Amlodipine suppresses Ang-II-induced endothelium dysfunction by diminishing ROCK1 expression.

OBJECTIVE: To investigate the effects and mechanisms of amlodipine therapy on endothelium dysfunction induced by angiotensin-II (Ang-II) stimulation. METHODS: Human umbilical vein endothelial cells (HUVECs) were used and divided into five groups: Blank control, Ang-II (10(-6 )mol/L), levorotatory amlodipine (5 × 10(-6 )mol/L) + Ang-II (10(-6 )mol/L), dextrorotatory amlodipine (5 × 10(-6 )mol/L) + Ang-II (10(-6 )mol/L) and racemic amlodipine (5 × 10(-6 )mol/L) + Ang-II (10(-6 )mol/L) groups. Twenty-four hours later, HUVECs were collected for evaluating endothelial nitric oxide synthase (eNOS), p-eNOS, rho-associated kinase 1 (ROCK1), Bcl-2 and Bax expressions. Nitric oxide (NO) concentration within endothelium was also detected. Flow cytometry was conducted to assess HUVECs apoptosis. RESULTS: With 24 hours of Ang-II stimulation, compared to blank control group, expressions of eNOS and p-eNOS and NO production were significantly reduced in Ang-II group (p < 0.05), while adding amlodipine-protected HUVECs from dysfunction induced by Ang-II. In contrast, ROCK1 expression was promoted in Ang-II group (p < 0.05). However, the expression of ROCK1 in each enantiomer of amlodipine group was significantly decreased (p < 0.05). Compared to levorotatory amlodipine group, the magnitude of ROCK1 diminishment in dextrorotatory amlodipine group was more profound (p < 0.05). The pro-survival protein (Bcl-2) was significantly upregulated, while the pro-apoptotic protein (Bax) was significantly downregulated in three amlodipine groups compared to Ang-II group. Flow cytometry revealed that amlodipine therapy could protect HUVECs from apoptosis, and no significant difference between three amlodipine groups was observed. CONCLUSION: Amlodipine could suppress Ang-II-induced endothelial dysfunction and apoptosis through diminishing ROCK1 expression.

Atorvastatin protects endothelium by decreasing asymmetric dimethylarginine in dyslipidemia rats.

BACKGROUND: Asymmetric Dimethylarginine (ADMA) is an inhibitor of endogenous nitric oxide synthase, which is the key synthase for nitric oxide (NO) production. Whether statins could protect endothelium by reducing ADMA concentration is unclear, and whether this effect is associated with the dose of statins usage is also needed further studied. METHODS: Dyslipidemia rat model was produced by giving high-fat and high-cholesterol diet for 8 weeks. Thereafter, low-dose (5 mg/kg body weight/day) and high-dose (20 mg/kg body weight/day) atorvastatin were orally prescribed for 4 weeks. Parameters of interest including lipid profiles, inflammatory and oxidative markers, NO production and plasma levels of ADMA and ADMA concentration of myocardium were evaluated. Liver enzymes and creatinine kinase (CK) were also detected for safety concern. RESULTS: At baseline, all parameters were comparable between the sham and the dyslipidemia groups. At 8 weeks of dyslipidemia establishment, as compared to the sham group, body weight and lipid profiles were significantly elevated, and plasma levels of C-reactive protein (CRP), malondialdehyde (MDA) and ADMA were concomitantly increased in accompanying with NO reduction in the dyslipidemia groups. With 4 weeks of atorvastatin therapy, as compared to the control group, lipid disorders and NO production were improved, and plasma levels of CRP, MDA and ADMA were significantly decreased in the high-dose atorvastatin group. ADMA concentration of cardiac tissues was also significantly reduced in the high-dose atorvastatin group. Notably, there was a trend to similar effects which did not reach statistical significance in the low-dose atorvastatin group when compared to the control group. Liver enzyme and CK were comparable after 4 weeks of atorvastatin therapy between groups. CONCLUSION: In rats with dyslipidemia, atorvastatin therapy could reduce plasma level of ADMA and ADMA concentration in cardiac tissues, and these effects are associated with the dose of atorvastatin therapy.

Baseline elevated Lp-PLA2 is associated with increased risk for re-stenosis after stent placement.

BACKGROUND: Lipoprotein associated phospholipase A2 (Lp-PLA2) is a novel biomarker for cardiovascular risk prediction. Whether increased Lp-PLA2 level is associated with re-stenosis after stent-placement is unclear. METHODS: Totally 326 participants eligible for stent-placement were enrolled and divided into two groups according to baseline Lp-PLA2 levels (named normal and elevated groups). Baseline characteristics and clinical outcomes were compared between normal and elevated groups. The relationships between Lp-PLA2 and other risk factors with re-stenosis were evaluated. RESULTS: Only the between-group difference of Lp-PLA2 was significant (123.2 ± 33.6 ng/mL vs 336.8 ± 85.4 ng/mL, P < 0.001) while other demographic and clinical characteristics between these two groups were comparable. Approximately 55.1% and 58.5% of participants in normal and elevated groups presented with acute coronary syndrome, and the percentage of tri-vessels stenoses was significantly higher in elevated group (40.8% vs 32.1%, P = 0.016). Nearly 96.0% and 94.0% of participants in normal and elevated Lp-PLA2 groups were placed with drug-eluting stents, and the others were with bare-metal stents. After 1 year's follow-up, the incidence of clinical end-points was comparable (13.3% vs 15.4%, P = 0.172). Nevertheless, the incidence of re-stenosis was marginally higher in elevated Lp-PLA2 group (8.5% versus 4.6%, P = 0.047). With multivariate analysis, after adjustment for other risk factors, Lp-PLA2 remained an independent predictor for re-stenosis with a hazard ratio of 1.140. No synergistic effect between Lp-PLA2 and other risk factors for re-stenosis was found. CONCLUSION: Increased Lp-PLA2 level is associated with an increased risk of re-stenosis. Lp-PLA2 assessment may be useful in predicting subjects who are at increased risk for re-stenosis.

Bone marrow stromal cell transplantation combined with angiotensin-converting enzyme inhibitor treatment in rat with acute myocardial infarction and the role of insulin-like growth factor-1.

BACKGROUND AIMS: We investigated bone marrow stromal cell (BMSC) transplantation combined with angiotensin-converting enzyme inhibitor (ACEI) treatment in acute myocardial infarction (AMI) and the role of insulin-like growth factor-1 (IGF-1). METHODS: AMI models were established in Sprague-Dawley rats by ligation of the left anterior descending coronary artery and grouped into blank control (BC), ACEI treatment (ACEI), BMSC transplantation (BMSC) and BMSC transplantation plus ACEI (combined). Perindopril (2.5 mg/kg) was administered by gavage to ACEI and combined groups from the day after AMI. BMSC (2 × 10(8)) were injected into the border of the MI area a week later in the BMSC and combined groups. RESULTS: After 4 weeks, hemodynamics in the BMSC and combined groups were significantly improved (P < 0.05 versus BC), with the greatest improvement in the combined group (P < 0.05). In addition, an increased number of BMSC survived in the combined group (P < 0.05 versus BMSC). A proportion of BMSC was positive for troponin T, as detected by immunofluorescence. The number of apoptotic cardiomyocytes was decreased in the BMSC and ACEI groups, and even further in the combined group (P < 0.05). IGF-1 expression was up-regulated in the BMSC and combined groups (P < 0.05 versus BC), but not in the ACEI group. B cell lymphoma-2 (Bcl-2) expression was up-regulated in the ACEI, BMSC and combined groups, with the highest expression in the combined group (P < 0.05). CONCLUSIONS: Our results show that BMSC engrafted in AMI can survive well and secrete IGF-1 and preserve cardiac function significantly. These data suggest that BMSC transplantation inhibits apoptosis of cardiomyocytes by up-regulation of Bcl-2 expression in the myocardium, and this effect might be sensitized by ACEI.

SDF-1α upregulation by atorvastatin in rats with acute myocardial infarction via nitric oxide production confers anti-inflammatory and anti-apoptotic effects.

BACKGROUND: The effects of atorvastatin on SDF-1α expression under acute myocardial infarction (AMI) are still unclear. Therefore, our present study is to investigate the roles and mechanisms of atorvastatin treatment on SDF-1α expression in rats with AMI. METHODS: Male Sprague-Dawley rats were underwent permanent coronary artery ligation and randomly assigned into four groups as follow: blank control (B), atorvastatin (A), atorvastatin plus L-NAME (A+L-NAME), and atorvastatin plus AMD3100 (A+AMD3100). Rats underwent similar procedure but without ligation were used as group sham operated (S). Atorvastatin (10mg/Kg/d body weight) was administrated by gavage to rats in three atorvastatin treated groups, and L-NAME (40 mg/Kg/d body weight) or AMD3100 (5mg/Kg/d body weight) was given to group A+L-NAME or A+AMD3100, respectively. RESULTS: Comparing with group B, NO production, SDF-1α and CXCR4 expression were significantly up-regulated in three atorvastatin treated groups at the seventh day. However, the increments of SDF-1α and CXCR4 expression in group A+L-NAME were reduced when NO production was inhibited by L-NAME. Anti-inflammatory and anti-apoptotic effects of atorvastatin were offset either by decrease of SDF-1α and CXCR4 expression (by L-NAME) or blockage of SDF-1α coupling with CXCR4 (by AMD3100). Expression of STAT3, a cardioprotective factor mediating SDF-1α/CXCR4 axis induced cardiac protection, was up-regulated most significantly in group A. The effects of atorvastatin therapy on cardiac function were also abrogated either when SDF-1α and CXCR4 expression was diminished or the coupling of SDF-1α with CXCR4 was blocked. CONCLUSION: SDF-1α upregulation by atorvastatin in rats with AMI was, at least partially, via the eNOS/NO dependent pathway, and SDF-1α upregulation and SDF-1α coupling with CXCR4 conferred anti-inflammatory and anti-apoptotic effects under AMI setting which we speculated that ultimately contributed to cardiac function improvement.

Efficacy of Atorvastatin combined with adipose-derived mesenchymal stem cell transplantation on cardiac function in rats with acute myocardial infarction.

Mesenchymal stem cells (MSCs) have been extensively applied for the restoration of cardiomyocytes loss after acute myocardial infarction (AMI). However, the optimal therapeutic efficacy of MSCs in ischemic heart diseases has been hampered by their poor survival and low differentiated rates. Therefore, the improvement of MSC survival and differentiated rates is warranted and critical for the efficacy of MSCs in AMI. In this paper, MSCs isolated from rat inguinal fat tissues were termed as adipose-derived mesenchymal stem cells (ASCs), and the fourth passage of ASCs was pre-specified by co-culturing with cardiomyocytes in a transwell system termed as co-ASCs. Fourteen days later, GATA-4 (a transcription factor) and cardiac troponin-I were detected by cellular immunofluorescence. Atorvastatin (Ator group) or vehicle (control group) was administrated for the first 24 h after AMI production in rats. Fourteen days later, inflammatory parameters and cardiac function were evaluated. The other surviving rats were injected with a total of 1 × 10(6) co-ASCs/100 µl phosphate-buffered saline (PBS), 1×10(6) ASCs/100 µl PBS, or 100 µl PBS. Twenty-eight days after cell injection, survival and differentiated rates of transplanted cells and cardiac function were evaluated. The percentage of GATA-4 expression in co-ASCs was 28.5% ± 5.6% and of cardiac troponin-I was 22.8% ± 3.2%. Compared with the control group, the number of infiltrating inflammatory cells, myeloperoxidase activity, inflammatory cytokines (VCAM-1, TNF-α, Hs-CRP) mRNA expression, and Bax protein expression were significantly reduced in the three Ator groups, accompanied by a significant improvement of Bcl-2 protein expression and cardiac function (P< 0.05). Compared with the Ator2 + ASCs group and Con + co-ASCs group, the number of 4-6-diamidino-2-phenylindole-stained cells and cardiac troponin-I-positive transplanted cells, concomitant with cardiac function, were improved most prominently in the Ator3 + co-ASCs group (P< 0.05). Pre-amelioration of the cardiac milieu, in conjunction with pre-specification of ASCs, was beneficial for enhancing ASCs' therapeutic efficacy on cardiac function after AMI.

[Analysis of fatty acid composition in cottonseed by gas chromatography with on-line pyrolytic methylation].

A method of on-line pyrolytic methylation-gas chromatography was developed for the analysis of fatty acid composition in cottonseed. Fatty acids in cottonseeds were converted to their corresponding fatty acid methyl esters in the presence of trimethylsulfonium hydroxide at 300℃. The major fatty acids were linoleic acid (C18:2), oleic acid (C18:1), palmitic acid (C16:0), stearic acid (C18:0), myristic acid (C14:0), palmitoleic acid (C16:1), arachidic acid (C20:0) and docosanoic acid (C22:0). The unsaturated fatty acid content varied from 66.30% to 72.54%, and linoleic acid content varied from 43.20% to 53.61%. The RSDs of the peak areas of the fatty acids were less than 10% (n=5). The fatty acid compositions in the cottonseed samples, obtained from different growing places and different edible oil samples were compared by statistical analysis. The results showed that fatty acid compositions in cottonseed samples from different regions were similar. The fatty acid composition in cottonseed samples was closest to that of corn oil, and the similarity varied from 0.960 to 0.992. The method is simple, rapid, accurate, and is suitable for the analysis of fatty acid composition in cottonseed.

Determination of methacrylic acid in food simulants by pyrolytic butylation-gas chromatography.

An on-line pyrolytic butylation approach was proposed to determine methacrylic acid (MA) in food simulants by gas chromatography (GC) without an expensive pyrolyzer. MA in food simulants was converted into butyl methacrylate in the presence of tetrabutylammonium hydroxide (TBAH) without any pretreatment at 330°C in the injection-port, contributing to high GC signal response. The derivatizing conditions for the proposed method were optimized, namely the injection-port temperature, type and amount of the organic alkaline used for derivatization. A series of standard solutions of MA in the range of 1.0-50mg/kg were analyzed with correlation coefficient r≥0.9975. The limits of detection (LODs) were less than 0.15mg/kg for MA in four matrix simulants (distilled water, 3%w/v acetic acid, 10%v/v ethanol, and isooctane). Relative standard deviations (RSDs) for retention time, peak height and peak area were all less than 3.88%. The technique was successfully applied to the analysis of MA migrating from plastic cup samples, with recoveries of added MA in the range of 96.5-123.0%. Direct injection of the simulants into the GC system after migration tests, without any pretreatment step, makes the developed method of great value for rapid screening analysis of samples in bulks.

Lipoprotein-associated phospholipase A2 (Lp-PLA(2)): a novel and promising biomarker for cardiovascular risks assessment.

Atherosclerosis and its manifestations namely cardiovascular diseases (CVD) are still the leading cause of morbidity and mortality worldwide. Although intensified interventions have been applied, the residual cardiovascular (CV) risks are still very high. Lipoprotein-associated phospholipase A2 (Lp-PLA(2)) is a novel and unique biomarker highly specific for vascular inflammation and atherosclerosis. Both pro-atherogenic property of Lp-PLA(2) and positive correlation with CV events have already been demonstrated by a large number of scientific and clinical studies. Currently, in the Adult Treatment Panel III (ATP III) guideline, Lp-PLA(2) has been recommended as an adjunct to traditional risk factors in assessing future CV risks. Encouragingly, darapladib, an orally Lp-PLA(2) specific inhibitor, has been tested in basic research and preclinical trials and the outcomes are quite striking. Additionally, there are two phase III ongoing clinical trials in evaluating the efficacy and safety of darapladib on cardiovascular outcomes. With regard to the potential values of Lp-PLA(2) in risk stratification, therapeutic regimen establishment and prognosis evaluation in patients with moderate or high risk, our present review is going to summarize the relevant data about the bio-chemical characteristics of Lp-PLA(2), the actions of Lp-PLA(2) on atherosclerosis and the results of Lp-PLA(2) in scientific research and clinical studies.

Atorvastatin treatment of rats with ischemia-reperfusion injury improves adipose-derived mesenchymal stem cell migration and survival via the SDF-1α/CXCR-4 axis.

BACKGROUND: Adipose-derived mesenchymal stem cells (ASCs) transplantation is a promising approach for myocardium repair. Promotion of ASCs migration and survival is the key for improving ASCs efficiency. SDF-1α is a critical factor responsible for ASCs migration and survival. Atorvastatin (Ator) is capable of up-regulating SDF-1α. Therefore, we're going to investigate whether ASCs migration and survival could be improved with atorvastatin. METHODS: In vitro study, cardiomyocytes were subjected to anoxia-reoxygenation injury and subsequently divided into different groups: group blank control, Ator, Ator plus L-NAME (A+L-NAME) and Ator plus AMD3100 (A+AMD3100).When migration analysis completed, cardiomyocytes were used for subsequent analyses. In vivo study, rats underwent ischemia-reperfusion injury were assigned into different groups corresponding to in vitro protocols. ASCs were transplanted on the seventh day of atorvastatin therapy. Seven days later, the rates of migration, differentiation and apoptosis were evaluated. RESULTS: Compared with other groups, ASCs migration in vitro was significantly improved in group Ator, which was dependent on SDF-1α/CXCR-4 coupling. Results of in vivo study were consistent with that of in vitro study, further supporting the notion that the efficacy of atorvastatin on ASCs migration improvement was related to SDF-1α/CXCR-4 axis. Higher vessel density in group Ator might be another mechanism responsible for migration improvement. Concomitantly, apoptosis was significantly reduced in group Ator, whereas no significant difference of differentiation was found. CONCLUSION: Migration and survival of ASCs could be improved by atorvastatin under ischemia-reperfusion injury, which were ascribed to SDF-1α/CXCR-4 axis.

[Effect of atorvastatin on cardiac function and TGF-ß1 signaling pathway after acute myocardial infarction in rats].

OBJECTIVE: To investigate the effect of atorvastatin on cardiac remodeling and function after acute myocardial infarction (AMI) in rats and whether this effect is mediated by transforming growth factor-ß1 (TGF-ß1) signaling pathway. METHODS: AMI was induced by left coronary artery ligation in 64 male Sprague-Dawley rats, and 45 surviving rats were randomized into control group (n=15), low-dose atorvastatin group (10 mg/kg, n=15) and high-dose atorvastatin group (20 mg/kg, n=15). Similar surgical procedure was performed in sham-operated rats (n=15) without coronary ligation. Atorvastatin was given daily by gavage from the first day after AMI. Eight weeks later, the cardiac function, left ventricular weight/body mass index (LVMI), collagen volume fraction (CVF), and the expressions of TGF-ß1 and Smad2 were compared between the groups. RESULTS: AMI caused significantly reduced cardiac function, increased LVMI and CVF, and upregulated expressions of TGF-ß1 and Smad2 mRNA and proteins in the control group (P<0.05). The cardiac function, LVMI, and CVF were improved by atorvastatin, which also down-regulated the expressions of TGF-ß1 and Smad2 (P<0.05), and the effects were more prominent in high-dose atorvastatin group (P<0.05). CONCLUSION: Atorvastatin can dose-dependently improve cardiac remodeling and function after AMI in rats, which is mediated by regulating the activity of TGF-ß1/Smad2 signaling pathway.

The effect of zolpidem on sleep quality, stress status, and nondipping hypertension.

OBJECTIVE: Poor sleep quality and stress status have previously been shown to be closely associated with higher activation of the sympathetic nervous system and to be independent predictors of nondipping hypertension. This study aimed to evaluate the effects of the non-hypotensive sedative zolpidem on sleep quality, stress status, and nondipping hypertension. METHODS: A total of 103 nondippers were defined as poor or good sleepers by the Pittsburgh Sleep Quality Index. They were randomized to receive zolpidem or placebo treatment for 30 days. Stress status was assessed by the Perceived Stress Scale, and levels of epinephrine and norepinephrine were examined to investigate the underlying mechanisms. RESULTS: Poor sleepers treated with zolpidem for 30 days showed significant improvements in sleep quality and stress levels (P<0.01). More nondippers were converted to dippers in the group of poor sleepers treated with zolpidem (11 of 22 patients, 50.0%) than in the placebo (2 of 23, 8.7%) (P<0.01). Epinephrine and norepinephrine levels were significantly reduced in poor sleepers treated with zolpidem (P<0.05). CONCLUSION: The results of this study suggest that zolpidem can improve sleep quality and stress status, and can convert nondippers with poor sleep quality into dippers. It may be an option for treating nondipping hypertensive patients with poor sleep quality.

Effects of insulin-like growth factor-1 on the properties of mesenchymal stem cells in vitro.

OBJECTIVE: To explore the effects of insulin-like growth factor-1 (IGF-1) on migration, proliferation and differentiation of mesenchymal stem cells (MSCs). METHODS: MSCs were obtained from Sprague-Dawley rats by a combination of gradient centrifugation and cell culture techniques and treated with IGF-1 at concentrations of 5-20 ng/ml. Proliferation of MSCs was determined as the mean doubling time. Expression of CXC chemokine receptor 4 (CXCR4) and migration property were determined by flow cytometry and transwell migration essay, respectively. mRNA expression of GATA-4 and collagen II was determined by reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: The mean doubling time of MSC proliferation was decreased, and the expression of CXCR4 on MSCs and migration of MSCs were increased by IGF-1, all in a dose-dependent manner, while the optimal concentration of IGF-1 on proliferation and migration was different. IGF-1 did not affect the expression of GATA-4 or collagen II mRNA. CONCLUSIONS: IGF-1 dose-dependently stimulated the proliferation of MSCs, upregulated the expression of CXCR4, and accelerated migration. There was no apparent differentiation of MSCs to cardiomyocytes or chondrocytes after culturing with IGF-1 alone.

Association of N-terminal pro brain natriuretic peptide and impaired aortic elastic property in hypertensive patients.

BACKGROUND: N-terminal pro brain natriuretic peptide (NT-proBNP) is closely related to risk stratification in many cardiovascular diseases. The objective of this study was to evaluate the association of NT-proBNP and impaired aortic elastic property in hypertensive patients. METHODS: One hundred fifty-five hypertensive patients without obvious cardiac dysfunction were included and divided in tertiles based on their NT-proBNP concentration. Eighty-six normotensive healthy volunteers were also enrolled as controls. All subjects underwent Doppler echocardiography to assess cardiac parameters and aortic distensibility index. Plasma NT-proBNP was measured by electrochemiluminescence. RESULTS: The parameters of aortic elastic property were decreased and NT-proBNP was significantly increased in hypertensive patients compared with controls (all P<0.05). Among hypertensive patients, higher NT-proBNP tertiles were associated with larger systolic and diastolic aortic diameters, longer deceleration time of the E wave velocity (DT) and isovolumic relaxation time; decreased E/A ratio and more percent of diastolic dysfunction. The parameters of aortic elastic property showed stepwise decreases from the first tertiles to the third tertiles (P<0.05). Multiple linear regression analysis showed that concentrations of NT-proBNP were significantly correlated with age and impaired aortic distensibility. CONCLUSIONS: NT-proBNP is a marker for impaired aortic elastic property in hypertensive patients. Measurement of NT-proBNP could be indicated in hypertensive patients for further risk stratification.

Poor sleep quality, stress status, and sympathetic nervous system activation in nondipping hypertension.

OBJECTIVE: It has been reported that poor sleep quality is associated with nondipping hypertension, but the underlying mechanisms were not reported. This study was carried out to evaluate whether poor sleep quality is associated with stress status and sympathetic nervous system activation in nondippers. MATERIALS AND METHODS: A total of 307 Chinese essential hypertensive patients were defined as dippers or nondippers by ambulatory blood pressure monitoring. Sleep quality was assessed by Pittsburgh Sleep Quality Index (PSQI), and stress status was assessed by Perceived Stress Scale (PSS). The levels of epinephrine and norepinephrine were examined to investigate the underlying mechanisms. RESULTS: A total of 204 (66.4%) and 103 cases (33.6%) were found to be dippers and nondippers, respectively. Nondippers were with poorer sleep quality (P<0.05), more stressful status (P<0.05), and with an increased activity of sympathetic nervous system (P<0.01). The decline of systolic BP (SBP) and diastolic BP (DBP) at night was inversely related with the PSQI score (r=-0.469, P<0.01 and r=-0.421, P<0.01), PSS score (r=-0.432, P<0.01 and r=-0.404, P<0.01), epinephrine (r=-0.304, P<0.05 and r=-0.293, P<0.05), and norepinephrine (r=-0.321, P<0.05 and r=-0.357, P<0.05). Multiple logistic regression analyses showed that older age [odds ratio (OR): 1.69; 95% confidence interval (CI): 1.22-2.43], PSQI score (OR: 2.78; 95% CI: 1.65-6.87), and PSS score (OR: 2.43; 95% CI: 1.56-5.93) were independently correlated with the nondipping pattern. CONCLUSION: Poor sleep quality and stressful status were closely associated with higher activation of sympathetic nervous system, and they are independent predictors of nondipping hypertension.