No description available.

The renin-angiotensin system (RAS) has been implicated in vascular inflammation and atherosclerosis. Angiotensin II via the ATR1 can activate monocytes to produce inflammatory factors and increase adhesion. ATR1 expression is partly regulated by alternate splicing of the ATR1 gene. The RAS may also regulate immune function as part of the stress response: a model is proposed. ATR1 expression in two monocyte cell lines (U937 and THP-1) compared to a human microvascular endothelial cell line (HMEC1) was investigated. Western blot showed ATR1 protein expression in all cell types. PCR protocols targeted to the terminal protein-coding exon common to all transcript variants confirmed mRNA expression of the ATR1 gene in EC and monocytes. The 5 known splice variants were not identified in monocytes. 5-RLM RACE was used to identify the 5 untranslated ATR1 exons in monocytes. These data suggest a novel monocyte-specific splice variant, which may function in the cardiovascular disease process.

During a single bout of aerobic exercise, blood flow is shunted to exercising tissues while blood flow is maintained or reduced to less metabolically active areas (i.e. splanchnic area and non-working muscles). Although increased sympathetic activation and multiple metabolic factors participate in redistributing blood flow during aerobic exercise, the precise mechanism is not entirely known. The renin-angiotensin system (RAS), specifically the local vascular wall RAS, has been hypothesized to participate in the redistribution of blood flow during exercise. This study aimed to investigate whether vascular wall RAS in the femoral arteries (an artery which feeds active tissues during exercise) was altered by acute exercise, and if these vascular RAS alterations led to specific changes in vasomotor function. Male Sprague Dawley rats were exercised on a motorized treadmill for 1h at 21m/min with 15% grade. Immediately following exercise femoral arteries were excised, cleaned of surrounding connective tissue, and vascular RAS was evaluated. There was a decrease in femoral ACE activity (~40%) and expression (~20%) following a single bout of exercise. No change was observed in AT1 and AT2 receptor expression. To evaluate the effect of acute exercise and vascular RAS on vessel reactivity, vasomotor properties of the femoral arteries were assessed via vasoconstrictor and vasodilatory dose-response curves. No changes were observed in femoral artery responses to potassium chloride (KCl), signifying that electromechanical coupling was not affected by exercise or RAS pharmacological interventions. However, a significant decrease in maximum phenylephrine (PE) constriction was observed for acutely exercise animals (~13%). Paired with the observed maintenance KCl-mediated constriction, it appears an acute bout of exercise is able to attenuate α-adrenergic receptor-mediated vasoconstriction in the femoral artery. The decrease in maximum α-adrenergic vasoconstriction may be attributed to vascular RAS. The decrease in ACE activity supports the production of local vasodilating factors. Blocking AT1 receptors with telmisartan decreased PE constriction in control and exercised animals. Combining AT1 and AT2 receptor blockade (with PD123319) eliminated the attenuating effect of telmisartan alone on PE constriction. This data suggests that the attenuating effect of AT1 receptor blockade, on PE constriction, may depend on AT2 receptor activation. In addition, combined AT1 receptor blockade and nitric oxide synthase inhibition eliminated both the lone AT1 receptor blockade effect and exercise effect on PE constriction. Together, this data suggests that reduced PE constriction following acute exercise, and AT1 receptor blockade, is dependent on nitric oxide production. Vasodilation to the nitric oxide donor sodium nitroprusside (SNP) was not altered following exercise or RAS pharmacological intervention, signifying no change in signaling downstream of NO production/release. Endothelium-dependent vasodilation to acetylcholine (ACh) was not affected by acute exercise. However, responses to ACh were modulated by RAS pharmacological interventions supporting the responses seen in PE constriction and signifying the participation of vascular RAS in vasomotor function.

During a single bout of aerobic exercise, blood flow is shunted to exercising tissues while blood flow is maintained or reduced to less metabolically active areas (i.e. splanchnic area and non-working muscles). Although increased sympathetic activation and multiple metabolic factors participate in redistributing blood flow during aerobic exercise, the precise mechanism is not entirely known. The renin-angiotensin system (RAS), specifically the local vascular wall RAS, has been hypothesized to participate in the redistribution of blood flow during exercise. This study aimed to investigate whether vascular wall RAS in the femoral arteries (an artery which feeds active tissues during exercise) was altered by acute exercise, and if these vascular RAS alterations led to specific changes in vasomotor function. Male Sprague Dawley rats were exercised on a motorized treadmill for 1h at 21m/min with 15% grade. Immediately following exercise femoral arteries were excised, cleaned of surrounding connective tissue, and vascular RAS was evaluated. There was a decrease in femoral ACE activity (~40%) and expression (~20%) following a single bout of exercise. No change was observed in AT1 and AT2 receptor expression. To evaluate the effect of acute exercise and vascular RAS on vessel reactivity, vasomotor properties of the femoral arteries were assessed via vasoconstrictor and vasodilatory dose-response curves. No changes were observed in femoral artery responses to potassium chloride (KCl), signifying that electromechanical coupling was not affected by exercise or RAS pharmacological interventions. However, a significant decrease in maximum phenylephrine (PE) constriction was observed for acutely exercise animals (~13%). Paired with the observed maintenance KCl-mediated constriction, it appears an acute bout of exercise is able to attenuate α-adrenergic receptor-mediated vasoconstriction in the femoral artery. The decrease in maximum α-adrenergic vasoconstriction may be attributed to vascular RAS. The decrease in ACE activity supports the production of local vasodilating factors. Blocking AT1 receptors with telmisartan decreased PE constriction in control and exercised animals. Combining AT1 and AT2 receptor blockade (with PD123319) eliminated the attenuating effect of telmisartan alone on PE constriction. This data suggests that the attenuating effect of AT1 receptor blockade, on PE constriction, may depend on AT2 receptor activation. In addition, combined AT1 receptor blockade and nitric oxide synthase inhibition eliminated both the lone AT1 receptor blockade effect and exercise effect on PE constriction. Together, this data suggests that reduced PE constriction following acute exercise, and AT1 receptor blockade, is dependent on nitric oxide production. Vasodilation to the nitric oxide donor sodium nitroprusside (SNP) was not altered following exercise or RAS pharmacological intervention, signifying no change in signaling downstream of NO production/release. Endothelium-dependent vasodilation to acetylcholine (ACh) was not affected by acute exercise. However, responses to ACh were modulated by RAS pharmacological interventions supporting the responses seen in PE constriction and signifying the participation of vascular RAS in vasomotor function.

published_or_final_version / Physiology / Master / Master of Philosophy

No description available.

The renin angiotensin aldosterone system is the dominant hormonal regulatory system controlling sodium balance and therefore blood pres- sure homeostasis. Abnormal modulation of this system is implicated in the pathogenesis of hypertension and end organ injury. We have previously developed the Cyp1a1-Ren2 transgenic rat to model an- giotensin II (ANG II) dependent hypertension. In this model hyper- tension causes renal injury, predominantly in the preglomerular vas- culature. The susceptibility to renal injury has a genetic component. A consomic/congenic study identified angiotensin converting enzyme (Ace) as an important modifer. However, renal injury is unlikely to be in uenced by a single gene. In this thesis it was hypothesised that examination of a renal microar- ray to compare the relative expression in F344 (susceptible) and Lewis (relatively protected) strains would reveal further genetic factors me- diating renal injury susceptibility. Genome wide expression analysis confirmed that Ace was a key modifier gene. Furthermore, the puriner- gic receptors P2x7 and P2x4 were identified as additional candidates. Gene and protein expression of these P2X receptors were both higher in F344 compared with Lewis. Immunohistochemistry localised P2X7 and P2X4 to the renal vasculature and tubules: the expression pattern was similar in both strains but became distinct in the renal medulla. F344, but not Lewis, responded to acute antagonism of P2X7 and P2X4. F344 showed a significant drop in blood pressure but maintained renal blood ow, indicative of tonic renal vasoconstriction. When ANG II was infused into F344 rats, there was a modest increase in blood pressure and an impairment of the pressure-natriuresis mecha- nism but no overt injury. Blood oxygenation-level dependent magnetic resonance imaging of the kidney identified a decrease in renal R2* sig- nal following P2X7 and P2X4 antagonism in ANG II infused F344 rats. P2X7/4 receptor activation reduces oxygenation and suppresses pressure-natriuresis. These effects are pro-biotic and may underpin susceptibility to renal injury.

No description available.

Despite the number of therapeutic interventions currently available for treating hypertension, approximately one-third of adult patients in the United States currently being treated remain hypertensive (43). As the number of hypertensive patients continues to grow, it is becoming increasingly important to investigate the different types of hypertension in order to have a greater understanding of the pathogenesis and identify potential targets for treatment. Neurogenic hypertension refers to hypertension resulting from a centrally mediated mechanism, likely involving a sustained increase in sympathetic nervous system activity. The renin-angiotensin aldosterone system (RAAS) is a physiological cascade responsible for restoring blood pressure when it drops. The rate-limiting step involves the enzyme renin. Although there is evidence of local RAAS activity in the brain, expression of renin in the brain is very low (125). The (pro)renin receptor ((P)RR) is able to bind and activate both renin and (pro)renin. Because the (P)RR and (pro)renin expression is high in the brain, it is possible that local RAAS activity is orchestrated by the (P)RR. In this study, we investigated if neuroinflammatory conditions could foster an environment that would allow for a rise in sympathetic nervous system activity (SNA) resulting from brain RAAS activity and the (P)RR. By treating neuronal cell cultures with proinflammatory cytokines, an anti-inflammatory agent, and (pro)renin, we explored any changes or differences in mRNA expression levels. Additionally, the effects of antioxidants were investigated. The results of this study showed that cells lacking antioxidants were more vulnerable to cellular stress and inflammation in the presence of increased (pro)renin. Proinflammatory stress was correlated with increased mRNA expression of proinflammatory and immune system regulatory genes in addition to increased expression of angiotensin II type I receptor, a vital component of RAAS. This could indicate that neuroinflammatory stress can be exacerbated and contribute to increased RAAS activity in the brain mediated by the (P)RR.

Ph.D., Faculty of Health Sciences, University of the Witwatersrand, 2011 / In groups of African ancestry, who have a high prevalence of “salt-sensitive, low-renin” hypertension, there is considerable uncertainty as to relevance of the renin-angiotensin-aldosterone system (RAAS) in the pathophysiology of primary hypertension. In the present thesis I explored the possibility that the RAAS, through interactions with environmental effects, contributes to blood pressure (BP) in this ethnic group. After excluding participants with aldosterone-to-renin ratios (ARR) above the threshold for primary aldosteronism, in 575 participants of African ancestry, I demonstrated that with adjustments for confounders, an interaction between ARR and urinary Na+/K+ (and index of salt intake obtained from 24-hour urine samples) was independently associated with BP (p<0.0001). This effect was accounted for by interactions between serum aldosterone concentrations and urinary Na+/K+ (p<0.0001), but not between plasma renin concentrations and urinary Na+/K+ (p=0.52). The interaction between ARR and urinary Na+/K+ translated into a marked difference in the relationship between urinary Na+/K+ and BP in participants above and below the median for ARR (p<0.0001 for a comparison of the relationships). Having demonstrated that circulating aldosterone concentrations may account for a substantial proportion of the relationship between salt intake and BP in this community sample, I subsequently assessed whether genetic factors contribute toward serum aldosterone concentrations. In 153 randomly selected nuclear families of African ancestry consisting of 448 participants without primary aldosteronism, with, but not without adjustments for plasma renin concentrations, independent correlations were noted for iii serum aldosterone concentrations between parents and children (p<0.05), with parent-child partial correlation coefficients being greater than those for father-mother relationships (p<0.05). Furthermore, after, but not before adjustments for plasma renin concentrations, serum aldosterone concentrations showed significant heritability (h2=0.25±0.12, p<0.02). No independent relationships between RAAS gene polymorphisms and serum aldosterone concentrations were observed. I also aimed to assess whether RAAS genes modify the relationship between cigarette smoking and BP in groups of African descent. However, as the impact of mild smoking on BP is uncertain, and in the community studied only 14.5% smoked and the majority of smokers were mild smokers (mean=7.4±4.6 cigarettes per day) in 689 randomly participants I initially assessed the relationship between smoking habits and out-of-office BP. In this regard, current smokers had higher unadjusted and multivariate adjusted 24-hour systolic/diastolic BP (SBP/DBP in mm Hg) (p<0.005-p<0.0005) than non-smokers, effects that were replicated in sex-specific groups, non-drinkers, and in the overweight and obese. Current smoking was second only to age and at least equivalent to body mass index in the quantitative impact on out-of-office BP and the risk of uncontrolled out-of-office BP was increased in smokers as compared to non-smokers. Thus, despite minimal effects on in-office BP, predominantly mild current smoking was independently associated with an appreciable proportion of out-of-office BP in a community of African ancestry. In 652 participants I subsequently assessed whether the angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism accounts for the strong relationships between predominantly mild smoking and out-of-office BP. After iv appropriate adjustments, an interaction between ACE DD genotype and current cigarette smoking, or the number of cigarettes smoked per day was independently associated with 24-hour and day diastolic BP (DBP) (p<0.05-0.005). This effect translated into a relationship between smoking and out-of-office BP or the risk for uncontrolled out-of-office BP only in participants with the DD as compared to the ID + II genotypes. In conclusion therefore, I afford evidence to suggest that in groups of African ancestry, aldosterone, within ranges that cannot be accounted for by the presence of primary aldosteronism, modifies the relationship between salt intake and BP, and that genetic factors account for the variation in serum aldosterone concentrations in this group. Furthermore, I show that the ACE gene modifies the relationship between smoking and out-of-office BP and hence accounts for even predominantly mild smoking producing a marked and clinically important effect on out-of-office BP. The present thesis therefore provides further evidence in favour of an important pathophysiological role for the RAAS in contributing toward BP in groups of African ancestry.