Aminoguanidine ameliorates albuminuria in diabetic hypertensive rats

Summary We studied the effect of aminoguanidine, an inhibitor of advanced glycation product formation, on albuminuria in chronically diabetic spontaneously hypertensive rats. At the time of killing, there was no statistically significant difference in blood glucose concentration between the treated and untreated diabetic animals (18.2±0.69 mmol/l), nor was there any difference among the non-diabetic, diabetic untreated, and diabetic treated rats with respect to blood pressure (169±6.9 mm Hg). However, non-diabetic hypertensive animals had a mean quantitative 24-h urinary albumin excretion of 28±2 mg albumin/24-h, while untreated diabetic hypertensive animals averaged nearly four times that amount (106 ±3 mg albumin/24 h). Without affecting blood pressure, aminoguanidine treatment of diabetic hypertensive animals decreased the diabetic-associated elevation in urinary albumin excretion by 75% (48±2 mg/24 h). These data suggest than inhibition of advanced glycation product formation ameliorates the glomerular dysfunction caused by chronic hyperglycaemia.     

Lymphocyte membrane sodium-proton exchange in spontaneously hypertensive rats

The sodium-proton exchange activity was determined in lymphocytes of spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY), and domestic Wistar rats. Uptake of sodium was determined by measuring the osmotic swelling of lymphocytes after activation of the exchanger by suspension of the cells in sodium propionate and consequent intracellular acidification by the permeant weak acid. Fractional swelling (mean +/- SEM) in 16 SHR and 16 WKY was 0.44 +/- 0.03 and 0.35 +/- 0.02, respectively (p less than 0.01). The swelling was partially inhibitable by amiloride and, at 10(-4) M concentration, the amiloride-sensitive swelling was 0.21 +/- 0.02 in SHR and 0.11 +/- 0.01 in WKY (p = 0.001). Progressive extracellular ion substitutions of chloride for propionate or of potassium for sodium showed that the exchange activity was related linearly to cellular acidification; however, the dependence on extracellular sodium displayed saturation characteristics, with the same apparent Km for cells from SHR and WKY and a Vmax of 0.54 +/- 0.03 for SHR and 0.39 +/- 0.02 for WKY (p less than 0.002). External lithium could replace sodium on the exchanger but abolished the differences between strains. Results in the domestic Wistar rats were similar to those of WKY. These results suggest that lymphocytes of the SHR have a greater capacity for sodium uptake through the sodium-proton exchanger, as compared with normotensive strains. If shared by other cells, such an increased capacity could have a pathophysiological role in genetic hypertension. In particular, its presence in proximal renal tubular cells would support the hypothesis of a primary role for the kidney in the pathogenesis of genetic hypertension.     

L-arginine reverses severe nephrosclerosis in aged spontaneously hypertensive rats

OBJECTIVE: Acute and prolonged effects of L-arginine on systemic and renal hemodynamics and on renal pathological changes were examined in 85-week-old spontaneously hypertensive rats (SHR). RESULTS: After 3 weeks of L-arginine administration (n = 9; 2 g/l in drinking water), mean arterial pressure remained unchanged, although the cardiac index increased (187 +/- 26 versus 263 +/- 15 ml/min per kg; P < 0.05) and total peripheral resistance decreased (1.15 +/- 0.18 versus 0.67 +/- 0.06 AU; P < 0.05); the glomerular filtration rate increased (0.41 +/- 0.07 versus 0.79 +/- 0.07 ml/min; P < 0.01). Control untreated, aged SHR (n = 10) demonstrated severe nephrosclerosis histologically, but those treated with L-arginine demonstrated a markedly reduced glomerular injury score (164 +/- 22 versus 83 +/- 9; P < 0.005), and their urinary protein excretion (39 +/- 5 versus 19 +/- 5 mg/100 g body weight per day; P < 0.05) and serum creatinine concentration (1.4 +/- 0.1 versus 0.9 +/- 0.1 mg/dl; P < 0.05) diminished. Intravenous L-arginine (300 mg/kg body weight) given to untreated SHR reduced mean arterial pressure, increased the cardiac index (+98 versus +1%; P < 0.05) and decreased total peripheral resistance (+56 versus +13%, P < 0.005); however, these variables remained unchanged after 3 weeks of L-arginine treatment. CONCLUSIONS: Three weeks of treatment with L-arginine improved systemic hemodynamics, renal function and renal histologic changes in aged SHR with naturally occurring nephrosclerosis. These data provide an important insight into the pathophysiology of nephrosclerosis in hypertension and with aging, which is seen clinically.     

奥美沙坦酯对自发性高血压大鼠主动脉衰老的作用

目的探讨奥美沙坦酯对自发性高血压大鼠（SHR）主动脉衰老的作用。方法实验大鼠分为对照组（WKY组）、SHR组和SHR奥美沙坦酯处理组（OLM组）。每2周测鼠尾动脉压,饲养6周后处死取主动脉组织,一部分制做冰冻切片后β-半乳糖苷酶（β-gal）染色,其余用Western blot法测定Ras、p53、p21及β-actin蛋白的表达。结果与WKY组相比,各检测时间点SHR组血压升高（P〈0.05）,给药后OLM组血压降低（P〈0.05）。WKY组主动脉β-gal染色未见蓝染颗粒;SHR组可见大量蓝染颗粒;OLM组也可见蓝染颗粒,但与SHR组相比明显减少。与WKY组相比,SHR组Ras、p53及p21的蛋白表达增加（P〈0.05）,OLM组上述指标降低（P〈0.05）。结论 SHR通过Ras-p53/p21途径导致主动脉衰老,奥美沙坦酯对其具有显著的抑制作用,在降低血压的同时抑制血管病变的发生。     

Renin-angiotensin inhibition reverses advanced cardiac remodeling in aging spontaneously hypertensive rats

BACKGROUND: Many experiments using young hypertensive animal models support the evidence that angiotensin-converting enzyme inhibitor or angiotensin receptor type 1 blocker attenuates the progression of cardiac hypertrophy. However, it is still unclear whether inhibiting the renin-angiotensin system can reverse age-related cardiac hypertrophy. To clarify the role of renin-angiotensin system inhibition in naturally advanced myocardial hypertrophy we treated spontaneously hypertensive, aging rats with an angiotensin-converting enzyme inhibitor or an angiotensin receptor type 1 blocker. METHODS: We used osmotic pumps to deliver the blood-pressure reducers temocaprilat, olmesartan, hydralazine, or saline for 4 weeks. RESULTS: Heart and body weights were significantly reduced in animals treated with temocaprilat or olmesartan compared with animals treated with hydralazine or saline. Histologic myocyte size and cardiac fibrosis were significantly attenuated by temocaprilat or olmesartan. Real-time polymerase chain reaction (PCR) revealed that temocaprilat or olmesartan suppressed expression of cardiac transforming growth factor-beta1 and fibroblast growth factor-2 mRNA, a marker of cardiac fibrosis. Cardiac and systemic oxidative stress assessed by 8-isoprostane levels was significantly reduced in animals treated with temocaprilat or olmesartan compared with hydralazine-treated or saline-treated rats. Renin-angiotensin system inhibition reduced cardiac expression of NAD(P)H oxidative components p22phox, p47phox, and gp91phox. CONCLUSIONS: Renin-angiotensin system inhibition can reverse age-related, advanced cardiac hypertrophy. The mechanism of reversal is partly due to suppression of cardiac oxidative stress.     

Ischemic preconditioning maintains cardioprotection in aging normotensive and spontaneously hypertensive rats

We determined whether ischemic preconditioning could reduce infarct size and improve cardiac function in both aging normotensive Wistar–Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The left anterior descending coronary artery was occluded for 1 h followed by 3 h reperfusion in aging (∼16 months old) SHR rats and age-matched WKY rats. Hearts were either preconditioned or not (control group) prior to 1 h of coronary artery occlusion. The preconditioning regimen consisted of three cycles of 3 min occlusion followed by 5 min reperfusion applied prior to the subsequent 1 h occlusion. In WKY (n = 12 each group), the risk zone was similar in the control (51 ± 2%) and preconditioned group (46 ± 2%; p = 0.1). Preconditioning significantly reduced infarct size (as a percentage of the ischemic risk zone) (24 ± 6%) compared to controls (51 ± 5%; p = 0.0026). In SHR rats (n = 9 each group), the risk zone was smaller in the preconditioning group (41 ± 3%) than in the control group (51 ± 3%; p = 0.035). Infarct size (as % of ischemic risk zone) was also significantly reduced in the preconditioned group (13 ± 4%) compared to controls (62 ± 5%; p < 0.0001). For both WKY and SHR rats, for any sized risk zone the infarct size was smaller in preconditioned hearts compared with the control hearts. Preconditioning improved aspects of LV function during ischemia and reperfusion phase in SHR rats, but these benefits were not observed in the WKY rats. Preconditioning maintains powerful cardioprotection in aging normotensive hearts as well as aging hypertrophied hearts.     

Impact of antihypertensive treatments on erectile responses in aging spontaneously hypertensive rats

OBJECTIVE: We previously demonstrated that brief, aggressive antihypertensive therapy recovered erectile function in 40-week-old spontaneously hypertensive rats (SHR). The present study examined the impact of antihypertensive and testosterone treatments on erectile function in aging SHR. DESIGN AND METHODS: Centrally initiated erections were determined in response to apomorphine throughout. At 30 and 49 weeks, SHR were treated for 2 weeks with enalapril or hydralazine. A third more aggressive treatment (68 weeks) involved enalapril or losartan plus a low salt diet or a triple therapy (hydralazine, nifedipine, hydrochlorothiazide). In a separate study, cross-over kidney transplantations were performed between untreated and losartan-treated SHR. Arterial pressure was assessed post-transplantation using radio-telemetric transducers. RESULTS: There was an age-related decrease in erections between 30 and 68 weeks (3.1 +/- 0.79 versus 0.2 +/- 0.38) that was not improved by testosterone administration. Early treatment with enalapril or hydralazine did not prevent this decline, although the second treatment resulted in significant improvements (enalapril, 0.8 +/- 0.70; hydralazine, 0.8 +/- 0.41 versus control, 0.3 +/- 0.60). A 2-week aggressive antihypertensive treatment at 68 weeks increased erections approximately two-fold, with the previously treated rats receiving triple therapy having markedly improved erectile responses (0.2 +/- 0.53 versus 1.1 +/- 1.67). In the transplantation study, previously losartan-treated SHR given an untreated kidney had higher arterial pressure but twice the number of erections in comparison with the SHR with lower arterial pressure resulting from transplanting a treated kidney. CONCLUSIONS: Aggressive antihypertensive treatments may be more beneficial in improving erectile function in aged SHR, via an effect that appears to be tissue specific, and not based on changes in blood pressure.     

Dissociation between albuminuria and insulinaemia in hypertensive and atherosclerotic men

To better understand the links between circulating insulin and albuminuria in essential hypertension, the plasma insulin response t alpha a 75 gram glucose load and albuminuria were evaluated in 53 glucose-tolerant essential hypertensives and 12 controls. To allow any direct pressure-independent albuminuric effect of insulin to emerge more clearly, those same parameters were also evaluated in 20 glucose-tolerant normotensive patients with stable atherosclerotic peripheral vascular disease, a condition in which hyperinsulinaemia could be anticipated on the basis of previous reports. In response to glucose ingestion, hyperinsulinaemia was evident in both hypertensive and normotensive atherosclerotic patients, while, on average, urine albumin was elevated only in the former. When plasma insulin, systolic and diastolic blood pressure (BP) (by 24-h ambulatory BP monitoring), plasma glucose, triglycerides and body mass index were entered into a multiple regression analysis, only systolic BP appeared to exert an independent effect on urine albumin. Post-glucose load plasma insulin did not differ between hypertensive patients with (n = 14) and without (n = 39) microalbuminuria (albuminuria > 20 micrograms/min). In further analyses, insulin and systolic BP values were divided in quartiles: albuminuria did not differ across insulin quartiles, while it was significantly higher in the top (n = 21) vs the bottom (n = 21) systolic BP quartile. Thus, hyperinsulinaemia and microalbuminuria were unrelated variables in these hypertensive and atherosclerotic patients. Blood pressure, particularly systolic, emerged as a primary predictor of urinary albumin excretion, although the importance of this parameter needs to be proved prospectively.     

Relationship between lactate dehydrogenase and albuminuria in Chinese hypertensive patients

Lactate dehydrogenase (LDH) has been reported to be positively correlated with albuminuria assessed by urinary albumin‐to‐creatinine ratio (UACR) in patients with sickle cell disease; both LDH and albuminuria are positively associated with the severity of hypertension (HTN). Here, a cross‐sectional study was performed to investigate the association between LDH and albuminuria in Chinese hypertensives. A total of 1169 Chinese individuals (aged 58.0 ± 11.5 years, 60.4% male), who were admitted to our hospital, were included in this study. Based on the level of LDH, all hypertensives (n = 802) were divided into three groups: HTN1 (lowest tertile of LDH, n = 264), HTN2 (mediate tertile of LDH, n = 268), and HTN3 (highest tertile of LDH, n = 270). Hypertensives with hyperhomocysteinemia were defined as hypertensives with homocysteine ≥15μmol/L. Meanwhile, 367 normotensives served as controls. Compared with normotensives, the levels of LDH and UACR were significantly higher in hypertensives (p < .05). There was an increasing trend of albuminuria (UACR ≥30 mg/g) from control, HTN1, HTN2 to HTN3 group (4% vs. 12.1% vs. 14.9% vs. 19.6%, χ² = 38.886, p < .001). Stepwise multiple regression analysis showed an independent association between LDH and UACR in patients with HTN (β = 0.085, p < .05), but not in normotensives. After further stratification in hypertensive patients, this correlation remained in the male (β = 0.161, p < .001), elderly (age ≥65 years, β = 0.174, p < .001) and especially hypertensives with hyperhomocysteinemia (β = 0.402, p < .001). LDH combined with white blood cell (WBC) counts was observed to have better discrimination for albuminuria than creatinine united with cystatin C in hypertensives according to receiver operation characteristic curves (area under curve: 0.637 vs. 0.535, z = 2.563, p = .0104). In conclusion, the level of LDH was associated with albuminuria in Chinese patients with HTN, particularly in hypertensives with hyperhomocysteinemia. LDH combined with WBC provided better prediction of albuminuria than routine renal function assessment in hypertensives. Further studies are needed to confirm LDH as an early marker for the risk of kidney involvement among hypertensives.     

Thiazolidinedione derivatives ameliorate albuminuria in streptozotocin-induced diabetic spontaneous hypertensive rat

Recent reports have shown that thiazolidinediones have preventive effects on urinary albumin excretion in diabetes. However, the mechanism leading to these effects has not yet been elucidated. We studied here the effects of thiazolidinediones on albuminuria and hemodynamic and morphological changes in the kidneys of streptozotocin (STZ)-induced diabetic spontaneous hypertensive rats (SHRs). Diabetes was induced in SHRs by intravenous injection of STZ (50 mg/kg). The diabetic SHRs were divided into the following 3 groups: (1) STZ-SHRs given normal chow (STZ), (2) STZ-SHRs given chow mixed with 0.1% troglitazone (STZ + tro), and (3) STZ-SHRs given chow mixed with 0.001% pioglitazone (STZ + pio). Three groups of nondiabetic SHRs were also investigated: (4) SHR, (5) tro, and (6) pio. We evaluated the urinary albumin excretion rate (AER) every 4 weeks. After 12 weeks of treatment, the animals were killed and renal morphological examinations were performed. Thiazolidinediones did not affect blood pressure or blood glucose levels. Urinary AER were markedly increased in STZ-SHRs. After 12 weeks of treatment with thiazolidinediones, the urinary AER was significantly decreased while creatinine (Cr) clearance was left unchanged. Histologically, the loss of anionic sites of glomerular basement membranes (GBM) evaluated with polyetyleneimine was suppressed significantly in the diabetic SHRs treated with thiazolidinediones. In conclusion, administration of thiazolidinediones in diabetic SHRs decreased the urinary AER and suppressed the loss of anionic sites of GBM without affecting blood pressure, blood glucose levels, or Cr clearance. These results clarify the novel therapeutic action of thiazolidinediones on diabetic nephropathy.     

Inhibitors of Na+/Mg2+ exchange activity attenuate the development of hypertension in angiotensin II-induced hypertensive rats

OBJECTIVES: To investigate whether imipramine and quinidine, inhibitors of the Na /Mg exchanger, influence development of hypertension in rats infused with angiotensin (Ang) II. METHODS: Sprague-Dawley rats were divided into six groups: (1) control (vehicle); (2) Ang II (150 ng/kg per min subcutaneously); (3) imipramine alone (5 mg/kg per day in drinking water); (4) quinidine alone (5 mg/kg per day in drinking water); (5) Ang II plus imipramine; (6) Ang II plus quinidine. Rats were studied for 3 weeks. To verify that Ang II directly influences Na -dependent Mg exchange, in-vitro studies were performed in vascular smooth muscle cells (VSMCs) derived from mesenteric arteries. RESULTS: Ang II increased systolic blood pressure (SBP) in all groups. The magnitude of the increase was lower ( 0.01) in Ang II groups treated with imipramine (151 +/- 7.4 mmHg) or quinidine (163 +/- 4 mmHg) than in the Ang II only group (205 +/- 4 mmHg). Neither imipramine nor quinidine influenced SBP in vehicle-treated rats. Plasma concentrations of Mg and K were decreased in Ang II rats compared with controls (P < 0.05). Platelet intracellular free Mg concentration was reduced and platelet intracellular free Na concentration was increased in the Ang II group compared with control and treated groups (P < 0.01). These effects were normalized by imipramine and quinidine. Ang II stimulated Na -dependent Mg transport in VSMCs. These actions were abrogated by imipramine and quinidine and in Na -free conditions. CONCLUSIONS: Our data demonstrate that inhibitors of Na -dependent Mg transport attenuate development of hypertension in rats infused with Ang II. These findings suggest a possible role for Na /Mg exchange activity in the pathogenesis of Ang II-dependent hypertension.     

Upregulation of angiotensin-converting enzyme 2 by all-trans retinoic acid in spontaneously hypertensive rats

There is increasing evidence that all-trans retinoic acid (atRA) influences gene expression of components of renin-angiotensin system (RAS), which plays a pivotal role in the pathophysiology of essential hypertension. To further validate effects of atRA on the RAS and to assess the possibility that atRA affects the activity of angiotensin-converting enzyme 2 (ACE2), gene, and protein expression of ACE2 have been examined by real-time polymerase chain reaction and Western blot methods in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. Rats were treated with atRA (10 or 20 mg x kg(-1) x day(-1)) or placebo given as daily intraperitoneal injection for 1 month. ACE2 expression was markedly decreased in placebo-treated SHR when compared with WKY rats. However, in atRA-treated SHR, a significant upregulation of ACE2 expression was observed in heart and kidney. In conclusion, chronic atRA treatment increases gene and protein expressions of ACE2, resulting in the reduction of blood pressure and the attenuation of myocardial damage in SHR, which suggests that atRA may be an attractive candidate for the potential prevention and treatment of human essential hypertension.     

Effects of aging and antihypertensive treatment on aortic internal diameter in spontaneously hypertensive rats.

The effect of antihypertensive treatment on the development of large-artery remodeling in young animals has been widely studied, but reversal of established changes in older hypertensive animals has been largely ignored, although the latter represents a better paradigm for the human condition. We studied the effect of treatment with captopril plus hydrochlorothiazide, from 3 months onward, on geometry and wall stress of the thoracic aorta of adult (9 months, maturation) and old (15 months, senescence) spontaneously hypertensive rats; normotensive Wistar-Kyoto rats were used as controls. At 3 months of age, blood pressure, medial cross-sectional area, and internal diameter were higher in spontaneously hypertensive rats than in Wistar-Kyoto rats. In both strains, medial cross-sectional area and lumen diameter increased during maturation; there was little change with senescence. Changes in blood pressure were minor. Because medial hypertrophy failed to compensate for the wider lumen and higher intraluminal pressure in spontaneously hypertensive rats, medial stress was higher in these rats than in Wistar-Kyoto rats. Captopril plus hydrochlorothiazide rapidly lowered blood pressure and medial cross-sectional area. Despite a marked fall in blood pressure, the internal diameter of the thoracic aorta of treated animals was similar to that of untreated animals after 6 months of treatment and started to fall only after the animals had been treated for 1 year. Thus, under treatment with captopril plus hydrochlorothiazide, medial stress remained elevated, even after very-long-term treatment, because medial cross-sectional area was not adapted to internal diameter. We suggest that some changes in large-artery structure associated with hypertension and aging, such as the increase in diameter, take considerable time to regress after blood pressure is lowered, and this may explain why, despite treatment, wall stress remains elevated.     

硝普钠对过氧化氢诱导增龄大鼠血小板活化影响

目的:探讨过氧化氢对增龄大鼠血小板活化及NO(nitric oxide)供体硝普钠,对过氧化氢诱导下血小板活化的影响。方法:使用8个月龄、13个月龄Wistar大鼠血小板悬浮液,测定一氧化氮(nitricoxide,NO)、环磷鸟苷(cGMP)含量、血管舒张因子刺激的磷酸蛋白(vasodilator-stimulated phosphoprotein,VASP)磷酸化以及活性氧族(reactive oxygen species,ROS)水平。结果:过氧化氢刺激血小板活化时,8个月龄、13个月龄大鼠的血小板NO含量均有降低,硝普钠以剂量依赖的方式增加了大鼠血小板内的NO含量,但2组之间差异无统计学意义;硝普钠能明显增强8个月龄大鼠过氧化氢刺激的血小板VASP磷酸化水平,但对13个月龄大鼠血小板的VASP磷酸化无明显影响;硝普钠明显增加了8个月龄大鼠细胞内cGMP含量,但对13个月龄大鼠cGMP的产生无明显影响;硝普钠对2组大鼠血小板ROS产生没有抑制作用。结论:硝普钠明显增加8个月龄大鼠过氧化氢刺激血小板的cGMP含量以及VASP磷酸化,但硝普钠对8个月龄和13个月龄大鼠血小板NO产生的影响差异无统计学意义。硝普钠对13个月龄大鼠血小板VASP磷酸化以及cGMP产生的影响较小。提示老龄机体血小板功能改变与cGMP活性下降、VASP磷酸化水平降低相关。这一结果为今后抗血栓药物研究提供了新的思路靶点。     

Immunohistochemical study of vascular lesions in severe hypertension induced by DOCA and salt administration to spontaneously hypertensive rats

In order to evaluate whether immunoglobulin deposition in vessels plays some role in the development of vascular lesions in severe hypertension, an immunohistochemical study was performed in spontaneously hypertensive rats (SHRs), to which deoxycorticosterone acetate (DOCA) and salt were administered. DOCA and salt rapidly induced severe hypertensive vascular lesions, including necrotizing arteriolitis and productive endarteritis. In these rats, considerable deposits of IgG and IgM were found in the small arteries and arterioles of the kidneys. These deposits were accompanied by complement (C3), and could be eluted by acid incubation. They were localized in periodic acid-Schiff-positive insudative lesions, which were thought to be an early phase of the hypertensive vascular lesions. These results suggest that the immunoglobulins might be bound to an unknown antigen in the vascular lesions and that some immunological mechanism mediated by the immunoglobulins is involved in the development of vascular lesions in severe hypertension.