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

Chronic treatment with progesterone but not medroxyprogesterone acetate restores the endothelial control of vascular tone in the mesenteric artery of ovariectomized rats

OBJECTIVE

To examine whether chronic administration of the natural hormone progesterone or a synthetic progestogen, medroxyprogesterone acetate, to ovariectomized rats affects the endothelial control of arterial tone in the isolated mesenteric artery.

DESIGN

Sham-operated rats received a daily subcutaneous injection of solvent (sesame oil), whereas ovariectomized rats received either sesame oil, progesterone (22 mg kg/day), or medroxyprogesterone acetate (22 mg kg/day) for 4 weeks, according to their respective group.

RESULTS

Phenylephrine-induced contractions were significantly increased (about 200% at 10 microM) by N-nitro-L-arginine, a nitric oxide synthase inhibitor, in intact mesenteric arterial rings from the sham-operated but not from the ovariectomized group. The progesterone but not the medroxyprogesterone treatment restored the potentiating effect of N-nitro-L-arginine on phenylephrine-induced contraction (about 180% at 10 microM). Contractions to phenylephrine were not affected by the combination of charybdotoxin plus apamin, two inhibitors of endothelium-derived hyperpolarizing factor-mediated responses, in all groups. Acetylcholine induced endothelium-dependent relaxations, which were partially inhibited by N-nitro-L-arginine and abolished by the combination of N-nitro-L-arginine plus charybdotoxin and apamin, in all groups. Acetylcholine induced similar charybdotoxin and apamin-sensitive hyperpolarizations in intact mesenteric artery segments from all groups.

CONCLUSIONS

Chronic administration of progesterone, but not medroxyprogesterone, to ovarictomized rats restores the endothelium-dependent attenuation of contractile responses to phenylephrine in mesenteric arterial rings through the endothelial formation of nitric oxide. Thus, an enhancement of the protective effect of endothelial cells on the arterial wall might contribute to the beneficial effect of certain progestogen-containing preparations during hormonal treatment.

Endothelial mediators of 17ß-estradiol-induced coronary vasodilation in the isolated rat heart

The present study was designed to determine relaxation in response to 17 beta-estradiol by isolated perfused hearts from intact normotensive male and female rats as well as the contribution of endothelium and its relaxing factors to this action. Baseline coronary perfusion pressure was determined and the vasoactive effects of 17 beta-estradiol (10 microM) were assessed by in bolus administration before and after endothelium denudation by infusion of 0.25 microM sodium deoxycholate or perfusion with 100 microM L-NAME, 2.8 microM indomethacin, 0.75 microM clotrimazole, 100 microM L-NAME plus 2.8 microM indomethacin, and 100 microM L-NAME plus 0.75 microM clotrimazole. Baseline coronary perfusion pressure differed significantly between males (84 +/- 2 mmHg, N = 61) and females (102 +/- 2 mmHg, N = 61). Bolus injection of 10 microM 17 beta-estradiol elicited a transient relaxing response in all groups, which was greater in coronary beds from females. For both sexes, the relaxing response to 17 beta-estradiol was at least in part endothelium-dependent. In the presence of the nitric oxide synthase inhibitor L-NAME, the relaxing response to 17 beta-estradiol was reduced only in females. Nevertheless, in the presence of indomethacin, a cyclooxygenase inhibitor, or clotrimazole, a cytochrome P450 inhibitor, the 17 beta-estradiol response was significantly reduced in both groups. In addition, combined treatment with L-NAME plus indomethacin or L-NAME plus clotrimazole also reduced the 17 beta-estradiol response in both groups. These results indicate the importance of prostacyclin and endothelium-derived hyperpolarizing factor in the relaxing response to 17 beta-estradiol. 17 beta-estradiol-induced relaxation may play an important role in the regulation of coronary tone and this may be one of the reasons why estrogen replacement therapy reduces the risk of coronary heart disease in postmenopausal women.

Female Sex Steroid Hormones and Pregnancy Regulate Receptors for Calcitonin Gene-Related Peptide in Rat Mesenteric Arteries, but Not in Aorta1

Calcitonin gene-related peptide (CGRP) is a potent vasodilator neuropeptide known to be involved in the regulation of vascular tone. Results of previous studies from our laboratory and others suggest that vascular sensitivity to CGRP is enhanced during pregnancy and that the female sex steroid hormones estradiol-17beta (E2) and progesterone (P4) may be involved in this process. We hypothesized that CGRP receptors in the mesenteric artery are increased during pregnancy and with sex steroid hormone treatments. In the present study, we investigated whether pregnancy and female sex steroid hormones modulate the CGRP-receptors CGRP-A and CGRP-B in the mesenteric artery in the rat. The CGRP-A receptor consists of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1); however, the CGRP-B receptor needs to be further characterized. Messenger RNA levels for CRLR and RAMP1 were assessed by reverse transcription-polymerase chain reaction, and CGRP-B receptor proteins levels were determined by Western blot analysis. In addition, [125I]CGRP binding was measured by Scatchard analysis. Both mRNA for CGRP-A (CRLR and RAMP1) and the protein for CGRP-B receptors in mesenteric arteries were increased with pregnancy compared to nonpregnant, diestrous animals. A P4 antagonist, RU-486, downregulated and P4 upregulated these receptors in mesenteric arteries (P < 0.05) in pregnant rats. In adult ovariectomized rats, P4 upregulated CRLR and RAMP1 mRNA levels as well as [125I]CGRP-binding sites. The CGRP-B-receptor protein levels were significantly (P < 0.05) elevated by P4 and by combined E2 and P4 treatment. Together with earlier findings, these data suggest that increases in the expression of CGRP-A (CRLR and RAMP1) and CGRP-B receptors in mesenteric arteries may be important in reducing vascular resistance and in vascular adaptations that occur during pregnancy; in addition, P4 may be involved in this process.

Influence of Gender on K + -Induced Cerebral Vasodilatation

Background and Purpose— It is not known whether cerebral vasoprotective mechanisms in females include increased function of arterial K + channels. We hypothesized that vasodilator responses mediated by activation of inwardly rectifying K + (K IR ) channels are greater in cerebral arteries of female versus male rats and that this is due to the effects of estrogen.

Methods— Changes in basilar artery diameter were measured with a cranial window preparation in anesthetized Sprague-Dawley rats.

Results— K + (5 and 10 mmol/L) caused greater vasodilatation in females (percent maximum, 21±3% and 58±7%, respectively) versus males (11±1% and 37±4%, respectively; P <0.05). In contrast, vasodilator responses to aprikalim (1 and 3 μmol/L) or acetylcholine (ACh, 1 and 10 μmol/L) did not differ between the genders. The selective K IR channel inhibitor barium ion (30 μmol/L) decreased basilar artery diameter in males but not females (−7±1% versus −2±1%, P <0.05) and selectively inhibited K + -induced vasodilatation by ≈50% in both groups. Ovariectomy of female rats resulted in smaller vasodilator effects of K + , and chronic treatment of these rats with 17β-estradiol (0.01 mg/kg per day for 7 days) normalized K+-induced vasodilatation. Furthermore, the selective M2 muscarinic ACh receptor antagonist methoctramine (1 μmol/L) increased responses to K + in males to levels equivalent to responses in females but had no effect on responses to K + in females.

Conclusions— K + is a more powerful vasodilator in the female versus male cerebral circulation. This difference is estrogen dependent and could be due to a lack of M2 muscarinic ACh receptor–induced inhibition of K IR channel activation by K + in female cerebral arteries.

Gender differences in small intestinal endothelial function: inhibitory role of androgens

Although gender differences exist in cardiovascular endothelial function, it remains unclear whether such differences are also seen in small intestinal endothelial function. To determine this, untreated male, age-matched proestrus female, castrated male, and 17beta-estradiol (E2)-treated noncastrated male rats were studied. Dose response curves to ACh and nitroglycerin (NTG) were determined by measuring changes in perfusion pressure by using an isolated small intestinal perfusion model. Endothelium-derived nitric oxide (NO) production/release was indirectly determined by the ability of intact endothelium to suppress serotonin (10(-5) M)-induced perfusion pressure changes. Intestinal tissue levels of NO were also measured. Moreover, plasma levels of androgen and E2 were determined and correlated with ACh (10(-8) M)-induced perfusion pressure reductions. ACh-induced intestinal perfusion pressure reductions in proestrus females, castrated males, and E2-treated noncastrated males were significantly higher than in untreated males. NTG-induced perfusion pressure reductions were not significantly different among groups. Perfusion pressures after administration of serotonin (10(-5) M) and intestinal tissue levels of NO in proestrus females, castrated males, and E2-treated noncastrated males were also significantly higher than in untreated males. Plasma androgen levels in proestrus females, castrated males, and in E2-treated noncastrated males were significantly lower compared with untreated males. There was a positive correlation between plasma androgen and ACh-reduced perfusion pressure; however, E2 levels did not show a similar relationship. Thus androgens appear to play an inhibitory role in small intestinal endothelial function. These properties in male vessels can be modulated by decreasing the level of circulating androgens or by E2 treatment.

Cyclooxygenase pathway is involved in the vascular reactivity and inhibition of the Na+, K+-ATPase activity in the tail artery from L-NAME-treated rats

L-NAME (LN) induces hypertension by blocking nitric oxide (NO) synthesis. It produces vascular hyperreactivity to phenylephrine (PHE) associated with a reduced vascular Na+, K+-ATPase activity. The aim of this work was to investigate whether products of the cyclooxygenase pathway are involved in alterations of vascular reactivity and Na+-pump activity in the tail artery from LN-induced hypertension rats. Four groups of rats were used: Control (CT, normotensive), LN (50 mg/kg/day, hypertensive), indomethacin (Indo-4 mg/kg/day, normotensive), and LN plus Indo (LN + Indo, partially prevented hypertension). All drugs were administered in drinking water during 7 days. In isolated rat tail vascular beds; the reactivity to PHE, acetylcholine (ACh), sodium nitroprusside (SNP), the functional activity of the Na+, K+-ATPase (K+-induced relaxation) and the modulation of PHE-induced vasoconstriction by constitutively available NO were evaluated. LN increased vascular sensitivity (pD2) and reactivity (Emax) to PHE and Indo blocked the effect of LN on Emax without changing pD2. Emax and pD2 values for ACh were reduced by LN and partially reverted by Indo. SNP-induced vasodilatation was similar in all groups. LN reduced the activity of Na+, K+-ATPase and Indo prevented LN effects. LN also abolished NO ability to modulate PHE-induced contractions. This effect was partially prevented by Indo suggesting that products from the cyclooxygenase pathway might reduce NO actions. Indo itself did not affect vascular reactivity to PHE, ACh or SNP or the Na+,K+-ATPase activity. Results suggested that products from cyclooxygenase pathway are involved in the genesis or maintenance of LN-induced hypertension, playing a role in the increased vascular reactivity, in the reduction of the endothelium-dependent relaxation and in the inhibition of the functional activity of the Na+, K+-ATPase.

Vascular ECE-1 mRNA expression decreases in response to estrogens

DNA microarrays were used to identify new targets of estrogen in the vasculature. Ovariectomized rats were treated with estradiol, genistein or daidzein, for four days. [33P]dCTP-labelled probes synthesized from mesenteric artery RNA were hybridized with DNA microarrays. Analysis of the microarray data identified endothelin converting enzyme-1 (ECE-1) as a gene whose expression was inhibited by treatment with estrogen, genistein, or daidzein. Semi-quantitative RT-PCR was used to confirm the data from the DNA microarrays. Reversal of the estrogen and phytoestrogen effect on ECE-1 expression by ICI 182,780 suggested that the inhibition was an estrogen receptor response. An inhibition of ECE-1 mRNA expression by estrogen or the phytoestrogens has not been previously reported. These data highlight the power of DNA microarray technology to identify new gene expression targets of estrogen in the vasculature. Moreover, the data suggest that genistein and daidzein inhibit ECE-1 expression by an estrogen receptor-mediated mechanism.

Effects of estrogen on the vascular system

The cardiovascular protective actions of estrogen are partially mediated by a direct effect on the vessel wall. Estrogen is active both on vascular smooth muscle and endothelial cells where functionally competent estrogen receptors have been identified. Estrogen administration promotes vasodilation in humans and in experimental animals, in part by stimulating prostacyclin and nitric oxide synthesis, as well as by decreasing the production of vasoconstrictor agents such as cyclooxygenase-derived products, reactive oxygen species, angiotensin II, and endothelin-1. In vitro, estrogen exerts a direct inhibitory effect on smooth muscle by activating potassium efflux and by inhibiting calcium influx. In addition, estrogen inhibits vascular smooth muscle cell proliferation. In vivo, 17beta-estradiol prevents neointimal thickening after balloon injury and also ameliorates the lesions occurring in atherosclerotic conditions. As is the case for other steroids, the effect of estrogen on the vessel wall has a rapid non-genomic component involving membrane phenomena, such as alteration of membrane ionic permeability and activation of membrane-bound enzymes, as well as the classical genomic effect involving estrogen receptor activation and gene expression.

Mechanisms of vasorelaxation to 17beta-oestradiol in rat arteries

We have investigated the involvement of the endothelium, K+ channels, oestradiol receptors, and Ca2+ influx in 17beta-oestradiol-induced vasorelaxation in rat mesenteric arterial beds and aortae. 17beta-Oestradiol (10 pM-1 mM) caused acute vasorelaxations in mesenteric arterial beds and aortae from male and female rats. In male rat mesenteric vessels and aortae, the vasorelaxations were mostly independent of the endothelium and nitric oxide (NO). However, indomethacin (10 microM) enhanced the relaxant responses to 17beta-oestradiol. In male rat mesenteric beds, 60 mM KCl, tetrabutylammonium chloride (300 microM), 4-aminopyridine (1 mM), and barium chloride (30 microM), charybdotoxin (100 nM), but not glibenclamide (10 microM) and tamoxifen (10 microM), inhibited vasorelaxation to 17beta-oestradiol. In male rat aortae, 60 mM KCl did not affect vasorelaxation to 17beta-oestradiol. However, in the presence of indomethacin, vasorelaxation to 17beta-oestradiol was enhanced but this was sensitive to 60 mM KCl. Pre-treatment with 17beta-oestradiol (100 microM) inhibited CaCl2-induced contraction. The present findings indicate that, in rat mesenteric beds and aortae, 17beta-oestradiol causes acute and potent vasorelaxation which may be enhanced in the presence of a cyclooxygenase inhibitor. In mesenteric arterial bed, 17beta-oestradiol-induced vasorelaxation occurs primarily via activation of K+ channels. In the aorta, vasorelaxations involved activation of K+ efflux when the cyclooxygenase pathway was inhibited, and also inhibition of Ca2+ influx.

Gender, exercise training, and eNOS expression in porcine skeletal muscle arteries

Our purpose was to determine the effects of gender and exercise training on endothelial nitric oxide synthase (eNOS) and superoxide dismutase (SOD) protein content of porcine skeletal muscle arteries and to evaluate the role of 17beta-estradiol (E2) in these effects. We measured eNOS and SOD content with immunoblots and immunohistochemistry in femoral and brachial arteries of trained and sedentary male and female pigs and measured estrogen receptor (ER) mRNA and alpha-ER and beta-ER protein in aortas of male and female pigs. Results indicate that female arteries contain more eNOS than male arteries and that exercise training increases eNOS content independent of gender. Male and female pigs expressed similar levels of alpha-ER mRNA and protein and similar amounts beta-ER protein in their arteries. E2 concentrations as measured by RIA were 180 +/- 34 pg/ml in male sera and approximately 5 pg/ml in female sera, and neither was changed by training. However, bioassay indicated that biologically active estrogen equivalent to only 35 +/- 5 pg/ml was present in male sera. E2 in female pigs, whether measured by RIA or bioassay, was approximately 24 pg/ml at peak estrous and 2 pg/ml on day 5 diestrus. The free fraction of E2 in sera did not explain the low measurements, relative to RIA, of E2. We conclude that 1). gender has significant influence on eNOS and SOD content of porcine skeletal muscle arteries; 2). the effects of gender and exercise training vary among arteries of different anatomic origin; 3). male sera contains compounds that cause RIA to overestimate circulating estrogenic activity; and 4). relative to human men, the male pig is not biologically estrogenized by high levels of E2 reported by RIA, whereas in female pigs E2 levels are lower than in the blood of human women.

Sarpogrelate HCl, a selective 5-HT2A antagonist, retards the progression of atherosclerosis through a novel mechanism

Although sarpogrelate HCl is widely used for the prevention of arterial thrombosis, its effect on atherosclerosis is unknown. Accordingly, we here investigated the effects of sarpogrelate HCl on a rabbit model of atherosclerosis. Male rabbits were fed a 0.5% cholesterol diet (HCD) (Gp 1), HCD with vitamin E (Gp 2), HCD with vitamin E and sarpogrelate (Gp 3), or HCD with sarpogrelate alone (Gp 4) for 8 weeks. The atherosclerotic area was decreased by feeding of vitamin E and sarpogrelate (16.9+/-2.0% in Gp 1 vs. 8.2+/-2.0% in Gp 3). Tone-related basal NO release was higher in Gps 3 and 4. Acetylcholine-induced relaxation tended to be improved in Gp 3. The amount of eNOS mRNA was increased in Gp 4, and aortic cyclic GMP concentration showed the same tendency. O(2)(-) release tended to be decreased in Gps 2 and 3. The matrix metalloproteinase-1 (MMP-1)-positive area was decreased, and the percentage ratio of cell numbers of smooth muscle cells/macrophages in the plaque was increased in Gp 3. The results demonstrated that sarpogrelate HCl retards the progression of atherosclerosis in rabbits, and that this effect is enhanced by concomitant administration of vitamin E. Although upregulation of eNOS may play a role as one of the underlying mechanisms, our results suggest that an additional mechanism-possibly involving the antiproliferative effects of sarpogrelate HCl on smooth muscle cells and macrophages-may also play an important role.

Estrogen alone or combined with medroxyprogesterone but not raloxifene reduce myocardial infarct size

We investigated whether estrogen protects the ischemic myocardium in oophorectomized female rabbits fed with a cholesterol-enriched diet, whether the addition of a progestin compound attenuates the beneficial effect of estrogen and whether raloxifene also limits myocardial necrosis. We treated 32 female oophorectomized hypercholesterolemic rabbits with (a) placebo (N=8, group I), (b) conjugated estrogens alone (N=8, group II), (c) conjugated estrogens combined continuously with medroxyprogesterone acetate (N=8, group III) and (d) raloxifene (N=8, group IV) all for 4 weeks. All rabbits underwent 30 min of ischemia and 120 min of reperfusion. Both infarct size (0.38+/-0.08 and 0.45+/-0.05 in groups II and III, respectively, vs. 0.78+/-0.07 in group I, P<0.005) and infarct size/risk zone% (26.34+/-4.18 and 35.01+/-4.39 in groups II and III, respectively, vs. 52.18+/-7.84 in group I, P<0.05) were significantly smaller in the estrogen treatment groups compared to placebo. No significant difference was observed between groups II and III. There was no significant difference between groups I and IV for infarct size (0.78+/-0.07 vs. 0.69+/-0.08, respectively) or for infarct size/risk zone% (52.18+/-7.84 vs. 47.17+/-4.3). Short-term estrogen protects ischemic myocardium in hypercholesterolemic oophorectomized female rabbits; this effect is not attenuated by the addition of a progestin compound. Raloxifene, however, does not decrease infarct size compared to placebo.

17 beta-estradiol increases inducible nitric oxide synthase expression in macrophages

In some tissues 17beta-estradiol (E2) is known to increase endothelial NOS expression. In the present study we examined the effects of E2 on estrogen receptors (ERalpha and beta) and inducible nitric oxide synthase (iNOS) expression and analyzed the mechanisms in rat peritoneal macrophages. Reverse-transcription polymerase chain (RT-PCR) and transient transfection experiments using a reporter plasmid that contained a luciferase gene under the transcriptional control of an estrogen-responsive elements revealed that peritoneal macrophages are responsive to E2 and express both ERalpha and ERbeta mRNAs. Incubation with E2 leads to an increased ERbeta mRNA expression. When rat peritoneal macrophages were incubated with physiological concentrations of E2, E2 induced a dose-dependent increase in NO production. E2 significantly affected secretion at concentration levels of more than 10(-11)M, and its maximum effect was at a concentration of 10(-8)M. RT-PCR reactions showed that increases in NO secretion were due to an increase in iNOS mRNA. Coincubation with ICI 182.780, an estrogen-receptor antagonist, inhibited the influence of E2 on NO production and iNOS expression. Thus E2 stimulated iNOS expression by a classic receptor-mediated pathway. We hereby prove that E2 increases the iNOS expression in macrophages and this effect appears to be the consequence of ER activation.

17-epiestriol, an estrogen metabolite, is more potent than estradiol in inhibiting vascular cell adhesion molecule 1 (VCAM-1) mRNA expression

17-beta estradiol (17-beta E(2)) attenuates the expression of vascular cell adhesion molecule 1 (VCAM-1) in vivo at physiological levels (pg/ml), whereas supraphysiological concentrations of 17-beta E(2) (ng/ml) are required in vitro. We assessed whether a metabolite of estrogen, which could only be generated in vivo, might be a more potent inhibitor of VCAM-1 expression and thereby explain this discrepancy. We report here that 17-epiestriol, an estrogen metabolite and a selective estrogen receptor (ER) beta agonist, is approximately 400x more potent than 17-beta E(2) in suppressing tumor necrosis factor (TNF) alpha-induced VCAM-1 mRNA as well as protein expression in human umbilical vein endothelial cells. Genistein, an ERbeta agonist, at low concentrations (1 and 10 nm) also suppressed TNFalpha-induced VCAM-1 mRNA expression. These actions of 17-epiestriol and genistein were significantly attenuated in the presence of the estrogen receptor antagonist ICI-182780. Other estrogenic compounds such as ethinyl estradiol and estrone did not have any effect on TNFalpha-induced VCAM-1 expression at the concentrations tested. We further show that, 1) 17-epiestriol induces the expression of endothelial nitric-oxide synthase mRNA and protein, 2) 17-epiestriol prevents TNFalpha-induced migration of NFkappaB into the nucleus, 3) N(G)-nitro-l-arginine methyl ester, an inhibitor of NO synthesis, abolishes 17-epiestriol-mediated inhibition of TNFalpha-induced VCAM-1 expression and migration of NFkappaB from the cytoplasm to the nucleus. Our results indicate that 17-epiestriol is more potent than 17-beta E(2) in suppressing TNFalpha-induced VCAM-1 expression and that this action is modulated at least in part through NO.

Exercise training regulates SOD-1 and oxidative stress in porcine aortic endothelium

Vascular oxidative stress contributes to endothelial dysfunction. Aerobic exercise training improves vascular function. The purpose of this study was to test the hypothesis that exercise training would improve the balance of antioxidant to prooxidant enzymes and reduce markers of oxidative stress in aortic endothelial cells (AEC). Female Yucatan miniature pigs either remained sedentary (SED) or were exercise trained (EX) for 16-19 wk. EX pigs had increased AEC SOD-1 protein levels and Cu/Zn SOD activity of the whole aorta compared with SED pigs. Protein levels of other antioxidant enzymes (SOD-2, catalase) were not affected by exercise training. Protein levels of p67(phox), a subunit of the prooxidant enzyme NAD(P)H oxidase, were reduced in EX vs. SED AEC. These EX adaptations were associated with lower AEC malondialdehyde levels and decreased phosphorylation of ERK-1/2. Endothelial nitric oxide synthase protein, protein nitrotyrosine content, and heme oxygenase-1 protein were not different in EX vs. SED pigs. We conclude that chronic aerobic exercise training influenced both antioxidant and prooxidant enzymes and decreased indexes of oxidative stress in AEC. These adaptations may contribute to improved endothelial function with exercise training.

Androgens and coronary artery disease

A significant and independent association between endogenous testosterone (T) levels and coronary events in men and women has not been confirmed in large prospective studies, although cross-sectional data have suggested coronary heart disease can be associated with low T in men. Hypoandrogenemia in men and hyperandrogenemia in women are associated with visceral obesity; insulin resistance; low high-density lipoprotein (HDL) cholesterol (HDL-C); and elevated triglycerides, low-density lipoprotein cholesterol, and plasminogen activator type 1. These gender differences and confounders render the precise role of endogenous T in atherosclerosis unclear. Observational studies do not support the hypothesis that dehydroepiandrosterone sulfate deficiency is a risk factor for coronary artery disease. The effects of exogenous T on cardiovascular mortality or morbidity have not been extensively investigated in prospective controlled studies; preliminary data suggest there may be short-term improvements in electrocardiographic changes in men with coronary artery disease. In the majority of animal experiments, exogenous T exerts either neutral or beneficial effects on the development of atherosclerosis. Exogenous androgens induce both apparently beneficial and deleterious effects on cardiovascular risk factors by decreasing serum levels of HDL-C, plasminogen activator type 1 (apparently deleterious), lipoprotein (a), fibrinogen, insulin, leptin, and visceral fat mass (apparently beneficial) in men as well as women. However, androgen-induced declines in circulating HDL-C should not automatically be assumed to be proatherogenic, because these declines may instead reflect accelerated reverse cholesterol transport. Supraphysiological concentrations of T stimulate vasorelaxation; but at physiological concentrations, beneficial, neutral, and detrimental effects on vascular reactivity have been observed. T exerts proatherogenic effects on macrophage function by facilitating the uptake of modified lipoproteins and an antiatherogenic effect by stimulating efflux of cellular cholesterol to HDL. In conclusion, the inconsistent data, which can only be partly explained by differences in dose and source of androgens, militate against a meaningful assessment of the net effect of T on atherosclerosis. Based on current evidence, the therapeutic use of T in men need not be restricted by concerns regarding cardiovascular side effects. Available data also do not justify the uncontrolled use of T or dehydroepiandrosterone for the prevention or treatment of coronary heart disease.

Cytoskeletal protein degradation and neurodegeneration evolves differently in males and females following experimental head injury

The resulting neuropathological degeneration that occurs following a traumatic brain injury (TBI) is a consequence of both immediate and secondary neurochemical sequelae. Proteolysis of cytoskeletal proteins, triggered by calcium-mediated events, is believed to be a particularly significant contributor to TBI-induced neuronal death. To date, efforts to associate cytoskeletal degradation and neurodegeneration in TBI have been primarily qualitative or semiquantitative. The objectives of this study were (1). to quantitatively describe, over a posttraumatic time course, the relationship and mechanisms of cytoskeletal degradation (Western blot) and neurodegeneration (silver staining) in male and female mice following a moderately severe weight-drop impact-acceleration head injury; (2). to evaluate gender differences in the response to TBI; and (3). to examine the potential therapeutic window for future pharmacological treatment strategies. In male and female mice, we report a close correlation in the time courses of neurofilament M protein degradation and alpha-spectrin breakdown products (SBDP 150 and 145) with the peak magnitude of neurodegeneration, as quantified by silver staining. Evidence from the increased patterns of SBDPs suggests that both calpain and caspase-3 are involved. In general, males incurred peak protein degradation and neurodegeneration within 3 days after injury, while in females this did not occur until 14 days. The neuroprotective effects of estrogen are believed to be key factors in the superior outcome of female vs male mice following TBI. In mice, the therapeutic window of opportunity for pharmacological intervention aimed at limiting cytoskeletal degradation might be as much as 24 h following injury. Evidence of a protracted time course of cytoskeletal degradation, especially in females, suggests a potential for an extended treatment-duration following TBI.

Gender differences in ET and NOS systems in ETB receptor-deficient rats: effect of a high salt diet

The purpose of this study was to determine if rats lacking the ETB receptor have altered renal endothelin (ET) production and NO synthase (NOS) activity in response to high salt and if female rats are better able to control blood pressure through higher NOS activity in rats heterozygous (sl/+) and homozygous (sl/sl) for ETB receptor deficiency. On normal salt (0.4% NaCl; NS), male sl/sl rats had higher systolic blood pressures compared with male sl/+ and female sl/+ and sl/sl rats. On a high salt diet (10% NaCl; HS), blood pressure in male sl/+ rats was significantly higher than female sl/+ rats. However, ETB receptor deficiency caused much larger increases in blood pressure in male and female rats. On NS, urinary ET excretion was not different between male and female of either genotype. HS significantly increased ET excretion in male and female sl/+ rats, but the increase was significantly less in sl/sl compared with sl/+. Homogenates of inner medullary collecting duct tissue were separated into particulate and cytosolic fractions and total NOS activity measured by conversion of [3H]L-arginine to [3H]L-citrulline. Female rats had significantly greater cytosolic NOS activity compared with male rats on NS. On HS, cytosolic NOS activity was lower in all groups compared with NS rats, whereas particulate NOS activity was significantly greater in male and female sl/+ rats compared with male and female sl/sl rats. These data support our hypothesis that NOS protects against rises in blood pressure in female rats and ETB receptors prevent further increases in blood pressure due to increases in renal ET production and NOS activity.

An emerging role for nitric oxide in sickle cell disease vascular homeostasis and therapy

Nitric oxide participates in the compensatory response to chronic vascular injury in patients with sickle cell disease. The authors have found reductions of basal and stimulated nitric oxide production and responses to exogenous nitric oxide in male patients with sickle cell disease. Gender differences in nitric oxide bioavailability are probably caused in part by the protective effects of ovarian estrogen on nitric oxide synthase expression and activity in women. Further, in men, and likely all patients during vaso-occlusive crisis and the acute chest syndrome, nitric oxide is destroyed by increased circulating plasma hemoglobin and superoxide. The combined effects of inhaled nitric oxide gas of improving pulmonary ventilation to perfusion matching and hemodynamics, reducing alveolar and systemic inflammation, and inhibiting circulating plasma hemoglobin (and thus restoring peripheral nitric oxide bioavailability) may modulate the course of the disease, including the frequency and severity of vaso-occlusive crises and acute chest syndrome episodes. Possible effects of chronic nitric oxide-based therapies on erythrocyte density, pulmonary artery pressures, and fetal hemoglobin induction deserve study.

Divergent nitric oxide bioavailability in men and women with sickle cell disease

BACKGROUND

Although reduced endothelial nitric oxide (NO) bioavailability has been demonstrated in arteriosclerotic vascular disease, the integrity of this system in sickle cell disease remains uncertain.

METHODS AND RESULTS

We measured forearm blood flow in 21 patients with sickle cell disease (hemoglobin SS genotype) and 18 black control subjects before and after intra-arterial infusions of acetylcholine, nitroprusside, and the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA). Endothelium-dependent vasodilation, measured by the percent increase in flow induced by acetylcholine infusion, was significantly greater than in controls (252+/-37% for patients versus 134+/-24% for controls; P<0.0001). However, there was a large sex difference in blood flow responses between female and male patients (340+/-46% versus 173+/-41%; P=0.035). Similarly, basal NO bioactivity, as measured by the percent decrease in flow induced by L-NMMA, was depressed in male compared with female patients (-17+/-5% versus -34+/-4%; P=0.01), as was the response to nitroprusside (86+/-21% versus 171+/-22%; P=0.008). L-NMMA reduced the blood flow response to acetylcholine in women, but not in men. Sex differences in vascular cell adhesion molecule-1 were appreciated, with significant correlations between levels of soluble vascular cell adhesion molecule-1 and blood flow responses to L-NMMA and nitroprusside (r=0.53, P=0.004 and r=-0.66, P<0.001, respectively).

CONCLUSIONS

NO bioavailability and NO responsiveness are greater in women than in men with sickle cell disease and determines adhesion molecule expression. Endothelium-dependent blood flows are largely non-NO mediated in male patients. These results provide a possible mechanism for reported sex differences in sickle cell disease morbidity and mortality and provide a basis for novel pharmacological interventions.

Time-dependent hyperreactivity to phenylephrine in aorta from untreated diabetic rats: role of prostanoids and calcium mobilization

Diabetes alters vascular smooth muscle contractility. Changes in reactivity to phenylephrine (Phe) in aortas from controls and untreated 1- and 4-week streptozotocin (STZ)-induced diabetic rats were investigated. In 1-week diabetic (DB1) aortas, the maximum response (E(max)) and sensitivity (pD(2)) to Phe were similar to controls (CT1), but in 4-week diabetic (DB4) aortas, the E(max) for Phe was increased compared to CT4 aortas (E(max), DB4: 125+/-8.4% vs. CT4: 89.8+/-4.5%, P<.001). Endothelial denudation increased the response to Phe, and E(max) was increased in the DB4 aortas compared to CT4 (E(max), DB4: 156+/-4.2% vs. CT4: 125+/-3.8%, P<.001). Pretreatment of CT4 and DB4 aortas with indomethacin reduced E(max) and pD(2) for Phe. After indomethacin treatment, no differences in E(max) and pD(2) to Phe were observed in either group. SQ 29548 did not alter the Phe actions in CT4 aortas. However, in DB4 aortas, E(max) was reduced to control level. CT4 and DB4 aortas incubated in free-Ca(2+) solution plus Phe, contracted upon addition of CaCl(2), this response was increased in DB4 aortas. No changes were observed for acetylcholine (ACh) or sodium nitroprusside (SNP) responses. Nitric oxide (NO) release in response to Phe determined by acute L-NAME administration showed no differences in the percentage increase of the contraction in CT1 and DB1 aortas, but was enhanced in DB4 aortas. Results suggested that diabetes induces time-dependent changes in the vascular reactivity to Phe. This response is not related to a reduction of endothelium-derived NO but might be due to an increase in prostaglandin H(2) (PGH(2))/thromboxane A(2) (TxA(2)) and/or an enhanced extracellular Ca(2+) influx.

Effects of hormone replacement therapy on serum angiotensin-converting enzyme activity and plasma bradykinin in postmenopausal women according to angiotensin-converting enzyme-genotype

An insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme (ACE) gene determines serum ACE levels. The D allele is associated with increased ACE activity and is linked to cardiovascular disease. Hormone replacement therapy (HRT) in postmenopausal women (PMW) decreases serum ACE activity and concomitantly increases plasma bradykinin. We investigated the effect of HRT on these parameters in PMW according to ACE-genotype. We assessed 68 PMW during 12-month oral HRT (0.625 mg conjugated estrogen +2.5 mg medroxyprogesterone acetate). ACE genotype was determined at baseline, and serum ACE activity and plasma bradykinin were measured at baseline and after 3-, 6-, and 12-month HRT. We divided the PMW into three groups according to ACE genotype: groups I/I (n = 26), I/D (n = 33), and D/D (n = 9). HRT resulted in a significant reduction in the genotype-associated increase in ACE activity in the ACE I/D and D/D groups after 6-month (p < 0.001 and p < 0.05, respectively) and 12-month HRT (p < 0.001 and p < 0.01, respectively), but not in the I/I group. While the reduction of ACE activity was expected to increase bradykinin in the ACE I/D and D/D groups, HRT significantly increased the bradykinin levels not only in these two groups but also in the ACE I/I group at both 6 months (p < 0.01, p < 0.05, and p < 0.001, respectively) and 12 months after the start of HRT (p < 0.01, p < 0.01, and p < 0.01, respectively). These results suggest that the increased plasma bradykinin of PMW by HRT might not be induced solely by the reduction in serum ACE activity.

Ovariectomy attenuates hyperpolarization and relaxation mediated by endothelium-derived hyperpolarizing factor in female rat mesenteric artery: a concomitant decrease in connexin-43 expression

Estrogen status is known to affect the incidence of cardiovascular disease. Experiments were designed to prove the influences of in vivo estrogen manipulations on vascular hyperpolarization and relaxation mediated by endothelium-derived hyperpolarizing factor (EDHF), and to explore the possible mechanism contributing to the altered EDHF responses in estrogen-deficient states. Mesenteric arteries with intact endothelium were isolated from sham-operated (control), ovariectomized (OVX), or OVX with 17beta-estradiol replacement (OVX + E ) female rats. In the presence of apamin and charybdotoxin, there was no difference between groups in relaxations to the Ca ionophore A23187 and the endoplasmic reticulum Ca -adenosine triphosphatase inhibitor cyclopiazonic acid (CPA). However, N -nitro-L-arginine produced a marked decrease in A23187- and CPA-induced relaxations in OVX compared with control and OVX + E arteries. In control arteries, A23187 and CPA elicited membrane hyperpolarization in a sustained manner. In contrast, A23187 produced only a small and transient hyperpolarizing effect in OVX arteries. OVX also greatly attenuated the sustained pattern of hyperpolarization to CPA. Such changes in hyperpolarizations were not seen in OVX + E arteries. The EDHF-mediated relaxant and hyperpolarizing responses of control arteries to A23187 and CPA were significantly inhibited by the gap junction inhibitor 18 alpha-glycyrrhetinic acid. Immunohistochemical examination for connexin-43 showed that the expression was abundant along the endothelial layer in control and OVX + E arteries, while being much less in OVX arteries. It was concluded that estrogen deficiency specifically impairs EDHF-mediated vascular actions. This may be partly explained by the reduced expression of connexin-43, a protein molecule that could form myoendothelial gap junction channels.

17β-Estradiol rapid stimulation of rat aorta NOS activity is prevented by oestrogen deficiency

OBJECTIVES

The purpose of this study was to determine the effects of chronic oestrogen deficiency on rat aorta rapid response to 17beta-estradiol treatment.

METHODS

Rat aortic strips (RAS) were isolated from Wistar female rats of three different groups: rats 6-7-month old with normal oestrogen levels (NER); aged rats, 24-month old, with low oestrogen levels (LER); and young rats after 2 months of bilateral ovariectomy (OVX). Platelet aggregation was measured after incubation of RAS in a platelet rich plasma by addition of 10 microM ADP. NO production by RAS was measured by 3H-citrulline technique.

RESULTS

RAS obtained from NER treated with 17beta-estradiol produced an inhibition of platelet aggregation specific for ovarian hormones, since testosterone was devoid of any effect. In aortic tissue isolated from male rats no increment in nitric oxide (NO) production was found. RAS from LER and OVX treated with 1-10 nM failed to induce a significant inhibition of platelet aggregation compared with NER (5 and 17%; 6 and 20% vs. 45 and 77% inhibition of platelet aggregation respect to control, respectively). In contrast to NER, 5 min treatment of LER and OVX aortic tissue with 1 nM 17beta-estradiol did not incremented NO production (NER 1.14 vs. 2.3 (P < 0.05); LER 1.14 vs. 1.42; OVX 1.24 vs. 1.52 pmol NO per mg protein).

CONCLUSIONS

These results suggest that chronic oestrogen deprivation impairs the inhibition of platelet aggregation and suppresses the rapid stimulation of aortic NOS induced by acute 'in vitro' treatment with 17beta-estradiol.

Effects of tibolone on plasma levels of nitric oxide in postmenopausal women

OBJECTIVE

To determine the effects of tibolone on nitric oxide (NO) plasma levels in postmenopausal women.

DESIGN

Randomized, double-blind, placebo-controlled, cross-over trial.

SETTING

Healthy volunteers in an academic research environment.

PATIENT(S)

Eighteen healthy women who have been in postmenopause for 1-4 years.

INTERVENTION(S)

Women received either tibolone 2.5 mg/day (group A) or placebo (group B) for 1 month; then the treatment was inverted for the second month.

MAIN OUTCOME MEASURE(S)

Plasma concentration of NO stable oxidation products and blood pressure were evaluated at baseline, month 1, and month 2.

RESULT(S)

Baseline concentration of NO metabolites were similar in both groups. At month 1, mean concentration of NO metabolites increased significantly in group A alone. At the end of month 2, NO metabolite levels in group A returned to baseline, whereas in group B they increased significantly.

CONCLUSION(S)

Tibolone induced a sustained increase in plasma levels of NO in postmenopausal women, suggesting that tibolone may exert a direct cardiovascular protective effect in postmenopausal women.

Male-female differences in the relative contribution of endothelial vasodilators released by rat tail artery

Several different vasodilator substances can be released by vascular endothelium in response to mechanical stimuli and vasoactive agents. The purpose of this study was to determine whether there is a male-female difference in the relative contributions of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) to endothelium-dependent vasodilation. Perfusion pressure was measured in isolated tail arteries from male and female rats. Vasodilators released by mechanical shear stress were assessed by constricting the artery with methoxamine; acetylcholine was applied to induce receptor-mediated vasodilation. We used an inhibitor of NO synthase, N(G)-monomethyl-L-arginine acetate (L-NMMA), and elevated levels of K(+) (27 mM) to reveal the relative contributions of NO and EDHF, respectively. Indomethacin was present in all experiments to block prostanoid production. The results indicate that NO was the primary vasodilator released by male tail arteries in response to both mechanical stress and acetylcholine (the L-NMMA-sensitive component of the combined L-NMMA/K(+) effect was 83 +/- 8% and 101 +/- 4%, respectively). However female tail arteries appeared to utilize both NO and EDHF for vascular relaxation (e.g., L-NMMA sensitivity: 58 +/- 9%; K+-sensitivity: 42 +/- 9% in mechanical stress experiments). These findings suggest endothelial regulation differs between males and females.

Infusion of pregnant rats with calcitonin gene-related peptide (CGRP)(8-37), a CGRP receptor antagonist, increases blood pressure and fetal mortality and decreases fetal growth

Calcitonin gene-related peptide (CGRP) is the most potent endogenous vasodilatory peptide, and is involved in the regulation of blood flow to vital organs. We have previously shown that CGRP may be involved in vascular adaptations that occur during pregnancy, and that steroid hormones may be involved in these mechanisms. We hypothesized that endogenous CGRP is required for maintaining blood pressure and fetoplacental growth in pregnant rats, and that progesterone will enhance CGRP effects. The vasodilatory effects of CGRP are known to be inhibited by a competitive CGRP receptor antagonist, the C-terminal fragment CGRP(8-37). In the present study, we investigated whether continuous s.c. infusion of CGRP(8-37) to pregnant rats will reduce fetoplacental growth and increase systolic blood pressure. We also assessed whether progesterone will alter the effects of CGRP(8-37) on blood pressure during postpartum. Groups of five pregnant rats were s.c. infused with varying doses of CGRP(8-37) from Day 17 of pregnancy. Daily systolic blood pressures, pup weight, mortality at term delivery, and fetoplacental weights on Day 20 of gestation were measured. CGRP(8-37) at a dose of 0.083 mg day(-1) kg(-1) body weight (BW) showed no effects; however, doses of 0.33 and 1.33 mg day(-1) kg(-1) BW increased (P < 0.05) blood pressure during pregnancy, and these elevated blood pressures persisted during postpartum with the highest dose used. Progesterone (2 mg per injection, twice a day; s.c.) treatment significantly elevated blood pressure in rats infused with CGRP(8-37) during postpartum, suggesting that progesterone regulates CGRP-induced vascular effects. CGRP(8-37) infusion caused significant reductions in pup weight with an increase in mortality rate, and these effects were dose-dependent. Placental and fetal weights were also decreased prior to term on Day 20 of gestation, 72 h after CGRP(8-37) infusion, indicating effects on uteroplacental tissues. Therefore, we suggest that endogenous CGRP plays an important role in maintaining normal fetoplacental development, fetal survival, and vascular adaptations during pregnancy.

Medroxyprogesterone acetate does not antagonize estrogen-induced increases in endothelium-dependent vasodilation: potential clinical implications

OBJECTIVE

Determine the effect of combined 17beta-estradiol benzoate (E2) and medroxyprogesterone acetate (MPA) administration on endothelium-dependent vasorelaxation to acetylcholine (ACh).

DESIGN

Prospective, ex vivo study.

SETTING

Academic research laboratory.

ANIMAL(S)

Mature female rats.

INTERVENTION(S)

Ovariectomized rats received one of the following interventions daily for 3 days: [1] corn oil via IM injection, [2] E2 (20 microg/kg IM), or [3] E2 (20 microg/kg IM) and MPA (10 mg/kg IM).

MAIN OUTCOME MEASURE(S)

Basal release of nitric oxide (NO) and endothelium-dependent and endothelium-independent vasodilation from thoracic aortas obtained from each group.

RESULT(S)

Estradiol treatment potentiated the endothelium-dependent relaxation to ACh when compared with the control group. Administration of MPA with E2 did not antagonize the beneficial effect of E2 on endothelium-dependent relaxation. Estradiol treatment alone or in combination with MPA did not affect endothelium-independent vasodilation as compared with the case of the control group. Administration of E2 resulted in increased basal NO release (assessed indirectly by measuring the constrictor response to N(G)-nitro-L-arginine [methyl ester (L-NAME)]) when compared with the case of the control group, and the addition of MPA to E2 did not alter the effect of E2 on basal NO release.

CONCLUSION(S)

Estradiol potentiates endothelium-dependent relaxant responses and increases basal endothelial NO release. Medroxyprogesterone acetate does not antagonize these effects of E2.

Is estradiol cardioprotection a nitric oxide-mediated effect?

BACKGROUND

Estradiol exerts a number of biological effects that support extensive observational data suggesting a protective role for estrogen in cardiovascular disease prevention. These include effects on lipid and carbohydrate metabolism, coagulation/fibrinolysis as well as a possible effect on vascular reactivity. It has been proposed that this might be mediated by vascular endothelial nitric oxide (NO) production. Accordingly, we designed complementary in-vivo and in-vitro studies to investigate this hypothesis further.

METHODS

Firstly, in a group of 10 healthy post-menopausal women, bilateral venous occlusion plethysmography was used to examine forearm vasoconstrictor responses to intrabrachial N(G)-monomethyl-l-arginine (l-NMMA; a substrate inhibitor of nitric oxide synthase) both before and after 4 weeks of treatment with transdermal 17beta-estradiol (E(2)) (80 microg/day). Secondly, we examined the direct effects of acute (24 h) and chronic (7 days) treatment with E(2) (10 pmol/l and 10 nmol/l) on endothelial nitric oxide synthase (eNOS) gene expression in cultured human aortic endothelial cells.

RESULTS

No significant differences were observed between the vasoconstrictor responses to l-NMMA (2, 4, 8 micromol/min) before and after E(2) treatment. Comparison of E(2)-treated endothelial cells with control cells showed no significant increase in eNOS mRNA expression following either acute or chronic estradiol treatment.

CONCLUSIONS

The present studies do not provide evidence for an eNOS-mediated cardioprotective response to estrogen and therefore suggest that additional mechanisms other than the endothelial NO system may have an important role in the cardiovascular effects of estrogen.

Production of nitric oxide, but not prostacyclin, is reduced in klotho mice

A novel murine model of aging (kl/kl mice) has been developed by in vivo mutagenesis. We analyzed endothelial function in this strain. Ring preparations of the thoracic aorta were obtained from 6- to 9-week old wild-type (+/+) and heterozygous (kl/+) klotho mice. The aortas of kl/+ mice showed an exaggerated contractile response to norepinephrine and attenuated vasodilator responses to acetylcholine and lecithinized superoxide dismutase (SOD) compared to +/+ mice. The response to sodium nitroprusside was unaltered in kl/+ mice. The contraction in response to norepinephrine was augmented by treatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) to a greater extent in +/+ mice than in kl/+ mice. Treatment with L-NAME abolished the vasodilator responses to both acetylcholine and lecithinized SOD. NO metabolites (NO2- and NO3-) and cGMP concentrations in the urine were significantly reduced in kl/+ mice compared to +/+ mice. However, the urinary excretion of 6-keto-prostaglandin F1alpha was unaltered. There was little immunostaining for NO synthase and vascular endothelial growth factor (VEGF) in the aorta of kl/+ mice. No immunostaining for NO synthase was noted in the aorta of kl/kl mice. The expression of the klotho gene product may have a role in the regulation of VEGF expression and is tightly linked to endothelial release of NO.

Update on cardiovascular disease in post-menopausal women

Cardiovascular disease (CVD), and in particular coronary artery heart disease (CAHD), is the leading cause of morbidity and mortality in women. Until recently, most of our knowledge about the pathophysiology of CVD in women - and, subsequently, management guidelines - were based on studies conducted mostly in men. While similar mechanisms operate to induce CVD in women and men, gender-related differences exist in the anatomy and physiology of the myocardium, and sex hormones modify the course of disease in women. Women, more than men, have their initial manifestation of CAHD as angina pectoris; are likely to be referred for diagnostic tests at a more advanced stage of disease, and are less likely than men to have corrective invasive procedures. The overall morbidity and mortality following the initial ischaemic heart event is worse in women, and the case fatality rate is greater in women than in men. Also, the relative impact of impaired vasoreactivity of the coronary artery, increased viscosity of the blood and dysregulation of automaticity and arrhythmia, is greater in women than in men. The most effective means of decreasing the impact of CVD on women's health is by an active approach from childhood to proper principles of healthcare in order to modify the contribution of specific risk factors. The latter include obesity, abnormal plasma lipid profile, hypertension, diabetes mellitus, cigarette smoking, sedentary lifestyle, increased blood viscosity, augmented platelet aggregability, stress and autonomic imbalance. The use of lipid-lowering drugs has not been adequately studied in women but reports from studies conducted mostly in men do predict an advantage also to women. Oestrogen deficiency after spontaneous or medically induced menopause is an important risk factor for CVD and CAHD. Observational and mechanistic data suggest a role for oestrogen replacement after menopause for primary, and possibly secondary, prevention of CVD. However, two recent prospective trials suggest that treatment de novo with hormone replacement of older post-menopausal women after an acute coronary event may not confer cardiovascular protection and may increase the risk of thromboembolic disease. Results of ongoing long-term studies may determine the beneficial role of hormone replacement versus potential risks involved with this treatment.

Estriol retards and stabilizes atherosclerosis through an NO-mediated system

Estriol (E3) has little effect on the female genitals. E3 is used in hormone replacement therapy, particularly in Europe and Japan, since it obviates the need for progestin administration. However, the effect of E3 on atherosclerosis has not been elucidated. In this study, we evaluated the effect of E3 on the progression of atherosclerosis in a rabbit model. Thirty-six rabbits total were used. Twenty-eight were bilaterally oophorectomized, and 8 were not. The rabbits were divided into 5 groups and treated for 12 weeks as follows. Gp I (n = 8) was fed a high cholesterol diet (HCD; standard diet plus 0.5% cholesterol); Gp II (n = 8) was fed a HCD with E3 (0.3 mg/kg/day); Gp III (n = 8) was fed a HCD with 17beta estradiol (E2) (0.1 mg/kg/day); Gp IV (n = 8), the non oophorectomized group, was fed a HCD; and Gp NC was oophorectomized (n = 4), and fed a regular diet. E3 treatment increased the plasma E2 and E3 levels in Gp II. The plasma lipid levels were not altered by the E2 or E3 treatment. A HCD diminished the acetylcholine-induced NO mediated relaxation in the thoracic aorta. The E2 treatment (Gp III) and E3 treatment (Gp II) restored the aortic basal NO release and the aortic cyclic GMP levels, particularly effectively in the E3 group. E3 treatment also decreased the atherosclerotic area, and its effect was comparable with E2 (surface involvement: 41.2 +/- 5.1% in Gp I; 10.1 +/- 2.7% in Gp II; and 6.5 +/- 1.3% in Gp III). All four hyperlipidemic groups showed an increase of eNOS mRNA in the aortae, and this was especially pronounced in Gps II and III. The level of peroxynitrite, as determined by immunohistochemical nitrotyrosine staining, was lower in Gps II and III than in Gp I. E3 strongly activates NO-mediated systems, and could play a role in retarding the progression of atherosclerosis and in stabilizing atheroma.

Nongenomic action of progesterone in rat aorta: role of nitric oxide and prostaglandins

The mechanism of action of progesterone (Pg) on rat vascular tissue was investigated. We obtained evidence that 10-nM Pg inhibited platelet aggregation at 1-5 min. Previously, we reported that nitric oxide (NO) mediated this antiaggregatory effect. Rat aortic strips (RAS) NO synthase (NOS) activity in response to "in vitro" treatment with other sex steroids hormones was measured. The stimulatory action of Pg on NO production was specific for ovarian hormones and depends on sex. The effect was nongenomic since cycloheximide did not suppress the increment in NO induced by Pg. Finally, we demonstrated that Pg (5 min) increased prostacyclin release (42-182% above control) in a dose-dependent manner (1-100 nM). Indeed, indomethacin (10 microM) completely suppressed the increment in citrulline levels induced by the hormone. These results suggest that Pg exerts a direct nongenomic action on rat aortic metabolism, which involves NOS and cyclooxygenase (COX) activation and a cross-talk between NO- and prostacyclin (PGI(2))-dependent pathways.

Hormonal influence on the release of endothelial nitric oxide: gender-related dimorphic sensitivity of rat aorta for noradrenaline

Male gender shows a higher incidence of vascular disorders and this phenomenon could be explained by sexual dimorphic behaviour of vessels. Both gonadal hormones and endothelial nitric oxide (NO) are involved in the regulation of the vascular reactivity. This study aimed to evaluate a possible sexual dimorphic sensitivity of rat aorta for the catecholamine noradrenaline. To understand the role played by physiological concentrations of sex hormones, the experimental procedures were performed on isolated preparations from intact (sham-operated) and gonadectomized rats of both sexes. In parallel sets of experiments, the biosynthesis of NO was inhibited by N'-nitro-L-arginine methyl ester (L-NAME) to reveal any potential involvement of the endothelial modulator and its possible link with the endocrinous factor. In aortae from intact male and female rats, noradrenaline induced contractile effects with different potencies (mean+s.d. EC50 values 12.15 +/- 5.25 nM and 84.10 +/- 18.68 nM, respectively). Gonadectomy resulted in an increased sensitivity for noradrenaline in female vessels and a decreased sensitivity for the agonist in male vessels (EC50 values 25.64 +/- 5.04 nM and 21.70 +/ 1 1.13 nM, respectively). In aortae from intact male rats, the inhibition of NO biosynthesis resulted in a weak increase in sensitivity for noradrenaline (EC50 value 6.08 +/- 4.53 nM), whereas the increase was higher in vessels from intact female rats (EC50 value 10.38 +/- 8.40 nM). After treatment with L-NAME, aortae from gonadectomized male and female rats presented almost equivalent increases in sensitivity for the adrenergic agonist (EC50 values 6.02 +/- 3.63 nM and 9.10+/- 9.63 nM,respectively),and no significant difference in sensitivity could be recorded between intact and orchidectomized male rats, or between intact and ovariectomized female rats. It was concluded that rat aorta showed a sexual dimorphic sensitivity for noradrenaline and the female sex was more protected against the adrenergic contractile stimulus because of a higher release of endothelial NO. The gender-related difference in NO release was influenced by gonadal hormones, with the female hormones inducing an increase and the male hormones causing a reduction.

Influence of gender on dilatation of the basilar artery during diabetes mellitus

The first goal of the present study was to examine the influence of gender on reactivity of the basilar artery. The second goal of this study was to examine the effect of diabetes mellitus on reactivity of the basilar artery in male and female rats. We examined in vivo responses of the basilar artery in male and female nondiabetic and diabetic rats in response to a nitric oxide synthase (NOS)-dependent (acetylcholine) and -independent (nitroglycerin) agonist. In nondiabetic male and female rats, acetylcholine and nitroglycerin produced dose-related dilatation of the basilar artery. However, the magnitude of vasodilatation in response to acetylcholine and a high concentration of nitroglycerin was significantly greater in female than in male rats. Acetylcholine (1.0 microM) dilated the basilar artery by 11 +/- 2% in nondiabetic males versus 25 +/- 4% in nondiabetic females (P<0.05). Nitroglycerin (1.0 microM) dilated the basilar artery by 37 +/- 8% in nondiabetic males versus 62 +/- 5% in nondiabetic females (P<0.05). Thus, there is a significant effect of gender on reactivity of the basilar artery during physiologic conditions. Dilatation of the basilar artery in response to acetylcholine, but not nitroglycerin, was impaired in diabetic male and female rats compared to their nondiabetic counterparts. Acetylcholine (1.0 microM) dilated the basilar artery by only 5 +/- 1% in diabetic males and by only 4 +/- 1% in diabetic females. In summary, dilatation of the basilar artery in response to NOS-dependent agonist was significantly greater in nondiabetic female than in nondiabetic male rats. In addition, diabetes mellitus impaired NOS-dependent dilatation of the basilar artery not only in male rats, but also in female rats. We suggest that the results of these studies provide insight into the pathogenesis of cerebrovascular abnormalities observed in postmenopausal women.

Estradiol alters nitric oxide production in the mouse aorta through the alpha-, but not beta-, estrogen receptor

Although estradiol (E(2)) has been recognized to exert several vasculoprotective effects in several species, its effects in mouse vasomotion are unknown, and consequently, so is the estrogen receptor subtype mediating these effects. We investigated the effect of E(2) (80 microg/kg/day for 15 days) on NO production in the thoracic aorta of ovariectomized C57Bl/6 mice compared with those given placebo. E(2) increased basal NO production. In contrast, the relaxation in response to ATP, to the calcium ionophore A23187, and to sodium nitroprusside was unaltered by E(2), whereas acetylcholine-elicited relaxation was decreased. The abundance of NO synthase I, II, and III immunoreactive proteins (using Western blot) in thoracic aorta homogenates was unchanged by E(2). To determine the estrogen receptor (ER) subtype involved in these effects, transgenic mice in which either the ERalpha or ERbeta has been disrupted were ovariectomized and treated, or not, with E(2). Basal NO production was increased and the sensitivity to acetylcholine decreased in ERbeta knockout mice in response to E(2), whereas this effect was abolished in ERalpha knockout mice. Finally, these effects of E(2) on vasomotion required long-term and/or in vivo exposure, as short-term incubation of aortic rings with 10 nmol/L E(2) in the isolated organ chamber did not elicit any vasoactive effects. In conclusion, this study demonstrates that ERalpha, but not ERbeta, mediates the beneficial effect of E(2) on basal NO production.

Effect of estrogen on endothelial function and angiogenesis

Animal studies evaluating gender difference, the effects of gonadectomy and estrogen replacement and clinical studies in post-menopausal women with and without estrogen replacement therapy (ERT) proved that estrogen exerts significant benefits on the cardiovascular system. Since effects on the plasma lipoprotein profile is responsible for only approximately 25-40% of the cardiovascular protection exerted by estrogens, it is postulated that direct effects of estrogen on the vascular wall must play an important role. Indeed, experimental and clinical evidence accumulated over the past decade, and reviewed briefly here, indicate that at least a part of cardiovascular benefits of 17 beta-estradiol can be attributed to the direct effect of the ovarian sex steroid hormone on vascular endothelial cells. Maintenance and upregulation of endothelial nitric oxide production and suppression of EDCF generation by 17 beta-estradiol may play an important role in preventing or reversing endothelial dysfunction, associated with atherosclerosis, hypertension and other cardiovascular diseases. Stimulation of angiogenesis (especially collateral vessel formation in ischemic tissues) by the ovarian steroid hormone could be beneficial in coronary artery disease, peripheral vascular disease, cerebral ischemia (stroke) and congestive heart failure. Despite these indisputable beneficial effects, several key questions remain to be answered in the future, including the better understanding of the apparently opposite effects of estrogen on prevention of cardiovascular disease vs. treatment of existing disease.

Anti-atherosclerotic effect of beta-blocker with nitric oxide-releasing action on the severe atherosclerosis

It is not completely understood whether nitric oxide donors and beta-adrenoceptor antagonists have anti-atherosclerotic effects. The anti-atherosclerotic effects of beta-adrenergic receptor antagonists and nitric oxide donors on severe atherosclerosis induced by cholesterol and inhibition of nitric oxide synthesis were determined. Six groups of New Zealand white male rabbits were treated for 10 weeks, under the following regimens: group I: high-cholesterol diet (HCD) (standard diet plus 0.5% cholesterol); group II: HCD plus N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase; group III: HCD plus L-NAME and isosorbide dinitrate; group IV: HCD plus L-NAME and nitroglycerin; group V: HCD plus L-NAME and nipradilol (beta-blocker with nitric oxide-releasing action); and group VI: HCD plus L-NAME and atenolol (beta-blocker). Serum lipid levels did not differ among the six groups. Blood pressure and heart rates were slightly decreased in groups V and VI. The atherosclerotic area and aortic cholesterol increased in L-NAME-treated animals but not in animals in group V. The endothelium-dependent relaxations and basal nitric oxide release were impaired in the L-NAME treatment group, though not in group V, in comparison with those in group I. cGMP in the aorta was increased in groups III, IV, and V as compared with that in group II. Endothelial nitric oxide synthase mRNA was decreased in the aortae of L-NAME-treated rabbits and increased in aortae in group V, in comparison with that in group I. Conclusively, nipradilol, beta-blocker with nitric oxide-releasing action, in contrast to the other beta-blockers and nitric oxide donors, showed a successful anti-atherosclerotic effect through the restoration of nitric oxide bioavailability and possible interaction with oxygen radicals.

Estrogen and vascular function

The effects of estrogen on the female reproductive system are well known. In contrast, comparatively recent research has demonstrated that estrogen also exerts specific effects on the cardiovascular system--particularly the vasculature. This review summarizes some of the current ideas of how estrogen regulates and modulates vascular function, and focuses primarily on potential mechanisms of estrogen-induced vasodilation. Although many studies indicate estrogen exerts beneficial effects on the circulatory system, the overall conclusions from clinical studies remain somewhat equivocal. In contrast, it is clear that estrogen reduces atherosclerosis by reducing low-density lipoproteins (LDL) and inflammatory processes in the vasculature, and may also act as an antioxidant; however, these effects account for only a portion of the total cardiovascular benefit of estrogen. Estrogen is also a vasodilator and hypotensive agent, and can induce vascular relaxation by stimulating release of endothelium-derived vasodilatory substances (e.g., nitric oxide [NO]) or by acting directly on the vascular smooth muscle (VSM). Recent evidence indicates that calcium and potassium channels in VSM cells play an important role in mediating estrogen-induced relaxation of many vascular beds, but elucidating the signal transduction mechanisms coupling estrogen receptor (ER alpha and/or ER beta) activation to generation of second messengers and effector mechanisms remains an area of intense study. Not surprisingly, it is becoming apparent that the molecular basis of estrogen's influence on vascular function is multifactorial. A better understanding of these signaling mechanisms should lead to the development of powerful therapeutic agents which can maximize the many beneficial effects of estrogen action, while helping minimize the harmful (and sometimes lethal) side effects.

Selected contribution: Effects of gender on reduced-size liver ischemia and reperfusion injury

Hepatic resection with concomitant periods of ischemia and reperfusion (I/R) is a common occurrence in resectional surgery as well as reduced-size liver transplantation (e.g., split liver or living donor transplantation). However, the I/R induced by these types of surgical manipulations may impair liver regeneration, ultimately leading to liver failure. The objectives of the study were to develop a murine model of reduced-size liver I/R and assess the role of gender in this model of hepatocellular injury. We found that 100% of female mice survived the surgery indefinitely, whereas all male mice had greater initial liver injury and died within 5 days after surgery. The protective effect observed in females appeared to be due to ovarian 17beta-estradiol, as ovariectomy of females or administration of a selective estrogen antagonist to female mice resulted in enhanced liver injury and greater mortality following reduced-size liver I/R. Conversely, 17beta-estradiol-treated male mice exhibited less hepatocellular damage and survived indefinitely. Taken together, these data demonstrate an estrogen-mediated protective pathway(s) that limits or attenuates hepatocellular injury induced by reduced-size liver I/R.

Gender differences and antioxidant treatment affect aortic reactivity in short-term diabetic rats

Diabetes is associated with gender-specific macrovascular complications arising from increased oxidant stress in the vascular wall. In this study, male and female rats were treated with two structurally unrelated drugs sharing antioxidant properties, lercanidipine and Leucoselect (both 3 mg/kg/day), for 1 week starting 1 day after streptozotocin-diabetes induction. Concentration-response curves to L-nitroarginine methylester (L-NAME), superoxide dismutase and acetylcholine in aortic rings showed significantly greater nitric oxide-mediated relaxation in female compared with male non-diabetic rats. Diabetes increased contractility to noradrenaline and L-NAME in both genders, whereas relaxation to acetylcholine and iloprost were significantly attenuated in females only. Treatment with lercanidipine and Leucoselect restored, at least in part, responses to noradrenaline, acetylcholine and iloprost without affecting those to L-NAME and sodium nitroprusside. Unexpectedly, both drugs impaired superoxide dismutase response in female tissues. In conclusion, female rat aorta is markedly exposed to short-term diabetic vascular injury, which may be prevented by antioxidant treatment.

Acute gender-specific hemodynamic and inotropic effects of 17beta-estradiol on rats

Estrogen has cardioprotective effects. In addition to beneficial effects on lipid metabolism, estrogen affects the vascular tone and may reduce endothelial dysfunction. In the present study, we examined acute gender-specific hemodynamic and inotropic effects of 17beta-estradiol (17beta-E) versus the control situation in open-chest rats. In addition to measurements in the intact circulation, myocardial function was examined on the basis of isovolumic registration independent of peripheral vascular effects. Regarding the dose-dependent and gender-specific effects of 17beta-E, in female rats, 17beta-E (50, 100, or 200 ng/kg) increased cardiac output (CO) (26%, 43%, and 59% versus control animals) as a result of reduction in total peripheral resistance (TPR) (-13%, -18%, and -24%) without any effect on myocardial contractility (isovolumic left ventricular systolic pressure, -1%, 0%, and -6%). These vascular effects are less pronounced in male rats (for 200 ng/kg 17beta-E: CO, 34%; TPR, -14%). We investigated gender-specific effects of 200 ng/kg 17beta-E after pretreatment with the estrogen receptor (ER) antagonist ICI 182,780. ER blockade reduced the effects of estrogen in female rats (CO, 29%; TPR, -17%) and male rats (CO, 19%; TPR, -11%). Regarding the effects of 200 ng/kg 17beta-E after pretreatment with N(G)-nitro-L-arginine methyl ester, NO synthesis inhibition completely prevented the acute vascular effects of estrogen in female rats (CO, -4%; TPR, 1%). In addition, immunohistochemical staining revealed no gender-specific differences of the vascular ER distribution. 17beta-E caused an acute dose-dependent and gender-specific reduction in the afterload. ERs are involved in both genders in this vasodilative effect that is mediated by NO. This NO-mediated effect may explain in part the cardioprotective effect of estrogen.

Sex differences and the effects of sex hormones on hemostasis and vascular reactivity

Thrombus formation and vasospasm are involved in the initiation of acute ischemic events in the heart. Gender differences in persons with coronary artery disease and the incidence of myocardial ischemia have been clearly documented. In addition, it is well established that sex hormones influence the risk of developing coronary artery disease. Epidemiologic studies suggest that estrogen may exert a protective effect, yet the results of recently completed and ongoing prospective trials of estrogen and hormone (estrogen + progesterone) replacement suggest that these hormones can increase thrombotic events in postmenopausal women. This review focuses on sex (gender) differences in hemostasis and vascular reactivity and on the influence that sex hormones have on these physiologic systems. This review takes the novel approach of focusing on sex differences in hemostasis and vascular reactivity in healthy premenopausal women and men of a similar age. By comparing men and women in this age group, the confounding issues of age, pathology, or decline in sex hormone levels are avoided. Animal and in vitro investigations pertinent to examining potential cellular mechanism(s) of sex hormones in mediating these sex differences are discussed. We assume there is a relationship between the normal physiologic and pathologic effects of sex hormones; elucidating sex differences in normal cardiovascular function will help clarify the basis for sex differences in the incidence and manifestations of coronary heart disease and will aid in the future development of gender-specific therapies for cardiovascular disease.

Protective effects of estrogen on gender-specific development of diet-induced hypertension

Dietary and humoral factors are thought to be involved in the development of hypertension. This study investigated the interaction between diet and gonadal hormone status in the development and reversibility of hypertension. Normal male and female and ovariectomized (OVX) female Fischer rats were placed on either a high-fat (primarily saturated), refined carbohydrate (sucrose) (HFS) or a low-fat, complex carbohydrate (LFCC) diet at 2 mo of age, and body weight and systolic blood pressure (BP) were measured. Male and OVX female rats were initially on the diets for 7 mo, whereas normal female rats were on the diets for 2 yr. After this initial phase, a group of rats from each of the normal HFS groups were converted to the LFCC diet for a period of 1 mo (males) and 2 mo (females). The OVX females were subcutaneously implanted with a 0.5-mg estradiol (E2) pellet for 1 mo. A significant rise in arterial BP occurred within 12 mo in female and only 2 mo in male rats on the HFS diet, exceeding 140 mmHg after 24 and 7 mo, respectively. Conversion from the HFS to the LFCC diet led to a normalization of BP in both female and male rats. HFS diet-induced hypertension was accelerated by OVX in female rats, approaching the pattern seen in male rats. The effect of OVX was completely reversed by E2 replacement. BP did not significantly change in any of the LFCC groups at any time point, and E2 replacement had no effect on BP in the OVX LFCC group. All HFS groups had significantly greater body weight, with differences occurring sooner in the male and OVX rats compared with the female rats. Diet modification resulted in a partial but significant reduction of body weight, but E2 replacement did not. These results demonstrate that long-term consumption of HFS diet induces hypertension in both genders and is reversible by diet modification. Hypertension is significantly delayed in females with functional ovaries. This protection is lost by OVX and restored by estrogen replacement. Thus hormone status contributes to the delayed onset of diet-induced hypertension in females compared with males.

Estrogen replacement therapy in postmenopausal women augments reactive hyperemia in the forearm by reducing angiotensin converting enzyme activity

The precise mechanism of the vasoprotective effect of estrogen replacement therapy in postmenopausal women is not fully understood. The present study sought to determine the role of nitric oxide (NO) and angiotensin-converting enzyme (ACE) in the vasodilator response of the forearm vessels induced by estrogen administration to postmenopausal women. Subjects were divided into two groups. One group received conjugated equine estrogen (0.625 mg daily) orally for 3 months (n=26), while the other received no treatment (control group, n=10). Forearm blood flow was measured by strain-gauge plethysmography. The concentrations of nitrite/nitrate (metabolites of NO), ACE activity, and lipid parameters were measured. Basal forearm blood flow, body weight, blood pressure, and heart rate were similar at baseline in both groups. After 3 months of estrogen administration, the maximal forearm blood flow response during reactive hyperemia and the serum level of nitrite/nitrate each showed a significant increase over baseline values: from 23.6+/-2.0 to 36.5+/-3.1 ml/min per 100 ml tissue (P<0.01), and from 24.8+/-2.3 to 38.6+/-3.6 micromol/l (P<0.01), respectively. Plasma levels of ACE activity were significantly reduced from baseline after 3 months of estrogen treatment (from 12.2+/-0.6 to 10.9+/-0.6 IU/l, P<0.01). No changes were seen in controls. The change in forearm blood flow after sublingual nitroglycerin was similar at baseline versus after 3 months of estrogen administration. The increase in the serum level of nitrite/nitrate after 3 months of estrogen therapy showed a significant inverse correlation (r=0.52, P<0.01) with the reduction in the plasma level of ACE activity. There was no significant correlation between the increase in serum nitrite/nitrate and any change in serum lipids, blood pressure, or other parameters. The administration of oral estrogen to postmenopausal women for 3 months increased the NO-mediated forearm endothelium-dependent vasodilatation. This was likely due, at least in part, to ACE inhibition. The latter may be one mechanism by which ERT provides its well-known cardiovascular benefit.

Hypopituitarism and atherosclerosis

In the last decade, retrospective cohort data has provided evidence of premature atherosclerosis in patients with hypopituitarism which may account for the recently observed increased death rate from vascular events in these patients. The exact mechanism(s) for such propensity to atherosclerotic vascular disease is not yet completely clear. It is possible that hormonal factors may be the initiating mechanisms with subsequent secondary metabolic abnormalities acting as risk factors for development of atherosclerosis. This seems to be more evident in female hypopituitary patients compared with their male counterparts. Female patients have higher frequency and more pronounced abnormalities of various risk factors as well as surrogate markers of early vascular disease. This may explain why morbidity and mortality in women is in excess of men in retrospective epidemiological studies. Addressing abnormal hormonal factors, especially in females, is a primary objective in managing these patients both in the clinical arena as well as in trials designed to reduce the risk of atherosclerotic vascular disease in these patients. While short-term growth hormone treatment may ameliorate some of the vascular risk factors and improve endothelial function, it remains to be shown whether this translates into long-term reduction in morbidity and mortality from vascular, especially cerebrovascular, disease.

Effect of estrogen replacement therapy on distribution of myocardial blood flow in female anesthetized rabbits

Estrogen replacement therapy reduces risk of cardiovascular events by altering coronary vasoregulation and distribution of blood flow. Vessel reactivity and blood flow distribution were assessed in anesthetized female rabbits in the following groups: 1) sham, 2) ovariectomy, 3) ovariectomy + 17beta-estradiol, and 4) ovariectomy + dehydroepiandrosterone. After a 2-wk treatment, cardiac hemodynamics, vascular reserve, and blood flow were evaluated during the following infusions: 1) NaCl, or vehicle (0.5 ml/min), 2) acetylcholine (2 mg/kg), 3) isoproterenol (2 mg. kg(-1). min(-1)), and 4) chromonar (8 mg/kg). In hearts from ovariectomized rabbits, autoregulatory blood flow was preserved despite lower diastolic perfusion pressures (55 +/- 8 vs. 64 +/- 8 mmHg in sham) and rate-pressure product (14.4 +/- 0.8 vs. 19.3 +/- 0.8 beats/min. mmHg x 10(-3)). Estrogen replacement therapy restored coronary pressure and reserve, and all drugs increased vascular conductance. In conclusion, in hearts from ovariectomized rabbits, vascular reserve declined because coronary pressure was lower; however, blood flow was preserved at a higher level than expected for oxygen demand. Estrogen replacement therapy restores myocardial oxygen supply-demand indices and returns coronary pressure-flow data to levels observed in animals with intact ovaries.

High-density lipoprotein binding to scavenger receptor-BI activates endothelial nitric oxide synthase

Atherosclerosis is the primary cause of cardiovascular disease, and the risk for atherosclerosis is inversely proportional to circulating levels of high-density lipoprotein (HDL) cholesterol. However, the mechanisms by which HDL is atheroprotective are complex and not well understood. Here we show that HDL stimulates endothelial nitric oxide synthase (eNOS) in cultured endothelial cells. In contrast, eNOS is not activated by purified forms of the major HDL apolipoproteins ApoA-I and ApoA-II or by low-density lipoprotein. Heterologous expression experiments in Chinese hamster ovary cells reveal that scavenger receptor-BI (SR-BI) mediates the effects of HDL on the enzyme. HDL activation of eNOS is demonstrable in isolated endothelial-cell caveolae where SR-BI and eNOS are colocalized, and the response in isolated plasma membranes is blocked by antibodies to ApoA-I and SR-BI, but not by antibody to ApoA-II. HDL also enhances endothelium- and nitric-oxide-dependent relaxation in aortae from wild-type mice, but not in aortae from homozygous null SR-BI knockout mice. Thus, HDL activates eNOS via SR-BI through a process that requires ApoA-I binding. The resulting increase in nitric-oxide production might be critical to the atheroprotective properties of HDL and ApoA-I.

HMG-CoA reductase inhibitor stabilizes rabbit atheroma by increasing basal NO and decreasing superoxide

Male rabbits fed a 0.5% cholesterol diet for 8 wk were divided into three groups. Group 1 was hypercholesterolemic; group 2 was fed a regular diet for an additional 12 wk; and group 3 was fed a regular diet with simvastatin (5 mg x kg(-1) x day(-1)). Simvastatin treatment reduced the atherosclerotic area and total and esterified cholesterol concentrations in the thoracic aorta. Tone-related basal nitric oxide (NO) release was highest in group 3. Acetylcholine-induced, NO-dependent relaxation was improved in group 3 compared with group 2. Amount of endothelial nitric oxide synthase (eNOS) mRNA in vessels increased in group 1, compared with normal aorta, and decreased in group 2; however, it did not decrease in group 3. The amount of O released from vessels increased in group 1 and group 2 compared with normal rabbits; however, it decreased in group 3, especially in the endothelial cells. Peroxynitrite determined by nitrotyrosine staining decreased in group 3. Additionally, the arteries of rabbits fed a regular diet with or without simvastatin were investigated. The aorta from simvastatin-treated group showed increase of tone-related basal NO release and eNOS mRNA and decrease of O release. Taken together, upregulation of eNOS and decrease of O treatment were observed in vivo in the process of the sufficient stabilization of atheroma following simvastatin.

Sex hormone modulation of serotonin-induced coronary vasodilation in isolated heart

The present study was designed to evaluate the differences in the coronary vasodilator actions of serotonin (5-HT) in isolated heart obtained from naive or castrated male and female rats that were treated with either estrogen or testosterone. Hearts from 12 groups of rats were used: male and female naive animals, castrated, castrated and treated with 17beta-estradiol (0.5 microg kg(-1) day(-1)) for 7 or 30 days, and castrated and treated with testosterone (0.5 mg kg(-1) day(-1)) for 7 or 30 days. After treatment, the vascular reactivity of the coronary bed was evaluated. Baseline coronary perfusion pressure (CPP) was determined and dose-response curves to 5-HT were generated. Baseline CPP differed between male (70 +/- 6 mmHg, N = 10) and female (115 +/- 6 mmHg, N = 12) naive rats. Maximal 5-HT-induced coronary vasodilation was higher (P<0.05) in naive female than in naive male rats. In both sexes, 5-HT produced endothelium-dependent coronary vasodilation. After castration, there was no significant difference in baseline CPP between hearts obtained from male and female rats (75 +/- 7 mmHg, N = 8, and 83 +/- 5 mmHg, N = 8, respectively). Castration reduced the 5-HT-induced maximal vasodilation in female and male rats (P<0.05). Estrogen treatment of castrated female rats restored (P<0.05) the vascular reactivity. In castrated male rats, 30 days of estrogen treatment increased (P<0.05) the responsiveness to 5-HT. The endothelium-dependent coronary vasodilator actions of 5-HT are greater in female rats and are modulated by estrogen. A knowledge of the mechanism of action of estrogen on coronary arteries could aid in the development of new therapeutic strategies and potentially decrease the incidence of cardiovascular disease in both sexes.