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The article discusses on the antihypertensive therapy in which renin–angiotensin system (RAS) is the most extensively studied regulatory pathway, citing the functions of all components of the RAS in brain.

The article explores whether blocking angiotensin II actions alters mean arterial pressure, baroreflex sensitivity or metabolic function. Mean arterial pressure was reduced in cadesartan-treated rats without significantly improving the vagal components of baroreflect function or heart rate variability. Findings demonstrate that blood pressure and baroreflex function can be essentially normalized independently of medullary nicotinamide adenine dinucleotide phosphate oxidase in hypertensive rats.

The article presents a study on the influence of the renin-angiotensin system to spontaneous baroreflex sensitivity (sBRS) resulting to increased mean arterial pressure. The investigation indicates that Betamethasone administration in premature infants deteriorates sBRS and heart rate in the future. The research emphasizes that gathered information will help evaluate humans exposed to steroids and delivered at full term.

We examined the impact of fetal programming on the functional responses of renal angiotensin receptors. Fetal sheep were exposed in utero to betamethasone (BMX; 0.17 mg/kg) or control (CON) at 80 to 81 days gestation with full-term delivery. Renal nuclear and plasma membrane fractions were isolated from sheep age 1.0 to 1.5 years for receptor binding and fluorescence detection of reactive oxygen species (ROS) or nitric oxide (NO). Mean arterial blood pressure and blood pressure variability were significantly higher in the BMX-exposed adult offspring versus CON sheep. The proportion of nuclear AT(1) receptors sensitive to losartan was 2-fold higher (67 ± 6% vs 27 ± 9%; P<0.01) in BMX compared with CON. In contrast, the proportion of AT(2) sites was only one third that of controls (BMX, 25 ± 11% vs CON, 78 ± 4%; P<0.01), with a similar reduction in sites sensitive to the Ang-(1-7) antagonist D-Ala7-Ang-(1-7) with BMX exposure. Functional studies revealed that Ang II stimulated ROS to a greater extent in BMX than in CON sheep (16 ± 3% vs 6 ± 4%; P<0.05); however, NO production to Ang II was attenuated in BMX (26 ± 7% vs 82 ± 14%; P<0.05). BMX exposure was also associated with a reduction in the Ang-(1-7) NO response (75 ± 8% vs 131 ± 26%; P<0.05). We conclude that altered expression of angiotensin receptor subtypes may be one mechanism whereby functional changes in NO- and ROS-dependent signaling pathways may favor the sustained increase in blood pressure evident in fetal programming. [ABSTRACT FROM AUTHOR]

Control of heart rate variability via modulation of sympathovagal balance is a key function of nucleus tractus solitarii and the dorsal motor nucleus of the vagus localized in the dorsomedial medulla oblongata. Normal blood pressure regulation involves precise balance of glutamate (Glu)-glutamine-gamma-aminobutyric acid transmitter systems, and angiotensin II modulates these transmitters to produce tonic suppression of reflex function. It is not known, however, whether other brain transmitters/metabolites are indicators of baroreflex function. This study establishes the concept that comprehensive baseline transmitter/metabolite profiles obtained using in vivo (1)H magnetic resonance spectroscopy in rats with well-characterized differences in resting blood pressure and baroreflex function can be used as indices of autonomic balance or baroreflex sensitivity. Transgenic rats with over-expression of renin [m(Ren2)27] or under-expression of glial-angiotensinogen (ASrAogen) were compared with Sprague-Dawley rats. Glu concentration in the dorsal medulla is significantly higher in ASrAogen rats compared with either Sprague-Dawley or (mRen2)27 rats. Glu levels and the ratio of Glu:glutamine correlated positively with indices of higher vagal tone consistent with the importance of these neurotransmitters in baroreflex function. Interestingly, the levels of choline-containing metabolites showed a significant positive correlation with spontaneous baroreflex sensitivity and a negative correlation with sympathetic tone. Thus, we demonstrate the concept that noninvasive assessment of neurochemical biomarkers may be used as an index of baroreflex sensitivity. [ABSTRACT FROM AUTHOR]

The angiotensin (Ang) type 1 receptor (AT(1)R) is highly expressed on renal nuclei and stimulates reactive oxygen species (ROS). It is not known whether other functional components of the Ang system regulate the nuclear Ang II-AT(1)R ROS pathway. Therefore, we examined the expression of Ang receptors in nuclei isolated from the kidneys of young adult (1.5 years) and older adult (3.0 to 5.0 years) sheep. Binding studies in renal nuclei revealed the AT(2)R as the predominant receptor subtype ( approximately 80%) in young sheep, with the Ang-(1-7) (AT(7)R; Mas protein) and AT(1)R antagonists competing for the remaining sites. Conversely, in older sheep, the AT(1)R accounted for approximately 85% of nuclear sites, whereas the Ang type 2 receptor and AT(7)R subtypes comprise approximately 20% of remaining sites. Ang II increased nuclear ROS to a greater extent in older (97+/-22%; n=6) versus young animals (7+/-2%; P=0.01; n=4), and this was abolished by an AT(1)R antagonist. The AT(7)R antagonist D-Ala(7)-Ang-(1-7) increased ROS formation to Ang II by approximately 2-fold (174+/-5% versus 97+/-22%; P<0.05) in older adults. Immunoblots of renal nuclei revealed protein bands for the AT(7)R and Ang-converting enzyme 2 (ACE2), which metabolizes Ang II to Ang-(1-7). The ACE2 inhibitor MLN4760 also exacerbated the Ang II-dependent formation of ROS (156+/-15%) and abolished the generation of Ang-(1-7) from Ang II. We conclude that an ACE2-Ang-(1-7)-AT(7)R pathway modulates Ang II-dependent ROS formation within the nucleus, providing a unique protective mechanism against oxidative stress and cell damage. [ABSTRACT FROM AUTHOR]

Circulating leptin is elevated in some forms of obesity-related hypertension, associated with impaired baroreflex function. Leptin receptors are present on vagal afferent fibers and neurons within the solitary tract nucleus, providing an anatomic distribution consistent with baroreflex modulation. Although solitary tract nucleus microinjection of 144 fmol/60 nL of leptin had no significant effect on baroreflex sensitivity for control of the heart rate in urethane/chloralose-anesthetized Sprague-Dawley rats, 500 fmol of leptin impaired baroreflex sensitivity for bradycardia in response to increases in pressure (1.15+/-0.04 versus 0.52+/-0.12 ms/mm Hg; P<0.01). Transgenic ASrAOGEN rats with low brain angiotensinogen have an upregulation of the leptin receptor and p85 alpha mRNA in the dorsal medulla relative to Sprague-Dawley rats. Consistent with these observations, the response to leptin was enhanced in ASrAOGEN rats, because both the 144-fmol (1.46+/-0.08 versus 0.75+/-0.10 ms/mm Hg; P<0.001) and 500-fmol (1.36+/-0.32 versus 0.44+/-0.06 ms/mm Hg; P<0.05) leptin microinjections impaired baroreflex sensitivity. At these doses, leptin microinjection had no effect on resting pressure, heart rate, or the tachycardic response to decreases in pressure in Sprague-Dawley or ASrAOGEN rats. Thus, exogenous leptin at sites within the solitary tract nucleus impairs the baroreflex sensitivity for bradycardia induced by increases in arterial pressure, consistent with a permissive role in mediating increases in arterial pressure. Baroreflex inhibition was enhanced in animals with evidence of increased leptin receptor and relevant signaling pathway mRNA. [ABSTRACT FROM AUTHOR]

Antenatal betamethasone treatment is a widely accepted therapy to accelerate lung development and improve survival in preterm infants. However, there are reports that infants who receive antenatal glucocorticoids exhibit higher systolic blood pressure in their early adolescent years. We have developed an experimental model of programming whereby the offspring of pregnant sheep administered clinically relevant doses of betamethasone exhibit elevated blood pressure. We tested the hypothesis as to whether alterations in angiotensin-converting enzyme (ACE), ACE2, and neprilysin in serum, urine, and proximal tubules are associated with this increase in mean arterial pressure. Male sheep were administered betamethasone (2 doses of 0.17 mg/kg, 24 hours apart) or vehicle at the 80th day of gestation and delivered at term. Sheep were instrumented at adulthood (1.8 years) for direct conscious recording of mean arterial pressure. Serum and urine were collected and proximal tubules isolated from the renal cortex. Betamethasone-treated animals had elevated mean arterial pressure (97+/-3 versus 83+/-2 mm Hg; P<0.05) and a 25% increase in serum ACE activity (48.4+/-7.0 versus 36.0+/-2.7 fmol/mL per minute) but a 40% reduction in serum ACE2 activity (18.8+/-1.2 versus 31.4+/-4.4 fmol/mL per minute). In isolated proximal tubules, ACE2 activity and expression were 50% lower in the treated sheep with no significant change in ACE or neprilysin activities. We conclude that antenatal steroid treatment results in the chronic alteration of ACE and ACE2 in the circulatory and tubular compartments, which may contribute to the higher blood pressure in this model of fetal programming-induced hypertension. [ABSTRACT FROM AUTHOR]

The article refers to research by Dr. Lewis K. Dahl concerning changes in systolic blood pressure that are caused by salt, and discusses the renin-angiotensin system (RAS). Regulation of RAS in the kidney during aging, renal function during therapy with angiotensin-converting enzyme inhibitors, the association of brain RAS in regulating intrarenal RAS, and experimentation on rats are mentioned.

Age-related impairments in baroreflex sensitivity in Sprague-Dawley rats are associated with low solitary tract nucleus content of angiotensin-(1-7). However, transgenic rats with low-brain angiotensinogen resulting from glial overexpression of an antisense oligonucleotide to angiotensinogen (ASrAOGEN) are spared age-related declines in cardiovascular function characteristic of Sprague-Dawley rats. We examine whether cardiovascular and reflex actions of angiotensin-(1-7) persist in the solitary tract nucleus of older (16 to 22 months) ASrAOGEN rats. Baroreflex sensitivity for control of heart rate and chemosensitive vagal afferent activation in response to phenylbiguanide were measured before and after bilateral microinjection of the angiotensin II type 1 receptor antagonist candesartan and angiotensin-(1-7) receptor antagonist (D-Ala(7))-angiotensin-(1-7) in urethane/chloralose-anesthetized rats. In older anesthetized ASrAOGEN rats, candesartan had no effect, whereas (D-Ala(7))-angiotensin-(1-7) significantly reduced baroreflex sensitivity (1.80+/-0.43 versus 0.50+/-0.17 ms/mm Hg). Phenylbiguanide responses were attenuated by injection of candesartan (-79+/-6 versus -55+/-12 mm Hg and -277+/-12 versus -156+/-27 bpm; P<0.05). In addition, resting blood pressure was reduced by injection of candesartan or (D-Ala(7))-angiotensin-(1-7). Within the solitary tract nucleus of older ASrAOGEN rats, it appears that glial angiotensinogen is the main source of angiotensin II attenuation of baroreflex sensitivity; endogenous angiotensin-(1-7) from nonglial sources enhances baroreflex sensitivity; nonglial sources of angiotensin II contribute to chemosensitive vagal afferent activation; and receptors for both peptides modulate resting arterial pressure under anesthesia. These results suggest a novel mechanism for the preservation of baroreflex sensitivity during aging. [ABSTRACT FROM AUTHOR]

The chorionic villi in the placenta are responsible for the regulation of fetal oxygen and nutrient transport. Although the peripheral renin-angiotensin system is activated during normal pregnancy, the regulation of the local chorionic villi renin-angiotensin system remains unknown. Therefore, placental chorionic villous tissue was collected from nulliparous third-trimester normotensive or preeclamptic subjects and was analyzed for angiotensin peptide content, angiotensinogen, renin, angiotensin-converting enzyme (ACE), ACE2, neprilysin, angiotensin II type 1 (AT(1)), angiotensin II type 2, Mas receptor mRNAs, and angiotensin receptor density and subtype. Angiotensin II in chorionic villi was significantly higher in preeclamptic subjects, whereas angiotensin (1-7) was not different. Angiotensinogen and AT(1) receptor gene expression was significantly higher in preeclamptic subjects. No differences were observed in renin, ACE, ACE2, or neprilysin gene expression. Mas receptor mRNA in preeclamptic subjects was decreased. The AT(1) receptor was the predominant receptor subtype in normal and preeclamptic chorionic villi. There was no difference in the density of the AT(1,) angiotensin II type 2, and angiotensin (1-7) receptors. These results indicate that enhanced chorionic villous expression of angiotensin II may result from increased angiotensinogen. Elevated angiotensin II, acting through the AT(1) receptor, may favor vasoconstriction in placental chorionic villi and contribute to impaired fetal blood flow and decreased fetal nutrition observed during preeclampsia. [ABSTRACT FROM AUTHOR]

We previously reported that ~70% of adolescents presenting to a Pediatric GI clinic for chronic nausea exhibit orthostatic intolerance (OI) in response to head upright tilt testing (HUT). The objective of this study was to determine whether supine mean arterial pressure or hemodynamic responses to HUT differ in these patients. Forty-eight patients (mean age of 15 [10-18] years, 36 females) completed a 45 minutes 0 to 70° HUT. Continuous blood pressure and heart rate recordings were acquired using non-invasive finger cuff. Thirteen subjects had normal tilt (Normal) while thirty five demonstrated OI. There were no differences between the two groups in supine blood pressures (BP), baroreflex sensitivity measured by frequency method in HF range (BRS), heart rate variability (HRV) measured as the root of mean square of successive differences (rMSSD), blood pressure variability (BPV) measured as standard deviation of mean arterial pressure (SDMAP) or the sympathovagal balance measure LFRRI/HFRRI. HUT caused a greater increase in heart rate in OI group (from 71 ± 6 beats/min to 104 ± 4 in OI vs from 75 ± 3 to 95 ±3 in normal, p=0.01) which was accompanied with lesser increase in BP (mainly due to lack of increase in diastolic) in the OI group. There was a trend for greater reduction in BRS in OI subjects (from 28.5 ± 13 ms/mm Hg to 6.3 ± 0.8 in OI vs from 21.1 ± 3.6 to 12.0 ± 2.9 in normal, p=0.09). HUT impaired HRV in both groups compared to supine values but the reduction was greater in OI group (-66.7 ± 4 % vs -52.0 ±5.6 in normal, p=<0.001). SDMAP increased by HUT compared to supine but to a greater extent in OI (40.6 ± 4 % vs 13.4 ± 8 in normal, p=0.02). LFRRI/HFRRI increased to a greater magnitude in OI group with HUT (from 1.8 ± 0.8 to 6.8 ± 0.8 in OI vs from 1.14 ± 0.18 to 4.1 ±0.7 in normal, p=0.02). These data reveal that the adolescents with orthostatic intolerance have attenuated parasympathetic responses and exaggerated activation of the sympathetic system to the heart and blood vessels. Despite these responses, subjects fail to maintain BP. Similar to previous studies in other subjects with OI, the excessive tachycardia often followed by syncope in most of these adolescents may reflect a loss of vascular responses to the activation of sympathetic and neurohumoral stimuli. Support: AHA12CRP9420029 [ABSTRACT FROM AUTHOR]

Hypertension and diminished blood flow to muscles and brain are common problems for the elderly that may lead to impaired cognition and physical performance and poor cardiovascular outcomes. Exercise improves blood pressure and brain blood flow. Thus, any intervention that can improve exercise effects in hypertensive individuals may have beneficial effects. High nitrate containing beetroot juice (BRJ) has been demonstrated to increase exercise tolerance and improve blood flow to working muscles. In this study we examined the effect of adding BRJ to an exercise regimen on exercise performance and cardiovascular measures in old subjects. Participant (n=26; mean age=65 yrs, range 57-77) with controlled hypertension (on 2 or more medications) were assigned to either exercise with BRJ+nitrate (BRJ+) (n=13, 6F) or BRJ-nitrate placebo drink (Placebo) (n=13, 7F). The exercise intervention was a 6-week treadmill walking program of self-paced. Participants walked 3 times per week for a maximum of 50 minutes per session. Participants also consumed 140 ml BRJ+ nitrate or BRJ-nitrate daily for 6 weeks. There were no differences between groups in mean VO2 max at the beginning of study (placebo = 19.4 ± 0.5 ml O2/kg/min; BRJ = 19.4 ± 0.5 ml O2/kg/min) and change VO2 max by the end of the intervention (increase of 1.15 ml O2/kg/min in placebo vs 0.9 ml O2/kg/min in BRJ+). There were no differences between groups in 24 hour ambulatory mean arterial pressure (MAP) or heart rate at the beginning of study. Heart rate and MAP showed similar reductions in both groups (4 beats/min for heart rate and 5 mm Hg for MAP). Similarly total arterial compliance was improved in both groups (placebo from 15.1 ± 3.7 ml/mm Hg to 18.3 ± 4.8, p = 0.02; BRJ+ from 18.3 ± 5.0 to 20.5 ± 3.9 ml/mm Hg; p = 0.04). There was no additional benefit of BRJ+ in the cardiovascular measures above that seen with exercise alone.In summary, in this cohort of controlled hypertensive elderly, addition of BRJ with nitrate to exercise has no additional benefits on physical performance or cardiovascular function. Further studies are warranted in different cohorts such as drug naïve or uncontrolled hypertensive to further characterize any possible benefits of BRJ. Support from WFU Translational Science Center [ABSTRACT FROM AUTHOR]

Children with chronic unexplained nausea have a high incidence of orthostatic intolerance (OI), with exaggerated suppression of baroreflexes upon standing. The renin-angiotensin system (RAS) is known to play a role in disorders related to OI likely as a compensatory mechanism for CV regulation. The objective of this study was to characterize the neurohumoral response to head upright tilt testing (HUT) in children with chronic nausea and OI. Forty-eight patients (mean age [range] of 15 [10-18] years)(36 females, 12 males) completed HUT. GI symptoms including nausea were reported during HUT. Subjects were maintained supine for 15 min before 45 min 70° HUT. Plasma hormones catecholamines (Cat), epinephrine (Epi), norepinephrine (NE), vasopressin (AVP), aldosterone (Aldo), renin, and angiotensins [Ang-(1-7) and AngII] were measured in blood sampled immediately before and after 15 min of upright tilt. Of the 48 HUTs, 35 subjects demonstrated OI. There were no differences in supine blood pressures (BP) or humoral measures between groups. OI subjects had lower systolic (105 ± 4 vs. 127 ± 4 mm Hg, p=0.001), diastolic (61 ± 2 vs. 77 ± 2, p<0.0001), and mean arterial (76 ± 2 vs. 93 ± 2, p=0.0002) BPs during HUT compared to normal subjects (mean ± SEM). They also had higher Cat (625 ±44 vs. 466 ± 61 pg/ml, p=0.02), AngII (48 ± 3 vs. 35 ± 4 pg/ml, p=0.04), and AVP (46 ± 12 vs. 18 ± 14 pg/ml, p=0.01) during HUT compared to non-OI subjects. There was a negative correlation between Ang-(1-7) and NE at baseline (r=-0.6, p<0.05) and HUT (r=-0.6, p=0.03) in Non-OI subjects that was not seen in OI subjects. Nausea was reproduced by HUT in 42% (20 of 48) of this cohort. Nausea subjects did not have a change in DBP (61 ± 2 vs. 61 ± 3 mm Hg) upon tilt, but had significantly higher AVP (72 ± 20 pg/ml, p=0.01) during HUT compared to subjects who did not experience nausea (15 ± 7, p=0.001). Children with chronic nausea testing positive for OI have elevated Cat, AngII, and AVP levels upon HUT. Elevated serum AVP may be a key trigger to nausea with orthostatic challenge independent of OI on HUT. In addition to this humoral response, the absence of change in DBP upon standing suggests a failure in both the sympathetic nervous system and RAS compensatory mechanisms necessary to sustain HUT in children with chronic nausea and OI. [ABSTRACT FROM AUTHOR]

Transgenic (mRen2)27 rats that over express the murine Ren2 gene are hypertensive and have impaired baroreflex sensitivity (BRS) for control of heart rate (HR). We previously showed that infusion of central angiotensin-(1-7) [Ang-(1-7)] improved the vagal components of the BRS independent of altering mean arterial pressure (MAP) but that, AT1 receptor blockade normalized MAP and blood pressure variability (BPV) without correcting the BRS. To determine if the overall sympathovagal imbalance and the BRS function can be corrected by supplementing Ang-(1-7) in combination with AT1 receptor blockade, we compared intracerebroventricular (ICV) infusions of the AT1 receptor antagonist candesartan (CV: 4 ug/5uL/hr) and Ang-(1-7) [0.1 ug/5uL/hr; n = 4] or artificial cerebrospinal fluid (aCSF; 5 uL/hr; n = 8) for 4 weeks in 18 week old male (mRen2)27 rats. MAP was significantly reduced in CV/ Ang-(1-7) treated rats [71 ± 13 vs. aCSF: 132 ± 12 mm Hg; p = 0.01] with no changes in HR. Lowering of MAP was associated with a reduction in low frequency systolic arterial pressure, an index of BPV, [LF-SAP%: 32 ± 8 vs. aCSF: 73 ± 10, p = 0.02] in these animals. Both vagal [high frequency alpha: 1.1 ± 0.3 vs. aCSF: 0.6 ± 0.1, p= 0.05 and Sequence UP: 1.7 ± 0.4 vs. aCSF: 0.7 ± 0.1, p= 0.03] and sympathetic [low frequency alpha: 0.65 ± 0.14 vs. aCSF: 0.34 ± 0.03, p= 0.02 and Sequence DOWN: 1.4 ± 0.3 vs. aCSF: 0.76 ± 0.1, p= 0.01] components of the BRS were significantly increased resulting in improvements in the overall BRS [Sequence ALL: 1.6 ± 0.3 vs. aCSF: 0.75 ± 0.1, p= 0.01] as well as the sympathovagal imbalance [LFRRI/HFRRI: 0.2 ± 0.1 vs. aCSF: 2.3 ± 0.6, p= 0.004] in treated animals. Thus, combination ICV therapy normalized MAP and corrected the sympathovagal imbalance leading to improved BRS function. Since impaired BRS significantly associates with cardiovascular pathologies independently from hypertension, specifically targeting an increase in central Ang-(1-7) with reduced Ang II actions to provide improved BRS and lower MAP may achieve a more optimal therapeutic benefit. [ABSTRACT FROM AUTHOR]

Children with chronic unexplained nausea have a high incidence of cardiovascular instability (~ 75%) manifesting as orthostatic intolerance (OI), with exaggerated suppression of baroreflexes upon standing. Because vasopressin (AVP) causes nausea and may be triggered by a fall in blood pressure (BP), we aimed to determine the relationship between AVP and tilt-induced changes in BP in children with OI. Forty-eight patients (mean age [range] of 15.2 [10-18] years) (36 females, 12 males) underwent tilt table testing for symptoms of OI and nausea. Subjects were maintained supine for 15 min before 45 min upright tilt (from 0 to 70 degrees). Plasma AVP was measured in blood sampled immediately before and 15 min into upright tilt. Of the 48 tilt tests: 9 were normal and 39 abnormal. Abnormal tests were classified as: postural orthostatic tachycardia syndrome (POTS, heart rate >120 bpm or increase by 30 bpm during first 10 min of tilt; n = 15), neutrally mediated hypotension (NMH, decrease in systolic BP [SBP] >25 mmHg during first 10 min of tilt; n = 2), and neurocardiogenic syncope (NCS, hypotension followed by syncope; n = 22). Mean supine SBP of normal subjects was 129 ± 9 mmHg and diastolic BP [DBP] was 64 ± 3 mm Hg (mean ± SEM). There were no differences in supine BPs among groups. Supine AVP levels were 4 ± 2 and 2 ± 1 in abnormal vs normal subjects (p = NS) There was a positive correlation between SBP and AVP in the supine position before tilt (0.34, p = 0.02). AVP increased by 44 ± 13 pg/mL vs. 1 ± 1 pg/mL for subjects with abnormal vs. normal tilt tests (p = 0.002), by 43 ± 17 pg/mL for NCS alone vs. normal (p = 0.02), and by 37 ± 20 pg/mL for POTS vs. normal (p = NS). There was a negative correlation between AVP and both SBP and DBP during tilt (-0.3, p = 0.035 and -0.4, p = 0.005, respectively). Hypotension and syncope upon tilt are associated with acute increases in AVP in subjects with OI and nausea. The increase in AVP may serve as a compensatory mechanism in the face of impaired autonomic reflexes. It is not known whether the increase in AVP contributes to the nausea observed during tilt, but better understanding of this relationship may allow for more effective treatment options for the management of nausea in these subjects. [ABSTRACT FROM AUTHOR]

The effect of the endocannabinoid system (ECS) on weight and energy metabolism is well accepted, but long term contributions of the ECS to cardiovascular regulation are not established. Evidence for receptor and signaling interactions between the ECS and the renin-angiotensin system (RAS) in brain and vasculature is emerging. In transgenic (mRen2)27 rats, a monogenetic angiotensin (Ang) II-dependent model of hypertension with increased body mass, acute blockade of CB1 receptors in the solitary tract nucleus (NTS) restores the impaired baroreflex sensitivity (BRS) for control of heart rate to normal levels. We interpret these data as evidence for upregulation of the ECS in brain of this RAS-dependent model of hypertension. Data from the acute studies prompted us to study the effects of chronic systemic CB1 receptor blockade in (mRen2)27 rats using rimonabant (SR141716A), an orally active antagonist with central and peripheral actions. Beginning at 16 weeks of age animals were given daily oral injections of SR141716A (10 mg/kg/day; n = 6) for 28 days. In comparison to rats receiving vehicle (0.1% Tween-80 in dH2O; n = 6), daily dosing of SR141716A significantly reduced systolic blood pressure within 1 wk and by day 25 values were 172 ± 1 in control vs. 151 ± 5 mmHg in treated rats (P < 0.01). This was accompanied by decreased cumulative weight gain (44 ± 3 vs. 26 ± 2 grams, P < 0.01) and adiposity index (2.8 ± 0.2 vs. 1.9 ± 0.2% of body weight, P < 0.05) without long-term changes in food or water consumption. At the end of the study, conscious pressure recordings were obtained via arterial catheter for spectral and sequence analysis of autonomic tone. Two-fold increases occurred in Sequence ALL (P < 0.05) and indices of vagal and sympathetic BRS, as well as in heart rate variability (SDRR, P < 0.01), a measure of vagus nerve tone. The chronic beneficial actions of SR141716A in (mRen2)27 animals are consistent with the interpretation that an upregulated ECS contributes to maintenance of hypertension and impaired BRS in this RAS-dependent model. We conclude that systemic blockade of CB1 receptors, perhaps in part via actions within the NTS, is an effective therapy for lowering blood pressure and body weight, with a concomitant positive influence cardiovagal reflexes in hypertension. [ABSTRACT FROM AUTHOR]

Antenatal betamethasone (BM) therapy accelerates lung development in preterm infants but may induce early programming events with long-term cardiovascular consequences. To elucidate these programming events, we developed a model of programming whereby pregnant ewes are administered BM (2 doses of 0.17 mg/kg) or vehicle at the 80th day of gestation and offspring are delivered at term. The BM-exposed (BMX) offspring develop elevated blood pressure, decreased baroreflex sensitivity, and alterations in the circulating, renal, and brain renin-angiotensin systems (RAS) by 6-months of age. While components of the RAS are present in cerebrospinal fluid (CSF), it is not known if BM exposure influences the CSF RAS to the same extent as other tissue compartments. Therefore, we characterized the CSF RAS in 6-month old male sheep, and established the impact of antenatal exposure on the RAS. Consistent with our previous findings of predominant ACE2 activity in the choroid plexus, CSF Ang-(1-7) levels are significantly higher than Ang I (320.8 ± 96.0 vs. 19.3 ± 4.6 pM; p<0.01, N = 12) or Ang II (1.4 ± 0.5 pM; p<0.01, N = 12). Moreover, Ang-(1-7) was 70% lower in the CSF of the BMX group (97.3 ± 31.4 pM; p<0.05) without changes in Ang I or Ang II. We next assessed the metabolism of Ang-(1-7) in the CSF and demonstrate a trend for increased enzyme activity in BMX males. Further analysis revealed two peptidases that contribute to Ang-(1-7) degradation in CSF of both groups. ACE accounted for approximately 15% (85 out of 100) of the overall Ang-(1-7) metabolism that hydrolyzed the peptide to Ang-(1-5) in CSF and ACE was 1.4-fold higher in the BMX group (6.5 ± 0.5 vs. 8.8 ± 0.5 fmol/min/ml; p<0.02, N = 4). We also identified a novel thiol peptidase activity (Ki = 4 μM PCMB) as the predominant activity that metabolized Ang-(1-7) to Ang-(1-4) in CSF; kinetic analysis of this peptidase in pooled CSF revealed Km and Vmax constants of 5.4 μM and 54 nmol/min/mg for control, and 4 μM and 60 nmol/min/mg for BMX. In summary, CSF levels of Ang-(1-7) were markedly lower following antenatal exposure. The reduced expression of central Ang-(1-7) potentially through an enhanced metabolism pathway may contribute to the long-term increase in blood pressure and an attenuated baroreflex in this model of fetal programming. [ABSTRACT FROM AUTHOR]

Hypotensive transgenic ASrAOGEN rats (AS) with low brain angiotensinogen resulting from glial overexpression of an antisense oligonucleotide to angiotensinogen, have enhanced baroreflex sensitivity (BRS) relative to hypertensive transgenic (mRen2)27 rats (mRen) that overexpress the murine Ren2 gene or normotensive Sprague Dawley rats (SD). The AS rats exhibit elevated protein expression and activity (less phosphorylated-ERK) of the MAP Kinase Phosphatase-1 [MKP-1], a negative regulator of MAP Kinase signaling in the brain dorsal medulla compared with either mRen or SD rats at 26 wks of age. To determine if MKP-1 plays a role in maintenance of BRS, we gave acute bilateral microinjections of an irreversible MKP-1 inhibitor {2,3-bis-[(2-Hydroxyethyl)thiol]-1,4-naphthoquinone, NSC 95397; 200 nM/120 nL} into the solitary tract nucleus (NTS), an important site in the dorsal medulla for modulation of BRS in urethane/chloralose anesthetized AS, mRen and SD rats at 21 wks of age. The MKP-1 inhibitor impaired the BRS for bradycardia in response to increases in pressure by 48 % at 10 min (1.01 ± 0.16 baseline vs. 0.49 ± 0.1 msec/mm Hg at 10 min), 56 % at 60 min and 64 % at 120 min in the AS rats (p = 0.02, n = 8), but not in the mRen or SD rats. In addition, NSC 95397 reduced resting pressure (91 ± 3 at baseline vs. 79 ± 3 at 60 min vs. 80 ± 3 mm Hg at 120 min) in the SD rats, with a similar trend in the other strains, without effects on resting heart rate in any strain. Thus, up-regulated expression of MKP-1 contributes to the higher resting BRS function in AS rats. AS animals are spared age-related declines in BRS and they maintain higher expression of MKP-1 protein in the dorsal medulla vs. either mRen or SD rats (AS: 1.6 ± 0.2, mRen: 0.8 ± 0.1, SD: 1 ± 0.1 arbitary units; p = 0.01, n = 6 per group) at 66 wks of age. Thus, higher MKP-1 may be involved the preservation of BRS in older AS rats, suggesting the phosphatase be a novel therapeutic target to improve BRS function in aging and hypertension. [ABSTRACT FROM AUTHOR]

There is growing evidence for a role of the endocannabinoid system in the pathogenesis of hypertension and associated metabolic syndrome. Presynaptic CB1 cannabinoid receptors, the neuronal target of endocannabinoids, are densely expressed in the solitary tract nucleus (NTS), the primary site for termination of baroreceptor afferent nerve fibers, and in vagal afferent neurons of the nodose ganglion. Our studies in anesthetized, normotensive Sprague-Dawley rats suggest that activation of cannabinoid receptors within the NTS via bilateral microinjection of the CB1 agonist CP55,940 modulates baroreflex sensitivity (BRS) for control of heart rate (HR) in a dose-related biphasic manner. Administration of the CB1-selective antagonist SR141716A (36 pmol) fully prevented or reversed these changes in BRS, and there was no significant effect of the antagonist alone in these normotensive animals (1.04 ± 0.05 ms/mmHg baseline vs. 1.12 ± 0.11 ms/mmHg after antagonist treatment, n = 5). We have now determined the effects of blockade of CB1 receptors in a model of angiotensin (Ang) II-dependent hypertension and insulin resistance with impaired BRS. In contrast to observations in normotensive rats, SR141716A dose-dependently improved BRS for control of HR when microinjected into the NTS of hypertensive, transgenic (mRen2)27 rats with impaired baseline BRS, without changing resting MAP or HR. Microinjection of 0.36 pmol SR141716A (n = 5) increased BRS from a baseline of 0.43 ± 0.03 ms/mmHg to 0.68 ± 0.02 (p < 0.001), and 36 pmol SR141716A (n = 5) increased BRS from 0.47 ± 0.02 to 1.05 ± 0.07 ms/mmHg (p < 0.001), a level that was comparable with baseline BRS of normotensive Sprague-Dawley rats. The demonstration of dose-dependent actions of the CB1 agonist on BRS in normotensive animals coupled with new findings that blockade of CB1 receptors improves BRS, an index of vagal function, in (mRen2)27 hypertensive animals is consistent with the interpretation that elevated endocannabinoids within the NTS contribute to impaired BRS. Thus, our findings suggest that blockade of CB1 receptors will influence cardiovagal reflexes in a positive manner in the context of hypertension and metabolic syndrome. [ABSTRACT FROM AUTHOR]

Fludrocortisone (Florinef) is commonly used to treat symptoms associated with postural orthostatic tachycardia syndrome (POTS). We have previously shown that Florinef treatment in children with POTS improved the changes in baroreflex sensitivity (BRS) and heart rate variability (HRV) measured as the root of mean square of successive differences (rMSSD) during upright tilt compared to untreated children with POTS. We noticed that a subgroup of our patients experienced POTS symptoms followed by syncope at later time points during the 45 min tilt test in both Florinef treated and untreated groups. We stratified based on syncope and compared the effect of Florinef treatment on both groups. Of the 32 POTS patients studied (15.0 ± 0.6 yrs old), 14 were treated with Florinef of whom 5 had syncope, and 18 were untreated of whom 5 had syncope. In the non-syncopal group, subjects treated with Florinef for a minimum of 4 wks compared with untreated POTS without syncope had similar baseline supine measures of MAP, HR, BRS and HRV before tilt, and less reduction in BRS during tilt measured as Seq UP (-7.1 ± 2.5 vs -15.1 ± 3.5 ms/mmHg; p<0.03), a trend for less attenuation in HRV (-22.4 ± 6.4 vs -35.3 ± 6.3 ms; p<0.07) and reduced tachycardia with tilt (25 ± 6 vs 38 ± 4 beats/min; p<0.02) compared with the untreated group. Meanwhile, in the syncopal group, Florinef-treated patients at baseline in the supine position before tilt had worse BRS function measured as Seq UP compared to untreated (11.9 ± 2.2 vs 26.0 ± 6.7 ms/mm Hg; p<0.04), a tendency for lower HRV (40.8 ± 7 vs 61.2 ± 12 ms; p<0.08) and higher HR (82 ± 3 vs 65 ± 7 beats/min; p<0.02) than untreated POTS patients with syncope. In contrast to non-syncopal POTS, the HR increase during tilt in syncopal POTS subjects was not reduced by the Florinef. The impairments in baseline supine autonomic function in POTS with syncope patients treated with Florinef relative to untreated patients and lack of improvement in the performance upon upright tilt suggests that POTS patients should be stratified by syncope status during the tilt test prior to assigning this treatment regimen. Additional studies are needed to better define these patients and to determine if other pharmacologic agents would provide a more optimal treatment. Support: AHA12CRP9420029 [ABSTRACT FROM AUTHOR]

The deleterious actions of angiotensin (Ang) II are generally thought to be mediated by NADPH oxidase (NOX)-derived reactive oxygen species (ROS) which may stimulate mitochondrial oxidant release leading to impaired energy metabolism. Hypertensive transgenic (mRen2)27 rats (mRen2) exhibit high NOX activity in brain dorsal medullary tissue compared to normotensive Hannover Sprague-Dawley (SD) control rats; however, the extent of mitochondrial involvement is unknown. Therefore, the present study evaluated mitochondrial ROS levels, ATP and mitochondrial content in the brain dorsal medulla of age-matched mRen2 and SD rats. Additional studies assessed AMP-activated kinase (AMPK) activation since altered mitochondrial oxidant and/or energy levels are associated with a stimulated AMPK pathway that is known to be activated in response to depleted cellular energy levels.Freshly isolated mitochondria from the dorsal medulla of 20 week old male heterozygous mRen2 [systolic blood pressure (SBP): 211 ± 4 mmHg] and SD [SBP: 120 ± 3 mmHg] rats were loaded with the sensitive ROS indicator dihydroethidium (HEt). Basal HEt fluorescence intensity was ∼16% higher in mRen2 as compared to SD rats suggesting higher ROS levels in mitochondria of the hypertensive strain [mRen2: 83 ± 4 vs. SD: 70 ± 4 mean fluorescence intensity; p=0.02, n=3]. Although ATP levels and mitochondrial content were similar between strains, AMPK was significantly activated (phosphorylated AMPK-α and β1 subunits) in the mRen2 compared to normotensive SD rats [AMPKα- mRen2: 3.5 ± 0.4 arbitary units vs. SD: 1.0 ± 0.2; p = 0.001, n = 5; and AMPKβ1- mRen2: 1.6 ± 0.04 arbitary units vs. SD: 1.0 ± 0.2; p = 0.05, n = 3]. The activation of AMPK may contribute to enhanced mitochondrial biogenesis since ATP and mitochondrial content were unchanged, thus representing a compensatory response to increased energy requirements in the hypertensive strain. We conclude that targeting of mitochondrial oxidants and increased AMPK activation may serve as a potential therapy to improve mitochondrial energy metabolism in hypertension. [ABSTRACT FROM AUTHOR]

Elevated supine mean arterial pressure (MAP) is often present in adults with dysautonomia. Children 15.1 ± 0.4 yrs of age (n = 22) with chronic unexplained nausea underwent continuous measures of supine blood pressure (BP) and heart rate (HR) pre- and post-tilt (0-70 degrees upright) and spectral analysis of their autonomic profile. Diagnostic workup revealed ∼77% have postural orthostatic tachycardia syndrome (POTS). The controls in this cohort had chronic nausea but were identified as normal upon tilt. Resting supine MAP and HR prior to tilt were higher in POTS subjects compared with controls, while most indices of autonomic function were similar (Table 1). Those diagnosed with POTS maintained MAP during tilt accompanied by a >5-fold increase in cardiac sympathetic drive (LFrri/HFrri) and >80% suppression of the baroreceptor reflex sensitivity (high frequency alpha index;HFα) in comparison to 2-fold and ∼60% responses in controls. BP variability (SDMAP) measured as the standard deviation of mean arterial presuure and HRV measured as the root of mean square of successive differences (rMSSD) were impaired to a greater extent in the POTS subjects. Exaggerated suppression of HRV during upright posture in POTS subjects is known. However, our studies reveal elevated supine MAP even at this young age. In adults, both impaired HRV and elevated supine MAP are risk factors for cardiovascular problems such hypertension and cardiac hypertrophy. Future studies are necessary to determine whether young adults with POTS are at greater risk of early onset cardiovascular disease, especially given the the potential impact of treatments aimed at increasing MAP. Support: AHA12CRP9420029 [ABSTRACT FROM AUTHOR]

Compelling evidence for an intracellular renin-angiotensin system (RAS) is evident in multiple tissues including the heart, vasculature, brain and kidney. Indeed, the full complement of angiotensin receptors is localized on renal cortical nuclei; however, elucidation of the intracellular pathways that contribute to the expression of Ang II or Ang-(1-7) is incomplete. The current study sought to identify a proximal tubule epithelial cell model to facilitate our understanding of the regulation and function of this intracellular system. Utilizing the rat-derived NRK52E epithelial cells, immunofluorescent staining and western blots revealed nuclear expression of angiotensinogen (Aogen), renin and the prorenin receptor (PRR). Further characterization of Aogen expression utilizing an antibody against the protein region distal to Ang I ([des-Ang I]-Aogen) revealed a single 60 kDa band evident in the nuclear and the cytosolic fractions of the cells. A second antibody to the Ang I sequence of Aogen revealed expression in the cytosol and collected cell media, but not the nuclear fraction. The large molecular form of renin in the nuclear fraction suggests the predominance of prorenin in the nucleus. Basal renin activity in the nuclear fraction as measured by Ang I generation was significantly inhibited by the specific renin inhibitor aliskiren [770 ± 46 vs. 129 ± 14 pg Ang I/mg protein, n=3; p<0.01]. Conversion of the proform to active renin (total renin) by trypsin treatment of the nuclear fraction increased renin activity 2-fold [1933 ± 230 pg Ang I/mg; n=3; p<0.01]; aliskiren significantly reduced total renin activity by 92% [167 ± 24 pg Ang I/mg, n=3; p<0.01]. Utilizing specific radioimmunoassays, we detected both Ang II and Ang-(1-7) at concentrations of 50 ± 24 and 51 ± 39 pg/mg protein, respectively (n=3) in nuclear extracts of NRK cells. Collectively, these data suggest that processing of Aogen from either prorenin or renin may occur on the nucleus forming [des-Ang I]-Aogen and the active peptides Ang II and Ang-(1-7). We conclude that a nuclear prorenin/renin-Aogen pathway may constitute one source of peptide ligands for intracellular angiotensin receptors. [ABSTRACT FROM AUTHOR]

Betamethasone (BMS) is administered to women entering into early preterm labor to facilitate fetal lung development and decrease infant mortality; however, fetal steroid exposure may lead to deleterious consequences long term. In a sheep model of BMS exposure in utero, we show elevated mean arterial pressure (MAP) and decreased baroreflex sensitivity (BRS) for control of heart rate at 6- and 20-months (mo) of age. The changes in MAP and BRS are associated with alterations in components of both the circulating and intra-renal renin-angiotensin systems (RAS) that may ultimately shift the balance to the pro-hypertensive peptide, angiotensin (Ang) II. In the brain solitary tract nucleus, Ang II actions through the AT1 receptor oppose the beneficial actions of Ang-(1-7) at the mas receptor for BRS regulation. We found decreased expression of the mas protein in the dorsal medulla of BMS-exposed animals at 6- and 20- months of age with no changes in the AT1 receptor expression. To determine whether tissue Ang peptides may contribute to altered BRS, the present study utilized three selective radioimmunoassay (RIAs) to quantify Ang I, Ang II and Ang-(1-7) in the dorsal medulla of 6-mo old male sheep. Comparisons of tissue peptide concentrations were not significantly different between groups; however, BMS-exposed offspring have a significant increase in the ratio of Ang II to Ang-(1-7) (Control: 0.61 ± 0.11, BMS: 2.3 ± 0.62; p<0.05). There was a significant increase in the ratio of Ang II to Ang I (Control: 0.66 ± 0.20, BMS: 2.35 ± 0.46), with no change in the ratio of Ang-(1-7) to Ang I. The altered peptide ratios potentially reflect a decrease in the ACE2 enzyme, which converts Ang II to Ang-(1-7), and an increase in ACE activity which concerts Ang I to Ang II. Future studies are required to determine enzymatic activity in dorsal medullary tissue, but data are consistent with previous observations on altered ACE and ACE2 in the circulation and kidney of BMS-exposed animals. We conclude that BMS-depedent fetal programming may influence the central RAS through alterations in the balance of Ang II and Ang-(1-7) that contribute to the elevated MAP, lower BRS, and altered renal function in this model. Support: HD0474584 [ABSTRACT FROM AUTHOR]