钙调神经磷酸酶在肾血管性高血压大鼠心肌肥厚发展中的作用

本文观察了钙调神经磷酸酶(calcineurin,CaN)在肾血管性高血压大鼠肥厚心肌中的表达和活性以及CaN抑制剂——环孢菌素A(cyclosporine A,CsA)对逆转心肌肥厚的影响。利用两肾一夹肾血管性高血压大鼠心肌肥厚模型,观察大鼠心肌肥厚程度、CaN mRNA和蛋白质表达及CaN活性的改变。结果显示:大鼠左室重与胫骨长度的比值和光镜下心肌细胞横截面积在两肾一夹2月和3月组都较相应假手术组增高(P<0.05),CsA组大鼠左室重与胫骨长度比值、心肌细胞横截面积较两肾一夹2月和3月组均显著下降(P<0.05),与假手术组无显著性差异。大鼠心肌CaN mRNA和蛋白质表达及CaN活性在两肾一夹2月和3月组均高于相应假手术组(P<0.05),在CsA组低于两肾一夹2月和3月组(P<0.05)。这些结果提示,CaN参与肾血管性高血压大鼠心肌肥厚发展,抑制CaN活性可逆转心肌肥厚。     

Angiotensinase activities in the kidney of renovascular hypertensive rats

In spite of the well-known contribution of angiotensin II (Ang II) in the pathogenesis of Goldblatt two-kidney one clip (G2K1C) hypertension, the importance of other Ang peptides, such as Ang III, Ang IV or Ang 2-10, is scarcely understood. The functional status of these peptides depends on the action of several aminopeptidases called angiotensinases. The metabolism of Ang III to Ang IV by aminopeptidase M (AlaAP) and of Ang I to Ang 2-10 by aspartyl aminopeptidase (AspAP) was evaluated in the renal cortex and medulla of normotensive (Sham-operated) and hypertensive (G2K1C) rats, treated or not with the AT(1) receptor antagonist valsartan. The results demonstrated a highly significant increase of membrane-bound (MEMB) AlaAP in the cortex of the non-ischemic kidney of G2K1C rats compared with the kidney of normal rats and with the clipped kidney of G2K1C rats. This suggests an increased formation of Ang IV in the non-clipped kidney of G2R1C rats. Valsartan reduced MEMB AlaAP and AspAP activities in the renal cortex of normotensive and in the clipped kidney of hypertensive rats. The reduced metabolism of Ang III may prolong its half-life in valsartan-treated animals. These results suggest a role for AlaAP in renovascular hypertension. In addition, the higher AspAP activity of the renal cortex compared to medulla reflects its relative functional difference between both locations.     

Vaccarin administration ameliorates hypertension and cardiovascular remodeling in renovascular hypertensive rats

Sympathetic overdrive, activation of renin angiotensin systems (RAS), and oxidative stress are vitally involved in the pathogenesis of hypertension and cardiovascular remodeling. We recently identified that vaccarin protected endothelial cell function from oxidative stress or high glucose. In this study, we aimed to investigate whether vaccarin attenuated hypertension and cardiovascular remodeling. Two‐kidney one‐clip (2K1C) model rats were used, and low dose of vaccarin (10 mg/kg), high dose of vaccarin (30 mg/kg), captopril (30 mg/kg) were intraperitoneally administrated. Herein, we showed that 2K1C rats exhibited higher systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), left ventricular mass/body weight ratio, myocardial hypertrophy or fibrosis, media thickness, and media thickness to lumen diameter, which were obviously alleviated by vaccarin and captopril. In addition, both vaccarin and captopril abrogated the increased plasma renin, angiotensin II (Ang II), norepinephrine (NE), and the basal sympathetic activity. The AT1R protein expressions, NADPH oxidase subunit NOX‐2 protein levels and malondialdehyde (MDA) content were significantly increased, whereas superoxide dismutase (SOD) and catalase (CAT) activities were decreased in myocardium, aorta, and mesenteric artery of 2K1C rats, both vaccarin and captopril treatment counteracted these changes in renovascular hypertensive rats. Collectively, we concluded that vaccarin may be a novel complementary therapeutic medicine for the prevention and treatment of hypertension. The mechanisms for antihypertensive effects of vaccarin may be associated with inhibition of sympathetic activity, RAS, and oxidative stress.     

Superoxide anions in the paraventricular nucleus mediate the enhanced cardiac sympathetic afferent reflex and sympathetic activity in renovascular hypertensive rats

An enhanced cardiac sympathetic afferent reflex (CSAR) is involved in the sympathetic activation in renovascular hypertension. The present study was designed to determine the role of superoxide anions in the paraventricular nucleus (PVN) in mediating the enhanced CSAR and sympathetic activity in renovascular hypertension in the two-kidney, one-clip (2K1C) model. Sinoaortic denervation and vagotomy were carried out, and renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded under anesthesia. The CSAR was evaluated by the response of RSNA to the epicardial application of capsaicin. Superoxide anion levels and NAD(P)H oxidase activity in the PVN increased in 2K1C rats and were much higher in 2K1C rats than in sham-operated (sham) rats after the epicardial application of capsaicin or PVN microinjection of ANG II. In both 2K1C and sham rats, PVN microinjection of the superoxide anion scavenger tempol or the NAD(P)H oxidase inhibitor apocynin abolished the CSAR, whereas the SOD inhibitor diethyldithiocarbamic acid (DETC) potentiated the CSAR. Tempol and apocynin decreased but DETC increased baseline RSNA and MAP. ANG II in the PVN caused larger responses of the CSAR, baseline RSNA, and baseline MAP in 2K1C rats than in sham rats. The effects of ANG II were abolished by pretreatment with tempol or apocynin in both 2K1C and sham rats and augmented by DETC in the PVN in 2K1C rats. These results indicate that superoxide anions in the PVN mediate the CSAR and the effects of ANG II in the PVN. Increased superoxide anions in the PVN contribute to the enhanced CSAR and sympathetic activity in renovascular hypertension.     

Long-term mineralocorticoid receptor blockade reduces fibrosis and improves cardiac performance and coronary hemodynamics in elderly SHR

Aldosterone has been implicated as one of the mediators of cardiovascular injury in various diseases. This study examines whether mineralocorticoid antagonism ameliorates or prevents the adverse cardiac effects of hypertension and aging. Male 22-wk-old spontaneously hypertensive rats (SHR) were divided into two groups, 15 rats in each. One group received no treatment; the other was given eplerenone ( approximately 100 mg.kg(-1).day(-1)). At the age of 54 wk, indexes of cardiovascular mass, systemic and regional hemodynamics, including coronary, left ventricular function, and myocardial collagen content, were determined in all rats. Hemodynamic studies were done in conscious rats. Arterial pressure was lowered only slightly in eplerenone-treated rats, and cardiac output and total peripheral resistance did not differ from control rats. Left and right ventricular and aortic mass indexes were unaffected by eplerenone; however, concentration of hydroxyproline in the right and left ventricle was decreased significantly (P < 0.05) by eplerenone. This was accompanied by an improvement in left ventricular diastolic function and coronary hemodynamics. In conclusion, long-term therapy with the mineralocorticoid receptor antagonist eplerenone ameliorated adverse cardiac effects of both hypertension and aging in SHR. Thus reduction in myocardial fibrosis, paralleled by improvements in left ventricular function and coronary hemodynamics, was observed in eplerenone-treated SHR.     

Intact female stroke-prone hypertensive rats lack responsiveness to mineralocorticoid receptor antagonists

Data from the Framingham Heart Study suggest that women may be more sensitive to the deleterious cardiovascular remodeling effects of aldosterone. Previous studies from our laboratory have shown that chronic treatment with spironolactone, a mineralocorticoid receptor (MR) antagonist, decreases ischemic cerebral infarct size and prevents remodeling of the middle cerebral artery (MCA) in male spontaneously hypertensive stroke-prone rats (SHRSP). Therefore, we hypothesized that MR antagonism would reduce ischemic infarct size and prevent MCA remodeling in female SHRSP. Six-week-old female SHRSP were treated for 6 wk with spironolactone (25 or 50 mg.kg(-1).day(-1)) or eplerenone (100 mg.kg(-1).day(-1)) and compared with untreated controls. At 12 wk, cerebral ischemia was induced for 18 h using the intraluminal suture occlusion technique, or the MCA was isolated for analysis of passive structure using a pressurized arteriograph. MR antagonism had no effect on infarct size or passive MCA structure in female SHRSP. To study the potential effects of estrogen, the above experiments were repeated in bilaterally ovariectomized (OVX) female SHRSP treated with spironolactone (25 mg.kg(-1).day(-1)). Infarct size and vessel structure in OVX SHRSP were not different from control SHRSP. Spironolactone had no effect on infarct size in OVX SHRSP. However, MCA lumen and outer diameters were increased in spironolactone-treated OVX SHRSP, suggesting an effect of estrogen. Cerebral artery MR expression, assessed by Western blotting, was increased in female, compared with male, SHRSP. These studies highlight an apparent sexual dimorphism of MR expression and activity in the cerebral vasculature from hypertensive rats.     

人工寒潮对高血压大鼠P-选择素的影响

目的:探讨人工寒潮对易卒中型肾血管性高血压大鼠(RHRSP)血小板活化影响.方法:健康雄性Sprague Dawley(SD)随机分成三组:高血压组、假手术组、正常对照组,高血压组大鼠按双肾双夹法复制成RHRSP模型;用鼠尾测压仪(HX21型)经尾动脉测量收缩压,肾动脉狭窄术前测量1次,术后每4周测量1次,观察12周,分别与对照组和假手术组比较;12周末对每只大鼠放入人工寒潮箱进行人工寒潮,4小时后舌下静脉取血约2ml.流式细胞仪检测RHRSP全血中p-选择素(CD62p)表达阳性率,取脑组织进行病理学检查.结果:不同时期各组全血中CD62p表达阳性率比较:a.方差分析结果表明:高血压组CD62p表达阳性率显著高于其它2对照组(P＜0.01);b.CD62p表达阳性率、随血压的升高而逐渐增多,与高血压大鼠MAP成正相关关系;c.t检验结果表明:高血压组CD62p表达阳性率在经历人工寒潮后较前显著升高(P＜0.0).结论:高血压大鼠的CD62p表达阳性率较对照组明显增高,在人工寒潮后CD62p表达更高.     

In vitro vasoconstriction induced by calcium in renovascular hypertensive or old rats

We studied the changes in calcium-induced vasoconstriction in isolated tail arteries from young (2 months) and old (12 months) normotensive, and young renovascular hypertensive rats (3 months old, with unilateral renal artery clipping at 6 weeks), pretreated with reserpine. The tail artery was removed and perfused/superfused with either a high potassium Krebs depolarizing solution or Krebs solution plus phenylephrine. Concentration-response curves to calcium were produced. Old rats had a low plasma renin activity and their depolarized tail arteries showed a weak vasoconstrictor response to calcium. Renovascular hypertensive rats had a high mean blood pressure and plasma renin activity. Responses of their depolarized tail arteries to calcium were greater. Responses to calcium in tail arteries perfused with phenylephrine were similar in all groups. We conclude that age and renovascular hypertension produce opposite changes in vasoconstriction induced by calcium in depolarized tail arteries.     

Effects of minoxidil on blood pressure and cardiac hypertrophy in two-kidney, one-clip hypertensive rats

Rats made severely hypertensive by renal arterial clipping were treated for 24 days with the arterial vasodilator minoxidil (40, 80, and 120 mg/L drinking water). In all three treated groups of animals, blood pressure initially decreased markedly and to a similar extent. Subsequently partial tolerance developed to the antihypertensive effects of minoxidil. All three doses induced hypertrophy of the right ventricle to a similar degree. In contrast, the hypertension-induced hypertrophy of the left ventricle was further increased in a dose-dependent fashion by minoxidil.     

Increased reactive oxygen species contributes to kidney injury in mineralocorticoid hypertensive rats.

Hypertension is associated with increased reactive oxygen species (ROS). Renal ROS production and their effects on renal function have never been investigated in mineralocorticoid hypertensive rats. In this study we hypothesized that increased ROS production in kidneys from deoxycorticosterone (DOCA)-salt rats contributes to adverse renal morphological changes and impaired renal function in DOCA-salt hypertensive rats. We also determined whether ROS-induced renal injury was dependent on blood pressure. DOCA-salt hypertensive rats exhibited a marked increase in blood pressure, renal ROS production, glomerular and tubular lesions, and microalbuminuria compared to sham rats. Treatment of DOCA-salt hypertensive rats with apocynin for 28 days resulted in attenuation of systolic blood pressure and improvement of renal morphology. Renal superoxide level in DOCA-salt rats was 215% of sham-operated rats and it was significantly decreased to 140% with apocynin treatment. Urinary protein level was decreased from 27 +/- 3 mg/day in DOCA-salt hypertensive rats to 9 +/- 2 mg/day. 28 days of Vitamin E treatment also reduced renal injury in regard to urinary protein level and renal morphology but had no effect on blood pressure in DOCA-salt rats. Increased urinary 8-isoprostane, a marker for oxidative stress, in DOCA-salt hypertensive rats (55 +/- 8 ng/day) was diminished by vitamin E treatment (24 +/- 6 ng/day). These data suggest that renal injury characteristic of mineralocorticoid hypertension is associated with oxidative stress and is partly independent of blood pressure.     

Alpha-tocopherol supplementation favorable effects on blood pressure, blood viscosity and cardiac remodeling of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) were separated into two groups (n = 6 per group) and, since 5 months old, received alpha-tocopherol (alpha-tocopherol acetate120 IU) or vehicle by daily gavage for 2 weeks. Blood viscosity, blood pressure (BP) and myocardial remodeling were analyzed. The SHRs treated with alpha-tocopherol showed a significant reduction of BP and a major reduction of blood viscosity in comparison with the control SHRs. The cardiac hypertrophy indices showed some differences when the two SHR groups were compared, the LV mass index was not different between the groups; however, the cardiomyocyte size was more than 20% smaller in SHRs treated with alpha-tocopherol than in control SHRs (P < .05). The intramyocardial vessels distribution was more than 45% greater in alpha-tocopherol-treated SHRs than in control rats, significantly improving the vessels-to-myocytes ratio in treated SHRs than in control SHRs (P < .05). In conclusion, present findings strongly suggest a beneficial effect of alpha-tocopherol supplementation to genetically hypertensive rats. This was observed by a reduction of both blood viscosity and BP, and a consequent cardiomyocyte hypertrophy in treated SHRs; an improvement of vessels-to-myocytes ratio in these rats was also observed.     

Beta-adrenergic mechanisms in arterial hemodynamics: A comparison between normotensive and hypertensive rats

The purpose of this study was to determine whether -adrenergically mediated cardiovascular functions such as arterial pressure (AP), heart rate (HR), stroke volume (SV), cardiac output (CO), peripheral resistance (R_p), arterial impedance (Z_c), mean arterial compliance (C_m) and pulse wave reflection (P_b) were altered in the spontaneously hypertensive rat (SHR) compared to the normotensive Wistar Kyoto rat (WKY). In pentobarbital-anesthetized and artificially ventilated rats, the aortic pressure wave was recorded with a high-fidelity Millar sensor, and aortic flow wave with an electromagnetic flow probe. The pressure and flow waves were subjected to Fourier transform so as to analyze impedance spectra. Acute -adrenergic blockade was produced by an intravenous injection of propranolol (nonselective) and atenolol (selective ₁-blocker) at doses of 2 and 5 mg/kg, respectively. Steady-state parameters were obtained 15–20 min after intravenous administration. The SHR had higher AP, HR, R_p and Z_c than the WKY. SV and CO remained unaltered while C_m was lower. In response to propranolol, the mean AP was increased by 7 mm Hg in the WKY, but did not change in the SHR. Moreover, significant decreases occurred in HR, CO and C_m in addition to increases in R_p, Z_c and P_b. These changes between the SHR and WKY were only slight. Atenolol caused decreases in AP, HR and CO in both SHR and WKY, but did not significantly alter the R_p, Z_c, C_m and P_b. Again, the atenolol-induced changes in AP, HR and CO did not appear to be significantly different between SHR and WKY. The results indicate that -adrenergic effects on the heart, Windkessel and resistance vessels are neither greatly enhanced nor impaired during the development of hypertension. In the hypertensive state, significant -adrenergic mechanisms still exert tonic vasodilatory effects on the large and small arterial system.     

Regional surface areas of spontaneously hypertensive and Wistar-Kyoto rats

Regional skin surface area and region-specific weighting factors for calculating mean skin temperature have not been determined for the rat. Therefore, measurements were made of total skin surface area segmented into five regions of 12 spontaneously hypertensive (SHR) and 12 normotensive Wistar-Kyoto (WKY) rats. SHR's were selected because chronically elevated core temperature and reduced ability of SHR's to withstand heat stress make them of interest for thermoregulatory studies. Area was determined by coating the skin with rubber base dental impression material, then measuring the area of the coating. The relationship between total skin surface area and mass of SHR's was not different from that of WKY's and is described by the equation SA = 8.62 M0.67. However, the ears of SHR's had larger surface area and their tails smaller surface area than those of WKY's. For the combined groups, the proportion of total surface area of the regions was as follows: ears, 0.022; front feet, 0.017; hind feet, 0.040; tail, 0.100; central skin, 0.826. These data provide a basis for calculating skin surface area, mean skin temperature, and related values for SHR and WKY rats.     

Angiotensin II via AT1 receptor accelerates arterial thrombosis in renovascular hypertensive rats.

Although there are some in vitro evidence that angiotensin II (Ang II) may promote thrombosis, there is still no data concerning effect of Ang II on arterial thrombus formation. In the present study we have investigated the influence of Ang II on electrically induced arterial thrombosis in a common carotid artery of renovascular hypertensive rats. Furthermore, we examined if Ang II effect is mediated via AT1 receptor. We measured some coagulation and fibrinolytic parameters at the same time. Since platelets play crucial role in the initiation of arterial thrombosis their contribution in the mode of Ang II action was also determined. Intravenous infusion of Ang II caused significant increase in arterial thrombus weight, which was reversed by losartan, selective AT1 receptor antagonist. The prothrombotic effect of Ang II was accompanied by increase in haemostatic and decrease in fibrinolytic potential of rat plasma. While number of data has clearly demonstrated that Ang II can augment human platelets aggregation, at least in rats, platelets were not involved in the mechanism of Ang II action. Our study shows that Ang II via AT1 receptor accelerates arterial thrombosis in renovascular hypertensive rat, therefore may be considered as a risk factor of myocardial infarction or stroke.     

Selective effect of tempol on renal medullary hemodynamics in spontaneously hypertensive rats

The present study assessed the short- and long-term effect of tempol, a membrane-permeable mimetic of superoxide dismutase, on renal medullary hemodynamics in spontaneously hypertensive rats (SHR). Tempol was given in the drinking water (1 mM) for 4 days or 7 wk (4-11 wk of age), and medullary blood flow (MBF) was measured over a wide range of renal arterial pressure by means of laser-Doppler flowmetry in anesthetized rats. In addition, the response of the medullary circulation to angiotensin II (5-50 ng x kg(-1) x min(-1) iv) was determined in SHR treated for 4 days with tempol. Compared with control SHR, short- and long-term treatment with tempol decreased arterial pressure by approximately 20 mmHg and increased MBF by 35-50% without altering total renal blood flow (RBF) or autoregulation of RBF. Angiotensin II decreased RBF and MBF dose dependently (approximately 30% at the highest dose) in control SHR. In SHR treated with tempol, angiotensin II decreased RBF (approximately 30% at the highest dose) but did not alter MBF significantly. These data indicate that the antihypertensive effect of short- and long-term administration of tempol in SHR is associated with a selective increase in MBF. Tempol also reduced the sensitivity of MBF to angiotensin II. Taken together, these data support the idea that tempol enhances vasodilator mechanisms of the medullary circulation, possibly by interacting with the nitric oxide system. Increased MBF and reduced sensitivity of MBF to angiotensin II may contribute to the antihypertensive action of tempol in SHR.     

A hypertensive substance found in the blood of spontaneously hypertensive rats

A substance has been obtained from the blood of spontaneously hypertensive rats which produces a hypertensive elevation of the blood pressure in normotensive rats. The substance is dialyzable and is associated with the erythrocyte membrane. It appears to be relatively long-lived in its effect on arterial pressure. The erythrocyte fractions that exhibit pressor activity also stimulate the in vitro uptake of calcium by aortas obtained from normotensive animals. This suggests that the hypertensive factor or related substances may influence the calcium metabolism of vascular tissue.     

Hyperhomocysteinemia leads to adverse cardiac remodeling in hypertensive rats

Hyperhomocysteinemia (Hhe), linked to cardiovascular disease by epidemiological studies, may be an important factor in adverse cardiac remodeling in hypertension. Specifically, convergence of myocardial and vascular alterations promoted by Hhe and hypertension may exacerbate cardiac remodeling and myocardial dysfunction. We studied male spontaneously hypertensive rats fed one of three diets: control, intermediate Hhe inducing, or severe Hhe inducing. After 10 wk of dietary intervention, cardiac function was assessed in vitro, and cardiac and coronary arteriolar remodeling were monitored by histomorphometric, immunohistochemical, and biochemical techniques. Results showed that Hhe induced diastolic dysfunction, as characterized by the diastolic pressure-volume curve, without significant changes in baseline systolic function. Perivascular collagen levels were increased by Hhe, and there was an increase in left ventricular hydroxyproline levels. Myocyte size was not affected. Coronary arteriolar wall thickness increased with Hhe due to smooth muscle hyperplasia. Mast cells increased in parallel with Hhe and collagen accumulation. In summary, 10 wk of Hhe caused coronary arteriolar remodeling, myocardial collagen deposition, and diastolic dysfunction in hypertensive rats.