Gender difference in myogenic tone of rat arterioles is due to estrogen-induced, enhanced release of NO

Gender-Related Difference in Skin Oxygenation in Young Patients with Uncomplicated Type 1 Diabetes

Gender, through genetic, epigenetic and hormonal regulation, is an important modifier of the physiological mechanisms and clinical course of diseases. In diabetes mellitus, there are gender differences in incidence, prevalence, morbidity, and mortality. This disease also has an impact on the microvascular function. Therefore, this cross-sectional study was designed to investigate how gender affects the cutaneous microcirculation. We hypothesized that gender should be an important factor in the interpretation of capillaroscopy and transcutaneous oxygen saturation results. The study group consisted of 42 boys and 55 girls, uncomplicated diabetic pediatric patients. Females (F) and males (M) did not differ in terms of age, age at onset of diabetes, or diabetes duration. Furthermore, they did not differ in metabolic parameters. The comparison showed that group F had lower BP, higher pulse, and higher HR than group M. Group F had significantly lower creatinine and hemoglobin levels than group M. In children and adolescents with type 1 diabetes without complications, there was a gender difference in microcirculatory parameters. The resting transcutaneous partial pressure of oxygen was significantly higher in females than in males. However, there were no gender-related differences in basal capillaroscopic parameters or vascular reactivity during the PORH test. Our results indicate that studies investigating the structure and function of the microcirculation should consider the role of gender in addition to known cofactors such as puberty, body mass index, physical activity, and cigarette smoking.

Sex-related differences in endothelium-dependent vasodilation of human gingiva

Background

Sex hormones influence circulation, periodontitis, and wound healing. The aim of the study was to compare the endothelium-dependent and independent vasodilation in human gingiva in men and women.

Methods

Gingival blood flow was evaluated in twelve male and twelve female subjects with healthy gingiva and no systemic conditions after acetylcholine or nitric oxide donor (NitroPOHL). Agonists were administered into the gingival sulcus at the right secondary incisor (test site). Regional gingival blood flow (GBF) was imaged by Laser Speckle Contrast Imager from the marginal gingiva to the mucogingival junction in four consecutive regions (coronal, midway1, midway2 and apical). Blood flow was expressed in Laser Speckle Perfusion Unit (LSPU). The absolute maximal blood flow change (Dmax), the area under the blood flow curve (AUC), and the time to peak (TTP) were calculated.

Results

Males had higher baseline GBF than females (257 ± 18.2 vs. 225 ± 18.8 LSPU, p < 0.001). Acetylcholine and NitroPOHL significantly increased the GBF in all test regions. The Dmax after the acetylcholine was reduced apically compared to the coronal (90 ± 13 LSPU vs. 117 ± 7 LSPU, p < 0.01), but it was similar after NitroPOHL (78 ± 9 LSPU vs. 86 ± 6 LSPU, p = 0.398) in both sexes. The Dmax and AUC were higher, and the TTP was smaller in men in most regions after acetylcholine but not after NitroPOHL.

Conclusion

In the human gingiva, the endothelium-independent vasodilation propagates without attenuation in the line of the vascular supply in both sexes. At the same time, the endothelium-dependent ascending vasodilation attenuates similarly in men and women. However, men had more pronounced endothelium-dependent vasodilation than women. Therefore, it might contribute to the increased severity of periodontal disease in men.

Trial registration

The study was registered with ClinicalTrials.gov on 09.06.2021 (NCT04918563).

Sexual dimorphism in the cerebrovascular network: Brain MRI shows lower arterial density in women

BACKGROUND AND PURPOSE

Accumulating evidence suggests that there is a sexual dimorphism in brain health, with women exhibiting greater disability following strokes of comparable size and having a higher prevalence of cognitive impairment later in life. Despite the critical implication of the cerebrovascular architecture in brain perfusion and brain health, it remains unclear whether structural differences in vessel density exist across the sexes.

METHODS

In this study, we used high-density MRI imaging to characterize the intracerebral arterial and venous density of 28 (14 women) sex-matched healthy young volunteers in vivo. Using an in-house vessel segmentation algorithm, we quantified and compared these vascular features across the cortical and subcortical deep gray matter, white matter, and periventricular white matter.

RESULTS

We found that, on average, women have reduced intracerebral arterial density in comparison to men (F 2.34 ± 0.48%, M 2.67 ± 0.39%; p<.05). This difference was most pronounced in the subcortical deep gray matter (F 1.78 ± 0.53%, M 2.38 ± 0.82%; p<.05) and periventricular white matter (F 0.68 ± 0.15%, M 1.14 ± 0.33%; p<.0005), indicating a potential sex-specific vulnerability to hypoperfusion in areas critical to core cerebral functions. In contrast, venous density did not exhibit a significant difference between sexes.

CONCLUSIONS

While this research remains exploratory, it raises important pathophysiological considerations for brain health, adverse cerebrovascular events, and dementia across the sexes. Our findings also highlight the need to take into account sex differences when investigating cerebral characteristics in humans.

Microvessel Density: Integrating Sex-Based Differences and Elevated Cardiovascular Risks in Metabolic Syndrome

Metabolic syndrome (MetS) is a complex pathological state consisting of metabolic risk factors such as hypertension, insulin resistance, and obesity. The interconnectivity of cellular pathways within various biological systems suggests that each individual component of MetS may share common pathological sources. Additionally, MetS is closely associated with vasculopathy, including a reduction in microvessel density (MVD) (rarefaction) and elevated risk for various cardiovascular diseases. Microvascular impairments may contribute to perfusion-demand mismatch, where local metabolic needs are insufficiently met due to the lack of nutrient and oxygen supply, thus creating pathological positive-feedback loops and furthering the progression of disease. Sexual dimorphism is evident in these underlying cellular mechanisms, which places males and females at different levels of risk for cardiovascular disease and acute ischemic events. Estrogen exhibits protective effects on the endothelium of pre-menopausal women, while androgens may be antagonistic to cardiovascular health. This review examines MetS and its influences on MVD, as well as sex differences relating to the components of MetS and cardiovascular risk profiles. Finally, translational relevance and interventions are discussed in the context of these sex-based differences.

The role of inorganic nitrate and nitrite in cardiovascular disease risk factors: a systematic review and meta-analysis of human evidence

Context

Depleted nitric oxide levels in the human body play a major role in cardiovascular disease pathogenesis. Inorganic nitrate/nitrite (rich dietary sources include beetroot and spinach) can act as a nitric oxide donor because nitrate/nitrite can be metabolized to produce nitric oxide.

Objective

This review and meta-analysis sought to investigate the role of inorganic nitrate/nitrite in preventing or treating cardiovascular disease risk factors in humans.

Data Sources

Electronic databases, including Medline, Embase, Cumulative Index to Nursing and Allied Health Literature, Cochrane, and Scopus, were searched.

Data Extraction

Experimental trials examining the effect of oral inorganic nitrate/nitrite intake on cardiovascular disease risk factors were included for systematic analysis.

Results

Thirty-four studies were included for qualitative synthesis, 23 of which were eligible for meta-analysis. Included studies measured the following outcomes: blood pressure, endothelial function, arterial stiffness, platelet aggregation, and/or blood lipids. Inorganic nitrate intake was found to significantly reduce resting blood pressure (systolic blood pressure: -4.80 mmHg, P < 0.0001; diastolic blood pressure: -1.74 mmHg, P = 0.001), improve endothelial function (flow-mediated dilatation: 0.59%, P < 0.0001), reduce arterial stiffness (pulse wave velocity: -0.23 m/s, P < 0.0001; augmentation index: -2.1%, P = 0.05), and reduce platelet aggregation by 18.9% (P < 0.0001).

Conclusions

Inorganic nitrate consumption represents a simple strategy for targeting cardiovascular disease risk factors. Future studies investigating the long-term effects of inorganic nitrate on cardiovascular disease outcomes are warranted.

Sex Difference in Gentamicin-induced Nephrotoxicity: Influence of L-arginine in Rat Model

Background:

L-arginine is an important precursor for the formation of nitric oxide (NO). According to previous studies, NO function is related to gender. Likewise, chronic renal diseases have lower prevalence in female. Gentamicin (GM) is an aminoglycoside antibiotic. According to some studies, males are more sensitive to GM renal nephrotoxicity. This study attempts to find protective effects of L-arginine on GM nephrotoxicity in male and female rats.

Methods:

Male and female rats were divided into eight groups: Rats were randomly assigned to 8 groups each including both male and female rats. The first and second groups received vehicle (saline), the third and fourth groups received gentamicin (80 mg/kg), the fifth and sixth groups received L-arginine (150 mg/kg), and finally, seventh and eighth groups received gentamicin+ L- arginine. Next, 9 days after administering drugs, blood samples were collected from the heart. After making sacrifices, the level of blood urea, creatinine (Cr), nitrite, and malondialdehyde (MDA) was measured in serums. Likewise, nitrite and MDA were measured in the homogenized kidney tissue.

Results:

GM significantly increased serum level of urea and Cr in male and female rats (P < 0.05). However, co-administration of GM + L-arginine significantly did not decrease urea and Cr level in male rats, whereas, in female rats, they significantly reduced (P < 0.05). In response to GM, renal MDA level increased in male and female rats (P < 0.05), and in the presence of GM + L-arginine, the level of MDA significantly decreased in both genders (P < 0.05).

Conclusions:

L-arginine demonstrated some protective effects in female rats but did not protect against GM nephrotoxicity in male rats for unknown reasons, probably related to the effects of sex hormones which needs further studies to be confirmed.

Sex differences in the vascular function and related mechanisms: role of 17β-estradiol

The incidence of cardiovascular disease (CVD) is lower in premenopausal women but increases with age and menopause compared with similarly aged men. Based on the prevalence of CVD in postmenopausal women, sex hormone-dependent mechanisms have been postulated to be the primary factors responsible for the protection from CVD in premenopausal women. Recent Women’s Health Initiative studies, Cochrane Review studies, the Early Versus Late Intervention Trial with Estradiol Study, and the Kronos Early Estrogen Prevention Study have suggested that beneficial effects of hormone replacement therapy (HRT) are seen in women of <60 yr of age and if initiated within <10 yr of menopause. In contrast, the beneficial effects of HRT are not seen in women of >60 yr of age and if commenced after 10 yr of menopause. The higher incidence of CVD and the failure of HRT in postmenopausal aged women could be partly associated with fundamental differences in the vascular structure and function between men and women and in between pre- and postmenopausal women, respectively. In this regard, previous studies from human and animal studies have identified several sex differences in vascular function and associated mechanisms. The female sex hormone 17β-estradiol regulates the majority of these mechanisms. In this review, we summarize the sex differences in vascular structure, myogenic properties, endothelium-dependent and -independent mechanisms, and the role of 17β-estradiol in the regulation of vascular function.

The effects of estradiol and testosterone on renal tissues oxidative after central injection of angiotensin II in female doca - salt treated rats

Background Although numerous studies have proven that estrogen (Est) has a protective effect on the development of hypertension, more research needs to be done to show its detailed mechanism in a variety of hypertension. The important role of active oxygen species in blood pressure is well defined. We examined whether or not sex hormones change the growth of reactive oxygen species (ROS) ‎in kidneys after central microinjection of angiotensin II (Ang II).‎ Materials and methods Female Wistar rats, 8 weeks old (200 ± 10 g) were used in this study. The animal groups were (1) Sham, (2) Ovariectomy (OVX), (3) Sham-Hypertension (Sham-Hyper), (4) OVX-Hypertension (OVX-Hyper), (5) Sham-Hyper-Est, (6) OVX-Hyper-Est‎;‎ (7) Sham-Hyper-Testosterone (Tst) and (8) OVX-Hyper-Tst. Solutions of 1% NaCl and 0.1 KCl ‎were used and desoxycorticostrone (doca-salt) was injected (45 mg/kg) 3 times a week in Hypertension groups. Estradiol and Tst (2 mg/kg and ‎5 mg/kg‎; daily; subcutaneously) for 4 weeks. Ang II (50 μM, 5 μL) was microinjected by intracerebroventricular ( i.c.v.) infusion and malondialdehyde (MDA) and thiol in the kidneys were measured. Results MDA in the kidneys was increased by Ang II and doca-salt treatments. Both estradiol and Tst decreased the kidney's MDA. The level of thiol was higher in Hyper ‎groups and reversed after treatment with estradiol and Tst. Conclusions Our findings suggest that central effect of Ang II on blood pressure and kidney ‎disease is accompanied with increased levels of oxidative stress in the kidneys. Indeed sex hormones change the ROS level in the kidneys after central ‎microinjection of Ang II.‎‎.

Gender differences in the regulation of MLC20 phosphorylation and smooth muscle contraction in rat stomach

Evidence of sex-related differences in gastrointestinal (GI) functions has been reported in the literature. In addition, various GI disorders have disproportionate prevalence between the sexes. An essential step in the initiation of smooth muscle contraction is the phosphorylation of the 20-kDa regulatory myosin light chain (MLC₂₀) by the Ca²⁺/calmodulin-dependent myosin light chain kinase (MLCK). However, whether male stomach smooth muscle inherits different contractile signaling mechanisms for the regulation of MLC₂₀ phosphorylation from that in females has not been established. The present study was designed to investigate sex-associated differences in the regulation of MLC₂₀ phosphorylation and thus muscle contraction in gastric smooth muscle cells (GSMCs). Experiments were performed on GSMCs freshly isolated from male and female rats. Contraction of the GSMCs in response to acetylcholine (ACh), a muscarinic agonist, was measured via scanning micrometry in the presence or absence of the MLCK inhibitor, ML-7. Additionally, the protein levels of MLC₂₀, MLCK and phosphorylated MLC₂₀ were measured by ELISA. The protein levels of MLC₂₀ and MLCK were indifferent between the sexes. ACh induced greater contraction (P<0.05) as well as greater MLC₂₀ phosphorylation (P<0.05) in male GSMCs compared with female. Pretreatment of GSMCs with ML-7 significantly reduced the ACh-induced contraction (P<0.05) and MLC₂₀ phosphorylation (P<0.05) in the male and female cells, and notably, abolished the contractile differences between the sexes. In conclusion, MLC₂₀ phosphorylation and thus muscle contraction may be activated to a greater extent in male rat stomach compared with that in females.

Sex-Specific Characteristics of the Microcirculation

The requirements of metabolizing tissue are both continuous and variable; accordingly, the microvasculature serving that tissue must be similarly dynamic. Just as it is recognized that males and females of the same species have differing metabolic requirements, is it not likely that the microvasculature serving these tissues will differ by sex? This section focusing on the constituents of the microcirculation identifies what is known presently about the role sex plays in matching metabolic demand with microvascular function and areas requiring additional study. Many of the identified sex differences are subtle and easily ignored. In the aggregate, though, they can profoundly alter phenotype, especially under stressful conditions including pregnancy, exercise, and disease states ranging from diabetes to heart failure. Although the features presently identified to "have sex" range from differences in growth, morphology, protein expression, and intracellular signaling, males and females alike achieve homeostasis, likely by different means. Studies of microvascular sexual dimorphism are also identifying age as an independent but interacting factor requiring additional attention. Overall, attempting to ignore either sex and/or age is inappropriate and will prevent the design and implementation of appropriate interventions to present, ameliorate, or correct microvascular dysfunction.

Menopause and Ischemic Stroke: A Brief Review

Ischemic stroke is one of the leading causes of morbidity and mortality worldwide. Females are protected against stroke before the onset of menopause. Menopause results in increased incidence of stroke when compared to men. The mechanisms of these differences remain to be elucidated. Considering that there is a postmenopausal phenomenon and females in general, are living longer sex hormone-dependent mechanisms have been postulated to be the primary factors responsible for the premenopausal protection from stroke and later to be responsible for the higher incidence and increased the severity of stroke after menopause. Animal studies suggest that administration of estrogen and progesterone is neuroprotective and decreases the incidence of stroke. However, the real-world outcomes of hormone replacement therapy have failed to decrease the stroke risk. Despite the multifactorial nature of sex differences in stroke, here, we briefly discuss the pathophysiology of sex steroid hormones, the molecular mechanisms of estrogen receptor-dependent signaling pathways in stroke, and the potential factors that determine the discrepant effects of hormone replacement therapy in stroke.

Gender differences in tibial microvascular flow responses to head down tilt and lower body negative pressure

The purpose of the investigation was to study lower body negative pressure recovery in response to head down tilt position in men and women. The study examined the primary hypothesis that tibial bone microvascular flow responses to HDT and lower body negative pressure (LBNP) differ in women and men. Nine women and nine men between 20 to 30 years of age participated in the study. Tibial microvascular flow, head and tibial oxygenation and calf circumference were measured using photoplethysmography (PPG), near‐infrared spectroscopy (NIRS) and strain gauge plethysmography (SGP), respectively, during sitting (control baseline), supine, 15° HDT, and 15° HDT with 25 mmHg LBNP. Tibial microvascular flow with HDT increased by 57% from supine position (from 1.4V ± 0.7 to 2.2V ± 1.0 HDT; ANOVA P < 0.05) in men but there is no significant difference between supine and HDT in women. Ten minutes of LBNP during 15^oHDT restored tibial bone microvascular flows to supine levels, (from 2.2V±1.0 HDT to 1.1V ± 0.7 supine; ANOVA P < 0.05) in men but not in women. These data support the concept that there are gender specific microvascular responses to a fluid‐shift countermeasure such as LBNP. Thus, gender differences should be considered while developing future countermeasure strategies to headward fluid shifts in microgravity.

Resistance or aerobic training decreases blood pressure and improves cardiovascular autonomic control and oxidative stress in hypertensive menopausal rats

We investigated whether resistance training (RT) vs. aerobic training (AT) differentially impacts on arterial pressure and related mechanisms in ovariectomized spontaneously hypertensive rats (SHRs). Female SHRs were ovariectomized and assigned to one of the following groups: sedentary, AT, or RT; sham sedentary SHR were used as control group. AT was performed on a treadmill, whereas RT was performed on a vertical ladder. Both exercise protocols were performed for 8 wk, 5 days/wk. Arterial pressure, baroreflex sensitivity, autonomic modulation, and cardiac oxidative stress parameters (lipid peroxidation, protein oxidation, redox balance, NADPH oxidase, and antioxidant enzymes activities) were analyzed. Ovariectomy increased mean arterial pressure (∼9 mmHg), sympathetic modulation (∼40%), and oxidative stress in sedentary rats. Both RT and AT reduced mean arterial pressure (∼20 and ∼8 mmHg, respectively) and improved baroreflex sensitivity compared with sedentary ovariectomized rats. However, RT-induced arterial pressure decrease was significantly less pronounced than AT. Lipid peroxidation and protein oxidation were decreased while antioxidant enzymes were increased in both trained groups vs. sedentaries. The reduced gluthatione was higher after AT vs. other groups, whereas oxidized gluthatione was lower after RT vs. AT. Moreover, sympathetic and parasympathetic modulations were highly correlated with cardiac oxidative stress parameters. In conclusion, both RT and AT can decrease arterial pressure in a model of hypertension and menopause; although, at different magnitudes this decrease was related to attenuated autonomic dysfunction in association with cardiac oxidative stress improvement in both exercise protocols.

Female-favorable attenuation of coronary myogenic constriction via reciprocal activations of epoxyeicosatrienoic acids and nitric oxide

Epoxyeicosatrienoic acids (EETs) are metabolites of arachidonic acid via CYP/epoxygenases, which are catabolized by soluble epoxide hydrolase (sEH) and known to possess cardioprotective properties. To date, the role of sEH in the modulation of pressure-induced myogenic response/constriction in coronary arteries, an important regulatory mechanism in the coronary circulation, and the issue as to whether the disruption of the sEH gene affects the myogenic response sex differentially have never been addressed. To this end, experiments were conducted on male (M) and female (F) wild-type (WT) and sEH-knockout (KO) mice. Pressure-diameter relationships were assessed in isolated and cannulated coronary arteries. All vessels constricted in response to increases in intraluminal pressure from 60 to 120 mmHg. Myogenic vasoconstriction was significantly attenuated, expressed as an upward shift in the pressure-diameter curve of vessels, associated with higher cardiac EETs in M-KO, F-WT, and F-KO mice compared with M-WT controls. Blockade of EETs via exposure of vessels to 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) prevented the attenuated myogenic constriction in sEH-KO mice. In the presence of 14,15-EEZE, pressure-diameter curves of females presented an upward shift from those of males, exhibiting a sex-different phenotype. Additional administration of N(ω)-nitro-l-arginine methyl ester eliminated the sex difference in myogenic responses, leading to four overlapped pressure-diameter curves. Cardiac sEH was downregulated in F-WT compared with M-WT mice, whereas expression of endothelial nitric oxide synthase and CYP4A (20-HETE synthase) was comparable among all groups. In summary, in combination with NO, the increased EET bioavailability as a function of genetic deletion and/or downregulation of sEH accounts for the female-favorable attenuation of pressure-induced vasoconstriction.

Sex- and isoform-specific mechanism of neuroprotection by transgenic expression of P450 epoxygenase in vascular endothelium

OBJECTIVE

Cytochrome P450 epoxygenases (CYP) metabolize arachidonic acid to epoxyeicosatrienoic acids (EETs), which exhibit vasodilatory, anti-inflammatory and neuroprotective actions in experimental cerebral ischemia. We evaluated the effect of endothelial-specific CYP overexpression on cerebral blood flow, inflammatory cytokine expression and tissue infarction after focal cerebral ischemia in transgenic mice.

APPROACH AND RESULTS

Male and female wild-type and transgenic mice overexpressing either human CYP2J2 or CYP2C8 epoxygenases in vascular endothelium under control of the Tie2 promoter (Tie2-CYP2J2 and Tie2-CYP2C8) were subjected to 60-min middle cerebral artery occlusion (MCAO). Microvascular cortical perfusion was monitored during vascular occlusion and reperfusion using laser-Doppler flowmetry and optical imaging. Infarct size and inflammatory cytokines were measured at 24h of reperfusion by TTC and real-time quantitative PCR, respectively. Infarct size was significantly reduced in both Tie2-CYP2J2 and Tie2-CYP2C8 transgenic male mice compared to corresponding WT male mice (n=10 per group, p<0.05). Tie2-CYP2J2, but not Tie2-CYP2C8 male mice maintained higher blood flow during MCAO; however, both Tie2-CYP2J2 and Tie2-CYP2C8 had lower inflammatory cytokine expression after ischemia compared to corresponding WT males (n=10 per group for CBF and n=3 for cytokines, p<0.05). In females, a reduction in infarct was observed in the caudate-putamen, but not in the cortex or hemisphere as a whole and no differences were observed in blood flow between female transgenic and WT mice (n=10 per group).

CONCLUSIONS

Overexpression of CYP epoxygenases in vascular endothelial cells protects against experimental cerebral ischemia in male mice. The mechanism of protection is in part linked to enhanced blood flow and suppression of inflammation, and is both sex- and CYP isoform-specific.

The role of the RhoA/ROCK pathway in gender-dependent differences in gastric smooth muscle contraction

Gender-related differences in various gastric functions and diseases have been reported, with women having a higher prevalence of gastrointestinal disturbances than men. The aim of this study was to investigate sex-dependent differences in activation of the Rho-associated protein kinase (ROCK; RhoA/Rho kinase) pathway and muscle contraction in the stomach using single gastric smooth muscle cells (GSMC) from male and female Sprague-Dawley rats. Expression of ROCK1 and ROCK2 protein and acetylcholine (ACh)-induced activation of RhoA and ROCK were measured using a specifically designed enzyme-linked immunosorbent assay and activity assay kits, respectively. Contraction of a single GSMC was measured by scanning micrometry in the presence or absence of the ROCK inhibitor Y27632 dihydrochloride. ACh-induced activation of RhoA and ROCK and subsequent contraction were greater in male rats than in female rats but neither was related to differences in the expression of ROCK1 or ROCK2 or total RhoA amount. Most important, Y27632 inhibited and abolished differences in ACh-induced contraction in both sexes. In conclusion, increased ACh-induced contraction in the GSMC of male rats is attributable to greater RhoA/ROCK activation independent of differences in the expression of ROCK isoforms or total RhoA.

Sex, Adiposity, and Hypertension Status Modify the Inverse Effect of Marine Food Intake on Blood Pressure in Alaska Native (Yup'ik) People

BACKGROUND

Alaska Native people currently have a higher prevalence of hypertension than do nonnative Alaskans, although in the 1950s hypertension was rare among Alaska Native people. A novel biomarker of marine foods, the nitrogen isotope ratio (δ¹⁵N) in RBCs was shown to be negatively associated with systolic and diastolic blood pressure. Few studies have examined how individual characteristics modify the association of marine food intake with blood pressure.

OBJECTIVE

This exploratory analysis examined whether sex, adiposity, and hypertension modify the inverse association between marine food intake and blood pressure.

METHODS

We used covariate-adjusted linear models to describe the association between δ¹⁵N and blood pressure in 873 adult Alaska Native (Yup'ik) people who resided in 8 communities in southwest Alaska. We separately stratified by sex, body mass index (BMI) group, abdominal obesity, and hypertension status and assessed the interaction between δ¹⁵N and participant characteristics on blood pressure via likelihood ratio tests.

RESULTS

The association between δ¹⁵N and systolic blood pressure was modified by sex, BMI status, and abdominal obesity, with the inverse association observed only in the male (β = -1.5; 95% CI: -2.4, -0.6 : , nonobese BMI (β = -1.7; 95% CI: -2.5, -1.0), and non-abdominally obese (β = -1.6; 95% CI: -2.4, -0.9) strata (all P-interaction < 0.0001). A reduction in diastolic blood pressure associated with δ¹⁵N was observed in the nonobese BMI (β = -1.1; 95% CI: -1.7, -0.5) and non-abdominally obese (β = -1.1; 95% CI: -1.7, -0.5) strata, although only the interaction between BMI group and δ¹⁵N with diastolic blood pressure was significant. The inverse association between δ¹⁵N and both systolic and diastolic blood pressure was observed in nonhypertensive individuals, although the comparison had limited power. The results were consistent with those identified by using combined RBC concentrations of eicosapentaenoic acid and docosahexaenoic acid as the biomarker of marine food intake, although the associations identified by using δ¹⁵N were larger.

CONCLUSIONS

Obesity status modified the inverse association between marine food intake and both systolic and diastolic blood pressure in adult Alaska Native (Yup'ik) people. The inverse association between δ¹⁵N and systolic blood pressure was also modified by sex.

Chronic treatment with atrial natriuretic peptide in spontaneously hypertensive rats: beneficial renal effects and sex differences

Objective

The aim of this study was to investigate the effects of chronic treatment with atrial natriuretic peptide (ANP) on renal function, nitric oxide (NO) system, oxidative stress, collagen content and apoptosis in kidneys of spontaneously hypertensive rats (SHR), as well as sex-related differences in the response to the treatment.

Methods

10 week-old male and female SHR were infused with ANP (100 ng/h/rat) or saline (NaCl 0.9%) for 14 days (subcutaneous osmotic pumps). Systolic blood pressure (SBP) was recorded and diuresis and natriuresis were determined. After treatment, renal NO synthase (NOS) activity and eNOS expression were evaluated. Thiobarbituric acid-reactive substances (TBARS), glutathione concentration and glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities were determined in the kidney. Collagen was identified in renal slices by Sirius red staining and apoptosis by Tunel assay.

Results

Female SHR showed lower SBP, oxidative stress, collagen content and apoptosis in kidney, and higher renal NOS activity and eNOS protein content, than males. ANP lowered SBP, increased diuresis, natriuresis, renal NOS activity and eNOS expression in both sexes. Renal response to ANP was more marked in females than in males. In kidney, ANP reduced TBARS, renal collagen content and apoptosis, and increased glutathione concentration and activity of GPx and SOD enzymes in both sexes.

Conclusions

Female SHR exhibited less organ damage than males. Chronic ANP treatment would ameliorate hypertension and end-organ damage in the kidney by reducing oxidative stress, increasing NO-system activity, and diminishing collagen content and apoptosis, in both sexes.

Distinct endothelial pathways underlie sexual dimorphism in vascular auto-regulation

BACKGROUND AND PURPOSE

Pre-menopausal females have a lower incidence of cardiovascular disease compared with age-matched males, implying differences in the mechanisms and pathways regulating vasoactivity. In small arteries, myogenic tone (constriction in response to raised intraluminal pressure) is a major determinant of vascular resistance. Endothelium-derived dilators, particularly NO, tonically moderate myogenic tone and, because the endothelium is an important target for female sex hormones, we investigated whether NO-mediated moderation of myogenic tone differed between the sexes.

EXPERIMENTAL APPROACH

Pressure-diameter or relaxation concentration-response curves to the NO donor spermine-NO or soluble guanylate cyclase (sGC) stimulation (BAY41-2272) were constructed before and following drug intervention in murine mesenteric resistance arteries. Hypotensive responses to activators of the NO-sGC pathway were determined. Quantitative PCR and Western blotting were used for expression analysis.

KEY RESULTS

NO synthase inhibition enhanced myogenic tone of arteries of both sexes while block of endothelium-derived hyperpolarizing factor (EDHF) enhanced responses in arteries of females only. Spermine-NO concentration-dependently relaxed mesenteric arteries isolated from either sex. However, while inhibition of sGC activity attenuated responses of arteries from male mice only, endothelial denudation attenuated responses of arteries from females only. BAY41-2272 and spermine-NO-induced vasodilatation and hypotension were greater in males than in females.

CONCLUSIONS AND IMPLICATIONS

NO moderated myogenic tone in arteries of male mice by a sGC-dependent pathway while EDHF was the predominant endothelial regulator in arteries of females. This is a potentially important sexual dimorphism in NO-mediated reactivity and further implicates EDHF as the predominant endothelial vasodilator in female resistance arteries.

Nitric oxide and coronary vascular endothelium adaptations in hypertension

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

Hypoxia during pregnancy in rats leads to early morphological changes of atherosclerosis in adult offspring

Exposure to an adverse intrauterine environment increases the risk of cardiovascular disease later in adult life. However, the time course relationship between prenatal hypoxia and the onset of atherosclerosis in offspring remains unknown. The purpose of this study is to evaluate the role of reduced fetal oxygen supply on early development of atherogenesis in the adult offspring and further assess its susceptibility to sex-, hyperlipidemia-, and postnatal hypoxemia-related differences. Based on a 4 x 2 full factorial design consisting of four factors of maternal hypoxia, sex, hyperlipidemia, and postnatal hypoxemia, characteristics of growth were determined, and histopathological observation and morphometric analysis of the thoracic aortas were performed in Sprague-Dawley rat offspring. Intrauterine growth restriction, altered body shape at birth, and accelerated postnatal weight gain occurred in the maternal hypoxia group but did not occur in the control group. In 16-mo-old maternal hypoxia offspring, the thoracic aortas exhibited lesions similar to early events in atherosclerosis that involved impaired endothelial cells, thickening and fibration of intimas, infiltration of inflammatory cells to the subendothelial space, and migration and proliferation of vascular smooth muscle cells to the intima. In contrast, no detectable pathological changes were observed in the offspring without maternal hypoxia exposure. Morphometric analysis further demonstrated that prenatal hypoxia caused a significant thickening of intima (P < 0.001) with a main effect of 5.5 mum, an approximately twofold increase compared with controls. In addition, there was a positive additive relationship between prenatal hypoxia and hyperlipidemia on the intimal thickness (P < 0.05). There were no other main effects or interaction among these four factors. In summary, our results indicate that maternal hypoxia during pregnancy leads to early pathological appearances of atherogenesis in adult offspring. This effect was enhanced with hyperlipemia but was unaffected by postnatal hypoxia or sex.

Physiology of cell volume regulation in vertebrates

The ability to control cell volume is pivotal for cell function. Cell volume perturbation elicits a wide array of signaling events, leading to protective (e.g., cytoskeletal rearrangement) and adaptive (e.g., altered expression of osmolyte transporters and heat shock proteins) measures and, in most cases, activation of volume regulatory osmolyte transport. After acute swelling, cell volume is regulated by the process of regulatory volume decrease (RVD), which involves the activation of KCl cotransport and of channels mediating K(+), Cl(-), and taurine efflux. Conversely, after acute shrinkage, cell volume is regulated by the process of regulatory volume increase (RVI), which is mediated primarily by Na(+)/H(+) exchange, Na(+)-K(+)-2Cl(-) cotransport, and Na(+) channels. Here, we review in detail the current knowledge regarding the molecular identity of these transport pathways and their regulation by, e.g., membrane deformation, ionic strength, Ca(2+), protein kinases and phosphatases, cytoskeletal elements, GTP binding proteins, lipid mediators, and reactive oxygen species, upon changes in cell volume. We also discuss the nature of the upstream elements in volume sensing in vertebrate organisms. Importantly, cell volume impacts on a wide array of physiological processes, including transepithelial transport; cell migration, proliferation, and death; and changes in cell volume function as specific signals regulating these processes. A discussion of this issue concludes the review.

The influence of estrogen and progesterone on parasympathetic vasodilatation in the rat submandibular gland

Previous studies suggest that NO- and PGI(2)-independent pathways play a greater role in parasympathetic vasodilatation in the submandibular glands (SMG) of female than of male rats. Thus, the purpose of this study was to determine whether estrogen and progesterone influence the relative contributions of NO and PGI(2) to parasympathetic vasodilatation in the SMG. Vascular responses to chorda-lingual nerve stimulation were examined in sham-operated (SHAM) and ovariectomized (OVX) female rats and in OVX rats treated with either 17beta-estradiol alone or a combination of 17beta-estradiol and progesterone. Compared with SHAM animals, increases in vascular conductance in OVX rats were reduced at 1, 2 and 5 Hz (p<0.05). Blood flow responses in OVX+17beta-estradiol and OVX+17beta-estradiol+progesterone rats were indistinguishable from those observed in SHAM animals. Indomethacin had no effect on vasodilatation in SHAM and OVX+17beta-estradiol rats, but increased vascular responses in OVX animals (p<0.02). The addition of L-NAME resulted in a significant reduction in vasodilatation at all frequencies. In OVX rats treated with both estrogen and progesterone, indomethacin caused a reduction in vasodilatation and L-NAME further diminished the remaining responses. Under all conditions, vasodilatation was due largely, if not exclusively, to direct parasympathetic rather than antidromic sensory nerve activation. Finally, both neuronally-derived and endothelium-derived NO appeared to be responsible for the NO-dependent vasodilatation, but endothelium-derived NO became increasingly important as the frequency of stimulation increased. We conclude that estrogen and progesterone influence parasympathetic vasodilatation through combined effects on NO-, PGI(2)- and non-NO/PGI(2)-mediated pathways.

Sex differences in limb vasoconstriction responses to increases in transmural pressures

Women compared with men are more likely to have orthostatic intolerance. The purpose of this study was to examine whether sex affects limb vasoconstrictor response to increases in transmural pressure. Brachial and femoral mean blood velocity (MBV) and diameter (Doppler Ultrasound) were measured in 10 women and 10 men as transmural pressure was altered by applying local suction (-25, -50, -75, and -100 mmHg) via pressurized-limb tanks for 1 min to a single arm and leg. With the abrupt application of forearm suction (-75 and -100 mmHg), women compared with men had a greater initial rise in MBV (peak), followed by a quicker dynamic rate of velocity reduction. In the leg, women had a tendency for higher peak MBV but had similar dynamic velocity reductions compared with men. After 60 s of suction, women compared with men had attenuated reductions in brachial flow and conductance (-8.05 +/- 1.71 vs. -16.25 +/- 1.71 ml/min; -0.12 +/- 0.03 vs. -0.20 +/- 0.03 ml x min(-1) x mmHg(-1); main effect, P < 0.05), as well as attenuated femoral flow and conductance to sustained leg negative pressure at -100 mmHg (P < 0.05). When the data were expressed as percent change, women compared with men continued to have attenuated brachial flow responses (-24 +/- 2 vs. -36 +/- 2%, main effect, P < 0.05), with a trend toward attenuation at the highest leg pressure (-25 +/- 11 vs. -46 +/- 4%; P = 0.08). These sex differences remained after normalizing the flow responses by limb volume (percent change). Our findings suggest that young women compared with men have attenuated brachial and femoral vasoconstrictor responses to increases in transmural pressure, which may have implications for the greater incidence of orthostatic intolerance in women.

Increased myogenic responsiveness of skeletal muscle arterioles with juvenile growth

Previous studies from this laboratory suggest that during juvenile growth, structural changes in the arteriolar network are accompanied by changes in some of the mechanisms responsible for regulation of tissue blood flow. To test the hypothesis that arteriolar myogenic behavior is altered with growth, we studied gracilis muscle arterioles isolated from Sprague-Dawley rats at two ages: 21-28 and 42-49 days. When studied at their respective in vivo pressures, the myogenic index (instantaneous slope of the active pressure-diameter curve) of arterioles from 42-49-day-old rats was more negative than that of arterioles from 21-28-day-old rats, indicating greater myogenic responsiveness. Endothelial denudation, or prostaglandin H(2) (PGH(2))/thromboxane A(2) (TxA(2)) receptor antagonism without denudation, significantly reduced the myogenic responsiveness of arterioles from the older rats over a wide range of pressures but had no consistent effects on the myogenic responsiveness of arterioles from the younger rats. The heme oxygenase inhibitor chromium (III) mesoporphyrin IX chloride had no effect on the myogenic activity of arterioles from either age group. These findings indicate that microvascular growth in young animals is accompanied by an increase in the myogenic behavior of arterioles, possibly because PGH(2) or TxA(2) assumes a role in reinforcing myogenic activity over this period. As a result, the relative contribution of myogenic activity to blood flow regulation in skeletal muscle may increase during rapid juvenile growth.

Decreased capillary filtration but maintained venous compliance in the lower limb of aging women

There are sex-related differences in venous compliance and capillary filtration in the lower limbs, which to some extent can explain the susceptibility to orthostatic intolerance in young women. With age, venous compliance and capacitance are reduced in men. This study was designed to evaluate age-related changes in venous compliance and capillary filtration in the lower limbs of healthy women. Included in this study were 22 young and 12 elderly women (23.1 +/- 0.4 and 66.4 +/- 1.4 yr). Lower body negative pressure (LBNP) of 11, 22, and 44 mmHg created defined transmural pressure gradients in the lower limbs. A plethysmographic technique was used on the calf to assess venous capacitance and net capillary filtration. Venous compliance was calculated with the aid of a quadratic regression equation. No age-related differences in venous compliance and capacitance were found. Net capillary filtration and capillary filtration coefficient (CFC) were lower in elderly women at a LBNP of 11 and 22 mmHg (0.0032 vs. 0.0044 and 0.0030 vs. 0.0041 ml.100 ml(-1).min(-1).mmHg(-1), P < 0.001). At higher transmural pressure (LBNP, 44 mmHg), CFC increased by approximately 1/3 (0.010 ml.100 ml(-1).min(-1).mmHg(-1)) in the elderly (P < 0.001) but remained unchanged in the young women. In conclusion, no age-related decrease in venous compliance and capacitance was seen in women. However, a decreased CFC was found with age, implying reduced capillary function. Increasing transmural pressure increased CFC in the elderly women, indicating an increased capillary susceptibility to transmural pressure load in dependent regions. These findings differ from earlier studies on age-related effects in men, indicating sex-specific vascular aging both in the venous section and microcirculation.

Endothelium-independent constriction of isolated, pressurized arterioles by Nomega-nitro-L-arginine methyl ester (L-NAME)

BACKGROUND AND PURPOSE

Nitric oxide synthase (NOS) inhibitors cause vasoconstriction in pressurized arterioles with myogenic tone. This suggests either tonic production of NO modulates myogenic tone or a direct, NOS-independent effect of the NOS inhibitors. The nature of the contractile effect of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) on pressurised arterioles was investigated.

EXPERIMENTAL APPROACH

Segments of rat cremaster muscle first-order arteriole were cannulated on glass micropipettes and maintained at an intraluminal pressure of 50, 70 or 120 mmHg.

KEY RESULTS

L-NAME and the related compound L-NA (100 microM) constricted pressurized vessels with myogenic tone. Removal of the endothelium did not cause constriction or alter myogenic tone, however the constrictor effect of L-NAME persisted. The constrictor effect of L-NAME was abolished by L-arginine (1 mM). Other NO and cGMP pathway inhibitors, including the nNOS inhibitor 7-nitroindazole (100 muM), the NO scavenger carboxy-PTIO (100 microM), the guanylate cyclase inhibitor ODQ (10 microM) and the cGMP inhibitor Rp-8CPT-cGMPS (10 microM) did not cause constriction of the arterioles. L-NAME caused a small (3-4 mV) but not statistically significant depolarization of the arteriolar smooth muscle at both pressures. The constrictor effect was not prevented by the K(+)-channel antagonist tetraethyl ammonium (TEA, 1 mM) or the K(ATP) channel antagonist glibenclamide (1 microM).

CONCLUSIONS AND IMPLICATIONS

These observations demonstrate that L-NAME causes an endothelium- and NOS-independent contraction of vascular smooth muscle in isolated skeletal muscle arterioles. It is suggested that the underlying mechanism relates to an arginine binding interaction.

Sex-related effects on venous compliance and capillary filtration in the lower limb

Recent studies in humans have suggested sex differences in venous compliance of the lower limb, with lower compliance in women. Capillary fluid filtration could, however, be a confounder in the evaluation of venous compliance. The venous capacitance and capillary filtration response in the calves of 12 women (23.2 ± 0.5 years) and 16 men (22.9 ± 0.5 years) were studied during 8 min lower body negative pressure (LBNP) of 11, 22, and 44 mmHg. Calf venous compliance is dependent on pressure and was determined using the first derivative of a quadratic regression equation that described the capacitance-pressure relationship [compliance = β1 + (2·β2· transmural pressure)]. We found a lower venous compliance in women at low transmural pressures, and the venous capacitance in men was increased ( P < 0.05). However, the difference in compliance between sexes was reduced and not seen at higher transmural pressures. Net capillary fluid filtration and capillary filtration coefficient (CFC) were greater in women than in men during LBNP ( P < 0.05). Furthermore, calf volume increase (capacitance response + total capillary filtration) during LBNP was equivalent in both sexes. When total capillary filtration was not subtracted from the calf capacitance response in the calculation of venous compliance, the sex differences disappeared, emphasizing that venous compliance measurement should be corrected for the contribution of CFC.

Roles of phospholipase A2 isoforms in swelling- and melittin-induced arachidonic acid release and taurine efflux in NIH3T3 fibroblasts

Osmotic swelling of NIH3T3 mouse fibroblasts activates a bromoenol lactone (BEL)-sensitive taurine efflux, pointing to the involvement of a Ca(2+)-independent phospholipase A(2) (iPLA(2)) (Lambert IH. J Membr Biol 192: 19-32, 2003). We report that taurine efflux from NIH3T3 cells was not only increased by cell swelling but also decreased by cell shrinkage. Arachidonic acid release to the cell exterior was similarly decreased by shrinkage yet not detectably increased by swelling. NIH3T3 cells were found to express cytosolic calcium-dependent cPLA(2)-IVA, cPLA(2)-IVB, cPLA(2)-IVC, iPLA(2)-VIA, iPLA(2)-VIB, and secretory sPLA(2)-V. Arachidonic acid release from swollen cells was partially inhibited by BEL and by the sPLA(2)-inhibitor manoalide. Cell swelling elicited BEL-sensitive arachidonic acid release from the nucleus, to which iPLA(2)-VIA localized. Exposure to the bee venom peptide melittin, to increase PLA(2) substrate availability, potentiated arachidonic acid release and osmolyte efflux in a volume-sensitive, 5-lipoxygenase-dependent, cyclooxygenase-independent manner. Melittin-induced arachidonic acid release was inhibited by manoalide and slightly but significantly by BEL. A BEL-sensitive, melittin-induced PLA(2) activity was also detected in lysates devoid of sPLA(2), indicating that both sPLA(2) and iPLA(2) contribute to arachidonic acid release in vivo. Swelling-induced taurine efflux was inhibited potently by BEL and partially by manoalide, whereas the reverse was true for melittin-induced taurine efflux. It is suggested that in NIH3T3 cells, swelling-induced taurine efflux is dependent at least in part on arachidonic acid release by iPLA(2) and possibly also by sPLA(2), whereas melittin-induced taurine efflux is dependent on arachidonic acid release by sPLA(2) and, to a lesser extent, iPLA(2).

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

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

Increased myogenic tone in 7-month-old adult male but not female offspring from rat dams exposed to hypoxia during pregnancy

Intrauterine growth restriction (IUGR) increases the risk of cardiovascular disease later in life. Vascular dysfunction occurs in adult offspring from animal models of IUGR including maternal undernutrition, but the influence of reduced fetal oxygen supply on adult vascular function is unclear. Myogenic responses, essential for vascular tone regulation, have not been evaluated in these offspring. We hypothesized that 7-mo-old offspring from hypoxic (12% O(2); H) or nutrient-restricted (40% of control; NR) rat dams would show greater myogenic responses than their 4-mo-old littermates or control (C) offspring through impaired modulation by vasodilators. Growth restriction occurred in male H (P < 0.01), male NR (P < 0.01), and female NR (P < 0.02), but not female H, offspring. Myogenic responses in mesenteric arteries from males but not females were increased at 7 mo in H (P < 0.01) and NR (P < 0.05) vs. C offspring. There was less modulation of myogenic responses after inhibition of nitric oxide synthase (P < 0.05), prostaglandin H synthase (P < 0.005), or both enzymes (P < 0.001) in arteries from 7-mo male H vs. C offspring. Thus reduced vasodilator modulation may explain elevated myogenic responses in 7-mo male H offspring. In contrast, there was increased modulation of myogenic responses in arteries from 7-mo female H vs. C or NR offspring after inhibition of both enzymes (P < 0.05). Thus increased vasodilator modulation may maintain myogenic responses in female H offspring at control levels. In summary, vascular responses in adult offspring from adverse intrauterine environments are impaired in a gender-specific, age-dependent, and maternal insult-dependent manner, with males more profoundly affected.

Estradiol-induced expression of N(+)-K(+)-ATPase catalytic isoforms in rat arteries: gender differences in activity mediated by nitric oxide donors

We tested the hypothesis that previously demonstrated gender differences in ACh-induced vascular relaxation could involve diverse Na(+)-K(+)-ATPase functions. We determined Na(+)-K(+)-ATPase by measuring arterial ouabain-sensitive 86Rb uptake in response to ACh. We found a significant increase of Na+ pump activity only in aortic rings from female rats (control 206 +/- 11 vs. 367 +/- 29 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.01). Ovariectomy eliminated sex differences in Na(+)-K(+)-ATPase function, and chronic in vivo hormone replacement with 17beta-estradiol restored the ACh effect on Na(+)-K(+)-ATPase. Because ACh acts by enhancing production of NO, we examined whether the NO donor sodium nitroprusside (SNP) mimics the action of ACh on Na(+)-K(+)-ATPase activity. SNP increased ouabain-sensitive 86Rb uptake in denuded female arteries (control 123 +/- 7 vs. 197 +/- 12 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.05). Methylene blue (an inhibitor of guanylate cyclase) and KT-5823 (a cGMP-dependent kinase inhibitor) blocked the stimulatory action of SNP. Exposure of female thoracic aorta to the Na+/K+ pump inhibitor ouabain significantly decreased SNP-induced and ACh-mediated relaxation of aortic rings. At the molecular level, Western blot analysis of arterial tissue revealed significant gender differences in the relative abundance of catalytic isoforms of Na(+)-K(+)-ATPase. Female-derived aortas exhibited a greater proportion of alpha2-isoform (44%) compared with male-derived aortas. Furthermore, estradiol upregulated the expression of alpha2 mRNA in male arterial explants. Our results demonstrate that enhancement of ACh-induced relaxation observed in female rats may be in part explained by 1) NO-dependent increased Na(+)-K(+)-ATPase activity in female vascular tissue and 2) greater abundance of Na(+)-K(+)-ATPase alpha2-isoform in females.

Effect of gender on endothelium-dependent dilation to bradykinin in human adipose microvessels

We examined the influence of gender and climacteric status, two coronary risk factors, on bradykinin (BK)-induced dilation in adipose arterioles from men and women of different ages [premenopausal women (Pre-W), postmenopausal women (Post-W), and similar aged men (Y-M and O-M), respectively]. We examined the responses from both omental (more closely associated with coronary disease) and subcutaneous fat. Tissues were obtained at surgery and cannulated (60 mmHg) for measurement of internal diameter. In vessels from omental tissue, dilation to BK was more sensitive in Pre-W than other groups, whereas in vessels from subcutaneous tissue, sensitivity to BK was greater in both Pre-W and Post-W compared with Y-M and O-M. Maximal dilation was similar among groups. Indomethacin (Indo; 10(-5) M) alone had no effect on dilation to BK in any groups, but Indo and N(omega)-nitro-L-arginine methyl ester (L-NAME; 10(-4) M) reduced dilation to BK in Pre-W more than in Y-M. L-NAME increased dilation to BK in subcutaneous fat from Y-M but had no effect in Post-W and O-M. Indo- and L-NAME-resistant dilation in all vessels was markedly reduced by 30 mM KCl. There was no difference in sodium nitroprusside-induced dilation among groups. We conclude that gender and climacteric state contribute to mechanisms of microvascular regulation in humans. Functional vascular differences in visceral and subcutaneous fat may underlie the proposed differential influence of these tissues on cardiovascular risk.

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.

Effect of estrogen on flow-induced dilation in NO deficiency: role of prostaglandins and EDHF

To investigate the role of estrogen in flow-induced dilation (FiD) in nitric oxide (NO) deficiency, FiD was examined in isolated gracilis arterioles of ovariectomized (OVX) and OVX rats with estrogen replacement (OVE). Both groups of rats were treated chronically with N(omega)-nitro-L-arginine methyl ester. Plasma concentration of NO(2)/NO(3) was reduced in both groups. Plasma concentration of estradiol was lower in OVX than in OVE rats. FiD was similar in vessels of the two groups; calculated wall shear stress and basal tone were significantly greater in OVX vs. OVE rats. Indomethacin did not affect FiD in vessels from OVE rats but abolished dilation in vessels from OVX rats. Valeryl salicylate or NS-398 inhibited FiD by approximately 50%, whereas their simultaneous administration eliminated the response in arterioles from OVX rats. In vessels from OVE rats, miconazole or charybdotoxin eliminated FiD. Thus, in NO deficiency, prostaglandins derived from both cyclooxygenase isoforms mediate FiD in gracilis arterioles of OVX rats. Estrogen replacement switches the mediation, showing dependence on endothelium-derived hyperpolarizing factor in the arterioles of OVE rats.

Selected contribution: cerebrovascular nos and cyclooxygenase are unaffected by estrogen in mice lacking estrogen receptor-alpha

Estrogen alters reactivity of cerebral arteries by modifying production of endothelium-dependent vasodilators. Estrogen receptors (ER) are thought to be involved, but the responsible ER subtype is unknown. ER-alpha knockout (alphaERKO) mice were used to test whether estrogen acts via ER-alpha. Mice were ovariectomized, with or without estrogen replacement, and cerebral blood vessels were isolated 1 mo later. Estrogen increased levels of endothelial nitric oxide synthase and cyclooxygenase-1 in vessels from wild-type mice but was ineffective in alphaERKO mice. Endothelium-denuded middle cerebral artery segments from all animals constricted when pressurized. In denuded arteries from alphaERKO but not wild-type mice, estrogen treatment enhanced constriction. In endothelium-intact, pressurized arteries from wild-type estrogen-treated mice, diameters were larger compared with arteries from untreated wild-type mice. In addition, contractile responses to indomethacin were greater in arteries from wild-type estrogen-treated mice compared with arteries from untreated wild-type mice. In contrast, estrogen treatment of alphaERKO mice had no effect on diameter or indomethacin responses of endothelium-intact arteries. Thus ER-alpha regulation of endothelial nitric oxide synthase and cyclooxygenase-1 pathways appears to contribute to effects of estrogen on cerebral artery reactivity.

Estrogen restores postischemic pial microvascular dilation

Estrogen protects the brain from experimental cerebral ischemia, likely through both vascular and neuronal cellular mechanisms. The purpose of this study was to determine whether chronic estrogen treatment in males and repletion in ovariectomized (Ovx) females reverses abnormalities in pial arteriolar reactivity during reperfusion from global forebrain ischemia (4-vessel occlusion, 15 min) and whether the site of protection is vascular endothelium. Male and Ovx female rats were implanted with either placebo or a 25-microg 17 beta-estradiol pellet 10 days before ischemia. With the use of intravital microscopy, pial vessel dilation to ACh (10 microM) and S-nitroso-N-acetyl-penicillamine (SNAP; 1 microM) and vasoconstriction to serotonin (10 microM) was examined in situ at 30--60 min of reperfusion. Postischemic changes in vessel diameter were compared with preischemic values for each agent. Postischemic response to both ACh and SNAP was lost in males and Ovx females, but not in estrogen pellet-implanted males and estrogen-implanted Ovx females, suggesting that estrogen protects both endothelial and smooth muscle-mediated vasodilation. Ischemia blunted vessel constriction to serotonin regardless of treatment. These data demonstrate that estrogen acts as a vasoprotective agent within the cerebral circulation and can improve microvascular function under conditions of an acutely evolving ischemic pathology.

Gender-specific compensation for the lack of NO in the mediation of flow-induced arteriolar dilation

Flow-induced dilation of gracilis muscle arterioles was examined in both genders of control rats and rats chronically treated with N ω-nitro-l-arginine methyl ester (l-NAME). After l-NAME treatment (4 wk), systolic blood pressure was significantly increased compared with control, whereas the plasma concentration of nitrate/nitrite was significantly reduced. Isolated and pressurized arterioles dilated significantly in response to increases in flow (0–25 μl/min). Flow-induced dilation was comparable in arterioles of control andl-NAME-treated rats but was significantly greater in female than in male rats. l-NAME + indomethacin, which abolished flow-induced dilation in arterioles of male control rats, inhibited the dilation by only ∼75% in female control rats. The residual portion of the response was eliminated by additional administration of miconazole, an inhibitor of cytochrome P-450. Indomethacin did not affect the dilation in femalel-NAME-treated rats but completely inhibited the response in male l-NAME-treated rats. The indomethacin-insensitive, flow-induced dilation in female l-NAME-treated arterioles was abolished by miconazole, 6-(2-proparglyoxyphenyl)hexanoic acid, or charybdotoxin. Thus an augmented release of endothelial prostaglandins accounts for the preserved flow-induced dilation in arterioles of male rats, whereas a metabolite of cytochrome P-450 is responsible for the maintenance of flow-induced dilation in female rats, suggesting important differences in the adaptation of the endothelium of arterioles from male and female rats to the lack of nitric oxide (NO) synthesis.

Gender-related differences in proliferative response of cardiac fibroblasts to hypoxia: effects of estrogen

Ischemic heart disease is more prevalent in men than in women. The remodeling of extracellular matrix, is a structural correlate of heart failure of ischemic origin and proliferation of cardiac fibroblasts is a key factor in this remodeling. We asked if proliferative response of male and female cardiac fibroblasts is differentially susceptible to hypoxia. DNA synthesis, using 3H-thymidine incorporation was compared under hypoxia (2% O2) in cardiac fibroblasts obtained from adult, age-matched male and female rat heart. In female cells DNA synthesis remained unchanged under hypoxia and this resistance was dependent on tyrosine kinase activation, as it was abolished in the presence of genistein, a tyrosine kinase inhibitor. Male cells, on the other hand, were susceptible to hypoxia and their DNA synthesis was reduced significantly (70%, (p < 0.0001). This effect was partially reversed by inhibition of tyrosine kinase. Western analysis showed a higher abundance of tyrosine phosphorylated proteins in male cells compared to female cells as well as differences in molecular weight of basal and hypoxia-induced tyrosine-phosphorylated proteins between male and female cells. The presence of estrogen (17-beta estradiol, 10 nM) altered the response of both cells to hypoxia. In female cells the combined effect of hypoxia and estrogen led to inhibition of DNA synthesis, whereas in male cells estrogen partially reversed the hypoxia-induced inhibition of DNA synthesis (37% (p < 0.01) inhibition in the presence of estrogen vs. 70% (p < 0.0001) inhibition in the absence of estrogen). The effects of estrogen in male and female cells were mediated via estrogen receptors as they were reversed by the pure anti-estrogen, ICI 182,780. Western analysis of cell lysate showed hypoxia-induced increase in the level of estrogen receptor beta in both male and female cells. Gel shift analysis showed hypoxia-induced increase in cytoplasmic ERE (estrogen response element)-binding activity and decrease in nuclear ERE-binding in male cells. In female cells cytoplasmic and nuclear ERE-binding activities remained unchanged under hypoxia. Together, these data demonstrate that while female cells are resistant to hypoxia-induced inhibition in DNA synthesis, male cells are susceptible; intracellular pathways involving tyrosine phosphorylation are involved in the response of both cells; and estrogen, via estrogen-receptor-dependent mechanisms, differentially alters the response of male and female cells to hypoxia.

17beta-estradiol prevents oxidative stress and decreases blood pressure in ovariectomized rats

In this study, we tested whether estrogen deficiency is associated with oxidative stress and decreased nitric oxide (NO) production, which could be responsible for an increased blood pressure in ovariectomized rats. Hemodynamic studies were performed on conscious, chronically instrumented rats. Chronic estrogen replacement on ovariectomized rats lowered blood pressure approximately 13 mmHg, from 119 +/- 3 mmHg in ovariectomized rats to 106 +/- 3 mmHg in ovariectomized-treated rats; it was also accompanied by an increase in cardiac index and vascular conductance, achieving hemodynamic values similar to those shown by sham-operated rats. N(G)-nitro-L-arginine methyl ester administration lowered significantly less the vascular conductance (0.14 +/- 0.01 vs. 0.22 +/- 0.03 and 0.26 +/- 0.01 ml. min(-1). mmHg(-1)/100 g; P < 0.05) in ovariectomized rats than in the sham-operated and estrogen-treated ovariectomized rats, respectively. Estrogen replacement prevented the lower plasma levels of nitrites/nitrates observed in ovariectomized rats. The lower plasma total antioxidant status and reduced thiol groups and the increase in plasma lipoperoxides presented in ovariectomized animals were reestablished with the estrogen treatment. These results show that estrogen administration decreases blood pressure and increases vascular conductance in ovariectomized rats. This effect may be related to an increase in NO synthesis and/or preventing oxidative stress, then improving endothelial function.

Estrogen reduces mouse cerebral artery tone through endothelial NOS- and cyclooxygenase-dependent mechanisms

Gender and estrogen status are known to influence the incidence and severity of cerebrovascular disease. The vasoprotective effects of estrogen are thought to include both nitric oxide-dependent and independent mechanisms. Therefore, using small, resistance-sized arteries pressurized in vitro, the present study determined the effect of gender and estrogen status on myogenic reactivity of mouse cerebral arteries. Luminal diameter was measured in middle cerebral artery segments from males and from females that were either untreated, ovariectomized (OVX), or OVX with estrogen replacement (OVX + EST). The maximal passive diameters of arteries from all four groups were similar. In response to increases in transmural pressure, diameters of arteries from males and OVX females were smaller compared with diameters of arteries from either untreated or OVX + EST females. In the presence of N(G)-nitro-L-arginine methyl ester, artery diameters decreased in all groups, but diameters remained significantly smaller in arteries from males and OVX females compared with untreated and OVX + EST females. After endothelium removal or when inhibition of nitric oxide synthase and cyclooxygenase were combined, differences in diameters of arteries from OVX and OVX + EST were abolished. These data suggest that chronic estrogen treatment modulates myogenic reactivity of mouse cerebral arteries through both endothelium-derived cyclooxygenase- and nitric oxide synthase-dependent mechanisms.

17beta-estradiol restores endothelial nitric oxide release to shear stress in arterioles of male hypertensive rats

BACKGROUND

Endothelial nitric oxide (NO)-mediated responses are impaired in arterioles of male spontaneously hypertensive rats (SHR), but they are still present in female SHR. We hypothesized that in vitro incubation of arterioles of male SHR with estrogen will restore NO-mediated responses by upregulation of endothelial NO synthase.

METHODS AND RESULTS

Responses to increases in perfusate flow (from 0 to 25 microL/min) and to the calcium ionophore A23187 (5 x 10(-8) to 10(-6) mol/L), norepinephrine (NE; 10(-7) to 3 x 10(-7) mol/L), sodium nitroprusside (SNP; 10(-8) to 10(-6) mol/L), and adenosine (ADO; 10(-6) to 5 x 10(-5) mol/L) were studied in cannulated and pressurized gracilis muscle arterioles ( approximately 75 microm in diameter) isolated from 12-week-old male SHR before and after incubation with 10(-9) mol/L 17beta-estradiol (17beta-E(2)) for 16 to 18 hours. After incubation with 17beta-E(2), basal diameter of arterioles was significantly increased (by approximately 10%), and flow-induced dilation was significantly enhanced (79.8+/-2.9 versus 103.7+/-3.7 microm at 25 microL/min), resulting in a lowered shear stress (62.0+/-9.1 versus 32.5+/-4.2 dyne/cm(2)). Also, vasoconstrictions to A23187 were reversed to dilations (-18.7+/-2.2 versus 18.8+/-1.7 microm), and constrictions to NE were significantly attenuated (-30.7+/-3.0 versus -21.2+/-2.8 microm). These alterations were eliminated by ICI 182,780 (10(-7) mol/L), an estrogen receptor antagonist; 5, 6-dichloro-1-beta-D-ribofuranosylbenzimidazole (10(-5) mol/L), a transcription inhibitor; or N(omega)-nitro-L-arginine methyl ester (10(-4) mol/L), an inhibitor of NO synthase, whereas they were not affected by aminoguanidine (5 x 10(-5) mol/L), a specific inhibitor of inducible NO synthase. Arteriolar responses were not altered by incubation with 17alpha-estradiol.

CONCLUSIONS

Estrogen, via a receptor-mediated pathway, upregulates endothelial NO synthase gene expression, leading to increased NO production, and restores the regulation of wall shear stress in arterioles of male SHR.

Effect of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in the rat aorta

1. This study sought to evaluate whether the effects of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in rat aortic rings are mediated through the same mechanism. 2. Ovariectomized rats were treated daily with either 17-beta-estradiol-3-benzoate (100 microg kg(-1)) or vehicle for 1 week. 3. The effect of long-term 17-beta-estradiol treatment on the responses to cumulative doses of phenylephrine, 5-HT, calcium, potassium and 17-beta-estradiol was determined in aortic rings. In the same rings, the effect of acute exposure to 17-beta-estradiol (5 and 10 microM) on the dose response curves for phenylephrine, 5-HT, calcium, potassium and acetylcholine were estimated. The measurements were made in rings with and without intact endothelium. The tone-related basal release of nitric oxide (NO) was measured in rings with intact endothelium. 4. Long-term 17-beta-estradiol treatment reduced the maximum developed contraction to all contracting agents studied. This effect was abolished in endothelium denuded vessels. Acute 17-beta-estradiol treatment also reduced maximal contraction. This effect, however, was independent of the endothelium. 5. Long-term 17-beta-estradiol treatment significantly increased the ability of the rings to dilate in response to acetylcholine whereas acute exposure to 17-beta-estradiol had no effect. The tone-related release of NO was significantly increased after long-term exposure to 17-beta-estradiol. 6. In conclusion, this study indicate that the acute and long-term effects of 17-beta-estradiol in the rat aorta are mediated through different mechanisms. The long-term effect is mediated through the endothelium most likely by increasing NO release. In contrast, the acute effect of 17-beta-estradiol seems to be through an effect on the vascular smooth muscle cells.

Estrogen maintains nitric oxide synthesis in arterioles of female hypertensive rats

We hypothesized that in female spontaneously hypertensive rats (SHR), estrogen moderates the dysfunction of arterioles by preserving nitric oxide synthesis. To this end, we conducted experiments on isolated gracilis muscle arterioles (approximately 55 microns in diameter) of 12-week-old (SHR divided into four groups: females (fSHR), ovariectomized females (fSHR-OV), ovariectomized females with estrogen replacement (fSHR-OV+ES, 50 micrograms/kg SC 17 beta-estradiol benzoate every 48 hours), and males (mSHR). Arteriolar diameter in the presence of perfusion pressures of 60, 80, 100, and 120 mm Hg were obtained, and diameter changes were measured (at 80 mm Hg) in response to various concentrations of substance P (10(-9) to 5 x 10(-8) mol/L), sodium nitroprusside (10(-8) to 10(-6) mol/L), and A23187 (5 x 10(-8) to 10(-6) mol/L). The pressure-induced diameter of mSHR and fSHR-OV arterioles was significantly less (by approximately 10%) than that of fSHR and fSHR-OV+ES arterioles. N omega-nitro-L-arginine (10(-4) mol/L), a nitric oxide synthase inhibitor, elicited a significant decrease in basal arteriolar diameter of fSHR (by approximately 19%) and fSHR-OV+ES (by approximately 17%), thereby eliminating the differences in tone among the various groups. Dilations of fSHR and fSHR-OV+ES arterioles to substance P were significantly greater (by 140% at a concentration of 5 x 10(-8) mol/L) than those of mSHR and fSHR-OV arterioles, whereas dilations to sodium nitroprusside were not different among the groups. A23187 (a nitric oxide releaser) elicited dilations in arterioles of fSHR (5.9 +/- 1.5%, 13.0 +/- 1.8%, and 19.2 +/- 2.1%) and fSHR-OV+ES (4.3 +/- 1.0%, 10.3 +/- 2.4%, and 15.0 +/- 4.0%) but constrictions in those of mSHR (-7.5 +/- 1.6%, -25.3 +/- 39%, and -36.9 +/- 4.1%) and fSHR-OV (-2.6 +/- 1.7%, 7.4 +/- 3.3%, and -11.5 +/- 6.1%). We conclude that estrogen in fSHR is responsible for the preservation of nitric oxide synthesis in skeletal muscle arterioles, resulting in a greater modulation of pressure-induced myogenic tone than in mSHR and maintenance of nitric oxide-mediated dilations.