Long-term estradiol replacement decreases contractility of guinea pig coronary arteries to the thromboxane mimetic U46619

Estrogen regulation of the transient outward K(+) current involves estrogen receptor α in mouse heart

BACKGROUND AND OBJECTIVE

We have previously shown that androgens upregulate cardiac K(+) channels and shorten repolarization. However, the effects that estrogens (E2) and estrogen receptors (ER) might have on the various repolarizing K(+) currents and underlying ion channels remain incompletely understood. Accordingly, our objective was to verify whether and how E2 and its ERs subtypes influence these K(+) currents.

METHODS AND RESULTS

In order to examine the influence of E2 and ERs on K(+) currents we drastically lowered the E2 level through ovariectomy (OVX; 74% reduction vs CTL) and in parallel, we used female mice lacking either ERα (ERαKO) or ERβ (ERβKO). In OVX mice, results showed a specific increase of 35% in the density of the Ca(2+)-independent transient outward K(+) current (Ito) compared to CTL. Western blots showed increase in Kv4.2 and Kv4.3 sarcolemmal protein expression while qPCR revealed higher mRNA expression of only Kv4.3 in OVX mice. This upregulation of Ito was correlated with a shorter ventricular action potential duration and QTc interval. In ERαKO but not ERβKO mice, the mRNA of Kv4.3 was selectively increased. Furthermore, when ventricular myocytes obtained from ERαKO and ERβKO were cultured in the presence of E2, results showed that E2 reduced Ito density only in ERβKO myocytes confirming the repressive role of E2-ERα in regulating Ito.

CONCLUSION

Altogether, these results suggest that E2 negatively regulates the density of Ito through ERα, this highlights a potential role for this female hormone and its α-subtype receptor in modulating cardiac electrical activity.

Endothelial dysfunction and enhanced contractility in microvessels from ovariectomized rats: roles of oxidative stress and perivascular adipose tissue

Ovarian hormone loss increases reactive oxidative species, endothelial dysfunction, and cardiovascular disease. Because perivascular adipose tissue (PVAT) regulates endothelial function, we hypothesized that reactive oxidative species in PVAT mediate adverse microvascular effects of ovarian hormone deficiency. Rats were ovariectomized or sham operated and given vehicle or tempol for 6 weeks. Mesenteric resistance arterioles from ovariectomized compared with sham-operated rats had dysfunctional responses to acetylcholine (ACh) including decreased ACh-induced endothelium-dependent relaxation (50±6% versus 72±2%) and endothelium-dependent relaxation factor (17±4% versus 37±2%) and increased endothelium-dependent contracting factor (27±5% versus 9±3%). OVX rat mesenteric arterioles had increased contractions to the thromboxane/prostanoid receptor agonist U-46 619 (58±3% versus 40±5%) and increased reactive oxidative species (tempo-9-AC fluorescence) with U-46 619 (0.65±0.17 versus 0.14±0.06 Δ unit) or ACh (0.49±0.09 versus 0.09±0.05 Δ unit) and increased p22(phox) protein expression (0.89±0.05 versus 0.18±0.04 Δ unit), whereas nitric oxide activity (DAF-FM [4-amino-5-methylamino-2',7'-difluorofluorescein diacetate] fluorescence) with ACh was reduced (0.39±0.1 versus 0.70±0.10 Δ unit). No differences were found in endothelium-dependent hyperpolarizing factor or contractile responses to phenylephrine. PVAT enhanced ACh-induced relaxation, endothelium-dependent relaxation factor, and nitric oxide only in sham-operated rats. Tempol prevented ovariectomy-induced endothelial dysfunction and restored the enhancing effects of PVAT on ACh-induced relaxation, endothelium-dependent relaxation factor, and nitric oxide in ovariectomized rat vessels, but both tempol and PVAT were required to normalize the enhanced U-46 619 contractions after ovariectomy. In conclusion, ovariectomy redirects endothelial responses from relaxation to contraction by reducing vascular nitric oxide, augmenting thromboxane/prostanoid receptor signaling, and attenuating the vasodilatory effects of PVAT, all of which were dependent on reactive oxidative species.

Nitric oxide and coronary vascular endothelium adaptations in hypertension

This review highlights a number of nitric oxide (NO)-related mechanisms that contribute to coronary vascular function and that are likely affected by hypertension and thus become important clinically as potential considerations in prevention, diagnosis, and treatment of coronary complications of hypertension. Coronary vascular resistance is elevated in hypertension in part due to impaired endothelium-dependent function of coronary arteries. Several lines of evidence suggest that other NO synthase isoforms and dilators other than NO may compensate for impairments in endothelial NO synthase (eNOS) to protect coronary artery function, and that NO-dependent function of coronary blood vessels depends on the position of the vessel in the vascular tree. Adaptations in NOS isoforms in the coronary circulation to hypertension are not well described so the compensatory relationship between these and eNOS in hypertensive vessels is not clear. It is important to understand potential functional consequences of these adaptations as they will impact the efficacy of treatments designed to control hypertension and coronary vascular disease. Polymorphisms of the eNOS gene result in significant associations with incidence of hypertension, although mechanistic details linking the polymorphisms with alterations in coronary vasomotor responses and adaptations to hypertension are not established. This understanding should be developed in order to better predict those individuals at the highest risk for coronary vascular complications of hypertension. Greater endothelium-dependent dilation observed in female coronary arteries is likely related to endothelial Ca(2+) control and eNOS expression and activity. In hypertension models, the coronary vasculature has not been studied extensively to establish mechanisms for sex differences in NO-dependent function. Genomic and nongenomic effects of estrogen on eNOS and direct and indirect antioxidant activities of estrogen are discussed as potential mechanisms of interest in coronary circulation that could have implications for sex- and estrogen status-dependent therapy for hypertension and coronary dysfunction. The current review identifies some important basic knowledge gaps and speculates on the potential clinical relevance of hypertension adaptations in factors regulating coronary NO function.

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.

Changes in vasoactive factors associated with altered vessel morphology in the tibial metaphysis during ovariectomy-induced bone loss in rats

We hypothesized that estrogen deficiency induces changes in bone vascularization which might be involved in bone loss mechanisms. First, we studied gene expression of angiogenic (vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF-2)) and vasodilator (endothelial nitric oxide synthase (ecNOS), neuronal NOS (nNOS), inducible NOS (iNOS), PTH-related protein (PTHrP), and its receptor PTH/PTHrP) factors in proximal tibial metaphysis of ovariectomized (OVX) rats and OVX 17beta-estradiol-treated rats at 3, 7, and 14 days. We then evaluated bone and vessel histomorphometry in secondary spongiosae by infusing vessels with a mixture of India ink/barium sulfate after 7 and 14 days of OVX. After 7 days expression of angiogenic and vasodilator factors decreased, concomitant with a decrease in the bone vessel number and possibly area. After 14 days all factors except FGF-2 exhibited either increased or normalized expression, which was associated with the stimulation of both bone formation and resorption. 17beta-Estradiol administration for 7 or 14 days prevented not only the OVX-induced changes in bone remodeling but also the morphological alterations observed in bone vessels. It also prevented the alterations in the expression of genes modified by OVX, except for that of FGF-2 whose transcription was similarly down-regulated in OVX rats with or without estrogen treatment.

A novel concept to preserve the beneficial effects of hormone replacement therapy in bilaterally female ovariectomized rats: role of lovastatin therapy

Estrogen replacement therapy (ERT) is claimed to reduce cardiovascular mortality by about 50% in postmenopausal women. This improvement is caused by favorable changes in lipid and lipoproteins metabolism, however, it also increases the incidence of the endometrial hyperplasia. Addition of progestin to ERT, referred to as hormone replacement therapy (HRT), has been shown to successively reduce this risk to the endometrium. Unfortunately, it has an adverse effect on high-density lipoprotein cholesterol (HDLC) concentration, thus compromising the benefits of ERT. Therefore the issue here whether HRT given alone and/or concomitantly with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (lovastatin) could exert any significant additional favorable effect on the lipid profile in bilaterally ovariectomized female rats. Sixty female Wistar rats were ovariectomized and treated with ERT (0.625 mg kg (-1)estradiol, E (2), IM every 2 weeks), HRT (estradiol plus progesterone, E (2)+ P, 0.625 mg kg (-1)estradiol and 5 mg progesterone kg (-1) respectively, IM every 2 weeks), and lovastatin (20 mg kg (-1)day (-1)orally) plus HRT (L + HRT) for 6 weeks. Blood aliquots were collected for serum and plasma separation. Serum vitamin E and plasma levels of C-reactive protein (CRP), nitric oxide (NO), lipid profile, and the susceptibility of non-HDLC to oxidation were determined. Moreover, thoracic aortas were dissected and directed for measurement of its lipid peroxide and NO contents. Treatment of ovariectomized rats with HRT showed a significant decrease ( P< 0.0001) in HDLC concentration compared to the group treated alone with ERT and increase ( P< 0.0001) in CRP levels compared to ovariectomized rats. HDLC and CRP are two powerful and significant predictors for increased cardiovascular risk in postmenopausal women. Addition of lovastatin as a complementary therapy to HRT revealed a significant 27% increment in HDLC and 48% decrement in CRP concentrations. Moreover, it significantly increased vitamin E, each of plasma and tissue content of NO and decreased atherogenic indexes (TC/HDLC, LDLC/HDLC), aortic lipid peroxide and susceptibility of non-HDLC to oxidation. In conclusion, this current study demonstrated that lovastatin together with continuous combined HRT seems to be more effective in the secondary prevention of coronary heart disease not only due to lipid lowering properties but also related to several other additive effects such as modification of endothelial function and inflammatory responses.

Progesterone regulation of vascular thromboxane A(2) receptors in rhesus monkeys

We hypothesized that progesterone regulates thromboxane A(2) receptor (TxA(2)R) density in primate vascular muscle and that TxA(2)R density correlates with coronary reactivity in vivo and in vitro. Reactivity to serotonin + U-46619 was determined by angiography in surgically postmenopausal [ovariectomized (Ovx)] rhesus monkeys without progesterone replacement and after 2-wk progesterone treatment (1-2 ng/ml). In untreated Ovx animals, 100 micromol/l serotonin + 1 micromol/l U-46619 (syringe concentrations) provoked vasospasm-like constrictions in six of six monkeys; zero of six progesterone-treated monkeys developed vasospasms. Sustained Ca(2+) responses in vascular muscle cells isolated from Ovx coronaries (208 +/- 63% of basal 20 min after stimulation) treated with serotonin + U-46619 contrasted with transient Ca(2+) responses (143 +/- 18% of basal and decreasing 5 min after stimulation) in progesterone-treated monkeys. The maximum density of [1S-(1I,2J(5Z),3I(1E,3R*),4I)]-7-[3-(3-hydroxy-4-(4'-[(125)I]iodophenoxy)- 1-butenyl)-7-oxabicyclo[2.2.1]heptan-2-yl]-5-heptenoic acid ([(125)I]-BOP) binding was greater (P < 0.01) in carotid arteries and aortic membranes from Ovx (109 +/- 11 fmol/mg) compared with progesterone-treated (43 +/- 15 fmol/mg) monkeys. TxA(2)R immunolabeling revealed greater coronary TxA(2)R labeling in Ovx compared with progesterone-treated monkeys. The results suggest that progesterone can decrease arterial TxA(2)R in Ovx monkeys.

Estrogen increases eNOS and NOx release in human coronary artery endothelium

Estrogen protects against the development of coronary heart disease in women. This study was designed to examine the direct effects of estrogen on nitric oxide release and endothelial nitric oxide synthase (eNOS) expression in cultured human coronary artery endothelial cells (HCAECs). NOx (nitrate, nitrite, and nitric oxide) was measured by the chemiluminescence method. Prolonged treatment (48 h) of the cells with 17beta-estradiol (E2beta), but not 17alpha-estradiol (E2alpha), resulted in a 2.3-fold increase in basal NOx release in HCAECs and an enhanced adenosine triphosphate (ATP)- and calcium ionophore A23187-induced NOx release. The effects of E2beta on endothelial NOx release were blocked by estrogen-receptor antagonist ICI 182,780. E2beta had no effect on basal and ATP-stimulated intracellular Ca2+ concentrations in HCAECs. However, E2beta significantly increased eNOS protein levels, as determined by Western analysis. We conclude that estrogen increases NOx release in HCAECs, which is independent of cytosolic Ca2+ mobilization and is mediated by the upregulation of eNOS.

Estrogen as a neuroprotectant in stroke

Recent evidence suggests that reproductive steroids are important players in shaping stroke outcome and cerebrovascular pathophysiologic features. Although women are at lower risk for stroke than men, this native protection is lost in the postmenopausal years. Therefore, aging women sustain a large burden for stroke, contrary to a popular misconception that cancer is the main killer of women. Further, the value of hormone replacement therapy in stroke prevention or in improving outcome remains controversial. Estrogen has been the best studied of the sex steroids in both laboratory and clinical settings and is considered increasingly to be an endogenous neuroprotective agent. A growing number of studies demonstrate that exogenous estradiol reduces tissue damage resulting from experimental ischemic stroke in both sexes. This new concept suggests that dissecting interactions between estrogen and cerebral ischemia will yield novel insights into generalized cellular mechanisms of injury. Less is known about estrogen's undesirable effects in brain, for example, the potential for increasing seizure susceptibility and migraine. This review summarizes gender-specific aspects of clinical and experimental stroke and results of estrogen treatment on outcome in animal models of cerebral ischemia, and briefly discusses potential vascular and parenchymal mechanisms by which estrogen salvages brain.

Gender differences in coronary artery diameter reflect changes in both endothelial Ca2+ and ecNOS activity

Elevation of nitric oxide (NO) release from the vascular endothelium may contribute to some of the gender-associated differences in coronary artery function. The mechanisms by which gender affects NO release from the endothelium of coronary arteries are not known. In this study, endothelial function was examined in pressurized coronary arteries from female and male rats. Diameter and endothelial cell intracellular Ca2+ concentration ([Ca2+]i) in intact arteries, as well as enzymatic activity of endothelial constitutive nitric oxide synthase (ecNOS) in arterial lysates, was measured. Elevation of intravascular pressure to 60 mmHg constricted coronary arteries from female animals less than coronary arteries from male animals (18% and 31% constriction, respectively). The increased arterial diameter of coronary arteries from females was associated with elevated endothelial [Ca2+]i (female 174 nM, male 90 nM; P < 0.001). Elevation of Ca2+ activated ecNOS with a similar slope and half-activation constant ( approximately 160 nM) for both female and male coronary arteries. However, at [Ca2+] > 100 nM, ecNOS activity was significantly higher in coronary arteries from female rats compared with their male equivalents (P < 0.01). Maximal activity for ecNOS at saturating Ca2+ (300 nM) was 37% higher in coronary arteries from female animals compared with male animals (P < 0.05). Thus elevated [Ca2+]i in the endothelium of female coronary arteries alone is predicted to increase the production of NO (by nearly 2-fold). This gender difference combined with increased ecNOS activity at a given [Ca2+] in females indicates that tonic NO production should be nearly threefold greater in female coronary arteries compared with male coronary arteries. We conclude that, in the regulation of endothelial Ca2+ and ecNOS, gender differences contribute significantly to the overall decrease in myogenic tone observed in coronary arteries of females.

The effect of 17beta-oestradiol on regional blood flow in anaesthetized pigs

1. The present study was designed to investigate the effects of 17beta-oestradiol on the mesenteric, renal, iliac and coronary circulations and to determine the mechanisms involved. 2. In pigs anaesthetized with sodium pentobarbitone, changes in blood flow in the superior mesenteric, left renal, left external iliac and left circumflex coronary arteries caused by intravenous infusion of 17beta-oestradiol at constant heart rate and arterial pressure were assessed using electromagnetic flowmeters. 3. In eight pigs, infusion of 2 microg h-1 of the hormone caused an increase in renal, iliac and coronary blood flow without affecting mesenteric blood flow, left ventricular dP/dtmax (rate of change of left ventricular systolic pressure) and filling pressures of the heart. In four pigs, these vasodilator effects were enhanced by graded increases in the dose of the hormone between 1, 2 and 3 microg h-1; the highest dose also caused an increase in mesenteric blood flow. 4. In five pigs, blockade of muscarinic cholinoceptors and adrenoceptors with the intravenous administration of atropine, propranolol and phentolamine did not affect the vasodilator responses caused by infusion of 2 microg h-1 of 17beta-oestradiol. 5. The increases in renal, iliac and coronary blood flow caused by infusion of 2 microg h-1 of 17beta-oestradiol were prevented, respectively, by the injection of Nomega-nitro-L-arginine methyl ester (L-NAME) into the renal artery (five pigs), the iliac artery (five pigs) or the coronary artery (five pigs). In five pigs, all responses were prevented by injection of L-NAME into all three arteries. In two pigs, injection of L-NAME into the mesenteric, renal, iliac and coronary arteries abolished the vasodilator responses to the infusion of 3 microg h-1 of 17beta-oestradiol. 6. The present study shows that intravenous infusion of 2 microg h-1 of 17beta-oestradiol primarily dilated renal, iliac and coronary circulations and that a higher dose of the hormone also caused vasodilatation in the mesenteric vascular bed. The mechanism of these responses was shown to be nitric oxide dependent.