Genome and Hormones: Gender Differences in Physiology: Selected Contribution: Cerebrovascular NOS and cyclooxygenase are unaffected by estrogen in mice lacking estrogen receptor-alpha

Estrogen alters reactivity of cerebral arteries by modifyingproduction of endothelium-dependent vasodilators. Estrogen receptors (ER) are thought to be involved, but the responsible ER subtype isunknown. ER- knockout (ERKO) mice were used to test whether estrogen acts via ER-. Mice were ovariectomized, with or without estrogen replacement, and cerebral blood vessels were isolated 1 molater. Estrogen increased levels of endothelial nitric oxide synthaseand cyclooxygenase-1 in vessels from wild-type mice but was ineffectivein ERKO mice. Endothelium-denuded middle cerebral artery segmentsfrom all animals constricted when pressurized. In denuded arteries fromERKO but not wild-type mice, estrogen treatment enhancedconstriction. In endothelium-intact, pressurized arteries fromwild-type estrogen-treated mice, diameters were larger compared witharteries from untreated wild-type mice. In addition, contractileresponses to indomethacin were greater in arteries from wild-typeestrogen-treated mice compared with arteries from untreated wild-typemice. In contrast, estrogen treatment of ERKO mice had no effect ondiameter or indomethacin responses of endothelium-intact arteries. ThusER- regulation of endothelial nitric oxide synthase andcyclooxygenase-1 pathways appears to contribute to effects of estrogenon cerebral artery reactivity.

     

Effect of estrogen on cerebrovascular prostaglandins is amplified in mice with dysfunctional NOS

Chronic estrogen treatment increases endothelial vasodilator function in cerebral arteries. Endothelial nitric oxide (NO) synthase (eNOS) is a primary target of the hormone, but other endothelial factors may be modulated as well. In light of possible interactions between NO and prostaglandins, we tested the hypothesis that estrogen treatment increases prostanoid-mediated dilation using NOS-deficient female mouse models, i.e., mice treated with a NOS inhibitor [N(G)-nitro-l-arginine methyl ester (l-NAME)] for 21 days or transgenic mice with the eNOS gene disrupted (eNOS(-/-)). All mice were ovariectomized; some in each group were treated chronically with estrogen. Cerebral blood vessels then were isolated for biochemical and functional analyses. In vessels from control mice, estrogen increased protein levels of eNOS but had no significant effect on cyclooxygenase (COX)-1 protein, prostacyclin production, or constriction of pressurized, middle cerebral arteries to indomethacin, a COX inhibitor. In l-NAME-treated mice, however, cerebrovascular COX-1 levels, prostacyclin production, and constriction to indomethacin, as well as eNOS protein, were all greater in estrogen-treated animals. In vessels from eNOS(-/-) mice, estrogen treatment also increased levels of COX-1 protein and constriction to indomethacin, but no effect on prostacyclin production was detected. Thus cerebral blood vessels of control mice did not exhibit effects of estrogen on the prostacyclin pathway. However, when NO production was dysfunctional, the impact of estrogen on a COX-sensitive vasodilator was revealed. Estrogen has multiple endothelial targets; estrogen effects may be modified by interactions among these factors.     

Multiple forms of estrogen receptor-alpha in cerebral blood vessels: regulation by estrogen

The cerebral vasculature is an important target tissue for estrogen, as evidenced by significant effects of estrogen on vascular reactivity and protein levels of endothelial nitric oxide synthase and prostacyclin synthase. However, the presence, localization, and regulation of estrogen receptors in the cerebral vasculature have not been investigated. In this study, we identified the presence of estrogen receptor-alpha (ER-alpha) in female rat cerebral blood vessels and localized this receptor to both smooth muscle and endothelial cells by use of immunohistochemistry and confocal microscopy. With immunoblot analysis, multiple forms of ER-alpha were detected at 110, 93, 82, 50, and 45 kDa in addition to a relatively weak band corresponding to the 66-kDa putative unmodified receptor. The 82-kDa band was identified as Ser(118)-phosphorylated ER-alpha, whereas the 50-kDa band lacks the normal NH(2) terminus, suggestive of an ER-alpha splice variant. Lower molecular mass bands persisted after in vivo inhibition of 26S proteasome activity with lactacystin, whereas the 110- and 93-kDa bands increased. All forms of ER-alpha in cerebral vessels were decreased after ovariectomy but significantly increased after chronic estrogen exposure in vivo.     

Regulation of nitric oxide-dependent vasodilation in coronary arteries of estrogen receptor-alpha-deficient mice

Estrogen has been shown to increase endothelium-dependent vasodilation and expression of endothelial nitric oxide (NO) synthase (eNOS); however, the role of estrogen receptors in mediating estrogen effects on endothelial function remains to be elucidated. The purpose of this study was to test the hypothesis that estrogen modulates NO-dependent vasodilation of coronary arteries through its action on estrogen receptor-alpha (ER-alpha) to increase protein levels of eNOS and Cu/Zn superoxide dismutase (SOD-1). Vasodilation to acetylcholine (ACh) and sodium nitroprusside was assessed in isolated coronary arteries from intact and ovariectomized female wild-type (WT) and ER-alpha knockout (ERalphaKO) mice. Protein levels for eNOS and SOD-1 were also evaluated. Vasodilation to ACh was not significantly altered in ERalphaKO mice compared with WT mice. Ovariectomy reduced responsiveness to ACh in ERalphaKO mice but not WT mice. Responses to sodium nitroprusside were not altered by disruption of ER-alpha or by ovariectomy. Supplementation with estrogen restored ACh-induced vasodilation in ovariectomized ERalphaKO mice. eNOS protein was reduced in ERalphaKO mice compared with WT mice. Ovariectomy caused a further reduction in eNOS protein in ERalphaKO mice, but this reduction was reversed by estrogen treatment. SOD-1 protein levels were increased by disruption of ER-alpha. Ovariectomy reduced SOD-1 protein in ERalphaKO mice, but this reduction was partially reversed by estrogen replacement. These results suggest that estrogen modulation of eNOS protein content is mediated in part through ER-alpha. NO-dependent responses are preserved in ERalphaKO mice, possibly through increased SOD-1 expression and enhanced bioavailability of NO.     

Estrogen reduces mouse cerebral artery tone through endothelial NOS- and cyclooxygenase-dependent mechanisms

Gender and estrogen status are known to influence the incidence and severity of cerebrovascular disease. The vasoprotective effects of estrogen are thought to include both nitric oxide-dependent and independent mechanisms. Therefore, using small, resistance-sized arteries pressurized in vitro, the present study determined the effect of gender and estrogen status on myogenic reactivity of mouse cerebral arteries. Luminal diameter was measured in middle cerebral artery segments from males and from females that were either untreated, ovariectomized (OVX), or OVX with estrogen replacement (OVX + EST). The maximal passive diameters of arteries from all four groups were similar. In response to increases in transmural pressure, diameters of arteries from males and OVX females were smaller compared with diameters of arteries from either untreated or OVX + EST females. In the presence of N(G)-nitro-L-arginine methyl ester, artery diameters decreased in all groups, but diameters remained significantly smaller in arteries from males and OVX females compared with untreated and OVX + EST females. After endothelium removal or when inhibition of nitric oxide synthase and cyclooxygenase were combined, differences in diameters of arteries from OVX and OVX + EST were abolished. These data suggest that chronic estrogen treatment modulates myogenic reactivity of mouse cerebral arteries through both endothelium-derived cyclooxygenase- and nitric oxide synthase-dependent mechanisms.     

Age alters cerebrovascular inflammation and effects of estrogen

In young adult females, estrogen treatment suppresses the cerebrovascular inflammatory response; this is mediated in part via NF-kappaB, a key regulator of inflammatory genes. To examine whether age modifies effects of estrogen on vascular inflammation in the brain, female rats, 3 and 12 mo of age, were ovariectomized; half were treated with estrogen for 4 wk. Cerebral blood vessels were isolated from the animals at 4 and 13 mo of age. Inflammation was induced by LPS, either injected in vivo or incubated with isolated vessels ex vivo. Basal levels of cytoplasmic NF-kappaB were significantly higher in cerebral vessels of young rats, but the ratio of nuclear to cytoplasmic levels was greater in middle-aged animals. LPS exposure increased nuclear NF-kappaB DNA binding activity, protein levels of inducible nitric oxide synthase and cyclooxygenase-2, and production of nitric oxide and PGE(2) in cerebral vessels. All effects of LPS were markedly greater in vessels from the older animals. Estrogen significantly inhibited the LPS-induced increase in NF-kappaB DNA binding activity in cerebral vessels from animals at both ages. In 4-mo-old rats, estrogen also significantly suppressed LPS induction of inducible nitric oxide synthase and cyclooxygenase-2 proteins, as well as production of nitric oxide and PGE(2). In contrast, in 13-mo-old females, estrogen did not significantly affect these indexes of cerebrovascular inflammation. Thus the protective, anti-inflammatory effect of estrogen on cerebral blood vessels that is observed in young adults may be attenuated in aged animals, which exhibit a greater overall cerebrovascular response to inflammatory stimuli.     

17beta-estradiol decreases vascular tone in cerebral arteries by shifting COX-dependent vasoconstriction to vasodilation

We have previously shown that estrogen treatment increases cerebrovascular cyclooxygenase-1, prostacyclin synthase, and production of prostacyclin. Therefore, vascular tone and prostanoid production were measured to investigate functional consequences of estrogen exposure. Middle cerebral arteries were isolated from ovariectomized female Fischer-344 rats with or without chronic in vivo 17beta-estradiol treatment. In vivo 17beta-estradiol treatment increased cerebral artery diameter; functional endothelium was required for expression of these differences. The nonspecific cyclooxygenase inhibitor indomethacin constricted, whereas arachidonic acid dilated, cerebral arteries from estrogen-treated animals. Estrogen exposure increased production of prostacyclin by cerebral arteries. Conversely, in estrogen-deficient animals, indomethacin dilated and arachidonic acid constricted cerebral blood vessels. This correlated with vasorelaxation following inhibition of the thromboxane-endoperoxide receptor with SQ-29548 but not after selective blockade of thromboxane synthase with furegrelate, suggesting prostaglandin endoperoxide (i.e., PGH2) activity. Removal of the endothelium or selective blockade of cyclooxygenase-1 with SC-560 abolished estrogen-mediated differences in the effects of arachidonate on vessel diameter and on prostacyclin production by cerebral arteries. These data suggest 17beta-estradiol decreases cerebrovascular tone by shifting the primary end product of the endothelial cyclooxygenase-1 pathway from the constrictor prostaglandin PGH2 to the vasodilator prostacyclin. These effects of estrogen may contribute to the heightened thromboresistance and enhanced cerebral blood flow documented in pre-versus postmenopausal women.     

Rapid activation of endothelial nitric oxide synthase by estrogen.

Estrogen is an important atheroprotective molecule that causes the rapid dilation of blood vessels by stimulating endothelial nitric oxide synthase (eNOS). There is also evidence that estrogen modulates airway epithelial NO production, thereby potentially affecting bronchial hyperresponsiveness. Studies in cultured endothelial and airway epithelial cells indicate that physiologic concentrations of estrogen cause rapid direct activation of eNOS that is unaffected by actinomycin D, but fully inhibited by estrogen receptor (ER) antagonism. Overexpression of ERalpha leads to marked enhancement of the acute response to estrogen, and this process is blocked by ER antagonism, it is specific to estrogen, and it requires the ERalpha hormone binding domain. In addition, the acute response of eNOS to estrogen can be reconstituted in COS-7 cells cotransfected with wild-type ERalpha and eNOS, but not by transfection with eNOS alone. Furthermore, the inhibition of calcium influx, or tyrosine kinases or MAP kinase prevents the stimulation of eNOS by estrogen, and estrogen causes rapid ER-dependent activation of MAP kinase. These findings indicate that the acute effects of estrogen on both endothelial and airway epithelial eNOS are mediated by ERalpha functioning in a novel, nongenomic manner to activate the enzyme via calcium-dependent, MAP kinase-dependent mechanisms.     

Regulation of progesterone receptors and decidualization in uterine stroma of the estrogen receptor-alpha knockout mouse

Regulation of progesterone receptor (PR) in uterine stroma (endometrial stroma plus myometrium) by estrogen was investigated in estrogen receptor-alpha (ERalpha) knockout (alphaERKO) mice. 17 beta-Estradiol (E(2)) increased PR levels in uterine stroma of ovariectomized alphaERKO mice, and ICI 182 780 (ICI) inhibited this E(2)-induced PR expression. Estrogen receptor-beta(ER beta) was detected in both uterine epithelium and stroma of wild-type and alphaERKO mice by immunohistochemistry. In organ cultures of alphaERKO uterus, both E(2) and diethylstilbestrol induced stromal PR, and ICI inhibited this induction. These findings suggest that estrogen induces stromal PR via ERbeta in alphaERKO uterus. However, this process is not mediated exclusively by ERbeta+, because in ERbeta knockout mice, which express ERalpha, PR was up-regulated by E(2) in uterine stroma. In both wild-type and alphaERKO mice, progesterone and mechanical traumatization were essential and sufficient to induce decidual cells, even though E(2) and ERalpha were also required for increase in uterine weight. Progesterone receptor was strongly expressed in decidual cells in alphaERKO mice, and ICI did not inhibit decidualization or PR expression. This study suggests that up-regulation of PR in endometrial stroma is mediated through at least three mechanisms: 1) classical estrogen signaling through ERalpha, 2) estrogen signaling through ERbeta, and 3) as a result of mechanical stimulation plus progesterone, which induces stromal cells to differentiate into decidual cells. Each of these pathways can function independently of the others.     

Contribution of epoxyeicosatrienoic acids to flow-induced dilation in arteries of male ERalpha knockout mice: role of aromatase

We studied the roles of estrogen receptors (ER) and aromatase in the mediation of flow-induced dilation (FID) in isolated arteries of male ERalpha-knockout (ERalpha-KO) and wild-type (WT) mice. FID was comparable between gracilis arteries of WT and ERalpha-KO mice. In WT arteries, inhibition of NO and prostaglandins eliminated FID. In ERalpha-KO arteries, N(omega)-nitro-L-arginine methyl ester (L-NAME) inhibited FID by approximately 26%, whereas indomethacin inhibited dilations by approximately 50%. The remaining portion of the dilation was abolished by additional administration of 6-(2-proparglyoxyphenyl)hexanoic acid (PPOH) or iberiotoxin, inhibitors of epoxyeicosatrienoic acid (EET) synthesis and large-conductance potassium channels, respectively. By using an electrophysiological technique, we found that, in the presence of 10 dyne/cm(2) shear stress, perfusate passing through donor vessels isolated from gracilis muscle of ERalpha-KO mice subjected to L-NAME and indomethacin elicited smooth muscle hyperpolarization and a dilator response of endothelium-denuded detector vessels. These responses were prevented by the presence of iberiotoxin in detector or PPOH in donor vessels. Gas chromatography-mass spectrometry (GC-MS) analysis indicated a significant increase in arterial production of EETs in ERalpha-KO compared with WT mice. Western blot analysis showed a significantly reduced endothelial nitric oxide synthase expression but enhanced expressions of aromatase and ERbeta in ERalpha-KO arteries. Treatment of ERalpha-KO arteries with specific aromatase short-interfering RNA for 72 h, knocked down the aromatase mRNA and protein associated with elimination of EET-mediation of FID. Thus, FID in male ERalpha-KO arteries is maintained via an endothelium-derived hyperpolarizing factor/EET-mediated mechanism compensating for reduced NO mediation due, at least in part, to estrogen aromatized from testosterone.     

Vascular protection by estrogen in ischemia-reperfusion injury requires endothelial nitric oxide synthase

Estrogen increases nitric oxide (NO) production by inducing the activity of endothelial NO synthase (eNOS) (Simoncini et al. Nature 407: 538, 2000). Ischemia (30 min) and reperfusion (I/R) increased the number of adherent leukocytes and decreased their rolling velocities in mouse cremaster muscle venules with a strong dependence on wall shear rate. Minimum rolling velocity at approximately 5 min after the onset of reperfusion was accompanied by increased P-selectin expression. This preceded the peak in leukocyte adhesion (at 10-15 min). In untreated wild-type mice, I/R caused a decrease of leukocyte rolling velocity from 37 to 26 microm/s and a 2.0-fold increase in leukocyte adhesion. Both were completely abolished by 0.25 mg ip estrogen 1 h before surgery. In eNOS(-/-) mice, the decrease of leukocyte rolling velocity and increase in adhesion were similar but were only marginally improved by estrogen. We conclude that the protective effect of estrogen, as measured by leukocyte rolling and adhesion, is significantly reduced in eNOS(-/-) mice, suggesting that induction of eNOS activity is the major mechanism of vasoprotection by estrogen in this model.     

Dilation of rat diaphragmatic arterioles by flow and hypoxia: roles of nitric oxide and prostaglandins.

The in vitro responses to ACh, flow, and hypoxia were studied in arterioles isolated from the diaphragms of rats. The endothelium was removed in some vessels by low-pressure air perfusion. In endothelium-intact arterioles, pressurized to 70 mmHg in the absence of luminal flow, ACh (10(-5) M) elicited dilation (from 103 +/- 10 to 156 +/- 13 microm). The response to ACh was eliminated by endothelial ablation and by the nitric oxide synthase antagonists NG-nitro-L-arginine (L-NNA; 10(-5) M) and NG-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) but not by indomethacin (10(-5) M). Increases in luminal flow (5-35 microl/min in 5 microl/min steps) at constant distending pressure (70 mmHg) elicited dilation (from 98 +/- 8 to 159 +/- 12 microm) in endothelium-intact arterioles. The response to flow was partially inhibited by L-NNA, L-NAME, and indomethacin and eliminated by endothelial ablation and by concurrent treatment with L-NAME and indomethacin. The response to hypoxia was determined by reducing the periarteriolar PO2 from 100 to 25-30 Torr by changing the composition of the gas used to bubble the superfusing solution. Hypoxia elicited dilation (from 110 +/- 9 to 165 +/- 12 microm) in endothelium-intact arterioles but not in arterioles from which the endothelium had been removed. Hypoxic vasodilation was eliminated by treatment with indomethacin and was not affected by L-NAME or L-NNA. In rat diaphragmatic arterioles, the response to ACh is dependent on endothelial nitric oxide release, whereas the response to hypoxia is mediated by endothelium-derived prostaglandins. Flow-dilation requires that both nitric oxide and cyclooxygenase pathways be intact.     

Maturation depresses mouse cerebrovascular tone through endothelium-dependent mechanisms

In light of previous observations that the range of arterial pressures over which cerebral blood flow is autoregulated differs dramatically in neonates and adults, the present experiments explored the hypothesis that pressure-induced intrinsic arterial tone is regulated differently in neonatal and adult cerebral arteries. In cannulated and pressurized endothelium-intact mouse cerebral arteries <150 microm in diameter, active intrinsic tone was evident at intraluminal pressures as low as 10 mmHg in neonatal arteries, but only at pressures of 60 mmHg or greater in adult arteries. Administration of 10 microM indomethacin produced no significant effect on tone at any pressure in either neonatal or adult arteries, but subsequent addition of 100 microroarginine methyl ester (NAME) significantly vasoconstricted both neonatal and adult arteries at all pressures. Conversely, administration of 100 microE alone significantly vasoconstricted adult arteries only, and subsequent addition of 10 microomethacin produced a significant additional vasoconstriction in adult arteries only, indicating an important interaction between the nitric oxide synthase and cyclooxygenase pathways, at least in adult arteries. In the presence of both indomethacin and NAME, intrinsic tone was significantly greater in neonatal than adult arteries, but when the endothelium was removed, tone was similar in neonatal and adult arteries at all pressures. Together, these results suggest that pressure-induced myogenic tone is regulated similarly in neonatal and adult mouse cerebral arteries but that the contribution of endothelial vasoactive factors to intrinsic tone is highly age dependent.     

Simulated microgravity upregulates an endothelial vasoconstrictor prostaglandin.

Endothelial nitric oxide contributes to the vascular hyporesponsiveness to norepinephrine (NE) observed in carotid arteries from rats exposed to simulated microgravity. The goal of the present study was to determine whether a cyclooxygenase product of arachidonic acid also influences vascular responsiveness in this setting. Microgravity was simulated in rats by hindlimb unweighting (HU). After 20 days of HU, carotid arteries were isolated from control and HU-treated rats, and vascular rings were mounted in tissue baths for the measurement of isometric contraction. Two cyclooxygenase inhibitors, indomethacin and ibuprofen, and the selective thromboxane A(2) prostanoid-receptor antagonist, SQ-29548, had no effect on the contraction to NE in control vessels but markedly reduced contraction to NE in HU vessels. When the endothelium was removed, indomethacin no longer had any effect on the NE-induced contraction in HU vessels. In endothelium-intact vessels in the presence of indomethacin, the addition of the nitric oxide synthase inhibitor, N(G)-L-nitro-arginine methyl ester, to the medium bathing HU vessels increased the contraction to NE to the level of that of the control vessels. These results indicate that HU treatment induced two endothelial changes in carotid artery that opposed each other. Nitric oxide activity was increased and was responsible for the vascular hyporesponsiveness to NE. The activity of a vasoconstrictor prostaglandin was also increased, and attenuated the vasodilating effect of nitric oxide.     

Dilatory responses to estrogenic compounds in small femoral arteries of male and female estrogen receptor-beta knockout mice

The objectives of this study were to determine whether acute dilatory responses to estrogen receptor agonists are altered in isolated arteries from estrogen receptor beta-deficient mice (beta-ERKO) and to gain insight into the role of nitric oxide (NO) in these responses. Femoral arteries (approximately 250 microm) from male and female beta-ERKO mice and wild-type (WT) littermates (26 female, 13 in each group; and 24 male, 12 in each group) were mounted on a Multi-Myograph. Concentration-response curves to 17beta-estradiol (17beta-E2) and the selective estrogen receptor-alpha (ER-alpha) agonist propyl-[1H]-pyrazole-1,3,5-triy-trisphenol (PPT) were obtained before and after NO synthase (NOS) inhibition [Nomega-nitro-L-arginine methyl ester (L-NAME), 0.1 mM] in arteries preconstricted with U-46619 (a thromboxane analog). In WT mice, responses to the potent estrogen receptor-beta (ER-beta) agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) and the contribution of NO were also assessed. Concentration-response curves to 17beta-E2 and PPT were similar in arteries from WT and -ERKO mice of both genders, but NO-mediated relaxation was different, since L-NAME reduced 17-E2 mediated relaxation in arteries from male and female beta-ERKO but not WT mice (P < 0.05). NOS inhibition reduced dilation to PPT in arteries from male and female WT mice, as well as arteries from female beta-ERKO mice (P < 0.05). Responses to DPN in arteries from WT female and male mice did not differ after NOS inhibition. The acute dilatory responses to estrogenic compounds are similar in WT and beta-ERKO mice but differ mechanistically. Because NO appeared to contribute to responses to 17beta-E2 in arteries from beta-ERKO but not WT mice, the presence of ER- apparently inhibits ER--mediated NO relaxation.     

Estrogen induces vascular wall dilation: mediation through kinase signaling to nitric oxide and estrogen receptors alpha and beta

Estrogen has been shown to affect vascular cell and arterial function in vitro and in vivo. Here we examined the ability of estradiol (E(2)) to cause rapid arterial dilation of elastic and muscular arteries in vivo and the mechanisms involved. E(2) administration caused a rapid increase in the outer wall diameter of both types of arteries in ovariectomized female mice. This resulted from estrogen receptor (ER)-mediated stimulation of nitric oxide production, demonstrated by preinjecting the mice arteries with a soluble inhibitor of nitric oxide (monomethyl l-arginine) and by showing the absence of E(2) action in eNOS-/- mice. Rapid activation of both ERK/MAP kinase and phosphatidylinositol 3-kinase activity was found in the E(2)-exposed arteries, and inhibiting either kinase prevented the vasodilatory action of E(2). Kinase activation and vasodilator responses to E(2) were absent in either ERalpha or ERbeta knock-out mice, implicating both receptor subtypes as mediating this E(2) action. These results indicate that E(2) modulation of arterial tonus through plasma membrane ER and rapid signaling could underlie many previously observed actions of estrogen reported to occur in women.     

Effect of ovariectomy on adipose tissue of mice in the absence of estrogen receptor alpha (ERalpha): a potential role for estrogen receptor beta (ERbeta).

Adipose tissue deposition is highly responsive to estrogen; ovariectomy increases adipose deposition, and estrogen replacement reverses this. Estrogen receptor alpha (ERalpha) plays a major role in adipose tissue. ERalpha knockout (alphaERKO) mice show an increase in adipose tissue of over a 100 % compared to wild-type mice. However, alphaERKO mice undergo a 10-fold increase in 17beta-estradiol (E2), and persistent or even increased signaling through ERbeta could be a factor in obesity of alphaERKO mice. To test the hypothesis that ERbeta plays a role in adipose tissue, adult female alphaERKO mice were ovariectomized or sham-ovariectomized and fed a phytoestrogen-free diet. Ovariectomized mice were treated with vehicle or E2, and bodyweights and food consumption were measured. Mice were killed after 28 days and inguinal and parametrial fat pads collected. Sham-ovariectomized alphaERKO mice had increased body weight, ovariectomized alphaERKO mice showed a 6 % decrease, and E2 replacement restored body weight to sham levels. Fat pads of ovariectomized alphaERKO mice showed 45 % and 16 % decreases in weight and adipocyte circumference, respectively, compared to sham-ovariectomized or E2-replaced ovariectomized alphaERKO mice. Ovariectomized alphaERKO mice showed a trend towards decreased feed consumption that did not reach significance. Blood glucose levels were lower both before and after glucose injection in ovariectomized compared to sham alphaERKO mice, and E2 treatment reversed this. Insulin levels following glucose challenge were lower in ovariectomized compared to sham-ovariectomized alphaERKO mice, indicating that ovariectomy ameliorated the glucose intolerance and insulin resistance in alphaERKO mice. Immunohistochemical analysis revealed strong staining for ERbeta in adipose tissue. These observations indicate that removing E2/ERbeta signaling in alphaERKO mice by ovariectomy decreases body and fat-pad weights and adipocyte size, while improving insulin and glucose metabolism. ERbeta mediated effects on adipose tissue are opposite those of ERalpha, although E2 effects on adipose tissue are predominately through ERalpha.     

Vasodilator mechanisms in the coronary circulation of endothelial nitric oxide synthase-deficient mice

Previous studies have demonstrated that responses to endothelium-dependent vasodilators are absent in the aortas from mice deficient in expression of endothelial nitric oxide synthase (eNOS -/- mice), whereas responses in the cerebral microcirculation are preserved. We tested the hypothesis that in the absence of eNOS, other vasodilator pathways compensate to preserve endothelium-dependent relaxation in the coronary circulation. Diameters of isolated, pressurized coronary arteries from eNOS -/-, eNOS heterozygous (+/-), and wild-type mice (eNOS +/+ and C57BL/6J) were measured by video microscopy. ACh (an endothelium-dependent agonist) produced vasodilation in wild-type mice. This response was normal in eNOS +/- mice and was largely preserved in eNOS -/- mice. Responses to nitroprusside were also similar in arteries from eNOS +/+, eNOS +/-, and eNOS -/- mice. Dilation to ACh was inhibited by N(G)-nitro-L-arginine, an inhibitor of NOS in control and eNOS -/- mice. In contrast, trifluoromethylphenylimidazole, an inhibitor of neuronal NOS (nNOS), decreased ACh-induced dilation in arteries from eNOS-deficient mice but had no effect on responses in wild-type mice. Indomethacin, an inhibitor of cyclooxygenase, decreased vasodilation to ACh in eNOS-deficient, but not wild-type, mice. Thus, in the absence of eNOS, dilation of coronary arteries to ACh is preserved by other vasodilator mechanisms.     

Angiotensin II stimulates nitric oxide production in pulmonary artery endothelium via the type 2 receptor

We previously reported that angiotensin II stimulates an increase in nitric oxide production in pulmonary artery endothelial cells. The aims of this study were to determine which receptor subtype mediates the angiotensin II-dependent increase in nitric oxide production and to investigate the roles of the angiotensin type 1 and type 2 receptors in modulating angiotensin II-dependent vasoconstriction in pulmonary arteries. Pulmonary artery endothelial cells express both angiotensin II type 1 and type 2 receptors as assessed by RT-PCR, Western blot analysis, and flow cytometry. Treatment of the endothelial cells with PD-123319, a type 2 receptor antagonist, prevented the angiotensin II-dependent increase in nitric oxide synthase mRNA, protein levels, and nitric oxide production. In contrast, the type 1 receptor antagonist losartan enhanced nitric oxide synthase mRNA levels, protein expression, and nitric oxide production. Pretreatment of the endothelial cells with either PD-123319 or an anti-angiotensin II antibody prevented this losartan enhancement of nitric oxide production. Angiotensin II-dependent enhanced hypoxic contractions in pulmonary arteries were blocked by the type 1 receptor antagonist candesartan; however, PD-123319 enhanced hypoxic contractions in angiotensin II-treated endothelium-intact vessels. These data demonstrate that angiotensin II stimulates an increase in nitric oxide synthase mRNA, protein expression, and nitric oxide production via the type 2 receptor, whereas signaling via the type 1 receptor negatively regulates nitric oxide production in the pulmonary endothelium. This endothelial, type 2 receptor-dependent increase in nitric oxide may serve to counterbalance the angiotensin II-dependent vasoconstriction in smooth muscle cells, ultimately regulating pulmonary vascular tone.     

A change in the redox environment and thromboxane A2 production precede endothelial dysfunction in mice

We reported that the endothelial dysfunction that develops with age was associated with a proinflammatory phenotype. In this study, we hypothesized that an increased production of proinflammatory cyclooxygenase (COX) products occurs before endothelial dysfunction. Dilations to acetylcholine (ACh) were recorded from pressurized renal arteries isolated from 3- and 6-mo-old C57Bl/6 male mice treated or not with the polyphenol catechin (30 mg x kg(-1) x day(-1)) in drinking water for 3 mo. Release of thromboxane (TX) B(2), the metabolite of TXA(2), was measured by using immunoenzymatic assays, and free radical production was measured by using the fluorescent dye CM-H(2)DCFDA. Endothelial nitric oxide synthase (eNOS) and COX-1/2 mRNA expression were quantified by quantitative PCR. N(G)-nitro-L-arginine (L-NNA) reduced (P < 0.05) ACh-induced dilation in vessels isolated from 3- and 6-mo-old mice. In the presence of L-NNA, indomethacin normalized (P < 0.05) the dilation in vessels from 6-mo-old mice only. SQ-29548 (PGH(2)/TXA(2) receptor antagonist) and furegrelate (TXA(2) synthase inhibitor), in the presence of L-NNA, also improved (P < 0.05) dilation. L-NNA increased TXA(2) release and free radical-associated fluorescence, the latter being prevented by SQ-29548. In vessels from 6-mo-old mice treated with catechin for 3 mo, L-NNA-dependent reduction in ACh-mediated dilation was insensitive to indomethacin, whereas TXA(2) release and free radical-associated fluorescence were prevented. eNOS mRNA expression was significantly increased by catechin treatment. Our results suggest that an augmented production of TXA(2) and the associated change in redox regulation precede the development of the endothelial dysfunction.