Basal release of nitric oxide from aortic rings is greater in female rabbits than in male rabbits: implications for atherosclerosis

Sexual dimorphism in rabbit aortic endothelial function under acute hyperglycemic conditions and gender-specific responses to acute 17beta-estradiol

Epidemiological data suggest that hyperglycemia abrogates the gender-based cardiovascular protection possibly associated with estrogens. This study was designed to investigate 1) whether rabbit aortic rings show gender differences in the development of abnormal endothelium-dependent vasodilation (EDV) under acute hyperglycemic conditions, 2) the potential role of PKC isoforms and superoxide (O2-) in acute hyperglycemia-induced vascular dysfunction, and 3) the effect of acute estrogen administration on hyperglycemia-induced endothelial dysfunction in male and female rabbits. EDV to ACh was determined before and after 3 h of treatment with high glucose (HG) in phenylephrine-precontracted aortic rings from male and female New Zealand White rabbits. Similar experiments were conducted in the presence of inhibitors of PKC-alpha, PKC-beta, and PKC-delta or an O2- scavenger. The effect of acute estrogen administration was evaluated in the presence and absence of HG. Finally, mRNA expression of PKC isoforms was measured by real-time PCR. We found that 1) 3 h of incubation with HG impairs EDV to a greater extent in female than male aorta, 2) inhibition of PKC-beta or O2- prevents HG-induced impairment of EDV in female aorta, 3) acute 17beta-estradiol aggravates HG-induced endothelial dysfunction in female, but not male, aorta, and 4) PKC-alpha and PKC-beta expression are significantly higher in female than male aorta. This study reveals the predisposition of female rabbit aorta to vascular injury under hyperglycemic conditions, possibly via activation of PKC-beta and O2- production. Furthermore, it suggests that, under hyperglycemic conditions, acute estrogen treatment is detrimental to endothelial function in female rabbits.

Estrogen potentiates constrictor prostanoid function in female rat aorta by upregulation of cyclooxygenase-2 and thromboxane pathway expression

Estrogen potentiates vascular reactivity to vasopressin (VP) by enhancing constrictor prostanoid function. To determine the cellular and molecular mechanisms, the effects of estrogen on arachidonic acid metabolism and on the expression of constrictor prostanoid pathway enzymes and endoperoxide/thromboxane receptor (TP) were determined in the female rat aorta. The release of thromboxane A2 (TxA2) and prostacyclin (PGI2) was measured in male (M), intact-female (Int-F), ovariectomized-female (OvX-F), and OvX + 17beta-estradiol-replaced female (OvX + ER-F) rats. The expression of mRNA for cyclooxygenase (COX)-1, COX-2, thromboxane synthase (TxS), and TP by aortic endothelium (Endo) and vascular smooth muscle (VSM) of these four experimental groups was measured by RT-PCR. The expression of COX-1, COX-2, and TxS proteins by Endo and VSM was also estimated by immunohistochemistry (IHC). Basal release of TxA2 and PGI2 was similar in M (18.8 +/- 1.9 and 1,723 +/- 153 pg/mg ring wt/45 min, respectively) and Int-F (20.2 +/- 4.2 and 1,488 +/- 123 pg, respectively) rat aortas. VP stimulated the dose-dependent release of TxA2 and PGI2 from both male and female rat aorta. OvX markedly attenuated and ER therapy restored VP-stimulated release of TxA2 and PGI2 in female rats. No differences in COX-1 mRNA levels were detected in either Endo or VSM of the four experimental groups (P > 0.1). The expression of both COX-2 and TxS mRNA were significantly higher (P < 0.05) in both Endo and VSM of Int-F and OvX + ER-F, compared with M or OvX-F. Expression of TP mRNA was significantly higher in VSM of Int-F and OvX + ER-F compared with M or OvX-F. IHC revealed the uniform staining of COX-1 in VSM of the four experimental groups, whereas staining of COX-2 and TxS was greater in Endo and VSM of Int-F and OvX + ER-F than in OvX-F or M rats. These data reveal that estrogen enhances constrictor prostanoid function in female rat aorta by upregulating the expression of COX-2 and TxS in both Endo and VSM and by upregulating the expression of TP in VSM.

Effect of ovariectomy on cardiac gene expression: inflammation and changes in SOCS gene expression

Basic research on estrogen-related changes in cardiomyocyte gene expression is needed to provide a greater understanding of the effects of estrogen, so that hormone replacement trials and treatment can be based on a true comprehension of estrogen's pleiotropic effects. Therefore, we compared gene expression in models of estrogen depletion and estrogen replacement. Using gene expression array analysis, we examined differences in expression in cardiac tissue from ovariectomized (OVX), ovariectomized with 17β-estradiol replacement (OVX/E2), and intact rats undergoing sham procedures (Sham). We found that OVX results in at least twofold changes in expression of genes involved in inflammation, vascular tone, apoptosis, and proteolysis compared with OVX/E2. With confirmation via real-time PCR, we found an OVX-induced increase in genes mediating inflammation (inhibin βa, IL-6, TNF-α, SOCS2, SOCS3), an OVX-related decrease in the myocardial mRNA expression of genes involved in regulating vasodilation (endothelial NOS, soluble guanyl cyclase), an OVX-associated increase in extracellular matrix genes (collagen12alpha1, connexin 43), and an OVX-related increase in proapoptotic genes (caspase 3, calpain). Because details of cardiac signaling by SOCS genes are virtually unknown, we examined the protein expression for these genes via Western analyses. Although we observed OVX-related increases in SOCS2 and SOCS3 mRNA, SOCS2 and SOCS3 protein did not differ among groups. In light of these findings, investigation into the net effect of OVX on inflammation is warranted. These experiments add to existing evidence that estrogen can protect against negative changes associated with estrogen removal.

Endothelin stimulates vascular hydroxyl radical formation: effect of obesity

Reactive oxygen species (ROS) and endothelin-1 (ET-1) contribute to vascular pathophysiology in obesity. In this context, whether ET-1 modulates hydroxyl radical (•OH) formation and the function of ROS/•OH in obesity is not known. In the present study, formation and function of ROS, including •OH, were investigated in the aorta of lean and leptin-deficient obese ob/ob mice. Hydroxyl radical formation was detected ex vivo using terephthalic acid in intact aortic rings and the involvement of ROS in ET-1-mediated vasoreactivity was analyzed using the antioxidant EPC-K1, a combination of α-tocopherol and ascorbic acid. Generation of either •OH, •O2−, and H2O2was strongly inhibited by EPC-K1 (all P < 0.05). In obese mice, basal vascular •OH formation and ROS activity were reduced by 3-fold and 5-fold, respectively ( P < 0.05 vs. lean). ET-1 markedly enhanced •OH formation in lean (6-fold, P < 0.05 vs. untreated) but not in obese mice. Obesity increased ET-1-induced contractions ( P < 0.05 vs. lean), and ROS scavenging further enhanced the response ( P < 0.05 vs. untreated). Exogenous ROS, including •OH caused stronger vasodilation in obese animals ( P < 0.05 vs. lean), whereas endothelium-dependent relaxation was similar between lean and obese animals. In conclusion, we present a sensitive method allowing ex vivo measurement of vascular •OH generation and provide evidence that ET-1 regulates vascular •OH formation. The data indicate that in obesity, vascular formation of ROS, including •OH is lower, whereas the sensitivity to ROS is increased, suggesting a novel and important role of ROS, including •OH in the regulation of vascular tone in disease status associated with increased body weight.

Gender-specific vascular effects elicited by chronic ethanol consumption in rats: a role for inducible nitric oxide synthase

BACKGROUND AND PURPOSE

Epidemiological data suggest that the risk of ethanol-associated cardiovascular disease is greater in men than in women. This study investigates the mechanisms underlying gender-specific vascular effects elicited by chronic ethanol consumption in rats.

EXPERIMENTAL APPROACH

Vascular reactivity experiments using standard muscle bath procedures were performed on isolated thoracic aortae from rats. mRNA and protein for inducible NO synthase (iNOS) and for endothelial NOS (eNOS) was assessed by RT-PCR or western blotting, respectively.

KEY RESULTS

In male rats, chronic ethanol consumption enhanced phenylephrine-induced contraction in both endothelium-intact and denuded aortic rings. However, in female rats, chronic ethanol consumption enhanced phenylephrine-induced contraction only in endothelium denuded aortic rings. After pre-incubation of endothelium-intact rings with L-NAME, both male and female ethanol-treated rats showed larger phenylephrine-induced contractions in aortic rings, compared to the control group. Acetylcholine-induced relaxation was not affected by ethanol consumption. The effects of ethanol on responses to phenylephrine were similar in ovariectomized (OVX) and intact (non-OVX) female rats. In the presence of aminoguanidine, but not 7-nitroindazole, the contractions to phenylephrine in rings from ethanol-treated female rats were greater than that found in control tissues in the presence of the inhibitors. mRNA levels for eNOS and iNOS were not altered by ethanol consumption. Ethanol intake reduced eNOS protein levels and increased iNOS protein levels in aorta from female rats.

CONCLUSIONS AND IMPLICATIONS

Gender differences in the vascular effects elicited by chronic ethanol consumption were not related to ovarian hormones but seemed to involve the upregulation of iNOS.

Oestrogen synthesis, oestrogen metabolism and functional oestrogen receptors in bovine aortic endothelial cells

In order to investigate the mechanisms by which oestrogenic hormones influence the vascular system, we have studied their metabolism and the functioning of oestrogen receptors in bovine aortic endothelial cells from primo-secondary cultures, a widely studied model of vascular pathophysiology. We have demonstrated the enzymic activity of oestradiol-17 beta-hydroxysteroid dehydrogenase, 17-ketoreductase and aromatase in these cells. Immunocytochemical analyses, using two different monoclonal antibodies that recognize epitopes in the A/B domain of the oestrogen receptor, showed that this molecule has a predominantly cytoplasmic localization even after the addition of oestrogen to the culture medium. We showed that the hormone-receptor complexes were functional by demonstrating their transactivating ability in transfection experiments using the luciferase gene reporter and an oestrogen-responsive element transcriptional enhancer, although the amplitude of the response was in the range of only 140-150%: this was not a consequence of the presence of a specific limiting factor, but instead might be related to the peculiar subcellular localization of the oestrogen receptor.

Sex-related differences in nitric oxide content in healthy and hypertensive rats at rest and under stress conditions

Immobilization was followed by an increase in blood NO concentration in male and female rats. After renovascular hypertension modeling blood pressure was higher and the decrease in nitric oxide concentration was more pronounced in males than in females. The levels of nitric oxide in healthy and hypertensive females at rest and during stress were higher than in males. These specific features probably contribute to higher resistance of the cardiovascular system in females to pathological changes.

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.

Vasoactive drugs enhance pancreatic islet blood flow, augment insulin secretion and improve glucose tolerance in female rats

Pravastatin, irbesartan and captopril are frequently used in the treatment of patients with Type 2 diabetes. These drugs also exert beneficial metabolic effects, causing an improved glucose tolerance in patients, but the precise mechanisms by which this is achieved remain elusive. To this end, we have studied whether these drugs influence insulin secretion in vivo through effects on islet blood perfusion. Captopril (3 mg/kg of body weight), irbesartan (3 mg/kg of body weight) and pravastatin (0.5 mg/kg of body weight) were injected intravenously into anaesthetized female Wistar rats. Blood flow rates were determined by a microsphere technique. Blood glucose concentrations were measured with test reagent strips and serum insulin concentrations were measured by ELISA. Pancreatic blood flow was markedly increased by pravastatin (P<0.001), captopril (P<0.05) and irbesartan (P<0.01). Pancreatic islet blood flow was significantly and preferentially enhanced after the administration of captopril (P<0.01), irbesartan (P<0.01) and pravastatin (P<0.001). Kidney blood flow was enhanced significantly by pravastatin (P<0.01), irbesartan (P<0.05) and captopril (P<0.01). Captopril and pravastatin also enhanced late-phase insulin secretion and positively influenced glycaemia in intraperitoneal glucose tolerance tests. In conclusion, the present study suggests that a local pancreatic renin-angiotensin system and pravastatin treatment may be selectively controlling pancreatic islet blood flow, augmenting insulin secretion and thereby improving glucose tolerance. Our findings indicate significant gender-related differences in the vascular response to these agents. Since statins and renin-angiotensin system inhibitors are frequently used by diabetic patients, the antidiabetic actions of these drugs reported previously might occur, in part, through the beneficial direct islet effects shown in the present study.

Effect of oestrogen on reactive oxygen species production in the aortas of ovariectomized Dahl salt-sensitive rats

OBJECTIVE

In the present study, we examined whether ovariectomy increases reactive oxygen species (ROS) and the expression of nicotinamide adenine dinucleotide phosphate, reduced form (NADPH) oxidase and modulates the scavenger enzymes for ROS in the aortas of Dahl salt-sensitive (DSS) rats fed a high salt diet.

METHODS

DSS female rats were ovariectomized and fed a high salt diet (8% NaCl), or a high salt diet plus oestrogen supplement for 4 weeks. Urinary levels of hydrogen peroxide (H2O2) were measured by using 2',7'-dichlorofluorescein. The expression of an NADPH oxidase subunit p22phox, extracellular superoxide dismutase (ecSOD), glutathione peroxidase (GPx)1, GPx4 and monocyte chemoattractant protein 1 (MCP-1) messenger RNA was assessed by reverse transcription-polymerase chain reaction. The expression of MCP-1, and macrophage infiltration were examined by immunohistochemical analysis.

RESULTS

Ovariectomy increased superoxide production and the expression of NADPH oxidase subunit p22phox mRNA and protein in the aortas of DSS rats fed a high salt diet. In contrast, ovariectomy reduced the expression of ecSOD mRNA and protein and the expression of GPx1 and GPx4 mRNA in the aorta. Ovariectomy increased MCP-1 mRNA and protein expression and ED1-positive cells in the aorta.

CONCLUSIONS

Ovariectomy leads to an amplification of oxidative stress in DSS rats fed a high salt diet synergistically by an increase in the ROS-generating system and a decrease in the ROS-eliminating system, as shown in the increase in superoxide production and the urinary excretion of H2O2. Oestrogen supplementation counteracted these alterations, showing how oestrogen is antioxidative.

Gender differences in endothelial function and inflammatory markers along the occurrence of pathological events in stroke-prone rats

Spontaneously hypertensive stroke-prone rats (SHRSP) feature an established model for human cerebrovascular disease. SHRSP, kept on a high-salt permissive diet (JPD), develop hypertension, renal and brain damage. In this report we compared the behavior of female and male SHRSP regarding the main aspects of their pathological condition. Brain abnormalities, detected by magnetic resonance imaging, developed spontaneously in males after 42+/-3 days, in females after 114+/-14 days from the start of JPD. Survival was >3-fold longer for females than for males. The development of brain damage was preceded, in both genders, by an inflammatory condition characterized by the accumulation in serum and urine of acute-phase proteins. The increase in thiostatin level was significantly lower and delayed in female in comparison to male SHRSP. During JPD female and male SHRSP developed massive proteinuria, its worsening being significantly slower in females. The alterations of vasculature-bound barriers in kidney and brain were connected with endothelial dysfunction and relative deficiency in nitric oxide (NO). In thoracic aortic rings, basal release of NO was significantly higher in female than in male SHRSP, both if receiving and if not receiving JPD. The gender differences in SHRSP thus appear to be connected to a more efficient control in females of inflammation and of endothelial dysfunction.

17beta-estradiol antagonizes the down-regulation of endothelial nitric-oxide synthase and GTP cyclohydrolase I by high glucose: relevance to postmenopausal diabetic cardiovascular disease

In postmenopausal women, the risk of diabetic cardiovascular disease drastically increases compared with that of men or premenopausal women. However, the mechanism of this phenomenon has not yet been clarified. We hypothesized that the beneficial effects of estrogen on endothelial function may be relevant to protection against hyperglycemia-induced vascular derangement. Bovine aortic endothelial cells were incubated for 72 h in the presence and absence of the physiological concentration of 17beta-estradiol (17beta-E2) under normal and high-glucose conditions. The presence of 17beta-E2 significantly counteracted the reduction in basal nitric oxide production under high-glucose conditions. This finding was associated with the recovery of endothelial nitric-oxide synthase (eNOS) protein expression, tetrahydrobiopterin (BH4) levels, and the activity and gene expression of GTP cyclohydrolase I (GTPCH-I), a rate-limiting enzyme for BH4 synthesis. Both the gene transfer of estrogen receptor alpha using adenovirus and treatment with the protein kinase C inhibitor bisindolylmaleimide I significantly enhanced the effects of 17beta-E2 treatment under high-glucose conditions, whereas these effects were abolished by the estrogen receptor antagonist ICI 182,780 (faslodex). Transfection of small-interfering RNA targeting eNOS resulted in a marked reduction in GTPCH-I mRNA under both normal and high-glucose conditions, but this reduction was strongly reversed by 17beta-E2. These results suggest that the activation of ERalpha with 17beta-E2 can counteract high-glucose-induced down-regulation of eNOS and GTPCH-I in endothelial cells. Therefore, estrogen deficiency may result in an exaggeration of hyperglycemia-induced endothelial dysfunction, leading to the development of cardiovascular disease in postmenopausal diabetic women.

β1 antagonist and β2 agonist, celiprolol, restores the impaired endothelial dependent and independent responses and decreased TNFα in rat with type II diabetes

The effect of beta antagonists in the diabetic vascular lesion is controversial. We investigated the effect of celiprolol hydrochloride, a beta1 antagonist and mild beta2 agonist, on the lesions and function in type II male Otsuka Long-Evans Tokushima Fatty (OLETF) diabetic rats. OLETF rats were fed regular chow with or without atenolol (25 mg/kg/day) or celiprolol (100 mg/kg/day) treatment (group DM, no treatment; group DM-a, atenolol treatment; group DM-c, celiprolol treatment), and treatment was continued for 31 days. Separately, normoglycemic control rats, LETO, were prepared as group C. On day 3, endothelial cells of the right internal carotid artery were removed by balloon injury, and the rats were evaluated 4 weeks after balloon injury. The plasma glucose and lipid levels were unchanged throughout the treatment period. Intimal thickening was observed in the right carotid artery in the DM and DM-a groups; however, little thickening was observed in those of DM-c rats. Acetylcholine-induced NO-dependent relaxation in arteries was improved in DM-c rats compared with DM and DM-a rats (maximum relaxation DM 30.8+/-4.5, DM-a 37.4+/-3.9, DM-c 48.8+/-4.6%, *P<0.05 vs. DM for DM-c rats). Tone-related basal NO release and acetylcholine-induced NO-dependent relaxation in the arteries and plasma NO(x) (sum of NO(2)(-) and NO(3)(-)) were greater in DM-c and C groups than in DM and DM-a groups. The serum TNFalpha levels did not increase in DM-c rats compared with those of the DM or DM-a groups, and were comparable with those of group C.

CONCLUSION

In conclusion, Celiprolol improves endothelial function in the arteries of OLETF rats, and further restore it 4 weeks after endothelial denudation in the arteries of OLETF rats. NO and O(2)(-) may have a role in the important underlying mechanisms by reducing the TNFalpha levels.

Nuclear factor-kappab (NF-kappaB): an unsuspected major culprit in the pathogenesis of endometriosis that is still at large?

Endometriosis, defined as the ectopic presence of endometrial glandular and stromal cells outside the uterine cavity, is a common benign gynecological disorder with an enigmatic pathogenesis. Many genes and gene products have been reported to be altered in endometriosis, yet some of them may not be major culprits but merely unwitting accomplices or even innocent bystanders. Therefore, the identification and apprehension of major culprits in the pathogenesis of endometriosis are crucial to the understanding of the pathogenesis and would help to develop better therapeutics for endometriosis. Although so far NF-kappaB only has left few traces of incriminating fingerprints, several lines of investigation suggest that NF-kappaB, a pivotal pro-inflammatory transcription factor, could promote and maintain endometriosis. Various inflammatory agents, growth factors, and oxidative stress activate NF-kappaB. NF-kappaB proteins themselves and proteins regulated by them have been linked to cellular transformation, proliferation, apoptosis, angiogenesis, and invasion. Interestingly, all existing and nearly all investigational medications for endometriosis appear to act through suppression of NF-kappaB activation. In endometriotic cells, NF-kappaB appears to be constitutively activated, and suppression of NF-kappaB activity by NF-kappaB inhibitors or proteasome inhibitors suppresses proliferation in vitro. Viewing NF-kappaB as a major culprit, an autoregulatory loop model can be postulated, which is consistent with existing data and, more importantly, can explain several puzzling phenomena that are otherwise difficult to interpret based on prevailing theories. This view has immediate and important implications for novel ways to treat endometriosis. Further research is warranted to precisely delineate the roles of NF-kappaB in the pathogenesis of endometriosis and to indict and convict its aiders and abettors.

Changes in coronary resistance related to the stages of the female life cycle

BACKGROUND

Estrogen is known to dilate the coronary vascular system mainly through nitric oxide (NO) release. However, it has not been determined whether or not this effect occurs equally throughout all stages of the female life cycle. We examined the changes in coronary flow properties in adolescent, adult and ovariectomized (OVX) female rats using the endothelial NO synthetase blocker, L-N (omega) nitroarginine (L-NNA).

METHODS AND RESULTS

Female rats were divided into 3 groups: adolescent (13 weeks, n=6), adult (19 weeks, n=8) and OVX (20 weeks, n=7, 12 weeks after oophorectomy). Coronary effluent was measured using the Langendorff non-working heart model before and 15 min after the use of L-NNA. In OVX rats, coronary effluent was significantly decreased in comparison with adolescent and adult rats (adolescent vs OVX: p<0.001; adult vs OVX: p<0.05). After treatment with L-NNA, coronary effluent was significantly higher in the adolescent group compared with the adult and OVX groups (adolescent vs adult: p<0.01; adolescent vs OVX: p<0.0005).

CONCLUSIONS

Oophorectomy brought about an increase in coronary vascular resistance. L-NNA exacerbated coronary vascular resistance in relation to maturation. It is suggested that the effect of estrogen on vascular dilatation in adolescents is largely dependent on a non-NO pathway, whereas adults are largely dependent on an NO pathway.

Novel aspects of endothelium-dependent regulation of vascular tone

The vascular endothelium plays a crucial role in the regulation of vascular homeostasis and in preventing the initiation and progress of cardiovascular disease by controlling mechanical functions of the underlying vascular smooth muscle. Three vasodilators: nitric oxide (NO), prostacyclin, and endothelium-derived hyperpolarizing factor, produced by the endothelium, underlie this activity. These substances act in a co-ordinated interactive manner to maintain normal endothelial function and operate as support mechanisms when one pathway malfunctions. In this review, we discuss recent advances in our understanding of how gender influences the interaction of these factors resulting in the vascular protective effects seen in pre-menopausal women. We also discuss how endothelial NO synthase (NOS) can act in both a pro- and anti-inflammatory action and therefore is likely to be pivotal in the initiation and time course of an inflammatory response, particularly with respect to inflammatory cardiovascular disorders. Finally, we review recent evidence demonstrating that it is not solely NOS-derived NO that mediates many of the beneficial effects of the endothelium, in particular, nitrite acts as a store of NO released during pathological episodes associated with NOS inactivity (ischemia/hypoxia). Each of these more recent findings has emphasized new pathways involved in endothelial biology, and following further research and understanding of the significance and mechanisms of these systems, it is likely that new and improved treatments for cardiovascular disease will result.

Gender-specificity of delayed preconditioning by isoflurane in rabbits: potential role of endothelial nitric oxide synthase

INTRODUCTION

Female gender confers cardioprotection against ischemia-reperfusion injury, in part because estrogen enhances nitric oxide production by endothelial nitric oxide synthase (eNOS). Whether ischemic preconditioning occurs in females remains controversial. Delayed myocardial preconditioning by isoflurane is mediated by eNOS in male rabbits, but whether females are similarly protected by isoflurane is unknown. We tested the hypothesis that gender-specific reductions in myocardial infarct size occur in female rabbits, but that this inherent cardioprotection abrogates further beneficial effects of isoflurane-induced delayed preconditioning.

METHODS

Rabbits (n = 115) underwent a 30 min coronary artery occlusion and 3 h reperfusion with or without a 2 h administration of 1.0 minimum alveolar concentration isoflurane one day before experimentation. Rabbits received saline or a nonselective, selective inducible, or selective neuronal NOS inhibitor [N-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg), aminoguanidine (AG, 300 mg/kg), or 7-nitroindazole (7-NI, 50 mg/kg), respectively].

RESULTS

Isoflurane reduced infarct size in males (mean+/- sd, 26 +/- 5% of the left ventricular area at risk) versus saline (45 +/- 2%). L-NAME, but not AG or 7-NI, abolished isoflurane-induced protection in males (41 +/- 9, 24 +/- 4 and 22 +/- 2%, respectively). Infarct size was reduced, and eNOS protein expression was greater, in female versus male rabbits. Infarct size was unchanged in female rabbits with, versus without, isoflurane pretreatment (27 +/- 9 and 27 +/- 10%, respectively). L-NAME, but not AG or 7-NI, increased infarct size with or without isoflurane pretreatment in females.

CONCLUSIONS

Female gender-induced reductions in infarct size are mediated by eNOS, but remote isoflurane exposure (1.0 MAC) before ischemia and reperfusion does not produce additional cardioprotection in vivo.

Modulating role of estradiol on arginase II expression in hyperlipidemic rabbits as an atheroprotective mechanism

We evaluated the effects of a 0.5% cholesterol-enriched diet (HCD) on nitric-oxide synthase (NOS) and arginase expression and the modulating role of 17beta-estradiol (E(2)) on this phenomenon. Thirty oopherectomized rabbits were divided into three groups and treated for 15 weeks. Group I received normal chow; group II, HCD; and group III, HCD plus E(2) pellets. Animals in group II showed an increase in plasma lipids, and they demonstrated atheromatous lesions as well as expression of arginase I and II accompanied by a significant number of BrdU-positive cells in endothelial cells and intimal muscle cells, suggestive of an increase in cellular proliferation. There was significant expression of inducible NOS and increased staining of nitrotyrosine-positive areas. These were not observed in group I animals. In both groups, E(2) levels were low. In group III animals, E(2) supplementation led to a decrease in atheromatous lesions and BrdU-positive cells and reduced expression of both inducible NOS and arginase I and II accompanied by a decrease in nitrotyrosine staining. E(2) levels were increased. Our results suggest that E(2) was responsible for these effects, despite the animals being hyperlipidemic, similar to those in group II. Because arginase is responsible for cell proliferation by converting l-arginine to polyamines, our results indicate that expression of arginase may play an important role in cellular proliferation in atherosclerosis, and inhibition of arginase expression by E(2) may be another potential mechanism in attenuating atherogenesis.

Estrogen and phytoestrogens: Effect on eNOS expression and in vitro vasodilation in cerebral arteries in ovariectomized Watanabe heritable hyperlipidemic rabbits

OBJECTIVES

To evaluate the effect of estrogen replacement therapy or soy isoflavones supplement on endothelium-dependent relaxation in vitro and gene expression of endothelial nitric oxide synthase (eNOS) in cerebral arteries in a rabbit model of human hypercholesterolemia.

STUDY DESIGN

Thirty-six female ovariectomized Watanabe heritable hyperlipidemic (WHHL) rabbits were randomised to treatment with 17beta-estradiol (17beta-E(2)), SoyLife 150 or control for 16 weeks. Ring segments of basilar artery (BA) and posterior cerebral artery (PCA) were mounted in myographs for isometric tension recordings. Concentration response curves to carbamylcholine chloride, sodium nitroprusside (SNP) and l-NAME were evaluated after precontraction with potassium. Total RNA was extracted, reverse transcribed and eNOS quantitated by real-time polymerase chain reaction (real-time PCR).

RESULTS

Plasma cholesterol was significantly higher at termination in the SoyLife group (P<0.0001), whereas low-density lipoprotein (LDL) cholesterol was comparable in all treatment groups. Neither treatment influenced the endothelium-dependent responses to carbamylcholine chloride or l-NAME or the endothelium-independent response to SNP in any of the arteries. Correspondingly, eNOS mRNA was similarly expressed in all treatment groups in both arteries.

CONCLUSIONS

Improvement of cerebral endothelial function by estrogen or soy isoflavones in ovariectomized WHHL rabbits is not supported by the present data. The findings may be unique to the WHHL rabbit in which the hypocholesterolemic effect of estrogens mediated by upregulation of liver LDL receptors is excluded.

Vitamin K1 (phylloquinone) induces vascular endothelial dysfunction: Role of oxidative stress

We aimed to investigate the mechanisms underlying the vascular effects induced by phylloquinone (Vitamin K1; VK1). Vascular reactivity experiments, using standard muscle bath procedures, showed that VK1 (5 and 50 microM) enhances the contractile response of endothelium-intact, but not denuded, rat carotid rings to phenylephrine. Similarly, maximal contraction induced by phenylephrine was enhanced in the presence of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME). The combination of L-NAME and VK1 did not produce any further additional effect. Pre-incubation of intact-rings with VK1 reduced both acetylcholine- and bradykinin-induced relaxation. VK1 induced an increment in tension on carotid rings submaximally pre-contracted with phenylephrine. VK1-induced increment in tension was completely abolished by endothelial removal or incubation of intact rings with L-NAME and L-NNA. Conversely, 7-nitroindazole, 1400 W, or indomethacin did not affect VK1-induced contraction. Moreover, VK1 reduced L-arginine-induced relaxation in endothelium-intact rings. Lucigenin-amplified chemiluminescence assays showed that VK1 induced an increase in the level of superoxide anions in endothelium-intact but not denuded rings. Measurement of nitrite and nitrate generation showed that VK1 did not alter nitrate formation but strongly inhibited the generation of nitrite. Finally, the superoxide anions scavenger tiron prevented the endothelial vasomotor dysfunction caused by VK1 on phenyleprine-induced contraction and acetylcholine or bradykinin-induced relaxation. In conclusion, our data show that VK1 disrupts the vasomotor function of rat carotid. Our results suggest that VK1-induced oxidative stress through production of superoxide anion is interfering with the NO pathway, which in turn is responsible for the altered vascular reactivity induced by VK1.

Raloxifene prevents endothelial dysfunction in aging ovariectomized female rats

Lack of an appropriate animal model has delayed the better understanding of mechanisms related to higher cardiovascular risk in women after menopause. The aging female rat may share some menopausal changes observed in women. However, most studies have attempted to mimic menopause by ovariectomizing young (6-12 weeks old) animals without taking into accounts the influence of aging and of declining ovarian function. Therefore, the present study examined changes in vascular reactivity in the aging (15 months old) female rat after ovariectomy and the effects of chronic raloxifene therapy on vascular reactivity and eNOS protein expression. Aortic rings were prepared from the three experimental groups of rats: sham-operated control, ovariectomized and ovariectomized aging rats receiving daily oral administration of raloxifene for 3 months. Aortic rings were suspended in organ baths for the measurement of isometric tension. Rings with endothelium contracted significantly more to phenylephrine after inhibition of nitric oxide/cyclic GMP-signaling pathway by L-NAME or ODQ (as an index of basal nitric oxide release) in control and raloxifene-treated ovariectomized rats than in ovariectomized rats. This effect was abolished upon mechanical removal of the endothelium. Phenylephrine induced greater contractions only in rings with endothelium from ovariectomized rats as compared with control rats and raloxifene treatment normalized this response. In the presence of L-NAME or ODQ, phenylephrine-induced contraction was similar in rings from the three groups. Rings relaxed more to thapsigargin and acetylcholine in raloxifene-treated ovariectomized rats than in ovariectomized rats. There was no significant difference in aortic eNOS protein contents among the different groups. These results suggest that chronic oral administration of raloxifene to aging ovariectomized female rats augmented the bioavailability of endothelial nitric oxide in isolated aortic rings without altering eNOS protein levels.

Short-term transdermal estradiol enhances nitric oxide synthase III and estrogen receptor mRNA expression in arteries of women with coronary artery disease

OBJECTIVE

To analyze the short-term effects of estradiol (E2) on the expression of nitric oxide synthase (NOS III) and estrogen receptors (ER) alpha and beta.

METHODS

We studied 20 post-menopausal women with coronary artery disease (CAD) undergoing CABG surgery with left internal mammary artery (LIMA) grafting. Ten women received treatment with transdermal E2 prior to surgery (48-72 h) and 10 did not. The distal segment of the LIMA was excised and processed to determine mRNA expression of NOS III and ER alpha and beta (RT-PCR). Expression of NOS III and ER alpha and beta was measured in arbitrary densitometric units (ADUs) relative to GPdH expression, constitutively expressed in human vessels.

RESULTS

NOS III and ER alpha and beta mRNA expression was enhanced in women treated with E2 as compared to the control group (NOS III: 1.69+/-0.61 versus 1.14+/-0.48 ADUs, p=0.04; ER alpha: 6.52+/-6.80 versus 1.83+/-1.22 ADUs, p=0.04; ER beta: 4.20+/-3.42 versus 1.56+/-0.59 ADUs, p=0.03). ER alpha, but not ER beta expression, correlated with NOS III expression (r=0.70, p<0.001).

CONCLUSIONS

After treatment with E2, NOS III, ER alpha, and ER beta mRNA expression was enhanced in arterial vessels of postmenopausal women with CAD. NOS III mRNA expression was only correlated to ER alpha expression, suggesting that NOS III activation could be more mediated by ER alpha.

Chronic treatment with 17beta-estradiol increases susceptibility of smooth muscle cells to nitric oxide

The purpose of this study was to evaluate the role of estrogen as a vasodilator or relaxing modulator during vascular tonus through chronic estrogen treatment. Experiments were conducted using isolated basilar arteries from ovariectomized female rabbits divided into two groups (the with and without estrogen replacement groups, respectively). Both acetylcholine and carbachol relaxed the basilar arteries of rabbits in the with estrogen replacement group (pre-contracted by 30 mM K(+)) more strongly than in the without estrogen replacement group. Vasodilatation effects of (+/-)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3 -hexenamide (NOR1) and S-nitroso-N-acetyl-penicillamine (SNAP) were greater in rabbits in the with estrogen replacement group than the without estrogen replacement both with endothelium-intact and denuded preparations. On the other hand, vasodilatation effects of nicardipine, 17beta-estradiol and membrane-permeable cyclic-GMP or cyclic-AMP were the same in both groups. These results suggest that chronic administration of estradiol potentiates reactivity to nitric oxide (NO) in smooth muscle cells, which could be a therapeutic target for cardiovascular diseases in postmenopausal women.

Sex dimorphism in cardiac pathophysiology: experimental findings, hormonal mechanisms, and molecular mechanisms

The higher cardiovascular risk in men and post-menopausal women implies a protective action of estrogen. A large number of experimental studies have provided strong support to this concept. However, the recent clinical trials with negative outcomes regarding hormone replacement therapy call for "post hoc" reassessment of existing information, models, and research strategies as well as a summary of recent findings. Sex steroid hormones, in particular estrogen, regulate numerous processes that are related to the development and progression of cardiovascular disease through a variety of signaling pathways. Use of genetically modified models has resulted in interesting information on diverse actions mediated by steroid receptors. By focusing on experimental findings, we have reviewed hormonal, cellular, and signaling mechanisms responsible for sex dimorphism and actions of hormone replacement therapy and addressed current limitations and future directions of experimental research.

Deficiencies in estrogen-mediated regulation of cerebrovascular homeostasis may contribute to an increased risk of cerebral aneurysm pathogenesis and rupture in menopausal and postmenopausal women

Despite the catastrophic consequence of ruptured intracranial aneurysms, very little is understood regarding their pathogenesis, and there are no reliable predictive markers for identifying at-risk individuals. Few studies have addressed the molecular pathological basis and mechanisms of intracranial aneurysm formation, growth, and rupture. The pathogenesis and rupture of cerebral aneurysms have been associated with inflammatory processes, and these have been implicated in the digestion and breakdown of vascular wall matrix. Epidemiological data indicate that the risk of cerebral aneurysm pathogenesis and rupture in women rises during and after menopause as compared to premenopausal women, and has been attributed to hormonal factors. Moreover, experimental evidence supports a role for estrogen in the modulation of each phase of the inflammatory response implicated in cerebral aneurysm pathogenesis and rupture. While the risk of aneurysm rupture in men also increases with age, this increased risk has been attributed to other recognized risk factors including cigarette smoking, use of alcohol, and history of hypertension, all of which are more common in men than women. We hypothesize, therefore, that decreases in both circulating estrogen levels and cerebrovascular estrogen receptor density may contribute to an increased risk of cerebral aneurysm pathogenesis and rupture in women during and after menopause. To test our hypothesis, experiments are needed to identify genes regulated by estrogen and to evaluate gene expression and intracellular mechanisms in cells/tissues exposed to varying concentrations and duration of treatment with estrogen, metabolites of estrogen, and selective estrogen receptor modulators (SERMs). Furthermore, it is not likely that the regulation of cerebrovascular homeostasis is due to the actions of estrogen alone, but rather the interplay of estrogen and other hormones and their associated receptor expression. The potential interactions of these hormones in the maintenance of normal cerebrovascular tone need to be elucidated. Additional studies are needed to define the role that estrogen and other sex hormones may play in the cerebrovascular circulation and the pathogenesis and rupture of cerebral aneurysms. Efforts directed at understanding the basic pathophysiological mechanisms of aneurysm pathogenesis and rupture promise to yield dividends that may have important therapeutic and clinical implications. The development of non-invasive tools such as molecular MRI for the detection of specific cells, molecular markers, and tissues may facilitate early diagnosis of initial pathophysiological changes that are undetectable by clinical examination or other diagnostic tools, and can also be used to evaluate the state of activity of cerebral aneurysm pathogenesis before, during, and after treatment.

Rapid Endocytosis of Copper-Zinc Superoxide Dismutase into Human Endothelial Cells: Role for Its Vascular Activity

Cytosolic CuZn-SOD (SOD1) is a dimeric, carbohydrate-free enzyme with a molecular weight of about 32 kDa and also circulates in human blood plasma. Due to its molecular mass it has been believed that the enzyme cannot penetrate the cell membrane. Here we report that rapid endocytosis of FITC-CuZn-SOD into human endothelial cells occurs within 5 min. Moreover, relaxation of rat aortic rings in response to CuZn-SOD is associated with a lag time of 45-60 s and only observed in the presence of intact endothelial cells. The results indicate acute and rapid endothelial cell endocytosis of CuZn-SOD, possibly via activation of a receptor-mediated pathway. Intracellular uptake via endocytosis may contribute to the vascular effects of CuZn-SOD, including vasodilation, and is likely to play a role in regulation of vascular tone and diseases such as atherosclerosis.

Gender-related differences in advanced glycation endproducts, oxidative stress markers and nitric oxide synthases in rats

An age- and blood pressure-associated increase in methylglyoxal (MG) and MG-induced advanced glycation endproducts (AGEs), including N(epsilon)-carboxyethyl-lysine (CEL) and N(epsilon)-carboxymethyl-lysine (CML), in the kidney of spontaneously hypertensive rats (SHR) has been shown. In the present study, gender-related changes in AGEs and nitric oxide synthase were investigated in Sprague-Dawley (SD) and stroke-prone SHR (SHRsp) rats. Immunohistochemical analyses were conducted on kidneys from 24-week-old male and female SD rats as well as SHRsp. The systolic blood pressure of SHRsp was significantly higher than that of SD rats. Male SD rats had more intense kidney staining for CEL than female SD rats. Both male and female SHRsp had more marked CEL and CML staining localized to kidney tubules, as opposed to SD rats. Female rats showed more staining in glomerular vessels than male rats in both SD and SHRsp. Nuclei containing nuclear factor-kappaB (NF-kappaB) p65 and activated macrophages were seen in the kidney from SHRsp, not so much in SD rats, localized to renal tubules in male and glomerular vessels in female SHRsp. A higher protein level of NF-kappaB p65 was found in SHRsp than in SD rats. SD rats had more intense kidney neuronal nitric oxide synthase staining than SHRsp. The intensity of inducible nitric oxide synthase staining was significantly higher in SHRsp than in SD rats, with no gender differences in either strain. SHRsp and male rats exhibited higher AGEs and oxidative stress than SD and female rats, respectively. These differences might partly account for the development of hypertension in SHRsp and the higher vulnerability of male animals to renal pathology.

Factors associated with dyspnea in adult patients with sickle cell disease

OBJECTIVE

The aim of this prospective study was to determine the cardiorespiratory factors associated with dyspnea in patients with sickle cell SS-hemoglobin disease, with a specific interest in lung vascular involvement.

MEASUREMENTS

Forty-nine patients (29 women and 20 men; mean [+/- SD] age: women, 29 +/- 6 years; men, 31 +/- 11 years) underwent direct evaluations (Borg scale evaluation during a 6-min walk test) and indirect evaluations (modified Medical Research Council [MRC]score) of their dyspnea, pulmonary function tests (PFTs) [spirometry, volumes, diffusing capacity of the lung for carbon monoxide (Dlco), diffusing capacity of the alveolar-capillary membrane, and pulmonary capillary blood volume measurements], echocardiography, and biological evaluation.

RESULTS

Thirty-four patients complained of significant breathlessness (MRC score, > 1). Indirect and direct evaluations of dyspnea were correlated. PFT results depicted a very mild restrictive pattern (mean total pulmonary capacity, 86 +/- 11% predicted) and an impairment of Dlco (mean Dlco corrected for the degree of anemia, 69 +/- 13% predicted). The statistical analysis demonstrated that dyspnea and exercise performance were closely linked to indexes of Dlco but not with any echocardiographic or biological measure including anemia. Nevertheless, only approximately 25% of the variability was explained by these associations. Despite having a similar history of vasoocclusive crisis events, women had more severe anemia, dyspnea, decreases in Dlco (corrected for the degree of anemia), and a higher capillary blood volume (corrected for alveolar volume) than men.

CONCLUSION

Lung vascular disease contributes to dyspnea and the exercise limitation of patients with sickle cell disease. A sequential assessment of Dlco would therefore constitute one of the objective functional end points for follow-up studies of these patients.

Harnessing Hormonal Signaling for Cardioprotection

Cardiovascular disease is the leading cause of death in women in the Western world and is predominant among the elderly. A large body of evidence suggests that hormonal signaling plays a critical role in the regulation of cardioprotective mechanisms, as premenopausal women are at significantly lower risk of heart disease compared with men, but the risk greatly increases with the onset of menopause. This association indicates that estrogen may protect the heart from cardiovascular disease. Whereas a number of analyses of the effects of hormone replacement therapy (HRT) on postmenopausal women supported the idea that estrogen is a cardioprotective factor, the findings of the more recent Women's Health Initiative (WHI) study suggested that HRT may actually increase the risk of cardiovascular events. These conflicting reports have left both patients and clinicians reluctant to continue using current HRT regimes. The WHI findings do not, however, negate the epidemiological link between menopause and increased cardiovascular risk. Hence, the identification of the specific actions of estrogen that promote cardioprotective pathways without enhancing deleterious vascular mechanisms may provide novel estrogen-based alternatives to current HRT strategies. In this Review, we outline the known actions of estrogen on the cardiovascular system, focusing on cardioprotective mechanisms that may be targeted for the development of new therapeutic approaches.

Selective iNOS inhibitor, ONO1714 successfully retards the development of high-cholesterol diet induced atherosclerosis by novel mechanism

OBJECTIVE

We have reported that inducible nitric oxide synthase (iNOS) is present only in deep areas of plaque in atherosclerosis. However, the role of iNOS in the development of atherosclerosis is not well known. We therefore investigated the relevance of iNOS inhibition.

METHODS AND RESULTS

Seven groups of male rabbits were fed a 0.5% high-cholesterol diet (HCD) for 8 weeks. Gp1-HCD was fed HCD only; Gp2-O17 was fed HCD with ONO1714, an iNOS inhibitor; Gp3-AG was fed HCD with amino-guanidine (AG), an iNOS inhibitor; Gp4-AR was fed HCD with l-arginine; Gp5-AR-O17 was fed HCD with l-arginine with ONO1714; Gp6-LNA was fed HCD with l-NAME (a NOS inhibitor); and Gp7-LN-O17 was fed HCD with l-NAME plus ONO1714. ONO1714 decreased atherosclerosis by about 70% (area occupied by lesions: 3.0+/-0.4% in Gp2-O17 versus 10.3+/-1.6% in Gp1-HCD) and also decreased atherosclerosis in Gp7-LN-O17. The ONO compound enhanced the atheroprotective effect of l-arginine. Amino-guanidine also showed an anti-atherosclerotic effect. Tone-related basal NO release and acetylcholine-induced NO-dependent relaxation were improved in Gp2-O17 and Gp5-AR-O17. O(2)(-) release was decreased in Gp2-O17 and Gp7-LN-O17.

CONCLUSION

ONO1714 retards the progression of atherosclerosis in rabbits. Although the up-regulation of endothelial nitric oxide synthase (eNOS) and the decrease of O(2)(-) may play roles in this retardation, the inhibition of iNOS may be the principal factor, alone was not sufficient.

Metformin reduces blood pressure and restores endothelial function in aorta of streptozotocin-induced diabetic rats

Effect of metformin treatment on blood pressure, endothelial function and oxidative stress in streptozotocin (STZ)-induced diabetes in rats was studied. In vitro effect of metformin on vascular reactivity to various agonist in the presence of metformin in untreated nondiabetic and STZ-diabetic rats were also studied. Sprague-Dawley rats were randomized into nondiabetic and STZ-diabetic groups. Rats were further randomized to receive metformin (150 mg/kg) or vehicle for 4 weeks. Metformin treatment reduced blood pressure without having any significant effect on blood glucose level in STZ-diabetic rats. Enhanced phenylephrine (PE)-induced contraction and impaired acetylcholine (Ach)-induced relaxation in STZ-diabetic rats were restored to normal by metformin treatment. Enhanced Ach-induced relaxation in metformin-treated STZ-diabetic rats was blocked due to pretreatment with 100 microM of Nomega-nitro-L-arginine-methyl ester (L-NAME) or 10 microM of methylene blue but not 10 microM of indomethacin. Metformin treatment significantly increased antioxidant enzymes and reduced lipid peroxidation in STZ-diabetic rats. In vitro studies in aortic rings of untreated nondiabetic and STZ-diabetic rats showed that the presence of higher concentration of metformin (1 mM and 10 mM) significantly reduced PE-induced contraction and increased Ach-induced relaxation. Metformin per se relaxed precontracted aortic rings of untreated nondiabetic and STZ-diabetic rats in a dose-dependent manner. Pretreatment with L-NAME or removal of endothelium blocked metformin-induced relaxation at lower concentration (up to 30 microM) but not at higher concentration (above 30 microM). Metformin-induced relaxation was blocked in the presence of 1 mM of 4-aminopyridine, or 1 mM of tetraethylammonium but not in the presence of 100 microM of barium ion or 10 microM of glybenclamide. The restored endothelial function along with direct effect of metformin on aortic rings and reduced oxidative stress contributes to reduced blood pressure in STZ-diabetic rats. From the present study, it can be concluded that metformin administration to STZ-diabetic rats lowers blood pressure, and restores endothelial function.

Estrogen modulates the mechanical homeostasis of mouse arterial vessels through nitric oxide

We have recently shown that estrogen causes vessel dilation through receptor-mediated stimulation of nitric oxide (NO) production. Here, we hypothesize that estrogen modulates the mechanical homeostasis in the blood vessel wall through NO production. The mechanical properties of female ovariectomized (ovx) mice, female mice lacking the gene for endothelial NO synthase (eNOS(-/-)), and control female and male mice were studied to test the hypothesis. The femoral and carotid arteries and aorta were cannulated in situ and mechanically distended. The stress, strain, elastic modulus, and wall thickness of vessels in ovx and eNOS(-/-) mice, as well as intact female and male mice, were determined. Western blot and immunohistochemistry were used to assess eNOS protein expression in the aorta. Moreover, NO by-products of the femoral and carotid artery were determined by measuring the levels of nitrite and nitrate. Our results show that ovariectomy and eNOS(-/-) significantly decrease the strain in all arteries. Furthermore, the eNOS protein was significantly reduced in ovx mice. Finally, the NO metabolites were significantly decreased both in ovx and eNOS(-/-) mice. We found statistically significant correlations between the structural (wall thickness), mechanical (stress, strain, and elastic modulus), and biochemical parameters (NO by-products). These novel results connect NO to the structural and mechanical properties of the vessel wall. Hence, the effect of endogenous estrogen on the arterial mechanical properties is mediated by the regulation of NO derived from eNOS.

Isoflavone genistein and daidzein up-regulate LPS-induced inducible nitric oxide synthase activity through estrogen receptor pathway in RAW264.7 cells

Isoflavones, such as genistein and daidzein, are found in abundance in soybeans. These plant-derived substances have estrogenic activities and can bind to the estrogen receptors (ERs). In this study, we investigated that the effects of 17beta-estradiol (E2), genistein and daidzein on nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) activity in RAW264.7 cells. We found that these isoflavones significantly increased lipopolysaccharide-induced NO production and iNOS expression as much as E2 at physiological concentrations. Moreover, E2 and isoflavone enhanced the production of tumor necrosis factor-alpha that is one of the important cytokines regarding NO production. The enhancing effects of E2 and isoflavones on NO production were markedly inhibited by not only N(G)-nitro-L-arginine methyl ester (an inhibitor of NOS), but also ICI 182780 (ERs antagonist). Two types of ERs were identified as ERalpha and ERbeta. An ERalpha agonist could increase iNOS expression in RAW264.7 cells, while an ERbeta agonist could not. In conclusion, our results suggest E2, genistein and daidzein activate iNOS, and then up-regulate NO production. This enhancing effect is aroused through ERalpha pathway in RAW264.7 cells.

Time-Dependent Changes in Antioxidant Enzymes and Vascular Reactivity of Aorta in Streptozotocin-Induced Diabetic Rats Treated With Curcumin

In the present study changes in oxidative stress and vascular reactivity in aortic rings of chronic streptozotocin-diabetic (STZ-CON) and nondiabetic (ND-CON) rats is studied at 4 weekly intervals up to 24 weeks. The effect of chronic curcumin (200 mg/kg) treatment was also studied. Blood glucose and blood pressure levels were significantly higher in the STZ-CON group and curcumin administration had no significant effect on it. Superoxide dismutase and catalase activity were either unchanged or significantly increased during the early stage of diabetes whereas during the medium and late stage were significantly reduced. Reduced glutathione and lipid peroxidation levels significantly decreased as time after STZ administration increased. Phenylephrine (PE)-induced contraction was significantly (P < 0.05) increased during the early stage of diabetes, whereas it was significantly (P < 0.05) reduced at the medium and late stage of diabetes. Acetylcholine (Ach)-induced relaxation significantly decreased with respect to time after STZ administration. Sodium nitroprusside (SNP)-induced relaxation was unaltered up to initial stage but after medium stage there was a rightward shift and the pD2 value significantly decreased. Though curcumin treatment had no significant effect on superoxide dismutase, catalase, and reduced glutathione levels, it significantly reduced lipid peroxidation compared with diabetic control. Curcumin treatment attenuated the phenylephrine-induced increase in contraction during the early stage. However, curcumin treatment had no significant effect at the medium and late stage. Though curcumin administration improved Ach-induced relaxation it did not restore it to normal. Inability of curcumin to prevent oxidative stress during the late stage may be due to the fact that chronic diabetes (hyperglycemia) leads to excessive production of free radicals. Hence the present study shows that variations reported in antioxidant enzymes and vascular reactivity are due to the duration of diabetes or time after diabetes induction in STZ model and this can not be completely reversed by chronic treatment with curcumin.

Bridging advanced glycation end product, receptor for advanced glycation end product and nitric oxide with hormonal replacement/estrogen therapy in healthy versus diabetic postmenopausal women: A perspective

Cardiovascular diseases (CVD) are the most significant cause of death in postmenopausal women. The loss of estrogen biosynthesis with advanced age is suggested as one of the major causes of higher CVD in postmenopausal women. While some studies show beneficial effects of estrogen therapy (ET)/hormonal replacement therapy (HRT) in the cardiovascular system of healthy postmenopausal women, similar studies in diabetic counterparts contradict these findings. In particular, ET/HRT in diabetic postmenopausal women results in a seemingly detrimental effect on the cardiovascular system. In this review, the comparative role of estrogens is discussed in the context of CVD in both healthy and diabetic postmenopausal women in regard to the synthesis or expression of proinflammatory molecules like advanced glycation end products (AGEs), receptor for advanced glycation end products (RAGEs), inducible nitric oxide synthases (iNOS) and the anti-inflammatory endothelial nitric oxide synthases (eNOS). The interaction of AGE-RAGE signaling with molecular nitric oxide (NO) may determine the level of reactive oxygen species (ROS) and influence the overall redox status of the vascular microenvironment that may further determine the ultimate outcome of the effects of estrogens on the CVD in healthy versus diabetic women.

NADPH oxidase inhibitor, apocynin, restores the impaired endothelial-dependent and -independent responses and scavenges superoxide anion in rats with type 2 diabetes complicated by NO dysfunction

OBJECTIVE

We investigated the effect of apocynin, an NADPH oxidase inhibitor, in the impairment of vascular responses in Otsuka Long-Evans Tokushima Fatty (OLETF) rats (type 2 diabetic rat model) with or without (w/wo) N-nitro-l-arginine methyl ester treatment.

METHODS

Male OLETF and littermate Long-Evans Tokushima Otsuka (LETO) (28 weeks old) rats were separated as follows: LETO w/wo apocynin (Gp C, Gp C-apo), OLETF w/wo apocynin (Gp DM, Gp DM-apo) and OLETF plus l-nitro arginine acetate ester w/wo apocynin (Gp DMLN, Gp DMLN-apo). Five days after, peritoneal macrophages were stimulated with thioglycolate. Two days after, they were evaluated.

RESULTS

Plasma glucose and lipid levels remained unchanged. Acetylcholine-induced nitric oxide-dependent (NO-dependent) relaxation and nitroglycerin-induced NO-independent relaxation were improved in the Gp DMLN-apo, compared with that in Gp DMLN. Tone-related basal NO release and plasma NO(2) (-) and NO(3) (-) tended to be lower in Gp DM and Gp DMLN groups. The increased amount of superoxide anion released from macrophages in Gp DM and Gp DMLN was restored by apocynin. Intimal thickening was observed in aortae of Gp DM and Gp DMLN animals; however, there was little in aortae of Gp DM-apo and Gp DMLN(-) apo rats. Increased tumour necrosis factor-alpha (TNF-alpha) in the Gp DM and Gp DMLN was also restored by apocynin treatment.

CONCLUSION

Apocynin restores the impairment of endothelial and non-endothelial function in diabetic angiopathy in OLETF without changing plasma glucose and lipid levels. NO and O(2) (-) may play a role in this process by decreasing TNF-alpha levels.

Sex differences and the effect of hormonal therapy on ischemic brain injury

Epidemiological data emphasize the importance of sex differences in the mortality and morbidity of stroke and cardiovascular disease. The importance of hormonal influences on stroke outcome has pointed out the importance of gender, age, and presence of neural hormones. This clinical data has been substantiated by various experimental studies using clinically relevant models of cerebral ischemia and stroke. Published findings emphasize that male and female animals respond differently to periods of cerebral ischemia and that various combinations of hormonal treatments can provide protection, both histopathological and behavioral. Mechanisms underlying the hormonal effects on ischemic outcome are multifactorial. These include effects on vascular integrity and cerebral blood flow, excitotoxicity, oxidation pathways, inflammation, and apoptosis. Although many studies have shown positive results with hormonal treatments, negative findings have also been presented. Explanations for the limitations of hormonal treatment include uncertainties regarding therapeutic window, specific therapeutic dose range, as well as the specific pathophysiological processes being targeted. Additional studies are therefore required to clarify under what conditions hormonal therapy is most protective or not warranted. Experimental studies utilizing a variety of cerebral ischemia and stroke models are reviewed to indicate under what conditions sex differences and hormonal therapy are most important in terms of functional outcome.

Gender differences in vascular reactivity of aortas from rats with and without portal hypertension

BACKGROUND

Inflammatory responses related to portal hypertension may be different in male and female rats. Most experimental studies of portal hypertension have involved male animals, and little information is available on gender differences in this setting. The aim of the present study was to compare aortic reactivity in female and male rats with and without portal hypertension.

METHODS

Contraction response curves to phenylephrine were studied with aortic rings, with and without endothelium. For relaxation studies, rings were precontracted with phenylephrine 10(-7) mol/L and then exposed to acetylcholine 10(-4) mol/L. Portal hypertension was provoked by calibrated portal stenosis performed 2 weeks before experiments.

RESULTS

In non-hypertensive conditions, the contractile response to increasing phenylephrine concentrations was significantly stronger in rings from male than female rats, both with and without endothelium. In male rats with portal hypertension, the phenylephrine concentration-response curves were lowered and shifted to the right in aortic rings both with and without endothelium. In female rats, portal hypertension did not induce significant changes in the phenylephrine concentration-response curves. In female rats, portal hypertension induced a marked increase in relaxation (157 +/- 123% vs 81 +/- 64% in controls); the increase was also stronger than that in male rats with portal hypertension (95 +/- 6%; P < 0.01).

CONCLUSION

Clear gender differences were observed in vasoconstrictor responsiveness of aortic rings from rats with and without portal hypertension. Contrary that in male rats, portal hypertension did not induce vascular hyporesponsiveness in female rats. Further investigations are required to explain these differences.

Vascular effects of ovariectomy and chronic oestrogen treatment in rats: controversy or experimental protocol diversity?

Several clinical studies have indicated that oestrogens have protective properties on the cardiovascular system. Although the beneficial effect has been attributable, at least in part, to their ability to stimulate the endothelial formation of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF), the underlying mechanism still remains unclear. In a study from this issue of British Journal of Pharmacology, Nawate et al. have examined the effects of rat ovariectomy and chronic treatment with 17beta-oestradiol on the endothelial function as assessed ex vivo. The data indicate that acetylcholine-induced endothelium-dependent relaxations of the isolated mesenteric artery are affected by neither ovariectomy nor chronic hormonal treatment. Despite the maintained endothelium-dependent relaxation, the contribution of the two major endothelial factors NO and EDHF was changed. Indeed, ovariectomy increased the NO-mediated component of the relaxation, most likely as a consequence of the downregulation of the physiological allosteric inhibitor of endothelial NO synthase, caveolin-1. In addition, ovariectomy decreased the EDHF-mediated component of the relaxation and membrane hyperpolarization of the smooth muscle cells, an effect which might be explained by a concomitant decrease of the expression of the gap junction connexin-40 and connexin-43. Furthermore, chronic administration of 17beta-estradiol to ovariectomized rats normalized all these effects. This study provides further experimental evidence indicating that the hormonal status plays a determinant role in the control of the endothelial formation of both NO and EDHF.

Chronic tumor necrosis factor-alpha inhibition enhances NO modulation of vascular function in estrogen-deficient rats

Tumor necrosis factor-alpha (TNF-alpha) is involved in the pathogenesis of vascular disease. Clinical studies have shown that postmenopausal women have higher serum TNF-alpha levels; however, whether this increase in TNF-alpha is associated with vascular dysfunction is unknown. We investigated whether estrogen deficiency is associated with increased serum TNF-alpha levels and tested the effects of in vivo TNF-alpha inhibition on vascular reactivity. Aged (12 to 15 months) Sprague-Dawley rats were ovariectomized and treated with placebo, estrogen, or a TNF-alpha inhibitor (Etanercept; 0.3 mg/kg) for 4 weeks. Serum TNF-alpha was determined by a bioassay, and vascular function was evaluated in the myograph system. Estrogen-deficient animals had higher serum levels of TNF-alpha compared with either estrogen-replaced animals or animals treated with Etanercept. Moreover, in estrogen-deficient rats, TNF-alpha inhibition reduced the constriction of mesenteric arteries to phenylephrine, increased the modulation of this vasoconstriction by the NO synthase inhibitor nitro-l-arginine methyl ester, and decreased the modulation by a superoxide scavenger (Mn(III)tetrakis(4-benzoic acid) porphyrin chloride). Furthermore, endothelium-dependent relaxation was also enhanced by TNF-alpha antagonism. Additionally, vascular expression of endothelial NO synthase was increased in animals treated with Etanercept, whereas the expression of NAD(P)H oxidase gp91phox and p22phox subunits was decreased. These data show that estrogen-deficient female rats have higher bioactive serum TNF-alpha levels compared with estrogen-replaced animals. Moreover, a decrease in serum bioactive TNF-alpha by a soluble TNF-alpha receptor (Etanercept) results in increased modulation of vascular function by NO. These observations suggest that TNF-alpha could be a mediator of vascular dysfunction associated with estrogen deficiency.

Treatment with 17-beta-estradiol reduces superoxide production in aorta of ovariectomized rats

OBJECTIVE

Oxidant stress contributes to vascular injury and atherosclerosis. We hypothesized that estrogen treatment of ovariectomized rats decreases O(2)(-) by decreasing the activity of NAD(P)H oxidase and this reduction in O(2)(-) could have a vasculoprotective effect.

METHODS AND RESULTS

Ovariectomized rats were treated with 17-beta-estradiol E2 (0.25mg) or oil placebo for 21 days. Aorta were removed for contractility studies and O(2)(-) production was measured by lucigenin enhanced chemiluminescence (230 and 5microM). E2 treatment decreased basal O(2)(-) production but did not alter NADH or NADPH stimulated O(2)(-) production. Total p47phox and p47phox in membrane fractions of cardiac tissue were decreased, which suggests less activation of NAD(P)H oxidase in E2 treated rats. E2 did not change expression of other components of NAD(P)H oxidase in heart, lung, spleen and diaphragm. Expression of eNOS was also lower in E2 treated rats. E2 did not affect the contractile response to phenylepherine, dilation with acetylcholine, dilation with superoxide dismutase or constriction with l-NAME. This argues against changes in bioavailable NO.

CONCLUSIONS

E2 decreases activation of p47phox and O(2)(-) production by NAD(P)H oxidase. This did not affect contractile properties of the vessel, but could still potentially alter cell signaling from oxidant increasing stresses.

Emerging drugs in migraine treatment

Ergot alkaloids have been the mainstay of acute migraine therapy for most of the 20th century. They have been supplanted by sumatriptan-like drugs ('triptans'), which, while keeping some of the ergotś mechanisms of action, show improved safety profiles due to their increased receptor selectivity. However, triptans are still far from being perfect drugs: they can constrict human coronary arteries at therapeutic doses and, therefore, are contra-indicated in the presence of cardiovascular disease. Another problem with these agents is recurrence of moderate-to-severe pain within 24 h of initial headache relief. While mechanism-driven drug design has led to the development of various novel, albeit still imperfect, acute antimigraine medications, only a few new prophylactic agents have been made available to migraine clinicians. The efficacy of most, if not all of them has been discovered serendipitously. This is probably due to the fact that, while the pathophysiology of a migraine attack is now reasonably understood, the mechanisms leading to an attack are still mostly unknown. This update analyses the profile of some antimigraine drugs in clinical trials, their mode of action and their potential advantages or drawbacks over already available agents.

Estrogen modulation of endothelium-derived relaxing factors by human endothelial cells

We report the modulatory effects of estrogen on release of endothelium-derived relaxing factors (EDRFs) in a human endothelial cell line, EA.hy926. Using bioassay, we showed that EA.hy926 released EDRF including nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) measured by relaxation of pre-contracted endothelium-denuded rabbit aortic rings. This EDRF production was significantly higher in cells treated for 24 h with 17-beta-estradiol (10(-6)mol/L) than control cells. Addition of L-NAME to the perfusate of cells caused the relaxation induced by the endothelial cell perfusate to become transient and abolished the enhancement of relaxation due to estrogen treatment. Addition of K(Ca) channel blockers to the perfusate abolished the L-NAME-resistant relaxation of the bioassay ring. Using real-time PCR, we demonstrated that eNOS expression in estrogen-treated cells was significantly higher than controls. These results show that estrogen exerts a potentially important vasculo-protective effect by stimulating NO but not EDHF production.

A new HMG-CoA reductase inhibitor, pitavastatin remarkably retards the progression of high cholesterol induced atherosclerosis in rabbits

BACKGROUND

The remarkable anti-atherosclerotic effects of 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitor have not been demonstrated in diet induced severe hyperlipidemia in rabbit model.

OBJECTIVE

We have investigated the effect of pitavastatin, a newly developed statin, on atherosclerosis in rabbits.

METHODS AND RESULTS

Oophorectomized female NZW rabbits were fed 0.3% cholesterol chow for 12 weeks with or without pitavastatin (0.1mg/kg per day) (Gp.NK and HCD). The level of serum cholesterol was decreased in Gp.NK compared with Gp.HCD (772.8 +/- 70.2 versus 1056.9 +/- 108.3 mg/d), whereas no significant alterations were observed in triglyceride and HDL-cholesterol. NO dependent response stimulated by acetylcholine and calcium ionophore A23187 and tone related basal NO response induced by N(G)-monomethyl-l-arginine acetate were all improved by pitavastatin treatment. Pitavastatin treatment increased the level of cyclic GMP in the aorta of cholesterol fed rabbits. In the aorta, the expression of eNOS mRNA was significantly up regulated and O(2)(-) production was slightly reduced in Gp.NK animals. Atherosclerotic area was significantly decreased in aortic arch and thoracic aorta from Gp.NK compared with those from Gp.HCD ( 15.1 +/- 5.3 versus 41.9 +/- 10.2%, 3.1 +/- 1.1versus 7.9 +/- 1.2% in Gp.NK and Gp.HCD aortic arch and thoracic aorta). Anti-macrophage staining area, the MMP1 or 2 and the nitrotyrosine positive area were decreased in Gp.NK.

CONCLUSION

Pitavastatin retards the progression of atherosclerosis formation and it improves NO bioavailability by eNOS up-regulation and decrease of O(2)(-).

Lipids: potential regulators of nitric oxide generation

The endothelium is a dynamic organ that secretes several biologically active substances and plays a major functional role in the health of an organism in both physiological and pathological conditions. For instance, the endothelium is involved in control of the exchange of plasma and tissue biomolecules, regulation of vessel tone, inflammation, lipid metabolism, vessel growth and remodeling, and modulation of coagulation and fibrinolysis. The endothelium generates nitric oxide, which is a key regulator of vasodilation and plays important roles in preventing, or in some cases promoting, numerous cardiovascular diseases. Several recent studies have examined the interplay between lipids and nitric oxide generation, especially in relation to atherosclerosis. The endothelium is continuously exposed to circulating lipids in the form of lipoproteins and protein carriers that may have a direct impact on nitric oxide synthesis and function. The purpose of this review is to illustrate some of the recent findings that link lipids (plasma and cellular) to nitric oxide generation (see Fig. 1).

Estrogen induced changes in Akt-dependent activation of endothelial nitric oxide synthase and vasodilation

OBJECTIVES

Acute administration of estrogen results in vasodilation and increased nitric oxide (NO) production. We examined the hypothesis that this is due to activation of Akt/PKB which subsequently increases eNOS activity.

METHODS AND RESULTS

Treatment of bovine microvascular and human umbilical endothelial cells (HUVEC) with 17-beta-estradiol (E2) (10(-9) to 10(-5)M) increased phosphorylation of Akt within 1 min and this was followed by phosphorylation of eNOS. These effects were blocked by wortmannin, a PI(3)K inhibitor and the upstream activator of Akt. The estrogen receptor antagonist, ICI 182,780, inhibited eNOS phosphorylation. E2 increased calcium dependent NOS activity and nitrite production and this was inhibited by wortmannin and ICI 182,780. E2 increased the vasodilatory response of aortic rings to acetylcholine and wortmannin blocked the effect. E2 (10(-9)M) dilated cerebral microvascular vessels under conditions of no flow, constant flow and increasing flow and this was blocked by wortmannin. Tamoxifen, a partial estrogen receptor antagonist, also dilated the microvessels.

CONCLUSIONS

: E2 increases NO production through an Akt/PKB dependent pathway. This is associated with increased sensitivity to endothelial dependent dilation. In cerebral microvessels, E2 and tamoxifen produce significant dilation at low concentrations with and without acetylcholine induced stimulation of endothelial vasodilation.

Evidence that estrogen suppresses rho-kinase function in the cerebral circulation in vivo

BACKGROUND AND PURPOSE

Premenopausal women are less susceptible to cardiovascular diseases than men or postmenopausal women. Such disease states are often associated with increased vascular RhoA/Rho-kinase activity and decreased activity of nitric oxide (NO). This study tested whether female gender is associated with lower Rho-kinase activity or higher NO activity in cerebral arteries in vivo and whether estrogen contributes to any such gender differences.

METHODS

Changes in basilar artery diameter were measured with the use of a cranial window preparation in anesthetized Sprague-Dawley rats. Some female rats were ovariectomized (OVX) and treated subcutaneously daily for 14 days with vehicle (dimethyl sulfoxide) or 17beta-estradiol. Vascular expression of RhoA or Rho-kinase was assessed by Western blotting.

RESULTS

The Rho-kinase inhibitor Y-27632 was selectively approximately 3-fold more potent as a cerebral vasodilator in males versus females. Expression of total RhoA or Rho-kinase did not differ between males and females. In OVX rats, vasodilator responses to Y-27632 resembled responses in males. Treatment of OVX rats with 17beta-estradiol normalized the vasodilator effects of Y-27632 to be equivalent to responses in intact female controls. The NO synthase inhibitor N-nitro-l-arginine methyl ester caused approximately 50% greater constriction of the basilar artery in females versus males, but responses in OVX rats treated with either vehicle or 17beta-estradiol did not differ from those recorded in intact females.

CONCLUSIONS

These data indicate that vascular Rho-kinase function is suppressed in females because of the effects of estrogen, whereas the higher NO activity in females is estrogen independent.

Endothelium-dependent and independent enhancement of vascular contractility in the ovariectomized rabbit

OBJECTIVE

Estrogen suppresses contractile response and increases vasodilator response, partly by modulating endothelial function. However, the effect of estrogen on the contractility of vascular smooth muscle remains to be elucidated. We investigated the effect of a long-term estrogen deficiency on vascular contractility and the Ca(2+) sensitivity of the contractile apparatus in arterial smooth muscle.

METHODS

Female rabbits were divided into the following three groups: control group, an ovariectomized group (OVX), and a group supplemented with 17beta-estradiol after ovariectomy (OVX+E2). Twelve weeks later, the mesenteric artery was isolated, and the vascular contractility was evaluated.

RESULTS

In OVX, the contractile responses to phenylephrine and 118 mM potassium were enhanced, and the basal release of nitric oxide decreased in the strips with endothelium compared with either OVX+E2 or control. An enhancement of contraction was also observed in the strips without endothelium. However, the extent of enhancement was smaller than that observed in the presence of endothelium. The simultaneous measurement of calcium ([Ca(2+)](i)) and tension revealed no significant difference in the [Ca(2+)](i) elevations induced by phenylephrine among the three groups. In the alpha-toxin permeabilized strips, the Ca(2+)-tension relationships obtained both with and without phenylephrine and guanosine triphosphate were similar among the three groups. No difference in the myosin expression and the histology of vascular tissue was observed among the three groups.

CONCLUSION

Long-term estrogen deficiency increased the vascular tone mainly by enhancing smooth muscle contractility. Endothelial dysfunction is considered to play a minor role in the augmentation of vascular tone.