Arterial remodeling in chronic sinoaortic-denervated rats

Relationship of 24-h ambulatory blood pressure variability with micro and macrovascular parameters and hypertension status

OBJECTIVES

Increased blood pressure variability (BPV) has been associated with an increased risk of subclinical organ damage and cardiovascular events, independently of elevated average BP values. We aimed to investigate the association of BPV indices with micro- and macrovascular parameters, some of them not previously studied.

METHODS

We evaluated 344 individuals (233 never-treated/newly diagnosed hypertensive and 111 normotensive individuals). BPV was assessed using average real variability (ARV) during 24-h, daytime and night-time ambulatory blood pressure monitoring, and systolic weighted standard deviation (wSD). Retinal microvascular diameter was assessed by nonmydriatic retinal photography. Arterial stiffness was assessed by pulse wave velocity (PWV) and aortic augmentation index (AIx); subendocardial variability ratio (SEVR) was used as an index of myocardial perfusion. Carotid intima-media thickness (cIMT) was measured by ultrasound. Data were analyzed using multiple regression analysis.

RESULTS

After adjusting for potential confounders, PWV and cIMT were independently associated with ARV components in the total sample (P < 0.023 and P < 0.014, respectively). Within hypertensives only PWV and cIMT were independently associated with ARV components (P < 0.002 for PWV and P < 0.003 for cIMT). In contrast, within normotensives, only retinal parameters and AIx were associated with ARV components (P < 0.017 and P = 0.013, respectively). None of the univariate correlations between vascular parameters and wSD remained significant after adjustment for potential confounders.

CONCLUSION

Short-term BPV as assessed by ARV is independently associated with macrovascular parameters in untreated hypertensive patients, and with microvascular parameters in normotensive individuals.

Pharmacological characterization of MT-1207, a novel multitarget antihypertensive agent

Hypertension is a serious public health problem worldwide. MT-1207, chemically named 3-(4-(4-(1H-benzotriazole-1-yl)butyl)piperazine-1-yl) benzisothiazole hydrochloride, is a new chemical entity that has entered into clinical trial as antihypertensive agent in China. In this paper we report the pharmacological profile of MT-1207 regarding its acute, subacute, and long-term effects on hypertensive animal models, and its actions on isolated organs in vitro as well as its molecular targets. Blood pressure (BP) was measured in conscious animals; amlodipine was taken as a positive control drug. We showed that both single dose of MT-1207 (1.25-20 mg/kg, ig) in spontaneously hypertensive rats (SHR) and MT-1207 (0.25-6 mg/kg, ig) in two-kidney one-clip (2K1C) dogs dose-dependently decreased BP. MT-1207 quickly decreased BP within 5 min after administration; the hypotensive effect lasted for 8 and 12 h, respectively, in SHR and 2K1C dogs without reflex increase in heart rate. Multiple doses of MT-1207 (5 mg · kg-1 · d-1 in SHR; 2 mg · kg-1 · d-1 in 2K1C dogs, for 7 days) significantly decreased BP, slightly reduced heart rate, and both of them recovered after withdrawal. Long-term administration of MT-1207 (10 mg · kg-1 · d-1 for 4 months or more time) produced a stable BP reduction, improved baroreflex sensitivity, reduced renal and cardiovascular damage in SHR, and delayed stroke occurrence and death in stroke-prone SHR. In isolated rat aortic rings precontracted by adrenaline, KCl, noradrenaline or 5-hydroxytryptamine (5-HT), MT-1207 (10-9-10-4 M) caused concentration-dependent relaxation. In a panel of enzyme activity or radioligand binding assays of 87 molecular targets, MT-1207 potently inhibited adrenergic α1A, α1B, α1D, and 5-HT2A receptors with Ki < 1 nM. The antagonism of MT-1207 against these receptors was confirmed in isolated rabbit arteries. We conclude that MT-1207 is a novel and promising single-molecule multitarget agent for hypertension treatment to reduce hypertensive organ damage and stroke mortality.

Synergism of amlodipine and candesartan on blood pressure reduction and organ protection in hypertensive rats

This study was designed to investigate the possible synergism of amlodipine and candesartan on the reduction of blood pressure (BP) in hypertensive rats. The end organ protection was also observed. In acute experiment, spontaneously hypertensive rats (SHRs) were treated with intragastric administration of amlodipine (0.5, 1, 2, 3 mg/kg), candesartan (1, 2, 3, 4, 6, 8 mg/kg), and 14 different combinations to find the possible ratio of synergistic interaction. In two kidneys, one clip (2K1C) rats, the effects of amlodipine (1 mg/kg), canderastan (2 mg/kg) and their combination on BP reduction were also observed. In chronic study, SHRs were treated with amlodipine (1 mg/kg), candesartan (2 mg/kg), and their combination for 5 months. Organ damage evaluation was performed after BP recording. The probability sum test (q test) was used to evaluate the synergistic action. There is a synergistic interaction between amlodipine and candesartan on BP reduction. The optimal dose ratio is 1:2. The synergistic effect was also confirmed by 2K1C hypertensive rats. In chronic study, this combination (1:2) possessed an obvious synergism on the reduction of BP and BP variability (BPV) and protection on end organs. Multiple regression analysis showed that heart and aortic hypertrophy indexes and glomerular damage parameters were positively related to BP and BPV. In conclusion, combination of amlodipine and candesartan exhibited a potent antihypertensive effect and possessed an obvious synergism on BP reduction and organ protection in hypertension. The optimal proportion was 1:2. BP and BPV reduction may both importantly contribute to end organ protection.

Effects of losartan on vasomotor function and canonical transient receptor potential channels in the aortas of sinoaortic denervation rats

Increased short-term blood pressure variability (BPV) is strongly correlated with target organ damage. However, the molecular mechanisms underlying abnormal BPV-induced organ damage and effective therapeutic targets are poorly understood. The purpose of this study was to investigate the effects of losartan on vasomotor function and canonical transient receptor potential (TRPC) channels in the aortas of rats with arterial pressure lability induced by sinoaortic denervation (SAD). SAD was performed in male Sprague-Dawley rats at the age of 10 weeks. The experiment included sham-operated (Sham), SAD, and losartan-treated SAD (SAD+Los) groups. After 8 weeks of treatment, hemodynamic parameters were measured via catheterization, thoracic aortic vasomotor functions were evaluated using a physiological vascular ring tension recording system, and TRPC1 and 6 mRNA and protein expression levels in the endothelial cells (ECs) and smooth muscle cells (SMCs) of the thoracic aorta were determined via reverse transcription polymerase chain reaction (RT-PCR) and Western-blotting, respectively. Compared with Sham rats, SAD rats exhibited significantly increased BPV, enhanced norepinephrine-induced aortic contraction, and attenuated acetylcholine-induced aortic relaxation. Both the mRNA and the protein expression levels of TRPC1 and 6 were significantly downregulated in the ECs and upregulated in the SMCs of the thoracic aortas of SAD rats. Losartan treatment prevented these SAD-induced changes. In conclusion, losartan efficiently prevented vasomotor function impairment in SAD rats by reducing BPV and regulating TRPC1 and 6 expression levels.

Molecular Mechanisms Linking Autonomic Dysfunction and Impaired Cardiac Contractility in Critical Illness

OBJECTIVES

Molecular mechanisms linking autonomic dysfunction with poorer clinical outcomes in critical illness remain unclear. We hypothesized that baroreflex dysfunction alone is sufficient to cause cardiac impairment through neurohormonal activation of (nicotinamide adenine dinucleotide phosphate oxidase dependent) oxidative stress resulting in increased expression of G-protein-coupled receptor kinase 2, a key negative regulator of cardiac function.

DESIGN

Laboratory/clinical investigations.

SETTING

University laboratory/medical centers.

SUBJECTS

Adult rats; wild-type/nicotinamide adenine dinucleotide phosphate oxidase subunit-2-deficient mice; elective surgical patients.

INTERVENTIONS

Cardiac performance was assessed by transthoracic echocardiography following experimental baroreflex dysfunction (sino-aortic denervation) in rats and mice. Immunoblots assessed G-protein-coupled receptor recycling proteins expression in rodent cardiomyocytes and patient mononuclear leukocytes. In surgical patients, heart rate recovery after cardiopulmonary exercise testing, time/frequency measures of parasympathetic variables were related to the presence/absence of baroreflex dysfunction (defined by spontaneous baroreflex sensitivity of <6 ms mm Hg). The associations of baroreflex dysfunction with intraoperative cardiac function and outcomes were assessed.

MEASUREMENTS AND MAIN RESULTS

Experimental baroreflex dysfunction in rats and mice resulted in impaired cardiac contractility and upregulation of G-protein-coupled receptor kinase 2 expression. In mice, genetic deficiency of gp91 nicotinamide adenine dinucleotide phosphate oxidase subunit-2 prevented upregulation of G-protein-coupled receptor kinase 2 expression in conditions of baroreflex dysfunction and preserved cardiac function. Baroreflex dysfunction was present in 81 of 249 patients (32.5%) and was characterized by lower parasympathetic tone and increased G-protein-coupled receptor kinase 2 expression in mononuclear leukocytes. Baroreflex dysfunction in patients was also associated with impaired intraoperative cardiac contractility. Critical illness and mortality were more frequent in surgical patients with baroreflex dysfunction (relative risk, 1.66 [95% CI, 1.16-2.39]; p = 0.006).

CONCLUSIONS

Reduced baroreflex sensitivity is associated with nicotinamide adenine dinucleotide phosphate oxidase subunit-2-mediated upregulation of G-protein-coupled receptor kinase 2 expression in cardiomyocytes and impaired cardiac contractility. Autonomic dysfunction predisposes patients to the development of critical illness and increases mortality.

Angiotensin converting enzyme is involved in the cardiac hypertrophy induced by sinoaortic denervation in rats

INTRODUCTION

The present study was designed to test the hypothesis that local angiotensin converting enzyme (ACE) was involved in the cardiac hypertrophy induced by sinoaortic denervation (SAD) in rats.

METHODS

Experiment 1: Six weeks after SAD of rats, components of renin-angiotensin system (RAS) in left ventricles were assayed by quantitative real-time PCR and Western blotting analysis. Experiment 2: Rats were divided into five groups treated as follows: (1) sham-operated group; (2) SAD group; (3) SAD group treated with angiotensin II type 1 receptor (AT1R) antagonist losartan (10 mg·kg(-1)·day(-1), orally); (4) SAD group treated by ACE inhibitor ramipril (1 mg·kg(-1)·day(-1), orally); (5) SAD group treated by ramipril and the B2-kinin receptor selective antagonist HOE-140 (0.25 mg·kg(-1)·day(-1), subcutaneously).

RESULTS

SAD led to augmentation of the mRNA levels and protein expression of left ventricular ACE and AT1R. Both losartan and ramipril ameliorated SAD-induced left ventricular hypertrophy. Both losartan and ramipril abated oxidative stress, suppressed inflammation, and reduced expression TGFβ-R in left ventricles. In addition, the protective effect of ramipril could be abolished by HOE-140.

CONCLUSION

Local ACE is involved in the left ventricular hypertrophy induced by sinoaortic denervation in rats, via both angiotensin II/AT1R and bradykinin/B2R pathways.

Telemetric ambulatory arterial stiffness index, a predictor of cardio-cerebro-vascular mortality, is associated with aortic stiffness-determining factors

BACKGROUND

Ambulatory arterial stiffness index (AASI) has been proposed as a new measure of arterial stiffness for predicting cardio-cerebro-vascular morbidity and mortality. However, there has been no research on the direct relationships between AASI and arterial stiffness-determining factors.

METHODS

We utilized beat-to-beat intra-aortic blood pressure (BP) telemetry to characterize AASI in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). By determination of aortic structural components and analysis of their correlations with AASI, we provided the first direct evidence for the associations between AASI and arterial stiffness-determining factors including the collagen content and collagen/elastin.

RESULTS

Ambulatory arterial stiffness index was positively correlated with pulse pressure in both WKY and SHR, less dependent on BP and BP variability than pulse pressure, and relatively stable, especially the number of BP readings not less than ~36. The correlations between AASI and aortic components were comparable for various AASI values derived from BP readings not less than ~36. Not only AASI but also BP variability and pulse pressure demonstrated a direct relationship with arterial stiffness.

CONCLUSIONS

These findings indicate AASI may become a routine measure in human arterial stiffness assessment. It is recommended to use a cluster of parameters such as AASI, BP variability, and pulse pressure for evaluating arterial stiffness.

Visit-to-visit and 24-h blood pressure variability: association with endothelial and smooth muscle function in African Americans

The purpose of this study was to investigate the association of visit-to-visit and 24-h BP variability with markers of endothelial injury and vascular function. We recruited 72 African Americans who were non-diabetic, non-smoking, and free of cardiovascular and renal disease. Office BP was measured at three visits and 24-h ambulatory BP monitoring was conducted to measure visit-to-visit and 24-h BP variability, respectively. The 5-min time-course of brachial artery flow-mediated dilation and nitroglycerin-mediated dilation were assessed as measures of endothelial and smooth muscle function. Fasted blood samples were analyzed for circulating endothelial microparticles. Significantly lower CD31+CD42− endothelial microparticles were found in participants with high visit-to-visit SBP variability or high 24-h DBP variability. Participants with high visit-to-visit DBP variability had significantly lower flow-mediated dilation and higher nitroglycerin-mediated dilation at multiple time-points. When analyzed as continuous variables, 24-h mean arterial pressure variability was inversely associated with CD62+ endothelial microparticles; visit-to-visit DBP variability was inversely associated with flow-mediated dilation normalized by smooth muscle function and was positively associated with nitroglycerin-mediated dilation; and 24-h DBP variability was positively associated with nitroglycerin-mediated dilation. All associations were independent of age, gender, BMI, and mean BP. In conclusion, in this cohort of African Americans visit-to-visit and 24-h BP variability were associated with measures of endothelial injury, endothelial function, and smooth muscle function. These results suggest that BP variability may influence the pathogenesis of cardiovascular disease, in part, through influences on vascular health.

Synergism of irbesartan and amlodipine on hemodynamic amelioration and organ protection in spontaneously hypertensive rats

AIM

To investigate the synergism of low-doses of amlodipine and irbesartan on reduction of blood pressure variability (BPV), amelioration of baroreflex sensitivity (BRS) and organ protection in spontaneously hypertensive rats (SHR).

METHODS

The rats were administered amlodipine (1 mg·kg(-1)·d(-1)) alone, irbesartan (10 mg·kg(-1)·d(-1)) alone, or the combination of the two drugs for 4 months. The drugs were mixed into the rat chow. Blood pressure (BP) was continuously monitored in conscious animals. After the determination of BRS, the rats were killed for morphological evaluation of organ damages.

RESULTS

The combination of low-dose irbesartan and amlodipine had statistically significant synergism on reduction of BP and BPV, amelioration of BRS and organ protection in SHR. Multiple regression analysis showed that the decrease in left ventricular hypertrophy was associated with the decrease in systolic BPV (r=0.665, P<0.01); the decrease in aortic hypertrophy was associated with the increase in BRS (r=0.656, P<0.01); and the amelioration in renal lesion was associated with the increase in BRS (r=0.763, P<0.01) and the decrease in systolic BPV (r=0.706, P<0.01).

CONCLUSION

Long-term treatment with a combination of low-doses of amlodipine and irbesartan showed significant synergism on reduction of BP and BPV, restoration of BRS and organ protection in SHR. Besides BP reduction, the enhancement of BRS and reduction of BPV might contribute to the organ protection.

Relationship of visit-to-visit and ambulatory blood pressure variability to vascular function in African Americans

Visit-to-visit clinic blood pressure variability (BPV) and 24-h BPV have both been identified as independent risk factors for cardiovascular (CV) morbidity and mortality; however, the mechanisms contributing to the increased CV risk as yet are unclear. The purpose of this study was to assess the relationship between BPV and endothelial function in a cohort of putatively healthy African Americans. A total of 36 African Americans who were sedentary, non-diabetic, non-smoking, free of CV and renal disease and not on antihypertensive medication followed an American Heart Association low fat, low salt diet for 6 weeks. Upon completion of the 6-week dietary stabilization period, participants underwent 24-h ambulatory BP monitoring and had their office blood pressure (BP) measured on 3 separate days. Right brachial artery diameter was assessed at rest, during reactive hyperemia (flow-mediated vasodilation: FMD), and after nitroglycerin administration (nitroglycerin-mediated vasodilation: NMD). Participants classified as having decreased endothelial function according to either %FMD or the FMD/NMD ratio had significantly higher 24-h BPV and a trend for higher visit-to-visit BPV when compared with participants with normal endothelial function. Continuous variable analyses revealed a significant positive association between NMD and 24-h diastolic BPV (DBPV). Visit-to-visit systolic BPV (SBPV), 24-h SBPV and 24-h DBPV were all negatively associated with the FMD/NMD ratio. All relationships remained significant after adjustment for age, body mass index and mean BP levels. These results may suggest that BPV is increased in African Americans with decreased endothelial function and is associated with the vascular smooth muscle response to nitric oxide.

The coefficient variation of home blood pressure is a novel factor associated with macroalbuminuria in type 2 diabetes mellitus

The purpose of this study was to investigate the association between day-by-day variability in home blood pressure (HBP) on 14 consecutive days and macroalbuminuria in patients with type 2 diabetes. We compared the coefficient of variation (CV) of HBP in 858 Japanese patients with and without macroalbuminuria. Next, we analyzed the relationship between the logarithm of urinary albumin excretion (UAE) and the CV of HBP using linear regression analysis. Then, we evaluated the association between the CV of HBP and macroalbuminuria, defined as UAE ≥300 mg g(-1) creatinine, using logistic regression analysis. The CVs of morning and evening systolic blood pressure (SBP) were significantly greater in patients with macroalbuminuria than in those without (8.08±3.35 vs. 7.19±2.25%, P<0.05 and 9.01±3.58 vs. 7.98±2.57%, P<0.05, respectively). Multivariate linear regression analyses indicated that the CVs of morning SBP (P<0.05) and diastolic blood pressure (DBP; P<0.05), and those of evening SBP (P<0.05) were the independent explanatory variables for the logarithm of UAE. Multivariate logistic regression analyses also demonstrated that the odds ratio for the CVs of morning SBP, morning DBP and evening SBP for macroalbuminuria were 1.35 (P<0.05), 1.29 (P<0.05) and 1.44 (P<0.05), respectively. We conclude that the CV of HBP is correlated with macroalbuminuria, independent of the known risk factors, in Japanese patients with type 2 diabetes.

Variability--the drama of the circulation

The two most common vital signs, ie, pulse and blood pressure (BP), are obtained to seek guidance in clinical management of patients in virtually all primary care practices. Even a cursory glance at their values, whether it is within a person over time or between patients on a particular day, reflects an amazing degree of variability. In this brief editorial we provide a focused review of the assessment and the importance of variability in within-patient heart rate and BP and conclude with a few thoughts about the discordance in significance attached to these ubiquitous clinical measures.

Fosinopril prevents the pulmonary arterial remodeling in sinoaortic-denervated rats by regulating phosphodiesterase

AIM

To study the effects of fosinopril on sinoaortic denervation (SAD)-induced pulmonary vascular remodeling and on phosphodiesterases (PDE) 1 in rats.

METHODS

SAD was performed in male Sprague-Dawley rats at the age of 10 weeks. The experiment included sham-operated (Sham), SAD, and fosinopril-treated SAD groups. Fosinopril (15 mg/kg/d) was given in rat chow. After 16 weeks of treatment, the pulmonary arteries were taken for investigations, including pharmacological study, measurement of cGMP, light microscopy, immunohistochemistry, Western blotting, and quantitative real-time RT-PCR.

RESULTS

Compared with Sham rats, blood pressure variability (BPV) was significantly increased in the SAD group. However, the mean pulmonary artery pressure (mPAP) was not significant change among 3 groups. After SAD, maximal contraction of pulmonary artery rings to phenylephrine was markedly decreased; the most prominent morphological change in the lung included thickening vascular walls, increasing number of smooth muscle cells, and greater wall-to-lumen ratio; the tissue concentrations of cGMP was reduced significantly; PDE1A or PDE1C expression was upregulated significantly, and endothelial nitric oxide synthase (eNOS) expression was downregulated significantly. Fosinopril treatment prevented these changes induced by SAD.

CONCLUSION

Pulmonary artery remodeling (structural and functional abnormalities) was induced by SAD. Fosinopril, an angiotensin-converting enzyme inhibitor, mainly via potentiating eNOS pathway and inhibiting AngII formation, effectively prevented increased blood pressure variability and vascular remodeling of the pulmonary artery after SAD by regulating the activity levels or expression of eNOS, cGMP, and PDE1s.

Effects of K+ channel modulators on oscillatory contractions in sinoaortic denervated rat aortas

Sinoaortic denervated (SAD) rats present arterial pressure lability without sustained hypertension. We investigated the relation between sinoaortic denervation and the occurrence of oscillatory contractions in SAD rat aortas, as well as the effect of various K(+) channel modulators on these oscillations. Aortas were removed and concentration-effect curves to phenylephrine (0.01 to 10 muM) were constructed in arteries from SAD and Sham-operated rats in order to verify the occurrence of oscillations. We also evaluated the effects of various K(+) channel modulators on these oscillations. Only SAD rat aortas exhibited oscillatory contractions. Tetraethylammonium increased the frequency (28.5+/-3.5 to 41.5+/-4.5 counts/5 min) and amplitude (0.435+/-0.07 to 0.630+/-0.09 g) of the oscillations. Apamin and 4-aminopyridine did not alter the oscillations. Barium chloride converted the oscillatory contractions to a tonic contraction. Pinacidil rapidly blocked the oscillatory contractions and glibenclamide evoked reduction in amplitude from 0.410+/-0.07 to 0.180+/-0.06 g. Iberiotoxin increased the frequency of oscillatory contractions (from 28.0+/-3.5 to 51.5+/-7.5 counts/5 min) but decreased the amplitude (from 0.410+/-0.08 to 0.195+/-0.2 g). Our results demonstrate that SAD rat aortas exhibit oscillatory contractions and K(+) channels, mainly K(ATP) and BK(Ca), play a dominant role in these oscillations.

SPONTANEOUS OSCILLATORY CONTRACTIONS IN AORTAS OF RATS WITH ARTERIAL PRESSURE LABILITY CAUSED BY SINOAORTIC DENERVATION

1. The spontaneous variation of blood pressure is defined as arterial pressure lability. Sinoaortic denervation (SAD) is characterized by arterial pressure lability without sustained hypertension. 2. The phenomenon of spontaneous oscillatory contractions (SOCs) occurs more frequently in the vascular beds of hypertensive animals. In large arteries, such as the aorta, SOCs occur only occasionally or they can be initiated by application of chemical stimuli. 3. In the present study, we investigated whether the arterial pressure lability evoked by SAD could be related to the emergence of SOCs in the aorta of rats submitted to SAD compared with sham-operated rats (SO). Three days after surgery (SAD or SO), aortic rings were placed in an organ chamber and the incidence (percentage of rats presenting SOCs), frequency (number of SOCs in 10 min) and amplitude (mN) of SOCs were measured. The participation of external Ca(2+) and K(+) channels in the maintenance of SOCs was also verified. 4. The incidence and frequency of SOCs were higher in endothelium-denuded aortas from SAD rats (82% and 38 +/- 4 SOCs/10 min, respectively) than in aortas from SO rats (40% and 14 +/- 2 SOCs/10 min, respectively). In aortas from SAD rats, verapamil (0.2 micromol/L), pinacidil (0.3 micromol/L) and tetraethylammonium (TEA; 5 mmol/L) totally inhibited SOCs, whereas increasing the CaCl(2) concentration to 2.0 and 2.5 mmol/L increased the frequency of SOCs. Interestingly, increasing the concentration of CaCl(2) to 3.5 mmol/L inhibited these contractions in aortas from SAD rats. 5. These results show that although SAD rats did not become hypertensive, their aortas were capable of initiating SOCs without the application of any chemical stimuli. The SOCs seem to be dependent on Ca(2+) influx sensitive to verapamil and also involve K(+) channels sensitive to pinacidil and TEA.

Treatment of hypertension based on measurement of blood pressure variability: lessons from animal studies

PURPOSE OF REVIEW

Blood pressure variability, a quantitative index for the spontaneous variation in blood pressure, has been proposed as a risk factor for end-organ damage and to determine the efficacy of hypertension treatment.

RECENT FINDINGS

Animal studies indicate that blood pressure variability is as important as blood pressure level in determining end-organ damage, and that high blood pressure variability is associated with end-organ damage, including myocardial lesions, aortic hypertrophy, vascular remodeling and renal damage. Although the organ damage induced by high blood pressure variability was similar to that induced by hypertension, comparative studies in sinoaortic-denervated and spontaneously hypertensive rats revealed that aortic hypertrophy is a sensitive index of high blood pressure variability, and left ventricular hypertrophy is a sensitive index of high blood pressure level. The possible mechanisms for high blood pressure variability-induced end-organ damage include: direct endothelial lesions, renin-angiotensin system activation, inflammation initiation and cardiomyocyte apoptosis augmentation. Blood pressure variability reduction contributes importantly to the organ-protective effect of some antihypertensive drugs.

SUMMARY

Although animal studies suggest some advantages in blood pressure variability measurements, clinical trials are necessary before the widespread use of blood pressure variability as a predictor of hypertensive organ damage and a new strategy for the treatment of hypertension.

Blood pressure variability, baroreflex sensitivity and organ damage in spontaneously hypertensive rats treated with various antihypertensive drugs

Besides blood pressure, blood pressure variability and baroreflex sensitivity maybe important factors determining organ damage in hypertension. This study was designed to investigate the effects of various antihypertensive drugs on blood pressure and blood pressure variability reductions, baroreflex sensitivity, and target organ damage in spontaneously hypertensive rats (SHR). The dose is 20 mg/kg/day for atenolol, and 10 mg/kg/day for nifedipine, irbesartan and hydrochlorothiazide. We used relatively low doses of drugs to avoid a very remarkable normalization of blood pressure in the treatment, which would make it much difficult to distinguish the contribution of blood pressure variability and baroreflex sensitivity to organ protection from that of blood pressure. Drugs at the aforementioned doses were mixed into rat chow. SHR were treated for 4 months. Blood pressure was then continuously recorded for 24 h. After the determination of baroreflex sensitivity, rats were killed for organ-damage evaluation. It was found that long-term treatment with atenolol, nifedipine, irbesartan or hydrochlorothiazide all markedly reduced blood pressure variability, enhanced baroreflex sensitivity, and produced significant organ protection. Compared with blood pressure level, blood pressure variability and baroreflex sensitivity values showed a much closer or similar relationship with organ-damage parameters in every treatment group of rats. Multiple-regression analysis showed that the decrease in left ventricular hypertrophy, the decrease in aortic hypertrophy and the amelioration in renal lesion were all most closely correlated with the increase in baroreflex sensitivity and the decrease in systolic blood pressure variability. In conclusion, long-term treatment with atenolol, nifedipine, irbesartan or hydrochlorothiazide produced organ protection in SHR. Besides the blood pressure reduction, the decrease in blood pressure variability and the restoration of baroreflex sensitivity may contribute to this organ protection.

Blood pressure variability, cardiac baroreflex sensitivity and organ damage in experimentally hypertensive rats

1. The present study was designed to investigate the haemodynamic features and morphological changes in experimentally hypertensive rat models. 2. Sprague-Dawley rats were used to prepare the experimentally hypertensive models, including two-kidney, one-clip renovascular hypertensive (2K1C) rats, deoxycorticosterone acetate salt hypertensive (DOCA) rats and N(G)-nitro-l-arginine methyl ester-induced hypertensive (l-NAME) rats. Six weeks after the induction of hypertension, 24 h blood pressure was recorded and blood pressure variability (BPV) expressed by 24 h (or 12 h in the daytime and night-time study) standard deviation of the variables was calculated. Then, cardiac baroreflex sensitivity (BRS) was determined and four endogenous factors (tumour necrosis factor-alpha, interleukin-1beta, angiotensin II and endothelin-1) were measured. Finally, morphological changes were examined. 3. It was found that an increase in BPV and a decrease in BRS were accompanied by an elevation of blood pressure in all three hypertensive models. The DOCA rats had the highest BPV, whereas the l-NAME rats had the lowest BRS. 4. Morphological changes were similar in DOCA and l-NAME rats and the cardiac changes were relatively slight in 2K1C rats. Tumour necrosis factor-alpha was increased in all the three models, especially in DOCA rats. Endothelin-1 was higher in DOCA rats and angiotensin II was increased in 2K1C rats and decreased in DOCA rats. 5. In conclusion, increased BPV and decreased BRS accompanied the elevation of blood pressure in all three hypertensive models. The DOCA rats had the highest BPV and the l-NAME rats had the lowest BRS. Obvious organ damage was seen in all three hypertensive models 6 weeks after the induction of hypertension.

EARLY STRUCTURAL CHANGES OF AORTIC WALL IN SINOAORTIC-DENERVATED RATS

1. The present work was designed to observe the early structural changes in the aortic wall in Sprague-Dawley rats 1, 2 and 4 weeks after sinoaortic denervation (SAD). 2. Rats were examined 1, 2 and 4 weeks after SAD. Blood pressure (BP) was recorded in the conscious state. The thoracic aortas were taken for investigations, including: light microscopy, electron microscopy, immunohistochemistry and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labelling (TUNEL). 3. Blood pressure variability (BPV) was significantly increased in the SAD groups 1, 2 and 4 after the operation when compared with the sham-operated ones. 4. Two weeks after SAD the percentage proportion of smooth muscle cell density (SMC%) was obviously increased. 5. Four weeks after SAD: the SMC%, percentage proportion of collagen density (CD%) and aortic wall thickness (WT) were obviously increased with vascular smooth muscle cells blebbing concomitantly. Endothelial cells showed degenerative changes and swelling with blebbing of the cell membrane and increased condensation of peripheral nuclear chromatin and cytoplasmic vacuolization. It was also found that the number of apoptotic endothelial cells was increased and expression of eNOS was reduced. 6. This is the first study that shows the time-course of aortic wall and endothelial cell changes induced by SAD. Increased BPV might be the priming factor in the development of organ damage induced by SAD.

Essential role of Smad3 in angiotensin II-induced vascular fibrosis

Angiotensin II (Ang II) plays a pivotal role in vascular fibrosis, which leads to serious complications in hypertension and diabetes. However, the underlying signaling mechanisms are largely unclear. In hypertensive patients, we found that arteriosclerosis was associated with the activation of Smad2/3. This observation was further investigated in vitro by stimulating mouse primary aorta vascular smooth muscle cells (VSMCs) with Ang II. There were several novel findings. First, Ang II was able to activate an early Smad signaling pathway directly at 15 to 30 minutes. This was extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinase (MAPK) dependent but transforming growth factor-beta (TGF-beta) independent because Ang II-induced Smad signaling was blocked by addition of ERK1/2 inhibitor and by dominant-negative (DN) ERK1/2 but not by DN-TGF-beta receptor II (TbetaRII) or conditional deletion of TbetaRII. Second, Ang II was also able to activate the late Smad2/3 signaling pathway at 24 hours, which was TGF-beta dependent because it was blocked by the anti-TGF-beta antibody and DN-TbetaRII. Finally, activation of Smad3 but not Smad2 was a key and necessary mechanism of Ang II-induced vascular fibrosis because Ang II induced Smad3/4 promoter activities and collagen matrix expression was abolished in VSMCs null for Smad3 but not Smad2. Thus, we concluded that Ang II induces vascular fibrosis via both TGF-beta-dependent and ERK1/2 MAPK-dependent Smad signaling pathways. Activation of Smad3 but not Smad2 is a key mechanism by which Ang II mediates arteriosclerosis.

Effects of Long-Term Treatment with Candesartan on Hemodynamics and Organ Damage in Spontaneously Hypertensive Rats

This study was designed to investigate the effects of candesartan on blood pressure (BP) and blood pressure variability (BPV) reductions, baroreflex sensitivity (BRS) amelioration, and organ protection in spontaneously hypertensive rats (SHR).

METHODS

Studies were performed in two groups of SHR (n = 13 for control rats; and n = 20 for candesartan-treated rats) and one group of WKY rats (n = 13). Candesartan (3 mg /kg/d) was given in rat chow for 4 months. BP was then continuously recorded for 24 hours in conscious state. After the determination of BRS, rats were killed for organ-damage evaluation.

RESULTS

Long-term treatment with candesartan significantly reduced BP and BPV expressed by both standard deviation and variation coefficient of BP, enhanced BRS and produced obvious organ protection. Compared with BP level, BPV and BRS values showed a closer or similar relationship with organ-damage parameters in SHR. Multiple regression analysis showed that the decrease in left ventricular hypertrophy was most closely associated with the increase in BRS, whereas the decrease in aortic hypertrophy was most closely associated with the decrease in 24-hour systolic BPV, and the amelioration in renal lesions, with the increase in BRS and the decrease in 24-hour systolic BPV.

CONCLUSION

long-term treatment with candesartan results in organ protection in SHR. Besides BP reduction, the decrease in BPV and the restoration of BRS are significantly related to this organ protection.

Isolated home hypertension in the morning is associated with target organ damage in patients with type 2 diabetes

To investigate the relationship between the blood pressure control level and cardiovascular risk in type 2 diabetic patients, we evaluated home blood pressure, office blood pressure, biochemical data, and carotid echographic and echocardiographic findings in 148 patients with type 2 diabetes. According to the criteria for hypertension in the guidelines of the Japanese Society of Hypertension, we classified patients into a normotensive group with home systolic blood pressure in the morning (morning HSBP)<135 mmHg and office systolic blood pressure (OSBP)<140 mmHg, an office hypertension group with a morning HSBP<135 mmHg and OSBP>or=140 mmHg, an isolated home hypertension in the morning group with morning HSBP>or=135 mmHg and OSBP<140 mmHg, and a sustained hypertension group with morning HSBP>or=135 mmHg and OSBP>or=140 mmHg. In the isolated home hypertension in the morning group, the fasting insulin level, urinary albumin excretion, maximum carotid artery intima-media complex thickness, and left ventricular posterior wall thickness were significantly higher and the coefficient of variation for RR intervals was significantly lower than in the normotensive group. These results suggest that isolated home hypertension in the morning is a risk factor for target organ damage in type 2 diabetic patients.

Post-Vagotomy Mechanical Characteristics and Structure of the Thoracic Aortic Wall

This study assessed the long-term effect of vagotomy on the structure and passive mechanical characteristics of the thoracic aorta under a wide range of stresses in vitro. Eight healthy Landrace pigs underwent bilateral vagotomy distal to the origin of the recurrent laryngeal nerve, and 10 pigs were sham-operated. Three months post-surgery, the aorta was excised and specimens from the ascending aorta, arch, and descending thoracic aorta were subjected to histomorphometrical evaluation and uniaxial tensile-testing until failure. Elastic modulus-stress data were plotted and submitted to regression analysis. Structural remodeling after vagotomy was characterized as vascular growth in the ascending aorta and arch, and as thinning in the descending thoracic aorta. In the aortic segments of vagotomized animals, the area density of elastin and collagen was increased, but smooth muscle density was decreased. Similar differences in regression parameters and failure strength between groups were found in all aortic segments, indicating that the vessel wall was stiffer and stronger in vagotomized animals. In the clinical setting, disease states or drugs blocking the regulatory role of the vagi nerves on the aortic wall may have undesirable consequences on the mechanical performance of the thoracic aorta, and therefore on hemodynamic homeostasis.

Blood pressure, baroreflex sensitivity, and end organ damage in hybrid offspring of spontaneously hypertensive rats and Sprague-Dawley rats

AIM

To investigate the blood pressure (BP), baroreflex sensitivity (BRS), and organ damage in hybrids of spontaneously hypertensive rats and Sprague-Dawley rats.

METHODS

Spontaneously hypertensive rats and Sprague-Dawley rats were crossbred, and the F1 hybrids were inbred randomly to produce an F2 generation. At the age of 52 weeks, the F1 and F2 hybrids were tested to determine BP and BRS in a conscious state. Histopathological examinations were carried out after BP recording and BRS studies.

RESULTS

BP and BRS were not different in F1 and F2 hybrids. BRS was inversely related to systolic BP (SBP) in male, female, or whole populations of hybrids. Quantitatively, BRS values were one-third determined by SBP level (the determinant coefficient was 0.326). The indexes for left ventricular hypertrophy, aortic hypertrophy, and renal damage were all positively related to BP, and negatively related to BRS. In multiple-regression analysis, left ventricular and aortic hypertrophy and glomerulosclerosis score were all most significantly associated with lower BRS and higher systolic BP. The contribution of BRS to left ventricular and aortic hypertrophy and glomerulosclerosis was greater than that of SBP.

CONCLUSION

The present work with hybrid rats demonstrated quantitatively that the BRS value was one-third determined by SBP level. Both BP level and BRS value contributed greatly to the hypertensive organ damage. However, the contribution of BRS to the hypertensive organ damage was greater than that of BP level in these rats.

Reduction of blood pressure variability: a new strategy for the treatment of hypertension

The main aims of the treatment of hypertension are to prevent end-organ damage (EOD) and to avoid consequent lethal complications associated with hypertension. Blood pressure level is a well-known determinant of EOD. However, recent studies suggest that blood pressure variability (BPV) is as important as blood pressure level in determining EOD. The reduction of BPV is an important contributory factor of the organ protection provided by some antihypertensive drugs. Thus, reduction of BPV might represent a new strategy for the treatment of hypertension.

Synergism of atenolol and nitrendipine on hemodynamic amelioration and organ protection in hypertensive rats

OBJECTIVE

This study was designed to investigate the possible synergism of atenolol and nitrendipine on blood pressure (BP) and blood pressure variability (BPV) reductions, baroreflex sensitivity (BRS) amelioration, and organ protection in hypertensive rats.

METHOD

The dose was 20 mg/kg for atenolol, 10 mg/kg for nitrendipine and 20 + 10 mg/kg for the combination of these two drugs. In an acute study, a single dose was given via a catheter previously inserted into the stomach in spontaneously hypertensive rats (SHR). In a subacute study, SHR, deoxycorticosterone acetate (DOCA)-salt rats, and two-kidney, one-clip (2K1C) rats were used. They received the same dose by gavage daily for 10 days. BP was measured 24 h after drug administration. In chronic studies, these drugs at the aforementioned dose were mixed into rat chow. SHR were treated for 4 months. BP was then continuously recorded for 24 h. After the determination of BRS, rats were killed for organ-damage evaluation.

RESULTS

In the acute study, it was found that the combination of atenolol and nitrendipine had an obviously greater and longer BP reduction than treatment with each of these two drugs separately. In the subacute study, an effective decrease in BP 24 h after administration was found only in the rats treated with the combination. In chronic studies, it was found that the combination possessed the obvious synergism on BP and BPV reduction, BRS amelioration and organ protection in SHR. Multiple-regression analysis showed that the decrease in left ventricular hypertrophy was most significantly related to the decrease in systolic BPV and BP, the decrease in aortic hypertrophy was most significantly related to the increase in BRS and the decrease in systolic BPV, and amelioration in the renal lesion was most significantly associated with the restoration of BRS.

CONCLUSION

Treatment with a combination of atenolol and nitrendipine exhibited a rapid and persistent antihypertensive effect and possessed an obvious synergism on BP and BPV reduction, BRS restoration and organ protection in hypertensive rats. The decrease in BPV and the restoration of BRS may importantly contribute to organ protection in SHR with chronic treatment.

Effects of low-dose ketanserin on blood pressure variability, baroreflex sensitivity and end-organ damage in spontaneously hypertensive rats

The present study was designed to investigate the effects of low-dose ketanserin on BPV (blood pressure variability), BRS (baroreflex sensitivity) and organ damage in SHR (spontaneously hypertensive rats). Ketanserin was mixed in rat chow at an estimated dose of 0.1 mg·kg−1 of body weight·day−1. SHR were treated for 4 months. BP (blood pressure) was then recorded continuously for 24 h in a conscious state. After determination of BRS, rats were killed for organ damage evaluation. It was found that long-term treatment with low-dose ketanserin did not lower BP levels, but significantly decreased BPV, enhanced BRS and reduced organ damage in SHR. Multiple regression analysis showed that the decrease in left ventricular hypertrophy was most closely correlated (or associated) with the increase in BRS, whereas the decrease in aortic hypertrophy was most closely associated with the decrease in diastolic BPV and the amelioration in renal lesion, with the increase in BRS and the decrease in diastolic BPV. In conclusion, low-dose ketanserin produces organ protection independently of its BP-lowering action in SHR, and this organ protection was importantly attributable to the enhancement of BRS and decrease in BPV.

Mechanisms of blood pressure variability-induced cardiac hypertrophy and dysfunction in mice with impaired baroreflex

Enhanced blood pressure variability contributes to left ventricular hypertrophy and end-organ damage, even in the absence of hypertension. We hypothesized that the greater number of high-blood pressure episodes associated with enhanced blood pressure variability causes cardiac hypertrophy and dysfunction by activation of mechanosensitive and autocrine pathways. Normotensive mice were subjected to sinoaortic baroreceptor denervation (SAD) or sham surgery. Twelve weeks later, blood pressure variability was doubled in SAD compared with sham-operated mice. Blood pressure did not differ. Cardiac hypertrophy was reflected in greater heart/body weight ratios, larger myocyte cross-sectional areas, and greater left ventricular collagen deposition. Furthermore, left ventricular atrial and brain natriuretic peptide mRNA expression was greater in SAD than in sham-operated mice. SAD had higher left ventricular end-diastolic pressures and lower myocardial contractility indexes, indicating cardiac dysfunction. Cardiac protein content of phosphorylated p125 focal adhesion kinase (p125 FAK) and phosphorylated p38 mitogen-activated protein kinase (p38 MAPK) was greater in SAD than in sham-operated mice, indicating activation of mechanosensitive pathways of cardiac hypertrophy. Furthermore, enhanced cardiac renin and transforming growth factor-β1 (TGFbeta1) protein content indicates activation of autocrine pathways of cardiac hypertrophy. Adrenal tyrosine hydroxylase protein content and the number of renin-positive glomeruli were not different, suggesting that sympathetic activation and the systemic renin-angiotensin system did not contribute to cardiac hypertrophy. In conclusion, more frequent blood pressure rises in subjects with high blood pressure variability activate mechanosensitive and autocrine pathways leading to cardiac hypertrophy and dysfunction even in the absence of hypertension.

Inflammation is involved in the organ damage induced by sinoaortic denervation in rats

OBJECTIVE

The present study was designed to test the hypothesis that inflammation is involved in the end-organ damage (EOD) induced by sinoaortic denervation (SAD) in rats.

METHOD

SAD was performed in male Sprague-Dawley rats at the age of 10 weeks. Under anaesthesia, aortic nerves were cut and the sinus region of the carotid artery was stripped and painted with 10% phenol. Pathological evaluation of EOD and the determination of plasma or tissue levels of the factors related to inflammation, including thromboxane B2 (TXB2) interleukin-1 (IL-1), tumour necrosis factor alpha (TNF-alpha) and reactive oxygen species (ROS) were performed at 16 weeks after SAD. Pathological evaluation of EOD included heart weight ratio, myocardial and blood vessel hydroxyproline and collagen volume fraction, glomerular injury score and number of infiltrating inflammatory cells. Indomethacin (20 mg/kg per day, orally) or vitamin E (100 mg/kg per day, orally) was administered for 12 weeks, beginning from 4 weeks after SAD, to observe their effects on SAD-induced EOD.

RESULTS

There were significant fibrosis and inflammatory infiltration in the myocardium and blood vessels, represented by higher hydroxyproline and collagen volume fraction, and a large amount of inflammatory cells in the tissues of SAD rats. Heart weight and kidney glomerular injury score were significantly higher in SAD than in sham-operated rats. Plasma TXB2, TNF-alpha, IL-1 and tissue ROS increased significantly after SAD. Indomethacin and vitamin E significantly decreased the contents of some factors related to inflammation in SAD rats. Both drugs also alleviated myocardial and vessel fibrosis, inflammatory infiltration and kidney damage.

CONCLUSION

Inflammation is involved in the organ damage induced by SAD in rats.

Contribution of blood pressure variability to the effect of nitrendipine on end-organ damage in spontaneously hypertensive rats

OBJECTIVE

It has been proposed that blood pressure variability (BPV) is positively related to end-organ damage (EOD) in hypertension. The present work was designed to observe the effects of long-term treatment with nitrendipine and hydralazine on BPV and EOD in spontaneously hypertensive rats (SHR), to examine the hypothesis that lowering BPV with an antihypertensive drug is an important factor in organ protection.

DESIGN AND METHODS

Drugs were mixed in rat chow. After 4 months of drug administration, blood pressure was recorded continuously in conscious freely moving rats for 24 h. The heart, kidneys, and brain were then isolated and examined.

RESULTS

It was found that nitrendipine significantly decreased blood pressure and BPV, and significantly decreased EOD score in SHR. Hydralazine decreased blood pressure, but did not lower BPV. No effect on EOD was found in hydralazine-treated rats. In control rats (n = 38), EOD score was weakly related to systolic blood pressure (r = 0.331, P < 0.05) and closely related to long-term systolic BPV (r = 0.551, P < 0.01). In nitrendipine-treated rats, EOD score was closely related to long-term systolic BPV (r = 0.602, P < 0.01), but not to BP level (r = 0.174, P > 0.05).

CONCLUSION

BPV plays an important role in the organ-protecting effects of nitrendipine.

Restoration of baroreflex function by ketanserin is not blood pressure dependent in conscious freely moving rats

OBJECTIVE

Since the end of the 1980s, the pathological importance of baroreflex function has attracted the attention of many investigators. In our previous studies, it was found that ketanserin lowered blood pressure (BP), decreased BP variability and enhanced baroreflex sensitivity (BRS). The present work was designed to test the hypothesis that the restoration of BRS by ketanserin is not dependent on BP level in conscious rats.

DESIGN AND METHODS

Spontaneously hypertensive rats (SHR) aged 8-12 months were used. Blood pressure was recorded for 60 min and BRS was determined separately before and after intragastric administration of ketanserin, with four doses. In a second experiment, 10-week-old Sprague-Dawley rats were used for preparing a myocardial infarction (MI) model by ligating the coronary artery. MI rats were treated with ketanserin for 5 weeks, with two doses. At the end of the treatment, BP and BRS of the MI rats were studied in conscious state. In addition, the effects of ketanserin on BRS in Sprague-Dawley rats with normal BRS and the effects of prazosin and ritanserin on BRS in SHR were also observed.

RESULTS

It was found that ketanserin significantly decreased BP and improved BRS in the conscious SHR. The decrease in BP was dose-dependent but the improvement of BRS was not. At the smallest dose (0.3 mg/kg), ketanserin did not lower BP but enhanced BRS. In MI rats, the treatment with ketanserin did not significantly decrease BP, but it improved BRS at both doses administered (0.6 and 10 mg/kg). Ketanserin [3 and 10 mg/kg, intragastric (i.g.)] did not affect BRS in SD rats with normal BRS. Prazosin and ritanserin did not enhance BRS in SHR when administered intravenously. Ritanserin markedly and prazosin slightly enhanced BRS in SHR following intracerebroventricular administration.

CONCLUSION

The restoration of baroreflex function by ketanserin is not BP dependent and this effect is mediated by central 5-HT2A receptor.

Inhibition of Inflammation Contributes to Organ Protection of Atenolol in Sinoaortic-Denervated Rats

The present study was designed to test the hypothesis that inhibition of inflammation contributes to the protective effects of atenolol on the organ damage induced by sinoaortic denervation (SAD) in rats. SAD was performed in male Sprague-Dawley rats at the age of 10 weeks. Atenolol (20 mg/kg/d, po) was administered for 12 weeks beginning from 4 weeks after SAD. Organ damage evaluation and the determination of plasma TXB2, serum IL-1, TNF-alpha and tissue reactive oxygen species (ROS) were performed at 16 weeks after SAD. It was found that there existed obvious organ damage including increased cardiac and aortic collagen, and glomerular injury, in SAD rats. Plasma TXB2, serum TNF-alpha IL-1, and tissue ROS increased significantly after SAD. Long-term treatment with atenolol significantly prevented the organ damage with a decrease in left ventricular weight, cardiac and aortic collagen contents, and glomerular injury score in SAD rats. Plasma TXB2, serum IL-1, and tissue ROS were found to be significantly decreased by the long-term treatment with atenolol. Furthermore, it was found that the levels of inflammation-related factors were significantly related to all the organ-damage parameters studied in this experiment. These results suggest that inhibition of inflammation and oxygen stress contributes to the organ-protective effects of atenolol in SAD rats.

INCREASED SUSCEPTIBILITY OF VENTRICULAR ARRHYTHMIAS TO ACONITINE IN ANAESTHETIZED RATS IS ATTRIBUTED TO THE INHIBITION OF BAROREFLEX

1. Aconitine is widely used to produce ventricular arrhythmias in anaesthetized rats. The present work was designed to test the hypothesis that anaesthesia may increase the susceptibility of ventricular arrhythmia to aconitine due to the inhibition of arterial baroreflex. In addition, the susceptibility of ventricular arrhythmia to aconitine at different times during the course of a whole day was also investigated. 2. Male Sprague-Dawley rats were used. Arrhthymias were induced by aconitine infusion at six time points (01.00, 05.00, 09.00, 13.00, 17.00 and 21.00 h) with rats in both anaesthetized and conscious states. In sinoaortic-denervated (SAD) rats, ventricular arrhythmias were induced by aconitine infusion between 09.00 and 13.00 h. 3. There was a significant difference in the lethal dose of aconitine between anaesthetized and conscious rats (99.6 +/- 30.1 vs 58.2 +/- 14.7 micro g/kg; P < 0.001). Anaesthesia did increase the susceptibility of rats to ventricular arrhythmias following aconitine. 4. In SAD rats, the lethal dose of aconitine was less than that for baroreflex-intact rats when determined in the conscious state. The difference in the lethal dose of aconitine between SAD and baroreflex-intact rats disappeared when it was determined in anaesthetized rats. 5. The time of day did not affect the susceptibility of either anaesthetized or conscious rats to ventricular arrhythmias following aconitine, except for a difference in the ventricullar fibrillation threshold dose between 13.00 and 17.00 h in anaesthetized rats. 6. In conclusion, anaesthesia may increase the risk of ventricular arrhythmias following aconitine. Intact arterial baroreflex function is necessary to prevent drug-induced ventricular arrhythmias.

High-level apoptosis is persistent in myocardiocytes of sinoaortic-denervated rats

BACKGROUND

Arterial baroreflex plays an important part in the regulation of cardiovascular activity. Sinoaortic denervation (SAD) produces organ damage in rats. A previous study suggested that apoptosis in myocardium is involved in the organ damage induced by SAD.

OBJECTIVE

To study the time course of cardiomyocyte apoptosis in SAD rats by evaluating apoptotic cells and expression of apoptosis-related genes in the left ventricles of SAD rats, 4, 8, 16 and 32 weeks after SAD operation.

METHODS

Male Sprague-Dawley rats underwent SAD or sham operation at the age of 10 weeks. Four, 8, 16 or 32 weeks after operation, blood samples and heart tissues were taken for the following studies: determination of angiotensin II in plasma and heart, pathological evaluations, terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labelling and immunohistochemistry. Some observations were also made in rats 1 and 2 weeks after denervation.

RESULTS

Loss of body weight gain, cardiac hypertrophy, an increase in left ventricular collagen volume and an increase in cardiac angiotensin II content were observed in SAD rats from 2 to 32 weeks after SAD operation. The apoptotic myocardiocytes were increased in SAD rats compared with sham-operated rats. The expression of Bcl-2 protein, an inhibiting factor of apoptosis, was markedly decreased in the myocardiocytes of SAD rats. In contrast, the expression of Bax, Fas and Fas-L proteins, promoting factors of apoptosis, was significantly increased in the myocardiocytes of SAD rats. All these modifications were persistent from 4 to 32 weeks after SAD operation.

CONCLUSION

These findings demonstrate that a high level of apoptosis is persistent in myocardiocytes in SAD rats. We propose that apoptosis may be one of the mechanisms underlying the cardiac damage induced by SAD.

Asynchronism of the Recovery of Baroreflex Sensitivity, Blood Pressure, and Consciousness from Anesthesia in Rats

Anesthesia inhibits arterial baroreflex functions such as baroreflex sensitivity (BRS). The main objective of the present study was to determine the time course of BRS recovery from anesthesia and to determine whether BRS recovery is synchronous with the recovery of consciousness and blood pressure (BP). Experiments were performed in male Sprague-Dawley rats using different commonly used anesthetics at routine doses through intraperitoneal administration: (1) diazepam/ketamine, a mixture of diazepam (5 mg/kg) and ketamine (50 mg/kg); (2) chloral hydrate (0.3 g/kg); (3) sodium pentobarbital (30 mg/kg); and (4) urethane (1.0 g/kg). The anesthetic state, evaluated by algesthesia and cornea reflex, was maintained for 1-2.5 hours. The BRS, assessed by intravenous injection of phenylephrine, was inhibited rapidly and dramatically, with maximum depressions of 51%-80%. The BRS recovery time was approximately 5 hours for diazepam/ketamine, chloral hydrate, and pentobarbital, but more than 24 hours for urethane. Compared with BRS inhibition, BP reduction was less pronounced by 8% (not significant) for diazepam/ketamine and by 12%-30% for the others. The BP recovery time was approximately 2 hours, with the exception of chloral hydrate (>6 hours). In conclusion, after anesthesia, BRS inhibition is more obvious than BP reduction, and the recovery of BRS lags behind the recovery of consciousness or BP.

Morphological evidence of reinnervation of the baroreceptive regions in sinoaortic-denervated rats

1. The arterial baroreflex (ABR) plays an important role in the maintenance of the stability of blood pressure. Sinoaortic denervation (SAD) destroys the integrity of the reflex arc and produces severe organ damage in rats. However, partial recovery of ABR function has been observed following chronic denervation. The aim of the present study was to determine whether there was morphological evidence of reinnervation of the aortic arch and carotid sinus following SAD. 2. A substantial body of physiological and morphological evidence suggests that substance P (SP) may be a neurotransmitter contained in first-order sensory baroreceptor afferents; therefore, the patterns of vascular SP and neurofilament (NF) immunoreactive (IR) innervation of the aortic arch and carotid sinus were investigated in the present study. 3. Ten-week-old male Sprague-Dawley rats underwent SAD or sham operation. Whole mounts of carotid bifurcation and aortic arch were prepared for immunohistochemical study at various time points (1, 9 and 16 weeks after operation). 4. The results of computerized image analysis show that the mean density of NF- and SP-IR nerves of SAD rats 9 and 16 weeks after operation increased gradually and significantly compared with that of rats 1 week after operation. 5. In conclusion, the results indicate that there is reinnervation of the aortic arch and carotid sinus by NF- and SP-IR fibres in SAD rats, which may be the morphological basis for the partial restoration of ABR function over time after SAD.

Apoptosis is involved in the cardiac damage induced by sinoaortic denervation in rats

1. The arterial baroreflex plays an important role in the maintenance of the stability of blood pressure. Sinoaortic denervation (SAD) produces severe organ damage in rats. The present study was designed to investigate whether apoptosis, which is a ubiquitous physiological mode of cell death distinct from cell mortality induced by injury and necrosis, is involved in SAD-induced cardiac damage. 2. Male Sprague-Dawley rats (10 weeks old) were used. Rats underwent SAD (n = 9) or sham operation (n = 10). Sixteen weeks after operation, the heart tissues were taken for investigations including electron microscopy, immunohistochemistry, terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labelling (TUNEL) and reverse transcription-polymerase chain reaction (RT-PCR). 3. Cardiac hypertrophy and fibrosis was found in SAD rats. The number apoptotic cardiomyocytes was increased in SAD rats compared with sham-operated rats. 4. The expression of Bcl-2mRNA and protein (an inhibitory factor of apoptosis) in cardiomyocytes was decreased in SAD rats. In contrast, the expression of Bax, Fas and Fas ligand mRNA and proteins (promoters of apoptosis) in cardiomyocytes was significantly increased in SAD rats. 5. In conclusion, the present study reveals a high level of apoptosis in cardiomyocytes in SAD rats. It is proposed that apoptosis is involved in SAD-induced cardiac damage.

Ketanserin stabilizes blood pressure in conscious spontaneously hypertensive rats

1. It has been demonstrated that blood pressure variability (BPV) is increased in hypertension and related to organ damage. It will be important to lower BPV in the treatment of hypertension. The present study was designed to investigate the effect of ketanserin, a 5-HT2A receptor antagonist with a weak alpha1-adrenoceptor blocking effect, on BPV in conscious spontaneously hypertensive rats (SHR). 2. It was found that ketanserin decreased blood pressure (BP) and BPV in SHR when administered intravenously (3 mg/kg, i.v.). Ketanserin decreased BPV, but not the BP level, when administered intracerebroventricularly (50 microg/rat, i.c.v.). 3. Prazosin, an alpha1-adrenoceptor antagonist, lowered BP but did not affect BPV when given either i.v. (0.5 mg/kg) or i.c.v. (30 microg/rat). Ritanserin (0.625 mg/kg, i.v.; 40 microg/rat, i.c.v.), a 5-HT2A receptor antagonist, decreased BPV only when administered i.c.v. and did not modify the BP level. 4. Ketanserin enhanced arterial baroreflex function in SHR when given either i.v. or i.c.v. 5. The stabilizing effect of ketanserin on BP was persistent when administered intragastrically. This administration route is similar to oral administration clinically. 6. It is concluded that ketanserin is an antihypertensive agent with an effect of reducing BPV. This effect is mainly mediated by central 5-HT2A receptors and is probably attributable to the restoration of arterial baroreflex function.

Effects of long-term treatment with candesartan on organ damages in sinoaortic denervated rats

The study was designed to observe the effects of long-term treatment with candesartan cilexetil (candesartan) on blood pressure (BP), blood pressure variability (BPV), baroreflex sensitivity (BRS) and end-organ damage (EOD) in sinoaortic denervated (SAD) rats. Candesartan was mixed in rat chow at an estimated dose of 3 mg/kg/day. After 12 weeks of drug administration, rats were instrumented to determine BP, BPV and BRS in conscious state. Organ damage was estimated by observation of morphologic changes. When compared with sham-operated rats, SAD rats exhibited increased BPV, decreased BRS, and normal BP and plasma angiotensin II level. Left ventricular and aortic hypertrophies and renal lesion were found in SAD rats. Candesartan significantly decreased BP and BPV, ameliorated impaired BRS, increased plasma angiotensin II level and obviously diminished the EOD in SAD rats. Multiple-regression analysis shows that decrease in left ventricular hypertrophy was mainly related to decrease in systolic BPV. Decrease in aortic hypertrophy was mainly determined by increase in BRS and decrease in systolic BP. Amelioration in renal lesion was predicted by increase in BRS and decrease in systolic BPV. BRS was the most important determinant for renal lesion and aortic hypertrophy in SAD rats. In addition, plasma angiotensin II level was higher in candesartan-treated rats. In conclusion, long-term treatment with candesartan prevented SAD-induced organ damage. Restoration of arterial baroreflex function, decrease in BPV, and blockade of activated renin-angiotensin system may contribute to the organ protective action of candesartan in SAD rats.

Effects of long-term treatment with ketanserin on blood pressure variability and end-organ damage in spontaneously hypertensive rats

It has been proposed that instability of blood pressure may produce organ damage. Ketanserin is an anti-hypertensive drug with an ability to reduce blood pressure variability (BPV) in acute experiments in spontaneously hypertensive rats (SHRs). The present work was designed to observe the effects of long-term treatment with ketanserin on BPV and end-organ damage in SHRs. Ketanserin was mixed in rat chow at an estimated dose of 10 mg/kg/d. After 5 months of drug administration, BP was continuously recorded in conscious, freely moving rats for 24 h. The heart, kidneys, and abdominal aorta were then isolated and examined by using histologic methods and computer image analysis. In another work, the effects of hydralazine (40 mg/kg/d, for 5 months) on BP, BPV, and organ damage were observed in SHRs. Ketanserin significantly decreased BP and BPV, ameliorated impaired arterial baroreflex function, and significantly prevented the target organs of SHRs from being damaged. This preventive effect was characterized by decrease in left ventricular hypertrophy, diminution of glomerulus damage, and amelioration in vascular lesion. Hydralazine decreased BP but did not lower BPV. No organ protection was found in hydralazine-treated rats. In conclusion, long-term treatment with ketanserin reduced hypertensive organ damage. Lowering BP, decreasing BPV, and ameliorating arterial baroreflex function may contribute together to this effect.

Restoration of arterial baroreflex function contributes to organ protection in spontaneously hypertensive rats treated with long-term hydrochlorothiazide mixture

1. Hydrochlorothiazide mixture (HCTM) is widely used in China for the treatment of hypertension. This mixture consists of hydrochlorothiazide, triamterene, reserpine, hydralazine and chlordiazpoxide, with small (one-third to one-fifth of normal) doses of each drug. The present study was designed to investigate the effects of this mixture on blood pressure, blood pressure variability (BPV), baroreflex sensitivity (BRS) and end-organ damage in spontaneously hypertensive rats (SHR). 2. The HCTM was mixed in the rat chow and rats were treated for 4 months. After treatment, rats were catheterized and their blood pressure, BPV and BRS were measured in the conscious state. Organ damage was examined after these measurements had been completed. 3. It was found that HCTM not only decreased blood pressure and BPV, but also ameliorated impaired BRS in SHR. The HCTM had an obvious effect on organ protection in SHR. 4. The HCTM prevented left ventricular hypertrophy and this effect was mainly related to a decrease in systolic blood pressure. The effects of HCTM on preventing renal atrophy were mainly determined by BRS. Baroreflex sensitivity was the most important determinant for predicting organ damage in HCTM-treated SHR. 5. In conclusion, long-term treatment of rats with HCTM prevented hypertensive organ damage. Restoration of arterial baroreflex function contributes to organ protection in SHR treated in the long term with HCTM.

Reduced Endothelial Vasomotor Function and Enhanced Neointimal Formation after Vascular Injury in a Rat Model of Blood Pressure Lability

Increased short-term blood pressure variability is known to be associated with hypertensive target organ damage. Sinoaortic denervation (SAD) induces a marked increase in blood pressure lability without affecting the average blood pressure level. The aim of this study was to investigate the effects of blood pressure lability on endothelial vasomotor function and neointimal formation after balloon injury in SAD rats. Direct longterm measurement of mean arterial pressure showed no significant difference in the average of mean arterial pressure between the SAD group and sham-operated control group. In contrast, the standard deviation of mean arterial pressure, as an index of blood pressure lability, was 3-fold greater in SAD rats. To study endothelial function, isometric tension of aortic rings was measured 4 weeks after SAD or sham operation. Endothelium-dependent vasorelaxation induced by acetylcholine was significantly reduced in the SAD group (20% reduction at maximum relaxation). Endothelium-independent vasorelaxation induced by sodium nitroprusside was similar in each group. Acetylcholine-induced NO release from aortic rings was significantly reduced in the SAD group. Next, we examined neointimal formation in carotid arteries in SAD and sham-operated rats at 2 weeks after balloon injury. The neointimal-to-medial area ratio in the SAD group was 50% higher than that in the sham-operated group. The percentage of proliferating cell nuclear antigen-positive cells in the intima was significantly higher in the SAD group. These findings suggest that increased blood pressure lability, independently of average blood pressure level, impairs endothelial function by inhibiting NO production, enhances neointimal formation after balloon injury, and may thereby contribute to atherogenesis.