Borderline Hypertensive Rats Research Articles

Dimethyl Fumarate Prevents the Development of Chronic Social Stress-Induced Hypertension in Borderline Hypertensive Rats.

This study investigated the effects of chronic crowding-induced social stress and dimethyl fumarate (DMF) on borderline hypertensive rats, focusing on the transcription nuclear factor (erythroid-derived 2)-like 2 (NRF2) gene Nfe2l2, on the expression of selected NFR2-mediated gene expressions in the heart, and on vascular function. Rats were exposed to chronic crowding, DMF treatment (30 mg/kg/day, p.o.), or a combination of both for six weeks. Blood pressure (BP) was measured non-invasively, gene expressions were analysed using RT-qPCR, and vascular function was assessed by measuring noradrenaline (NA)-induced vasoconstriction and endothelium-dependent and -independent relaxations in the femoral arteries using a wire myograph. Chronic stress increased BP, Nfe2l2 expression, and NA-induced vasoconstriction, though it did not affect relaxation responses nor the left heart ventricle-to-body weight (LHV/BW) ratio. DMF elevated Nfe2l2 expression (as the main effect) in the heart but did not alter BP and vascular functions vs. control when administered alone. Interestingly, DMF increased the LHV/BW ratio, supposedly due to reductive stress induced by continuous NRF2 activation. When combined with stress, DMF treatment prevented stress-induced hypertension and mitigated NA-induced vasoconstriction without altering relaxation functions. In addition, the combination of stress and DMF increased Tnf and Nos2 expression and the expressions of several genes involved in iron metabolism. In conclusion, these findings suggest that DMF can prevent chronic stress-induced hypertension by reducing vascular contractility. Moreover, DMF itself may produce reductive stress in the heart and induce inflammation when combined with stress. This indicates a need for the careful consideration of long-term DMF treatment considering its impact on the heart.

Regulation of tight junction proteins and cell death by peroxisome proliferator-activated receptor γ agonist in brainstem of hypertensive rats.

The decrease in tight junction proteins and their adapter proteins in the hypertensive brain is remarkable. Here, we aimed to investigate tight junction proteins and peroxisome proliferator-activated receptor (PPARγ) activation as well as inflammation factors and cell death proteins in the brainstem of hypertension models, namely spontaneously hypertensive rats (SHR) and borderline hypertensive rats (BHR). At first, SHR and BHR groups were treated with PPARγ agonist, pioglitazone. Then, occludin, claudin-1, claudin-2, claudin-12, ZO-1, and NF-κB p65 gene expression levels; pIKKβ, NF-κB p65, TNF, IL-1β, caspase-3, caspase-9 levels, and PARP-1 cleavage were evaluated. Significantly lower pIKKβ, NF-κB p65, TNF, and IL-1β levels were measured in pioglitazone-treated SHR. Results from this study confirm higher occludin (1.35-fold), claudin-2 (7.45-fold), claudin-12 (1.12-fold), and NF-κB p65 subunit (4.76-fold) expressions in the BHR group when compared to the SHR group. Pioglitazone was found effective in terms of regulating gene expression in SHR. Pioglitazone significantly increased occludin (8.17-fold), claudin-2 (2.41-fold), and claudin-12 (1.85-fold) mRNA levels, which were accompanied by decreased cleaved caspase-3, caspase-9 levels, PARP-1 activation, and proinflammatory factor levels in SHR (p ˂ 0.05). Our work has led us to conclude that alterations in tight junction proteins, particularly occludin, and cell death parameters in the brainstem following PPARγ activation may contribute to neuroprotection in essential hypertension.

Effects of salt and stress on blood pressure parameters and antioxidant enzyme function in the heart and aorta of borderline hypertensive rats.

What is the central question of this study? Although the involvement of reactive oxidative species in triggering hypertension has been documented, there are no data about the role of antioxidant enzymes in the heart and aorta of borderline hypertensive rats kept in baseline conditions or exposed to high salt with or without repeated stress. What is the main finding and its importance? In borderline hypertensive rats, high salt intake and stress contribute significantly to increase blood pressure and antioxidative defence in the aorta but decrease it in the heart. Elucidating the early changes that accompany elevated blood pressure could provide new therapeutical venues for prevention and treatment of the condition. Hypertension and its complications are a leading cause of death in the human population. Several factors can contribute to development of hypertension, such as genetic predisposition, high salt intake and environmental stressors, underlying oxidative stress as one of its key trademarks. We studied the effects of increased salt intake and chronic stress on blood pressure parameters and the activity and protein levels of antioxidant enzymes in the heart and aorta of borderline hypertensive rats (BHRs) with genetic susceptibility to hypertension. All animals were randomized into four groups: (1) Wistar rats kept in baseline conditions; (2) BHRs kept in baseline conditions; (3) BHRs drinking 0.9% saline solution; and (4) BHRs drinking 0.9% saline solution and exposed to repeated heterotypic stress. The BHRs exhibited significantly higher blood pressure, mitochondrial superoxide dismutase (SOD2) and catalase (CAT) protein levels and lower glutathione peroxidase (GPx) and glutathione reductase (GR) activities in the aorta, followed by lower CAT and GPx protein levels and higher CAT and GR activities in the heart, compared with normotensive Wistar rats. In the BHR aorta, high salt intake elevated CAT and GPx activities, and when combined with stress it increased GPx and GR activities. In BHR hearts, high salt intake provoked lower CAT activity. Adding repeated stress to salt treatment further decreased CAT activity, in addition to Cu2+ -Zn2+ superoxide dismutase (SOD1) and GR activities. The protein level of CAT was lower, whereas SOD2 and GPx increased. Overall, our results suggest that BHR hearts are better adapted to oxidative pressure, compared with the aorta, when exposed to salt and stress.

Corticotropin-releasing hormone neurons in the central nucleus of amygdala are required for chronic stress-induced hypertension.

Chronic stress is a well-known risk factor for the development of hypertension. However, the underlying mechanisms remain unclear. Corticotropin-releasing hormone (CRH) neurons in the central nucleus of the amygdala (CeA) are involved in the autonomic responses to chronic stress. Here, we determined the role of CeA-CRH neurons in chronic stress-induced hypertension. Borderline hypertensive rats (BHRs) and Wistar-Kyoto (WKY) rats were subjected to chronic unpredictable stress (CUS). Firing activity and M-currents of CeA-CRH neurons were assessed, and a CRH-Cre-directed chemogenetic approach was used to suppress CeA-CRH neurons. CUS induced a sustained elevation of arterial blood pressure (ABP) and heart rate (HR) in BHRs, while in WKY rats, CUS-induced increases in ABP and HR quickly returned to baseline levels after CUS ended. CeA-CRH neurons displayed significantly higher firing activities in CUS-treated BHRs than unstressed BHRs. Selectively suppressing CeA-CRH neurons by chemogenetic approach attenuated CUS-induced hypertension and decreased elevated sympathetic outflow in CUS-treated BHRs. Also, CUS significantly decreased protein and mRNA levels of Kv7.2 and Kv7.3 channels in the CeA of BHRs. M-currents in CeA-CRH neurons were significantly decreased in CUS-treated BHRs compared with unstressed BHRs. Blocking Kv7 channel with its blocker XE-991 increased the excitability of CeA-CRH neurons in unstressed BHRs but not in CUS-treated BHRs. Microinjection of XE-991 into the CeA increased sympathetic outflow and ABP in unstressed BHRs but not in CUS-treated BHRs. CeA-CRH neurons are required for chronic stress-induced sustained hypertension. The hyperactivity of CeA-CRH neurons may be due to impaired Kv7 channel activity, which represents a new mechanism involved in chronic stress-induced hypertension.

α2δ-1-Dependent NMDA Receptor Activity in the Hypothalamus Is an Effector of Genetic-Environment Interactions That Drive Persistent Hypertension.

The interplay between genetic and environmental factors is critically involved in hypertension development. The paraventricular nucleus (PVN) of the hypothalamus regulates sympathetic output during stress responses and chronic hypertension. In this study, we determined mechanisms of synaptic plasticity in the PVN in chronic stress-induced persistent hypertension in male borderline hypertensive rats (BHR), the first offspring of spontaneously hypertensive rats and normotensive Wistar-Kyoto rats. In Wistar-Kyoto rats, chronic unpredictable mild stress (CUMS) increased arterial blood pressure (ABP) and heart rate, which quickly returned to baseline after CUMS ended. In contrast, in BHR, CUMS caused persistent elevation in ABP, which lasted at least 2 weeks after CUMS ended. CUMS also increased the mRNA level of α2δ-1 and synaptic protein levels of GluN1, α2δ-1, and α2δ-1-GluN1 complexes in the PVN in BHR. Furthermore, CUMS significantly increased the frequency of miniature EPSCs and the amplitude of NMDAR currents in spinally projecting PVN neurons in BHR; these increases were normalized by blocking NMDARs with AP5, inhibiting α2δ-1 with gabapentin, or disrupting the α2δ-1-NMDAR interaction with α2δ-1Tat peptide. Microinjection of AP5 or α2δ-1Tat peptide into the PVN normalized elevated ABP and renal sympathetic nerve activity in stressed BHR. In addition, systemically administered gabapentin or memantine attenuated higher ABP induced by CUMS in BHR. Our findings indicate that chronic stress-induced persistent hypertension is mediated by augmented sympathetic outflow via α2δ-1-bound NMDARs in the PVN. This new information provides a cellular and molecular basis for how the genetic-environment interactions cause persistent hypertension.SIGNIFICANCE STATEMENT Chronic stress is a major risk factor for hypertension development, especially for individuals with a genetic predisposition to hypertension. Using a rat model of borderline hypertension, we showed that chronic stress induced long-lasting hypertension and sympathetic nerve hyperactivity, which were maintained by NMDAR activation in the hypothalamus. Chronic stress also increased the expression of α2δ-1, previously regarded as a Ca2+ channel subunit, promoting physical interaction with and synaptic trafficking of NMDARs in the hypothalamus. Inhibiting α2δ-1, blocking NMDARs, or disrupting α2δ-1-bound NMDARs reversed chronic stress-induced sympathetic outflow and persistent hypertension. Thus, α2δ-1-dependent NMDAR activity in the hypothalamus is an effector of genetic-environment interactions and may be targeted for treating stress-induced neurogenic hypertension.

Vasopressin and v1br gene expression is increased in the hypothalamic pvn of borderline hypertensive rats.

Vasopressin (VP) is a neurohypophyseal peptide best known for its role in maintaining osmotic and cardiovascular homeostasis. The main sources of VP are the supraoptic and paraventricular (PVN) nuclei of the hypothalamus, which coexpress the vasopressin V1a and V1b receptors (V1aR and V1bR). Here, we investigated the level of expression of VP and VP receptors in the PVN of borderline hypertensive rats (BHRs), a key integrative nucleus for neuroendocrine cardiovascular control. Experiments were performed in male BHRs and Wistar rats (WRs) equipped with a radiotelemetry device for continuous hemodynamic recording under baseline conditions and after saline load without or with stress. Autonomic control of the circulation was evaluated by spectral analysis of blood pressure (BP) and heart rate (HR) variability and baroreceptor reflex sensitivity (BRS) using the sequence method. Plasma VP was determined by radioimmunoassay, and VP, V1aR, and V1bR gene expression was determined by RT-qPCR. Under baseline conditions, BHRs had higher BP, lower HR, and stronger BRS than WRs. BP and HR variability was unchanged. In the PVN, overexpression of the VP and V1bR genes was found, and plasma VP was increased. Saline load downregulated V1bR mRNA expression without affecting VP mRNA expression or plasma VP and BP. Adding stress increased BP, HR, and low-frequency sympathetic spectral markers and decreased plasma VP without altering the level of expression of VP and VP receptors in the PVN. It follows that overexpression of VP and V1bR in the PVN is a characteristic trait of BHRs and that sympathetic hyperactivity underlies stress-induced hypertension.

Chronic Stress Induces Persistent Hypertension and Increases NMDA Receptor Activity in the Paraventricular Nucleus in Borderline Hypertensive Rats

Stress activates sympathetic outflow and promotes hypertension development in humans with genetic predisposition. The enhanced N‐methyl‐D‐aspartate receptor (NMDAR) activity in the hypothalamus paraventricular nucleus (PVN) plays a critical role in controlling sympathetic output in hypertension. However, it is unclear how chronic stress affects NMDAR activity in the PVN in borderline hypertensive rats (BHR). BHR are the F1 male offspring from crossing female spontaneously hypertensive rats with male Wistars Kyoto rats (WKY). Arterial blood pressure (ABP) was monitored in free moving rats by using radiotelemetry. Using a 6‐week chronic unpredictable stress protocol, we found that stressed WKY rats had increased ABP during chronic stress but ABP returned to the normal level within a few days after stress. However, the stressed BHR showed a greater increase in ABP during stress and the elevated ABP was sustained for at least 2 weeks after discontinuing stress. Furthermore, whole‐cell voltage clamp recording in brain slices showed that the amplitude of evoked‐NMDAR currents in spinally projecting PVN neurons was significantly higher in stressed BHR than in non‐stressed BHR controls. Inhibiting α2δ‐1 with gabapentin normalized the increased synaptic NMDAR activity of spinally projecting PVN neurons in stressed BHR. In addition, the expression level of GluN1 and α2δ‐1 in the PVN was significantly greater in stressed BHR than in stressed WKY or non‐stressed BHR. These results suggest that chronic stress induces persistent hypertension in BHR, which is associated with α2δ‐1‐mediated NMDAR hyperactivity in PVN presympathetic neurons.Support or Funding InformationAcknowledgmentsSupported by NIH grants HL131161 and HL142133.

(-)-Epicatechin Reduces the Blood Pressure of Young Borderline Hypertensive Rats During the Post-Treatment Period.

This study investigated the effects of (–)-epicatechin (Epi) in young male borderline hypertensive rats (BHR) during two weeks of treatment (Epi group, 100 mg/kg/day p.o.) and two weeks post treatment (PE group). Epi reduced blood pressure (BP), which persisted for two weeks post treatment. This was associated with delayed reduction of anxiety-like behaviour. Epi significantly increased nitric oxide synthase (NOS) activities in the aorta and left heart ventricle (LHV) vs. the age-matched controls without affecting the brainstem and frontal neocortex. Furthermore, Epi significantly reduced the superoxide production in the aorta and relative content of iron-containing compounds in blood. Two weeks post treatment, the NOS activities and superoxide productions in the heart and aorta did not differ from the age-matched controls. The gene expressions of the NOSs (nNOS, iNOS, eNOS), nuclear factor erythroid 2-related factor 2 (Nrf2), and peroxisome proliferator-activated receptor-γ (PPAR-γ) remained unaltered in the aorta and LHV of the Epi and PE groups. In conclusion, while Epi-induced a decrease of the rats’ BP persisted for two weeks post treatment, continuous Epi treatments seem to be necessary for maintaining elevated NO production as well as redox balance in the heart and aorta without changes in the NOSs, Nrf2, and PPAR-γ gene expressions.

Age-dependent effect of PPARγ agonist pioglitazone on kidney signaling in borderline hypertensive rats.

The peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor and nutrition factor which takes part in the cellular signaling by several agonists such as pioglitazone. PPARγ can serve as potential target in treatments of metabolic syndrome diseases and/or hypertension. In the present study we investigated the effects of pioglitazone, a PPARγ agonist, on hypertension development in young and adult borderline hypertensive rats (BHR). In renal signaling we observed connections between PPARγ and Nrf2, antioxidant in adult animals and differences between young and adult BHR in Nrf2-activated detoxificant outputs (NQO1, HO-1) and NO-synthases. Blood pressure in animals had been detected by cuff plethysmography, cell signaling in the kidney was studied by gene expression determination using qPCR, and nitric oxide synthase (NOS) activity was measured by radioactive detection. Pioglitazone treatment in adult BHR caused no detectable changes in antioxidant and detoxificant responses. The main effects were observed in blood pressure improvement, endothelial NOS expression and NOS activities in both young and adult BHR.

Abstract P340: Variable Pressor and Sympathetic Responsiveness Reflects Neurotransmitter Imbalance in the Paraventricular Nucleus that is Prevented by Loss of Renal Sensory Nerves

The paraventricular nucleus of the hypothalamus (PVN), a key regulator of sympathetic activity, is dependent on a balance of excitatory (NMDA) and inhibitory (nNOS) neurotransmission. Ischemic heart failure (HF), hypertension and renal disease are associated with excessive NMDA and reduced nNOS in the PVN. Individuals with essential hypertension have greater sympathetic tone and exaggerated pressor responsiveness to acute behavioral stress. We observed variable pressor responsiveness in Sprague-Dawley and Borderline Hypertensive rats (SDR and BHR). We hypothesized that those SDR or BHR with greater pressor responses to stress have greater NMDA and/or reduced nNOS activity in PVN. We proposed that renal denervation (RDN) or deafferentation resolves the difference in stress responses and the PVN imbalance. We recorded arterial pressure (AP), and, in some rats, cardiac output and sympathetic nerve activity. After recovery, SDR and BHR were exposed to acute stress (1 cm deep cold water) repeatedly. Average AP responses were greater in male BHR compared to SDR (X=60±2 vs 49±1 mmHg). Responses were divided between those with AP responses greater or lesser than these means. SDR with larger pressor responses (LP), had elevated NMDA NR1 mRNA and protein levels in the PVN and reduced nNOS mRNA (p<0.05). Likewise, in female BHR, larger AP responses (X=57±3 mmHg) LP had greater NMDA NR1 mRNA and protein in the PVN and reduced nNOS protein. Therefore, the imbalance in PVN exists in normotensive rats and correlates with greater AP and sympathetic responses predisposing an individual to cardiovascular disease. In related studies in male SDR and BHR, we examined the effects of RDN on acute stress responses to cold water and to air jet. In both rat strains, RDN or selective renal deafferentation with capsaicin or resiniferatoxin selectively prevented the exaggerated AP responses only in LP rats. Finally, RDN or deafferentation reversed the HF-induced increase in sympathetic nerve activity and the increase NADPH-diaphorase and nNOS staining and protein levels in the PVN. These data suggest that renal sensory nerves are responsible for variable excitatory and inhibitory influences in the PVN that contribute to the predisposition to cardiovascular disease.

Chronic Stress Produces Persistent Increases in Plasma Corticosterone, Reductions in Brain and Cardiac Nitric Oxide Production, and Delayed Alterations in Endothelial Function in Young Prehypertensive Rats.

This study was designed to investigate whether oxidative stress, nitric oxide (NO) deficiency and/or endothelial dysfunction (ED) are present in young borderline hypertensive rats (BHR) and whether these pathologies can be causally involved in the initiation of blood pressure (BP) increases. Additionally, we tested the hypothesis that crowding stress, experienced during the peripubertal period, may produce persistent or delayed disorders in corticosterone release, NO synthesis, oxidative status and/or endothelial function that could accelerate BP increases. To test these hypotheses, 5-week-old male BHR and normotensive Wistar-Kyoto rats (WKY) were either kept in control conditions (for 2 and 4 weeks, respectively) or exposed to social stress produced by crowding for 2 weeks (stress). After cessation of crowding, a group of rats of each phenotype was kept in control conditions for the next 2 weeks (post-stress). Systolic BP of 5-week-old BHR was significantly increased vs. age-matched WKY (127 ± 3 vs. 104 ± 3 mmHg, p < 0.01) and remained significantly higher throughout the course of the experiment. Despite elevated BP, no signs of oxidative damage to plasma lipids, NO deficiency or ED were observed in control BHR vs. age-matched WKY. Crowding stress elevated plasma corticosterone and accelerated BP increases only in BHR; these effects persisted 2 weeks post-stress. Crowding failed to induce oxidative damage to plasma lipids in either phenotype, but it produced persistent decreases in NO production in the hypothalamus and brainstem of both strains of rats, as well as in the hearts of BHR. In contrast, crowding failed to reduce NO production in the aortae or acetylcholine-induced relaxations of the femoral arteries in both strains investigated. However, significantly reduced aortic NO production was observed in BHR 2 weeks post-stress vs. age-matched controls, which was in agreement with reduced NO-dependent components of vasorelaxation. In conclusion, this study’s data showed that oxidative stress, NO deficiency and ED are not causally involved in initiation of blood pressure increase in BHR. However, exposure to stressful environments produced persistent increases in plasma corticosterone and reductions of brain and cardiac NO production followed by a delayed decrease in the NO-dependent component of endothelium-dependent relaxation—changes that collectively accelerated BP increases only in BHR.

The peroxisome proliferator-activated receptor gamma agonist pioglitazone improves nitric oxide availability, renin-angiotensin system and aberrant redox regulation in the kidney of pre-hypertensive rats.

The peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-dependent nuclear receptor. It plays an important role in kidney physiology, where it might contribute to arterial blood pressure regulation and hypertension development by modulation of several signaling pathways. In our study we focused on the effect of PPARγ agonist pioglitazone on changes in the nitric oxide synthase (NOS) expression and activity, the renin-angiotensin system (RAS) cascade, and redox homeostasis signaling pathways in the renal cortex of young pre hypertensive rat models. Young (5-weeks old) spontaneously hypertensive (SHR) and borderline hypertensive (BHR) rats were treated by pioglitazone (PIO, 10 mg/kg/day) during 10 days. Blood pressure (BP) was determined by plethysmography method. Changes in lipid profile were detected in plasma with standard kits using biochemical analyser. Gene expression has been detected by qRT-PCR and protein level was determined using Western blot analysis. Superoxide dismutase (SOD) and catalase (CAT) activities were determined spectrophotometrically and the total enzyme activity of NOS was measured using a radioactive assay based on conversion of [3H] L-arginine to [3H] L- citrulline. Administration of pioglitazone decreased BP in BHR and slowed down the development of BP increase in young SHR animals. For NOS, activation by PPARγ correlated with increase in gene and protein expression of NOS isoforms and in total enzyme activity both in BHR and SHR. In the AT1R/Nox pathway, the treatment did not significantly influence mRNA expression of the p22phox subunit of NADPH oxidase (Nox) and AT1R, but up-regulated the 'pro-vasodilatatory' Mas and AT2R receptors in both BHR and SHR groups. Pioglitazone treatment affected redox regulation. Increase in gene expression of nuclear factor E2-related factor 2 (Nrf2) and SOD isoforms correlated with SOD and CAT enzyme activities. The group treatment-to-control ratios, BHR Pioglitazone to BHR control and SHR Pioglitazone to SHR control for gene expression increased by 10% to 230%. The largest effect of PPARγ has been observed in SOD1, SOD3 and the Mas receptor gene treatment-to-control ratios. The most prominent differences between BHR and SHR were observed in SOD1 and Mas receptor expressions, with large effects of opposite sign in BHR versus SHR. Our data indicate that an increase of NO release activates signaling in the renal cortex of pre-hypertensive rats after pioglitazone treatment. Improvement of NO availability, AT2R, Mas receptors and aberrant redox regulation is thought to be the major correlated mechanisms mediating the BP decrease affected by the PPARγ agonist treatment. We also observed that the most sensitive tissue responses to PPARγ-dependent activation of Nrf2 have been primarily found in the kidney of young hypertensive animals.

P-387 - PPARγ regulation improved RAS/ NO/ ADMA signaling and antioxidant responce in pathophysiology of young hypertensive rats

PPARγ plays an important role in kidney physiology of cardiovascular system, contributes in hypertension and signaling pathways. In our study we focused on the effect of PPARγ agonist pioglitazone (PIO) on the RAS, redox regulation, NOS activities, redox regulation and ADMA levels in two models of young borderline hypertensive (BHR) and spontaneously hypertensive (SHR) rats. Gene expression was detected by qRT-PCR. Protein level was determined using Western blot analysis. Superoxide dismutase (SOD) and nitric oxide synthase (NOS) activities was determined spectrophotometrically and with radioactive method. ADMA levels has been analysed by HPLC method with fluorescence detection. PIO decreased (in BHR) and slowed blood pressure development (in SHR). Gene and protein expressions of NOS isoforms and total NOS activities was improved in both experimental rats and affected ADMA changes. In AT1R/NADPH - oxidase pathway the treatment was not significantly influenced, but mRNA expression in Mas, AT2R receptors and redox regulation (Nrf2 and SOD isoforms) was up-regulated. The largest effect of PPARγ has been observed in SOD1, SOD3 and Mas receptor genes in different way: SOD1 was increased in SHR and Mas receptor in BHR rats.

Differences in Excitatory and Inhibitory Balance within the Paraventricular Nucleus Reflects Response Variability to Acute Stress

The cardiovascular reactivity hypothesis states that humans have highly variable pressor responses to acute stress and that those susceptible to the development of hypertension have greater pressor responses to stress. Our studies have shown similar stress‐evoked pressor response variability in outbred Sprague‐Dawley rats (SDR). Several laboratories have reported that excessive excitatory (glutamate) and reduced inhibitory (nitric oxide) neurotransmission within the paraventricular nucleus of the hypothalamus (PVN) exists in animals with hypertension, heart failure or after chronic stress. Moreover, these changes have been linked to elevated sympathetic nerve activity. We hypothesize that those rats predisposed to develop hypertension as predicted by the cardiovascular reactivity hypothesis already have an imbalance of neurotransmission favoring excitation in the PVN. Therefore, we tested two different rat strains to determine whether rats with larger pressor responses to acute stress had greater excitatory and/or reduced inhibitory neurotransmission in the PVN. We tested male SDR and female borderline hypertensive rats (BHR). Rats were instrumented for recording arterial pressure (AP) and heart rate. After 5–7 days recovery, rats were tested for their pressor responsiveness to air jet (20 psi, 1–2 sec) and to cold water stress (1 cm deep for 1 min). Rats were separated into those with larger pressor responsiveness (LP) to startle with air jet or cold water and compared to those with smaller pressor responses (SP). In both rat strains, the initial pressor responses were averaged for each stressor. Those with responses above or below the mean were determined to be LP or SP, respectively. Expression of nNOS and NMDA‐NR1 were determined at transcriptional level by real‐time PCR and at protein level by Western blot, in PVN punches. Male SDR identified as SP or LP rats had cold stress‐induced increases in AP of 41.3 ± 0.9 and 58.6 ± 1.1 mmHg, respectively. In 12 rats tested, mRNA levels for nNOS were significantly lower in LP compared to SP and NMDA‐NR1 was significantly greater in LP compared to SP. There was a corresponding increase in protein expression for NMDA‐NR1 in LP rats. In response to cold water stress, female BHR had significantly greater pressor responses in SP or LP rats (47.2 ± 2.1 and 66.6 ± 2.8 mmHg, respectively) compared to SDR. As in SDR, female BHR (n=12) characterized as LP had significantly greater mRNA and protein expression of NMDA‐NR1 as well as reduced nNOS protein expression in the PVN compared to SP BHR. We propose that changes in nNOS and glutamatergic tone within the PVN reflect not only the existence of sympathetic overactivity but the predisposition towards sympathetic overactivity and development of hypertension. In addition, these changes can be seen in normotensive (SDR) and in stress‐sensitive BHR and in both sexes suggesting that they are universal traits contributing to elevated sympathetic nerve activity and predisposition to cardiovascular disease.Support or Funding InformationSupported by NIH P01 HL062222 and R01 DK114663 (KPP) and St. Louis Univ. (MMK)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Social stress-induced blood pressure increase in borderline hypertensive rats is associated with endothelial dysfunction in the resistant arteries

ObjectivesSeveral studies have observed that altered endothelial function is involved in the development of stress-induced hypertension. The aim of this study was to investigate the effects of chronic social stress (crowding) on endothelium-dependent relaxation (EDR) of the superior mesenteric artery (SMA) and of small resistant mesenteric arteries (MA) as well as on neurogenic contractions of SMA in adult borderline hypertensive rats (BHR).MethodsTwelve-week-old BHR (offspring of spontaneously hypertensive dams and Wistar-Kyoto sires) males were exposed to crowding (living space: 200 cm2/rat) for eight weeks. Control BHR were kept in the groups of four rats per cage (living space: 480 cm2/rat). Systolic blood pressure (sBP) was determined by the tail-cuff method.Vascular function was investigated in the isolated arteries at isometric conditions.EDR was assessed using acetylcholine test.ResultsCrowding significantly increased sBP of BHR to the hypertensive values. Results showed that stress did not affect total acetylcholine-induced relaxation and its nitric oxide (NO)-dependent and NO-independent components in the SMA. In the resistant MA, stress reduced total acetylcholine-induced relaxation by reducing NO-independent component, without the alterations of its NO-dependent component.However, stress failed to affect significantly neurogenic contractions of SMA elicited by electrical stimulation of perivascular sympathetic nerves and vasoconstriction induced by exogenous noradrenaline in SMA.ConclusionIn conclusion, chronic social stress can accelerate the development of hypertension in BHR, which seems to be associated with NO-independent endothelial dysfunction in small resistant arteries.Supported by the grants VEGA No. 2/0190/17 and APVV-16-0263.

Sex differences in the blood antioxidant defense system in juvenile rats with various genetic predispositions to hypertension.

This study investigated the contribution of blood oxidative stress (OS) to the development of hypertension, as well as sex differences in the antioxidant defense system (ADS) in genetic models of hypertension. Nine-week-old normotensive Wistar-Kyoto (WKY) rats, borderline hypertensive rats (BHR) and spontaneously hypertensive rats (SHR) of both sexes were used. Systolic blood pressure (SBP) was determined by tail-cuff plethysmography, the trolox equivalent antioxidant capacity (TEAC) and the concentration of lipid peroxides (LP) were determined in plasma. The activity of the antioxidant enzymes Cu/Zn-superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) was determined in erythrocytes. SBP was significantly elevated in BHR and SHR in both sexes. BHR and SHR males had a higher SBP than the respective females. Sex-dependent differences in the ADS were found only in SHR, in which TEAC, SOD and CAT were significantly higher in males than in females. No differences in TEAC, SOD, CAT and GPx were observed between BHR (males and females) and WKY controls. LP levels were similar in all the groups investigated. Significant positive correlations were observed between SBP and both SOD and CAT. TEAC correlated positively with SOD and LP. As no signs of oxidative damage to lipids were found in young BHR and SHR of either sex, OS in the blood does not seem to be causatively related to the development of hypertension in these rats. However, despite activated antioxidant defenses, the positive correlation between plasma TEAC and LP suggests that oxidative damage is progressing slowly and therefore it seems to be a consequence rather than the cause of hypertension.

Effects of risk-factor clustering on baroreflex sensitivity and blood pressure variability in borderline hypertensive rats

Effects of risk-factor clustering on baroreflex sensitivity and blood pressure variability in borderline hypertensive rats

Endothelial Dysfunction in Femoral Artery of the Hypertensive Rats Is Nitric Oxide Independent

This study examined nitric oxide (NO) production, oxidative load and endothelium-dependent relaxation (NO-dependent and NO-independent) in adult male borderline hypertensive (BHR) and spontaneously hypertensive (SHR) rats as compared to normotensive Wistar-Kyoto (WKY) rats. Systolic blood pressure (BP) was determined by tail-cuff. NO production was determined by conversion of [(3)H]-L-arginine. Conjugated dienes (CD) and concentrations of thiobarbituric acid-reactive substances (TBARS) were measured for assessment of oxidative load. Vascular function was investigated in rings of the femoral artery (FA) using a wire myograph. BP of WKY, BHR and SHR was 106+/-2, 143+/-3 and 191+/-3 mm Hg, respectively (p<0.01 for each). Significant left ventricle (LV) hypertrophy and elevated levels of CD and TBARS in the LV were present in BHR and SHR as compared to WKY. NO production was elevated significantly in the aorta of BHR and SHR vs. WKY as well as in the LV of SHR vs. WKY. Acetylcholine (ACh)-induced relaxation of the FA was reduced significantly in both BHR and SHR vs. WKY. The NO-dependent component of ACh-induced relaxation had increasing tendency in hypertensive groups and it correlated positively with BP. The NO-independent component of vasorelaxation was reduced significantly in BHR and SHR vs. WKY and it correlated negatively with BP. In conclusion, the results showed that endothelial dysfunction in the experimental model of borderline hypertensive and hypertensive rats is NO-independent. The results suggest that borderline hypertension represents a risk of other cardiovascular disorders which is qualitatively similar to that of fully developed hypertension.

Unbiased entropy estimates in stress: A parameter study

This study proposes a method for obtaining a stable working point that enables the unbiased estimates of the approximate entropy and the sample entropy. Pattern length, normalized threshold, time delay and tines series length are levels of freedom that are considered. Pulse interval signals used for the experiment are recorded from laboratory animals with different likelihood of developing cardiovascular disease – normal and borderline hypertensive rats – exposed to the acute and to the chronic stress. It is shown that the threshold level is the major source of the instability, and that the generally accepted and widely used methods for a threshold choice may lead to an incorrect psychological interpretation. A method for the threshold level correction is proposed.

Autonomic mechanisms underpinning the stress response in borderline hypertensive rats

This study investigates blood pressure (BP) and heart rate (HR) short-term variability and spontaneous baroreflex functioning in adult borderline hypertensive rats and normotensive control animals kept on normal-salt diet. Arterial pulse pressure was recorded by radio telemetry. Systolic BP, diastolic BP and HR variabilities and baroreflex were assessed by spectral analysis and the sequence method, respectively. In all experimental conditions (baseline and stress), borderline hypertensive rats exhibited higher BP, increased baroreflex sensitivity and resetting, relative to control animals. Acute shaker stress (single exposure to 200 cycles min-1 shaking platform) increased BP in both strains, while chronic shaker stress (3-day exposure to shaking platform) increased systolic BP in borderline hypertensive rats alone. Low- and high-frequency HR variability increased only in control animals in response to acute and chronic shaker (single exposure to restrainer) stress. Acute restraint stress increased BP, HR, low- and high-frequency variability of BP and HR in both strains to a greater extent than acute shaker stress. Only normotensive rats exhibited a reduced ratio of low- to high-frequency HR variability, pointing to domination of vagal cardiac control. In borderline hypertensive rats, but not in control animals, chronic restraint stress (9-day exposure to restrainer) increased low- and high-frequency BP and HR variability and their ratio, indicating a shift towards sympathetic cardiovascular control. It is concluded that maintenance of BP in borderline hypertensive rats in basal conditions and during stress is associated with enhanced baroreflex sensitivity and resetting. Imbalance in sympathovagal control was evident only during exposure of borderline hypertensive rats to stressors.