Amanda K. Sampson

Enhanced Angiotensin II Type 2 Receptor Mechanisms Mediate Decreases in Arterial Pressure Attributable to Chronic Low-Dose Angiotensin II in Female Rats

The renin-angiotensin system is a far more complex enzymatic cascade than realized previously. Mounting evidence suggests sex-specific differences in the regulation of the renin-angiotensin system and arterial pressure. We examined the hemodynamic responses, angiotensin II receptor subtypes, and angiotensin-converting enzyme 2 gene expression levels after graded doses of angiotensin II in males and females. Mean arterial pressure was measured via telemetry in male and female rats in response to a 2-week infusion of vehicle, low-dose (50 ng/kg per minute SC) or high-dose (400 ng/kg per minute SC) angiotensin II. The effect of concurrent infusion of the angiotensin II type 2 receptor (AT2R) blocker (PD123319) was also examined. The arterial pressure response to high-dose angiotensin II was attenuated in females compared with males (24±8 mm Hg versus 42±5 mm Hg; P for the interaction between sex and treatment <0.002). Remarkably, low-dose angiotensin II decreased arterial pressure (11±4 mm Hg; P for the interaction between sex and treatment <0.02) at a dose that did not have an effect in males. This decrease in arterial pressure in females was abolished by AT2R blockade. Renal AT2R, angiotensin-converting enzyme 2, and left ventricular AT2R mRNA gene expressions were markedly greater in females than in males with a renal angiotensin II type 1a receptor:AT2R ratio of ≈1 in females. Angiotensin II infusion did not affect renal AT2R mRNA expression but resulted in significantly less left ventricular mRNA expression. Renal angiotensin-converting enzyme 2 mRNA expression levels were greater in females than in males treated with high-dose angiotensin II (≈2.5 fold; P for the interaction between sex and treatment <0.05). In females, enhancement of the vasodilatory arm of the renin-angiotensin system, in particular, AT2R and angiotensin-converting enzyme 2 mRNA expression, may contribute to the sex-specific differences in response to renin-angiotensin system activation.

The "his and hers" of the renin-angiotensin system.

Sex differences exist in the regulation of arterial pressure and renal function by the renin-angiotensin system (RAS). This may in part stem from a differential balance in the pressor and depressor arms of the RAS. In males, the ACE/AngII/AT1R pathways are enhanced, whereas, in females, the balance is shifted towards the ACE2/Ang(1-7)/MasR and AT2R pathways. Evidence clearly demonstrates that premenopausal women, as compared to aged-matched men, are protected from renal and cardiovascular disease, and this differential balance of the RAS between the sexes likely contributes. With aging, this cardiovascular protection in women is lost and this may be related to loss of estrogen postmenopause but the possible contribution of other sex hormones needs to be further examined. Restoration of these RAS depressor pathways in older women, or up-regulation of these in males, represents a therapeutic target that is worth pursuing.

Gender Differences in Pressure-Natriuresis and Renal Autoregulation: Role of the Angiotensin Type 2 Receptor

Sexual dimorphism in arterial pressure regulation has been observed in humans and animal models. The mechanisms underlying this gender difference are not fully known. Previous studies in rats have shown that females excrete more salt than males at a similar arterial pressure. The renin-angiotensin system is a powerful regulator of arterial pressure and body fluid volume. This study examined the role of the angiotensin type 2 receptor (AT2R) in pressure-natriuresis in male and female rats because AT2R expression has been reported to be enhanced in females. Renal function was examined at renal perfusion pressures of 120, 100, and 80 mm Hg in vehicle-treated and AT2R antagonist-treated (PD123319; 1 mg/kg/h) groups. The pressure-natriuresis relationship was gender-dependent such that it was shifted upward in female vs male rats (P<0.001). AT2R blockade modulated the pressure-natriuresis relationship, shifting the curve downward in male (P<0.01) and female (P<0.01) rats to a similar extent. In females, AT2R blockade also reduced the lower end of the autoregulatory range of renal blood flow (P<0.05) and glomerular filtration rate (P<0.01). Subsequently, the renal blood flow response to graded angiotensin II infusion was also measured with and without AT2R blockade. We found that AT2R blockade enhanced the renal vasoconstrictor response to angiotensin II in females but not in males (P<0.05). In conclusion, the AT2R modulates pressure-natriuresis, allowing the same level of sodium to be excreted at a lower pressure in both genders. However, a gender-specific role for the AT2R in renal autoregulation was evident in females, which may be a direct vascular AT2R effect.

The arterial depressor response to chronic low-dose angiotensin II infusion in female rats is estrogen dependent

The complex role of the renin-angiotensin-system (RAS) in arterial pressure regulation has been well documented. Recently, we demonstrated that chronic low-dose angiotensin II (ANG II) infusion decreases arterial pressure in female rats via an AT(2)R-mediated mechanism. Estrogen can differentially regulate components of the RAS and is known to influence arterial pressure regulation. We hypothesized that AT(2)R-mediated depressor effects evident in females were estrogen dependent and thus would be abolished by ovariectomy and restored by estrogen replacement. Female Sprague-Dawley rats underwent ovariectomy or sham surgery and were treated with 17β-estradiol or placebo. Mean arterial pressure (MAP) was measured via telemetry in response to a 2-wk infusion of ANG II (50 ng·kg(-1)·min(-1) sc) or saline. MAP significantly decreased in females treated with ANG II (-10 ± 2 mmHg), a response that was abolished by ovariectomy (+4 ± 2 mmHg) and restored with estrogen replacement (-6 ± 2 mmHg). Cardiac and renal gene expression of components of the RAS was differentially regulated by estrogen, such that overall, estrogen shifted the balance of the RAS toward the vasodilatory axis. In conclusion, estrogen-dependent mechanisms offset the vasopressor actions of ANG II by enhancing RAS vasodilator pathways in females. This highlights the potential for these vasodilator pathways as therapeutic targets, particularly in women.

Postnatal Ontogeny of Angiotensin Receptors and ACE2 in Male and Female Rats

BACKGROUND Sex differences in the expression of the angiotensin (Ang) II receptors and angiotensin-converting enzyme 2 (ACE2) have been hypothesized to be a potential mechanism contributing to sex-specific differences in arterial pressure. Currently, sex differences in the expression of the angiotensin receptors and ACE2 remain undefined. OBJECTIVES The aim of this study was to define the postnatal ontogeny of mRNA expression, from birth to adulthood, of the Ang II and Ang-(1-7) receptors and ACE2 in male and female rats. METHODS Kidney and heart tissue was collected from male and female Sprague Dawley rats and snap-frozen at postnatal days (PNDs) 1, 30, 42, 70, and 110 (adult), and real-time polymerase chain reaction was performed to determine relative expression of the Ang II and Ang-(1-7) receptors (AT(1a)R, AT(1b)R, AT(2)R, and MasR) and ACE2. RESULTS All these components of the renin-angiotensin system (RAS) were detected in the kidney and left ventricle, although expression levels differed significantly between the sexes and across organs. Gene expression of most components of the RAS was high at birth and decreased with age in both sexes, except for ACE2 expression, which increased in the left ventricle with age (P(Age) < 0.001). Low levels of AT(2)R were observed in the ventricles in both sexes as adults. Most notably, AT(2)R expression was greatest in female kidneys and lowest in male kidneys compared with the left ventricle (P(Age*Sex) < 0.05). Interestingly, MasR expression in the female kidney was similar to the level of AT(2)R expression. Left ventricular MasR expression was greater than AT(2)R expression in both sexes but was not different between the sexes. The highest level of ACE2 expression was observed in adult female kidneys (P(AS) < 0.05). CONCLUSIONS The enhanced mRNA expression of the vasodilatory arm of the renal RAS (ACE2, AT(2)R) in females observed in the present study may contribute to sex differences in the regulation of arterial pressure and the incidence of cardiovascular disease in women.

Compound 21, a selective agonist of angiotensin AT2 receptors, prevents endothelial inflammation and leukocyte adhesion in vitro and in vivo

Angiotensin AT2 receptors are upregulated in disease states such as atherosclerosis and blockade of the AT2 receptors exacerbates plaque formation. Direct stimulation of these receptors is anti‐atherogenic but the mechanisms and pathways involved remain unknown. We examined the effect of direct AT2 receptor stimulation with Compound 21 (C21) on the leukocyte adhesion cascade in vitro, right through to plaque formation in vivo.

SEX‐DIFFERENCES IN CIRCADIAN BLOOD PRESSURE VARIATIONS IN RESPONSE TO CHRONIC ANGIOTENSIN II INFUSION IN RATS

1 The aim of this study was to investigate the effect of chronic angiotensin II (AngII) infusion on the circadian rhythms of arterial blood pressure, heart rate (HR) and locomotor activity (ACT) in male and female rats. 2 Radiotelemetry probes were implanted into the aorta in male and female rats and allowed 10 days for recovery. Control levels for mean arterial pressure (MAP), HR and ACT were recorded for 3 days, then AngII (400 ng/kg per min s.c via osmotic minipump) or vehicle (saline) was infused for 10 days (n = 6 per group). Further recordings of MAP, HR and ACT were made during days 8, 9 and 10 of the infusion period. 3 In response to AngII infusion, night and day‐time MAP increased significantly in female (18 ± 2 mmHg; 28 ± 7 mmHg) and male (27 ± 4 mmHg; 30 ± 3 mmHg) rats, respectively. The degree of elevation in MAP in response to AngII was attenuated in the females during the night period (Psex < 0.05) but not the day (Psex = 0.2). Control night–day differences in MAP, HR and ACT averaged 7 ± 1 mmHg, 58 ± 5 b.p.m. and 30 ± 4 units in the female and 6 ± 1 mmHg, 43 ± 3 b.p.m. (Psex < 0.05) and 14 ± 2 units (Psex < 0.05) in male rats, respectively. AngII infusion disrupted MAP circadian rhythm in female (–4 ± 2 mmHg) and male rats (1 ± 2 mmHg; Ptreat < 0.01), but did not affect heart rate or locomotor activity. 4 In conclusion, sex differences in the circadian rhythm of heart rate and locomotor activity, but not arterial pressure exist under basal conditions. Circulating AngII modulated the circadian rhythm of MAP in female and male rats but not heart rate or locomotor activity. These findings have important implications for our understanding of circadian blood pressure rhythms in states of activation of the renin angiotensin system.

Y Are Males So Difficult to Understand?: A Case Where “X” Does Not Mark the Spot

Cardiovascular disease (CVD) remains one of the leading causes of death and disability in the Western world, accounting for 48 500 deaths and one third of all mortality in Australia in 2008.1 From 45 to 64 years of age there are significant sex differences in the mortality rates from CVD, with deaths rates in men ≈3 times that of age-matched women.2 Hypertension is the leading risk factor for the development of CVD, with men showing a higher arterial pressure than women during the ages of 20 to 65 years.3 Up until menopause, there are significant sex differences in blood pressure, vascular reactivity, and renal function.4–11 Not only are the rates of mortality sexually dimorphic but so are the symptoms experienced and disease development,4,12 resulting in a poorer outcome in men than in women. The response to treatment also differs between the sexes. For example, hypertensive women treated with an angiotensin receptor blocker have a better survival rate than women treated with an angiotensin-converting enzyme (ACE) inhibitor, whereas there is no difference in response to either agent in hypertensive men (as seen by the hazard ratio for treatment with an angiotensin receptor blocker versus treatment with ACE inhibitor of 0.69 in women and 1.10 in men).13–16 These data suggest that there are sex differences in the mechanisms underlying the development of hypertension. Despite these sex differences, the exact mechanism(s) underlying the increased morbidity and mortality in men remains elusive. Previous human studies have reported significant associations between the Y chromosome and blood pressure in Australian, Polish, and Scottish populations, suggesting that the Y chromosome may play a role17,18; however, this was not the case in a Spanish cohort.19 Further evidence from population studies suggests …

Caregiver outcomes and interventions: a systematic scoping review of the traumatic brain injury and spinal cord injury literature:

Aim: To identify factors reported with negative and positive outcomes for caregivers of the traumatic brain injury and spinal cord injury cohorts, to investigate what interventions have been studied to support carers and to report what effectiveness has been found. Methods: Scoping systematic review. Electronic databases and websites were searched from 1990 to December 2015. Studies were agreed for inclusion using pre-defined criteria. Relevant information from included studies was extracted and quality assessment was completed. Data were synthesised using qualitative methods. Results: A total of 62 studies reported caregiver outcomes for the traumatic brain injury cohort; 51 reported negative outcomes and 11 reported positive outcomes. For the spinal cord injury cohort, 18 studies reported caregiver outcomes; 15 reported negative outcomes and three reported positive outcomes. Burden of care was over-represented in the literature for both cohorts, with few studies looking at factors associated with positive outcomes. Good family functioning, coping skills and social support were reported to mediate caregiver burden and promote positive outcomes. A total of 21 studies further described interventions to support traumatic brain injury caregivers and four described interventions to support spinal cord injury caregivers, with emerging evidence for the effectiveness of problem-solving training. Further research is required to explore the effects of injury severity of the care recipient, as well as caregiver age, on the outcome of the interventions. Conclusion: Most studies reported negative outcomes, suggesting that barriers to caregiving have been established, but not facilitators. The interventions described to support carers are limited and require further testing to confirm their effectiveness.

Endothelial dysfunction in patients with type 2 diabetes post acute coronary syndrome

This single visit study examined whether endothelial function, in addition to cardiovascular (CV) risk factors and plasma microparticle content, was normalised in 15 patients with type 2 diabetes + acute coronary syndrome (ACS) (6 weeks–6 months post cardiac event) undergoing standard clinical care compared to 16 sex- and age-matched healthy controls. Results: While total and low-density lipoprotein (LDL) cholesterol levels were well controlled in the patients with type 2 diabetes + ACS, residual CV risk profiles such as increased body mass index (BMI), systolic blood pressure, glucose levels and triglycerides and lower high-density lipoprotein (HDL) levels were still apparent. Endothelium-dependent responses to acetylcholine (ACh) were significantly lower in type 2 diabetes + ACS patients compared to controls. Correspondingly, the reactive hyperaemic index (RHI) was lower in the patient cohort. Endothelial microparticle (EMP) levels (CD31+, CD41−) were 40% lower in the patient cohort. Simultaneous analysis of platelet microparticle (PMP) levels (CD41+) showed no difference between cohorts. Conclusions: Patients with type 2 diabetes suffering from recent ACS exhibit residual CV risk factors despite being on standard clinical care. In addition, these patients continue to present with endothelial dysfunction despite having lower levels of EMPs.