Regulation of types I and III NOS in ovine uterine arteries by daily and acute estrogen exposure

Ca2+-Activated K+ Channels and the Regulation of the Uteroplacental Circulation

Adequate uteroplacental blood supply is essential for the development and growth of the placenta and fetus during pregnancy. Aberrant uteroplacental perfusion is associated with pregnancy complications such as preeclampsia, fetal growth restriction (FGR), and gestational diabetes. The regulation of uteroplacental blood flow is thus vital to the well-being of the mother and fetus. Ca²⁺-activated K⁺ (K_Ca) channels of small, intermediate, and large conductance participate in setting and regulating the resting membrane potential of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) and play a critical role in controlling vascular tone and blood pressure. K_Ca channels are important mediators of estrogen/pregnancy-induced adaptive changes in the uteroplacental circulation. Activation of the channels hyperpolarizes uteroplacental VSMCs/ECs, leading to attenuated vascular tone, blunted vasopressor responses, and increased uteroplacental blood flow. However, the regulation of uteroplacental vascular function by K_Ca channels is compromised in pregnancy complications. This review intends to provide a comprehensive overview of roles of K_Ca channels in the regulation of the uteroplacental circulation under physiological and pathophysiological conditions.

Potassium Channels in the Uterine Vasculature: Role in Healthy and Complicated Pregnancies

A progressive increase in maternal uterine and placental blood flow must occur during pregnancy to sustain the development of the fetus. Changes in maternal vasculature enable an increased uterine blood flow, placental nutrient and oxygen exchange, and subsequent fetal development. K⁺ channels are important modulators of vascular function, promoting vasodilation, inducing cell proliferation, and regulating cell signaling. Different types of K⁺ channels, such as Ca²⁺-activated, ATP-sensitive, and voltage-gated, have been implicated in the adaptation of maternal vasculature during pregnancy. Conversely, K⁺ channel dysfunction has been associated with vascular-related complications of pregnancy, including intrauterine growth restriction and pre-eclampsia. In this article, we provide an updated and comprehensive literature review that highlights the relevance of K⁺ channels as regulators of uterine vascular reactivity and their potential as therapeutic targets.

Uteroplacental Circulation in Normal Pregnancy and Preeclampsia: Functional Adaptation and Maladaptation

Uteroplacental blood flow increases as pregnancy advances. Adequate supply of nutrients and oxygen carried by uteroplacental blood flow is essential for the well-being of the mother and growth/development of the fetus. The uteroplacental hemodynamic change is accomplished primarily through uterine vascular adaptation, involving hormonal regulation of myogenic tone, vasoreactivity, release of vasoactive factors and others, in addition to the remodeling of spiral arteries. In preeclampsia, hormonal and angiogenic imbalance, proinflammatory cytokines and autoantibodies cause dysfunction of both endothelium and vascular smooth muscle cells of the uteroplacental vasculature. Consequently, the vascular dysfunction leads to increased vascular resistance and reduced blood flow in the uteroplacental circulation. In this article, the (mal)adaptation of uteroplacental vascular function in normal pregnancy and preeclampsia and underlying mechanisms are reviewed.

Effect of Oxidative Stress on the Estrogen-NOS-NO-KCa Channel Pathway in Uteroplacental Dysfunction: Its Implication in Pregnancy Complications

During pregnancy, the adaptive changes in uterine circulation and the formation of the placenta are essential for the growth of the fetus and the well-being of the mother. The steroid hormone estrogen plays a pivotal role in this adaptive process. An insufficient blood supply to the placenta due to uteroplacental dysfunction has been associated with pregnancy complications including preeclampsia and intrauterine fetal growth restriction (IUGR). Oxidative stress is caused by an imbalance between free radical formation and antioxidant defense. Pregnancy itself presents a mild oxidative stress, which is exaggerated in pregnancy complications. Increasing evidence indicates that oxidative stress plays an important role in the maladaptation of uteroplacental circulation partly by impairing estrogen signaling pathways. This review is aimed at providing both an overview of our current understanding of regulation of the estrogen-NOS-NO-K_Ca pathway by reactive oxygen species (ROS) in uteroplacental tissues and a link between oxidative stress and uteroplacental dysfunction in pregnancy complications. A better understanding of the mechanisms will facilitate the development of novel and effective therapeutic interventions.

PM2.5 exposure during pregnancy induces hypermethylation of estrogen receptor promoter region in rat uterus and declines offspring birth weights

Particulate matter 2.5 (PM_2.5) exposures during pregnancy could lead to declined birth weight, intrauterine developmental restriction, and premature delivery, however, the underlying mechanisms are still not elucidated. There are few studies concerning the effects of PM_2.5 exposure on maternal and child health in Xi'an (one of the cities with severe air pollution of PM_2.5 in North China). Then, this study aimed to investigate the effect of PM_2.5 exposure in Xi'an on the offspring birth weights and the possibly associated epigenetic mechanisms. We found the Low and High groups: the offspring with declined birth weights; the decreased mRNA and protein expression of the estrogen receptor (ERs) and eNOs in the uterus; the decreased endometria vascular diameter maximum (EVDM); the increased mRNA and protein expressions of the DNMT1 and 3b in the uterus; the elevated methylation levels of the CpG sites in the CpG island of ERα promoter region in the uterus. However, no differences were observed in the mRNA or protein expressions of ERβ and DNMT3a between the Clean and PM_2.5 exposure groups, as well as endometriavascular density (EVD). Additionally, PM_2.5 level was negatively correlated with the ERα protein expression, EVDM and offspring birth weight, as well as the methylation level of the CpG sites in the CpG island of ERα promoter region and the ERα protein expression in the uterus; whereas the ERα protein expression was positively correlated with the offspring birth weight, as well as PM_2.5 level and the methylation level of the CpG sites in the CpG island of ERα promoter region in the uterus. Taken together, elevated methylation level of the CpG sites in the CpG island of ERα promoter region reduces ERα expression in the uterus, which could be one of the epigenetic mechanisms that pregnant PM_2.5 exposure reduces the offspring birth weights.

Prolonged uterine artery nitric oxide synthase inhibition modestly alters basal uteroplacental vasodilation in the last third of ovine pregnancy

Mechanisms regulating uteroplacental blood flow (UPBF) in pregnancy remain unclear, but they likely involve several integrated signaling systems. Endothelium-derived nitric oxide (NO) is considered an important contributor, but the extent of its involvement is unclear. Bolus intra-arterial infusions of nitro-l-arginine methyl ester (l-NAME) modestly decrease ovine basal UPBF; however, the doses and duration of infusion may have been insufficient. We, therefore, examined prolonged uterine artery (UA) NO synthase inhibition with l-NAME throughout the last third of ovine pregnancy by performing either continuous 30-min UA infusion dose responses (n = 4) or 72-h UA infusions (0.01 mg/ml) at 104-108, 118-125, and 131-137 days of gestation (n = 7) while monitoring mean arterial pressure (MAP), heart rate (HR), and UPBF. Uteroplacental vascular resistance (UPVR) was calculated, and uterine cGMP synthesis was measured. Thirty-minute UA l-NAME infusions did not dose dependently decrease UPBF, increase UPVR, or decrease uterine cGMP synthesis (P > 0.1); however, MAP rose and HR fell modestly. Prolonged continuous 72-h UA l-NAME infusions decreased UPBF ∼32%, increased UPVR ∼68% (P ≤ 0.001), and decreased uterine cGMP synthesis 70% at 54-72 h (P ≤ 0.004); the noninfused uterine horn was unaffected. These findings were associated with ∼10% increases in MAP and decreases in HR that were greater at 104-108 than 118-125 and 131-137 days of gestation (P = 0.006). Although uterine and UA NO and cGMP synthesis increase severalfold during ovine pregnancy, they contribute modestly to the maintenance and rise in UPBF in the last third of gestation. Thus, local UA NO may primarily modulate vasoconstrictor responses. Notably, the systemic vasculature appears more sensitive than the uterine vasculature to NO synthase inhibition.

[Regulation of uterine blood flow. I. Functions of estrogen and estrogen receptor α/β in the uterine vascular endothelium during pregnancy]

Estrogen and classical estrogen receptors (ERs), ER-α and ER-β, have been shown to be partially responsible for short and long term uterine endothelial adaptations during pregnancy. The molecular and structural differences, together with the various effects caused by these receptors in cells and tissues, suggest that their function varies depending upon estrogen and estrogen receptor signaling. In this review, we discuss the role of estrogen and its classic receptors in the cardiovascular adaptations during pregnancy and the expression of ERs in vivo and in vitro in the uterine artery endothelium during the ovarian cycle and pregnancy, while comparing their expression in arterial endothelium from reproductive and non-reproductive tissues. These themes integrate current knowledge of this broad scientific field with various interpretations and hypothesis that related estrogenic effects by either one or both ERs. This review also includes the relationship with vasodilator and angiogenic adaptations required to modulate the dramatic physiological increase to the uteroplacental perfusion observed during normal pregnancy.

GPER: a novel target for non-genomic estrogen action in the cardiovascular system

A key to harnessing the enormous therapeutic potential of estrogens is understanding the diversity of estrogen receptors and their signaling mechanisms. In addition to the classic nuclear estrogen receptors (i.e., ERα and ERβ), over the past decade a novel G-protein-coupled estrogen receptor (GPER) has been discovered in cancer and other cell types. More recently, this non-genomic signaling mechanism has been found in blood vessels, and mediates vasodilatory responses to estrogen and estrogen-like agents; however, downstream signaling events involved acute estrogen action remain unclear. The purpose of this review is to discuss the latest knowledge concerning GPER modulation of cardiovascular function, with a particular emphasis upon how activation of this receptor could mediate acute estrogen effects in the heart and blood vessels (i.e., vascular tone, cell growth and differentiation, apoptosis, endothelial function, myocardial protection). Understanding the role of GPER in estrogen signaling may help resolve some of the controversies associated with estrogen and cardiovascular function. Moreover, a more thorough understanding of GPER function could also open significant opportunities for the development of new pharmacological strategies that would provide the cardiovascular benefits of estrogen while limiting the potentially dangerous side effects.

Large conductance Ca2+-activated and voltage-activated K+ channels contribute to the rise and maintenance of estrogen-induced uterine vasodilation and maintenance of blood pressure

Uterine blood flow (UBF) increases greater than 4-fold 90 min after systemic estradiol-17β (E2β) in nonpregnant sheep and remains elevated longer than 6-8 h; mean arterial pressure (MAP) is unchanged. Large-conductance Ca(+2)-activated (BK(Ca)) and voltage-activated (K(V)) K(+) channels contribute to the acute rise in UBF; their role in maintaining UBF and MAP longer than 90 min is unknown. We examined this in five nonpregnant, ovariectomized ewes with uterine artery (UA) flow probes and catheters in a UA for infusion of K(+) channel inhibitors and uterine vein to sample venous effluent. Animals received systemic E2β (1.0 μg/kg; control), E2β+UA tetraethylammonium (TEA; 0.4-0.8 mm, n = 4), and E2β+UA 4-aminopyridine (4-AP; 0.01-0.08 mm, n = 4) to block BK(Ca) and K(V), respectively, while monitoring MAP, heart rate, and UBF. Uterine cGMP synthesis was measured. Ninety minutes after E2β, UBF rose 4.5-fold, uterine vascular resistance (UVR) fell greater than 5-fold and MAP was unchanged [78 ± 0.8 (sem) vs. 77 ± 1.5 mm Hg] in control studies and before UA inhibition with TEA and 4-AP. Between 90 and 120min, UBF, UVR, and MAP were unchanged after E2β alone. E2β+TEA dose dependently decreased ipsilateral UBF and increased UVR (24 ± 8.9 and 38 ± 16%, respectively, at 0.8 mm; P < 0.03); MAP was unchanged. Contralateral UBF/UVR were unaffected. E2β+4-AP also dose dependently decreased ipsilateral UBF and increased UVR (27 ± 5.3 and 76 ± 18%, respectively, at 0.08 mm; P < 0.001); however, MAP rose 27 ± 6.9% (P ≤ 0.006). E2β increased uterine cGMP synthesis greater than 3.5-fold and was unaffected by local K(+) channel inhibition. BK(Ca) and K(V) contribute to the rise and maintenance of E2β-induced uterine vasodilation, which is partially cGMP dependent. Systemic vascular K(V) also contributes to maintaining MAP after systemic E2β.

Pregnancy increases myometrial artery myogenic tone via NOS- or COX-independent mechanisms

Myogenic tone (MT) is a primary modulator of blood flow in the resistance vasculature of the brain, kidney, skeletal muscle, and perhaps in other high-flow organs such as the pregnant uterus. MT is known to be regulated by endothelium-derived factors, including products of the nitric oxide synthase (NOS) and/or the cyclooxygenase (COX) pathways. We asked whether pregnancy influenced MT in myometrial arteries (MA), and if so, whether such an effect could be attributed to alterations in NOS and/or COX. MA (200-300 μm internal diameter, 2-3 mm length) were isolated from 10 nonpregnant and 12 pregnant women undergoing elective hysterectomy or cesarean section, respectively. In the absence of NOS and/or COX inhibition, pregnancy was associated with increased MT in endothelium-intact MA compared with MA from nonpregnant women (P < 0.01). The increase in MT was not due to increased Ca(2+) entry via voltage-dependent channels since both groups of MA exhibited similar levels of constriction when exposed to 50 mM KCl. NOS inhibition (N(ω)-nitro-L-arginine methyl ester, L-NAME) or combined NOS/COX inhibition (L-NAME/indomethacin) increased MT in MA from pregnant women (P = 0.001 and P = 0.042, respectively) but was without effect in arteries from nonpregnant women. Indomethacin alone was without effect on MT in MA from either nonpregnant or pregnant women. We concluded that MT increases in MA during human pregnancy and that this effect was partially opposed by enhanced NOS activity.

Estrogen receptor-α and estrogen receptor-β in the uterine vascular endothelium during pregnancy: functional implications for regulating uterine blood flow

The steroid hormone estrogen and its classical estrogen receptors (ERs), ER-α and ER-β, have been shown to be partly responsible for the short- and long-term uterine endothelial adaptations during pregnancy. The ER-subtype molecular and structural differences coupled with the differential effects of estrogen in target cells and tissues suggest a substantial functional heterogeneity of the ERs in estrogen signaling. In this review we discuss (1) the role of estrogen and ERs in cardiovascular adaptations during pregnancy, (2) in vivo and in vitro expression of ERs in uterine artery endothelium during the ovarian cycle and pregnancy, contrasting reproductive and nonreproductive arterial endothelia, (3) the structural basis for functional diversity of the ERs and estrogen subtype selectivity, (4) the role of estrogen and ERs on genomic responses of uterine artery endothelial cells, and (5) the role of estrogen and ERs on nongenomic responses in uterine artery endothelia. These topics integrate current knowledge of this very rapidly expanding scientific field with diverse interpretations and hypotheses regarding the estrogenic effects that are mediated by either or both ERs and their relationship with vasodilatory and angiogenic vascular adaptations required for modulating the dramatic physiological rises in uteroplacental perfusion observed during normal pregnancy.

Tetrahydrobiopterin restores diastolic function and attenuates superoxide production in ovariectomized mRen2.Lewis rats

After oophorectomy, mRen2.Lewis rats exhibit diastolic dysfunction associated with elevated superoxide, increased cardiac neuronal nitric oxide synthase (nNOS) expression, and diminished myocardial tetrahydrobiopterin (BH₄) content, effects that are attenuated with selective nNOS inhibition. BH₄ is an essential cofactor of nNOS catalytic activity leading to nitric oxide production. Therefore, we assessed the effect of 4 wk BH₄ supplementation on diastolic function and left ventricular (LV) remodeling in oophorectomized mRen2.Lewis rats compared with sham-operated controls. Female mRen2.Lewis rats underwent either bilateral ovariectomy (OVX) (n = 19) or sham operation (n = 13) at 4 wk of age. Beginning at 11 wk of age, OVX rats were randomized to receive either BH₄ (10 mg/kg · d) or saline, whereas the sham rats received saline via sc mini-pumps. Loss of ovarian hormones reduced cardiac BH₄ when compared with control hearts; this was associated with impaired myocardial relaxation, augmented filling pressures, increased collagen deposition, and thickened LV walls. Additionally, superoxide production increased and nitric oxide decreased in hearts from OVX compared with sham rats. Chronic BH₄ supplementation after OVX improved diastolic function and attenuated LV remodeling while restoring myocardial nitric oxide release and preventing reactive oxygen species generation. These data indicate that BH₄ supplementation protects against the adverse effects of ovarian hormonal loss on diastolic function and cardiac structure in mRen2.Lewis rats by restoring myocardial NO release and mitigating myocardial O₂⁻ generation. Whether BH₄ supplementation is a therapeutic option for the management of diastolic dysfunction in postmenopausal women will require direct testing in humans.

Neuronal nitric oxide synthase inhibition improves diastolic function and reduces oxidative stress in ovariectomized mRen2.Lewis rats

OBJECTIVE

The loss of estrogen in mRen2.Lewis rats leads to an exacerbation of diastolic dysfunction. Because specific neuronal nitric oxide synthase (nNOS) inhibition reverses renal damage in the same model, we assessed the effects of inhibiting neuronal nitric oxide on diastolic function, left ventricular remodeling, and the components of the cardiac nitric oxide system in ovariectomized (OVX) and sham-operated mRen2.Lewis rats treated with N5-(1-imino-3-butenyl)-L-ornithine (L-VNIO; 0.5 mg/kg per day for 28 d) or vehicle (saline).

METHODS

Female mRen2.Lewis rats underwent either bilateral oophorectomy (OVX; n = 15) or sham operation (or surgical procedure) (sham; n = 19) at 4 weeks of age. Beginning at 11 weeks of age, the rats were randomized to receive either L-VNIO or vehicle.

RESULTS

The surgical loss of ovarian hormones, particularly estrogen, led to exacerbated hypertension, impaired myocardial relaxation, diminished diastolic compliance, increased perivascular fibrosis, and increased relative wall thickness. The cardiac tetrahydrobiopterin-to-dihydrobiopterin levels were lower among OVX rats compared with sham-operated rats, and this altered cardiac biopterin profile was associated with enhanced myocardial superoxide production and decreased nitric oxide release. L-VNIO decreased myocardial reactive oxygen species production, increased nitrite concentrations, attenuated cardiac remodeling, and improved diastolic function.

CONCLUSIONS

Impaired relaxation, diastolic stiffness, and cardiac remodeling were found among OVX mRen2.Lewis rats. A possible mechanism for this unfavorable cardiac phenotype may have resulted from a deficiency in available tetrahydrobiopterin and subsequent increase in nNOS-derived superoxide and reduction in nitric oxide synthase metabolites within the heart. Selective nNOS inhibition with L-VNIO attenuated cardiac superoxide production and limited remodeling, leading to improved diastolic function in OVX mRen2.Lewis rats.

Nitric oxide production and blood corpuscle dynamics in response to the endocrine status of female rats

INTRODUCTION

Menopause is associated with marked changes in the endocrine profile, and increases the risk of vascular disease. However, the effect of hormones on the vascular system is still unclear. Therefore, the aim of this study was to examine the effects of endocrine status in female rats on nitric oxide (NO) production, inflammatory reactions and thrombus organization potency in the mesenteric microcirculation.

MATERIALS AND METHODS

Female Wistar rats were divided into four groups: proestrus, metestrus, ovariectomized (OVX) and OVX plus estradiol treatment (OVX+E2). NO was imaged using an NO-sensitive dye. The leukocyte and platelet velocities relative to the erythrocyte velocity (VW/VRC and VP/VRE, respectively) and thrombi sizes created by laser radiation were measured as thrombogenesis indices.

RESULTS

Changes in endocrine status did not affect vascular function in the arterioles. However, in venules, NO production, VW/VRC and VP/VRE were decreased in the OVX group compared with the proestrus and metestrus states. Thrombus size was significantly greater in the OVX group than in the proestrus and metestrus states. Administration of E2 for 2 weeks restored NO production, VW/VRC and VP/VRE to control levels.

CONCLUSIONS

Changes in endocrine status did not affect arterioles. In contrast, in venules, reduced estrogen levels led to a decrease in NO production, thereby increasing thrombogenesis. Estrogen replacement restored NO production and leukocyte and platelet velocities, reducing thrombus formation relative to OVX. Although it is unclear how E2 reduces thrombus formation, our results indicate that leukocyte and platelet adhesion to the endothelium is a target for E2 via NO.

Sildenafil increases uterine blood flow in nonpregnant nulliparous women

This study investigated the effect of sildenafil on uterine volumetric blood flow (UVF) and vascular impedance in nonpregnant, nulliparous women. Fifteen women were randomized in a double-blind fashion to receive either placebo or sildenafil (25 or 100 mg) during the luteal phase of the menstrual cycle. Color Doppler ultrasound of both uterine arteries was performed at baseline and at 1 and 3 hours postdosing to calculate resistance index (RI) and UVF. Those who received sildenafil significantly increased UVF and decreased RI over the 3-hour monitoring period. When UVF responses to sildenafil were examined as a function of baseline UVF, a significant increase in UVF was observed in only those participants with higher baseline UVF. Overall, women in the luteal phase demonstrated a significant increase in UVF in response to sildenafil. However, this increase appears to be directly associated with basal UVF.

Effects of sex and estrogen on chicken ductus arteriosus reactivity

Sex hormones have an important influence on cardiovascular physiology and pathophysiology and sex differences in vascular reactivity have been widely demonstrated. In the present study we hypothesized 1) the presence of sexual dimorphism in chicken ductus arteriosus (DA) responsiveness to contractile and relaxant stimuli and 2) that estrogens are vasoactive in the chicken DA. In vitro contractions (assessed with a wire myograph) induced by normoxia, KCl, 4-aminopyridine, norepinephrine, phenylephrine, U46619, or endothelin-1, as well as relaxations induced by ACh, sodium nitroprusside, BAY 41-2272, PGE(2), isoproterenol, forskolin,Y-27632, and hydroxyfasudil were not significantly different between males and females. The estrogen 17beta-estradiol elicited concentration-dependent relaxation of KCl-, phenylephrine-, and oxygen-induced active tone in male and female chicken DA. The stereoisomer 17alpha-estradiol showed lesser relaxant effects, and the selective estrogen receptor (ER) agonists 4,4',4''-(4-propyl-[(1)H]pyrazole-1,3,5-triyl)tris-phenol (ERalpha) and 2,3-bis(4-hydroxyphenyl)-propionitrile (ERbeta) did not show any effect. There were no sex differences in the responses to estrogen. Endothelium removal or the presence of the soluble guanylate cyclase inhibitor ODQ, the K(+) channel blockers tetraethylammonium, glibenclamide, and charybdotoxin, or the ER antagonist fulvestrant did not modify 17beta-estradiol-induced relaxation. CaCl(2) (30 muM-10 mM) induced concentration-dependent contraction in DA rings depolarized by 62.5 mM KCl or stimulated with 21% O(2) in Ca(2+)-free medium. Preincubation with 17beta-estradiol or the L-type Ca(2+) channel blocker nifedipine produced an inhibition of CaCl(2)-induced contractions. In conclusion, there are no sex-related differences in chicken DA reactivity. The estrogen 17beta-estradiol induces an endothelium-independent relaxation of chicken DA that is not mediated by ER activation. This relaxant effect is, at least partially, due to inhibition of Ca(2+) entry from extracellular space.

Regulation of the cGMP-cPKG pathway and large-conductance Ca2+-activated K+ channels in uterine arteries during the ovine ovarian cycle

The follicular phase of the ovine ovarian cycle demonstrates parallel increases in ovarian estrogens and uterine blood flow (UBF). Although estrogen and nitric oxide contribute to the rise in UBF, the signaling pathway remains unclear. We examined the relationship between the rise in UBF during the ovarian cycle of nonpregnant sheep and changes in the uterine vascular cGMP-dependent pathway and large-conductance Ca(2+)-activated K(+) channels (BK(Ca)). Nonpregnant ewes (n = 19) were synchronized to either follicular or luteal phase using a vaginal progesterone-releasing device (CIDR), followed by intramuscular PGF(2alpha), CIDR removal, and treatment with pregnant mare serum gonadotropin. UBF was measured with flow probes before tissue collection, and second-generation uterine artery segments were collected from nine follicular and seven luteal phase ewes. The pore-forming alpha- and regulatory beta-subunits that constitute the BK(Ca), soluble guanylyl cyclase (sGC), and cGMP-dependent protein kinase G (cPKG) isoforms (cPKG(1alpha) and cPKG(1beta)) were measured by Western analysis and cGMP levels by RIA. BK(Ca) subunits were localized by immunohistochemistry. UBF rose >3-fold (P < 0.04) in follicular phase ewes, paralleling a 2.3-fold rise in smooth muscle cGMP and 32% increase in cPKG(1alpha) (P < 0.05). sGC, cPKG(1beta), and the BK(Ca) alpha-subunit were unchanged. Notably, expression of beta(1)- and beta(2)-regulatory subunits rose 51 and 79% (P <or= 0.05), respectively. Increases in endogenous ovarian estrogens in follicular-phase ewes result in increases in UBF associated with upregulation of the cGMP- and cPKG-dependent pathway and increased vascular BK(Ca) beta/alpha-subunit stoichiometry, suggesting enhanced BK(Ca) activation contributes to the follicular phase rise in UBF.

Pregnancy modifies the large conductance Ca2+-activated K+ channel and cGMP-dependent signaling pathway in uterine vascular smooth muscle

Regulation of uteroplacental blood flow (UPBF) during pregnancy remains unclear. Large conductance, Ca(2+)-activated K(+) channels (BK(Ca)), consisting of alpha- and regulatory beta-subunits, are expressed in uterine vascular smooth muscle (UVSM) and contribute to the maintenance of UPBF in the last third of ovine pregnancy, but their expression pattern and activation pathways are unclear. We examined BK(Ca) subunit expression, the cGMP-dependent signaling pathway, and the functional role of BK(Ca) in uterine arteries (UA) from nonpregnant (n = 7), pregnant (n = 38; 56-145 days gestation; term, approximately 150 days), and postpartum (n = 15; 2-56 days) sheep. The alpha-subunit protein switched from 83-87 and 105 kDa forms in nonpregnant UVSM to 100 kDa throughout pregnancy, reversal occurring >30 days postpartum. The 39-kDa beta(1)-subunit was the primary regulatory subunit. Levels of 100-kDa alpha-subunit rose approximately 70% during placentation (P < 0.05) and were unchanged in the last two-thirds of pregnancy; in contrast, beta(1)-protein rose throughout pregnancy (R(2) = 0.996; P < 0.001; n = 13), increasing 50% during placentation and approximately twofold in the remainder of gestation. Although UVSM soluble guanylyl cyclase was unchanged, cGMP and protein kinase G(1alpha) increased (P < 0.02), paralleling the rise and fall in beta(1)-protein during pregnancy and the puerperium. BK(Ca) inhibition not only decreased UA nitric oxide (NO)-induced relaxation but also enhanced alpha-agonist-induced vasoconstriction. UVSM BK(Ca) modify relaxation-contraction responses in the last two-thirds of ovine pregnancy, and this is associated with alterations in alpha-subunit composition, alpha:beta(1)-subunit stoichiometry, and upregulation of the cGMP-dependent pathway, suggesting that BK(Ca) activation via NO-cGMP and beta(1) augmentation may contribute to the regulation of UPBF.

Review article: steroid hormones and uterine vascular adaptation to pregnancy

Pregnancy is a physiological state that involves a significant decrease in uterine vascular tone and an increase in uterine blood flow, which is mediated in part by steroid hormones, including estrogen, progesterone, and cortisol. Previous studies have demonstrated the involvement of these hormones in the regulation of uterine artery contractility through signaling pathways specific to the endothelium and the vascular smooth muscle. Alterations in endothelial nitric oxide synthase expression and activity, nitric oxide production, and expression of enzymes involved in PGI(2) production contribute to the uterine artery endothelium-specific responses. Steroid hormones also have an effect on calcium-activated potassium channel activity, PKC signaling pathway and myogenic tone, and alterations in pharmacomechanical coupling in the uterine artery smooth muscle. This review addresses current understanding of the molecular mechanisms by which steroid hormones including estrogen, progesterone, and cortisol modulate uterine artery contractility to alter uterine blood flow during pregnancy with an emphasis on the pregnant ewe model.

Vasorelaxant action of 17 -estradiol in rat uterine arteries: role of nitric oxide synthases and estrogen receptors

The uterine vasculature plays an important role during pregnancy by providing adequate perfusion of the maternal-fetal interface. To this end, substantial remodeling of the uterine vasculature occurs with consequent changes in responsiveness to contractile agents. The purpose of our study was to characterize the vasorelaxant effects of estrogens on vascular smooth muscles of the rat uterine artery during pregnancy and to evaluate the involvement of estrogen receptors (ESR) and nitric oxide synthases (NOS). To do so, we measured NOS expression in the whole uterine and mesenteric circulatory bed by Western blotting. Vasorelaxant effects of 17beta-estradiol (17beta-E(2)) were assessed on endothelium-denuded uterine arteries with wire myographs in the absence and presence of pharmacological modulators [nitro-L-arginine methyl ester (L-NAME), ICI-182780, tamoxifen]. All experiments were performed on arteries from nonpregnant (NP) and late pregnant (P) rats. In the uterine vasculature of the latter group, NOS3 (endothelial NOS) expression was increased, while NOS1 (neuronal NOS) was reduced compared with NP rats. Expression of the NOS2 (inducible NOS) isoform was undetectable in the two groups. Both 17beta-E(2) and 17alpha-E(2) induced uterine artery relaxation, but the latter evoked lower responses. Endothelium-denuded arteries from NP rats showed larger relaxation with 17beta-E(2) than P rats. This larger relaxation disappeared in the presence of L-NAME. The ESR antagonist ICI-182780 did not affect acute relaxation with 17beta-E(2) and 17alpha-E(2). Moreover, membrane-nonpermeant 17beta-E(2):BSA (estradiol conjugated to bovine serum albumin) did not induce any vasorelaxation. Our results indicate that estrogens exert direct acute vasorelaxant effects in smooth muscles of the rat uterine artery that are mediated by mechanisms independent of ESR activation, but with some stereospecificity. Part of this effect, in NP rats only, is due to nitric oxide produced from muscle NOS1.

The role of nitric oxide in the effects of ovarian steroids on spontaneous myometrial contractility in rats

Forty ovariectomized rats were apportioned into one control and three experimental groups (n=10 each) to evaluate the role of nitric oxide in the effects of ovarian steroids on spontaneous myometrial contractility in rats. The control group (group Ov) received sesame oil once daily for 10 days, whereas rats in the experimental groups were treated with progesterone (2 mg/(rat day); group P), 17beta-estradiol (10 microg/(rat day); group E2), or progesterone and 17beta-estradiol together (group E2+P). The functionality of the arginine-nitric oxide synthase (NOS)-nitric oxide (NO) pathway in the uterine horns of sacrificed rats was evaluated in an isolated organ bath. L-Arginine, sodium nitroprusside (SNP) and 8-Br-cGMP decreased uterine contractile tension induced by electric field stimulation (EFS) in the Ov, P, and E2+P groups, but not in the E2 group. In addition, L-arginine was ineffective when applied together with a NOS inhibitor, L-nitro-N-arginine (L-NNA). The percentage of contractile inhibition was higher in the Ov and P groups compared to the E2+P group. Immunohistochemical evaluation revealed that expression of neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS) in smooth muscles and nerve cells did not differ among the groups. Expression of nNOS and eNOS was strongly evident in the E2 and E2+P groups at both surface and glandular epithelium of the endometrium. iNOS expression was increased in surface epithelium of the E2 and E2+P groups. However, iNOS expression was only increased in glandular epithelial cells of the E2+P group. In conclusion, the L-arginine-NOS-NO pathway inhibits myometrial contractions via cGMP-dependent and -independent mechanisms, and while progesterone maintains the nitric oxide effects, estrogen prevents them. These results suggest that NOS does not mediate the effects of estrogen.

Nongenomic, endothelium-independent effects of estrogen on human coronary smooth muscle are mediated by type I (neuronal) NOS and PI3-kinase-Akt signaling

Sex steroids exert profound and controversial effects on cardiovascular function. For example, estrogens have been reported to either ameliorate or exacerbate coronary heart disease. Although estrogen dilates coronary arteries from a variety of species, the molecular basis for this acute, nongenomic effect is unclear. Moreover, we know very little of how estrogen affects human coronary artery smooth muscle cells (HCASMC). The purpose of this study was to elucidate nongenomic estrogen signal transduction in HCASMC. We have used tissue (arterial tension studies), cellular (single-channel patch clamp, fluorescence), and molecular (protein expression) techniques to now identify novel targets of estrogen action in HCASMC: type I (neuronal) nitric oxide synthase (nNOS) and phosphatidylinositol 3-kinase (PI3-kinase)Akt. 17beta-Estradiol (E(2)) increased NO-stimulated fluorescence in HCASMC, and cell-attached patch-clamp experiments revealed that stimulation of nNOS leads to increased activity of calcium-activated potassium (BK(Ca)) channels in these cells. Furthermore, overexpression of nNOS protein in HCASMC greatly enhanced BK(Ca) channel activity. Immunoblot studies demonstrated that E(2) enhances Akt phosphorylation in HCASMC and that wortmannin, an inhibitor of PI3-kinase, attenuated E(2)-stimulated channel activity, NO production, Akt phosphorylation, and estrogen-stimulated coronary relaxation. These studies implicate the PI3-kinase/Akt signaling axis as an estrogen transduction component in vascular smooth muscle cells. We conclude, therefore, that estrogen opens BK(Ca) channels in HCASMC by stimulating nNOS via a transduction sequence involving PI3-kinase and Akt. These findings now provide a molecular mechanism that can explain the clinical observation that estrogen enhances coronary blood flow in patients with diseased or damaged coronary arteries.

Large-conductance Ca2+-dependent K+ channels regulate basal uteroplacental blood flow in ovine pregnancy

OBJECTIVES

The mechanisms regulating basal uteroplacental blood flow (UBF) and the greater than 30-fold increase observed in normal pregnancy remain unclear. Although vascular growth contributes in early gestation, vasodilation accounts for the exponential rise seen in the last third of pregnancy. Large conductance potassium channels (BK(Ca)) are expressed in uterine vascular smooth muscle (VSM), but the extent of their role in regulating UBF in pregnancy is unclear. Therefore, we determined if BK(Ca) regulate basal UBF during ovine pregnancy.

METHODS

Studies were performed at 113 to 127 days and 135 to 150 days of gestation in eight pregnant ewes instrumented with uterine artery flow probes and uterine arterial and venous catheters. Tetraethylammonium chloride (TEA), a BK(Ca)-specific inhibitor at less than 1.0 mM, was infused intra-arterially into the pregnant uterine horn over 60 minutes to achieve levels of 0.001-0.35 mM while continuously monitoring UBF, arterial pressure (MAP), and heart rate (HR). Uterine arterial and venous blood was collected simultaneously to measure uterine cyclic guanosine monophosphate (cGMP) synthesis.

RESULTS

Intra-arterial TEA dose-dependently decreased basal UBF in the early (R = 0.81, n = 36, P <.001) and late (R = 0.72, n = 31, P <.001) study periods without altering contralateral UBF, MAP, and HR. The IC(50) was 0.2 mM and basal UBF decreased >or=80% at 0.35 mM in both periods. Although UBF fell greater than 40% at estimated plasma TEA levels of 0.3 mM, uterine arterial cGMP was unchanged, uterine venous cGMP rose, and uterine cGMP synthesis was unchanged; therefore, upstream events associated with BK(Ca) activation were unaffected by blockade.

CONCLUSIONS

These are the first data demonstrating that BK(Ca) are essential in the maintenance of basal UBF in the last third of ovine pregnancy.

Dilatory responses to estrogenic compounds in small femoral arteries of male and female estrogen receptor-β 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 β-deficient mice (β-ERKO) and to gain insight into the role of nitric oxide (NO) in these responses. Femoral arteries (∼250 μm) from male and female β-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 17β-estradiol (17β-E2) and the selective estrogen receptor-α (ER-α) agonist propyl-[1H]-pyrazole-1,3,5-triy-trisphenol (PPT) were obtained before and after NO synthase (NOS) inhibition [ Nω-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-β (ER-β) agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) and the contribution of NO were also assessed. Concentration-response curves to 17β-E2and PPT were similar in arteries from WT and β-ERKO mice of both genders, but NO-mediated relaxation was different, since l-NAME reduced 17β-E2mediated relaxation in arteries from male and female β-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 β-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 β-ERKO mice but differ mechanistically. Because NO appeared to contribute to responses to 17β-E2in arteries from β-ERKO but not WT mice, the presence of ER-β apparently inhibits ER-α-mediated NO relaxation.

Uterine artery remodeling in pseudopregnancy is comparable to that in early pregnancy

During pregnancy, the lumenal diameter and wall mass of the uterine artery (UA) increase, most likely in response to the increased hemodynamic strain resulting from the chronically elevated uterine blood flow (UBF). In this remodeling process, the phenotype of vascular smooth-muscle cells (VSMC) is transiently altered to enable VSMC proliferation. These phenomena are already seen during early pregnancy, when the rise in UBF is still modest. This raises the question whether the newly instituted endocrine environment of pregnancy is involved in the onset of the pregnancy-related UA remodeling. We tested the hypothesis that the conceptus is not essential for the onset of UA remodeling of pregnancy. Six control and 18 pseudopregnant (Postcopulation Days 5, 11, and 17; n = 6 per subgroup) C57Bl/6 mice were killed and UAs were dissected and processed for either morphometric analysis or immunohistochemistry. The latter consisted of staining UA cross sections for the differentiation markers smooth muscle alpha-actin and smoothelin, and for the proliferation marker MKI67. We analyzed the UA changes in response to pseudopregnancy by ANOVA. Data are presented as mean +/- SD. By Day 11 of pseudopregnancy, the UA lumen was 25% wider and the media cross-sectional area 71% larger than in control mice. These differences were accompanied by reduced smoothelin expression and increased proliferation of UA medial VSMC. All UA morphological differences had returned or were in the process of returning to baseline values by Day 17 of pseudopregnancy. The structural and cellular aspects of UA remodeling as seen at midpregnancy are also seen in pseudopregnancy. These results support the concept that the conceptus does not contribute to the initiation of UA remodeling. We suggest that ovarian hormones trigger the onset of UA remodeling.

Estrogen regulates {beta}1-subunit expression in Ca(2+)-activated K(+) channels in arteries from reproductive tissues

Daily estradiol-17beta (E(2)beta) increases basal uterine blood flow (UBF) and enhances acute E(2)beta-mediated increases in UBF in ovariectomized nonpregnant ewes. The acute E(2)beta-mediated rise in UBF involves vascular smooth muscle (VSM) large-conductance Ca(2+)-activated K(+) channels (BK(Ca)). BK(Ca) consist of pore-forming alpha-subunits and regulatory beta(1)-subunits that modulate channel function and E(2)beta responsiveness. It is unclear whether E(2)beta also alters subunit expression and thus channel density and/or function, thereby contributing to the rise in basal UBF and enhanced UBF responses that follow daily E(2)beta. Therefore, we examined BK(Ca) subunit expression by using reverse transcription-PCR and immunoblot analysis of arterial VSM from reproductive and nonreproductive tissues and myometrium from ovariectomized nonpregnant ewes after daily E(2)beta (1 microg/kg iv) or vehicle without or with acute E(2)beta (1 microg/kg). Tissue distribution was determined by immunohistochemistry. Acute E(2)beta did not alter alpha- or beta(1)-subunit expression in any tissue (P > 0.1). Daily E(2)beta also did not affect alpha-subunit mRNA or protein in any tissue (P > 0.1) or mesenteric arterial VSM beta(1)-subunit. However, daily E(2)beta increased uterine and mammary arterial VSM beta(1)-subunit mRNA by 32% and 83% (P < 0.05), uterine VSM protein by 30%, and myometrial beta(1)-subunit mRNA and protein by 74% (P < or = 0.005). Immunostaining of uterine arteries, myometrium, and intramyometrial arteries paralleled immunoblot analyses for both subunits. Although BK(Ca) density is unaffected by daily and acute E(2)beta, daily E(2)beta increases beta(1)-subunit in proximal and distal uterine arterial VSM. Thus prolonged E(2)beta exposure may alter BK(Ca) function, estrogen responsiveness, and basal vascular tone and reactivity in reproductive arteries by modifying alpha:beta(1) stoichiometry.

Uterine Artery Remodeling and Reproductive Performance Are Impaired in Endothelial Nitric Oxide Synthase-Deficient Mice1

The progressive rise in uterine blood flow during pregnancy is accompanied by outward hypertrophic remodeling of the uterine artery (UA). This process involves changes of the arterial smooth muscle cells and extracellular matrix. Acute increases in blood flow stimulate endothelial production of nitric oxide (NO). It remains to be established whether endothelial NO synthase (eNOS) is involved in pregnancy-related arterial remodeling. We tested the hypothesis that absence of eNOS results in a reduced remodeling capacity of the UA during pregnancy leading to a decline in neonatal outcome. UA of nonpregnant and pregnant wild-type (Nos3+/+) and eNOS-deficient (Nos3-/-) mice were collected and processed for standard morphometrical analyses. In addition, cross sections of UA were processed for cytological (smoothelin, smooth muscle alpha-actin) and proliferation (Ki-67) immunostaining. We compared the pregnancy-related changes longitudinally and, together with the data on pregnancy outcome, transversally by analysis of variance with Bonferroni correction. During pregnancy, the increases in radius and medial cross sectional area of Nos3-/- UA was significantly less than those of Nos3+/+ UA. Smooth muscle cell dedifferentiation and proliferation were impaired in gravid Nos3-/- mice as deduced from the lack of change in the expression of smoothelin and smooth muscle alpha-actin, and the reduced Ki-67 expression. Until 17 days of gestation, litter size did not differ between both genotypes, but at birth the number of viable newborn pups and their weights were smaller in Nos3-/- than in Nos3+/+ mice. We conclude that absence of eNOS adversely affects UA remodeling in pregnancy, which may explain the impaired pregnancy outcome observed in these mice.

Uterine blood flow responses to ICI 182 780 in ovariectomized oestradiol-17beta-treated, intact follicular and pregnant sheep

Oestrogen dramatically increases uterine blood flow (UBF) in ovariectomized (Ovx) ewes. Both the follicular phase and pregnancy are normal physiological states with elevated levels of circulating oestrogen. ICI 182 780 is a pure steroidal oestrogen receptor (ER) antagonist that blocks oestrogenic actions in oestrogen-responsive tissue. We hypothesized that an ER-mediated mechanism is responsible for in vivo rises in UBF in physiological states of high oestrogen. The purpose of the study was to examine the effect of an ER antagonist on exogenous and endogenous oestradiol-17beta (E2beta)-mediated elevations in UBF. Sheep were surgically instrumented with bilateral uterine artery blood flow transducers, and uterine and femoral artery catheters. Ovx animals (n = 8) were infused with vehicle (35% ethanol) or ICI 182 780 (0.1-3.0 microg min(-1)) into one uterine artery for 10 min before and 50 min after E2beta was given (1 microg kg(-1) I.V. bolus) and UBF was recorded for an additional hour. Intact, cycling sheep were synchronized to the follicular phase using progesterone, prostaglandin F2alpha(PGF2alpha) and pregnant mare serum gonadotrophin (PMSG). When peri-ovulatory rises in UBF reached near peak levels, ICI 182 780 (1 or 2 microg (ml uterine blood flow)-1) was infused unilaterally (n = 4 sheep). Ewes in the last stages of pregnancy (late pregnant ewes) were also given ICI 182 780 (0.23-2.0 microg (ml uterine blood flow)-1; 60 min infusion) into one uterine artery (n = 8 sheep). In Ovx sheep, local infusion of ICI 182 780 did not alter systemic cardiovascular parameters, such as mean arterial blood pressure or heart rate; however, it maximally decreased ipsilateral, but not contralateral, UBF vasodilatory responses to exogenous E2beta by approximately 55-60% (P < 0.01). In two models of elevated endogenous E2beta, local ICI 182 780 infusion inhibited the elevated UBF seen in follicular phase and late pregnant ewes in a time-dependent manner by approximately 60% and 37%, respectively; ipsilateral >> contralateral effects (P < 0.01). In late pregnant sheep ICI 182 780 also mildly and acutely (for 5-30 min) elevated mean arterial pressure and heart rate (P < 0.05). We conclude that exogenous E2beta-induced increases in UBF in the Ovx animal and endogenous E2beta-mediated elevations of UBF during the follicular phase and late pregnancy are partially mediated by ER-dependent mechanisms.

Endothelial vasodilator production by ovine uterine and systemic arteries: ovarian steroid and pregnancy control of ERalpha and ERbeta levels

Pregnancy and the follicular phase are physiological states of elevated oestrogen levels and rises in uterine blood flow (UBF). The dramatic increase in utero-placental blood flow during gestation is required for normal fetal growth and development. Oestrogen exerts its vasodilatory effect by binding to its specific oestrogen receptors (ER) in target cells, resulting in increased expression and activity of endothelial nitric oxide synthase (eNOS) to relax vascular smooth muscle (VSM). However, the regulation of endothelial versus VSM ERalpha and ERbeta expression in uterine arteries (UAs) during the ovarian cycle, pregnancy and with exogenous hormone replacement therapy (HRT) are currently unknown. ER mRNA and protein localization was determined by in situ hybridization (ISH) using 35S-labelled riboprobes and immunohistochemistry (IHC), respectively. UA endothelial (UAendo), UA VSM, omental artery endothelium (OA endo), and OA VSM proteins were isolated and ERalpha and ERbeta protein expression was determined by Western analysis. We observed by ISH and IHC that ERalpha and ERbeta mRNA and protein were localized in both UAendo and UA VSM. Immunoblot data demonstrated ovarian hormone specific regulation of ERalpha and ERbeta protein in UAendo and UA VSM. Compared to luteal phase sheep, both ERalpha and ERbeta levels in UAendo were elevated in follicular phase sheep. Whereas ERbeta was elevated by pregnancy in UAendo and UA VSM, ERalpha was not appreciably altered. eNOS was increased in UAendo from follicular and pregnant sheep. Ovariectomized ewes (OVEX) had substantially reduced UAendo ERbeta, but not UAendo ERalpha or OAendo ERalpha and ERbeta. In contrast, OVEX increased UA VSM ERalpha and ERbeta and decreased OA VSM ERalpha and ERbeta. Treatment with oestradiol-17beta (E2beta), but not progesterone or their combination, increased UAendo ERalpha levels. The reduced ERbeta in UAendo from OVEX ewes was reversed by E(2)beta and progesterone treatment. While ERalpha and eNOS were not elevated in any other reproductive or non-reproductive endothelia tested, ERbeta was augmented by pregnancy in uterine, mammary, placenta, and coronary artery endothelia. ERalpha and ERbeta mRNA and protein are expressed in UA endothelium with expression levels depending on the endocrine status of the animal, indicating UA endothelium is a target for oestrogen action in vivo, and that the two receptors appear to be differentially regulated in a spatial and temporal fashion with regard to the reproductive status or HRT.

Expression of estrogen receptors-alpha and -beta in the pregnant ovine uterine artery endothelial cells in vivo and in vitro

Estrogen is recognized to be one of the driving forces in increases in uterine blood flow through both rapid and delayed actions via binding to its receptors, ER alpha and ER beta at the uterine artery (UA) wall, and especially in UA endothelium (UAE). However, information regarding estrogen receptor (ER) expression in UAE is limited. This study was designed to test whether ERs are expressed in UAE in vivo, and if they are, whether these receptors are maintained in cultured UA endothelial cells (UAECs) in vitro. By using immunohistochemical and Western blot analyses, we clearly demonstrated ER alpha and ER beta protein expression in pregnant (Days 120-130) sheep UA and UAE in vivo and as well as cultured UAECs in vitro. Reverse transcription-polymerase chain reaction (RT-PCR) amplified both ER alpha and ER beta mRNAs in UA, UAE, and UAECs. Of interest, a truncated ER beta (ER beta2) variant due to a splicing deletion of exon 5 of the ER beta gene was detected in these cells. Quantitative RT-PCR analysis revealed that ER alpha mRNA levels are approximately 8-fold (P < 0.01) higher than that of ER beta in UAECs, indicating that ER alpha may play a more important role than ER beta in the UAEC responses to estrogen. Fluorescence immunolabeling analysis showed that ER alpha is present in both nuclei and plasma membranes in UAECs, and the latter is also colocalized with caveolin-1. The membrane and nuclear ER alpha presumably participate in rapid and delayed responses, respectively, to estrogen on UAE. Taken together, our data demonstrated that UAE is a direct target of estrogen actions and that the UAEC culture model we established is suitable for dissecting estrogen actions on UAE.

Nitric oxide synthase 1 is partly compensating for nitric oxide synthase 3 deficiency in nitric oxide synthase 3 knock-out mice and is elevated in murine and human cirrhosis

BACKGROUND

The role of endothelial nitric oxide synthase 3 (NOS-3) in the hyperdynamic circulation associated with cirrhosis is established but not that of the neuronal (NOS-1) isoform. We therefore investigated aortic NOS-1 levels in NOS-3 knock-out (KO) and wildtype (WT) mice and in hepatic arteries of patients.

METHODS

Mice rendered cirrhotic by bile duct ligation (BDL) were compared with sham-operated controls. Hepatic arteries of cirrhotic patients were collected during liver transplantation; donor vessels served as controls. mRNA levels were quantified by real-time PCR, protein levels by Western blotting and NO production by Nomega-nitro-L-arginine methyl ester inhibitable arginine-citrulline assay.

RESULTS

Aortae of NOS-3 KO mice exhibited higher NOS-1mRNA (5.6-fold, P < 0.004) and protein levels (8.8-fold) compared with WT. NO production in aortae of NOS-3 KO mice was 52% compared with WT (P = 0.002). BDL increased NOS-1 mRNA (2.4-fold, P = 0.01) and protein (7.1-fold) levels in aortae of WT, but no further in the NOS-3 KO mice. Hepatic artery NOS-1 mRNA levels in cirrhotic patients were markedly increased compared with controls (24.5-fold, P = 0.0007).

CONCLUSIONS

Increased NOS-1 mRNA and protein levels and partially maintained in vitro NO-production in aortae of NOS-3 KO mice suggest that NOS-1 may partially compensate for NOS-3 deficiency. BDL-induced increase in aortic NOS-1 mRNA and protein levels hint that not only NOS-3, but also NOS-1 may be involved in the regulation of systemic hyperdynamic circulation and portal hypertension. Upregulation of NOS-1 mRNA levels in hepatic arteries of portal hypertensive patients suggests possible clinical significance for these experimental findings.

Myogenic reactivity is enhanced in rat radial uterine arteries in a model of maternal undernutrition

OBJECTIVES

The purpose of this study was to determine if maternal undernutrition during pregnancy altered myogenic tone in small radial uterine arteries.

STUDY DESIGN

Myogenic tone of radial uterine arteries was studied from late pregnant rats (day 20) that were fed either ad libitum or globally restricted diet (moderately severe dietary restriction) throughout pregnancy.

RESULTS

Myogenic tone was enhanced in the radial uterine arteries from the diet-restricted compared with the ad libitum group. Nitric oxide synthase inhibition enhanced myogenic tone in the arteries from the ad libitum group only. Prostaglandin H synthase inhibition had no effect on myogenic tone in either group.

CONCLUSION

Diet restriction during pregnancy enhances myogenic tone in the radial uterine arteries partly as a result of impairment of the nitric oxide synthase pathway. Enhanced myogenic tone in turn may reduce uteroplacental blood flow and, thus, contribute to reduced birth weight, and lead to effects of fetal programming in utero that can have long-term consequences into adulthood.

Development and use of an ovarian synchronization model to study the effects of endogenous estrogen and nitric oxide on uterine blood flow during ovarian cycles in sheep

The objective of the current study was to develop an ovine animal model for consistent study of uterine blood flow (UBF) changes during synchronized ovarian cycles regardless of season. Sheep were surgically bilaterally instrumented with uterine artery blood flow transducers and 5-7 days later implanted with a vaginal progesterone (P(4))-controlled internal drug-releasing device (CIDR; 0.3 g) for 7 days. On Day 6 of P(4), sheep were given two prostaglandin F(2 alpha) injections (7.5 mg i.m. 4 h apart). At CIDR removal, Experimental Day 0, zero (n = 9), 500 IU (n = 8), or 1000 IU (n = 7) eCG was injected i.m.; UBF was monitored continuously for 55-75 h. Jugular blood was sampled every 8 h to evaluate levels of P(4), estradiol-17 beta (E(2)beta) and luteinizing hormone (LH). The inhibitor of nitric oxide synthase, L-nitro-arginine methyl ester (L-NAME) was infused in a stepwise fashion unilaterally into one uterine artery at 48-50 h after 500 IU eCG and the effects on UBF were examined (n = 7). The zero-eCG group gradually increased UBF from a baseline of 17.4 +/- 3.9 to 80.5 +/- 1.1 ml/min. The 500-IU-eCG group increased UBF between 10 and 15 h from a baseline of 11 +/- 3.3 to 83.3 +/- 1.0 ml/min, whereas UBF for the 1000-IU-eCG group was higher (100.1 +/- 1.7 ml/min) than that seen in either of the other groups. Plasma P(4) fell to baseline within 8 h of CIDR removal, while E(2)beta rose gradually in association with elevations in UBF. LH surges occurred between 32 and 56 h after CIDR removal and the LH surge occurred earlier in the 1000-IU-eCG group than the other two groups (P < 0.01). L-NAME infusion dose dependently reduced maximum levels of UBF ipsilaterally by 54.6% +/- 6.2%, but contralaterally only by 27.4% +/- 8.5%. Regardless of season, either dose of eCG will result in analogous UBF responses. During the follicular phase, elevations in UBF are in part locally controlled by the de novo production of nitric oxide.

Long‐term up‐regulation of eNOS and improvement of endothelial function by inhibition of the ubiquitin–proteasome pathway

The ubiquitin-proteasome system is the major pathway for intracellular protein degradation in eukaryotic cells. Endothelial nitric oxide synthase (eNOS) is the key enzyme of vascular homeostasis involved in the pathophysiology of several cardiovascular diseases. The aim of our study was to investigate whether eNOS expression and activity are regulated by the proteasome. Bovine pulmonary artery endothelial cells (CPAE cells) were treated with the proteasome inhibitor MG132. MG132 (50-250 nmol/L) dose-dependently increased mRNA and protein levels of eNOS. Comparable results were obtained with other specific proteasome inhibitors, whereas the nonproteasomal calpain and cathepsin inhibitor ALLM had no effect. Efficacy of proteasome inhibition was evidenced by accumulation of poly-ubiquitinylated proteins and by measuring proteasomal activity in cell extracts. Cycloheximide prevented up-regulation of eNOS protein, indicating that post-translational stabilization of eNOS is not involved. eNOS activity was increased up to 2.8-fold (MG132 100 nmol/L, 48 h). Incubation of rat aortic rings with MG132 significantly enhanced endothelial-dependent vasorelaxation. Single MG132 treatment (100 nmol/L) induced long-term effects in CPAE cells, with increases of eNOS protein and activity for up to 10 days. Our results indicate that low-dose proteasome inhibition enhances eNOS expression and activity, and improves endothelial function.

Possible mechanisms underlying pregnancy-induced changes in uterine artery endothelial function

The last 10 years has seen a dramatic increase in our understanding of the mechanisms underlying the pregnancy-specific adaptation in cardiovascular function in general and the dramatic changes that occur in uterine artery endothelium in particular to support the growing fetus. The importance of these changes is clear from a number of studies linking restriction of uterine blood flow (UBF) and/or endothelial dysfunction and clinical conditions such as intrauterine growth retardation (IUGR) and/or preeclampsia in both humans and animal models; these topics are covered only briefly here. The recent developments that prompts this review are twofold. The first is advances in an understanding of the cell signaling processes that regulate endothelial nitric oxide synthase (eNOS) in particular (Govers R and Rabelink TJ. Am J Physiol Renal Physiol 280: F193-F206, 2001). The second is the emerging picture that uterine artery (UA) endothelial cell production of nitric oxide (NO) as well as prostacyclin (PGI2) may be as much a consequence of cellular reprogramming at the level of cell signaling as due to tonic stimuli inducing changes in the level of expression of eNOS or the enzymes of the PGI2 biosynthetic pathway (cPLA2, COX-1, PGIS). In reviewing just how we came to this conclusion and outlining the implications of such a finding, we draw mostly on data from ovine or human studies, with reference to other species only where directly relevant.

Functional NOS 1 in the rat mesenteric arterial bed

Previously we have demonstrated functional nitric oxide synthase (NOS) 1 in large arteries. Because resistance arteries largely determine blood pressure, this study examined whether functional NOS 1 also exists in resistance arteries. Phenylephrine (PE) contraction was measured in the absence and presence of the NOS 1 inhibitor N(5)-(1-imino-3-butenyl)-L-ornithine (VNIO) in isolated mesenteric resistance arteries (endothelium intact and denuded) from Sprague-Dawley rats. For NOS 1 activity and expression, the mesenteric arterial bed was separated into cytosolic and particulate fractions. NOS activity was assayed by measuring the conversion of [(3)H]arginine to [(3)H]citrulline inhibited by a nonselective NOS inhibitor or VNIO. VNIO increased PE sensitivity in endothelium-intact and -denuded arteries. In cytosolic and particulate fractions of the arterial bed, approximately 40% of NOS activity was inhibited by VNIO. Immunoprecipitation and Western blot analysis revealed two NOS 1 immunoreactive bands. One band corresponded to the rat brain isoform, whereas the second was of a slightly lower molecular mass. The cytosolic fraction contained both isoforms; however, the particulate fraction had only the lower molecular mass form. These studies demonstrate the existence of functional NOS 1 in resistance arteries.

Endothelial vasodilator production by uterine and systemic arteries. IX. eNOS gradients in cycling and pregnant ewes

The follicular phase (FOL) and pregnancy exhibit increases in uterine blood flow (UBF), estrogen levels, and uterine artery (UA) endothelial nitric oxide synthase (eNOS) expression. UA branching within the mesometrium increases the total vascular cross-sectional area, which reduces the vascular perfusion pressure gradient, thus locally decreasing the blood flow velocity. Shear stress (SS) activates eNOS and may be associated with UBF elevations during FOL and pregnancy. We hypothesized that regional differences in eNOS responses are observed with both decreases in vessel diameter and during the ovarian cycle and pregnancy. Endothelial isolated proteins were collected from renal (RA) and internal iliac arteries (II) as well as from primary (UA 1 degrees ), secondary (UA 2 degrees), and tertiary (UA 3 degrees) UA branches of nonpregnant luteal phase (LUT; n = 6) and FOL (n = 6) as well as midpregnant (MP; 82 +/- 1 days gestation, n = 6) and late pregnant (LP; 127 +/- 3 days gestation, n = 6) ewes (term = 145 +/- 3 days gestation) for Western blot analysis. LUT RA, II, and UA 1 degrees eNOS levels were similar. There was a 60.7 +/- 9.8% reduction in eNOS expression in UA 2 degrees and UA 3 degrees. A similar decreasing eNOS regional expression gradient was observed in LP ewes. No eNOS regional expression gradient was observed in FOL or MP ewes because eNOS increased in UA 2 degrees and UA 3 degrees. In UA 2 degrees and UA 3 degrees, MP > LP = FOL > LUT. Thus, with increasing UBF, FOL and pregnancy rises in SS may regulate eNOS protein expression in smaller diameter UAs. A decrease in LUT and LP UA 2 degrees and UA 3 degrees endothelial eNOS suggest a possible negative feedback mechanism due to downregulation of eNOS if SS is normalized.

Mechanisms regulating angiotensin II responsiveness by the uteroplacental circulation

Pregnancy is associated with increases in cardiac output and uterine blood flow (UBF) and a fall in systemic vascular resistance. In ovine pregnancy, UBF rises from approximately 3% of cardiac output to approximately 25% at term gestation, reflecting a >30-fold rise in UBF by term. This increase in UBF supports exponential fetal growth during the last trimester and maintains fetal well-being by providing excess oxygen and nutrient delivery. These hemodynamic changes are associated with numerous hormonal changes, including increases in placental steroid hormones and enhanced activation of the renin-angiotensin and sympathetic nervous systems, all of which are believed to modulate systemic and uterine vascular adaptation and vascular reactivity. Systemic pressor responses to infused ANG II are attenuated in normotensive pregnancies and the uteroplacental vasculature is even less sensitive, suggesting development of mechanisms to maintain basal UBF and permit the rise in UBF necessary for fetal growth and well-being. The effects of ANG II on the uteroplacental vasculature are reviewed, and the mechanisms that may account for attenuated vascular sensitivity are examined, including ANG II metabolism, vascular production of antagonists, ANG II-receptor subtype expression, and the role of indirect mechanisms.

Ca(2+)-activated K(+) channels modulate basal and E(2)beta-induced rises in uterine blood flow in ovine pregnancy

Uterine blood flow (UBF) increases >30-fold during ovine pregnancy. During the last trimester, this reflects vasodilation, which may be due to placentally derived estrogens. In nonpregnant ewes, estradiol-17 beta (E(2)beta) increases UBF >10-fold by activating nitric oxide synthase and large conductance calcium-dependent potassium channels (BK(Ca)). To determine whether BK(Ca) channels modulate basal and E(2)beta-induced increases in UBF, studies were performed in near-term pregnant ewes with uterine artery flow probes and catheters for intra-arterial infusions of tetraethylammonium (TEA), a selective BK(Ca) channel antagonist at <1 mM, in the absence or presence of E(2)beta (1 microg/kg iv). Uterine arteries were collected to measure BK(Ca) channel mRNA. TEA (0.15 mM) decreased basal UBF (P < 0.0001) 40 +/- 8% and 55 +/- 7% (n = 11) at 60 and 90 min, respectively, and increased resistance 175 +/- 48% without affecting (P > 0.1) mean arterial pressure (MAP), heart rate, or contralateral UBF. Systemic E(2)beta increased UBF 30 +/- 6% and heart rate 13 +/- 1% (P < or = 0.0001, n = 13) without altering MAP. Local TEA (0.15 mM) inhibited E(2)beta-induced increases in UBF without affecting increases in heart rate (10 +/- 4%; P = 0.006). BK(Ca) channel mRNA was present in uterine artery myocytes from pregnant and nonpregnant ewes. Exponential increases in ovine UBF in late pregnancy may reflect BK(Ca) channel activation, which may be mediated by placentally derived estrogens.

Endothelial vasodilator production by uterine and systemic arteries. VI. Ovarian and pregnancy effects on eNOS and NO(x)

Normal pregnancy and the follicular phase of the ovarian cycle are both estrogen-dominated physiological states that are characterized by elevations in uterine blood flow and endothelial nitric oxide synthase (eNOS) protein expression in the uterine artery (UA) endothelium. It is unknown if elevations in mRNA level account for the changes in protein or eNOS activity. We tested the hypothesis that pregnancy and the follicular phase are associated with increases in eNOS mRNA and the consequent elevated expression of eNOS protein results in increased circulating nitric oxide (NO) levels. UA were obtained from pregnant (PREG; n = 8; 110-130 days gestation; term = 145 +/- 3 days), nonpregnant luteal (LUT; n = 6), nonpregnant follicular (FOL; n = 6), and nonpregnant ovariectomized (OVEX; n = 6) sheep. Circulating NO levels were analyzed as total NO(2)-NO(3) (NO(x)). Western analysis performed on UA endothelial-isolated proteins demonstrated that eNOS protein levels were OVEX = LUT < or = FOL < PREG (P < 0.05), whereas eNOS mRNA expression (RT-PCR) in UA endothelial cells obtained by limited collagenase digestion was OVEX < LUT < FOL < PREG (P < 0.05). Pregnancy dramatically elevated eNOS protein (4.1- to 6.9-fold) and mRNA (2.4- to 6.9-fold) over LUT controls (P < 0.01). Circulating NO(x) levels were not altered by ovariectomy or the ovarian cycle but were elevated from 4.4 +/- 1.1 microM in LUT to 12 +/- 4, 22 +/- 3, and 41 +/- 3 microM at 110, 120, and 130 days gestation (P < 0.01). Systemic NO(x) levels in singleton (12.5 +/- 1.6 microM) were less (P < 0.01) than in multiple (twin 27.6 +/- 6.5 microM; triplet = 46 +/- 10 microM) pregnancies. Therefore, the follicular phase and, to a much greater extent, pregnancy are associated with elevations in UA endothelium-derived eNOS expression, although significant increases in systemic NO(x) levels were only observed in the PREG group (multiple > singleton). Thus, although UA endothelial increases in eNOS protein and mRNA levels are associated with high estrogen states, increases in local UA NO production may require additional eNOS protein activation to play its important role in the maintenance of uterine blood flow in pregnancy.

Endothelial vasodilator production by uterine and systemic arteries. VII. Estrogen and progesterone effects on eNOS

Uterine blood flow (UBF) and uterine artery endothelial nitric oxide synthase (eNOS) expression are greatest during the follicular vs. luteal phase. 17 beta-Estradiol (E(2)beta) increases UBF and elevates eNOS in ovine uterine but not systemic arteries; progesterone (P(4)) effects on E(2)beta changes of eNOS remain unclear. Nonpregnant ovariectomized sheep received either vehicle (n = 10), P(4) (0.9 g Controlled Internal Drug Release vaginal implants; n = 13), E(2)beta (5 microg/kg bolus + 6 microg x kg(-1) x day(-1); n = 10), or P(4) + E(2)beta (n = 12). Reproductive (uterine/mammary) and nonreproductive (omental/renal) artery endothelial proteins were procured on day 10, and eNOS was measured by Western analysis. P(4) and E(2)beta alone and in combination increased (P < 0.05) eNOS expression in uterine artery endothelium (vehicle = 100 +/- 16%, P(4) = 251 +/- 59%, E(2)beta = 566 +/- 147%, P(4) + E(2)beta = 772 +/- 211% of vehicle). Neither omental, renal, nor mammary artery eNOS was altered, demonstrating the local nature of steroid-induced maintenance of uterine arterial eNOS. In the myometrial microvasculature, eNOS was increased slightly (P = 0.06) with E(2)beta and significantly with P(4) + E(2)beta. Systemic NO(x) was increased with P(4) and P(4) + E(2)beta, but not E(2)beta, suggesting differential regulation of eNOS expression and activity, since P(4) increased eNOS in uterine artery endothelium while E(2)beta and the combination further increased eNOS protein.