Normotensive Sprague-Dawley Research Articles

The comparative research of aspirin-ethanol induced acute gastric mucosal injury in sprague dawley rats and hypertensive rats

Hypertension is a prevalent chronic health condition that complicates the understanding of gastric injury mechanisms. The aim of this research was to investigate the impact of hypertension on acute gastric mucosal injury induced by aspirin-ethanol in spontaneously hypertensive rats (SHR) and normotensive Sprague Dawley (SD) rats. Both groups were gavaged with 120 mg/ml aspirin and 70 % ethanol, followed by evaluation of gastric injury using gross pathology and histological analysis. SHR rats exhibited significantly less severe gastric mucosal damage compared to SD rats, with lower ulcer index and injury grade scores. Histopathological examination revealed milder edema and hemorrhage in SHR rats. Additionally, gastric tissue from SHR rats showed localized lesions with less epithelial tissue damage compared to SD rats, which exhibited more widespread damage and severe hemorrhagic erosions. These findings suggest that hypertension may reduce the extent of aspirin-ethanol-induced gastric injury, potentially due to thicker vascular walls, enhanced coagulation, and altered vascular responses in hypertensive animals. The study highlights the complex interplay between hypertension and gastric injury, demonstrating that hypertensive conditions may offer some protection against aspirin-induced gastric damage. These insights call for further research to better understand the underlying mechanisms and explore potential therapeutic strategies for gastric injury in hypertensive individuals.

Sex differences in dietary sodium evoked NCC regulation and blood pressure in male and female Sprague-Dawley, Dahl salt-resistant, and Dahl salt-sensitive rats.

Hypertension affects approximately one in two United States adults and sex plays an important role in the pathogenesis of hypertension. The Na+-Cl- cotransporter (NCC), regulated by a kinase network including with-no-lysine kinase (WNK)1 and WNK4, STE20/SPS1-related proline alanine-rich kinase (SPAK), and oxidative stress response 1 (OxSR1), is critical to Na+ reabsorption and blood pressure regulation. Dietary salt differentially modulates NCC in salt-sensitive and salt-resistant rats, in part by modulation of WNK/SPAK/OxSR1 signaling. In this study, we tested the hypothesis that sex-dependent differences in NCC regulation contribute to the development of the salt sensitivity of blood pressure using male and female Sprague-Dawley (SD), Dahl salt-resistant (DSR), and Dahl salt-sensitive (DSS) rats. In normotensive salt-resistant SD and DSR rats, a high-salt diet evoked significant decreases in NCC activity, expression, and phosphorylation. In males, these changes were associated with no change in WNK1 expression, a decrease in WNK4 levels, and suppression of SPAK/OxSR1 expression and phosphorylation. In contrast, in females, there was decreased NCC activity associated with suppression of SPAK/OxSR1 expression and phosphorylation. In hypertensive DSS rats, the ability of females to suppress NCC (in opposition to males) via a SPAK/OxSR1 mechanism likely contributes to their lower magnitude of salt-sensitive hypertension. Collectively, our findings support the existence of sex differences in male versus female rats with NCC regulation during dietary salt intake involving suppression of WNK4 expression in male rats only and the involvement of SPAK/OxSR1 signaling in both males and females.NEW & NOTEWORTHY NCC regulation is sex dependent. In normotensive male and female Sprague-Dawley and Dahl salt-resistant rats, which exhibit dietary Na+-evoked NCC suppression, male rats exhibit decreased WNK4 expression and decreased SPAK and OxSR1 levels, whereas female rats only suppress SPAK and OxSR1. In hypertensive Dahl salt-sensitive rats, the ability of females to suppress NCC (in opposition to males) via a SPAK/OxSR1 mechanism likely contributes to their lower magnitude of salt-sensitive hypertension.

Exaggerated renal sympathetic nerve and pressor responses during spontaneously occurring motor activity in hypertensive rats.

Stimulation of the mesencephalic locomotor region elicits exaggerated sympathetic nerve and pressor responses in spontaneously hypertensive rats (SHR) as compared with normotensive Wistar-Kyoto rats (WKY). This suggests that central command or its influence on vasomotor centers is augmented in hypertension. The decerebrate animal model possesses an ability to evoke intermittent bouts of spontaneously occurring motor activity (SpMA) and generates cardiovascular responses associated with the SpMA. It remains unknown whether the changes in sympathetic nerve activity and hemodynamics during SpMA are altered by hypertension. To test the hypothesis that the responses in renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) during SpMA are exaggerated with hypertension, this study aimed to compare the responses in decerebrate, paralyzed SHR, WKY, and normotensive Sprague-Dawley (SD) rats. In all strains, an abrupt increase in RSNA occurred in synchronization with tibial motor discharge (an index of motor activity) and was followed by rises in MAP and heart rate. The centrally evoked increase in RSNA and MAP during SpMA was much greater (306 ± 110%) in SHR than WKY (187 ± 146%) and SD (165 ± 44%). Although resting baroreflex-mediated changes in RSNA were not different across strains, mechanically or pharmacologically induced elevations in MAP attenuated or abolished the RSNA increase during SpMA in WKY and SD but had no effect in SHR. It is likely that the exaggerated sympathetic nerve and pressor responses during SpMA in SHR are induced along a central command pathway independent of the arterial baroreflex and/or result from central command-induced inhibition of the baroreflex.

Mineralocorticoid receptor antagonism improves transient receptor potential vanilloid 4-dependent dilation of cerebral parenchymal arterioles and cognition in a genetic model of hypertension.

In a model of secondary hypertension, mineralocorticoid receptor (MR) antagonism during the development of hypertension prevents the impairment of transient receptor potential vanilloid 4 (TRPV4) activation in parenchymal arterioles (PAs) and cognitive impairment. However, it is unknown whether MR antagonism can improve these impairments when treatment begins after the onset of essential hypertension. We tested the hypothesis that MR activation in stroke-prone spontaneously hypertensive rats (SHRSP) leads to impaired TRPV4-mediated dilation in PAs that is associated with cognitive dysfunction and neuroinflammation. 20-22-week-old male SHRSP ± eplerenone (EPL; 100 mg/kg daily for 4 weeks) were compared to normotensive Sprague-Dawley (SD) rats. Pressure myography was used to assess PA function. Cognition was tested using Y-maze. Neuroinflammation was assessed using immunofluorescence and qRT-PCR. Carbachol-mediated endothelium-dependent dilation was impaired in SHRSP, and MR antagonism improved this without affecting myogenic tone. Dilation to TRPV4 agonist GSK1016790A was impaired in SHRSP, and ELP treatment restored this. Intermediate conductance potassium channel (IKCa)/small conductance potassium channel (SKCa)-mediated dilation was impaired by hypertension and unaffected by EPL treatment. TRPV4 and IKCa/SKCa channel mRNA expression were reduced in PAs from hypertensive rats, and EPL did not improve this. Impairments in PA dilation in SHRSP were associated with cognitive decline, microglial activation, reactive astrogliosis, and neuroinflammation; cognitive and inflammatory changes were improved with MR blockade. These data advance our understanding of the effects of hypertension on cerebral arterioles using a clinically relevant model and treatment paradigm. Our studies suggest TRPV4 and the MR are potential therapeutic targets to improve cerebrovascular function and cognition during hypertension.

Exaggerated pressor and sympathetic nerve responses during spontaneously‐occurring motor activity in decerebrate spontaneously hypertensive rats

Stimulation of the mesencephalic locomotor region (a putative component of the central command pathway) has been shown to elicit exaggerated pressor and sympathetic nerve responses in decerebrate spontaneously hypertensive rats (SHR) as compared to normotensive Wister-Kyoto rats. This finding suggests that central command activity and/or influence on caudal vasomotor centers may be augmented in hypertension. In the normotensive decerebrate rat model, mean arterial pressure (MAP) and sympathetic nerve activity are known to increase during intermittent bouts of spontaneous motor activity. Moreover, evidence suggests that simulated central command influences at the brainstem may evoke these pressor and sympathetic responses. However, it remains unknown whether these spontaneous changes in cardiovascular hemodynamics are altered with the pathogenesis of hypertension. Based on this background, we hypothesized that the pressor and sympathetic nerve responses during spontaneously-occurring motor activity are exaggerated in hypertension. MAP, renal sympathetic nerve activity (RSNA), and tibial nerve discharge were measured in decerebrate SHR (n=8) and normotensive Sprague-Dawley (SD) rats (n=6). The present study aimed to compare resting baroreflex changes in RSNA (in response to pharmacological alterations in MAP) and central command-evoked responses in MAP and RSNA during spontaneously-occurring motor activity between SHR and normotensive SD. Results demonstrated that the baroreflex-mediated RSNA response was not different between SHR and SD. In both SHR and SD, abrupt, spontaneous increases in RSNA were synchronized with tibial motor discharge and followed by a rise in MAP. These potentially central command-evoked increases in MAP and RSNA were greater in SHR than SD. Phenylephrine-induced elevations in MAP did not suppress the central command-induced RSNA increase in SHR, whereas it abolished the rise in RSNA in SD. Taken together, it is concluded that 1) the arterial baroreflex is operative during resting conditions in SHR as well as SD; 2) the pressor and sympathetic nerve responses during spontaneously-occurring motor activity are exaggerated in hypertensive rats; and 3) exaggerated RSNA responses in SHR may be induced along a central command pathway independent of the arterial baroreflex and/or as a result of central command-induced inhibition of the arterial baroreflex itself.

Abstract P053: Enhanced Exercise Capacity By Muscadine Grape Extract Treatment Is Only Evident In Older Hypertensive Female Rats And Is Independent Of Blood Pressure

Physical performance and systolic blood pressure (SBP) during aging in normotensive female Sprague-Dawley (SD) and hypertensive (mRen2)27 transgenic rats were assessed following long-term treatment with a Muscadine Grape Extract (MGE, Piedmont Research and Development Corp). MGE was administered at a dose of 0.2 mg/mL in the drinking water starting at 14 weeks (wks) of age with an endpoint at 70 wks of age (total time of treatment of 56 wks). At 20-, 40- and 70-wks of age, physical performance (exercise capacity in seconds and workload in grams - meters) was determined using a treadmill at a velocity of 17 cm/second with a 5% incline. SBP was determined by tail-cuff plethysmography in trained rats. There were no significant differences in physical performance between SD and (mRen2)27 female rats at any age despite the higher SBP in the (mRen2)27 rats at all ages. Long-term treatment with MGE had no significant effect on physical performance or SBP in SD rats at any age. In contrast, MGE treatment markedly increased exercise capacity (40 wks: 1615 ± 166 vs 4943 ± 442 seconds, p<0.01, n = 4-9; 70 wks: 2520 ± 374 vs 4117 ± 245 seconds, p<0.01, n = 4-8) and workload (40 wks: 4579 ± 490 vs 14730 ± 1353 grams - meters, p<0.01, n = 4-9; 70 wks: 8338 ± 1340 vs 13659 ± 933 grams - meters, p<0.01, n = 4-8) at the later ages in female (mRen2)27 rats, while there was no effect on SBP (20 wks: 167 ± 4 vs 173 ± 4 mm Hg, n = 4-6; 40 wks: 177 ± 8 vs 170 ± 7 mm Hg, n = 6-7; 70 wks:154 ± 6 vs 172 ± 6 mm Hg, n = 5) at any age. These data suggest that MGE treatment is effective in improving physical performance only in hypertensive female rats and may be independent of changes in blood pressure. The benefit of MGE in the older hypertensive female may reflect reductions in vascular stiffness and oxidative stress. Support: Chronic Disease Research Fund, Hypertension & Vascular Research Center

White mulberry fruit polysaccharides enhance endothelial nitric oxide production to relax arteries in vitro and reduce blood pressure in vivo

Mulberry fruit polysaccharides have demonstrated excellent anti-inflammatory, antioxidant, hypolipidemic, and hypoglycemic properties. This study tested the effect of white mulberry fruit polysaccharides (WMFPs) on blood pressure. WMFPs induced endothelium-dependent relaxation in rat mesenteric arteries and NO production in endothelial cells, both of which were reversed by the NO synthase inhibitor Nω-nitro-l-arginine methyl ester hydrochloride, a phosphoinositide 3-kinase inhibitor LY294002, a cell-permeable Ca2+ chelator (1,2-bis (o-aminophenoxy) ethane-N,N,N’,N’-tetraacetic acid (acetoxymethyl ester)), and inhibitors of molecules downstream of NO, including the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, the potassium channel inhibitor tetraethylammonium chloride, the large conductance calcium-activated potassium channel-specific inhibitor iberiotoxin, and the KATP channel inhibitor glibenclamide. Intravenous injection of WMFPs reduced mean arterial blood pressure in both normotensive Sprague-Dawley and spontaneously hypertensive rats through enhanced endothelial NO production. This study demonstrated that WMFPs induce endothelium-dependent relaxation in rat mesenteric arteries to regulate blood pressure, suggesting that development of WMFPs as a novel antihypertensive agent is warranted.

Hydrogen Peroxide Increases Intracellular Sodium Concentration in the Medullary Thick Ascending Limb Isolated from Sprague‐Dawley Rats

Elevations of renal medullary hydrogen peroxide (H2O2) produce a salt‐sensitive form of hypertension as shown by chronic infusion of H2O2 into the renal medulla of a single remaining kidney of normotensive Sprague‐Dawley (SD) rats (Makino et al., Hypertension, 2003) and salt‐resistant consomic SS.13BN rats. Conversely, chronic medullary infusion of catalase (H2O2 scavenger) into the renal medulla of Dahl salt‐sensitive rats significantly reduced salt induced hypertension (Taylor and Cowley, Am J Physiol Regul Integr Comp Physiol, 2005). The goal of this study was to assess the effects of H2O2 upon intracellular sodium concentration [Na+]i and the role of mTORC1 and mTORC2 signaling in the medullary thick ascending limb (mTAL) isolated from the outer medulla (OM) of SD rats.Methodsrats were anesthetized, the kidney flushed with saline, removed, and mTALs dissected from the inner stripe of the OM at 4°C under a stereomicroscope. The mTALs were attached to poly‐Lysine coated cover slips and incubated with HBSS containing 10 nM of the Na+‐sensitive fluorescence dye NaGreen and 0.05% Pluronic acid F‐127 for 30 min at room temperature. The mTALs were washed and then placed in a heated chamber (37°C) mounted on the stage of an inverted Nikon TE‐2000U microscope for recording.ResultsIt was found that 100 uM H2O2 resulted in a significant increase in [Na+]i (p<0.05). The responses to pretreatment of mTAL with 10 uM PP242 (mTORC1/2 inhibitor), 200 nM rapamycin (mTORC1 specific inhibitor), or 1 mM furosemide (Na+/K+/2Cl− inhibitor) were then studied. We found that each of these inhibitors nearly abolished H2O2 induced increases in intracellular Na+. Western blot analysis of isolated mTAL from SD rats for each of the treatments found that 100 uM H2O2 increased the activation of AKT (pAKTSer473; a surrogate for mTORC1/2 activation) and S6 (pS6Ser235/236; a surrogate for mTORC1 activation) and were inhibited by their respective inhibitors.ConclusionTogether these observations indicate that H2O2 acts through the mTOR signaling pathways to inhibit NKCC2 activity, which would in turn be expected to lead to sodium retention and hypertension.Support or Funding InformationHL 122662This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vasodilatory responses of renal interlobular arteries to epoxyeicosatrienoic acids analog are not enhanced in Ren-2 transgenic hypertensive rats: evidence against a role of direct vascular effects of epoxyeicosatrienoic acids in progression of experimental heart failure.

Pathophysiological mechanisms underlying the development of renal dysfunction and progression of congestive heart failure (CHF) remain poorly understood. Recent studies have revealed striking differences in the role of epoxyeicosatrienoic acids (EETs), active products of cytochrome P-450-dependent epoxygenase pathway of arachidonic acid, in the progression of aorto-caval fistula (ACF)-induced CHF between hypertensive Ren-2 renin transgenic rats (TGR) and transgene-negative normotensive Hannover Sprague-Dawley (HanSD) controls. Both ACF TGR and ACF HanSD strains exhibited marked intrarenal EETs deficiency and impairment of renal function, and in both strains chronic pharmacologic inhibition of soluble epoxide hydrolase (sEH) (which normally degrades EETs) normalized EETs levels. However, the treatment improved the survival rate and attenuated renal function impairment in ACF TGR only. Here we aimed to establish if the reported improved renal function and attenuation of progression of CHF in ACF TGR observed after she blockade depends on increased vasodilatory responsiveness of renal resistance arteries to EETs. Therefore, we examined the responses of interlobar arteries from kidneys of ACF TGR and ACF HanSD rats to EET-A, a new stable 14,15-EET analog. We found that the arteries from ACF HanSD kidneys rats exhibited greater vasodilator responses when compared to the ACF TGR arteries. Hence, reduced renal vasodilatory responsiveness cannot be responsible for the lack of beneficial effects of chronic sEH inhibition on the development of renal dysfunction and progression of CHF in ACF HanSD rats.

GW26-e5397 Caloric Restriction Ameliorates Angiotensin Induced Mitochondrial Remodeling and Cardiac Hypertrophy

To discuss Caloric Restriction Ameliorates Angiotensin can induced Mitochondrial Remodeling and Cardiac Hypertrophy. We used fourty 4-week-old double transgenic rats (dTGRs) and 16 age-matched normotensive Sprague-Dawley (SD) rats described elsewhere .dTGRs and SD control rats were divided into 4

ABT-724 alleviated hyperactivity and spatial learning impairment in the spontaneously hypertensive rat model of attention-deficit/hyperactivity disorder

Dysfunction of dopamine D4 receptor (D4R) is linked to attention-deficit/hyperactivity disorder (ADHD) as well as ADHD associated cognitive impairment. Here, we tested the possible therapeutic benefit of the D4R-selective agonist ABT-724 in adolescent spontaneously hypertensive rats (SHRs). ABT-724-treated SHRs were administered ABT-724 (0.04mg/kg, 0.16mg/kg or 0.64mg/kg) from postnatal day (P) 28 to P32. Control SHRs and Sprague-Dawley (SD) rats were injected with saline. Then two cohorts of rats were tested in the open field and Làt maze that measured locomotion and non-selective attention (NSA), respectively. Another cohort of rats was subjected to water maze task for evaluation of spatial learning and memory. We found that control SHRs displayed hyperactivity as well as impaired NSA and spatial learning compared with normotensive SD rats. ABT-724 (0.16 and 0.64mg/kg) treatment alleviated hyperactivity and spatial learning impairment in SHRs. No dose of ABT-724 tested altered NSA in SHRs. Our results raise the possibility that ABT-724 may be used as a therapeutic intervention for ADHD patients during adolescence.

Abstract 182: Medullary Endocannabinoid Content Contributes to the Differential Resting Baroreflex Sensitivity in Rats with Altered Brain Renin-Angiotensin System Expression

Activation of CB1 receptors in the solitary tract nucleus (NTS) over a 100-fold dose range elicits biphasic effects, with high doses inhibiting baroreflex sensitivity (BRS) for control of heart rate and lower doses facilitating BRS. There is growing evidence for signaling interactions between the endocannabinoid system (ECS) and pathogenic actions of angiotensin (Ang) II at AT1 receptors in hypertension and the metabolic syndrome. Hypotensive ASrAOGEN (AS) rats, overexpressing an angiotensinogen antisense in glia, have significantly elevated medullary tissue glutamate levels and enhanced BRS compared to normotensive Sprague-Dawley (SD) rats (1.42 ± 0.11 vs. 1.04 ± 0.05 ms/mmHg; n = 5 - 6; P = 0.02). Transgenic (mRen2)27 rats, a monogenetic Ang II-dependent model of hypertension, have markedly impaired BRS compared to SD rats (0.43 ± 0.06 vs. 1.04 ± 0.05 mmHg; n = 5; P < 0.0001). There is no effect of the CB1 receptor antagonist SR141716 on BRS when microinjected into the NTS of SD rats; however, SR141716 injected into the NTS of hypertensive (mRen2)27 rats dose-dependently improved BRS. In contrast, SR141716 injected into the NTS of hypotensive AS rats dose-dependently reduced BRS. Microinjection of 0.36 pmol SR141716 (n = 3) reduced BRS from a baseline of 1.23 ± 0.05 ms/mmHg to 0.81 ± 0.14 (P = 0.01) and 36 pmol SR141716 (n = 3) decreased BRS from 1.60 ± 0.17 to 0.48 ± 0.06 ms/mmHg (P = 0.001), a level comparable with baseline BRS of hypertensive (mRen2)27 rats. The effects of CB1 receptor blockade on BRS parallel the endogenous levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) as measured by mass spectrometry with lower 2-AG in AS compared to (mRen2)27 rats (1.17 ± 0.09 vs. 2.70 ± 0.28 ng/mg tissue; n = 4 - 5; P = 0.002). Normotensive SD rats had intermediate 2-AG levels (1.85 ± 0.27 ng/mg tissue; n = 5; n.s. vs. other strains). These observations reveal that an upregulated ECS contributes to RAS-dependent suppression of BRS. That there is a reduction in BRS in response to NTS CB1 receptor blockade in hypotensive AS rats exhibiting elevated glutamate levels suggests differential regulatory functions of the brain ECS that may involve alterations in transmitters known to influence BRS and that parallel the Ang II:Ang-(1-7) ratio in these animals.

Abstract 622: Increased Mitochondrial Oxidative Stress and Activated AMP- Kinase In the Brain Dorsal Medulla of Hypertensive (mRen2)27 Transgenic Rats

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 β 1 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 AMPKβ 1 - 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.

Differences in oxidative stress status and expression of MKP-1 in dorsal medulla of transgenic rats with altered brain renin-angiotensin system

ANG II-stimulated production of reactive oxygen species (ROS) through NADPH oxidase is suggested to activate MAPK pathways, which are implicated in neurally mediated pressor effects of ANG II. Emerging evidence suggests that ANG-(1-7) up regulates MAPK phosphatases to reduce MAPK signaling and attenuate actions of ANG II. Whether angiotensin peptides participate in long-term regulation of these systems in the brain is not known. Therefore, we determined tissue and mitochondrial ROS, as well as expression and activity of MAPK phosphatase-1 (MKP-1) in brain dorsal medullary tissue of hypertensive transgenic (mRen2)27 rats exhibiting higher ANG II/ANG-(1-7) tone or hypotensive transgenic rats with targeted decreased glial expression of angiotensinogen, ASrAOGEN (AS) exhibiting lower ANG II/ANG-(1-7) tone compared with normotensive Sprague-Dawley (SD) rats that serve as the control strain. Transgenic (mRen2)27 rats showed higher medullary tissue NADPH oxidase activity and dihydroethidium fluorescence in isolated mitochondria vs. SD or AS rats. Mitochondrial uncoupling protein 2 was lower in AS and unchanged in (mRen2)27 compared with SD rats. MKP-1 mRNA and protein expression were higher in AS and unchanged in (mRen2)27 compared with SD rats. AS rats also had lower phosphorylated ERK1/2 and JNK consistent with higher MKP-1 activity. Thus, an altered brain renin-angiotensin system influences oxidative stress status and regulates MKP-1 expression. However, there is a dissociation between these effects and the hemodynamic profiles. Higher ROS was associated with hypertension in (mRen2)27 and normal MKP-1, whereas the higher MKP-1 was associated with hypotension in AS, where ROS was normal relative to SD rats.

Distribution and localisation of Gα proteins in the rostral ventrolateral medulla of normotensive and hypertensive rats: Focus on catecholaminergic neurons

About 860 G-protein-coupled receptors (GPCRs) mediate their actions via heterotrimeric G-proteins. Their activation releases Gα from Gβλ subunits. The type of Gα subunit dictates the major signalling proteins involved: adenylyl cyclase, PLC and rhoGEF. The rostral ventrolateral medulla (RVLM), containing the rostral C1 (rC1) cell group, sets and maintains the tonic and reflex control of blood pressure and a plethora of inputs converge onto these neurons. We determined the relative abundance of 10 Gα subunit mRNAs, representing the four major families, within the RVLM, using quantitative RT-PCR. In situ hybridisation (ISH) combined with immunohistochemistry (IHC) was used to quantify and compare this expression in rC1 with that in the A1 and A5 cell groups. The relative abundance of Gα subunit mRNAs and a comparison of gene expression levels were quantitatively determined in normotensive and hypertensive rat strains. All 10 Gα mRNAs were detected in the RVLM of Sprague–Dawley (SD) rats with relative abundance such that Gαs>Gαi2>Gαo>Gαq>GαL>Gα11>Gαi3>Gαi1>Gα12>Gα13. The high abundance of Gα mRNAs signalling via adenylyl cyclase indicates the importance of associated GPCRs. Within the rC1 and A1 groups similar differential Gα mRNA expression profiles were seen with Gαs being found in all rC1 cells, Gα11 absent and Gαi3 rarely expressed. Thus functionally distinct subgroups exist within the rC1 and A1 cell groups as differing distributions of Gα subunits must reflect the array of GPCRs that influence their activity. In contrast, all A5 cells expressed all Gα mRNAs suggesting a functionally homogeneous group. When the 10 Gα mRNAs of the RVLM in spontaneously hypertensive rats (SHR) were compared quantitatively to Wistar-Kyoto (WKY), only Gαs and Gα12 were significantly elevated. However when the expression in normotensive SD and WKY was compared with SHR no significant differences were evident. These findings demonstrate a range of GPCR signalling capabilities in brainstem neurons important for homeostasis and suggest a prominent role for signalling via adenylyl cyclase.

Mechanisms of K+ induced renal vasodilation in normo‐ and hypertensive rats in vivo

We investigated the mechanisms behind K(+) -induced renal vasodilation in vivo in normotensive Sprague-Dawley (SD) rats and spontaneously hypertensive rats (SHR). Renal blood flow (RBF) was measured utilizing an ultrasonic Doppler flow probe. Renal vascular resistance (RVR) was calculated as the ratio of mean arterial pressure (MAP) and RBF (RVR = MAP/RBF). Test drugs were introduced directly into the renal artery. Inward rectifier K(+) (K(ir) ) channels and Na(+) ,K(+) -ATPase were blocked by Ba(2+) and ouabain (estimated plasma concentrations ∼20 and ∼7 μm) respectively. Confocal immunofluorescence microscopy demonstrated K(ir) 2.1 channels in pre-glomerular vessels of SD and SHR. Ba(2+) caused a transient (6-13%) increase in baseline RVR in both SD and SHR. Ouabain had a similar effect. Elevated renal plasma [K(+) ] (∼12 mm) caused a small and sustained decrease (5-13%) in RVR in both strains. This decrease was significantly larger in SHR than in SD. The K(+) -induced vasodilation was attenuated by Ba(2+) in control SD and SHR and by ouabain in SD. Nitric oxide (NO) blockade using l-NAME treatment increased MAP and decreased RBF in both rat strains, but did not affect the K(+) -induced renal vasodilation. K(+) -induced renal vasodilation is larger in SHR, mediated by K(ir) channels in SD and SHR, and in addition, by Na(+) ,K(+) -ATPase in SD. In addition, NO is not essential for K(+) -induced renal vasodilation.

Connexin abundance in resistance vessels from the renal microcirculation in normo- and hypertensive rats

The expression of connexins in renal arterioles is believed to have a profound impact on conducted responses, regulation of arteriolar tonus and renal blood flow. We have previously shown that in renal preglomerular arterioles, conducted vasomotor responses are 40% greater in spontaneously hypertensive rats (SHR) than in normotensive Sprague–Dawley (SD) rats. Because conducted vasomotor responses depend on the cell–cell communication mediated through gap junctions, we hypothesized that the increased magnitude of conducted vasomotor response in SHR is associated with an increased amount of connexins in renal arterioles. To test this hypothesis, the amount of connexin 37 (Cx37), Cx40 and Cx43 was assessed in renal arterioles from normo- and hypertensive rats using quantitative immunofluorescence laser confocal miscroscopy. To account for differences in genetic background, we included both normotensive Wistar–Kyoto (WKY) and SD rats in the study. In all three strains of rats, and for all three isoforms, the expression of connexins was predominantly confined to the endothelial cells. We found a significantly increased abundance (240 ± 17.6%, p<0.05) of Cx37 in arterioles from WKY compared with SD and SHR. This high abundance of Cx37 was not related to blood pressure because normotensive SD demonstrated a level of Cx37 similar to that of SHR. Additionally, we found no evidence for an increased abundance of Cx40 and Cx43 in renal arterioles of SHR when compared with normotensive counterparts.

Renal autoregulation and passive pressure-flow relationships in diabetes and hypertension

We investigated renal hemodynamics in isolated, perfused kidneys from rat models of diabetes and hypertension. Autoregulation and passive vascular responses were measured using stepped pressure ramps in the presence of angiotensin II (pEC50) or papaverine (0.1 mM), respectively. Male diabetic heterozygote m(Ren2)27 rats were compared with three male control groups: nondiabetic, normotensive Sprague-Dawley (SD) rats; nondiabetic, hypertensive heterozygote m(Ren2)27 rats; and diabetic, normotensive SD rats. Kidney function (proteinuria, creatinine clearance) was monitored before induction and at monthly intervals. Vascular function was measured in vitro in rats of induction age (6-8 wk) and at 2 and 4 mo postinduction. Renal flow correlated with age, but not diabetes or the Ren2 gene. Kidney weight-specific and body weight-specific renal flow differed between diabetic and nondiabetic rats because diabetic rats had higher kidney but lower body weights. Kidneys from all groups showed effective autoregulation in the presence of angiotensin II. The autoregulatory pressure threshold of m(Ren2)27 rats was higher, and the autoregulation pressure range was wider, compared with SD rats. When vascular smooth muscle activity was blocked with papaverine, pressure-flow responses differed between groups and with time. The m(Ren2)27 rat groups showed higher renal vascular resistance at lower pressures, suggesting greater vascular stiffness. In contrast, diabetic SD rat kidneys demonstrated reduced vessel stiffness. Flow was impaired in diabetic m(Ren2)27 rats at 4 mo, and this correlated with a decline in creatinine clearance. The results suggest that the characteristic late decline in renal filtration function in diabetes- and hypertension-related renal disease follows changes in renal vascular compliance.

Abstract 3584: Comparison of the severity of imatinib-induced cardiotoxicity in normotensive Sprague-Dawley (SD) and spontaneously hypertensive (SHR) rats

Abstract Imatinib (IMNB) is a promising type of chemotherapeutic agent that specifically targets tyrosine kinase pathway-dependent tumors. However, cardiotoxicity has been reported with clinical use of IMNB. The characteristics of IMNB-induced cardiac alterations are not completely defined. The present study sought to examine the influence of a concomitant disease such as hypertension on the cardiotoxic effects of IMNB. Groups of adult male SD or SHR were dosed with 50 (5/group) or 100 mg/kg (10/group) IMNB or water (10/group)(p.o.) daily for 14 days (dose of 50 mg/kg is approximately 2x recommended human dose of 600 mg/m2). Tissues and blood samples were collected 24 hours after the last dosing. The 100 mg/kg dose caused a slight reduction in the rate of body weight gain. Serum levels of glucose were decreased and alanine transaminase (ALT) were increased in both SD and SHR dosed with IMNB. Changes from control were most pronounced in SD given 100mg/kg IMNB (ALT=175% vs 118% and glucose=81% vs 91% compared to SHR). White blood cell counts were depressed in SHR but not in SD rats. Dose-dependent cardiac lesions were noted in the groups of SD and SHR given either dose of IMNB (blinded evaluation). Cardiac lesions were characterized by cytoplasmic vacuolization, myofibrillar loss, interstitial infiltration with chronic inflammatory cells and fibrosis (proliferation of myofibroblasts). Mean lesion scores (based on a scale of 0 to 3) were higher in SHR than in SD (100mg/kg-1.9 vs 1.25 and 50 mg/kg-1.5 vs 1.1, p&amp;lt;0.05)(Tukey-Kramer test). Increased serum levels of cardiac troponin I were detected in all IMNB-treated groups. The overall mean cTnI levels were higher in SHR (31.5, 41.3 and 53.9 pg/ml) compared to SD (6.8, 25 and 30 pg/ml) at the vehicle control, 50 and 100 mg/kg doses, respectively. These results indicate that hypertension as expressed in SHR appears to be a factor that can intensify the cardiotoxic effects of IMNB and that monitoring for cardiac troponin I may provide a sensitive means of detecting IMNB toxicity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3584.

Influence of up-regulated renin—angiotensin system on the exploration, anxiety-related behavior and object recognition

The renin-angiotensin system (RAS) plays an important role in the development of hypertension and has serious consequences on behaviour. The aim of our study was to investigate the effect of hypertension, induced by up-regulated RAS, on the exploration, anxiety-related behaviour and object recognition in laboratory rats. In the experiment, 12 weeks old normotensive Sprague-Dawley (SD) and hypertensive TGR(mREN2)27 (TGR) male rats with up-regulated RAS were used. In the open-field test, the TGR rats were less active in ambulating, rearing and sniffing and more active in self-grooming and urinating than SD ones. In the elevated plus-maze test, the TGR rats showed lower frequency of total arm entries, closed arm entries and higher frequency of defecation than in controls. In the emergence test, TGR rats did not show significant differences. In the novel object recognition task, the TGR rats spent less time with exploration of both familiar and unfamiliar objects but preferred the novel object over the familiar one and exhibited higher percentage of the total exploring time spent with novel object exploration than SD rats. Our results indicate that the TGR rats are less actively exploring, show some modifications of emotional/anxiety-related behavior and exhibited better recognition abilities.