Adult Spontaneously Hypertensive Rats Research Articles

Hemodynamic Response to Gabapentin in Conscious Spontaneously Hypertensive Rats.

Ligands of auxiliary α2δ subunit of voltage-dependent calcium channels (VDCCs) decrease elevated L-type VDCCs surface expression in arterial myocytes and arterial constriction in spontaneously hypertensive rats (SHR). However, their effect on blood pressure (BP) is unclear. In this study, we investigated the hemodynamic response to acute and chronic administration of gabapentin, a ligand of auxiliary α2δ subunit of VDCCs, in adult SHR with established neurogenic hypertension. The acute gabapentin administration lowered BP and heart rate more in conscious SHR than Wistar-Kyoto rats. Both nifedipine (L-type VDCCs blocker) and ω-conotoxin GVIA (N-type VDCCs blocker) also decreased BP more in SHR, but only gabapentin and ω-conotoxin GVIA abolished the nitroprusside-induced reflex tachycardia of baroreceptor-heart rate control. Hypotensive effect of gabapentin was accompanied by a reduction of (1) plasma norepinephrine level, (2) depressor response to ganglionic blocker pentolinium, (3) power of low frequency component of systolic BP variability, and (4) pressor response of mesenteric vascular bed to periarterial nerve stimulation, suggesting the decrease of peripheral sympathetic nerve transmission. Moreover, gabapentin effects on BP and baroreflex were absent in sympathectomized rats. In conclusion, the acute (but not chronic) administration of gabapentin lowered BP more in SHR than in Wistar-Kyoto rats. Besides the known L-type VDCCs involvement in the vascular effect of gabapentin, our data revealed the important role of N-type VDCCs in acute gabapentin effect on sympathetic control of BP. Gabapentin-induced changes of sympathetic nerve transmission indicated major hemodynamic mechanism of the acute response to this drug.

Differences in autonomic innervation to the vertebrobasilar arteries in spontaneously hypertensive and Wistar rats.

Essential hypertension is associated with hyperactivity of the sympathetic nervous system and hypoperfusion of the brainstem area controlling arterial pressure. Sympathetic and parasympathetic innervation of vertebrobasilar arteries may regulate blood perfusion to the brainstem. We examined the autonomic innervation of these arteries in pre-hypertensive (PHSH) and hypertensive spontaneously hypertensive (SH) rats relative to age-matched Wistar rats. Our main findings were: (1) an unexpected decrease in noradrenergic sympathetic innervation in PHSH and SH compared to Wistar rats despite elevated sympathetic drive in PHSH rats; (2) a dramatic deficit in cholinergic and peptidergic parasympathetic innervation in PHSH and SH compared to Wistar rats; and (3) denervation of sympathetic fibres did not alter vertebrobasilar artery morphology or arterial pressure. Our results support a compromised vasodilatory capacity in PHSH and SH rats compared to Wistar rats, which may explain their hypoperfused brainstem. Neurogenic hypertension may result from brainstem hypoperfusion. We previously found remodelling (decreased lumen, increased wall thickness) in vertebrobasilar arteries of juvenile, pre-hypertensive spontaneously hypertensive (PHSH) and adult spontaneously hypertensive (SH) rats compared to age-matched normotensive rats. We tested the hypothesis that there would be a greater density of sympathetic to parasympathetic innervation of vertebrobasilar arteries in SH versus Wistar rats irrespective of the stage of development and that sympathetic denervation (ablation of the superior cervical ganglia bilaterally) would reverse the remodelling and lower blood pressure. Contrary to our hypothesis, immunohistochemistry revealed a decrease in the innervation density of noradrenergic sympathetic fibres in adult SH rats (P<0.01) compared to Wistar rats. Unexpectedly, there was a 65% deficit in parasympathetic fibres, as assessed by both vesicular acetylcholine transporter (α-VAChT) and vasoactive intestinal peptide (α-VIP) immunofluorescence (P<0.002) in PHSH rats compared to age-matched Wistar rats. Although the neural activity of the internal cervical sympathetic branch, which innervates the vertebrobasilar arteries, was higher in PHSH relative to Wistar rats, its denervation had no effect on the vertebrobasilar artery morphology or persistent effect on arterial pressure in SH rats. Our neuroanatomic and functional data do not support a role for sympathetic nerves in remodelling of the vertebrobasilar artery wall in PHSH or SH rats. The remodelling of vertebrobasilar arteries and the elevated activity in the internal cervical sympathetic nerve coupled with their reduced parasympathetic innervation suggests a compromised vasodilatory capacity in PHSH and SH rats that could explain their brainstem hypoperfusion.

Sodium nitroprusside is effective in preventing and/or reversing the development of schizophrenia-related behaviors in an animal model: The SHR strain.

The treatment of schizophrenia with antipsychotics is still unsatisfactory. Therefore, the search for new treatments and prevention is crucial, and animal models are fundamental tools for this objective. Preclinical and clinical data evidence the antipsychotic profile of sodium nitroprusside (SNP), a nitric oxide (NO) donor. We aimed to investigate SNP in treating and/or preventing the schizophrenia-related behaviors presented by the spontaneously hypertensive rats (SHR) strain. Wistar rats (WR) and SHRs were submitted to two schemes of treatment: (i) a single injection of SNP or vehicle in adulthood; (ii) a long-term early treatment from 30 to 60 postnatal day with SNP or vehicle. The following behaviors were evaluated 24hours after the acute treatment or 30days after the long-term treatment: locomotion, social interaction, and contextual fear conditioning. Spontaneously hypertensive rats presented hyperlocomotion, decreased social interaction, and impaired contextual fear conditioning. Single injection of SNP decreased social interaction in both strains and induced a deficit in contextual fear conditioning in WR. Oppositely, early treatment with SNP prevented the behavioral abnormalities in adult SHRs without promoting any effects in WR. Our preclinical data point to SNP as a preventive and safe strategy with a broad range of effectiveness to the positive, negative, and cognitive symptoms of schizophrenia.

Reconstitution of Autophagy Improves Vascular Reactivity in Spontaneously Hypertensive Rats

The accumulation of misfolded‐aggregated proteins is linked to an increasing number of degenerative diseases, including hypertension. Although protein damage and misfolding are an inevitable consequence of normal cellular function, multiple proteostasis mechanisms are devoted to the repair or clearance of damaged proteins in order to prevent proteotoxicity. Autophagy is the constitutive and basally active recycling mechanism responsible for protein quality control. Previously, our data has suggested decreased autophagy in conduit and resistance arteries from spontaneously hypertensive rats (SHR); however, direct measurement of autophagic activity, as well as the proteotoxic consequences of undegraded, misfolded protein has not been performed. Furthermore, the effects of reconstituting autophagic activity on vascular reactivity are currently unknown. We hypothesized that mesenteric resistance arteries (MRA) from adult (14 weeks old) SHR would have decreased autophagic activity in lysosomes extracted from arteries and this would be associated with increased misfolded protein oligomers. Therefore, we further hypothesized that upregulation of autophagy via mammalian target of rapamycin (mTOR) inhibition would decrease contraction and improve relaxation in isolated MRA from SHR mounted on wire myographs. We observed that the activity of acid phosphatase, the major acid hydrolase in lysosomes, from arterial lysosomes (pooled mesenteric arteries and aorta) was decreased in SHR (μmol/min, Wistar: 0.51±0.06 vs. SHR: 0.24±0.02, p&lt;0.05). This diminished arterial autophagic activity was observed in conjunction with the increased presence of insoluble protein deposition. Specifically, SHR MRA contained increased fibrillar amyloid oligomers, especially along the endothelium monolayer, as indicated by Congo red staining (Figure 1). When autophagy was reconstituted in isolated MRA via mTOR inhibition with Everolimus (EV; first generation mTOR inhibitor) for 1 hr, we observed that the maximum contraction to phenylephrine was reduced [Emax (mN), Vehicle: 19.8±0.5 vs. EV (0.1 nM): 10.7±0.5 vs. EV (0.1 μM): 8.5±1.0, p&lt;0.05] and the contraction to high concentrations acetylcholine was prevented [LogEC50, Vehicle: −6.9±0.1 vs. EV (0.1 nM): −9.2±0.4 vs. EV (0.1 μM): −8.2±0.1, p&lt;0.05]. Overall, these data reveal that SHR have impaired arterial lysosomal activity and this is associated with the accumulation of misfolded proteins. As a result, reconstituting arterial autophagic activity improved vascular function and could be a novel therapeutic treatment for proteotoxicity in hypertension.Support or Funding InformationNIH (K99GM118885 and P01HL134604).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Chronic Methylphenidate Alters Tonic and Phasic Glutamate Signaling in the Frontal Cortex of a Freely-Moving Rat Model of ADHD

Glutamate dysfunction has been implicated in a number of substance of abuse studies, including cocaine and methamphetamine. Moreover, in attention-deficit/hyperactivity disorder (ADHD), it has been discovered that when the initiation of stimulant treatment occurs during adolescence, there is an increased risk of developing a substance use disorder later in life. The spontaneously hypertensive rat (SHR) serves as a phenotype for ADHD and studies have found increased cocaine self-administration in adult SHRs when treated with the stimulant methylphenidate (MPH) during adolescence. For this reason, we wanted to examine glutamate signaling in the pre-limbic frontal cortex, a region implicated in ADHD and drug addiction, in the SHR and its progenitor control strain, the Wistar Kyoto (WKY). We chronically implanted glutamate-selective microelectrode arrays (MEAs) into 8-week-old animals and treated with MPH (2mg/kg, s.c.) for 11 days while measuring tonic and phasic extracellular glutamate concentrations. We observed that intermediate treatment with a clinically relevant dose of MPH increased tonic glutamate levels in the SHR but not the WKY compared to vehicle controls. After chronic treatment, both the SHR and WKY exhibited increased tonic glutamate levels; however, only the SHR was found to have decreased amplitudes of phasic glutamate signaling following chronic MPH administration. The findings from this study suggest that the MPH effects on extracellular glutamate levels in the SHR may potentiate the response for drug abuse later in life. Additionally, these data illuminate a pathway for investigating novel therapies for the treatment of ADHD and suggest that possibly targeting the group II metabotropic glutamate receptors may be a useful therapeutic avenue for adolescents diagnosed with ADHD.

Aging and hypertension decrease endothelial NO-related dilating function and gamma-glutamyl transferase activity but not S-nitrosoglutathione-induced aortic vasodilation.

S-nitrosoglutathione (GSNO), which is involved in the transport and the storage of NO, induces vasorelaxation. It requires gamma-glutamyl transferase (GGT), an enzyme present on the endothelium, to transfer NO into the cell. We evaluated whether aging and hypertension, which induce NO-related dilating dysfunction, are associated with decreased vascular GGT activity and modify the vasorelaxant effect of GSNO. Thoracic aortic rings isolated from male spontaneous hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) aged 20-22 (adult) or 57-60weeks (mature) were preconstricted with phenylephrine, then submitted to concentration-vasorelaxant response curves (maximal response: Emax ; pD2 ) to GSNO and carbachol (the latter to measure NO-related dilating function). GGT activity was measured using chromogenic substrate. Both aging and hypertension lowered Emax values for carbachol (Emax -8% in adult SHR, -42% in mature SHR vs. age-matched WKY, page and phypertension <0.05) demonstrating NO-related dilating dysfunction. Aortic GGT activity also decreased with aging and hypertension (-22% in adult and -75%, reaching 3nmol/min/g of tissue, in mature SHR vs. 12 in age-matched WKY and 23 in adult WKY, page and phypertension <0.05). The pD2 values of GSNO were similar in mature SHR and WKY but higher in adult SHR (pinteraction <0.05). Aging in hypertensive rats decreased NO-related vasorelaxant function and vascular GGT activity, but did not lower the vasorelaxant response to GSNO. This opens perspectives for GSNO-based therapeutics restoring nitric oxide bioavailability and vascular protection in a context of endothelial dysfunction.

Danhong Injection Protects Against Hypertension-Induced Renal Injury Via Down-Regulation of Myoglobin Expression in Spontaneously Hypertensive Rats

Background/Aims: High blood pressure is a major risk factor for chronic kidney disease. Currently, single-target anti-hypertensive drugs are not designed for high blood pressure-related organ damages. Danhong injection (DHI), made from the aqueous extracts of Radix Salviae miltiorrhizae and Flos Carthamus tinctorius, has various pharmacological effects, including BP lowering in SHR, mediated by the reduction of vascular remodeling and the up-regulation of Kallikrein-kinin system published recently by our team, yet if it renders renal protection remains unknown. The current study demonstrated a protective role of DHI in renal injury caused by hypertension and identified its molecular targets in the kidney of spontaneously hypertensive rats (SHR). Methods: Adult SHR and age/gender-matched normotensive Wistar-Kyoto (WKY) rats were treated with DHI, Losartan, or saline for 4 weeks. Serum levels of Creatinine (CRE), Micro-albumin (mAlb), Beta2-microglobulin (β2-MG), and Uric acid (UA) were detected using ELISA kits. Renal pathology was examined by hematoxylin and Eosin (H&E) stains. Microarray analysis was performed on kidney tissues, and gene expression changes were validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and Western blot analyses. Results: Renal histopathological scores showed that SHR exhibited serious kidney injury compared to normotensive WKY rats. The intervention with DHI potently suppressed the renal injury biomarker (KIM-1) and kidney lesions compared to the untreated hypertensive subjects. Microarray analysis revealed that among the 124 genes that were differentially expressed by DHI treatment in SHR kidney, down-regulation of renal myoglobin (Mb) gene was the most prominent and was subsequently confirmed by qRT-PCR and Western blot analysis. Conclusion: Hypertension-induced renal injury in SHR may be alleviated by DHI in part by local suppression of Kidney injury molecule-1 and down-regulation of Myoglobin. However, if this effect is independent of the known anti-hypertensive action of DHI in blood vessel remains to be determined.

Maintenance of Blood-Brain Barrier Integrity in Hypertension: A Novel Benefit of Exercise Training for Autonomic Control.

The blood-brain barrier (BBB) is a complex multicellular structure acting as selective barrier controlling the transport of substances between these compartments. Accumulating evidence has shown that chronic hypertension is accompanied by BBB dysfunction, deficient local perfusion and plasma angiotensin II (Ang II) access into the parenchyma of brain areas related to autonomic circulatory control. Knowing that spontaneously hypertensive rats (SHR) exhibit deficient autonomic control and brain Ang II hyperactivity and that exercise training is highly effective in correcting both, we hypothesized that training, by reducing Ang II content, could improve BBB function within autonomic brain areas of the SHR. After confirming the absence of BBB lesion in the pre-hypertensive SHR, but marked fluorescein isothiocyanate dextran (FITC, 10 kD) leakage into the brain parenchyma of the hypothalamic paraventricular nucleus (PVN), nucleus of the solitary tract, and rostral ventrolateral medulla during the established phase of hypertension, adult SHR, and age-matched WKY were submitted to a treadmill training (T) or kept sedentary (S) for 8 weeks. The robust FITC leakage within autonomic areas of the SHR-S was largely reduced and almost normalized since the 2nd week of training (T2). BBB leakage reduction occurred simultaneously and showed strong correlations with both decreased LF/HF ratio to the heart and reduced vasomotor sympathetic activity (power spectral analysis), these effects preceding the appearance of resting bradycardia (T4) and partial pressure fall (T8). In other groups of SHR-T simultaneously infused with icv Ang II or saline (osmotic mini-pumps connected to a lateral ventricle cannula) we proved that decreased local availability of this peptide and reduced microglia activation (IBA1 staining) are crucial mechanisms conditioning the restoration of BBB integrity. Our data also revealed that Ang II-induced BBB lesion was faster within the PVN (T2), suggesting the prominent role of this nucleus in driven hypertension-induced deficits. These original set of data suggest that reduced local Ang II content (and decreased activation of its downstream pathways) is an essential and early-activated mechanism to maintain BBB integrity in trained SHR and uncovers a novel beneficial effect of exercise training to improve autonomic control even in the presence of hypertension.

Early Supplementation of d-Cysteine or l-Cysteine Prevents Hypertension and Kidney Damage in Spontaneously Hypertensive Rats Exposed to High-Salt Intake.

We investigate whether early supplementation of precursors of hydrogen sulfide (H2 S), d- or l-cysteine can prevent hypertension and kidney damage in spontaneously hypertensive rats (SHR) treated with high-salt. We examine 12-week-old male SHRs from four groups: SHR, high salt SHR (SHRs received 1% NaCl in drinking water for 8 weeks), high salt SHR+d (SHRs received high salt and d-cysteine), and high salt SHR+l (SHRs received high salt and l-cysteine). d- or l-cysteine was supplemented at 8 mmol kg-1 body weight/day between 4 and 6 weeks of ages. High salt intake exacerbate hypertension and kidney damage in SHRs, which is prevented by d- or l-cysteine supplementation. d- or l-Cysteine supplementation reduce the degree of high salt-induced oxidative stress damage. Renal 3-mercaptopyruvate sulphurtransferase (3MST) protein levels and activity are reduced by d- or l-cysteine supplementation. Additionally, d- or l-Cysteine supplementation reduce renal angiotensin I and angiotensin II concentrations, decrease mRNA expression of Ren, and increase protein levels of type 2 angiotensin II receptor. Early supplementation of d- or l-cysteine before hypertension becomes evident and may protect against hypertension and kidney damage in adult SHRs exposed to high salt consumption via regulation of oxidative stress, renin-angiotensin system, and H2 S-generating pathways.

BKCa channel activity and vascular contractility alterations with hypertension and aging via β1 subunit promoter methylation in mesenteric arteries

Promoter methylation is a key mechanism in the epigenetic reprogramming of gene expression patterns. Here, we investigated the contribution of DNA methylation and the associated expression and function of large-conductance Ca2+-activated K+ (BKCa) channel in mesenteric arteries when hypertension was superimposed on aging. Male Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) at young (12 weeks), adult (36 weeks) and old (64 weeks) life stages were used. BKCa channel currents, BKCa channel activity in regulating vascular tone, and BKCa channel β1 subunit (BKβ1) function and expression were greater in mesenteric arteries from SHR than from age-matched WKY controls. Consistently, hypertension decreased CpG methylation of the BKβ1 promoter at all ages. Furthermore, aging triggered an increase in BKβ1 promoter methylation in both old WKY and SHR, with concomitant suppression of the β1 subunit and BKCa channel activity. Aging enhanced β1 gene promoter methylation and subunit expression without changing BKCa channel function between young and adult WKY animals. In contrast, aging did not alter CpG methylation but facilitated BKCa channel currents and upregulated BKβ1 expression and function in adult SHR. Taken together, our results provide compelling evidence that hypertension and aging exert opposing effects on DNA methylation at BKβ1 promoter, subsequently resulting in different β1 expression levels and functional modulation of mesenteric arterial contractility. Such information is useful in revealing the epigenetic regulation of BKCa channel function in vascular smooth muscle and in comprehensively understanding the molecular mechanisms in vascular physiology and pathophysiology.

Early short-term treatment with exogenous hydrogen sulfide postpones the transition from prehypertension to hypertension in spontaneously hypertensive rat

ABSTACTHydrogen sulfide (H2S), nitric oxide (NO), and renin–angiotensin system (RAS) are involved in hypertension. We examined whether early treatment with sodium hydrosulfide (NaHS), an exogenous H2S donor, can regulate H2S-generating pathway, NO pathway, and the RAS, to prevent the transition from prehypertension to hypertension in spontaneously hypertensive rats (SHRs). Four-week-old SHRs and control normotensive Wistar–Kyoto (WKY) rats were assigned into three groups: WKY, SHRs, and SHR + NaHS; SHRs were injected intraperitoneally with sodium hydrosulfide (14 μmol/kg/day) for 4 weeks. SHRs exhibited hypertension at 12 weeks of age, which was blocked by early sodium hydrosulfide administration. Concentrations of H2S were increased in the kidney in SHR + NaHS group versus WKY. Sodium hydrosulfide reduces mRNA expression of four H2S-generating enzymes and decreased 3-mercaptopyruvate sulphurtransferase protein level in SHRs. Early administration of sodium hydrosulfide decreases plasma NG monomethyl-l-arginine (l-NMMA, an inhibitor of NO synthase) level and increases plasma NO level in SHRs. Next, sodium hydrosulfide administration reduces renal mRNA expression of Ren, Atp6ap2, Agt, Ace, and Agtr1a in SHRs. We conclude that early short-term sodium hydrosulfide treatment increases renal H2S concentrations, restores NO bioavailability, and blocks the RAS in the kidney, in favor of vasodilatation to prevent the development of hypertension in adult SHRs.

Abstract P477: Effect of Zamicastat on Blood Pressure and Heart Rate - Comparison Between Acute and Repeated Dosing in the SHR

The sympathetic nervous system (SNS) can alter blood pressure by modulation of cardiac output, peripheral vascular resistance and renal function. One strategy for the modulation of sympathetic nerve function is to reduce the biosynthesis of norepinephrine (NE) via inhibition of dopamine β-hydroxylase (DβH), the enzyme that catalyses the conversion of dopamine to NE in sympathetic nerves. Zamicastat is a new peripheral DβH inhibitor that decreases NE levels in sympathetically innervated tissues and slows down the drive of SNS. In order to compare the effect of zamicastat on blood pressure and heart rate after acute and repeated dosing in spontaneously hypertensive rats (SHR), male adult SHR were implanted with telemetry devices (TA11PA-C40, DSI). Zamicastat (30 mg/kg p.o.) was given either as a single dose (n=8) or once a day for five days (n=6). On day 1, the maximal effect (E max ) of zamicastat on systolic blood pressure (SBP) was attained 15h after dosing. E max was similar in the acute and repeated dosing groups: -21.1±3.9 and -22.0±8.2 mmHg, respectively. In the acute treatment group, a gradual return of the SBP to the high baseline levels was observed over time. On the other hand, in the repeat dosing group the E max were consistent across the five administrations -22.0±8.2, -25.2±7.9, -22.0±7.5, -20.0±6.0 and -16.1±2.8 mmHg, respectively day 1 to 5. On day 5, after reaching E max a gradual return of SBP to baseline levels was also observed. The effect of zamicastat on diastolic blood pressure was similar with an E max of -18.4±3.5 mmHg in the acute dosing group and -18.8±8.7, -19.2±7.2, -18.2±6.6, -19.6±6.6 and -15.7±4.7 mmHg over the five days of administration in the repeated dosing group. Zamicastat did not affect heart rate under each dosing regimen. In conclusion, there is no tachyphylaxis or sensitization to the cardiovascular effects of zamicastat in this model and blood pressure returns to basal levels after zamicastat treatment discontinuation.

Abstract 208: Excessive Autophagy Contributes to Microvascular Endothelial Dysfunction in Prehypertensive Spontaneously Hypertensive Rats

Autophagy exists in vascular endothelial cells, however, the exact role of autophagy in hypertensive-associated vascular endothelial dysfunction remains largely elusive. We assessed the hypothesis that autophagy is one of the mechanisms of endothelial dysfunction in normotensive spontaneously hypertensive rats (SHRs). Age-matched male SHRs and Wistar Kyoto rats (WKY) aged 4 weeks (young) and 12 weeks (adult) were randomized into 2 groups and treated daily for 2 weeks by a) gavage with vehicle alone (normal saline) or b) intraperitoneally injection of rapamycin (1 mg/kg/day), and the vascular function of their isolated aorta and mesenteric artery was assessed in vitro . Furthermore, human umbilical vein endothelial cells (HUVECs) were incubated serum-starved for 6 h to induce excessive cell autophagy, and then incubated with DMEM containing 10% FBS and a) treated with 10 nmol/L insulin-like growth factor 1 (IGF-1) for 12 h, b) treated with 100 nmol/L Rapamycin for 1 h for 37°C. Compared with WKY, young and adult SHRs showed endothelial dysfunction of the aorta and mesenteric artery, along with decreased phosphorylated (p)-Akt, p-mTOR, and autophagic marker protein p62 and increased LC3 II/I in microvascular but not aortic tissues. Treatment of young SHRs with the mTOR inhibitor rapamycin aggravated the endothelial autophagy and subsequent impaired endothelial function. Moreover, IGF-1 significantly activated Akt/mTOR signaling in HUVECs and reduced autophagic levels, while rapamycin inhibited p-mTOR and increased autophagic levels. In conclusion, mesenteric endothelial dysfunction in prehypertensive SHRs is at least partly attributable to excessive autophagy in vascular tissues, and is likely mediated by the underactive Akt/mTOR signaling pathway; however, autophagy appears not to be responsible for the macrovascular endothelial dysfunction.

Blockade of α2-adrenergic receptors in prelimbic cortex: impact on cocaine self-administration in adult spontaneously hypertensive rats following adolescent atomoxetine treatment.

Research with the spontaneously hypertensive rat (SHR) model of attention deficit/hyperactivity disorder demonstrated that chronic methylphenidate treatment during adolescence increased cocaine self-administration established during adulthood under a progressive ratio (PR) schedule. Compared to vehicle, chronic atomoxetine treatment during adolescence failed to increase cocaine self-administration under a PR schedule in adult SHR. We determined if enhanced noradrenergic transmission at α2-adrenergic receptors within prefrontal cortex contributes to this neutral effect of adolescent atomoxetine treatment in adult SHR. Following treatment from postnatal days 28-55 with atomoxetine (0.3mg/kg) or vehicle, adult male SHR and control rats from Wistar-Kyoto (WKY) and Wistar (WIS) strains were trained to self-administer 0.3mg/kg cocaine. Self-administration performance was evaluated under a PR schedule of cocaine delivery following infusion of the α2-adrenergic receptor antagonist idazoxan (0 and 10-56μg/side) directly into prelimbic cortex. Adult SHR attained higher PR break points and had greater numbers of active lever responses and infusions than WKY and WIS. Idazoxan dose-dependently increased PR break points and active lever responses in SHR following adolescent atomoxetine vs. vehicle treatment. Behavioral changes were negligible after idazoxan pretreatment in SHR following adolescent vehicle or in WKY and WIS following adolescent atomoxetine or vehicle. α2-Adrenergic receptor blockade in prelimbic cortex of SHR masked the expected neutral effect of adolescent atomoxetine on adult cocaine self-administration behavior. Moreover, greater efficacy of acute idazoxan challenge in adult SHR after adolescent atomoxetine relative to vehicle is consistent with the idea that chronic atomoxetine may downregulate presynaptic α2A-adrenergic autoreceptors in SHR.

Age-dependent ventricular arrhythmias risk, structural and molecular remodeling in systemic arterial hypertension

IntroductionThe left ventricular hypertrophy (LVH)-ventricular arrhythmias relationship associated with arterial hypertension and aging remains controversial. We aimed to assess the age-dependency of ventricular arrhythmias in spontaneously hypertensive rats (SHRs) and the corresponding ventricular structural and molecular remodeling. Materials and methodsVentricular arrhythmias were quantified using 24-h radiotelemetry ECG monitoring in eight SHRs and four Wistar-Kyoto (WKY) rats at 14 (young), 24 (adult), and 48 (aging) weeks of age. Left ventricular histology and mRNA expressions of 89 proarrhythmogenic genes were assessed in six additional groups (n=4 each) of young, adult, and aging SHRs and WKYs. ResultsRegardless of their age, SHRs presented more premature ventricular contractions (PVCs) than age-matched WKYs (p<0.01). The arrhythmogenicity peak occurred in adult SHRs; ventricular tachycardias only occurred in adult SHRs. Among the SHRs, LV thickness, interstitial fibrosis, and the number of deregulated genes increased with age. Kcnj11 expression was deregulated in adult, but not in young or aging SHRs. DiscussionThis study confirms the presence of higher ventricular ectopy in SHRs than in age-matched WKYs. LVH appeared to be an adaptive, antiarrhythmic process. Myocardial energetic changes with advancing age, as reflected by Kcnj11 expression changes, could underlie this age-dependency of ventricular arrhythmias.

Greater transforming growth factor-β in adult female SHR is dependent on blood pressure, but does not account for sex differences in renal T-regulatory cells.

Female spontaneously hypertensive rats (SHR) have more renal regulatory T cells (Tregs) than males, and greater levels of Tregs in female SHR are dependent on blood pressure (BP). However, the molecular mechanism responsible for greater Tregs in female SHR is unknown. Transforming growth factor (TGF)-β is a pleiotropic cytokine critical in the differentiation of naïve T cells into Tregs, and female SHR have higher TGF-β excretion than male SHR. The goals of the current study were to test the hypotheses that 1) female SHR have greater renal TGF-β expression than male SHR, which is dependent on BP and 2) neutralizing TGF-β will decrease renal Tregs in female SHR. Renal cortices were isolated from 5- and 13-wk-old male and female SHR, and TGF-β levels were measured via Western blot and ELISA. Adult female SHR have more free, active TGF-β1 than 5-wk-old female SHR (46% more) or male SHR (44% more than 5-wk-old males and 56% more than 13-wk-old male SHR). We confirmed greater TGF-β1 in adult female SHR was due to increases in BP and not sexual maturation by measuring TGF-β1 levels following treatment with BP-lowering drugs or ovariectomy. Separate female SHR were treated with an antibody to TGF-β1,2,3; BP was measured, and T cells were assessed in whole blood and the kidney. Neutralizing TGF-β had no effect on BP, although circulating Tregs decreased by 32%, while Th17 cells increased by 64%. Renal Tregs were not altered by antibody treatment, although Th17 cells were decreased by 61%. In conclusion, although TGF-β promotes circulating Tregs in female SHR, it does not account for the sex difference in renal Tregs in SHR.

Increased Oxidative Parameters and Decreased Cytokine Levels in an Animal Model of Attention-Deficit/Hyperactivity Disorder.

Attention-deficit/hyperactivity disorder (ADHD) is a highly heterogeneous disorder characterized by impairing levels of hyperactivity, impulsivity and inattention. Oxidative and inflammatory parameters have been recognized among its multiple predisposing pathways, and clinical studies indicate that ADHD patients have increased oxidative stress. In this study, we aimed to evaluate oxidative (DCFH oxidation, glutathione levels, glutathione peroxidase, catalase and superoxide dismutase activities) and inflammatory (TNF-α, IL-1β and IL-10) parameters in the most widely accepted animal model of ADHD, the spontaneously hypertensive rats (SHR). Prefrontal cortex, cortex (remaining regions), striatum and hippocampus of adult male SHR and Wistar Kyoto rats were studied. SHR presented increased reactive oxygen species (ROS) production in the cortex, striatum and hippocampus. In SHR, glutathione peroxidase activity was decreased in the prefrontal cortex and hippocampus. TNF-α levels were reduced in the prefrontal cortex, cortex (remaining regions), hippocampus and striatum of SHR. Besides, IL-1β and IL-10 levels were decreased in the cortex of the ADHD model. Results indicate that SHR presented an oxidative profile that is characterized by an increase in ROS production without an effective antioxidant counterbalance. In addition, this strain showed a decrease in cytokine levels, mainly TNF-α, indicating a basal deficit. These results may present a new approach to the cognitive disturbances seen in the SHR.

P 189 - PPAR gamma activation can improve aberrant redox regulation in hypertension

Dysregulation of redox- sensitive signaling plays an important role in develompment of hypertension. PPAR gamma belongs to nuclear receptors and is a potent nutritional sensor and redox regulator. In our study we focused on the role of PPAR gamma activation of RAS/ROS regulation, and antioxidant response in spontaneously hypertensive rats (SHR). Treatment was performed by gavage with PPAR gamma agonist pioglitazone (PIO - 10 mg/kg/day, 10 days). Treatment with PPAR gamma agonist PIO in influenced blood pressure, redox- sensitive responses, lipid profile and homocystein level in age- dependent manner. The improvement parameters in hypertension and redox regulation have been observed in young animals, but not in adult SHR rats. PIO treatment influenced redox regulation (gene expression of Nrf2 and SOD isoforms) correlated with SOD a CAT activity and NO bioavailibility. PPAR gamma activation has been corelated with downregulation of and AT1R - RAS axis and „up-regulation“ of AT2R and Mas receptor. This most sensitive tissue responses in RAS/ROS signaling and NO level have been found primary in kidney of young hypertensive rats.

Vascular Remodelling Relates to an Elevated Oscillatory Shear Index and Relative Residence Time in Spontaneously Hypertensive Rats

Haemodynamic disorders are common clinical findings in hypertension and lead to adverse cardiovascular events. However, the haemodynamic conditions in hypertension models are poorly understood. This study aimed to observe the characteristics of haemodynamics in spontaneously hypertensive rats (SHRs) and antihypertensive-treated SHRs. Twenty-four adult male SHRs and Wistar-Kyoto rats (WKYs) were randomly divided into four groups and treated for 7 days as follows: WKY-CON (WKYs + saline), WKY-NIF (WKYs + nifedipine, 50 mg/kg/day), SHR-CON (SHRs + saline), and SHR-NIF (SHRs + nifedipine). Aortic computational fluid dynamics (CFD) models were simulated to obtain the haemodynamic parameters. We found that in the hypertensive (SHR-CON) and blood pressure-controlled (SHR-NIF) groups, the oscillatory shear index (OSI) and relative residence time (RRT), which are key haemodynamics indices, were markedly elevated. Furthermore, there was a correlation between both the elevated OSI and RRT with the vascular wall thickening in regions near the inner wall of the aortic arch. Our research demonstrates that haemodynamics remains disturbed even if the blood pressure is normalized. In addition, vascular remodelling may play an important role in maintaining elevated OSI and RRT values.

Brain Perivascular Macrophages Contribute to Developing Hypertension via Sensing Chronic Peripheral Inflammation

BackgroundRecent studies suggest an association between inflammation and hypertension. The essential pathophysiological mechanism by which peripheral inflammation induces sympathetic hyperactivity and blood pressure elevation is not fully clarified. Sympathetic nerve activity is regulated by the brain, which is separated from various peripheral substances by the blood brain barrier (BBB). Brain perivascular macrophages in the BBB can transfer peripheral inflammatory information to the brain. Therefore, we investigated whether peripheral proinflammatory cytokines accompany the development of hypertension, and if so, whether or not brain perivascular macrophage depletion attenuates the increase in blood pressure in hypertensive animal models.Methods and ResultsPeripheral proinflammatory interleukin‐6 levels measured by enzyme‐linked immunosorbent assay did not differ between young pre‐hypertensive spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats (WKY, 8‐week‐old SHR 64.8±9.5 pg/ml vs. 8‐week‐old WKY 42.8±9.5 pg/ml, p=0.15, respectively, n=4 for each). In adult hypertensive SHR, however, the interleukin‐6 level was significantly greater than that in WKY (12‐week‐old SHR 112.5±15.2 pg/ml vs. 12‐week‐old WKY 62.4±15.2 pg/ml, p&lt;0.05, n=5 for each). Clodronate, a unique agent that induces apoptosis of perivascular macrophages, was administered intracerebroventricularly to 6‐week‐old SHR to investigate the role of brain perivascular macrophages in blood pressure elevation in SHR. Although established natural history of blood pressure in SHR clearly showed that mean arterial pressure would be elevated to approximately 120–125 mmHg at 8 weeks of age, intracerebrovantricular injection of clodronate successfully attenuated telemetered mean blood pressure elevation from 6 to 8 weeks of age (from 113.3±4.2 mmHg to 114.7±4.2 mmHg, n=2) in SHR.ConclusionBrain perivascular macrophages potentially contribute to developing hypertension via sensing chronic peripheral inflammation.