hypertrophy in female mice.     

Enhancement of in vivo humoral immunity by estrogen: permissive effect of a thymic factor

Physiological levels of estrogen enhance humoral immune responses. Several in vitro studies indicate the hormone to have a direct effect on immune cells, and other studies show that estrogen may affect humoral immunity indirectly through the thymus. Therefore, we have conducted experiments to investigate the requirement of the thymus in the enhancement of humoral immune responsiveness by estrogen. In Exp I, adult ovariectomized Lewis rats were thymectomized or sham thymectomized and given estradiol (E2; 0.25 microgram E2 in sesame oil, sc, once every 4 days) or the oil vehicle in a 2 x 2 factorial design, and their antifluorescein responses were followed by enzyme-linked immunosorbant assay across 21 days. Only animals that were thymus intact and given estrogen replacement showed significantly (P less than 0.05) greater serum antifluorescein titers than all other treatments. In Exp II, ovariectomized thymectomized rats were submitted to a 2 x 3 factorial design of oil vehicle or E2 replacement and saline, gelatin, or thymus replacement (thymosin fraction 5; 1 mg/kg in saline, sc). As described above, only the animals receiving both thymosin fraction 5 and E2 replacement displayed antifluorescein titers that were significantly (P less than 0.03) increased over titers of all other treatment groups. These results indicate that the enhancement of in vivo humoral immunity by estrogen requires the thymus, and that a constitutive thymic factor, found in thymosin fraction 5, exerts a permissive influence on the action of E2 outside the thymus to increase a specific humoral immune response.     

Estradiol replacement enhances working memory in middle-aged rats when initiated immediately after ovariectomy but not after a long-term period of ovarian hormone deprivation

The goal of the present study was to explore the effects of long-term hormone deprivation on the ability of subsequent estrogen replacement to affect cognition. Female rats, 12 months of age, underwent ovariectomies (n = 30) or sham surgeries (n = 10). Intact rats and 20 ovariectomized rats received cholesterol implants. Ten ovariectomized rats received implants containing 25% estradiol. Five months later, implants were replaced. Half of the ovariectomized rats with cholesterol implants received estradiol implants and half received new cholesterol implants. Rats with estradiol implants received new estradiol implants. Intact rats were ovariectomized and given estradiol implants. Beginning 1 wk later, working memory performance was assessed in an eight-arm radial maze across 24 d of acquisition and during eight additional trials in which a 2.5-h delay was imposed between the fourth and fifth arm choices. Estradiol replacement initiated immediately after ovariectomy at either 12 or 17 months of age significantly improved performance during acquisition and delay trials, compared with control treatment. When estradiol replacement was initiated at 17 months of age, 5 months after ovariectomy, no enhancements were evident. Uteri of rats that experienced delayed estradiol replacement weighed significantly more than uteri of ovariectomized controls but significantly less than uteri of rats that received immediate estradiol replacement. Uterine weight negatively correlated with mean errors during acquisition. These results indicate that whereas chronic estradiol replacement regimens positively affect working memory in middle-aged animals when initiated immediately after ovariectomy, estradiol replacement is not effective when initiated after long-term hormone deprivation.     

葛根素联合雌二醇对去卵巢大鼠骨质疏松的治疗作用

目的了解小剂量葛根素联合雌二醇对去卵巢大鼠骨质疏松(OP)治疗作用,为中西医结合治疗Ⅰ型OP提供实验依据。方法 5月龄健康雌性大白鼠120只,分成5个实验组(n=24):①假手术组(sham);②去卵巢模型组(OVX);③葛根素组(Pr),皮下注射葛根素,50 mg/kg,1次/d;④雌二醇组(E2),皮下注射雌二醇200μg/kg,2次/w;⑤小剂量葛根素+雌二醇组(Pr+E2),皮下注射雌二醇100μg/kg,2次/w和葛根素25 mg/kg,1次/d。各实验组在第4、8、12和20周,随机取6只大鼠处死,取左股骨切片观察骨组织,取右股骨测量骨密度(BMD),取左心血测量血清雌二醇(E2)、碱性磷酸酶(AKP)。结果 OVX组的血清E2和BMD明显低于sham组(P<0.01),而血清AKP明显高于sham组(P<0.01);3个治疗组各时间的血清E2、AKP和BMD无显著差异(P>0.05)。小剂量的葛根素联合雌二醇治疗能使去卵巢大鼠骨组织、血清E2、AKP和BMD接近正常(P>0.05),与较大剂量的葛根素组或较大剂量的E2组相比无明显差异(P>0.05)。结论小剂量的E2与葛根素对去卵巢大鼠的治疗效果与单独使用较大剂量的葛根素或较大剂量的E2相比治疗效果相近。     

Estrogen receptor beta is involved in the anorectic action of estrogen

OBJECTIVE: Estrogen has been implicated in feeding behavior and adiposity. This study was undertaken to elucidate the mechanism underlying the anti-obesity and anorectic action of estrogen and the role of estrogen receptor (ER) in the central nervous system. METHODS AND RESULTS: Ovariectomy in 8-week-old female Wistar rats induced hyperphagia along with an increase in body weight and abdominal fat accumulation compared to control sham-operated rats. These changes were fully reversed by subcutaneous replacement of estradiol and were abrogated by pair-feeding. Then, the effects of intracerebroventricular infusion of estradiol, alone or in combination with antisense oligodeoxynucleotides (ODN), for ER in ovariectomized rats were examined. The estradiol group showed 10-20% lower daily food intake, and after the 2-week infusion period a 14% reduction in body weight with a similar reduction in abdominal fat compared to the vehicle group. The inhibitory effect of estradiol on food intake and body weight was blocked by co-administration of ER-beta antisense ODN, whereas ER-alpha antisense ODN did not show any influence. CONCLUSION: These results indicate that ER-beta in the central nervous system is involved in the anorectic action of estrogen.     

Effects of estrogen on cardiovascular injury in ovariectomized female DahlS.Z-Lepr(fa)/Lepr(fa) rats as a new animal model of metabolic syndrome

Although recent clinical trials have found an increased incidence of cardiovascular disease in women on estrogen replacement therapy, the underlying mechanism remains unclear. We have recently characterized DahlS.Z-Lepr(fa)/Lepr(fa) (DS/obese) rats, derived from a cross between Dahl salt-sensitive and Zucker rats, as a new animal model of metabolic syndrome. We have now examined the effects of estrogen replacement on cardiac pathophysiology in ovariectomized female DS/obese (Ovx-DS/obese) rats. Animals subjected to ovariectomy at 7 weeks of age were implanted subcutaneously with a 60-day release pellet containing 0.5 mg of 17β-estradiol (E(2)) or placebo at 8 weeks. Age-matched female homozygous lean littermates (DahlS.Z-Lepr(+)/Lepr(+) or DS/lean rats) of DS/obese rats served as controls. Animals were maintained on a normal diet and were subjected to echocardiography followed by various pathological analyses at 13 weeks of age. Ovx-DS/obese rats manifested hypertension at 7 weeks of age and thereafter and showed left ventricular (LV) fibrosis and diastolic dysfunction at 13 weeks. Treatment with E(2) attenuated hypertension in Ovx-DS/obese rats but had no effect on blood pressure in ovariectomized female DS/lean (Ovx-DS/lean) rats. E(2) treatment exacerbated LV fibrosis and diastolic dysfunction, as well as further increased cardiac oxidative stress and inflammation in Ovx-DS/obese rats, and it elicited similar effects in Ovx-DS/lean rats. E(2) reduced food intake, body weight, and visceral fat content in both Ovx-DS/obese and Ovx-DS/lean rats. E(2) treatment attenuated hypertension and obesity but exacerbated LV fibrosis and diastolic dysfunction in Ovx-DS/obese rats, with these latter effects being associated with increased cardiac oxidative stress and inflammation.     

Effect of growth hormone and estrogen administration on hepatocyte alterations in old ovariectomized female wistar rats

Aging could be due to the accumulation of oxidative damage. On the other hand, growth hormone (GH) and estrogen deficiency induce deleterious effects on different tissues, and hormonal replacement could counteract these effects. We have investigated whether GH and estrogen administration modify some parameters related to oxidative stress and inflammation in hepatocytes isolated from old ovariectomized female rats. Twenty-two month-old ovariectomized animals were divided into control rats, rats treated with GH, rats treated with estradiol, and rats treated with GH+estradiol. Two-month-old intact female rats were used as young reference group. Hepatocytes were isolated, cultured, and CO and NO release, ATP, cyclic-guanosyl monophosphate (cGMP), and lipid peroxide (LPO) content of cells, as well as phosphatidylcholine (PC) synthesis, were measured. Hepatocytes isolated from old ovariectomized rats showed a decrease in ATP content and PC synthesis compared to young rats. Age also induced an increase in LPO, NO, CO, and cGMP. Treating old rats with GH significantly increased ATP and reduced CO and cGMP levels. Estradiol administration improved all the parameters that were altered. Co-administration of GH and estrogens induced a more marked effect than estrogens alone only in cGMP content. In conclusion, administration of estrogens to old ovariectomized females seemed to prevent oxidative changes in hepatocytes, whereas the effect of GH is not so evident.     

Effect of ovariectomy and estrogen replacement on cardiovascular disease in heart failure-prone SHHF/Mcc- fa cp rats.

The importance of endogenous and exogenous estrogen levels to the development of cardiovascular disease in women in controversial. The purpose of our study was to examine the effect of estrogen on the development of hypertension, cardiac hypertrophy, ventricular function, and gene expression for atrial natriuretic peptide (ANP) and components of the renin angiotensin system in spontaneously hypertensive heart failure rats (SHHF/Mcc- facp). Development of hypertension was prevented in 3-month-old ovariectomized rats receiving subcutaneous 17 beta -estradiol implants (EST) compared to ovariectomized (OVX) and controls (CON). EST had the least left ventricular hypertrophy, CON were intermediate, and OVX had the most (P<0.05), correlating well with systolic blood pressure. OVX had significantly lower percentage V(1)myosin isoform compared to EST and CON, indicating reversion to a more immature phenotype associated with hypertrophy. Similarly, OVX had decreased percentage left ventricular shortening fraction by echocardiography compared to EST and CON. These changes were not accompanied by alterations in plasma ANP, or in expression of mRNA for left ventricular ANP, renal renin, or hepatic angiotensinogen. Serum angiotensin converting enzyme activity was lower in EST compared to CON or OVX. When 17 beta -estradiol was given to 17-month-old rats that had naturally ceased estrous cycling, there was no effect on hypertension, progression of cardiac functional decline, or survival. In conclusion, estradiol treatment given prior to the development of hypertension in SHHF prevented left ventricular hypertrophy and hypertension. Development of congestive heart failure was not delayed if 17 beta -estradiol was begun in the post-menopausal period. Effectiveness of estrogen therapy may depend on age or whether hypertension is already established at the time treatment is begun.     

补肾活血汤对去卵巢大鼠心肌微血管和CYP2J3的影响

目的 观察补肾活血汤（AED）对去卵巢大鼠心肌中细胞色素P4502J3蛋白（CYP2J3）表达、心肌微血管数目和血清雌二醇（E2）水平的影响。方法 48只成年SD雌鼠随机分为8组:正常对照组（Control组）、假手术组(Sham组)、去卵巢组(OVX组)、AED高剂量组(AED-H组)、AED低剂量组(AED-L组)、17β-雌二醇干预组(OVX/ERT组)、雌激素受体拮抗剂ICI182780干预组（AED-H/FET组及AED-L/FET组）。各组大鼠在处死前进行血液流变性指标的检测;Q-PCR和Western blot检测心肌CYP2J3的表达变化,免疫组化染色法检测心肌微血管数目变化,心脏B超检测心肌血流动力学变化,放射免疫法检测血清E2水平改变。结果 OVX组心肌微血管计数明显下降（P<0.01）,而OVX/ERT组与AED-H组心肌微血管计数改善明显;OVX组大鼠心肌CYP2J3 mRNA和蛋白表达明显下降,而OVX/ERT组与AED-H组的CYP2J3 mRNA和蛋白表达下降不明显;OVX组大鼠的全血黏度、血浆黏度及红细胞压积较Sham组大鼠增高,而OVX/ERT组及AED-H组全血黏度、血浆黏度及红细胞压积明显下降。OVX组大鼠的红细胞变形指数、红细胞刚性指数和红细胞电泳时间均明显增高（P<0.01）,但在OVX/ERT组及AED-H组较OVX组大鼠明显下降（P<0.05）。OVX组血流动力学各项指标均降低（P<0.05）,而与补充雌激素组相同,AED-H组左室射血分数改善明显。OVX组大鼠血清E2含量显著下降(P<0.05),高剂量、低剂量AED均可使OVX组大鼠E2含量显著升高(P<0.05)。结论 AED能增加心肌微血管数目,改善心肌血流动力学,其作用可能与增加OVX大鼠循环雌激素水平及促进CYP2J3蛋白表达有关。     

Effects of age on hormone levels and in vitro steroidogenesis by rat ovary and adrenal

In order to evaluate age-related changes in ovarian and adrenal steroid production, in vitro steroid production by adrenal glands and ovaries from young (3-4 mo) and middle-aged (10-11 mo) cycling rats was compared to serum steroid and gonadotropin levels on each morning of the estrous cycle. Basal LH levels were not different between young and mid-aged cycling rats except on estrus, when elevated estrogen (E) levels were correlated with depressed LH in the mid-aged rats. Basal FSH levels were generally elevated in mid-aged cycling and mid-aged constant estrus (CE) rats, but the FSH rise on estrus morning was not seen in the mid-aged rats. Serum progesterone levels were not changed with age or reproductive state, although in vitro ovarian progesterone secretion was decreased in mid-aged CE rats. Adrenal progesterone secretion increased significantly with age. Serum total testosterone was similar in young and mid-aged cycling and mid-aged CE rats, despite a highly significant increase in in vitro testosterone secretion by the CE ovary. Serum estradiol (E2) levels were significantly elevated on proestrus and estrus in the mid-aged rats. Although estrone (E1) levels appeared higher in the mid-aged than in the young cycling rats, the differences were not significant. Mid-aged CE rats had significantly elevated serum levels of both E1 and E2. In vitro ovarian estrone production was depressed in mid-aged cycling rats. Adrenal total estrogen production was similar in young and mid-aged animals. These results demonstrate that serum gonadotropin and steroid levels are altered in aging female rats prior to the loss of reproductive cycles. Changes in serum steroid levels are probably due to changes in circulating LH and FSH levels or the ovarian response to these gonadotropins, but changes in vitro basal steroid production suggest that intrinsic ovarian function may also change with advancing age. As rats enter a CE state, alterations in basal ovarian and adrenal steroid production are seen and may be partially responsible for maintenance of the acyclic state.     

Oestrogen modulates vascular adrenergic reactivity of the spontaneously hypertensive rat

BACKGROUND: Male spontaneously hypertensive rats (SHRs) show an increased vascular neurogenic response compared with normotensive Wistar-Kyoto (WKY) control rats. OBJECTIVE: To study the vascular adrenergic response in hypertensive and normotensive female rats, with a focus on the influence of oestrogen. METHODS: Female SHRs and WKY rats were allocated randomly to a control group or to groups to undergo ovariectomy or ovariectomy combined with oestrogen supplementation (17beta-oestradiol 150 microg/kg per day) for either 1 day (group 1E2) or 10 days (group 10E2). Mean arterial pressure (MAP) was recorded and small mesenteric arteries were mounted in a Multi Myograph 610M. Vascular reactivities to transmural nerve stimulation (TNS), exogenous noradrenaline and acetylcholine were analysed. RESULTS: MAP was significantly greater in SHRs than in WKY rats in all groups studied. Sensitivity to cumulative TNS (0.12-32 Hz) did not differ between vessels from control SHRs and WKY rats, expressed as the frequency giving 50% of maximal neurogenic response (Ef(50): 4.1 +/- 1.1 and 4.0 +/- 1.6 Hz, respectively). However, there was a greater reactivity to TNS in ovariectomized SHRs than in ovariectomized WKY rats (Ef(50) 1.8 +/- 0.7 and 6.8 +/- 2.2 Hz, respectively; P < 0.05). Oestradiol treatment significantly decreased the sensitivity to TNS in ovariectomized SHRs (P < 0.05), and after 10 days the frequency-response curves were almost identical (Ef(50) 6.3 +/- 1.9 Hz for group 10E2 SHRs and 5.6 +/- 0.8 Hz for group 10E2 WKY rats). The increased adrenergic reactivity in ovariectomized SHRs was inhibited by prazosin, an alpha(1)-adrenergic antagonist, and could not be explained by differences in endothelial function or sensitivity to applied noradrenaline. CONCLUSION: Increased adrenergic reactivity is not present in small arteries from female SHRs. The findings of this study suggest that oestrogen acts on prejunctional mechanisms, reducing full expression of hypertension and peripheral vascular pathology.     

Regulation of angiotensinogen gene expression by estrogen.

OBJECTIVE: Clarification of the role of estrogen in the regulation of angiotensinogen gene expression in multiple tissues. DESIGN: The effect of 17 beta-estradiol (E2; 10 micrograms/100 mg body weight) administration in ovariectomized (OVX) rats upon angiotensinogen messenger RNA (mRNA) levels in multiple tissues was assessed. Confounding ovarian factors were thus removed by studying the animals in the castrate state. Controls consisted of OVX and intact female rats. METHODS: Adult female Sprague-Dawley rats were ovariectomized and experiments begun 21 days postsurgery. Animals were injected with E2 and studied after 0, 1, 4, and 24 h of treatment. Levels of angiotensinogen mRNA were determined by Northern blot analysis using beta-actin mRNA as an internal standard. RESULTS: A single angiotensinogen mRNA species with molecular size of approximately 1800 bp was observed in rat liver, aorta, kidney, cardiac atria, hypothalamus and whole brain. Little or no angiotensinogen mRNA was identified in the pituitary gland. Angiotensinogen mRNA was most abundant in rat liver, hypothalamus, aorta and progressively less abundant in whole brain, cardiac atria and kidney. A twofold induction of hepatic angiotensinogen mRNA levels in E2-OVX rats was observed by 4h. The angiotensinogen mRNA levels in kidney were threefold higher by 4 h compared with OVX control animals. In aorta, the angiotensinogen mRNA level was also threefold higher by 1 h after E2 treatment. No significant effect of estradiol treatment was observed in cardiac atria although the level of angiotensinogen mRNA was higher in intact female rats compared with OVX controls. CONCLUSION: These results suggest that estrogen modulates angiotensinogen gene expression in a tissue-specific manner.     

17beta-estradiol differentially regulates blood-brain barrier permeability in young and aging female rats

Because both brain and its vasculature are potent targets of estrogen, age-related decline in estrogen levels or alterations in estrogen receptors may disrupt the integrity of the blood-brain barrier, leading to increased influx of toxic products. The present study tested the hypothesis that the blood-brain barrier is more permeable in reproductive senescent animals and will respond differently to estrogen replacement as compared with young adult females. Young adult and reproductive senescent rats were ovariectomized and replaced with an estrogen or control pellet. We found a 2- to 4-fold increase in extravasation of dye in the olfactory bulb and hippocampus of reproductive senescent females compared with young adults. Furthermore, estrogen significantly reduced dye extravasation in both olfactory bulb and hippocampus in young adults compared with age-matched counterparts that received a control pellet. However, estrogen replacement increased dye extravasation in the hippocampus of reproductive senescent females compared with age-matched control-pellet replaced animals, whereas dye extravasation was unchanged by estrogen in the olfactory bulb of senescent females. There were no age- and estrogen-related differences in dye accumulation in the pituitary gland, which is a circumventricular organ. These results support the hypothesis that the hormonal decline that marks reproductive senescence leads to increased permeability of the blood-brain barrier, which is further exacerbated by estrogen treatment in specific regions.     

Influence of sex and estrogen on vitamin D-induced arterial calcification in rats

Background:   It is known that the process of arteriosclerosis is affected by sex and estrogen. The present study was thus undertaken to examine the effects of these factors on arterial calcification, a form of arteriosclerosis, using a rat model of vitamin D toxicity.
Methods and results:   Vehicle or 5 µg/kg per day 1α(OH)D₃ was given to male and female 30-week-old Fisher rats for 2 weeks. Arterial calcification, evaluated by calcium content in the aorta, was 70% more marked in male rats compared to that in female rats, whereas calcium content in the aorta was similar in vehicle-treated male and female rats. Next, the effects of ovariectomy and estrogen replacement (estradiol dipropionate 20 µg/kg per week) were examined in female rats given 5 µg/kg per day 1α(OH)D₃ for 2 weeks. Calcium content in the aorta was significantly higher in ovariectomized rats than in sham-operated rats and in ovariectomized and estrogen-replaced rats. No difference between the groups was seen when vehicle was given to the animals.
Conclusions:   These results suggest that sex and estrogen can modify the process of arterial calcification. The mechanisms remain to be determined, although the effects were independent of serum calcium level.     

The expression of aromatase in gonadotropes is regulated by estradiol and gonadotropin-releasing hormone in a manner that differs from the regulation of luteinizing hormone

The role of estrogens is dual: they suppress basal expression of gonadotropins and enhance GnRH responsiveness at the time of the LH surge. Estrogens are synthesized by cytochrome P450 aromatase (P450arom), encoded by the cyp19 gene. We focused on the cyp19 gene in rat and showed that it is expressed in gonadotropes through promoters PII and PI.f, using RT-PCR and dual fluorescence labeling with anti-P450arom and -LH antibodies. Real-time PCR quantification revealed that aromatase mRNA levels varied during the estrous cycle and were significantly increased after ovariectomy. This effect is prevented by estradiol (E2) as well as GnRH antagonist administration, suggesting that GnRH may mediate the steroid effect. Interestingly, the long-acting GnRH agonist that induces LH desensitization does not modify aromatase expression in ovariectomized rats. Administration of E2 in ovariectomized rats receiving either GnRH agonist or GnRH antagonist clearly demonstrated that E2 also reduces cyp19 expression at the pituitary level. The selective estrogen receptor-alpha ligand propyl pyrazole triol and the selective estrogen receptor-beta ligand diarylpropionitrile both mimic the E2 effects. By contrast, propyl pyrazole triol reduces LH beta expression whereas diarylpropionitrile does not. In addition, using transient transfection assays in an L beta T2 gonadotrope cell line, we provided evidence that GnRH agonist stimulated, in a dose-dependant manner, cyp19 promoters PII and PI.f and that E2 decreased the GnRH stimulation. In conclusion, our data demonstrate that GnRH is an important signal in the regulation of cyp19 in gonadotrope cells. Both common and specific intracellular factors were responsible for dissociated variations of LH beta and cyp19 expression.     

Improvement of endothelial dysfunction by selective estrogen receptor-alpha stimulation in ovariectomized SHR

Both known estrogen receptors, ERalpha and ERbeta, are expressed in blood vessels. To gain further insight into the role of ERalpha in a functional setting, we investigated the effect of the novel highly selective ERalpha agonist Cpd1471 on vascular reactivity in ovariectomized spontaneously hypertensive rats (SHR). After ovariectomy or sham operation, 12-week-old female SHR received either 17beta-estradiol (E2, 2 microg/kg body wt per day), the selective ERalpha agonist Cpd1471 (30 microg/kg body wt per day), or placebo. Acetylcholine-induced endothelium-dependent vasorelaxation was significantly blunted in aortas from ovariectomized rats (Rmax, 53%+/-3% versus sham, 79%+/-2%; P<0.001). Treatment with E2 or Cpd1471 significantly augmented acetylcholine-induced relaxation in ovariectomized rats (Rmax, 70%+/-2%; resp, 73%+/-2%). Endothelium-independent relaxation induced by sodium nitroprusside was not different among the four groups. The contractile response induced by the nitric oxide (NO) synthase inhibitor Nomega-nitro-l-arginine, an index of basal NO formation, was significantly lower in ovariectomized rats compared with sham-operated animals (53+/-2% versus 77%+/-5%; P<0.01) and was normalized by both E2 (70%+/-2%) and Cpd1471 (70%+/-3%). Aortic endothelial NO synthase (eNOS) expression and phosphorylation of the vasodilator-stimulated phosphoprotein, an index of NO/cGMP-signaling, was reduced in ovariectomized SHR and normalized by E2 and Cpd1471. In SHR after ovariectomy, endothelium-dependent NO-mediated vasorelaxation and eNOS expression are attenuated. The novel selective ERalpha agonist Cpd1471 prevented these pathophysiological changes to a similar extent as E2. Thus, the pharmacological principle of selective ERalpha activation mediates positive vascular effects.