Estrogen replacement reduces age-associated remodeling in rat mesenteric arteries

Understanding the Role of Sex Hormones in Cardiovascular Kidney Metabolic Syndrome: Toward Personalized Therapeutic Approaches

Cardiovascular kidney metabolic (CKM) syndrome represents a complex interplay of cardiovascular disease (CVD), chronic kidney disease (CKD), and metabolic comorbidities, posing a significant public health challenge. Gender exerts a critical influence on CKM syndrome, affecting the disease severity and onset through intricate interactions involving sex hormones and key physiological pathways such as the renin-angiotensin system, oxidative stress, inflammation, vascular disease and insulin resistance. It is widely known that beyond the contribution of traditional risk factors, men and women exhibit significant differences in CKM syndrome and its components, with distinct patterns observed in premenopausal women and postmenopausal women compared to men. Despite women generally experiencing a lower incidence of CVD, their outcomes following cardiovascular events are often worse compared to men. The disparities also extend to the treatment approaches for kidney failure, with a higher prevalence of dialysis among men despite women exhibiting higher rates of CKD. The impact of endogenous sex hormones, the correlations between CKM and its components, as well as the long-term effects of treatment modalities using sex hormones, including hormone replacement therapies and gender-affirming therapies, have drawn attention to this topic. Current research on CKM syndrome is hindered by the scarcity of large-scale studies and insufficient integration of gender-specific considerations into treatment strategies. The underlying mechanisms driving the gender disparities in the pathogenesis of CKM syndrome, including the roles of estrogen, progesterone and testosterone derivatives, remain poorly understood, thus limiting their application in personalized therapeutic interventions. This review synthesizes existing knowledge to clarify the intricate relationship between sex hormones, gender disparities, and the progression of CVD within CKM syndrome. By addressing these knowledge gaps, this study aims to guide future research efforts and promote tailored approaches for effectively managing CKD syndrome.

Estrogen-mediated mechanisms in hypertension and other cardiovascular diseases

Cardiovascular disease (CVD) is the leading cause of death globally for men and women. Premenopausal women have a lower incidence of hypertension and other cardiovascular events than men of the same age, but diminished sex differences after menopause implicates 17-beta-estradiol (E2) as a protective agent. The cardioprotective effects of E2 are mediated by nuclear estrogen receptors (ERα and ERβ) and a G protein-coupled estrogen receptor (GPER). This review summarizes both established as well as emerging estrogen-mediated mechanisms that underlie sex differences in the vasculature during hypertension and CVD. In addition, remaining knowledge gaps inherent in the association of sex differences and E2 are identified, which may guide future clinical trials and experimental studies in this field.

Age and Menopause Effects on Ocular Compliance and Aqueous Outflow

Purpose

Glaucoma is the second leading cause of blindness worldwide. Recent work suggests that estrogen and the timing of menopause play a role in modulating the risk of developing glaucoma. Menopause is known to cause modest changes in intraocular pressure; yet, whether this change is mediated through the outflow pathway remains unknown. Menopause also affects tissue biomechanical properties throughout the body; however, the impact of menopause on ocular biomechanical properties is not well characterized.

Methods

Here, we simultaneously assessed the impact of menopause on aqueous outflow facility and ocular compliance, as a measure of corneoscleral shell biomechanics. We used young (3-4 months old) and middle-aged (9-10 months old) Brown Norway rats. Menopause was induced by ovariectomy (OVX), and control animals underwent sham surgery, resulting in the following groups: young sham (n = 5), young OVX (n = 6), middle-aged sham (n = 5), and middle-aged OVX (n = 5). Eight weeks postoperatively, we measured outflow facility and ocular compliance.

Results

Menopause resulted in a 34% decrease in outflow facility and a 19% increase in ocular compliance (P = 0.011) in OVX animals compared with sham controls (P = 0.019).

Conclusions

These observations reveal that menopause affects several key physiological factors known to be associated with glaucoma, suggesting that menopause may contribute to an increased risk of glaucoma in women.

Role of miRNA in the Regulatory Mechanisms of Estrogens in Cardiovascular Ageing

Cardiovascular diseases are a worldwide health problem and are the leading cause of mortality in developed countries. Together with experimental data, the lower incidence of cardiovascular diseases in women than in men of reproductive age points to the influence of sex hormones at the cardiovascular level and suggests that estrogens play a protective role against cardiovascular disease and that this role is also modified by ageing. Estrogens affect cardiovascular function via their specific estrogen receptors to trigger gene expression changes at the transcriptional level. In addition, emerging studies have proposed a role for microRNAs in the vascular effects mediated by estrogens. miRNAs regulate gene expression by repressing translational processes and have been estimated to be involved in the regulation of approximately 30% of all protein-coding genes in mammals. In this review, we highlight the current knowledge of the role of estrogen-sensitive miRNAs, and their influence in regulating vascular ageing.

Resistance training and caloric restriction prevent systolic blood pressure rise by improving the nitric oxide effect on smooth muscle and morphological changes in the aorta of ovariectomized rats

In this study, we investigated the effects of resistance training (RT), caloric restriction (CR), and the association of both interventions in aortic vascular reactivity and morphological alterations, matrix metalloproteinase-2 (MMP-2) activity, insulin resistance and systolic blood pressure (SBP) in ovariectomized rats. Fifty female Holtzman rats were subjected to ovariectomy and Sham surgery and distributed into the following groups: Sham-sedentary, ovariectomized-sedentary, ovariectomized-resistance training, ovariectomized-caloric restriction, and ovariectomized-resistance training and caloric restriction groups. RT and 30% CR protocols were performed for 13 weeks. Analyses were conducted to evaluate the following: acetylcholine and sodium nitroprusside-induced relaxation of aortic rings, MMP-2 activity, insulin tolerance test, highlighting of the aorta wall cross-sectional area by hematoxylin-eosin stain, aorta vessel remodeling and SBP. We observed that ovariectomy decreased the potency of dependent and independent endothelium relaxation and MMP-2 activity, prevented insulin resistance, promoted aorta vessel remodeling in the cross-sectional area, and promoted the media-to-lumen ratio, the collagen content, and the alteration of the structure and elastic fibers of the vessel. The effects of the ovariectomy could contribute to SBP increases. However, the association of exercise and diet improved the relaxation potency in dependent and independent endothelium relaxation, elevated MMP-2 activity, ameliorate insulin sensitivity, increased the aorta cross-sectional area and media-to-lumen ratio, decreased collagen content and promoted histological parameters of the aorta vessel wall, preventing the increase of SBP.

CONCLUSION

Our study revealed that the RT and CR separately, and even associatively, improved vascular function, activated MMP-2, and produced a beneficial hypertrophic remodeling, preventing the elevation of SBP in ovariectomized rats.

New insights into arterial stiffening: does sex matter?

This review discusses sexual dimorphism in arterial stiffening, disease pathology interactions, and the influence of sex on mechanisms and pathways. Arterial stiffness predicts cardiovascular mortality independent of blood pressure. Patients with increased arterial stiffness have a 48% higher risk for developing cardiovascular disease. Like other cardiovascular pathologies, arterial stiffness is sexually dimorphic. Young women have lower stiffness than aged-matched men, but this sex difference reverses during normal aging. Estrogen therapy does not attenuate progressive stiffening in postmenopausal women, indicating that currently prescribed drugs do not confer protection. Although remodeling of large arteries is a protective adaptation to higher wall stress, arterial stiffening increases afterload to the left ventricle and transmits higher pulsatile pressure to smaller arteries and target organs. Moreover, an increase in aortic stiffness may precede or exacerbate hypertension, particularly during aging. Additional studies are needed to elucidate the mechanisms by which females are protected from arterial stiffness to provide insight into its mechanisms and, ultimately, therapeutic targets for treating this pathology.

Relationship between matrix metalloproteinase-9 and common carotid artery intima media thickness

Atherosclerosis causes significant morbidity and mortality. Carotid intima media thickness (IMT) predicts future ischaemic strok e incidence. Matrix metalloproteinases (MMPs) play a considerable role in atherosclerosis and hold therapeutic promise as well. To investigate the relationship between serum level of matrix metalloproteinase-9 (MMP-9) and common carotid artery intima media thickness (CCA-IMT) in patients with ischaemic stroke and asymptomatic subjects. Thirty patients with a previous ischaemic stroke and 30 asymptomatic volunteers were recruited. Assessment of vascular risk factors, serum level of MMP-9 and CCA-IMT on both sides was performed. The IMT of both CCAs correlated positively with the serum MMP-9 level in asymptomatic subjects (p = 0.000), even after adjustment for other risk factors. In the patients group, this positive correlation was significant for the right but not for the left CCA (right CCA: p = 0.023, left CCA: p = 0.0284). Fasting blood sugar correlated positively with serum levels of MMP-9 in asymptomatic subjects (p = 0.005) but did not correlate positively in patients. There was no significant correlation between MMP-9 and age or other investigated laboratory risk factors in either the patient or asymptomatic groups. MMP-9 is positively correlated with CCA-IMT both in stroke patients and asymptomatic subjects. This may indicate that MMP-9 is a possible therapeutic target for stroke prevention.

Estrogen Replacement Therapy in Ovariectomized Nonpregnant Ewes Stimulates Uterine Artery Hydrogen Sulfide Biosynthesis by Selectively Up-Regulating Cystathionine β-Synthase Expression

Estrogens dramatically dilate numerous vascular beds with the greatest response in the uterus. Endogenous hydrogen sulfide (H2S) is a potent vasodilator and proangiogenic second messenger, which is synthesized from L-cysteine by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). We hypothesized that estrogen replacement therapy (ERT) selectively stimulates H2S biosynthesis in uterine artery (UA) and other systemic arteries. Intact and endothelium-denuded UA, mesenteric artery (MA), and carotid artery (CA) were obtained from ovariectomized nonpregnant ewes (n = 5/group) receiving vehicle or estradiol-17β replacement therapy (ERT). Total RNA and protein were extracted for measuring CBS and CSE, and H2S production was determined by the methylene blue assay. Paraffin-embedded UA rings were used to localize CBS and CSE proteins by immunofluorescence microscopy. ERT significantly stimulated CBS mRNA and protein without altering CSE mRNA or protein in intact and denuded UA. Quantitative immunofluorescence microscopic analyses showed CBS and CSE protein localization in endothelium and smooth muscle and confirmed that ERT stimulated CBS but not CSE protein expression in UA endothelium and smooth muscle. ERT also stimulated CBS, but not CSE, mRNA and protein expression in intact and denuded MA but not CA in ovariectomized ewes. Concomitantly, ERT stimulated UA and MA but not CA H2S production. ERT-stimulated UA H2S production was completely blocked by a specific CBS but not CSE inhibitor. Thus, ERT selectively stimulates UA and MA but not CA H2S biosynthesis by specifically up-regulating CBS expression, implicating a role of H2S in estrogen-induced vasodilation and postmenopausal women's health.

Effects of androgens on cardiovascular remodeling

Androgens, the male sex hormones, exert various biological effects on many target organs through the transcriptional effects of the nuclear androgen receptor (AR). ARs are expressed not only in classical target organs, such as the brain, genital organs, bone, and skeletal muscles, but also in the cardiovascular system. Because the female sex hormones estrogens are well-known to protect against cardiovascular disease, sex has been considered to have a significant clinical impact on cardiovascular mortality. However, the influence of androgens on the cardiovascular system has not been fully elucidated. To clarify this issue, we analyzed the effects of administration of angiotensin II and doxorubicin, an anticancer agent, in a loading model in male wild-type and AR-deficient mice. In this review, we focus on the actions of androgens as potential targets for the prevention of cardiovascular diseases in males.

Vascular Aging in Women: is Estrogen the Fountain of Youth?

Aging is associated with structural and functional changes in the vasculature, including endothelial dysfunction, arterial stiffening and remodeling, impaired angiogenesis, and defective vascular repair, and with increased prevalence of atherosclerosis. Cardiovascular risk is similar for older men and women, but lower in women during their fertile years. This age- and sex-related difference points to estrogen as a protective factor because menopause is marked by the loss of endogenous estrogen production. Experimental and some clinical studies have attributed most of the protective effects of estrogen to its modulatory action on vascular endothelium. Estrogen promotes endothelial-derived NO production through increased expression and activity of endothelial nitric oxide synthase, and modulates prostacyclin and thromboxane A(2) release. The thromboxane A(2) pathway is key to regulating vascular tone in females. Despite all the experimental evidence, some clinical trials have reported no cardiovascular benefit from estrogen replacement therapy in older postmenopausal women. The "Timing Hypothesis," which states that estrogen-mediated vascular benefits occur only before the detrimental effects of aging are established in the vasculature, offers a possible explanation for these discrepancies. Nevertheless, a gap remains in current knowledge of cardiovascular aging mechanisms in women. This review comprises clinical and experimental data on the effects of aging, estrogens, and hormone replacement therapy on vascular function of females. We aim to clarify how menopause and aging contribute jointly to vascular aging and how estrogen modulates vascular response at different ages.

Estrogen activates matrix metalloproteinases-2 and -9 to increase beta amyloid degradation

Estrogen is known to affect different aspects of β-amyloid (Aβ) synthesis and degradation. The present work was undertaken to evaluate specifically whether matrix metalloproteinases (MMP) -2 and -9 are involved in Aβ degradation induced by estrogen and whether this is relevant to estrogen-induced neuroprotection. In SH-SY5Y human neuroblastoma cells, 10 nM 17β-estradiol (17β-E2) increases mRNA and intracellular protein expression of MMP-2 and -9, as well as the levels of the active forms of both enzymes released in the medium. Specificity of the effect is proved by prevention with the estrogen receptor (ER) antagonist ICI 182,780 (1 μM) and involvement of the ERα subtype is confirmed by the use of selective ERα or ERβ agonists (PPT, DPN) and antagonists (MPP, PHTPP). 17β-E2 significantly increases the degradation of Aβ, either transferred with the conditioned medium of H4-APPSw human neuroglioma cells, engineered to overproduce Aβ(1-40) and Aβ(1-42), or exogenously added as 2 μM Aβ(1-42). Both these effects are completely prevented by preexposure to the broad spectrum MMP inhibitor GM6001 (5 μM). Importantly, the 17β-E2-induced rescue of neuroblastoma cells challenged with 2 μM Aβ(1-42), an effect prevented by ICI 182,780 (1 μM), is mediated by MMPs, as it appears significantly reduced by GM6001 (5 μM) as well as by both MMP-2 (200 nM) and MMP-9 (200nM) selective inhibitors. In conclusion, the present study shows for the first time that MMP-2 and -9 give a main contribution to estrogen's neuroprotective effect.

Ovariectomy in aged versus young rats augments matrix metalloproteinase-mediated vasoconstriction in mesenteric arteries

OBJECTIVE

Ovarian deficiency is known to undermine vasoprotective mechanisms and accelerate cardiovascular disease in postmenopausal women. In a rat model of menopause (aged ovariectomized [Ovx] rats), we recently revealed a vasoconstrictor pathway mediated by matrix metalloproteinases (MMPs) via cleavage of big endothelin-1 (ET-1). However, the specific impact of aging and/or Ovx on this pathway remains unknown. We hypothesized that aging exacerbates MMP-mediated vasoconstriction in an ovary-deficient state.

METHODS

Young and aged female Sprague-Dawley rats, either intact or Ovx, were assessed for MMP-dependent vasoreactivity. Dose responses to big ET-1 in the absence or presence of an MMP inhibitor (GM6001) were tested on small mesenteric arteries using a pressure myograph system. MMP levels in the vascular tissue were measured by gelatin zymography.

RESULTS

Both young Ovx and aged Ovx animals demonstrated a similar increase in the vasoconstriction to big ET-1 compared with the age-matched intact groups. MMP inhibition attenuated big ET-1 response in both Ovx groups and aged controls, but this effect was more pronounced in aged Ovx arteries (area under the curve reduction, 3.8 +/- 0.6 units in aged Ovx rats vs 1.5 +/- 0.5 units in young Ovx rats or 1.8 +/- 0.6 units in aged intact rats; P < 0.05). MMP-2 activity in the vascular tissue increased with age and was further augmented by Ovx.

CONCLUSIONS

Regardless of age, ovarian loss increases vascular reactivity to big ET-1, which is mediated, in part, by MMP. Superimposed with advancing age, ovarian deficiency further increases the proconstrictor role of MMP, which corresponds with higher MMP-2 levels in the aging vessel wall. MMP-mediated vasoconstriction may be a mechanism contributing to vascular dysfunction in postmenopausal women.

Estrogen improves TIMP-MMP balance and collagen distribution in volume-overloaded hearts of ovariectomized females

Our previous studies demonstrate that 17beta-estradiol limits chronic volume overload-induced hypertrophy and improves heart function in ovariectomized rats. One possible cardioprotective mechanism involves the interaction between estrogen, estrogen receptors, and proteins of the extracellular matrix (ECM). The impact of estrogen deficiency and replacement on left ventricular (LV) hypertrophy and ECM protein expression was studied using five female rat groups: intact sham-operated, ovariectomized sham-operated, intact with volume overload, ovariectomized with volume overload, and ovariectomized with volume overload treated with estrogen. After 8 wk, LV protein extracts were evaluated by Western blot analysis for matrix metalloproteinase-2 (MMP-2) and MMP-9, MT1-MMP, tissue inhibitors of MMPs (TIMP)-1, TIMP-2, TIMP-3 and TIMP-4, collagens type I and III, and estrogen receptor alpha and beta expression. MMP proteolytic activity was assessed by zymography. All volume-overloaded groups exhibited LV hypertrophy, which was associated with a loss of interstitial collagen and perivascular fibrosis. After 8 wk of volume overload, 70% of ovariectomized rats developed heart failure, in contrast to only one intact rat. A downregulation of MMP-2, estrogen receptor-alpha (ERalpha), and ERbeta, and upregulation of MMP-9 and MT1-MMP were found in the volume-overloaded hearts of ovariectomized rats. Estrogen treatment improved TIMP-2/MMP-2 and TIMP-1/MMP-9 protein balance, restored ERalpha expression, and prevented MMP-9 activation, perivascular collagen accumulation and development of heart failure. However, estrogen did not fully restore ERbeta expression and did not prevent the increase of MMP-9 expression or loss of interstitial collagen. These results support that estrogen limits undesirable ECM remodeling and LV dilation, in part, through modulation of ECM protein expression in volume-overloaded hearts of ovariectomized rats.

Effect of high soy diet on the cerebrovasculature and endothelial nitric oxide synthase in the ovariectomized rat

High soy (HS) diets are neuroprotective and promote vascular dilatation in the periphery. We hypothesized that an HS diet would promote vascular dilatation in the cerebrovasculature by mimicking estradiol's actions on the endothelial nitric oxide synthase (eNOS) system including increasing eNOS expression and decreasing caveolin-1 expression to increase nitric oxide (NO) production. Ovariectomized rats were fed HS or a soy-free diet (SF)+/-low physiological estradiol (E2) for 4weeks. Neither E2 nor HS altered middle cerebral artery (MCA) structure or vascular responses to acetylcholine, serotonin, or phenylephrine. Estradiol enhanced bradykinin-induced relaxation in an eNOS-dependent manner. Although E2 and HS increased eNOS mRNA expression in the brain and cerebrovasculature, they had no effect on eNOS protein expression or phosphorylation in the MCA. However, E2 decreased caveolin-1 protein in the MCA. In MCAs neither E2 nor HS altered estrogen receptor (ER) alpha expression, but E2 did reduce ER beta levels. These data suggest that HS diets have no effect on vascular NO production, and that E2 may modulate basal NO production by reducing the expression of caveolin-1, an allosteric inhibitor of NOS activity. However, the effects of E2 and HS on the cerebrovasculature are small and may not underlie their protective actions in pathological states.

The effect of ovariectomy and estrogen on penetrating brain arterioles and blood-brain barrier permeability

OBJECTIVE

We investigated the effect of estrogen replacement on the structure and function of penetrating brain arterioles (PA) and blood-brain barrier (BBB) permeability.

MATERIALS AND METHODS

Female ovariectomized Sprague-Dawley rats were replaced with estradiol (E(2)) and estriol (E(3)) (OVX + E; N=13) and compared to ovariectomized animals without replacement (OVX; N=14) and intact controls (CTL, proestrous; N=13). Passive and active diameters, percent tone, and passive distensibility of pressurized PA were compared. In addition, BBB permeability to Lucifer Yellow, a marker of transcellular transport, was compared in cerebral arteries.

RESULTS

Ovariectomy increased myogenic tone in PA, compared to CTL, that was not ameliorated by estrogen treatment. Percent tone at 75 mmHg for CTL vs. OVX and OVX + E was 44+/-3% vs. 51+/-1% and 54+/-3% (P<0.01 vs. CTL for both). No differences were found in passive diameters or distensibility between the groups. BBB permeability increased 500% in OVX vs. CTL animals; however, estrogen replacement restored barrier properties: flux of Lucifer Yellow for CTL, OVX, and OVX + E was (ng/mL): 3.4+/-1.2, 20.2+/-5.3 (P<0.01 vs. CTL), and 6.15+/-1.2 (n.s.).

CONCLUSIONS

These results suggest that estrogen replacement may not be beneficial for small-vessel disease in the brain, but may limit BBB disruption and edema under conditions that cause it.

Estrogen replacement increases matrix metalloproteinase contribution to vasoconstriction in a rat model of menopause

OBJECTIVE

Estrogen deficiency has been implicated in the pathogenesis of postmenopausal hypertension; yet hormone replacement therapy has controversial effects on the cardiovascular risk. Surprisingly, the effects of estrogen in the aging vascular system have been understudied. Aging is associated with vascular inflammation [elevated tumor necrosis factor (TNF)]. TNF is an activator of matrix metalloproteinases (MMPs) that can have vasoactive properties by specific cleavage of big endothelin-1 (ET-1). We hypothesized that MMPs are downstream mediators of vascular dysfunction in aging/estrogen deficiency.

METHODS

Aged rats (12 months) were ovariectomized (to model a menopausal phenotype) and treated with placebo, estrogen or TNF inhibitor (etanercept) for 4 weeks. Reactivity of resistance mesenteric arteries was evaluated on pressure arteriograph and vascular MMP activity measured by gelatin zymography.

RESULTS

Vasoconstriction to big ET-1 was greater in menopausal (relative to cycling) phenotype, but attenuated with MMP inhibition. Estrogen replacement reduced sensitivity to big ET-1, whereas further increased the role of MMP in the constriction, which was not mediated by TNF. MMP-2 activity in the mesenteric vascular bed was greater in menopausal compared with cycling females, but returned to control levels after estrogen treatment.

CONCLUSIONS

Our study indicates that MMPs are critical modulators of endothelin-mediated vasoconstriction in aging/estrogen deficiency that was not evident in cycling animals. Estrogen replacement is complex: although it reduces MMP expression, estrogen leads to a greater acute MMP modulation of vascular function. Thus, understanding the novel role of estrogen as a regulator of vascular MMPs may provide valuable insights into women's cardiovascular health issues in aging.

Maternal uterine vascular remodeling during pregnancy

Sufficient uteroplacental blood flow is essential for normal pregnancy outcome and is accomplished by the coordinated growth and remodeling of the entire uterine circulation, as well as the creation of a new fetal vascular organ: the placenta. The process of remodeling involves a number of cellular processes, including hyperplasia and hypertrophy, rearrangement of existing elements, and changes in extracellular matrix. In this review, we provide information on uterine blood flow increases during pregnancy, the influence of placentation type on the distribution of uterine vascular resistance, consideration of the patterns, nature, and extent of maternal uterine vascular remodeling during pregnancy, and what is known about the underlying cellular mechanisms.

Prolonged oestrogen treatment does not correlate with a sustained increase in anterior pituitary mitotic index in ovariectomized Wistar rats

Oestrogen is a powerful mitogen that is believed to exert a continuous, dose-dependent trophic stimulus at the anterior pituitary. This persistent mitotic effect contrasts with corticosterone and testosterone, changes in the levels of which induce only transient, self-limiting fluctuations in pituitary mitotic activity. To further define the putative long-term trophic effects of oestrogen, we have accurately analysed the effects of 7 and 28 days oestrogen treatment on anterior pituitary mitotic activity in ovariectomized 10-week-old Wistar rats using both bromodeoxyuridine (BrdU) and timed colchicine-induced mitotic arrest. An oestrogen dose-dependent increase in mitotic index was seen 7 days after the start of treatment as expected, representing an acceleration in gross mitotic activity from 1.7%/day in ovariectomized animals in the absence of any oestrogen replacement to 3.7%/day in the presence of a pharmacological dose of oestrogen (50 mcg/rat per day: approximately 230 mcg/kg per day). Despite continued exposure to high-dose oestrogen and persistence of the increase in pituitary wet weight, the increase in mitotic index was unexpectedly not sustained. After 28 days of high-dose oestrogen treatment, anterior pituitary mitotic index and BrdU-labelling index were not significantly different from baseline. Although a powerful pituitary mitogen in the short term, responsible, presumably, for increased trophic variability in oestrus cycling females, these data indicate that in keeping with other trophic stimuli to the pituitary and in contrast to a much established dogma, the mitotic response to longer-term high-dose oestrogen exposure is transient and is not the driver of persistent pituitary growth, at least in female Wistar rats.

Estrogen deficiency-induced alterations of vascular MMP-2, MT1-MMP, and TIMP-2 in ovariectomized rats

BACKGROUND

Matrix metalloproteinases (MMPs) activity may modulate hypertension-related accumulation of extracellular matrix (ECM) in arteries. We tested whether estrogen deficiency induces alterations of vascular collagen, MMP-2, membrane-type 1-MMP (MT1-MMP), or tissue inhibitor of metalloproteinases-2 (TIMP-2) expression in ovariectomized rats, which may be associated with postmenopausal hypertension.

METHODS

Estrogen deficiency was induced by ovariectomy (Ovx) in female rats. Time-course changes of aortic MMPs protein expression were evaluated. Treatment with tempol or aminoguanidine was used to examine the role of oxidative stress and nitric oxide (NO) on these changes.

RESULTS

The level of the active-form MMP-2 was markedly reduced during 1-4 weeks after Ovx, with a significant increase in collagen accumulation and increased MT1-MMP expression. Although active-form MMP-2 and collagen progressively returned to normal levels, the markedly increased collagen deposition appeared again at 8 weeks and persisted until 12 weeks, followed by induction of MMP-2 and MT1-MMP at 12 weeks. The TIMP-2 level reduced for 2 weeks after Ovx, but soon returned to normal. Treatment with 17beta-estradiol (E(2)), tempol, or aminoguanidine for 6 weeks prevented Ovx-induced blood pressure elevation and apparently reversed the MMPs changes.

CONCLUSIONS

In an initial period, E(2) deficiency induces a reduction of active-form MMP-2 leading to collagen accumulation, and induction of MT1-MMP, which may be a compensatory response to degrade collagen. At a latter stage, the concurrent elevation of active-form MMP-2 and MT1-MMP expression may be adaptive responses to regulate ECM composition in the vascular wall. Oxidative stress and NO contribute to activity modulation of vascular MMPs in Ovx rats.

Functional characterization and sex differences in small mesenteric arteries of the estrogen receptor-β knockout mouse

The role of the estrogen receptor (ER) subtypes in the modulation of vascular function is poorly understood. The aim of this study was to characterize ex vivo the functional properties of small arteries and their response to estrogens in the mesenteric circulation of female and male ER-β knockout mice (β-ERKO) and their wild-type (WT) littermates. Responses to changes in intraluminal flow and pressure were obtained before and after incubation with 17β-estradiol or ER-α agonist propyl-pyrazole-triol (3 h; 10 nM). Cumulative concentration-response curves to acetylcholine, norepinephrine, and passive distensibility were compared with respect to sex and genotype. The collagen and elastin content within the vascular wall and ER expression were also determined. Endothelial morphology was visualized by scanning electron microscopy. 17β-Estradiol and propyl-pyrazole-triol-treated arteries from female β-ERKO and WT mice showed enhanced flow-mediated dilation, but this was not evident in males. Distensibility was decreased in arteries from β-ERKO females. Sex differences in myogenic tone were observed in 17β-estradiol-treated arteries, but were similar between β-ERKO and WT mice. Acetylcholine- and norepinephrine-induced responses were similar between groups and sexes. ER-α was similarly expressed in the endothelium and media of arteries from all groups studied, as well as ER-β in WT animals. Endothelial morphology was similar in arteries from animals of both sexes and genotype; however, arterial elastin content was decreased, and collagen content was increased in β-ERKO male compared with WT male and with β-ERKO female. We suggest that ERs play a sex-specific role in estrogen-mediated flow responses and distensibility, and that deletion of ER-β affects artery structure but only in male animals. Further studies in β-ERKO mice with established hypertension and in α-ERKO mice are warranted.

Effects of ovariectomy and growth hormone administration on body composition and vascular function and structure in old female rats

Aging and estrogen-deprivation induce deleterious effects on body composition and vascular function in females. On the other hand, growth hormone (GH), whose production is reduced by age, exerts several vascular effects. The aim of this study was to investigate the effect of long-term estrogen deprivation and GH administration on body composition, vascular function and structure in aged female rats.

METHODS

Twelve female Wistar rats were ovariectomized at 10 months of age. At 20 months of age, half of the ovariectomized rats were treated with GH for 4 weeks. The remaining ovariectomized rats animals and one group of six intact females were used as control groups. After the treatment period, animals were sacrificed and Specific Gravity Index (SGI) and periuterine fat weigh, as well as vascular reactivity and morphometry in aortic rings, were studied.

RESULTS

No significant differences were found in SGI and periuterine fat weigh between ovariectomized and intact control rats. SGI was significantly increased by GH, and periuterine fat was reduced by the treatment. Dose-dependent relaxing responses to acetylcholine and isoproterenol were significantly diminished in ovariectomized rats as compared with intact animals, and GH treatment improved these responses. Ovariectomized animals showed significantly higher contracting responses to phenylephrine, acetylcholine + L-NAME and angiotensin-I than intact rats, and treatment with GH reduced them significantly. Media cross-sectional area was increased in ovariectomized rats as compared to intact animals, and GH reduced this area, but differences did not reach significance.

CONCLUSION

GH has beneficial effects in body composition and endothelial function in old ovariectomized female rats.

Extracellular matrix integrity: a possible mechanism for differential clinical effects among selective estrogen receptor modulators and estrogens?

Recent gene microarray studies have illustrated heterogeneity in gene expression changes not only between estrogens and selective estrogen receptor modulators (SERMs), but also across different SERM molecules. In ovariectomized rats, this phenomenon was observed with respect to a number of genes involved in collagen turnover and extracellular matrix (ECM) integrity in the uterus and vaginal tissues. Preliminary mechanistic data suggest that these effects on ECM integrity may have relevance in the context of the effect of estrogens and some SERMs to increase the risk of pelvic organ prolapse and the incidence of urinary incontinence in postmenopausal women. Given the pivotal role of ECM integrity and collagen turnover in other tissues and disease states, these processes may provide a fruitful target for future research into the mechanisms for the heterogeneous pharmacology of estrogens and SERMs across different cell types and target tissues.

Age-associated impairment in vasorelaxation to fluid shear stress in the female vasculature is improved by TNF-α antagonism

Aging is associated with alterations in vascular homeostasis, including a reduction in flow-mediated vasodilation, which in women is related to the onset of menopause. We previously found that in female animals, aging is associated with an increase in TNF-α. Thus we investigated the role of in vivo TNF-α inhibition on vascular responses to shear stress in aging female rats. Mesenteric arteries (∼150 μm) were isolated from young (3 mo) and ovariectomized Sprague-Dawley female rats approaching reproductive senescence (12 mo) treated with either placebo or a TNF-α inhibitor (etanercept; 0.3 mg/kg) and were mounted on a pressure myograph system. Vessels were equilibrated at an intraluminal pressure of 60 mmHg and then preconstricted with phenylephrine at ∼70% of their initial diameter. Perfusate flow was increased in steps from 0 to 150 μl/min. Compared with young vessels, aged vessels have a decrease in flow-mediated dilation [maximal dilation (means ± SE): 52 ± 4 vs. 24 ± 15%; P < 0.05], which was improved by TNF-α inhibition. Moreover, in aged vessels maximal dilation to flow was achieved at higher levels of shear stress compared with young vessels. In all groups, flow-mediated dilation was abolished by either endothelial removal or nitric oxide synthase inhibition with NG-nitro-l-arginine methyl ester. However, the modulation by NG-nitro-l-arginine methyl ester was reduced in vessels from aged animals compared with young animals but was improved in the etanercept-treated aged animals. In vivo chronic TNF-α inhibition improves flow-mediated arterial dilation in resistance arteries of aged female animals.

Cardiovascular consequences of life-long exposure to dietary isoflavones in the rat

Dietary soy intake in man is proposed to provide cardiovascular protection, but it is not established whether this property is attributable to the soy protein per se or to associated dietary isoflavones. This investigation aimed to establish whether the dietary isoflavones in soy protein affect cardiovascular function. Ten days prior to mating, male and female Wistar rats were habituated to either a soy based isoflavone rich diet (plasma concentration 1.87 micromol l(-1) isoflavones) or the same diet after isoflavone elution (plasma isoflavone not detectable). Offspring were weaned onto and maintained on the same diet as their dam and sire for 6 months. Blood pressure, and constrictor and dilator responses in the aorta and mesenteric resistance arteries were assessed at 3 and 6 months of age. There was no effect of isoflavone removal from the diet on blood pressure, heart rate, aortic function or mesenteric artery contractile function, at either 3 or 6 months of age. Resistance mesenteric arteries from 6-month-old female rats fed the isoflavone rich diet demonstrated a modest increase in arterial distensibility compared with those fed the depleted diet, and mesenteric arteries from male and female rats fed the isoflavone rich diet showed increased sensitivity to acetylcholine. In summary, the isoflavone content of soy protein has no influence on blood pressure in healthy rats fed a diet based on soy protein, but influences small artery function.

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.

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

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

Aging exacerbates neointimal formation, and increases proliferation and reduces susceptibility to apoptosis of vascular smooth muscle cells in mice

OBJECTIVES

In response to injury, aging mediates exaggerated neointimal formation, the pathologic hallmark of obliterative vascular diseases. We assessed the development of neointima in a model of mechanical vascular injury in aging mice (18 months old) and young mice (2 months old). To investigate the mechanisms by which aging affects neointimal formation, we also carried out a set of in vitro studies to characterize the biologic properties of vascular smooth muscle cells (VSMCs) derived from aging and young mice.

METHODS

Aging and young mice were subjected to wire injury to the carotid artery. Four weeks later injured arteries were harvested, and neointimal formation was histologically assessed. The profiles of angiogenesis-related genes between aortic VSMCs derived from aging and young mice were compared with complementary DNA arrays. Expression of platelet-derived growth factor receptor-alpha (PDGFR-alpha) and proliferation in response to platelet-derived growth factor-BB (PDGF-BB) by VSMCs were assessed. Susceptibility to apoptosis in aging and young VSMCs in response to nitric oxide and serum starvation was investigated. In addition, the level of apoptosis in neointimal VSMCs (by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay) was compared between aging and young animals.

RESULTS

When compared with young mice, aging mice exhibited exaggerated neointimal formation (intima-media ratio, 1.17 +/- 0.57 vs 0.49 +/- 0.16; P < .0001). Aging VSMCs expressed higher levels of PDGFR-alpha (12.0% +/- 2.7% vs 3.2 +/- 0.67%; P = .034) and greater proliferative response (4-fold increase) to PDGF-BB, compared with young VSMCs. However, aging VSMCs were less susceptible to apoptosis when subjected to serum starvation (75% less) and exposure to nitric oxide (50% less). Furthermore, there was more apoptosis in the neointima of young arteries than in their aging counterparts (8.75% +/- 3.3% vs 2.8% +/- 1.9; P = .021).

CONCLUSIONS

Age-dependent increases in PDGFR-alpha may alter VSMC proliferation, and when coupled with resistance to apoptosis could contribute to exaggerated neointima formation in aging animals. Of significance, our findings in the mouse will enable application of abundant molecular tools afforded by this species to further dissect the mechanisms of exaggerated neointimal formation associated with aging.

CLINICAL RELEVANCE

Neointimal formation is the pathologic hallmark of obliterative vascular diseases, including primary atherosclerosis, post stent restenosis, graft occlusion after vascular bypass procedures, and transplant allograft vasculopathy. Aging is an independent risk factor for development of cardiovascular diseases, and aging exaggerates neointimal formation after vascular injury. Understanding the mechanisms responsible for this phenomenon may facilitate prevention or provide new therapies for vascular occlusive diseases, which are so prevalent in the aging population. Our ability to reproduce the model in the mouse will no doubt facilitate such understanding.

Tempol improves vascular function in the mesenteric vascular bed of senescent rats

Ageing is associated with structural and functional alterations of the vasculature. The nature of age-related vascular disorders is not completely understood. Oxidative stress is hypothesized to play a crucial role in the pathophysiology of vascular complications. We investigated the effects of chronic treatment with the superoxide dismutase mimetic tempol (4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl) on vascular function in the mesenteric vasculature of aged rats. Young (3 weeks) and old (40 weeks) Sprague-Dawley rats were treated with tempol (1 mM in drinking water) or vehicle for 3 weeks. Arterial blood pressure was slightly, but significantly, higher in old than in young rats. Tempol had no effect on arterial blood pressure. The vasoconstrictor responses to norepinephrine (NE) and serotonin (5-HT) were exaggerated in the mesenteric vascular bed (MVB) removed from old rats. Vasodilator responses to acetylcholine (ACh), papaverine (PPV), and isoprenaline (ISO) were reduced in the MVB of old rats in comparison with young rats. Chronic treatment of old rats with tempol normalized their responses to NE and 5-HT. The dilator responses to ACh, PPV, and ISO were similar between old rats receiving tempol and young rats. The present findings suggest that oxidative stress contributes to vascular dysfunction in the mesentery of old rats. The vasculoprotective effects of tempol remain to be elucidated.

Dermal fibroblasts from pseudoxanthoma elasticum patients have raised MMP-2 degradative potential

Cultured fibroblasts from the dermis of normal subjects and of Pseudoxanthoma elasticum (PXE) patients were analysed for enzyme activity, protein and mRNA expression of metalloproteases (MMP-2, MMP-3, MMP-9, MT1-MMP) and of their specific inhibitors (TIMP-1, TIMP-2 and TIMP-3). MMP-3, MMP-9 and TIMP-3 mRNAs and proteins failed to be detected in both the medium and the cell layer of both controls and PXE patients. MMP-2 mRNA was significantly more expressed in PXE than in control cell lines, whereas MT1-MMP, TIMP-1 and TIMP-2 mRNAs appeared unchanged. MMP-2 was significantly higher in the cell extracts from PXE fibroblasts than in control cells, whereas differences were negligible in the cell medium. Data suggest that PXE fibroblasts have an increased proteolytic potential, and that MMP-2 may actively contribute to connective tissue alterations in this genetic disorder.

EFFECT OF MAGNESIUM ON MECHANICAL PROPERTIES OF PRESSURIZED MESENTERIC SMALL ARTERIES FROM OLD AND ADULT RATS

The purpose of the present study was to determine the effects of magnesium (Mg) on the mechanical properties of resistance arteries in adult and old rats. Studies were performed in adult (17 weeks) and old (104 weeks) male Wistar rats. The vasodilatory response and the passive mechanical properties of the wall of isolated perfused and pressurized arterial segments of mesenteric small arteries were investigated after Mg and verapamil application, both known for their calcium antagonistic properties. Mesenteric resistance arteries from old rats exhibited an outward hypertrophic remodelling, with enlargment of the lumen, thickening of the media and enlarged media cross-sectional area. The vasodilatory response induced by the application of increasing extracellular concentrations of Mg and verapamil was significantly smaller in preconstricted mesenteric arteries of old rats than in those of adult rats. Incremental distensibility in response to increasing intravascular pressures did not change. However, the stress-strain curve was shifted to the left in pressurized mesenteric arteries from old rats, indicating arterial wall stiffness. Verapamil (3 micro mol/L) did not modify the stress-strain curves in either adult or aged rats. However, Mg (4.8 mmol/L) significantly shifted the curve to the right in mesenteric arteries from adult rats and, to a greater degree, in those from old rats. Although Mg-induced vasodilatation is impaired in aged rats, increased Mg concentration improved the mechanics of pressurized mesenteric resistance arteries. The fact that Mg decreases arterial stiffness in arteries from old rats suggests that Mg has a beneficial effect on age-related changes to the vascular wall.

Effect of age on mechanical properties of rat mesenteric small arteries

With aging, large arteries become stiffer and systolic blood pressure consequently increases. Less is known, however, about the age-related change in mechanics of small resistance arteries. The aim of this study was to determine whether aging plays a role in the stiffening of the small mesenteric arteries of rats. Intra-arterial systolic, diastolic, mean and pulse pressures were measured in male Wistar rats aged 2, 4, 15 and 26 months. The passive mechanical properties of the wall of isolated perfused and pressurized arterial segments of mesenteric small arteries were also investigated. Intra-arterial systolic, diastolic and mean blood pressures tended to decrease with age and were significantly lower in the oldest rats (26-month-old group). Pulse pressure was significantly higher in the 15- and 26-month-old groups than in the two younger groups. Under isobaric conditions, increasing age is associated with an outward hypertrophic remodeling of the mesenteric arteries. Under relaxed conditions, incremental distensibility in response to increasing intravascular pressure did not change with aging. As a function of strain (under isometric conditions), stress shifted to the left as age increased, indicating an age-related vascular stiffening. Under isobaric conditions or in relation to wall stress, the elastic modulus was greater in the adult 15-month-old rats than in the younger rats. These findings suggest that distensibility seems to be preserved with aging, despite stiffness of the wall components, probably by arterial wall geometric adaptation, which limits the pulse pressure damage. It is interesting to note that elastic modulus in mesenteric arteries from the oldest rats (26-month-old), examined in relation to wall stress and intravascular pressure, did not differ from that of the youngest rats, thus suggesting that elasticity of wall components had been restored.Key words: age, arteries, elastic modulus, stiffness, pressure.

Linked common polymorphisms in the gelatinase a promoter are associated with diminished transcriptional response to estrogen and genetic fitness

Gelatinase A (matrix metalloproteinase-2) plays a prominent role in multiple biologic processes. Prior studies have established critical roles for gelatinase A transcriptional regulation by defined enhancer elements. To determine possible functional single nucleotide polymorphisms within these elements, we determined the single nucleotide polymorphism distribution within 1,665 bp of the gelatinase A 5'-flanking region, using a healthy homogeneous Caucasian study group of 463 individuals. Among the polymorphisms detected, a G --> A transition at bp -1575 was located immediately 5' to a half-palindromic potential estrogen receptor binding site. In estrogen receptor-positive MCF-7 cells the -1575G allele functioned as an enhancer, whereas the -1575A allele reduced transcription activity significantly. Gel shift assays confirmed that the differences in allelic expression affected binding of the estrogen receptor-alpha to this region. Cotransfection experiments with an estrogen receptor-alpha expression vector in MDA-MB-231 cells, which do not constitutively express an estrogen receptor, revealed that estrogen receptor is absolutely required for enhancing activity. Allelic distribution analysis indicated that a previously reported C --> T transition within an Sp1 binding site at -1306 was in linkage disequilibrium with the -1575G --> A transition. Luciferase reporter studies of the linked variant -1575A -1306T allele versus the wild type -1575G -1306C allele demonstrated an additive reduction in estrogen-dependent reporter activity. The frequency of the -1575G --> A transition deviated significantly from the expected Hardy-Weinberg distribution in two independently assembled study populations consisting of healthy adult blood donors and newborns of Caucasian origin, both with a calculated 21% reduction in genetic fitness. Gelatinase A is a known estrogen-responsive gene and the demonstration of a loss of function polymorphism within an operational estrogen receptor binding site associated with a decrease in genetic fitness underscores the biologic significance of promoter polymorphism analyses.

Linked common polymorphisms in the gelatinase a promoter are associated with diminished transcriptional response to estrogen and genetic fitness

Gelatinase A (matrix metalloproteinase-2) plays a prominent role in multiple biologic processes. Prior studies have established critical roles for gelatinase A transcriptional regulation by defined enhancer elements. To determine possible functional single nucleotide polymorphisms within these elements, we determined the single nucleotide polymorphism distribution within 1,665 bp of the gelatinase A 5'-flanking region, using a healthy homogeneous Caucasian study group of 463 individuals. Among the polymorphisms detected, a G --> A transition at bp -1575 was located immediately 5' to a half-palindromic potential estrogen receptor binding site. In estrogen receptor-positive MCF-7 cells the -1575G allele functioned as an enhancer, whereas the -1575A allele reduced transcription activity significantly. Gel shift assays confirmed that the differences in allelic expression affected binding of the estrogen receptor-alpha to this region. Cotransfection experiments with an estrogen receptor-alpha expression vector in MDA-MB-231 cells, which do not constitutively express an estrogen receptor, revealed that estrogen receptor is absolutely required for enhancing activity. Allelic distribution analysis indicated that a previously reported C --> T transition within an Sp1 binding site at -1306 was in linkage disequilibrium with the -1575G --> A transition. Luciferase reporter studies of the linked variant -1575A -1306T allele versus the wild type -1575G -1306C allele demonstrated an additive reduction in estrogen-dependent reporter activity. The frequency of the -1575G --> A transition deviated significantly from the expected Hardy-Weinberg distribution in two independently assembled study populations consisting of healthy adult blood donors and newborns of Caucasian origin, both with a calculated 21% reduction in genetic fitness. Gelatinase A is a known estrogen-responsive gene and the demonstration of a loss of function polymorphism within an operational estrogen receptor binding site associated with a decrease in genetic fitness underscores the biologic significance of promoter polymorphism analyses.

Hormone replacement therapy and hypertension

Hypertension, particularly systolic hypertension, affects postmenopausal women and is an important risk factor for cardiovascular disease in this group. In the last year, several papers have better defined the mechanisms by which hormone replacement therapy influences blood pressure in postmenopausal women, including effects on nitric oxide, angiotensin II and vascular stiffness (compliance). Currently, data concerning the influence of hormone replacement therapy on blood pressure in postmenopausal women are inconclusive because of the limitations of published studies. It is clear, however, that hypertension is not a contraindication to starting hormone replacement therapy.

Effects of age, gender, and blood pressure on myogenic responses of mesenteric arteries from C57BL/6 mice

The myogenic response (MR) may represent an important physiological parameter underlying arterial blood pressure (BP). We studied the effects of age, gender, and BP on the MR of mesenteric arteries from 8- to 52-wk-old mice. Increasing age and BP are associated with an increase in the perfusion pressure at which tone develops (myogenic set point). An inverse correlation exists between age and extent (magnitude) of the MR in male (r(2) = 0.93, P = 0.0087) and female mice (r(2) = 0.90, P = 0.013) as well as between BP and extent of the MR in male (r(2) = 0.96, P = 0.0036) and female (r(2) = 0.90, P = 0.014) mice. In contrast, the strength of the MR (slope of active diameter-pressure relationship) and phenylephrine-mediated constriction did not differ among these groups. Although gender had no effect on MR at any perfusion pressure or age, only male mice showed significant salt-induced hypertension and an associated increase in the set point and reduction in the extent of the MR. The set point and extent of the MR is linked to the in vivo pressure during development and experimental hypertension.

P-450 metabolites of arachidonic acid in the control of cardiovascular function

Recent studies have indicated that arachidonic acid is primarily metabolized by cytochrome P-450 (CYP) enzymes in the brain, lung, kidney, and peripheral vasculature to 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) and that these compounds play critical roles in the regulation of renal, pulmonary, and cardiac function and vascular tone. EETs are endothelium-derived vasodilators that hyperpolarize vascular smooth muscle (VSM) cells by activating K(+) channels. 20-HETE is a vasoconstrictor produced in VSM cells that reduces the open-state probability of Ca(2+)-activated K(+) channels. Inhibitors of the formation of 20-HETE block the myogenic response of renal, cerebral, and skeletal muscle arterioles in vitro and autoregulation of renal and cerebral blood flow in vivo. They also block tubuloglomerular feedback responses in vivo and the vasoconstrictor response to elevations in tissue PO(2) both in vivo and in vitro. The formation of 20-HETE in VSM is stimulated by angiotensin II and endothelin and is inhibited by nitric oxide (NO) and carbon monoxide (CO). Blockade of the formation of 20-HETE attenuates the vascular responses to angiotensin II, endothelin, norepinephrine, NO, and CO. In the kidney, EETs and 20-HETE are produced in the proximal tubule and the thick ascending loop of Henle. They regulate Na(+) transport in these nephron segments. 20-HETE also contributes to the mitogenic effects of a variety of growth factors in VSM, renal epithelial, and mesangial cells. The production of EETs and 20-HETE is altered in experimental and genetic models of hypertension, diabetes, uremia, toxemia of pregnancy, and hepatorenal syndrome. Given the importance of this pathway in the control of cardiovascular function, it is likely that CYP metabolites of arachidonic acid contribute to the changes in renal function and vascular tone associated with some of these conditions and that drugs that modify the formation and/or actions of EETs and 20-HETE may have therapeutic benefits.

How long should telomeres be?

What began as a study of the "end-replication problem" took on a new dimension as it became clear that telomeres are a "molecular clock" of replication in human somatic cells. Here we review the biology of telomeres in vitro and in vivo, in mice and humans. We suggest that, in humans, telomeres are involved in the biology of aging and pathobiology of disorders of aging, including cancer and cardiovascular disease. We also propose that the underlying dynamics of telomere biology is in line with broad principles of evolutionary theories.