自发性高血压大鼠肾上腺髓质素含量与中性内肽酶分布的关系

目的 测定自发性高血压大鼠(SHR)与WKY大鼠组织肾上腺髓质素(ADM)含量和中性内肽酶(NEP)活性及其表达水平，以探讨NEP的变化在高血压时组织ADM水平升高中的意义。方法 采用放射免疫分析方法和荧光分光光度法分别检测血浆和组织的ADM含量和NEP的活性，同时用半定量RT-PCR和免疫组织化学染色法分别检测组织NEP mRNA和NEP蛋白的表达和分布。结果 ADM和NEP广泛分布于大鼠的血浆和组织，SHR的ADM含量在各组织普遍高于WKY大鼠。SHR心脏和小肠NEP的活性和mRNA表达均显著低于WKY大鼠，ADM含量与NEP活性呈负相关。反之，SHR血浆和肾脏NEP活性、肾脏NEP mRNA水平与蛋白量均高于WKY大鼠，ADM含量与NEP活性呈正相关。在肺脏和主动脉，NEP的活性无明显变化。结论 NEP在自发性高血压大鼠各组织器官中的变化与ADM含量的变化不一致，提示高血压时组织局部的NEP对ADM含量的影响不同。     

Tissue-specific upregulation of angiotensin-converting enzyme 1 in spontaneously hypertensive rats through histone code modifications

The renin-angiotensin system has been implicated in the development of hypertension and damages several organs. The expressions of the components of a local renin-angiotensin system (RAS) in the hypertensive rats differ from those of the normotensive rats. We hypothesized that local tissue-specific upregulation of angiotensin-converting enzyme 1 (ACE1) in hypertension is caused by epigenetic changes. Adrenal gland, aorta, heart, kidney, liver, and lung tissues were excised from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). Ace1 mRNA and protein expressions were measured by real-time PCR and Western blot, respectively. Promoter methylation was revealed by bisulfite sequencing. Histone modifications, such as histone 3 acetylation (H3Ac), fourth lysine trimethylation (H3K4me3), and ninth lysine dimethylation (H3K9me2), were quantified by chromatin immunoprecipitation (ChIP), followed by real-time PCR. The expressions and associations of chromatin remodeling genes were analyzed by real-time PCR and ChIP, respectively. Local tissues from SHRs showed higher expressions of Ace1 mRNA and protein than those from the WKY rats. Ace1 promoter was mostly unmethylated in all of the tissues from both strains. The Ace1 promoter regions of SHR tissues were more enriched with H3Ac and H3K4me3, except in the lungs. The adrenal glands, hearts, and kidneys of SHRs showed less enrichment with H3K9me2. Valsartan treatment in SHRs decreased local Ace1 mRNA and protein expressions, which were accompanied by higher H3K9me2, as well as less H3Ac and H3K4me3. In conclusion, ACE1 is upregulated in local tissues of SHRs via histone code modifications.     

Maternal supplementation with citrulline increases renal nitric oxide in young spontaneously hypertensive rats and has long-term antihypertensive effects

NO deficiency is associated with development of hypertension. Defects in the renal citrulline-arginine pathway or arginine reabsorption potentially reduce renal NO in prehypertensive spontaneously hypertensive rats (SHRs). Hence, we investigated genes related to the citrulline-arginine pathway or arginine reabsorption, amino acid pools, and renal NO in 2-week-old prehypertensive SHRs. In addition, because perinatally supporting NO availability reduces blood pressure in SHRs, we supplemented SHR dams during pregnancy and lactation with citrulline, the rate-limiting amino acid for arginine synthesis. In female offspring, gene expression of argininosuccinate synthase (involved in renal arginine synthesis) and renal cationic amino acid Y-transporter (involved in arginine reabsorption) were both decreased in 2-day and 2-week SHRs compared with normotensive WKY, although no abnormalities in amino acid pools were observed. In addition, 2-week-old female SHRs had much less NO in their kidneys (0.46+/-0.01 versus 0.68+/-0.05 nmol/g of kidney weight, respectively; P<0.001) but not in their heart. Furthermore, perinatal supplementation with citrulline increased renal NO to 0.59+/-0.02 nmol/g of kidney weight (P<0.001) at 2 weeks and persistently ameliorated the development of hypertension in females and until 20 weeks in male SHR offspring. Defects in both the renal citrulline-arginine pathway and in arginine reabsorption precede hypertension in SHRs. We propose that the reduced cationic amino acid transporter disables the developing SHR kidney to use arginine reabsorption to compensate for reduced arginine synthesis, resulting in organ-specific NO deficiency. This early renal deficiency and its adverse sequels can be corrected by perinatal citrulline supplementation persistently in female and transiently in male SHRs.     

Differential regulation of cardiac adrenomedullin and natriuretic peptide gene expression by AT1 receptor antagonism and ACE inhibition in normotensive and hypertensive rats

OBJECTIVE: To study the effects of long-term treatment with the type 1 angiotensin (AT1) receptor antagonist losartan and the angiotensin-converting enzyme (ACE) inhibitor enalapril, on cardiac adrenomedullin (ADM), atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) gene expression. METHODS: Spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were given losartan (15 mg/kg per day) or enalapril (4 mg/kg per day) orally for 10 weeks. The effects of drugs on systolic blood pressure, cardiac hypertrophy, ANP, BNP and ADM mRNA and immunoreactive-ANP (IR)-ANP, IR-BNP and IR-ADM levels in the left ventricle and atria were compared. RESULTS: Losartan and enalapril treatments completely inhibited the increase of systolic blood pressure occurring with ageing in SHR. The ratio of heart to body weight was reduced in both losartan- and enalapril-treated SHR and WKY rats. Treatment with losartan or enalapril reduced left ventricular ANP mRNA and IR-ANP in both strains, and ventricular BNP mRNA levels in SHR rats. Inhibition of ACE, AT1 receptor antagonism, changes in blood pressure or cardiac mass had no effect on left ventricular ADM gene expression in SHR and WKY rats. In addition, atrial IR-ANP and IR-ADM levels increased in SHR whereas IR-BNP levels decreased in WKY and SHR rats in response to drug treatments. CONCLUSIONS: Our results show that ventricular ADM synthesis is an insensitive marker of changes in haemodynamic load or cardiac hypertrophy. Furthermore, the expression of ADM, ANP and BNP genes is differently regulated both in the left ventricle and atria in response to AT1 receptor antagonism and ACE inhibition.     

厄贝沙坦和咪哒普利对自发性高血压大鼠左室肥厚和c-Jun表达的影响

目的探讨厄贝沙坦和咪哒普利对自发性高血压大鼠（SHR）左室肥厚和c-Jun表达的影响。方法选用13周龄的SHR 30只,雌性9只,雄性21只,体质量（229±39）g,随机分为3组:SHR组,厄贝沙坦组,咪哒普利组,每组雌性3只,雄性7只。另选同源同系、血压正常的Wistar-Kyoto大鼠（WKY）10只,雌性5只,雄性5只,体质量（206±49）g,作为正常对照组（WKY组）。实验期14周。观察指标:血压、左室质量/体质量（LVW/BW）、左室厚度/体质量、左心室肌c-Jun蛋白及mRNA水平。结果26周龄SHR组血压、LVW/BW与左室厚度/体质量均增高,左心室肌c-Jun蛋白和mRNA的表达明显增加;咪哒普利组、厄贝沙坦组血压、LVW/BW、左室厚度/体质量、左心室肌c-Jun蛋白和mRNA的表达均降低。结论自发性高血压可明显导致心肌肥厚,而咪哒普利、厄贝沙坦可明显降低血压、抑制心肌肥厚的发生。     

Effects of continuous intermedin infusion on blood pressure and hemodynamic function in spontaneously hypertensive rats

Objective To examine the effects of exogenously administered intermedin (IMD, adrenomedullin-2) on arterial blood pressure, cardiac function and the cardiovascular IMD receptor system in spontaneously hypertensive rats (SHRs) as well as to investigate the associated mechanisms. Methods Thirteen week-old male rats were divided in Wistar Kyoto (WKY) group (n = 12), SHR group (n = 12), IMD group (SHRs infused with IMD 1-47 500 ng/kg per hour, n = 12), and ADM group (SHRs infused with adrenomedullin 500 ng/kg per hour, n = 12). Results A two-week continuous administration of low dose IMD 1-47 via mini-osmotic pumps markedly reduced blood pressure, the maximal rates of increase and decrease of left-ventricle pressure development (LV ± dp/dtmax), left ventricular systolic pressure and heart rate in SHRs. Furthermore, IMD also inhibited protein over-expression of cardiovascular IMD receptors, myocardial Receptor Activity-Modifying Proteins (RAMP1 and RAMP2), aortic RAMP1, RAMP2, RAMP3, and calcitonin receptor-like receptor (CRLR); suppressed up-regulation of aortic RAMP1, RAMP2, RAMP3 and CRLR gene expression; and markedly elevated the mRNA abundance of myocardial atrial natriuretic peptide (ANP) and myocardial brain natriuretic peptide (BNP). Additionally, IMD 1-47 administration in SHRs increased aortic cAMP concentration and reduced myocardial cAMP concentration. Conclusion These findings support the speculation that IMD, as a cardiovascular active peptide, is involved in blood pressure reduction and cardiac function amelioration during hypertension. The mechanism underlying this effect may involve IMD binding of a receptor complex formed by RAMPs and CRLR, and consequential regulation of cAMP levels and other cardiovascular active factors, such as ANP and BNP.     

RNA silencing targeting PIN (protein inhibitor of neuronal nitric oxide synthase) attenuates the development of hypertension in young spontaneously hypertensive rats

Nitric oxide (NO) deficiency contributes to hypertension. We previously showed that neuronal nitric oxide synthase (nNOS) was involved in hypertension and kidney damage in spontaneously hypertensive rats (SHRs). The protein inhibitor of nNOS (PIN) has been reported to inhibit activity of nNOS.Thus, we tested whether increased PIN in the kidney results in hypertension and whether small interfering RNA (siRNA) targeting PIN attenuates hypertension in SHRs. Four-week-old male SHRs were assigned into three groups (n = 6-7/group): SHR; SHR + PIN, SHR that received siRNA targeting PIN; and SHR + NC, SHR treated with random negative control siRNA. Rats were sacrificed at 12 weeks of age. PIN protein expression was inhibited considerably when PIN siRNA was transfected into NRK52E cells (90% siRNA at 1 nM). The increases of BP were attenuated by siRNA targeting PIN in12-week-old SHRs. Immunostaining of nNOS-α and total nNOS was greater in SHR + PIN group than SHR. Moreover, renal superoxide production and 8-hydroxydeoxyguanosine (8-OHdG) staining were more decreased in the SHR + PIN group than SHRs. We conclude that PIN siRNA reduced PIN expression in vitro and in vivo. PIN siRNA therapy attenuates hypertension in SHRs at 12 weeks of age. Our results suggest that PIN is involved in the development of hypertension.     

Improvement of Vascular Remodeling in Spontaneous Hypertensive Rats with Traditional Chinese Medicine

Qin-Dan-Jiang-Ya-Tang (QDJYT) is a traditional Chinese herbal medicine for the treatment of hypertension. The effect of QDJYT on blood pressure (BP) and vascular remodeling in hypertension was investigated in the model of spontaneous hypertensive rats (SHR). Sixteen SHRs were divided into two groups: the SHR group and the SHR+ QDJYT group. Eight Wistar-Kyoto (WKY) rats were in the normal control group. QDJYT (750mg/kg) was orally administered daily for 12 weeks to the SHR+QDJYT group. After 12 weeks, thoracic aortas were segregated. The media thickness (MT) and the lumen diameter (LD) of the aortic wall, the ratios of MT to LD, the expression of basic fibroblast growth factor (bFGF) mRNA, and the level of its proteinic production were examined by histology, real-time PCR, and Western blot analysis, respectively. It was observed in our study that MT, MT/LD, the expression of bFGF mRNA, and the level of its proteinic production in aortic walls were higher in SHRs than in WKY rats. However, in the SHRs treated with QDJYT, we found MT, MT/LD, the expression of bFGF mRNA and the level of its proteinic production were lower than SHRs. These results suggest that QDJYT can improve the vascular remodeling in SHRs, and the mechanisms may be related to the suppressive effect of QDJYT on bFGF mRNA and its proteic productions in the aortic walls of SHRs.     

Improvement of vascular remodeling in spontaneous hypertensive rats with traditional Chinese medicine

Qin-Dan-Jiang-Ya-Tang (QDJYT) is a traditional Chinese herbal medicine for the treatment of hypertension. The effect of QDJYT on blood pressure (BP) and vascular remodeling in hypertension was investigated in the model of spontaneous hypertensive rats (SHR). Sixteen SHRs were divided into two groups: the SHR group and the SHR+ QDJYT group. Eight Wistar-Kyoto (WKY) rats were in the normal control group. QDJYT (750 mg/kg) was orally administered daily for 12 weeks to the SHR+QDJYT group. After 12 weeks, thoracic aortas were segregated. The media thickness (MT) and the lumen diameter (LD) of the aortic wall, the ratios of MT to LD, the expression of basic fibroblast growth factor (bFGF) mRNA, and the level of its proteinic production were examined by histology, real-time PCR, and Western blot analysis, respectively. It was observed in our study that MT, MT/LD, the expression of bFGF mRNA, and the level of its proteinic production in aortic walls were higher in SHRs than in WKY rats. However, in the SHRs treated with QDJYT, we found MT, MT/LD, the expression of bFGF mRNA and the level of its proteinic production were lower than SHRs. These results suggest that QDJYT can improve the vascular remodeling in SHRs, and the mechanisms may be related to the suppressive effect of QDJYT on bFGF mRNA and its proteic productions in the aortic walls of SHRs.     

Effect of Decreased Dopamine Synthesis on the Development of Hypertension Induced by Salt Loading in Spontaneously Hypertensive Rats

To clarify role of dopamine in the development of hypertension, the effect of a dopamine synthesis inhibitor on blood pressure and urinary output of catecholamines was investigated in spontaneously hypertensive rats (SHR) fed with high sodium diet. Rats were orally given carbidopa, an inhibitor of peripheral DOPA decarboxylase, or the vehicle for 4 weeks. Carbidopa administration accelerated significantly the development of hypertension as compared to the control SHRs with the vehicle. Carbidopa administration resulted in a significant decrease of urinary excreted sodium, urinary dopamine and renal content of dopamine. Conversely, carbidopa administration resulted in a significant increase of urinary excreted norepinephrine, urinary epinephrine and renal content of norepinephrine as compared with control SHRs. These results suggest that decreased dopamine synthesis in kidneys and probably other peripheral tissue accelerates the development of hypertension, mediated by a decrease of natriuresis and an enhancement of sympatho-adrenomedullary activity. Dopamine plays an important role in its protective action against the development of hypertension enhanced by salt loading, and decreased dopaminergic mechanisms accelerated hypertension in SHR.     

Increased expression and activity of phospholipase C in renal arterioles of young spontaneously hypertensive rats

BACKGROUND: The aims of this study were to document the presence of phospholipase C (PLC) isozymes beta(1), gamma(1), and delta(1) in freshly isolated renal glomeruli and resistance vessels, to compare their expression and activity to that in aorta, and to contrast values between 6-week-old Wistar-Kyoto (WKY) controls and 6-week-old spontaneously hypertensive rats (SHR) during the developmental phase of genetic hypertension. METHODS: Aorta, preglomerular arterioles, and glomeruli were isolated from 6-week-old rats using standard techniques. PLC isozyme protein level and activity were determined with Western blot analysis and by measuring inositol 1, 4, 5-trisphosphate (IP(3)) production, respectively. RESULTS: Immunoblots indicate that all three PLC isozymes examined are detectable in freshly isolated preglomerular arterioles, glomeruli, and aorta. Increased levels of PLC-beta(1), and -delta(1) were found in all tested vascular tissues of SHR v WKY. No strain difference was noted for PLC-gamma(1). The relative abundance for both groups was glomeruli > preglomerular arterioles = aorta. The strain difference in protein expression correlated with increased PLC activity in each vascular bed of SHR. CONCLUSIONS: Protein levels of PLC-beta(1) and -delta(1) and PLC activity are upregulated in the systemic and renal vasculature in 6-week-old SHR, suggesting a role in exaggerated vascular reactivity during the development of genetic hypertension. A more complete understanding of the physiologic roles of PLC isozymes and their contributions to specific aspects of cellular function should advance our understanding of vascular tone/reactivity and hypertrophy/remodeling in normal and hypertensive states.     

Protein phosphatase 2A B56alpha during development in the spontaneously hypertensive rat

Mistargeting of the regulatory subunit of protein phosphatase 2A (PP2A), B56alpha is involved in the hyperphosphorylation and desensitization of the D1 dopamine receptor in renal proximal tubules of spontaneously hypertensive rats (SHRs). However, the renal expression of B56alpha before hypertension develops is not known. Therefore, we studied the expression of B56alpha and PP2A activity in the kidney during development in the SHR and its normotensive control, the Wistar-Kyoto (WKY) rat. PP2A B56alpha was expressed in proximal and distal tubules with no differences in the pattern of expression in WKY and SHRs at any age. In brush border membranes of renal proximal tubules, PP2A B56alpha protein was greatest in the immature rats and decreased with development. However, PP2A activity did not change with age. PP2A B56alpha protein and PP2A activity were similar in WKY and SHRs except at 2 weeks when both PP2A B56alpha protein and PP2A activity were higher in SHRs than in WKY rats. The PP2A catalytic subunit co-immunoprecipitated with the D1 receptor in renal proximal tubule cells. It is possible that the increased expression of PP2A B56alpha and increased basal PP2A activity in the young, especially in the SHRs, may serve as a compensatory mechanism in the increased phosphorylation and decreased renal D1 receptor function, including D1-receptor mediated stimulation in renal proximal tubules of SHRs.     

Modulation of Tissue Angiotensinogen Gene Expression by Glucocorticoids,Estrogens, and Androgens in Shr and Wky Rats

Local or tissue renin angiotensin systems are thought to participate in cardiovascular regulation. However, little information is available on the mechanisms by which renin and angiotensinogen synthesis and secretion are regulated in these tissues. In view of the importance of steroid hormones in the regulation of hepatic angiotensinogen, we have examined the effects of dexamethasone, ethinyl estradiol, or dihydrotestosterone on angiotensinogen gene expression in peripheral or cerebral tissues of Wistar Kyoto (WKY) or spontaneously hypertensive rats (SHR). Following a single injection of dexamethasone (7 mg/kg) the concentrations of angiotensinogen mRNA increased in nearly all organs examined. The differences to controls were higher in SHR than in WKY. Dexamethasone in low doses (10 μg/kg/day) given for 10 days did not alter angiotensinogen mRNA or blood pressure in control animals, but increased both parameters in the hypertensive strain. The reponse to a single dose of ethinyl estradiol (3 mg/kg) was not as uniform as that to dexamethasone, and a tendency for a higher sensitivity was found in SHR. High stimulation rates were found in liver and kidneys of both strains. A single dose of dihydrotestosterone (10 mg/kg) did not significantly affect angiotensinogen mRNA in any organ. Only when a high dose of 50 mg/kg was given daily for 20 days, was angiotensinogen mRNA increased in some tissues. These data indicate that glucocorti-coids and estrogens participate in the regulation of angiotensinogen gene expression in several extrahepatic tissues. The higher sensitivity to glucocorticoids in SHR may be relevant for the developement of hypertension in this strain.     

Tissue renin-angiotensin systems in renal hypertension.

Angiotensinogen messenger RNA (mRNA) levels were measured in the brain (hypothalamus, lower brain stem, cerebellum), liver, kidneys, and adrenal glands of rats made hypertensive by ligation of the aorta between the renal arteries. We also measured renin mRNA in the kidneys of these renal hypertensive rats. The early phase of hypertension (day 6) was associated with significant increases in plasma renin activity and levels of circulating angiotensin II. The circulating renin-angiotensin system was not activated in the later phase of hypertension (day 24). Angiotensinogen mRNA levels were elevated in the lower brain stem of hypertensive rats at both stages of hypertension. In contrast, angiotensinogen mRNA levels in the hypothalamus were increased only at day 6 after aortic ligation. Decreased levels of angiotensinogen mRNA were observed in the cerebellum in both the early and later phases of the hypertension. Angiotensinogen mRNA levels in the adrenal gland below the ligature fell in the early phases but rose in the later phases of hypertension. Renin mRNA levels of the ischemic kidney remained elevated at both the early and later phases, whereas in both ischemic and nonischemic kidneys, levels of angiotensinogen mRNA remained below sham values throughout the period of study. These results indicate differential expression of renin-angiotensin system mRNAs in tissues of renal hypertensive rats. The differential changes in the expression of angiotensinogen mRNA over the course of development and maintenance of renal hypertension suggest that factors in addition to angiotensin II are important in modulating the expression of renin-angiotensin system genes.     

PPARγ激动剂对自发性高血压大鼠基质金属蛋白酶2的影响

目的：观察过氧化物酶体增殖物激活受体γ（PPARγ）激动剂罗格列酮对自发性高血压大鼠（SHR）心、肾、动脉血管基质金属蛋白酶2（MMP-2）表达及活性的影响，探讨罗格列酮心血管保护作用的机制。方法：健康雄性12周龄SHR大鼠12只，体重245～255g，随机被分为2组：对照组及罗格列酮组（5mg／kg·d），每组6只。应用实时多聚酶链氏反应（PCR）、Western印迹法、明胶酶谱法（zymography）等方法对用药4周后的SHR心、肾、动脉MMP-2的表达进行测定。结果：罗格列酮治疗能使SHR心、肾MMP-2 mRNA的表达降低97．6％和58．9％（P〈0．01，P〈0．05），使胸主动脉、颈动脉MMP-2的活性降低30．7％和24．6％（P〈0．05），而蛋白表达无明显差异。结论：罗格列酮治疗逆转SHR靶器官损害的作用机制可能与降低MMP-2的作用有关。