Young Spontaneously Hypertensive Rats Research Articles

The Urotensin System Is Up-Regulated in the Pre-Hypertensive Spontaneously Hypertensive Rat

Urotensin II (UII) concentrations are raised both in humans with hypertension and in spontaneously hypertensive rats (SHR). Since the urotensin system acts to regulate glomerular filtration in the kidney it may play a greater role in the pre-hypertensive SHR in which renal dysfunction is known to precede the onset of severe hypertension. This study aimed to determine the renal actions and expression of the urotensin system in the young SHR. Intravenous rat UII (6 pmol. min-1. 100 g body weight-1) had no significant effect on GFR; however urotensin-related peptide (URP) reduced GFR (P<0.05) in 4-5 week old SHR. Administration of the UT antagonist SB-706375 evoked marked increases in GFR (baseline 0.38 ± 0.07 vs antagonist 0.76 ± 0.05 ml. min-1. 100 g body weight-1, P<0.05), urine flow and sodium excretion (baseline 2.5 ± 0.4 vs antagonist 9.1 ± 2.1 µmol. min-1. 100 g body weight-1, P<0.05) in the SHR. Normotensive Wistar-Kyoto rats showed little response to UT antagonism. Quantitative RT-PCR showed that neither UII nor UT mRNA expression differed between the kidneys of young SHR and WKY rats; however expression of URP was 4-fold higher in the SHR kidney. Renal transcriptional up-regulation indicates that URP is the major UT ligand in young SHR and WKY rats. Enhanced tonic UT activation may contribute to known renal dysfunction in pre-hypertensive SHR.

Abstract 18291: Vascular Smooth Muscle Cell Stiffness as a Novel Mechanism for the Increased Aortic Stiffness in Aging and Hypertension, Which is Augmented in Aging Hypertensive Animals

It is generally recognized that increased aortic stiffness occurs in hypertension and aging. However, less is known about their combined influence on aortic stiffness. Furthermore, most prior studies have attributed increased aortic stiffness to changes in the extracellular matrix, whereas the hypothesis of this investigation is that a significant component of vascular stiffness resides at the level of the vascular smooth muscle cells (VSMCs), and that the contribution of this mechanism would be enhanced when aging is superimposed on hypertension. Testing of this hypothesis was made possible by examining VSMC the mechanical properties of isolated VSMCs using atomic force microscopy (AFM). We examined aortic stiffness in young (16 wks) and old (64 wks) spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) wild-type controls and tested the hypothesis that the additional increase in aortic stiffness with combined aging and hypertension is mediated, in part, at the level of VSMCs. Systolic aortic pressure, measured by Millar micromanometer catheter, was significantly increased in the old compared to young SHR (191 ± 8 mmHg versus 148 ± 5 mmHg, p&lt;0.01), but not in WKY (old, 101 ± 10 mmHg versus young, 120 ± 8 mmHg). Excised aortic ring segments were subjected to physiological levels of mechanical stretch ex vivo, and the wall stress in these ring segments was greater in older SHR than WKY (p&lt;0.05). VSMCs were isolated from the thoracic aorta, and the stiffness of individual VSMCs was measured by an AFM nano-indentation technique. Isolated VSMC stiffness was 43 ± 8% greater, p&lt;0.05, in old SHR compared to young SHR (27 ± 4 kPa). VSMC stiffness was also increased, p&lt;0.05, in young SHR versus young WKY (14 ± 2 kPa), but this increase (92 ± 15%) was less, p&lt;0.05, than that observed between old SHR versus old WKY (131 ± 2%). Thus, increased VSMC stiffness is a significant component of the increased aortic stiffness of hypertension, but this increase is augmented in aging hypertensive rats.

Renoprotective Effects of Melatonin in Young Spontaneously Hypertensive Rats with L-NAME

Nitric oxide (NO) deficiency occurs in humans and animals with hypertension and chronic kidney disease (CKD). An inhibitor of NO synthase, N(G)-nitro-l-arginine methyl ester (L-NAME) exacerbates kidney damage in the adult spontaneously hypertensive rat (SHR). We examined whether L-NAME exacerbated hypertensive nephrosclerosis in young SHRs and whether melatonin protects SHRs against kidney damage by restoration of the asymmetric dimethylarginine (ADMA)-NO pathway. Rats aged 4 weeks were randomly assigned into three groups (n=10 for each group): Group 1 (control), SHRs without treatment; Group 2 (L-NAME), SHRs received L-NAME (80mg/L) in drinking water; and Group 3 (L-NAME+melatonin), SHRs received L-NAME (80mg/L) and 0.01% melatonin in drinking water. All rats were sacrificed at 10 weeks of age. L-NAME exacerbates the elevation of blood pressure, renal dysfunction, and glomerular sclerosis in young SHRs. L-NAME induced an increase of ADMA and a decrease of arginine-to-ADMA ratio in the SHR kidney. Melatonin therapy prevented L-NAME-exacerbated hypertension and nephrosclerosis in young SHRs. In addition, melatonin restored L-NAME-induced reduction of dimethylarginine dimethylaminohydrolase (DDAH; ADMA-metabolizing enzymes) activity in the SHR kidney. Next, melatonin decreased renal ADMA concentrations, increased renal arginine-to-ADMA ratio, and restored NO production in L-NAME-treated young SHRs. Moreover, melatonin reduced the degree of oxidative damaged DNA product, 8-hydroxydeoxyguanosine immunostaining in L-NAME-treated SHR kidney. Our results indicated that L-NAME/SHR is a useful model for hypertensive nephrosclerosis in young rats. The blood pressure-lowering and renoprotective effects of melatonin is due to increases of DDAH activity, decreases of ADMA, and reduction of oxidative stress in L-NAME-treated SHR kidney. Specific therapy targeting the DDAH-ADMA pathway may be a promising approach to slowing chronic kidney disease progression in children.

Two different approaches to restore renal nitric oxide and prevent hypertension in young spontaneously hypertensive rats: l-citrulline and nitrate

Nitric oxide (NO) deficiency mediates oxidative stress in the kidney and is involved in the development of hypertension. NO synthesis occurs via 2 pathways: nitric oxide synthase (NOS) dependent and NOS-independent. We tested whether the development of hypertension is prevented by restoration of NO by dietary l-citrulline or nitrate supplementation in young spontaneously hypertensive rats (SHRs). Male SHRs and normotensive Wistar Kyoto control rats (WKYs)s age 4weeks were assigned to 4groups: untreated SHRs and WKYs, and SHRs and WKYs that received 0.25% l-citrulline for 8weeks. In our second series of studies, we replaced l-citrulline with 1mmol/kg/d sodium nitrate. All rats were sacrificed at age 12weeks. We found an increase in the blood pressure of SHRs was prevented by dietary supplementation of l-citrulline or nitrate. Both treatments restored NO bioavailability and reduced oxidative stress in SHR kidneys. l-Citrulline therapy reduced levels of l-arginine and asymmetric dimethylarginine (ADMA)-an endogenous inhibitor of NOS-and increased the l-arginine-to-ADMA ratio in SHR kidneys. Nitrate treatment reduced plasma levels of l-arginine and ADMA concurrently in SHRs. Our findings suggest that both NOS-dependent and -independent approaches in the prehypertensive stage toward augmentation of NO can prevent the development of hypertension in young SHRs.

Abstract 316: Aortic Smooth Muscle Cell Stiffness as a Mechanism for the Increased Aortic Stiffness when Aging is Superimposed on Hypertension

It is generally recognized that increased aortic stiffness occurs in hypertension and aging. However, less is known about their combined influence on aortic stiffness. Furthermore, most prior studies have attributed increased aortic stiffness to changes in the extracellular matrix, whereas the hypothesis of this investigation is that a significant component of vascular stiffness resides at the level of the vascular smooth muscle cells (VSMCs), and that the contribution of this mechanism would be enhanced when aging is superimposed on hypertension. Accordingly, we examined aortic stiffness in young (16 wks) and old (64 wks) spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) wild type controls. We tested the hypothesis that the additional increase in aortic stiffness with combined aging and hypertension is mediated, in part, at the level of VSMCs. Systolic aortic pressure, measured by Millar micromanometer catheter, was significantly increased in the old compared to young SHR (191 ± 8 mmHg versus 148 ± 5 mmHg, p&lt;0.01), but not in WKY (old, 101 ± 10 mmHg versus young, 120 ± 8 mmHg). Excised aortic ring segments were subjected to physiological levels of mechanical stretch ex vivo, and the wall stress in these ring segments was greater in older SHR than WKY (p&lt;0.05). VSMCs were isolated from the thoracic aorta, and the stiffness of individual VSMCs was measured by atomic force microscopy nano-indentation. Isolated VSMC stiffness was 43 ± 8% greater, p&lt;0.05, in old SHR compared to young SHR (27 ± 4 kPa). VSMC stiffness was also increased, p&lt;0.05, in young SHR versus young WKY (14 ± 2 kPa), but this increase (92 ± 15%) was less, p&lt;0.05, than that observed between old SHR versus old WKY (131 ± 2%). Thus, increased VSMC stiffness is a significant component of the increased aortic stiffness of hypertension, but this increase is augmented in aging hypertensive rats.

Renal inflammatory markers during the onset of hypertension in spontaneously hypertensive rats

Early blockade of the renin-angiotensin system is successful in delaying the development of hypertension in spontaneously hypertensive rats (SHRs) and ameliorating organ damage by inhibition of the inflammatory response. In this study, we investigated the role of the angiotensin II type 1 receptor (AT1R) in the early renal inflammatory response in SHR. Blood pressure development and renal inflammatory markers were measured in 4-, 8- and 12-week-old SHR and age-matched Wistar Kyoto (WKY) rats. Separate groups of SHRs were transiently treated with the AT1R blocker losartan between 4 and 8 weeks of age. Urinary excretion of the renal injury markers osteopontin and neutrophil gelatinase-associated lipocalin increased in young SHR. Further, renal expression of inflammatory genes was also increased in young SHR. Losartan inhibited the increase of these inflammatory markers. In contrast, gene expression of the renal injury marker and T-cell inducer kidney injury molecule-1 (KIM-1) was reduced in 4-week-old SHR when compared with WKY. Similarly, the T-cell marker CD3 was significantly decreased in 4-week-old SHR. These effects were not antagonized by AT1R blockade. This study confirms the presence of an early renal inflammatory response in SHR that can be blocked by AT1R antagonism. In addition, it demonstrates that KIM-1 does not behave as a pure kidney injury marker in young SHR, but may reflect kidney maturation.

Cardiac sympathetic dysfunction in the prehypertensive spontaneously hypertensive rat

Recent studies in prehypertensive spontaneously hypertensive rats (SHR) have shown larger calcium transients and reduced norepinephrine transporter (NET) activity in cultured stellate neurons compared with Wistar-Kyoto (WKY) controls, although the functional significance of these results is unknown. We hypothesized that peripheral sympathetic responsiveness in the SHR at 4 wk of age would be exaggerated compared with the WKY. In vivo arterial pressure (under 2% isoflurane) was similar in SHRs (88 ± 2/50 ± 3 mmHg, n = 18) compared with WKYs (88 ± 3/49 ± 4 mmHg, n = 20). However, a small but significant (P < 0.05) tachycardia was observed in the young SHR despite the heart rate response to vagus stimulation (3 and 5 Hz) in vivo being similar (SHR: n = 12, WKY: n = 10). In isolated atrial preparations there was a significantly greater tachycardia during right stellate stimulation (5 and 7 Hz) in SHRs (n = 19) compared with WKYs (n = 16) but not in response to exogenous NE (0.025-5 μM, SHR: n = 10, WKY: n = 10). There was also a significantly greater release of [(3)H]NE to field stimulation (5 Hz) of atria in the SHR (SHR: n = 17, WKY: n = 16). Additionally, plasma levels of neuropeptide Y sampled from the right atria in vivo were also higher in the SHR (ELISA, n = 12 for both groups). The difference in [(3)H]NE release between SHR and WKY could be normalized by the NET inhibitor desipramine (1 μM, SHR: n = 10, WKY: n = 8) but not the α2-receptor antagonist yohimbine (1 μM, SHR: n = 7, WKY: n = 8). Increased cardiac sympathetic neurotransmission driven by larger neuronal calcium transients and reduced NE reuptake translates into enhanced cardiac sympathetic responsiveness at the end organ in prehypertensive SHRs.

GW24-e0815 The role of microRNA-29b in renal fibrosis induced by angiotensin II

ObjectivesPrimary study have demonstrated that the Angiotensin II (Ang II) contents and the its receptor density in the kidney of young spontaneously hypertensive rats (SHR) were significantly higher than age-matched...

Effect of renal denervation in aged spontaneously hypertensive rats

Catheter‐based renal nerve ablation (CBRNA) in resistant hypertension (HTN) is associated with long‐term blood pressure (BP) reduction as well as improvement of glucose intolerance, left ventricular hypertrophy, and atrial fibrillation. Evaluation of mechanisms underlying these improvements has been limited by lack of an appropriate animal model. Preliminary work in our lab identified the spontaneously hypertensive rat (SHR) as a potential model for such studies. To validate this model, we recorded ambulatory BP in male SHR (13wk) undergoing renal denervation (RDX: n=8) or sham(n=7) surgery. Within 24hrs, ΔMAP was greater in RDX compared to sham(−11.5±4.3 vs. 1.1±0.9mmHg), but was not sustained at 1 week. Sham animals aged to 21wks were subdivided into RDX (n=4) or sham (n=3) groups and the intervention repeated. ΔMAP was greater in RDX compared to sham within the first day (−28.4±2.3 vs −0.8±1.6mmHg). In contrast to young SHR, ΔMAP persisted after 1 week in older RDX animals vs older shams(−10.5±2.5 vs. −2.2±1.8mmHg). ΔMAP in these animals persisted for the duration of the study. These data demonstrate that older SHR may better model the effects of CBRNA, and may support the hypothesis that interruption of renal afferent nerves is critical in chronically lowering BP. Research Support from AHA 12PRE8190002

N-Acetylcysteine Prevents Hypertension via Regulation of the ADMA-DDAH Pathway in Young Spontaneously Hypertensive Rats

Asymmetric dimethylarginine (ADMA) reduces nitric oxide (NO), thus causing hypertension. ADMA is metabolized by dimethylarginine dimethylaminohydrolase (DDAH), which can be inhibited by oxidative stress. N-Acetylcysteine (NAC), an antioxidant, can facilitate glutathione (GSH) synthesis. We aimed to determine whether NAC can prevent hypertension by regulating the ADMA-DDAH pathway in spontaneously hypertensive rats (SHR). Rats aged 4 weeks were assigned into 3 groups (n = 8/group): control Wistar Kyoto rats (WKY), SHR, and SHR receiving 2% NAC in drinking water. All rats were sacrificed at 12 weeks of age. SHR had higher blood pressure than WKY, whereas NAC-treated animals did not. SHR had elevated plasma ADMA levels, which was prevented by NAC therapy. SHR had lower renal DDAH activity than WKY, whereas NAC-treated animals did not. Renal superoxide production was higher in SHR than in WKY, whereas NAC therapy prevented it. NAC therapy was also associated with higher GSH-to-oxidized GSH ratio in SHR kidneys. Moreover, NAC reduced oxidative stress damage in SHR. The observed antihypertensive effects of NAC in young SHR might be due to restoration of DDAH activity to reduce ADMA, leading to attenuation of oxidative stress. Our findings highlight the impact of NAC on the development of hypertension by regulating ADMA-DDAH pathway.

Long-term effect of prazosin and losartan administration on blood pressure, heart, carotid artery, and acetylcholine induced dilation of cardiovascular system of young Wistar rats and SHR

The long-term effects of prazosin and losartan administration on blood pressure, trophicity of the heart and carotid arteries, and responses of the cardiovascular system to acetylcholine, were studied in Wistar rats and spontaneously hypertensive rats (SHRs). Four-week-old rats were treated with prazosin (10 mg/kg b.w./day in tap water) or losartan (20 mg/kg b.w./day in tap water) for 5-6 weeks. BP was measured by plethysmographic method. Ten animals of each group were subjected to in vivo studies and subsequent to morphological investigations. The right jugular vein was cannulated for administration of acetylcholine (0.1, 1, and 10 µg). After perfusion with a glutaraldehyde fixative (120 mmHg), the carotid arteries were embedded in Durcupan ACM, and the inner diameter (ID), wall thickness (WT) (tunica intima and media), cross sectional area (CSA) (tunica intima and media), and WT/ID ratio were calculated. In Wistar rats and SHRs, prazosin and losartan administration produced a decrease in the blood pressure and trophicity of the heart. In Wistar rats, both drugs decreased the WT, CSA, and the WT/ID ratio. In addition, these drugs increased the circumferential stress of the artery without affecting the ID. In contrast, in the SHRs, only losartan administration produced these effects. Importantly, both the drugs improved the responses to acetylcholine in SHRs.

Age-dependent regulation of renal vasopressin V1A and V2 receptors in rats with genetic hypertension: implications for the treatment of hypertension

The role of arginine vasopressin (AVP) as a hypertensive hormone remains controversial. We have previously reported that intervention with a V1A receptor antagonist in 6-week-old prehypertensive spontaneously hypertensive rats (SHR) for 4 weeks attenuated the subsequent development of hypertension in adult SHR. This study assessed the age-dependent regulation of plasma AVP levels and kidney V1A and V2 receptor expression during the development of hypertension in SHR and in normotensive Sprague Dawley rats. Systolic blood pressure (SBP), plasma AVP, and plasma renin activity (PRA) and kidney V1A and V2 receptor expression were assessed. SHR were studied at three ages: prehypertensive (6 weeks), developed hypertension (10 weeks), and established hypertension (16 weeks). SBP increased with age in SHR (P < .01) and both plasma AVP (P < .01) and PRA (P < .05) were increased in 10-week-old SHR. Renal medulla V1A receptor gene expression decreased in 10-week and 16-week-old SHR (P < .01), with a reduction in V1A receptor protein in the inner medulla of 16-week-old SHR (P < .05) compared with young SHR. There was no change in V2 receptor expression during the development of hypertension. In normotensive rats, plasma AVP, PRA, and kidney V1A and V2 receptor expression were unchanged over time. These data suggest that in SHR, activation of plasma AVP and the renal V1A receptor occurs during developing hypertension, with downregulation when hypertension is established. The use of V1A receptor antagonists in prehypertension may provide a unique opportunity for the prevention of hypertension in high-risk individuals.

Upregulation of brain‐derived neurotrophic factor expression in nodose ganglia and the lower brainstem of hypertensive rats

Hypertension leads to structural and functional changes at baroreceptor synapses in the medial nucleus tractus solitarius (NTS), but the underlying molecular mechanisms remain unknown. Our previous studies show that brain-derived neurotrophic factor (BDNF) is abundantly expressed by rat nodose ganglion (NG) neurons, including baroreceptor afferents and their central terminals in the medial NTS. We hypothesized that hypertension leads to upregulation of BDNF expression in NG neurons. To test this hypothesis, we used two mechanistically distinct models of hypertension, the spontaneously hypertensive rat (SHR) and the deoxycorticosterone acetate (DOCA)-salt rat. Young adult SHRs, whose blood pressure was significantly elevated compared with age-matched Wistar-Kyoto (WKY) control rats, exhibited dramatic upregulation of BDNF mRNA and protein in the NG. BDNF transcripts from exon 4, known to be regulated by activity, and exon 9 (protein-coding region) showed the largest increases. Electrical stimulation of dispersed NG neurons with patterns that mimic baroreceptor activity during blood pressure elevations led to increases in BDNF mRNA that were also mediated through promoter 4. The increase in BDNF content of the NG in vivo was associated with a significant increase in the percentage of BDNF-immunoreactive NG neurons. Moreover, upregulation of BDNF in cell bodies of NG neurons was accompanied by a significant increase in BDNF in the NTS region, the primary central target of NG afferents. A dramatic increase in BDNF in the NG was also detected in DOCA-salt hypertensive rats. Together, our study identifies BDNF as a candidate molecular mediator of activity-dependent changes at baroafferent synapses during hypertension.

Targeted Neuronal Nitric Oxide Synthase Transgene Delivery Into Stellate Neurons Reverses Impaired Intracellular Calcium Transients in Prehypertensive Rats

Hypertension is associated with the early onset of cardiac sympathetic hyperresponsiveness and enhanced intracellular Ca(2+) concentration [Ca(2+)](i) in sympathetic neurons from both prehypertensive and hypertensive, spontaneously hypertensive rats (SHRs). Oxidative stress is a hallmark of hypertension, therefore, we tested the hypothesis that the inhibitory action of the nitric oxide-cGMP pathway on [Ca(2+)](i) transients is impaired in cardiac sympathetic neurons from the SHR. Stellate ganglia were isolated from young prehypertensive SHRs and age-matched normotensive Wistar-Kyoto rats. [Ca(2+)](i) was measured by ratiometric fluorescence imaging. Neurons from the prehypertensive SHR ganglia had a significantly higher depolarization evoked [Ca(2+)](i) transient that was also associated with decreased expression of neuronal nitric oxide synthase (nNOS), β1 subunit of soluble guanylate cyclase and cGMP when compared with the Wistar-Kyoto rat ganglia. Soluble guanylate cyclase inhibition or nNOS inhibition increased [Ca(2+)](i) in the Wistar-Kyoto rats but had no effect in SHR neurons. A nitric oxide donor decreased [Ca(2+)](i) in both sets of neurons, although this was markedly less in the SHR. A novel noradrenergic cell specific vector (Ad.PRSx8-nNOS/Cherry) or its control vector (Ad.PRSx8-Cherry) was expressed in sympathetic neurons. In the SHR, Ad.PRSx8-nNOS/Cherry-treated neurons had a significantly reduced peak [Ca(2+)](i) transient that was associated with increased tissue levels of nNOS protein and cGMP concentration compared with gene transfer of Ad.PRSx8-Cherry alone. nNOS inhibition significantly increased [Ca(2+)](i) after Ad.PRSx8-nNOS/Cherry expression. We conclude that artificial upregulation of stellate sympathetic nNOS via targeted gene transfer can directly attenuate intracellular Ca(2+) and may provide a novel method for decreasing enhanced cardiac sympathetic neurotransmission.

Dipeptidyl peptidase IV inhibition upregulates GLUT4 translocation and expression in heart and skeletal muscle of spontaneously hypertensive rats

The purpose of the current study was to test the hypothesis that the dipeptidyl peptidase IV (DPPIV) inhibitor sitagliptin, which exerts anti-hyperglycemic and anti-hypertensive effects, upregulates GLUT4 translocation, protein levels, and/or mRNA expression in heart and skeletal muscle of spontaneously hypertensive rats (SHRs). Ten days of treatment with sitagliptin (40mg/kg twice daily) decreased plasma DPPIV activity in both young (Y, 5-week-old) and adult (A, 20-week-old) SHRs to similar extents (∼85%). However, DPPIV inhibition only lowered blood pressure in Y-SHRs (119±3 vs. 136±4mmHg). GLUT4 translocation, total protein levels and mRNA expression were decreased in the heart, soleus and gastrocnemius muscle of SHRs compared to age-matched Wistar Kyoto (WKY) normotensive rats. These differences were much more pronounced between A-SHRs and A-WKY rats than between Y-SHRs and Y-WKY rats. In Y-SHRs, sitagliptin normalized GLUT4 expression in the heart, soleus and gastrocnemius. In A-SHRs, sitagliptin increased GLUT4 expression to levels that were even higher than those of A-WKY rats. Sitagliptin enhanced the circulating levels of the DPPIV substrate glucagon-like peptide-1 (GLP-1) in SHRs. In addition, stimulation of the GLP-1 receptor in cardiomyocytes isolated from SHRs increased the protein level of GLUT4 by 154±13%. Collectively, these results indicate that DPPIV inhibition upregulates GLUT4 in heart and skeletal muscle of SHRs. The underlying mechanism of sitagliptin-induced upregulation of GLUT4 in SHRs may be, at least partially, attributed to GLP-1.

Dual neural peptidase/endothelin-converting enzyme inhibition improves endothelial function in mesenteric resistance arteries of young spontaneously hypertensive rats

Endothelin-1 (ET1) is a potent vasoconstrictor peptide with pro-mitogenic and pro-inflammatory properties and is therefore of interest in the development of endothelial dysfunction, endothelium-dependent flow-related remodeling, and hypertension-related remodeling. ET1 can be formed through cleavage of big ET1 by endothelin-converting enzyme (ECE) and neutral endopeptidase (NEP). We investigated whether the dual NEP/ECE inhibitor SOL1 improves resistance artery function and structure in 12 weeks old spontaneously hypertensive rats (SHRs) and whether arterial structural responses to decreased (-90%) or increased (+100%) blood flow are impaired in young SHRs. To this end two groups of SHRs received chronic 4-week treatment at two different time points (4-8 and 8-12 weeks) prior to the experiment. We compared in-vitro effects of cyclo-oxygenase inhibition (1 μmol/l indomethacine), nitric oxide synthase inhibition (100 μmol/l N(ω)-L-nitro arginine methyl ester), and stimulation of the endothelium by 0.001-10 μmol/l acetylcholine (ACh) in isolated third-order mesenteric arteries of SHRs and aged-matched Wistar-Kyoto (WKY) rats. SOL1 had no effect on blood pressure in SHRs or WKY rats. ACh caused biphasic effects in mesenteric arteries of SHRs. The contractile component (endothelium-derived contractile factor) was absent in WKY and abolished by acute indomethacin administration or chronic SOL1 treatment. Endothelium-derived nitric oxide-type responses did not differ in both strains and were not influenced by SOL1 treatment. Endothelium-derived hyperpolarizing factor-type responses were severely impaired in SHRs as compared to WKY rats and were normalized by chronic SOL1 treatment. In first-order mesenteric arteries, outward flow-induced remodeling was impaired in SHRs. Chronic SOL1 treatment did not restore this response. Thus chronic SOL1 treatment during the development of hypertension in SHRs has no effect on blood pressure but improves several aspects of endothelium-dependent vasomotor responses but not arterial remodeling.

Abstract 354: Mitochondrial Hyper-function in Renal Proximal Tubule Cells from Young Spontaneously Hypertensive Rats

Recent evidence suggests that mitochondria play roles in the pathogenesis of hypertension. However, it is not clear whether mitochondrial dysfunction precedes or follows the development of hypertension. We hypothesize that mitochondrial bioenergetics is altered in renal proximal tubule (RPT) cells from spontaneously hypertensive rats (SHRs) and this alteration may occur prior to the development of sustained hypertension. Using immortalized RPT cells from 4-8 week old normotensive Wistar-Kyoto (WKY) and SHRs, we measured oxygen consumption rate (OCR) and compared the parameters of cellular bioenergetic in these RPT cells. Basal OCR was significantly higher in RPT cells from SHRs than WKY rats (245.5±31.9 vs. 154.4±43.7 pmol/min per 20,000 cells, mean±SD, P&lt;0.001);the ATP synthesis-coupled OCR (65.9±3.3% vs. 55.0±6.6%, of basal OCR, P&lt;0.001), maximum respiration (609.0±120.4 vs. 215.7±65.5 pmol/min per 20,000 cells, P&lt;0.001) and reserve respiration (147.8±39.0% vs, 40.0±15.4% of basal OCR P&lt;0.001) were also significantly higher in RPT cells from SHRs than WKY rats. In contrast, proton leak-linked OCR (15.4±3.6% vs. 19.2±5.9% of basal OCR, P&lt;0.05) was lower in RPT cells from SHRs than WKY rats, and non-mitochondrial OCRs were similar (45.2±7.0 vs. 41.3±19.8 pmol/min per 20,000 cells, P&gt;0.05). In support of these observations, adenosine triphosphate (ATP) levels were significantly higher in RPT cells from SHRs than WKY rats. Taken together, the observed bioenergetic alterations may contribute to the early mitochondrial dysfunction in RPT cells from SHRs prior to the onset of sustained hypertension.

Unprovoked atrial tachyarrhythmias in aging spontaneously hypertensive rats: the role of the autonomic nervous system

Experimental models of unprovoked atrial tachyarrhythmias (AT) in conscious, ambulatory animals are lacking. We hypothesized that the aging, spontaneously hypertensive rat (SHR) may provide such a model. Baseline ECG recordings were acquired with radiotelemetry in eight young (14-wk-old) and eight aging (55-wk-old) SHRs and in two groups of four age-matched Wistar-Kyoto (WKY) rats. Quantification of AT and heart rate variability (HRV) analysis were performed based on 24-h ECG recordings in unrestrained rats. All animals were submitted to an emotional stress protocol (air-jet). In SHRs, carbamylcholine injections were also performed. Spontaneous AT episodes were observed in all eight aging SHRs (median, 91.5; range, 4-444 episodes/24 h), but not in young SHRs or WKY rats. HRV analysis demonstrated significantly decreased low frequency components in aging SHRs compared with age-matched WKY rats (P < 0.01) and decreased low/high frequency ratios in both young (P < 0.01) and aging (P = 0.01) SHRs compared with normotensive controls. In aging SHRs, emotional stress significantly reduced the number of arrhythmic events, whereas carbamylcholine triggered AT and significantly increased atrial electrical instability. This study reports the occurrence of unprovoked episodes of atrial arrhythmia in hypertensive rats, and their increased incidence with aging. Our results suggest that autonomic imbalance with relative vagal hyperactivity may be responsible for the increased atrial arrhythmogenicity observed in this model. We also provide evidence that, in this model, the sympatho-vagal imbalance preceded the occurrence of arrhythmia. These results indicate that aging SHRs may provide valuable insight into the understanding of atrial arrhythmias.

Peripheral Chemoreceptors Contribute Significantly to Hypertension in Spontaneously Hypertensive Rats (SHR)

In carotid body glomus cells of young pre hypertensive SHR the overexpression of acid sensing ion channels increases their pH sensitivity and is associated with increased sympathetic nerve activity (Tan et al., Circ. Res. 2010). Here we tested the hypothesis that early resection of the carotid bodies might reduce hypertension in SHR. Under anesthesia both carotid bodies were resected (CBX) in young (&lt;5 weeks) SHR and in their normotensive control WKY. Arterial blood pressure (BP) recorded using a tail cuff twice a week over a 5 month period was lower in SHR with CBX than in sham‐operated SHR (p&lt;0.05 ANOVA). The 24 hour intra‐arterial BP recordings in awake rats at 23 weeks of age are below. Systolic BP (mmHg) Mean BP (mmHg) Sham CBX Sham CBX WKY 149±5 (n=5) 146±6 (n=6) 120±5 119±7 SHR 239±6* (n=10) 202±8*† (n=9) 185±3* 159±6*† p&lt;0.05 (SHR vs. WKY) p&lt;0.05 (CBX vs. Sham) Compared to WKY, the mean BP was 65±3 mmHg higher in SHR‐Sham and only 40±6 mmHg higher in SHR‐CBX. Under anesthesia ventilatory and renal nerve activity responses to chemoreceptor stimulation were measured. The left ventricular (LV) weight of SHR‐Sham (1.04±0.03 gm) was significantly greater (p&lt;0.002) than that of SHR‐CBX (0.92±0.01) and WKY (0.91±0.01).ConclusionThe contribution of the hypersensitive peripheral chemoreceptors to the increase in mean BP in SHR is estimated to be 38% and may account for most of the LV hypertrophy. (NIH/HL14388)

Effect of ageing in the mechanisms of endothelium dependent and independent vasorelaxation of [Ru(terpy)(bdq)NO+]3+ (TERPY) in spontaneously hypertensive rats (SHR)

Isolated aortic rings with and without endothelium of young (4 months) and old (16 months) SHR were incubated for 30 minutes with different pharmacological tools and the potency of relaxation of the NO donor TERPY was evaluated in concentration response curves made in phenylephrine (0,1 μM) contracted rings. Endothelium removal decreased the potency of TERPY in both groups, but this reduction was lower in old SHR. L‐NAME (NOS inhibitor; 0,1mM) incubated rings showed reduced the potency of TERPY in both groups. TIRON (superoxide anions scavenger; 0,1mM) decreased the potency of TERPY in aortic rings with endothelium of both groups. In denuded aortic rings, incubation with ODQ (guanilate cyclase inhibitor; 1μM) reduced the potency in both groups. TEA (potassium channels blocker; 1mM) and TIRON (0,1mM) didn't alter the potency of TERPY in denuded aortic rings of both groups. This results show that endothelium potentiates the effect of TERPY in aortic rings of young and old SHR, but this effect is decreased in old SHR. eNOS and superoxide anions are involved in this process. In denuded aortic rings, guanilate cyclase is involved in the relaxing response of TERPY, but potassium channels and superoxide anions are not. We conclude that ageing decreases the endothelium dependent potentiation of TERPY in SHR aorta.