High-phosphorus/zinc-free diet aggravates hypertension and cardiac dysfunction in a rat model of the metabolic syndrome

BackgroundCardiac dysfunction is reported in patients with the metabolic syndrome. We assessed the effects of high-phosphorus and zinc-free diet on cardiovascular system in spontaneously hypertensive rats (SHR)/NDmcr-cp (SHR/cp), a rat model of the metabolic syndrome. We also investigated the effects of N-acetyl-L-cysteine (NAC), an antioxidant, on the development of cardiac dysfunction under such conditions.MethodsMale SHR/cp and control [Wistar Kyoto (WKY)] rats were divided into three groups and fed control diet (P 0.3% w/w, Zn 0.2% w/w) or high-phosphorus and zinc-free (P 1.2% w/w, Zn 0.0% w/w) diet. The latter group was treated with either NAC (1.5 mg/g per day) or vehicle from 6 to 18 weeks of age (n=6 or 8 for each group).ResultsHigh-phosphate and zinc-free diet increased systolic blood pressure in both WKY and SHR/cp. Echocardiography showed that high-phosphate and zinc-free diet markedly reduced left ventricular systolic and diastolic function in SHR/cp. Histopathologically, the same diet induced severe myocardial fibrosis in SHR/cp, and this effect was prevented by NAC. Whereas treatment with NAC prevented diastolic dysfunction induced by the same diet in WKY, it only improved systolic function but not diastolic function in SHR/cp.ConclusionsHigh-phosphate and zinc-free diet induced hypertension and cardiac dysfunction. These changes hamper the protective effects of NAC in the metabolic syndrome.SummaryThe present study showed that consumption of high-phosphorus and zinc-free diet increased the myocardial expression of connective tissue growth factor and reduced the expression of metallothionein, which enhanced the development of severe cardiac dysfunction in rats with the metabolic syndrome. The results suggest that the metabolic syndrome seems to aggravate cardiac dysfunction and hamper the protective effects of antioxidant, NAC.     

Influence of a diet rich in fish oil on blood pressure,body weight and cardiac hypertrophy in spontaneously hypertensive rats

Summary The effects of a diet rich in fish oil on arterial blood pressure, body weight, left ventricular weight and heart rate have been investigated in 8 month old spontaneously hypertensive male rats (SHR) as compared to age-matched hypertensive controls. A diet containing 10% fish oil decreased blood pressure by about 40 mmHg within 20 days of starting the experiment, and this effect persisted over the observation period of 80 days. Permitting the animals free access to food, the body weight of the diet group increased by 25%. The degree of hypertrophy as evaluated by relating left ventricular weight to tibial length was significantly reduced (10%) in the diet fed group. Heart rate was increased by 53%. The study demonstrates that a diet rich in fish oil can lower arterial blood pressure over several weeks without a recognizable loss in function despite a considerable increase in body weight. It can be assumed that a more marked regression of left ventricular hypertrophy is counteracted by a reflex increase in sympathetic efferentation to the heart.     

The effects of beta adrenoceptor blockade with atenolol on myocardial cellular and subcellular hypertrophy in spontaneously hypertensive rats

In this study we investigated the effects of chronic β adrenoreceptor blockade with atenolol on cellular and subcellular hypertrophy in spontaneously hypertensive rats (SHR). Atenolol was injected subcutaneously (20 mg/kg) twice daily commencing in four-week-old rats. The treated animals (SHR-A) were compared to their nontreated controls and normotensive, Wistar-Kyoto (WKY) controls at the age of 16 weeks. A group of atenolol-treated WKY was also studied. Chronic drug treatment was effective in attenuating the rise in systolic blood pressure characteristic of SHR, but did not normalize the values to those of WKY. Cardiac hypertrophy, characteristic of SHR, was modified by drug treatment as evidenced by left ventricular weights as well as myocardial cell size. The cells from the subendocardium underwent selective hypertrophy in SHR which was attentuated by about 50% after atenolol treatment. Stereological analysis of electron micrographs showed that while relative mitochondrial volume was not affected by treatment, relative myofibrillar volume (%) decreased in both subepicardium (SHR = 63.28 ± 1.25; SHR-A = 56.72 ± 1.37) and subendocardium (SHR = 66.53 ± 1.27; SHR-A = 58.30 ± 1.51). This change raised the mitochondrial/myofibrillar volume ratio, which is characteristically low in SHR compared to WKY. Sarcoplasm, which included all cell constituents except mitochondria, increased with atenolol treatment, but water concentration remained unchanged. The data suggest that attenuation of hypertrophy in SHR after β blockade is associated with selective effects on the myocardial cell involving primarily the myofibrillar cell compartment.     

苯那普利对高血压大鼠细胞外信号调节激酶和B型钠尿肽的影响

目的：研究苯那普利对自发性高血压大鼠（SHR）细胞外信号调节激酶（ERK）和B型钠尿肽（BNP）的影响。方法：选择Wistar Kyoto（WKY）大鼠作对照，将21只14周龄雄性SHR随机分成3组：未治疗组、肼苯哒嗪组和苯那普利组，每组7只。药物溶于载体（0.5%羧甲基纤维素钠）以灌胃法给予，肼苯哒嗪10 mg·kg-1·d-1，苯那普利10 mg·kg-1·d-1，SHR未治疗组及WKY组灌喂载体，共10周。以左心室重量与体重的比值反映心肌肥厚的程度；用袖带式尾动脉测压法测量大鼠尾动脉血压；分别用Western blotting方法和RT-PCR法半定量测定大鼠心肌中磷酸化ERK（p-ERK）的蛋白表达以及BNP mRNA的含量；酶联免疫吸附法检测大鼠血浆BNP水平。结果：（1） 治疗后SHR苯那普利组和SHR肼苯哒嗪组血压相似，均显著低于SHR未治疗组（P<0.01）。（2） SHR苯那普利组心肌肥厚指数显著低于SHR肼苯哒嗪组和SHR未治疗组(P<0.01) ，与WKY组无显著差异(P>0.05)；SHR肼苯哒嗪组和SHR未治疗组心肌肥厚指数无显著差异(P>0.05)。（3）SHR苯那普利组大鼠心肌p-ERK表达显著低于SHR肼苯哒嗪组和SHR未治疗组(P<0.05) ，与WKY组无显著差异(P>0.05)。SHR肼苯哒嗪组和SHR未治疗组大鼠心肌p-ERK表达无明显差异(P>0.05)。（4） SHR苯那普利组大鼠心肌BNP mRNA和血浆BNP水平显著低于SHR肼苯哒嗪组和SHR未治疗组(P<0.05)，与WKY组无显著差异(P>0.05)；SHR肼苯哒嗪组和SHR未治疗组大鼠心肌BNP mRNA和血浆BNP水平无明显差异(P>0.05)。结论：苯那普利能通过抑制ERK活性逆转心肌肥厚，伴随BNP水平下降；而降压效果相似的肼苯哒嗪不能抑制心肌肥厚，对p-ERK和BNP水平没有影响，提示BNP水平可以反映逆转心肌肥厚药物疗效。     

上调miR-133a表达水平对自发性高血压大鼠心肌纤维化的影响

目的:观察上调微小RNA-133a(miR-133a)的表达水平对自发性高血压大鼠(SHR)心肌纤维化的影响。方法:以同源正常血压Wistar-Kyoto(WKY)大鼠为正常对照组,另将SHR随机分为SHR组、SHR+腺相关病毒(AAV)组和SHR+携带miR-133a的腺相关病毒(miR-133a-AAV)组。通过冠脉灌注法将miR-133a-AAV转染至SHR大鼠的心脏,监测大鼠的尾动脉压,Masson染色观察心肌胶原沉积情况,real-time PCR检测心肌组织中miR-133a的表达水平,免疫组化法和Western blot法检测心肌组织中转化生长因子-β1(TGF-β1)和结缔组织生长因子(CTGF)的蛋白表达水平。结果:与WKY大鼠相比,SHR的尾动脉压明显升高,心肌组织中miR133a表达水平降低,TGF-β1和CTGF蛋白表达水平升高,出现心肌纤维化;上调SHR心肌miR-133a的表达水平后,心肌纤维化程度明显减轻,TGF-β1和CTGF蛋白表达水平降低。结论:上调心肌组织中miR-133a的表达水平,对高血压导致的大鼠心肌纤维化有改善作用,其机制可能与抑制心肌组织中TGF-β1和CTGF蛋白表达有关。     

钩藤碱对自发性高血压大鼠心室重构过程中TGF-β_1/Smad通路的影响

目的:观察钩藤碱对自发性高血压大鼠血压、心肌肥厚及心肌纤维化的影响并探讨其可能的作用机制。方法:32只自发性高血压大鼠随机分为模型组、钩藤碱高(10 mg·kg-1·d-1)、低(2.5 mg·kg-1·d-1)剂量组、卡托普利组(17.5 mg·kg-1·d-1),每组8只。另设8只Wistar-Kyoto大鼠作为正常对照组。分别于给药前和给药后每2周测量尾动脉收缩压(SBP)。治疗10周后处死大鼠,取其心脏计算全心重量指数和左心室重量指数;检测心肌中羟脯氨酸(HYP)及血浆中血管紧张素Ⅱ(AngⅡ)的含量;HE染色观察心肌病理学变化,Masson染色观察心肌胶原纤维变化;免疫组化法和Western blot法测心肌组织转化生长因子-β1(TGF-β1)和Smad3蛋白的表达。结果:与模型组相比,钩藤碱能明显降低自发性高血压大鼠的血压(P0.05),降低心肌HYP含量及血浆AngⅡ的含量(P0.05),减轻心肌组织的病理损伤和胶原纤维沉积,下调TGF-β1和Smad3蛋白的表达(P0.01)。结论:钩藤碱能降低自发性高血压大鼠的血压、调节改善自发性高血压大鼠的心室重构,其机制可能与其影响TGF-β1/Smad通路以及降低AngⅡ含量有关。     

柳胺苄心定对急性心肌梗塞家兔心肌血流量梗死范围及左室功能的影响

本文观察了兼有α_1受体阻断作用的β受体阻断剂柳胺苄心定(labetalol,简称Lab)对急性心肌梗塞家兔心肌血流量(放射性微球法),梗死范围及左室功能的影响,并与心得安比较。结果表明:小剂量Lab(1mg/kg)主要显示β受体阻断效应,它能减慢心率,降低心肌耗氧量,降低非梗死区心肌血流量,缩小梗死范围,其效应与心得安相似,且能改善左室舒缩功能;大剂量Lab(5mg/kg),能同时阻断α_1和β受体,它能降低动脉血压,相对增加各区心肌血流量,显著减少心肌耗氧量,缩小梗死范围。结果提示:在急性心肌梗塞治疗中,同时阻断α_1和β受体较单纯阻断β受体优越。     

High fat/sucrose feeding attenuates the hypertension of spontaneously hypertensive rats

To assess the caloric and cardiovascular effects of dietary obesity on an important animal model of hypertension research, 60-day-old male spontaneously hypertensive (SHR) rats were fed either Agway pelleted chow (Pellet), a diet enriched in fat and sucrose (HF/M), or alternated (Cycled) between 2-week periods of HF/M diet and Agway pelleted chow. After 14 weeks, HF/M feeding elevated the body weight of SHR rats by 15% over the body weight of pellet-fed control rats. This relative obesity was accompanied by heavier white (retroperitoneal) and brown (interscapular) fat pads, heavier heart weights, and tachycardia. Paradoxically, the systolic blood pressure levels of SHR rats fed the HF/M diet were reduced. Ruled out as an explanation for the blood pressure reduction was the relative polyunsaturated to saturated fat (P/S) rati of the diet. The hypertension of SHR rats may be due in part to the effects of an underlying metabolic problem that is counteracted by the effects of HF/M feeding; HF/M feeding not only elevated body weight but also reversed the hypoinsulinemia found in pellet-fed SHR rats. The Cycled group evidenced large up-and-down swings in caloric intake that coincided with HF/M and Pellet feeding; this produced modest staircase-like changes in body weight gain. Similar to the HF/M group, the systolic blood pressure level of the Cycled group was also reduced in comparison to the blood pressure level of the Pellet group. However, the Cycled group was found to be more responsive to the pressor effects of intravenous phenylephrine, an alpha-adrenergic agonist.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prolonged protective effects following propranolol withdrawal against isoproterenol-induced myocardial infarction in normotensive and hypertensive rats

Young adult, male and female, normotensive Sprague-Dawley (S-D) and spontaneously hypertensive rats (SHR) were injected with propranolol three times daily for 3 weeks. None of the animals manifested signs of withdrawal when the injections were terminated. Seven days later, the animals were challenged with a dose of isoproterenol which would produce massive myocardial infarction and 50-60% mortality in non-treated animals. The propranolol pretreatment caused marked tranquilizing and blood pressure lowering effects in SHR exclusively. Despite the 7-day propranolol withdrawal period, very few animals died and myocardial damage was minimal. However, blood pressure levels dropped to shock-like levels, blood CPK and LDH levels showed dynamic increases, there was marked hypertriglyceridaemia, and plasma corticosterone rose to supranormal levels. Microscopically, the hearts of the propranolol pretreated animals showed little evidence of necrosis but the SHR hearts manifested large atrial and ventricular thrombi. It is suggested that in the rat, propranolol treatment causes positive myocardial protective effects mediated through hormonal and metabolic changes and propranolol withdrawal does not lead to hypersensitivity to catecholamines. In fact, the beta-blocking effects of propranolol remain effective for some time after withdrawal.     

Prolonged protective effects following propranolol withdrawal against isoproterenol-induced myocardial infarction in normotensive and hypertensive rats.

Young adult, male and female, normotensive Sprague-Dawley (S-D) and spontaneously hypertensive rats (SHR) were injected with propranolol three times daily for 3 weeks. None of the animals manifested signs of withdrawal when the injections were terminated. Seven days later, the animals were challenged with a dose of isoproterenol which would produce massive myocardial infarction and 50-60% mortality in non-treated animals. The propranolol pretreatment caused marked tranquilizing and blood pressure lowering effects in SHR exclusively. Despite the 7-day propranolol withdrawal period, very few animals died and myocardial damage was minimal. However, blood pressure levels dropped to shock-like levels, blood CPK and LDH levels showed dynamic increases, there was marked hypertriglyceridaemia, and plasma corticosterone rose to supranormal levels. Microscopically, the hearts of the propranolol pretreated animals showed little evidence of necrosis but the SHR hearts manifested large atrial and ventricular thrombi. It is suggested that in the rat, propranolol treatment causes positive myocardial protective effects mediated through hormonal and metabolic changes and propranolol withdrawal does not lead to hypersensitivity to catecholamines. In fact, the beta-blocking effects of propranolol remain effective for some time after withdrawal.     

体外反搏对心肌缺血犬血流动力学的影响及内皮素机制的探讨

目的：探讨体外反搏改善心肌缺血犬血流动力学的作用和内皮素机制。 方法： 19只健康杂种犬随机分为对照组、缺血组和反搏组，分别于冠状动脉左前降支结扎前和结扎后60 min、120 min、180 min记录以下指标：①主动脉根部血压；②左心室收缩和舒张末压、+dp/dtmax和-dp/dtmax；③头臂干血流量；④放免法检测血浆和心肌内皮素-1（ET-1）的含量。 结果： 冠脉结扎1 h，缺血组和反搏组犬血压、左心室收缩和舒张功能、头臂干血流量明显低于正常组（P<0.05），而血浆ET-1水平明显高于正常组（P<0.05）。经过体外反搏2 h，反搏组犬的收缩压、舒张压和平均压、左心室收缩和舒张功能、头臂干血流量明显高于缺血组（P<0.05）；而反搏组犬的血浆和心肌ET-1水平明显低于缺血组（P<0.05）。 结论： 体外反搏可改善心肌缺血犬血流动力学指标，其机制可能与降低ET-1的产生有关。     

高血压合并糖尿病大鼠心肌毛细血管周细胞的观察

目的:本研究利用免疫组织化学方法和电镜观察高血压、糖尿病和高血压合并糖尿病对心肌毛细血管周细胞的影响,探讨周细胞在高血压合并糖尿病并发心肌微血管病时的作用。方法:SD大鼠和自发性高血压大鼠(SHR)分别腹腔注射链脲佐菌素结合高能量饲料喂养,复制糖尿病和SHR合并糖尿病模型。动物分为4组:正常SD大鼠组(SD组)、自发性高血压大鼠组(SHR组)、糖尿病组(DM组)与SHR合并DM大鼠组(SHDM组)。16周后透射电镜观察心肌毛细血管周细胞超微结构,α-SMA免疫组织化学染色测定周细胞数量。结果:电镜下,SHR、DM和SHDM组心肌毛细血管周细胞多见,大小不一,胞浆富含细胞器及肌丝,与内皮细胞联系松散。免疫组化结果表明SHR、DM和SHDM组大鼠心肌毛细血管周细胞数均较SD组大鼠显著增多,SHDM组(11.8±3.6)个/视野较SHR组(3.9±1.1)个/视野增多非常显著(P<0.01),但与DM组(10.2±3.3)个/视野比较无显著差异(P>0.05)。结论:高血压合并糖尿病时周细胞表型发生改变,且数量增多,这些变化可能在心肌毛细血管肌化及毛细血管旁纤维化中起重要作用。     

Social stress, myocardial damage and arrhythmias in rats with cardiac hypertrophy.

In rat models of cardiac hypertrophy (moderate aortic coarctation: ACm, n=18; severe aortic coarctation: ACs, n=27; aging: OLD, n=25; spontaneous chronic hypertension: SHR, n=18) and properly matched control animals (C(ACm), n=17; C(ACs), n=19; C(OLD), n=24; C(SHR), n=22), we investigated the relative contribution of intense autonomic activity and cardiac structural damage to ventricular arrhythmogenesis. We used an "in vivo" to tissue level approach, by correlating in the same animal: (i) social stress-induced ventricular arrhythmias, telemetrically recorded, and (ii) left ventricular weights (LVW) and amount and geometrical properties of myocardial fibrosis (MF). Arterial blood pressure was significantly higher in ACm (+11%), ACs (+28%) and SHR (+34%) than in controls. LVW were approximately 20% greater in ACm, ACs and OLD and 50% greater in SHR. MF was about twice as great and characterized by more frequent occurrence of microscopic scarring in ACm and ACs, and eight times greater and associated with both a higher number and a larger size of fibrotic foci in OLD and SHR compared to controls. Social stress increased ventricular arrhythmia vulnerability in all models of cardiac hypertrophy, as well as in controls. The arrhythmogenic action of stress was facilitated in ACs, OLD and SHR. A correlation between structural cardiac remodeling and ventricular arrhythmias was found only in SHR and OLD, which exhibited the greatest increase in LVW and/or MF. Social stress proved to be a valuable tool for analyzing the combined effects of autonomic stimulation and altered myocardial substrate on the genesis of potentially life-threatening arrhythmias in social animals.     

自发性高血压大鼠心肌组织microRNA-133a与TGF-β1蛋白表达的改变及意义

 目的：观察microRNA-133a（miR-133a）与转化生长因子-β1（transforming growth factor β1,TGF-β1）蛋白在自发性高血压大鼠（spontaneously hypertensive rats,SHR）心肌组织中的表达改变和关系。方法：取12只18周龄雄性自发性高血压大鼠为SHR组,12只18周龄雄性Wistar-Kyoto （WKY）大鼠为对照组,通过无创血压测量分析系统测大鼠尾动脉血压,Masson染色检测心肌胶原容积分数（collagen volume fraction,CVF）和血管周围胶原面积比率（perivascular collagen area ratio, PVCA）,实时荧光定量PCR检测miR-133a表达水平,免疫组化和Western blotting法检测心肌TGF-β1蛋白表达。结果：与对照组比较,SHR组的收缩压和舒张压明显升高（P<0.01）,心肌CVF和PVCA明显升高（P<0.01）,TGF-β1蛋白表达水平明显升高（P＜0.01）,miR-133a表达水平明显降低（P<0.01）,SHR组心肌miR-133a表达水平为对照组的（23.9±4.6）%;SHR组心肌组织miR-133a与TGF-β1蛋白表达水平呈负相关（r=-0.791, P<0.01）。结论：SHR心肌组织miR-133a表达下调,伴随TGF-β1蛋白表达升高和胶原合成增加。miR-133a与TGF-β1可能参与SHR大鼠的心肌纤维化。     

氯沙坦逆转高血压大鼠心肌重塑的实验研究

目的探讨氯沙坦对自发性高血压大鼠(SHR)心肌重塑的影响。方法16周龄雄性SHR20只,随机分为氯沙坦治疗组和SHR对照组。同龄雄性WKY鼠10只作为正常对照组。给予氯沙坦每天30mg/kg溶于饮水灌胃治疗17周。测定动脉收缩压、左心室壁的厚度、左心室重量与体重之比(LVW/BW)。透射电镜评估左心室肥厚(LVH)的程度。用真彩色图像分析系统计算左心室胶原容积分数。结果氯沙坦治疗组血压、LVW/BW、左室壁厚度与SHR对照组相比明显降低,但与WKY相比有所升高。透射电镜下氯沙坦治疗组心肌的超微结构与WKY相似,SHR的结构有异常改变。与SHR对照组相比,氯沙坦治疗组左心室胶原容积分数下降。结论氯沙坦能有效地降低SHR的血压、逆转高血压左室重塑。     

Myocardial infarction in spontaneously hypertensive rats with superimposed adrenal-regeneration hypertension.

The elevated blood pressure of spontaneously hypertensive rats (SHR) was further exacerbated by subjecting these animals to surgically induced adrenal-regeneration hypertension (ARH). When chronic abnormally high blood pressure had been in effect for 12 weeks, the animals were subjected to an acute and massive myocardial infarction with isoprenaline. Hypertensive but intact SHR survived better than ARH-treated animals. Circulating enzyme (CPK, SGOT, SGPT and LDH), lipid and glucose levels and BUN manifested much greater excursions commensurate with more extensive myocardial infarction in ARH-treated than in intact SHR. ARH-treated SHR displayed a high incidence of atrial and ventricular thrombi associated with frequent left ventricular aneurysm formation. It is suggested that the more extensive myocardial connective tissue and ground-substance degeneration in ARH-treated SHR is due to the impoverished steroidogenic capacity of their regenerated adrenal glands.     

缓激肽在依那普利对心肌梗死大鼠心肌肥厚及心功能影响中的作用

目的:探讨依那普利(enalapril)对大鼠心肌梗塞(M1)后心肌肥厚及心功能的影响是否与其抑制缓激肽(BK)降解的途径有关。方法:将大鼠随机分为:①假手术对照组(sham-operated control),②心肌梗死组(MI),③依那普利干预组(MI+enalapril),④依那普利和BKB₂受体阻断剂Hoe-140共同干预组(MI+enalapril+Hoe-140),⑤血管紧张素ⅡⅠ型受体阻断剂losartan干预组(Ml+losartan)。3个药物干预组从MI术后第3d开始给药,持续4周,然后测定左心室舒张末压(LVEDP)、+dp/dt_max及左心室重/体重(LVW/BW)、左心室非梗死区组织的平均(每核)心肌细胞体积,并进行组间比较。结果:3个药物干预组的LVEDP、LVW/BW及V(m)n均低于MI组(均Pp/dt_max和MI组相比无显著差别。3个药物干预组之间平均动脉压(MAP)无明显差异,但Ml+enalapril+Hoe-140组的LVW/BW及V(m)n的值却高于MI+enalapril组。结论:Enalapril可阻抑大鼠MI后的心肌肥厚并改善左心室功能,这种作用的部分机制是由于其促使了心肌组织BK的积累,即BK参与了enalapril阻抑心肌肥厚及改善心功能的作用,且这些作用不依赖于血压的影响。     

Renal and cardiovascular effects of atrial natriuretic peptide in Wistar-Kyoto and spontaneously hypertensive rats during a chronic salt loading

Spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were maintained on tap water or 1.5% NaCl for 3 weeks. During the high sodium regime 24-h urinary sodium excretion increased 10-fold and the basal blood pressure increased in the SHR. After 3 weeks the rats received arterial (carotid artery), venous and bladder catheters (suprapubic). Saline was infused continuously and in conscious rats atrial natriuretic peptide (alpha-hANP) was administered as bolus injections (8 and 16 nmol kg-1) and the blood pressure and heart rate and the urinary excretions of sodium, potassium (flame photometry), noradrenaline and dopamine (HPLC) were followed at 5-min intervals. The administration of ANP caused a short-lasting blood pressure reduction, tachycardia, diuresis and increased urinary excretions of sodium, potassium, noradrenaline and dopamine. The blood pressure responses to ANP did not differ between the rat strains, irrespective of the diet. The natriuresis and diuresis to ANP was reduced in animals on a high sodium diet, especially in the SHR. This may be interpreted as a down-regulation of target organ responsiveness to ANP during a high sodium diet and the inappropriately large decrease in the responsiveness that was observed in the SHR may be related to increase in blood pressure during the high sodium diet.     

Functional and stereologic estimations of myocardial capillary exchange capacity in treated and untreated spontaneously hypertensive rats.

Myocardial capillary exchange capacity was investigated by stereologic and functional techniques in parallel during pressure-overload cardiac hypertrophy and after long-term antihypertensive therapy with the vasodilator felodipine. In 26-week-old female spontaneously hypertensive rats (SHR) blood pressure increased by 25% and left ventricular weight (LVW/BW) increased by 18% compared to Wistar-Kyoto rats (WKY). Myocardial capillary surface and volume densities normalized for organ weight were similar in both ventricles for both strains. Moreover, capillary surface density was higher sub-epicardially (EPI) than in the subendocardium (ENDO) in the left ventricle of SHR. Thirteen weeks of felodipine-therapy (SHR-Felo) normalized blood pressure without affecting LVW/BW although a transition from concentric to eccentric hypertrophy is known to occur. Myocardial capillary surface and volume densities and the left ventricular ENDO-EPI-gradient in surface density were similar to untreated SHR. However, felodipine-treatment increased right ventricular weight and capillary volume density. Functional capillary exchange was estimated in terms of permeability surface area products (PS) for Cr-EDTA and vitamin B12 and normalized for organ weight. PSCr-EDTA, PSB12 and the ratio PSCr-EDTA/PSB12 (an index of capillary permeability) were similar in SHR and WKY. Furthermore, the relation between functional and stereological indices of exchange capacity was investigated in a multiple linear regression analysis. However, no significant correlation between PS and neither capillary surface nor volume density was found. In conclusion, myocardial capillary exchange capacity was well adapted to the pressure overload cardiac hypertrophy present in female SHR. Despite induction of right ventricular hypertrophy, felodipine-treatment did not affect capillary exchange capacity. Furthermore, when functional and stereologic estimates were performed in parallel, the importance of dynamic factors for myocardial capillary exchange capacity (e.g. heterogeneity) was illustrated.     

Myocardial vasoactive intestinal peptide and fibrosis induced by nitric oxide synthase inhibition in the rat

AIMS: In both normotensive and hypertensive rats, the degree of myocardial fibrosis is inversely correlated with the concentration of vasoactive intestinal peptide (VIP) in the myocardium. Treatment with nitric oxide (NO) synthase inhibitors also causes myocardial fibrosis. In this study, we sought to determine whether the myocardial fibrosis induced by treatment with the NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) was also associated with depletion of VIP in the myocardium. METHODS: Male Wistar Kyoto (WKY) and spontaneous hypertensive rats (SHR) rats treated with l-NAME were randomized to low, intermediate or high salt content diets. After 4 weeks, the hearts were harvested, the degree of fibrosis quantified and VIP concentration measured. RESULTS: In WKY, systolic blood pressure increased with increasing dietary sodium (P < 0.05). Myocardial fibrosis also increased with increasing dietary sodium (P < 0.005). Myocardial VIP concentration decreased with increasing dietary sodium (P < 0.025). In contrast, in the SHR treated with l-NAME, systolic blood pressure increased but the increase was not affected by sodium intake. Further, myocardial fibrosis and myocardial VIP were unchanged by increased dietary sodium. Higher doses of l-NAME in the SHR did not increase the systolic blood pressure, increase the degree of myocardial fibrosis or decrease the myocardial concentration of VIP. These differences in myocardial VIP concentration may reflect differing effects of l-NAME on VIP metabolism, as l-NAME increased VIP metabolism in the WKY (P < 0.05) but did not change VIP metabolism in the SHR. CONCLUSIONS: We conclude that depletion of VIP in the myocardium is associated with increasing myocardial fibrosis in l-NAME treated WKY. As VIP depletion occurs in other models of myocardial fibrosis, it appears to be a common mechanism. Myocardial VIP depletion may therefore be a new and important factor in the pathogenesis of cardiac fibrosis.