Adult Spontaneously Hypertensive Rats Research Articles

Immunohistochemical evaluation of microvascular rarefaction in hypertensive humans and in spontaneously hypertensive rats

No data are presently available about changes in capillary density in the skeletal muscle and in the brain of spontaneously hypertensive rats (SHR) in relation to the development of hypertension. We have investigated 4 week-old and 12 week-old SHR and age-matched normotensive Wistar-Kyoto controls (WKY). Microvessel density (MVD) in the cerebral cortex and in a skeletal muscle were evaluated in sections stained for CD31. We also evaluated MVD in the dermal tissue of normotensive subjects and essential hypertensive patients. Subcutaneous small resistance arteries were dissected and mounted in a micromyograph and the media to lumen ratio (M/L) was measured. A significant reduction in MVD in the skeletal muscle and in the brain of SHR was clearly observed at 12 weeks of age, after the development of hypertension, but not at 4 weeks of age (pre-hypertensive condition). In hypertensive patients a significant reduction in the dermal MVD and an inverse correlation between M/L and MVD was observed. Our results suggest that, in the brain and skeletal muscle of adult SHR after the development of hypertension, and in the derma of adult essential hypertensive patients microvascular rarefaction may occur.

The Impact of α1-Adrenoceptors Up-Regulation Accompanied by the Impairment of β-Adrenergic Vasodilatation in Hypertension

In human and animal hypertension models, increased activity of G-protein-coupled receptor kinase (GRK) 2 determines a generalized decrease of beta-adrenergic vasodilatation. We analyzed the possibility of differential changes in the expression and functionality of alpha(1A), alpha(1B), alpha(1D), beta(1), beta(2), and beta(3)-ARs also being involved in the process. We combined the quantification of mRNA levels with immunoblotting and functional studies in aortas of young and adult spontaneously hypertensive rats (SHRs) and their controls (Wistar Kyoto). We found the expression and function of beta(1)-adrenoceptors in young prehypertensive SHRs to be higher, whereas a generalized increase in the expression of the six adrenoceptors and GRK2 was observed in aortas of adult hypertensive SHRs. alpha(1D)- and beta(3)-adrenoceptors, the subtypes that are more resistant to GRK2-mediated internalization and mostly expressed in rat aorta, exhibited an increased functional role in hypertensive animals, showing two hemodynamic consequences: 1) an increased sensitivity to the vasoconstrictor stimulus accompanied by a decreased sensitivity to the vasodilator stimulus (alpha(1D)-ARs are the most sensitive to agonists, and beta(3)-ARs are the least sensitive to agonists); and 2) a slower recovery of the basal tone after adrenergic stimulus removal because of the kinetic characteristic of the alpha(1D) subtype. These functional changes might be involved in the greater sympathetic vasoconstrictor tone observed in hypertension.

Chronic Blockade of Phosphatidylinositol 3-Kinase in the Nucleus Tractus Solitarii Is Prohypertensive in the Spontaneously Hypertensive Rat

Phosphatidylinositol 3-kinase (PI3K) within brain stem neurons has been implicated in hypertension in the spontaneously hypertensive rat (SHR). Previously, we demonstrated elevated expression of PI3K subunits in rostral ventrolateral medulla and paraventricular nucleus of SHRs compared with Wistar-Kyoto rats. Here, we considered expression levels of PI3K in the nucleus tractus solitarii, a pivotal region in reflex regulation of arterial pressure, and determined its functional role for arterial pressure homeostasis in SHRs and Wistar-Kyoto rats. We found elevated mRNA levels of p110beta and p110delta catalytic PI3K subunits in the nucleus tractus solitarii of adult (12 to 14 weeks old) SHRs relative to the age-matched Wistar-Kyoto rats (fold differences relative to beta-actin: 1.7+/-0.2 versus 1.01+/-0.08 for p110beta, n=6, P<0.05; 1.62+/-0.15 versus 1.02+/-0.1 for p110delta, n=6, P<0.05). After chronic blockade of PI3K signaling in the nucleus tractus solitarii by lentiviral-mediated expression of a mutant form of p85alpha, systolic pressure increased from 175+/-3 mm Hg to 191+/-6 mm Hg (P<0.01) in SHRs but not in Wistar-Kyoto rats. In addition, heart rate increased (from 331+/-6 to 342+/-6 bpm; P<0.05) and spontaneous baroreflex gain decreased (from 0.7+/-0.07 to 0.5+/-0.04 ms/mm Hg; P<0.001) in the SHRs. Thus, PI3K signaling in the nucleus tractus solitarii of SHR restrains arterial pressure in this animal model of neurogenic hypertension.

Chronic Hypoxia–Induced Angiogenesis Normalizes Blood Pressure in Spontaneously Hypertensive Rats

We hypothesized that activation of angiogenesis by chronic hypoxia may affect vascular resistance and, subsequently, blood pressure levels in spontaneously hypertensive rats (SHRs). Five-week-old prehypertensive SHRs and age-matched normotensive Wistar-Kyoto (WKY) rats (n=8 per group) were maintained under normobaric normoxic or hypoxic (10% O(2)) conditions for 8 weeks. Three weeks later, the systolic blood pressure was lower by 26% in hypoxic SHRs compared to normoxic SHRs (P<0.05) and remained at the normoxic WKY level. Total peripheral vascular resistance, calculated as the mean arterial pressure/cardiac output (assessed by ultrasound imaging and Doppler), was 30% lower in hypoxic than in normoxic SHRs (P<0.001) and returned to WKY levels. Interestingly, chronic hypoxia also significantly reduced systolic blood pressure in adult 12-week-old SHRs with established hypertension; blood pressure was normalized (versus normoxic WKY rats) after 4 weeks of hypoxia. Changes in hemodynamic parameters were associated with activation of proangiogenic pathways. Protein levels of vascular endothelial growth factor (VEGF)-A in the skeletal muscles were increased by 2.2-fold in hypoxic compared to normoxic SHRs (P<0.001). At the end of the hypoxic period, capillary density in the quadriceps muscle was 1.2-fold higher in hypoxic than in normoxic SHRs (P<0.001). Myocardial capillary density and VEGF-A protein contents were also 1.2- and 2.1-fold higher in hypoxic compared to normoxic SHRs (P<0.001 and P<0.05, respectively). Moreover, treatment with neutralizing VEGF-A antibody abrogated the hypoxia-induced angiogenesis and subsequently worsened arterial hypertension. Therefore, our results suggest that chronic normobaric hypoxia (1) activates VEGF-A-induced angiogenesis and thereafter (2) prevents the occurrence of hypertension in young prehypertensive SHRs and (3) normalizes blood pressure in adult SHRs with established hypertension.

Methylphenidate does not increase ethanol consumption in a rat model for attention-deficit hyperactivity disorder—the spontaneously hypertensive rat

Attention-deficit hyperactivity disorder (ADHD) is a behavioural disorder that has been suggested to result from disturbances in the dopaminergic system of the brain. The most effective drugs used to treat ADHD are the psychostimulants, methylphenidate and amphetamine. They block dopamine transporters and increase dopamine release, thereby increasing the extracellular concentration of dopamine and altering dopamine signaling. Drugs of abuse, such as cocaine, also block dopamine transporters, which raises the concern that treatment of children with ADHD with psychostimulants might increase their susceptibility to drug addiction. The present study was aimed at investigating whether treatment with methylphenidate at an early stage of development increased preference for ethanol in a widely used rat model for ADHD, the spontaneously hypertensive rat (SHR). SHR display the three major characteristics of ADHD (hyperactivity, impulsivity, poor sustained attention) compared to their progenitor Wistar-Kyoto (WKY) rat strain. Ethanol increased locomotor activity of SHR slightly more than WKY when injected intraperitoneally (0.6 g/kg). SHR also spent more time in the inner zone of the open field than WKY, consistent with SHR being less anxious than WKY. When given free access to ethanol-containing solutions of increasing concentration, SHR consumed less ethanol than WKY. Treatment with methylphenidate at an early age (P21 to P35) did not alter ethanol consumption in adult SHR or WKY, suggesting that it does not increase susceptibility to ethanol addiction in these rats. In vitro superfusion studies further demonstrated that preadolescent methylphenidate treatment did not have long-term effects on dopamine release in adult SHR and WKY striatum. A major finding of this study is the fact that methylphenidate treatment did not increase alcohol use in SHR.

Hypertension increases middle cerebral artery resting tone in spontaneously hypertensive rats: role of tonic vasoactive factor availability

The present study explores the contribution of alterations in resting tone to cerebral artery narrowing in SHRs (spontaneously hypertensive rats) and the role of hypertension development. Young pre-hypertensive and adult fully hypertensive SHRs and age-matched Wistar-Kyoto rat controls were used. The contribution of basal vasoactive factors to resting tone was studied in middle cerebral arteries with pressure myography. Basal NO and O(2)(-) (superoxide anion) availability were determined with fluorescent indicators using confocal microscopy and lucigenin-enhanced chemiluminescence. Basal O(2)(-) was also assessed in mesenteric resistance arteries. Middle cerebral arteries from adult rats, but not young pre-hypertensive rats, had augmented myogenic responses and resting tone and decreased relaxation to sodium nitroprusside compared with their normotensive counterparts. Cerebral arteries from adult SHRs also had an increase in tonic NO associated with a decrease in basal O(2)(-) availability. Basal O(2)(-) was instead increased in mesenteric arteries from SHRs. The present results indicate that large cerebral arteries from SHRs have an increase in their resting tone as a consequence of sustained hypertension and that this is related to a decrease in NO responsiveness. We suggest that this increase in resting tone and myogenic responses could act as a protective mechanism against the development of stroke in SHRs. The present study also demonstrates some unusual findings regarding the current understanding of the NO/O(2)(-) balance in hypertension with important differences between vascular beds and draws attention to the complexity of this balance in cardiovascular health and disease.

Effects of long-term losartan andl-arginine treatment on haemodynamics, glomerular filtration, and SOD activity in spontaneously hypertensive ratsThis article is one of a selection of papers published in the special issue Bridging the Gap: Where Progress in Cardiovascular and Neurophysiologic Research Meet.

Recently, it has been reported that losartan, an angiotensin II receptor (ATR) antagonist, depresses the angiotensin II-induced production of superoxide radicals. Also, in spontaneously hypertensive rats (SHR) endothelial dysfunction is associated with decreased nitric oxide (NO) synthesis. In this study, we examined the effects of long-term ATR blockade and L-arginine supplementation on the haemodynamic parameters, glomerular filtration, and oxidative status in SHR. Adult male SHR were treated with losartan (10 mg/kg) and with the NO donor L-arginine (2 g/kg) for 4 weeks. The animals were divided into the following experimental groups: control (n = 7), L-arginine (n = 7), losartan (n = 7), and L-arginine + losartan (n = 7). Mean arterial pressure (MAP), regional blood flow, urea clearance, and activity of superoxide dismutase (SOD) were measured at the end of treatment. MAP was significantly reduced in the losartan group compared with the control group (133.3 +/- 7.3 vs. 161.5 +/- 14.5 mm Hg). Aortic blood flow was significantly higher and aortic vascular resistance was significantly lower in all treated groups than in the control. Urea clearance rose significantly in the L-arginine + losartan group compared with control (393.27 +/- 37.58 vs. 218.68 +/- 42.03 microL x min(-1) x 100 g(-1)) as did the activity of SOD (1668.97 +/- 244.57 vs. 1083.18 +/- 169.96 U/g Hb). Our results suggest that the antihypertensive effect of losartan and L-arginine in SHR is not primarily mediated by increased SOD activity. Also, combined treatment with ATR blockade and L-arginine supplementation has a beneficial effect on renal function that is, at least in part, mediated by increased SOD activity in SHR.

Hemodynamic-independent anti-natriuretic effect of urotensin II in spontaneously hypertensive rats

The present study aims to test the hypothesis that U-II might have a direct anti-natriuretic action in spontaneously hypertensive rats (SHR). Bolus U-II injection (15 nmol kg(-1)) caused a transient decrease in glomerular filtration rate (GFR), urine flow rate (UV), urinary sodium (UNaV) and potassium excretion (U(K)V) that corresponded with a committed decrease in mean arterial pressure (MAP) and renal blood flow (RBF) during the first 30 min. Continuous U-II infusion (0.2 nmol kg(-1)h(-1)) following a bolus U-II injection (0.3 nmol kg(-1)) caused an anti-natriuretic effect without any significant change in MAP, RBF, GFR, UV and UKV during the entire 1.5-h perfusion period in SHR. The levels of aldosterone and angiotensin II were not altered in the plasma and kidney, while plasma antidiuretic hormone decreased in response to U-II injection (15 nmol kg(-1)). Protein levels of U-II receptors (UT) were significantly increased in the kidney of 17-week-old SHR when compared with the age-matched WKY rats, while mRNA transcripts of both U-II and UT were increased in the kidney, left ventricle and thoracic aorta. In conclusion, U-II exerts a hemodynamic-independent anti-natriuretic action in adult SHR. The anti-natriuretic action of U-II in SHR is probably associated with an increased expression of the U-II-UT system in the kidney, suggesting a potential renal role of U-II in the pathogenesis of hypertension.

Neurokinin‐1 receptor expressing neurons in the nucleus of the solitary tract are required for full expression of post‐exercise hypotension in spontaneously hypertensive rats

A single bout of exercise decreases blood pressure (post‐exercise hypotension; PEH) in both hypertensive humans and spontaneously hypertensive rats (SHR). Our recent studies suggest that in SHR, PEH may be dependent in part on activation of neurokinin‐1 receptors (NK1‐R) in the nucleus of the solitary tract (NTS). The current experiments were performed to test the hypothesis that selective elimination of NK1‐R expressing neurons in the NTS would attenuate PEH in SHR. The NK1‐R targeted neurotoxin, stable substance‐P saporin (SSP‐SAP) was microinjected into the NTS to ablate NK1‐R neurons in adult male SHR implanted with telemetry transmitters to measure blood pressure (BP) and heart rate. SSP‐SAP induced a transient (5 day) increase in BP after ablation relative to control (blank saporin; p&lt;0.01) rats. Blood pressure variability, assessed as the standard deviation of daily systolic BP, increased by the second week after NK1‐R neuron ablation (p&lt;0.05). Two weeks after NK1‐R neuron ablation, rats were subjected to a single bout of dynamic exercise or sham exercise. SSP‐SAP significantly blunted PEH (p&lt;0.005, 2‐way RM ANOVA). For example, by 120 min post‐exercise blood pressure was decreased by −15.2 ± 2 mmHg in control (n=4) versus 0.5 ± 2.7 mmHg in SSP‐SAP (n=6) treated rats. We conclude that ablation of NTS NK1‐R expressing neurons increases blood pressure variability and attenuates PEH in SHR. (Support: HL‐67183)

Gender is a factor that can impact the severity of doxorubicin (DXR) toxicity in spontaneously hypertensive rats (SHR)

Female pediatric patients appear to be more susceptible to doxorubicin cardiotoxicity than males. The present study sought to determine whether gender affects the severity of DXR‐induced cardiac and non cardiac tissue toxicity. Male and female SHR (14 weeks of age)(15/group) were administered 1 mg/kg DXR (iv) weekly for 9, 10 or 12 weeks. The study was terminated 1 week after the final dose. Four male SHR died after 9 or 10 DXR doses. Weight gain was retarded to a greater extent in DXR‐treated male than female SHR (5% of male control vs 46% of female control). Serum levels of urea nitrogen (BUN) were elevated only in male SHR (↑220–250%).Changes in serum concentration, over pretreatment levels, of cholesterol (↑630–960% vs 200–520% female), triglycerides (↑910–1790% vs 600% female) and albumin (↓75–77% vs 15–50% female) were significantly more profound in the DXR‐treated male SHR. DXR‐induced myocardial alterations were more severe in male (avg lesion score=2.3) compared to female SHR (avg lesion score=1.5)(p&lt;0.01). Serum levels of cardiac troponin T were significantly higher in male (avg 0.62 ng/ml) than female (avg 0.10 ng/ml)(p&lt;0.01). DXR caused more severe renal lesions in male (avg lesion score=3.9) than in female (avg lesion score=2.2) SHR (p&lt;0.01). The findings in adult male SHR imply that gender can play a significant role in the susceptibility of various tissues, such as the heart, to the toxic effects of DXR.

Central endocannabinoid modulation of baroreflex‐evoked sympathoinhibition in spontaneously hypertensive rats

GABAergic neurotransmission has been reported to be greater in the spontaneously hypertensive rat (SHR) as compared to normotensive Wistar Kyoto (WKY) and Sprague Dawley (SD) rats. Previously, we have shown that endocannabinoids prolong baroreflex inhibition of renal sympathetic nerve activity (RSNA) via modulation of GABAergic neurotransmission in the nucleus tractus solitarius (NTS). Thus we proposed that endocannabinoids could prolong baroreflex‐induced sympathoinhibition more in SHRs than in normotensive rats. This study characterized the physiological role of endogenously released endocannabinoids in the NTS on baroreflex control of RSNA evoked by pressor responses (phenylephrine bolus) or direct stimulation of the baroreflex (NTS microinjection of the excitatory amino acid agonist d,l‐homocysteic acid). Baroreflex responses were compared before and after a microinjection of an indirect cannabinoid 1 receptor agonist, AM404, into the barosensitive region of the NTS of adult male SD rats, WKY rats, and SHRs. AM404 microinjections into the NTS were found to significantly prolong baroreflex‐induced sympathoinhibition in SD and WKY rats, but had an insignificant effect in SHRs. This observation suggests that endocannabinoid modulation of GABAergic transmission in SHRs is reduced and could contribute to elevated sympathetic tone characteristic of this model. VA Medical Research Funds.

Endothelium‐dependent contractions in the carotid artery of young adult spontaneously hypertensive rats are mediated by cyclooxygenase and markedly augmented by nitric oxide inhibition

We have recently shown that ACh‐stimulated vasomotor activity in isolated PE‐precontracted common carotid artery (CCA) rings from young adult spontaneously hypertensive rats (SHR) involves a dose‐dependent relaxation phase from −9 to −7 LogM followed by a ‘re’‐contraction phase through to −4 LogM, whereas in normotensive Wistar Kyoto rats (WKY) only a robust relaxation phase existed. The objective of this study was to test the hypothesis that [ACh] &gt;−7 LogM stimulates contractions in quiescent CCA from SHR but not WKY. Reference KCl contractions in CCA were similar between strains and across all drug conditions (0.9−1.0g). [ACh] from −9 to −4 did not elicit vasomotor activity in WKY CCA, nor did [ACh] elicit vasomotor activity in SHR CCA from −9 to −7; however, [ACh] &gt;−7 stimulated a dose‐dependent contraction in SHR CCA reaching a plateau at −4 (0.16±0.03g). Endothelium denudation completely abolished these ACh‐stimulated contractions as did cyclooxygenase (COX) inhibition, whereas blocking endothelial nitric oxide (NO) synthase markedly increased the amplitude (0.61±0.08g) but not the threshold or sensitivity of the contractile response. These data demonstrate that only [ACh] &gt;−7 LogM can stimulate contractions in CCA from young adult SHR (but not WKY) that are endothelium‐dependent, COX‐mediated, and powerfully modulated by the availability of NO.Research Support: HSFO and NSERC

Single cell RT‐PCR indicates lower ASIC2a mRNA expression in aortic baroreceptor neurons of adult SHR vs WKY rats

We demonstrated that Acid‐Sensing Ion Channel 2 (ASIC2) contributes to mechanoelectrical transduction in baroreceptor neurons. Its expression in nodose sensory ganglia (NG) is decreased in association with development of hypertension in spontaneously hypertensive rats (SHR) (FASEB J, 21:A1407, 2007). Since NG neurons relay sensory signals from various visceral organs we sought to define more specifically the expression of ASIC2a in aortic baroreceptor nodose neurons (ABRNs) of SHR. We hypothesized that ASIC2a expression is reduced in ABRNs of SHR to account for the suppressed depolarizing potential responses to mechanical stimulation we observed earlier in SHR (FASEB J, 19:A607, 2005). ABRNs in NG were labeled with DiI injected into the aortic arch adventitia of SHR and WKY rats at 10 weeks of age. Two weeks later, both NG were removed and neurons were dissociated and cultured. Individual DiI labeled ABRNs and non‐labeled neurons were selected by fluorescence microscopy for quantitative single cell RT‐PCR. The results indicate first that DiI labeled ABRNs (n = 24) had a significant higher level of ASIC2 mRNA (2.99 ± 0.93) than non‐DiI neurons (1.00 ± 0.97) (p &lt; 0.05). Second, the ASIC2a mRNA level in DiI neurons relative to non‐DiI labeled neurons from the same ganglia was significantly lower in SHR (1.97 ± 0.59, n = 12) than in WKY (5.91 ± 0.61, n = 12) (p &lt; 0.05). The single cell RT‐PCR results were confirmed by RT‐PCR of pooled neurons (n = 10/grougp). We propose that the development of hypertension and impaired baroreceptor sensitivity in SHR are associated with significant reduction of ASIC2 expression (HL14388).

Neuroleptic Drugs Revert the Contextual Fear Conditioning Deficit Presented by Spontaneously Hypertensive Rats: A Potential Animal Model of Emotional Context Processing in Schizophrenia?

Schizophrenia, bipolar disorder, and attention deficit/hyperactivity disorder (ADHD) present abnormalities in emotion processing. A previous study showed that the spontaneously hypertensive rats (SHR), a putative animal model of ADHD, present reduced contextual fear conditioning (CFC). The aim of the present study was to characterize the deficit in CFC presented by SHR. Adult male normotensive Wistar rats and SHR were submitted to the CFC task. Sensitivity of the animals to the shock and the CFC performance after repeated exposure to the task were investigated. Pharmacological characterization consisted in the evaluation of the effects of the following drugs administered previously to the acquisition of the CFC: pentylenetetrazole (anxiogenic) and chlordiazepoxide (anxiolytic); methylphenidate and amphetamine (used for ADHD); lamotrigine, carbamazepine, and valproic acid (mood stabilizers); haloperidol, ziprasidone, risperidone, amisulpride, and clozapine (neuroleptic drugs); metoclopramide and SCH 23390 (dopamine antagonists without antipsychotic properties); and ketamine (a psychotomimmetic). The effects of paradoxical sleep deprivation (that worsens psychotic symptoms) and the performance in a latent inhibition protocol (an animal model of schizophrenia) were also verified. No differences in the sensitivity to the shock were observed. The repeated exposure to the CFC task did not modify the deficit in CFC presented by SHR. Considering pharmacological treatments, only the neuroleptic drugs reversed this deficit. This deficit was potentiated by proschizophrenia manipulations. Finally, a deficit in latent inhibition was also presented by SHR. These findings suggest that the deficit in CFC presented by SHR could be a useful animal model to study abnormalities in emotional context processing related to schizophrenia.

In situ delivery of bone marrow cells and mesenchymal stem cells improves cardiovascular function in hypertensive rats submitted to myocardial infarction

This work aimed to evaluate cardiac morphology/function and histological changes induced by bone marrow cells (BMCs) and cultured mesenchymal stem cells (MSCs) injected at the myocardium of spontaneously hypertensive rats (SHR) submitted to surgical coronary occlusion. Female syngeneic adult SHR, submitted (MI) or not (C) to coronary occlusion, were treated 24 h later with in situ injections of normal medium (NM), or with MSCs (MSC) or BMCs (BM) from male rats. The animals were evaluated after 1 and 30 days by echocardiography, histology of heart sections and PCR for the Y chromosome. Improved ejection fraction and reduced left ventricle infarcted area were observed in MSC rats as compared to the other experimental groups. Treated groups had significantly reduced lesion tissue score, increased capillary density and normal (not-atrophied) myocytes, as compared to NM and C groups. The survival rate was higher in C, NM and MSC groups as compared to MI and BM groups. In situ injection of both MSCs and BMCs resulted in improved cardiac morphology, in a more physiological model of myocardial infarction represented by surgical coronary occlusion of spontaneously hypertensive rats. Only treatment with MSCs, however, ameliorated left ventricle dysfunction, suggesting a positive role of these cells in heart remodeling in infarcted hypertensive subjects.

Late blood pressure reduction in shr subjected to transient captopril treatment in youth: possible mechanisms

Spontaneously hypertensive rats (SHR) are characterized by enhanced nifedipine-sensitive component of sympathetic vasoconstriction. Our study tried to elucidate the mechanisms responsible for long-term reduction of blood pressure (BP) in SHR subjected to early transient captopril treatment. Adult untreated SHR aged 30-34 weeks were compared with animals subjected to chronic captopril treatment for 6 weeks either in youth (between 4 and 10 weeks of age) or in adulthood (between 24 and 30 weeks of age). Antihypertensive effects of captopril were more pronounced in young than adult SHR. This was due to greater attenuation of sympathetic and nifedipine-sensitive BP components and prevention of residual BP rise in young captopril-treated SHR in which the reductions of nifedipine-sensitive BP component and residual BP persisted for 20 weeks after captopril withdrawal. The magnitude of nifedipine-sensitive component of sympathetic vasoconstriction is decisive for BP maintenance not only in untreated SHR but also in SHR during active captopril treatment by or after its withdrawal.

Hypertension in spontaneously hypertensive rats occurs despite low plasma levels of homocysteine

Hyperhomocysteinemia has been suggested to induce hypertension due to its role in endothelial dysfunction. However, it remains controversial whether homocysteine and hypertension are truly causally related or merely loosely associated. To test the hypothesis that hyperhomocysteinemia occurs in spontaneously hypertensive rats (SHR) we measured plasma levels of homocysteine in 10 male adult SHR and in 10 normotensive controls using ion exchange chromatography. In addition, plasma concentrations of the 22 most common amino acids were measured to explore the relation of homocysteine with amino acid metabolism. Plasma levels of homocysteine were significantly lower in SHR (4.1+/-0.1 micromol/l) than in controls (7.2+/-0.3 micromol/l) (p<0.00001). The amounts of aminobutyric acid, alanine, citrulline and valine were also decreased, whereas we found increased levels of aspartate, glutamate, glutamine, histidine and ornithine. Thus, contrary to our hypothesis, hypertension in SHR occurs despite low plasma levels of homocysteine. We provide a new hypothesis whereby reduced conversion of arginine to citrulline is related to increased ornithine levels, but decreased bioavailability of nitric oxide, resulting in impaired blood vessel relaxation and hypertension. In conclusion, our findings do not necessarily exclude that homocysteine and hypertension might be pathophysiologically connected, but corroborate the notion that hypertension can arise due to mechanisms independent of high homocysteine levels.

SYSTEMIC DELIVERY OF ADULT STEM CELLS IMPROVES CARDIAC FUNCTION IN SPONTANEOUSLY HYPERTENSIVE RATS

1. Heart regeneration after myocardial infarction (MI) can occur after cell therapy, but the mechanisms, cell types and delivery methods responsible for this improvement are still under investigation. In the present study, we evaluated the impact of systemic delivery of bone marrow cells (BMC) and cultivated mesenchymal stem cells (MSC) on cardiac morphology, function and mortality in spontaneously hypertensive rats (SHR) submitted to coronary occlusion. 2. Female syngeneic adult SHR, submitted or not (control group; C) to MI, were treated with intravenous injection of MSC (MI + MSC) or BMC (MI + BM) from male rats and evaluated after 1, 15 and 30 days by echocardiography. Systolic blood pressure (SBP), functional capacity, histology, mortality rate and polymerase chain reaction for the Y chromosome were also analysed. 3. Myocardial infarction induced a decrease in SBP and BMC, but not MSC, prevented this decrease. An improvement in functional capacity and ejection fraction (38 +/- 4, 39 +/- 3 and 58 +/- 2% for MI, MI + MSC and MI + BM, respectively; P < 0.05), as well as a reduction of the left ventricle infarcted area, were observed in rats from the MI + BM group compared with the other three groups. Treated animals had a significantly reduced lesion tissue score. The mortality rate in the C, MI + BM, MI + MSC and MI groups was 0, 0, 16.7 and 44.4%, respectively (P < 0.05 for the MI + MSC and MI groups compared with the C and MI + BM groups). 4. The results of the present study suggest that systemic administration of BMC can improve left ventricular function, functional capacity and, consequently, reduce mortality in an animal model of MI associated with hypertension. We speculate that the cells transiently home to the myocardium, releasing paracrine factors that recruit host cells to repair the lesion.

Abstract 181: Overexpression of Arachidonic Acid Cytochrome P450 Expoxygenases Prevents the Development of High Blood Pressure via Enhancing Atrial Natriuretic Peptide in Spontaneously Hypertensive Rats

Cytochrome P450 (CYP)-derived epoxyeicosatrienoic acids (EETs) have potent vasodilatory and diuretic feature, and therefore potentially hypotensive effect. No in vivo studies, however, were performed to support it. This study investigated the hypothesis via overexpressing CYP epoxygense genes in spontaneously hypertensive rats (SHR). Recombinant adeno-associated virus vector (rAAV) was utilized to mediate long-term transfection of CYP2J2 and CYP2C11 genes, respectively, in adult SHR, and animal systolic blood pressure (SBP) was monitored using arterial caudilis indirect manometric method. Results showed that at 2 months the urinary excretion of stable hydrolysis metabolic product of 14, 15-EE, 14–15-DHET increased by 11 and 8.7 folds in rAAV-2J2 and rAAV-2C11 groups, respectively, compared with AAV-GFP-treated rats. (2) SBP in 2J2- and 2C11-treated rats decreased from 175.0 ± 2.8mHg to 163.5 ± 5.8mmHg and 161.2 ± 6.1 mmHg, respectively, ( p &lt;0.01) at month 2, and it is 165.0 ± 4.7 mmHg and 173.0 ± 12.8 mmHg at month 6 after gene injection (~30mmHg and ~23mmHg lowerer than that in control animals, respectively, p &lt;0.001). (3) Before the rats were sacrificed, cardiac function tests with Pressure-Volume System showed that maximum intracardiac pressure was 202.1 ± 30.0 &amp; 209.1 ± 17.1mmHg in two gene-treated rats, respectively, significantly lower than control (241.2 ± 18.2mmHg, p &lt;0.01) and cardiac output in treatment rats were significantly higher than control (p&lt;0.05). (4) Interestingly, atrial natriuretic peptide (ANP) mRNA were up-regulated 6–14 folds respectively in myocardium of 2J2 and 2C11 groups; furthermore, C-type receptor mRNA of ANP was increased in heart, lung, kidney and aorta. (5) in cultured atrial cells (HLB2G5), exogenous EETs stimulated ANP production. In conclusions, for first time our data indicates overexpression of CYP2J2 or CYP2C11 could prevent development of hypertension in SHR, improve cardiac functions, which may involve up-regulating ANP expression and its receptors in target tissues, which suppresses collagen deposition and cardiovascular remodeling.

Age‐related loss of cardiac vagal preganglionic neurones in spontaneously hypertensive rats

Despite the findings that impaired vagal control of the heart rate occurs in human hypertension, leading to greater cardiovascular risk, the mechanism of this impairment is as yet unknown. Observations in humans and experiments in the spontaneously hypertensive rat (SHR) suggested that such impairment may be related to an anomaly in central vagal neurones. We therefore set out to determine whether the numbers and distribution of cardiac-projecting vagal preganglionic neurones in the medulla of adult (12 week) hypertensive SHR are different from those in young (4 week) prehypertensive SHR and in age-matched Wistar-Kyoto (WKY) rats of two age groups. The number of vagal neurones, identified by labelling with the fluorescent tracer DiI applied to the heart, was essentially similar in the three areas of the medulla analysed (dorsal vagal nucleus, nucleus ambiguus and intermediate reticular zone) in young SHR and young or adult WKY rats. In contrast, fewer vagal neurones were labelled in adult SHR compared with young SHR or WKY rats. This difference was due to highly significant reductions in vagal neurones in the dorsal vagal nucleus and nucleus ambiguus on the right side of the medulla. These observations suggest that a loss of parasympathetic preganglionic neurones supplying the heart with axons in the right vagus nerve, or a remodelling of their cardiac projections, may explain the known impairment of the baroreceptor reflex gain controlling heart rate in hypertension.