Chronic colchicine administration attenuates cardiac hypertrophy in spontaneously hypertensive rats.

To determine whether the long-term inhibition of microtubule integrity in vivo by colchicine could attenuate the development of cardiac hypertrophy, we studied five groups of rats: Wistar-Kyoto rats receiving saline for 4 weeks (WKYsaline); WKY receiving colchicine, which depolymerizes microtubules (WKYcolchicine); spontaneously hypertensive rats receiving saline (SHRsaline); SHRs receiving colchicine (SHRcolchicine); and SHRs receiving lumicolchicine, an inactive stereoisomer of colchicine (SHRlumicolchicine). Seven-week-old animals were administered drugs or control substances via alternate day intraperitoneal injection for a period of 4 weeks. Dosage was gradually increased from 0.6 to 1.0 mg/kg to avoid drug toxicity. Depolymerization of myocardial microtubules by the in vivo administration of colchicine into the rats was confirmed by both Western blot analysis and immunofluorescence of tubulin protein in the hearts. Body weight (BW) was lower, while systolic blood pressure was significantly elevated in SHRs vs the WKY rats. No significant difference was found in either of these parameters between the control or treatment groups of each strain. Left ventricular (LV) weight-to-BW ratio was elevated and showed significant increases in the SHRs as compared to WKY animals, indicative of cardiac hypertrophy. When the SHRs were treated with colchicine but not vehicle or lumicolchicine, LV/BW was similar to the WKY. Changes of myocyte cross-sectional area determined using LV mid-free wall specimens were concordant with the LV/BW data. No significant changes were found in collagen volume fraction between groups. Thus the inhibition of microtubule polymerization abolished the progression of cardiac myocyte hypertrophy in SHRs independently of blood pressure.     

Cardiac hypertrophy in spontaneously hypertensive rats.

The energy metabolism of cardiac hypertrophy in spontaneously hypertensive rats (SHR) was studied chronologically by histochemical and in part chemical methods. The activities of various enzymes, such as glucose-6-phosphate dehydrogenase (G6PDH), lactate dehydrogenase (LDH), isocitrate dehydrogenase, succinate dehydrogenase, beta-hydroxybutylate dehydrogenase (beta-HBDH) and monoamine oxidase (MAO) in the cardiac muscle were determined histochemically. beta-HBDH activity was greatly increased in the stage of developing hypertension in SHR. LDH activity increased simultaneously with the rise of beta-HBDH activity. Moreover, MAO activity increased markedly in later stages when the blood pressure was already elevated in SHR. To confirm the histochemical findings of beta-HBDH activity, the mitochondrial fraction of cardiac muscle was subjected to chemical assay. The chemical findings of myocardial beta-HBDH in SHR corresponded well with the histochemical findings. The myocardial beta-HBDH activity in SHR increased markedly at the age of 5 to 9 weeks, while no or minimal activity was found in controls of the same age. No significant difference of beta-HBDH activity was observed between SHR and controls in the mitochondrial fraction from the diaphragm and liver. The increase of beta-HBDH activity in the cardiac muscle of SHR prior to the development of cardiac hypertrophy suggests that the metabolism of ketone bodies may play an important role in providing the energy necessary for the development of cardiac hypertrophy in SHR.     

Effects of antihypertensive therapy on cardiac sodium/hydrogen ion exchanger activity and hypertrophy in spontaneously hypertensive rats

BACKGROUND: Sodium/hydrogen ion exchange is hyperactive in hypertension. Myocardial sodium/hydrogen ion exchange hyperactivity accompanies the regression of cardiac hypertrophy in spontaneously hypertensive rats (SHR) after long term control of blood pressure with enalapril. Objectives: To explore whether this effect is shared by other antihypertensive agents or is specific to angiotensin-converting enzyme inhibition. ANIMALS AND METHODS: SHR and normotensive Wistar Kyoto (WKY) rats were treated for five weeks with enalapril (20 mg/kg/day), nifedipine (10 mg/kg/day) or losartan (40 mg/kg/day). Sodium/hydrogen ion exchange activity was estimated in terms of both steady intracellular pH in HEPES buffer and the rate of intracellular pH recovery from intracellular acid loads in isolated superfused 2'-7'-bis(2-carboxyethyl)-5,-(and-6)-carboxyfluorescein, acetoxymethyl ester form-loaded papillary muscles. RESULTS: Enalapril, nifedipine and losartan decreased systolic blood pressure in SHR to about the same value (140 3, 140 2 and 146 3 mmHg, respectively, at the end the treatment). However, the index of cardiac hypertrophy (heart weight to body weight ratio) was decreased to a smaller value with losartan than with nifedipine or enalapril (2.66 0.09, 3.06 0.05 and 2.86 0.04 mg/g respectively; P<0.05 ANOVA). For the untreated SHR, the index of cardiac hypertrophy was 3.30 0.04 mg/g. Myocardial sodium/hydrogen ion exchange hyperactivity in SHR was normalized by all treatments. CONCLUSIONS: The three treatments regressed cardiac hypertrophy and normalized sodium/hydrogen ion exchange exchange activity in SHR, and losartan was the most effective treatment for reversing cardiac hypertrophy, despite producing effects on blood pressure and sodium/hydrogen exchange activity similar to that of other antihypertensive drugs.     

Tyrosine hydroxylase antisense gene therapy causes hypotensive effects in the spontaneously hypertensive rats

We investigated the effect of antisense oligodeoxynucleotides (AS ODN) against tyrosine hydroxylase (TH) on hypertension and sympathetic nervous system activity in spontaneously hypertensive rats (SHR). Systolic blood pressure (SBP) in SHR treated with TH AS ODN (50, 200 microg/rat, i.v.) was significantly lower than that of control SHR. Epinephrine and norepinephrine levels, TH activity, and TH protein levels in the adrenal medulla of SHR were reduced concomitant with TH AS ODN treatment-induced changes in SBP. In contrast, TH AS ODN (200 microg/rat) had no effect on SBP in Wistar-Kyoto rats (WKY), despite significantly decreased catecholamine levels, TH activity, and TH protein levels. These findings suggest that peripheral systemic injection of TH AS ODN may be effective as hypotensive therapy in SHR.     

Collagen synthesis in development and reversal of cardiac hypertrophy in spontaneously hypertensive rats.

An alteration in the rate of collagen synthesis was observed in spontaneously hypertensive rats during evolution of hypertension. An increase in rate of synthesis of collagen and a parallel increase in collagen content were observed in 4–8 week and 24 week old hypertensive rats. In the 4 week old rats, blood pressure was normal or nearly normal, whereas in the 24 week old rats the arterial pressure was significantly elevated. Use of some antihypertensive drugs, namely, α-methyldopa, converting enzyme inhibitor and a combination of reserpine, hydrochlorothiazide and apresoline, prevented hypertension and the late increase in collagen synthesis that was observed in the 24 week old hypertensive rats. In these rats, prevention of hypertension also reversed myocardial hypertrophy and reduced collagen content of the myocardium. The alteration of myocardial collagen synthesis in spontaneously hypertensive rats is a complex process in which at least two phases can be observed. In the young rats, in which blood pressure is normal, the stimulus to increase in collagen may be a humoral factor or a hemodynamic alteration such as hyperkinetic circulation or it may be a genetic factor. In the older hypertensive rats hypertension seemed more important in altering collagen synthesis because antihypertensive therapy inhibited the rate of collagen synthesis and protected the heart from excess accumulation of collagen.     

Prevention of nephrosclerosis and cardiac hypertrophy by captopril treatment of spontaneously hypertensive rats

The relationship between hypertension and cardiovascular damage was assessed in three groups of spontaneously hypertensive rats (SHR): 1. stroke prone SHR (SHR-SP) treated orally with an angiotensin I converting enzyme inhibitor (captopril) (100-400 mg/L in the drinking water) from 6 to 35 weeks of age, 2. SHR-SP maintained on tap water until 30 weeks of age, 3. stroke resistant SHR (SHR-SR) maintained on tap water. The controls were Wister Kyoto rats (WKY) maintained on tap water. Captopril-treated SHR-SP showed blood pressure lower than that of untreated SHR-SP, similar to SHR-SR. The ratio of heart weight to body weight was 0.55% in SHR-SP, 0.39% in captopril-treated SHR-SP, 0.46% in SHR-SR, and 0.39% in WKY. The kidneys of SHR-SP showed glomerular sclerosis, glomerular fibrosis, tubular casts, interstitial cell infiltration and vascular wall thickening or hyperplasia of the small arteries and arterioles. The severe glomerular sclerosis was mostly distributed in the inner and middle portions of cortex. Immunohistological study showed IgG, C3 and fibrinogen in the glomeruli and arterioles in SHR-SP. In captopril-treated SHR-SP, similar to SHR-SR, only minor histological changes were seen and there was no deposition of IgG, C3 or fibrinogen. No changes were seen in WKY. Thus, it was concluded that nephrosclerosis and cardiac hypertrophy in SHR-SP are prevented by captopril. The role of the renin-angiotensin and kallikrein-kinin systems in organ pathogenesis in SHR-SP is discussed.     

Effect of sodium deprivation on cardiac hypertrophy in spontaneously hypertensive rats: influence of aging.

Sodium has been identified as a causal factor in the development of hypertension in experimental animal models as well as in clinical human subjects. Sodium is also known to play a role in modulating myocardial mass and its pattern of myosin isozyme distribution. In the rodent model, the accumulation of V3 myosin isozyme (MI), due to the modulating influence of sodium, has been shown to be associated with persistent cardiac hypertrophy and heart failure. In this paper, we have examined the effect of the restriction of dietary sodium on blood pressure, ventricular weight and myosin isoforms in spontaneously hypertensive rats (SHR) and the relationship of these parameters with age. In 10- to 11-week-old SHR, dietary sodium restriction for 14 weeks resulted in a significant reduction in ventricular mass associated with systolic shifting of myosin isoform from V3 type to V1 type with no change in systolic blood pressure level; dietary sodium restriction also showed a significant reduction in body weight. When the effect of dietary sodium restriction (for 8 weeks) was studied in relation to age (in 11-, 16- and 24-week-old rats) a significant shift in myosin isoform from the V3 to the V1 type was noted in the 11-week-old rats; a slight but significant shift was noted in 16-week-old rats, and no change in myosin isoform distribution was noted in the 24-week-old SHR. The alteration in myosin isoform and myocardial mass in the 11- and 16-week-old rats was independent of changes in systolic blood pressure. This study demonstrates that sodium plays an important role not only in modulating myocardial mass but also in changing the biochemical composition of the heart. This study also suggests that in genetic hypertension, the restriction of sodium at a very young age may fully prevent the development of hypertension and hypertrophy. However, the mechanism by which the sodium ion modulates myocardial mass and the expression of either V1 or V3 myosin genes is unknown; the question of how sodium affects the cardiac function also remains. Some evidence suggests that sympathetic outflow may play an important role, but further studies are needed to validate this.     

Biochemical changes associated with development and reversal of cardiac hypertrophy in spontaneously hypertensive rats.

This study is the first report describing the sequence of biochemical alterations of myocardium during the progression of naturally occurring hypertrophy in spontaneously hypertensive rats (SHRs) and then with its reversal by alpha-methyldopa therapy. Changes in DNA, RNA, hydroxyproline, as well as incorporation of 14C lysine into cardiac myosin, were compared with the pattern found in suitably matched controls. A significant increase in RNA, hydroxyproline, and 14C incorporation was observed in SHRs. Antihypertensive treatment caused reversal of hypertrophy and normalization of all biochemical parameters except hydroxyproline, the concentration of which increased significantly as myocardial weight decreased. These compositional changes may help explain the conflicting result of the haemodynamic effects of cardiac hypertrophy.     

Vectorcardiographic study on left ventricular hypertrophy in spontaneously hypertensive rats.

To observe cardiac changes in spontaneously hypertensive rats (SHR) functionally, the vectrocardiographic approach was tried, applying the Takayasu lead system to rats. This vectrocardiogram (VCG) was shown to be sufficiently good to detect left ventricular hypertrophy (LVH) in SHR. VCG in SHR showed specific features, some of which were left upward deviation of the maximum QRS vector in the frontal plane, an increased magnitude of the maximum spatial QRS vector, and prolongations of such indices as the QRS duration, time to the maximum spatial QRS vector and QT interval with abnormal ST-T changes. The P wave of SHR in the X scalar electrocardiogram, lower and wider than that of Wistar-Kyoto rats may also be a significant feature of LVH in SHR. The angle of the maximum QRS vector in the horizontal plane was not proven to be a suitable index of LVH in SHR. Most of the histometrical findings were closely correlated to blood pressure. Some of the vectrocardiographic findings were significantly correlated both to blood pressure and to some of the characteristic findings of LVH, such as the weights of the heart and the left ventricle and so forth. This experiment also indicated that LVH in SHR was not limited only to quantitative myocardial hypertrophy. It also seemed to be related to reversible or irreversible qualitative changes of coronary arteries or myocardium, such as myocardial fibrosis. This vectrocardiographic method was shown to be useful in obtaining various information about the cardiovascular system in rats, especially in SHR, and it seemed to be helpful for further understanding hypertensive cardiac diseases in humans.     

血脂康胶囊对自发性高血压大鼠心肌肥厚的早期干预研究

目的研究血脂康胶囊对幼年自发性高血压大鼠（spontaneous hypertensive rat, SHR）心肌肥厚的影响。方法24只6周龄雄性SHR分为低剂量血脂康胶囊组（A组,n=8）、高剂量血脂康胶囊组（B组,n=8）和安慰剂组（C组,n=8）,另设WKY（Wistar—kyoto rats）组（W组,n=8）。A组和B组分别以血脂康胶囊20mg·kg^-1·d^-1和200mg·kg^-1·d^-1 0．9％氯化钠溶液溶解后灌胃;C组和W组以等容积0．9％氯化钠溶液灌胃,连续8周。腹主动脉采血,用酶联免疫吸附测定方法测定血浆一氧化氮（NO）和氧化低密度脂蛋白（oxidized low-density lipoprotein, ox-LDL）浓度;超声心动图测定室间隔舒张期厚度（interventricular septal thickness, IVSd）和左心室后壁舒张期厚度（left ventricular posterior wall thickness, LVPWd）;取心肌标本,称取左心室质量,计算左心室质量指数（left ventricular mass index, LVMI）,制备心肌组织石蜡切片,苏木精一伊红染色,观察心肌细胞直径和心肌细胞面积。结果与W组比较,C组血浆一氧化氮浓度降低,ox-LDL浓度升高,LVMI、IVSd、LYPWd、心肌细胞直径和心肌细胞面积均增加,差异有统计学意义（P〈0．05）;与C组比较,B组上述指标明显改善,差异有统计学意义（P〈0．05）;而A组仅血浆一氧化氮和ox—LDL浓度改善。结论自发性高血压大鼠发生心肌肥厚,血脂康胶囊早期干预可改善SHR心肌肥厚。     

Chronic imidazoline receptor activation in spontaneously hypertensive rats

BACKGROUND: Acute intravenous administration of moxonidine, an imidazoline I1-receptor agonist, reduces blood pressure (BP) in normotensive and hypertensive rats, induces diuresis and natriuresis, and stimulates plasma atrial natriuretic peptide (ANP). In these studies we investigated the involvement of natriuretic peptides (ANP and brain natriuretic peptide) in the effects of chronic activation of imidazoline receptors. METHODS: Spontaneously hypertensive rats (SHR; 12 to 14 weeks old) received 7-day moxonidine treatment at various doses (10, 20, 60, and 120 microg/kg/h) via subcutaneously implanted osmotic minipumps. RESULTS: Hemodynamic parameters (continuously monitored by telemetry) revealed that, compared with saline-treated rats, moxonidine dose-dependently decreased blood pressures (BPs). Maximal blood pressure lowering effect was achieved by day 4 of treatment, at which point 60 microg/kg/h reduced mean arterial pressure (MAP) by 14.5 +/- 6.8 mm Hg as compared with basal levels. The decrease in MAP was influenced by a drop in both diastolic and systolic pressures. Moxonidine treatment did not alter daily urinary sodium and potassium excretions, but 120 microg/kg/h moxonidine decreased urine volume after 2 days and increased cyclic guanosine 3'5'monophosphate excretion on days 4 to 7 of treatment. Chronic moxonidine treatment dose-dependently increased plasma ANP to reach, at 120 microg/kg/h, a 40% increase (P < .01) above that of corresponding saline-treated SHR, with a concomitant increase in left and right atrial ANP mRNA (more than twofold). Plasma BNP increased by 120 microg/kg/h moxonidine (11.0 +/- 1.1 v 16.5 +/- 1.9 pg/mL, P < .002) without significant increases in atrial and ventricular BNP mRNA. CONCLUSIONS: ANP and BNP may be involved in the antihypertensive effect of chronic moxonidine treatment. Accordingly, natriuretic peptides may contribute to the sympatholytic and cardioprotective effects of chronic activation of imidazoline I1-receptors.     

Non-corresponding effects of an angiotensin-converting enzyme inhibitor on cardiac and vascular hypertrophy in spontaneously hypertensive rats.

Angiotensin-converting enzyme inhibitors (ACEIs) may have different effects on cardiac hypertrophy than on vascular hypertrophy. Arginine vasopressin (AVP) may promote cardiac hypertrophy. Our aims were (1) to simultaneously examine the chronic effects of ACEIs on hypertrophy of the heart and hypertrophy of the coronary and renal interlobular arteries, and (2) to clarify the relation between AVP concentration (AVPC) and cardiac hypertrophy. ACEI (delapril: 30 mg/kg/day) or vehicle (5% arabic gum) was administered in a preventive (4 to 28 weeks of age) or a therapeutic (12-24 weeks of age) protocol in spontaneously hypertensive rats. In both protocols, delapril produced a slight but significant decrease in systolic blood pressure. In the therapeutic protocol, the weight of the left ventricle (mean+/-SE) was lower (p<0.05) in the ACEI group (64+/-2 mg/100 g body weight) than in the control group (69+/-1 mg/100 g body weight). Plasma renin activity was significantly higher in the ACEI group than in the control group in both the preventive (p <0.01) and therapeutic (p<0.01) protocols. In the therapeutic protocol, AVPC was significantly (p<0.05) lower in the ACEI group than in the control group. AVPC was significantly (p=0.02, r=0.46) correlated with the weight of the left ventricle in the therapeutic protocol. For both protocols, no differences were noted between the ACEI and control groups in the vascular hypertrophy of the coronary and renal interlobular arteries. We conclude that (1) the preventive or therapeutic effect of ACEIs on hypertrophy may not be the same in the heart as in the coronary and renal arteries; and (2) AVP was significantly correlated with the left ventricular weight. This indicates that AVP could play a role in the etiology of cardiac hypertrophy in SHR.     

糜酶抑制剂对自发性高血压大鼠心肌纤维化的影响

目的观察心脏糜酶在自发性高血压大鼠（SHR）心肌组织胶原合成和心肌纤维化中的作用。方法应用病理检查、计算机分析结合逆转录-聚合酶链式反应等方法,检测SHR应用糜酶抑制剂组（ChyI组）、SHR组及对照正常血压大鼠WistarKyoto组（WKY组）收缩压、心肌胶原容积分数（CVF）、心肌血管周围胶原面积比（PVCA）和心肌糜酶及I、III型胶原mRNA表达。结果ChyI组心脏CVF、PVCA分别为（27±9）%和0.4±0.1,SHR组分别为（46±8）%和1.9±0.9,WKY组为（24±11）%和0.4±0.1,ChyI组比SHR组显著下降（P<0.01）,与WKY组无显著差异。ChyI组心肌组织I、III型胶原和糜酶mRNA表达相对含量均显著低于SHR组（P<0.01）,与WKY组无显著差异。应用ChyI后大鼠血压与SHR比较,无显著改变。结论心肌组织糜酶参与胶原的合成,参与细胞外基质的形成和降解,促进SHR心肌纤维化,糜酶抑制剂可能对改善心肌纤维化有益。     

Converting enzyme inhibitors regressed cardiac hypertrophy and reduced tissue angiotensin II in spontaneously hypertensive rats.

To examine the role of the tissue renin-angiotensin system in left ventricular hypertrophy, converting enzyme inhibitors were administered orally to 12-week-old male spontaneously hypertensive rats (SHR) for 4 weeks, and cardiac tissue angiotensin II was measured. Treatment with enalapril (10 mg/kg per day) and trandolapril (1 mg/kg per day) lowered systolic blood pressure, left ventricular weight and left ventricular angiotensin II content. Plasma angiotensin II concentration was increased by the treatment with enalapril whereas trandolapril did not cause any change. There was significantly positive correlation between left ventricular weight and angiotensin II content. Because angiotensin II promotes cell proliferation, these results suggest that cardiac tissue angiotensin II, rather than circulating angiotensin II, may account for the pathophysiology of left ventricular hypertrophy in SHR.     

Role of angiotensin II type 2 receptor during regression of cardiac hypertrophy in spontaneously hypertensive rats

We previously reported that the AT₁ receptor antagonist valsartan and the angiotensin converting enzyme (ACE) inhibitor enalapril decrease DNA synthesis and stimulate apoptosis in interstitial fibroblasts and epicardial mesothelial cells during regression of ventricular hypertrophy in spontaneously hypertensive rats (SHR). To examine the role of the AT₂ receptor in this model, we studied hearts from SHR treated with valsartan or enalapril either alone or combined with the AT₂ antagonist PD123319 for 1 or 2 weeks. Apoptosis was evaluated by quantification of DNA fragmentation or by TUNEL labeling. At 1 week, valsartan significantly increased ventricular DNA fragmentation, increased apoptosis in epicardial mesothelial cells, and decreased DNA synthesis. At 2 weeks, ventricular DNA content and cardiomyocyte cross-sectional area were significantly reduced. These valsartan-induced changes were attenuated by PD123319 co-administration. However, valsartan-induced increases in apoptosis of left ventricular interstitial non-cardiomyocytes was unaffected by the AT₂ blocker. Enalapril-induced changes were similar to those observed with valsartan but were not affected by co-treatment with PD123319. These results demonstrate that AT₁ and AT₂ receptors act in a coordinated yet cell-specific manner to regulate cell growth and apoptosis in the left ventricle of SHR during AT₁ receptor blockade but not ACE inhibition.