Chronic infusion of low doses of atrial natriuretic factor (ANF Arg 101-Tyr 126) reduces blood pressure in conscious SHR without apparent changes in sodium excretion

Conscious SHR and WKY rats were infused during 7 days with synthetic ANF (Arg 101-Tyr 126), 100 ng/hr/rat (35 pmol/hr/rat) by means of miniosmotic pumps. The SHR initial blood pressure of 177 +/- 5 mmHg gradually dropped to 133 +/- 3 and 142 +/- 4 mmHg the last two days of infusion. No significant change in blood pressure was observed in the ANF-infused WKY group. No apparent difference in natriuresis or diuresis was observed in ANF-infused SHR and WKY when compared with non-infused control groups. A slight but significant lower immunoreactive ANF concentration was found in the atria of SHR than in their normotensive controls. No difference in cardiac weight was found between infused and non-infused rats. It is suggested that the hypotensive response observed in SHR and not in WKY is due to a decrease in vascular peripheral resistance. Whether ANF is involved in the development and maintenance of high blood pressure in SHR remains to be elucidated.     

自发性高血压大鼠多组织炎症状态

高血压是一种慢性血管性疾病,易累及肾、肝、心、脑等组织,引起脑卒中和心、肾损害等并发症.本研究对高血压时肾、肝、心、脑等组织的炎症状态进行了观察.实验采用自发性高血压大鼠(spontaneously hypertensive rat,SHR)和正常血压的Wistar-Kyoto(WKY)大鼠,用RT-PCR和Western blot法观察肾、肝、心、脑等组织炎症相关因子IL-1p、TNFα、ICAM-1、iNOS、C/EBPδ和PPARγ的基因表达;紫外分光光度法观察蛋白质羰基化水平和FRAP法检测组织总抗氧化能力.结果显示(1)SHR组织炎症相关因子表达较对照WKY增强,除IL-1βmRNA在肝和脑的增加不明显外,其余均有显著性差异(P＜0.05);(2)SHR和WKY大鼠肾、心、脑蛋白质羰基化水平(nmol/mg蛋白)分别为8.93±1.08和2.27±0.43、2.23±0.23和0.17±0.02、13.42±1.10和5.72±1.01,SHR明显增加(P＜0.05);而肝脏蛋白质羰基化水平无明显变化;(3)SHR肾、肝、心、脑总抗氧化能力水平显著低于WKY大鼠(P＜0.05).以上结果表明,SHR多个组织(肾、肝、心和脑)均存在炎症因子被诱导和氧化应激反应等明显的炎症状态,提示炎症可能在高血压及其并发症的病理改变中起重要作用.     

Cold-restraint induced gastric lesions in normotensive and spontaneously hypertensive rats

Spontaneously hypertensive (SHR) rats and normotensive Wistar-Kyoto (WKY) rats were subjected to 2 hr of cold-restraint stress at 2–6°C following a 24 hr fast. WKY rats had a significantly greater incidence and degree of ulceration of the gastric glandular mucosa than did SHR rats. Mean arterial pressure, obtained from a chronic arterial cannula, fell during 2 hr of cold-restraint stress in both SHR and WKY rats. Heart rate was unchanged in WKY but fell significantly in SHR. Plasma norepinephrine (NE) and epinephrine (E), determined by radioenzymatic assay, increased significantly following stress. Increased levels of NE remained similar for both SHR and WKY rats, while post-stress levels of E for the SHR rats greatly exceeded E levels for WKY rats. A greater degree of hypothermia was also noted in SHR rats. Decreased stress induced ulcerogenesis in the SHR may be due to the well-known altered hemodynamic and autonomic nervous system reactivity in this strain or other factors not yet discovered.     

Effects of acute and subacute cocaine administration on the CNS dopaminergic system in Wistar-Kyoto and spontaneously hypertensive rats: I. Levels of dopamine and metabolites

Effects of acute and subacute cocaine administration on dopamine (DA) and its metabolites in striata and nucleus accumbens of nine week-old Wistar-Kyoto and spontaneously hypertensive rats were studied. Levels of DA,3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined by HPLC-EC. There were no differences in DA levels in striata and nucleus accumbens between control WKY and SHR. Levels of DA in two brain regions were unaffected in groups treated acutely with cocaine. Both strains showed a significant increase in striatal HVA 2 hr after cocaine injection. Seven day treatment declined DA levels in striatum of WKY and in nucleus accumbens of SHR. However, only WKY treated subacutely with cocaine showed significantly increased HVA either with or without changes in DOPAC in nucleus accumbens and striatum, respectively. Increased DOPAC/DA and HVA/DA ratios appeared only in striatum of WKY and in nucleus accumbens of SHR following subacute treatment. These results suggest that subacute cocaine administration affects DA levels in striata and nucleus accumbens differently between WKY and SHR.     

Clonidine fails to reduce pressor responsiveness of conscious spontaneously hypertensive rats to vasopressin

Pressor responses and heart rate responses to intravenous injections (3.5-50.0 pmol/kg) of arginine vasopressin (AVP) were recorded in saline- and clonidine-treated spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Clonidine (20 micrograms/kg, i.v.) caused a marked fall of arterial pressure in SHR but not in WKY rats so that, 20 min after the injection of the alpha 2-adrenoceptor agonist, arterial pressure was similar in the two strains of rats. The curve expressing the relationship between the dose of AVP and the increase of arterial pressure for saline-treated SHR was positioned to the left of that for saline-treated WKY rats. This enhanced pressor responsiveness of SHR to AVP may have been related to impaired reflex activity since heart rate fell much less in SHR than in WKY rats for a given elevation in pressure. Pressure responses to AVP were augmented by clonidine in both SHR and WKY rats so that, similar to saline-treated rats, pressor responsiveness to the peptide was still greater in SHR. Heart rate responses to AVP were not altered significantly by clonidine. The results indicate that clonidine fails to enhance reflex activity and reduce pressor responsiveness of SHR to AVP. The increased pressor responsiveness of both SHR and WKY rats to AVP following clonidine was an unexpected finding and may be related to a peripheral interaction between alpha-adrenergic agonists and AVP.     

Effects of nitric oxide synthase inhibitor on tyrosine hydroxylase mRNA in the adrenal medulla of spontaneously hypertensive and Wistar Kyoto rats.

We studied the effects of N(G)-nitro-l-arginine methyl ester (L-NAME) on catecholamine levels, tyrosine hydroxylase (TH) activity, and TH mRNA levels in the adrenal medulla of spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). L-NAME (100 mg/L in drinking water) and atropine (10 mg/L in drinking water) were administered for 2 weeks. Epinephrine and norepinephrine levels, TH activity, and TH mRNA levels in the adrenal medulla of L-NAME-treated WKY were significantly decreased. These parameters were not significantly altered in the adrenal medulla of L-NAME-treated SHR. Nitrite/nitrate levels in the adrenal medulla of L-NAME-treated WKY were significantly decreased; however, no significant change in L-NAME-treated SHR was observed. Ca(2+)-dependent nitric oxide synthase (NOS) activity in the adrenal medulla of SHR was significantly decreased compared to that of WKY. TH mRNA levels in L-NAME + atropine-treated and L-NAME-treated WKY were significantly lower than TH mRNA levels in control WKY. These results suggest that nitric oxide in the adrenal medulla may enhance the catecholamine biosynthetic pathway via increased TH mRNA expression. Our results also suggest that this effect is suppressed in SHR due to decreased NOS activity in the adrenal medulla.     

Altered expression of G-protein mRNA in spontaneously hypertensive rats.

We have recently demonstrated that the decreased ability of hormones, forskolin and GTP to stimulate adenylate cyclase in heart and aorta from spontaneously hypertensive rats (SHR), as compared to their age-matched Wistar-Kyoto control rats (WKY), was associated with enhanced levels of Gi- and not with Gs-regulatory proteins. In the present studies we have investigated the expression of Gi-regulatory proteins at the mRNA level by Northern blotting. Total RNA of heart ventricle and aorta from WKY and SHR was probed with radiolabeled cDNA inserts encoding Gi alpha-2 and Gi alpha-3. The Gi alpha-2 and Gi alpha-3 probes detected a message of 2-3 and 3-5 kb, respectively, in both WKY and SHR, however, the message was significantly enhanced in SHR, as compared by WKY. On the other hand the cDNA probe encoding Gs alpha detected a message of 1.8 kb in heart and aorta from both WKY and SHR, however, no difference in the levels of Gs alpha mRNA was detected in SHR and WKY tissues. These results indicate that the mRNA levels of Gi alpha-2 and Gi alpha-3 and not of Gs are overexpressed in heart and aorta from SHR, which may be responsible for the increased levels of Gi as shown earlier by immunoblotting techniques. It may be suggested that the enhanced vascular tone and impaired cardiac contractility in hypertension may partly be the consequences of increased levels of Gi in heart and aorta.     

A comparative study on defense systems for lipid peroxidation by free radicals in spontaneously hypertensive and normotensive rat myocardium.

1. Antiperoxidation ability and lipid peroxidation in myocardium were examined in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) at 6 and 16 weeks of age. 2. Glutathione peroxidase activity was higher in SHR at 6 weeks of age, but lower at 16 weeks compared to that in WKY. alpha-Tocopherol content was lower in SHR at both 6 and 16 weeks of age than in WKY. 3. In vitro formation of free malondialdehyde was more pronounced in SHR myocardium than in WKY. 4. Coincidence of lower antiperoxidation ability and higher peroxidation of membrane phospholipid indicate myocardial cell vulnerability in SHR hypertrophied myocardium.     

Glutathione system in young spontaneously hypertensive rats

Glutathione (GSH) forms a part of the antioxidant system that plays a vital role in preventing oxidative stress, and an imbalance in the oxidant/antioxidant system has been linked to the pathogenesis of hypertension. The aim of this study was to investigate the status of the GSH system in the kidney of spontaneously hypertensive rats (SHR). Components of the GSH system, including glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST), and total GSH content, were measured in the kidneys of 4, 6, 8, 12, and 16 weeks old SHR and Wistar–Kyoto (WKY) rats. Systolic blood pressure of SHR was significantly higher from the age of 6 weeks onwards compared with age-matched WKY rats. GPx activity in the SHR was significantly lower from the age of 8 weeks onwards when compared to that in age-matched WKY rats. No significant differences were evident in the GPx-1 protein abundance, and its relative mRNA levels, GR, GST activity, and total GSH content between SHR and age-matched WKY rats. The lower GPx activity suggests of an impairment of the GSH system in the SHR, which might be due to an abnormality in its protein rather than non-availability of a cofactor. Its role in the development of hypertension in SHR however remains unclear.     

微小RNA在自发性高血压大鼠主动脉的差异表达

微小RNAs(microRNAs,miRNAs)是一类基因组编码、非蛋白质编码的小RNA,在转录后水平负性调节靶基因表达.本研究探讨miRNAs在自发性高血压大(spontaneously hypertensive rats,SHR)主动脉的表达特征及其与高血压的关系.取4、8、16和24周龄雄性SHR大鼠及同龄正常血压对照(Wistar-Kyoto,WKY)大鼠.MiRanda、TargetScan和PicTar用于候选miRNAs及靶基因预测分析.通过实时定量RT-PCR检测大鼠主动脉miR-1、miR-133a、miR-155及miR-208的表达,并进一步通过实时定量RT-PCR检测呈差异表达的miR-155和miR-208的预测靶基因mRNA表达.结果显示,SHR大鼠主动脉miR-155表达在4、8、24周时与同龄WKY大鼠无显著差异,但在16周时明显低于同龄WKY大鼠(P<0.05),且大鼠主动脉miR-155表达量与血压呈负相关(r=-0.525,P<0.05).MiR-208表达在4周龄时最高,随年龄增长明显下降(P<0.05),其表达水平与血压和年龄呈负相关(r=-0.400,P<0.05;r=-0.684,P<0.0001),但在SHR和WKY大鼠之间无显著差异.miR-1和miR-133a在各年龄组SHR和WKY大鼠间未呈现差异表达.MiR-155和miR-208表达与相应预测靶基因mRNA表达无显著负相关性.以上结果表明,miR-155表达在成年SHR大鼠主动脉明显低于WKY,并与血压呈负相关,提示miR-155可能参与高血压的发生发展,主动脉miR-155表达异常可能是SHR大鼠血压升高的原因之一.大鼠主动脉miR-208表达在幼年时最高,随年龄增长而明显下降,提示其可能与血管发育有关.     

Sleep-related sympathovagal imbalance in SHR

The role of the autonomic nervous system in spontaneous hypertension during each stage of the sleep-wake cycle remains unclear. The present study attempted to evaluate the differences in cardiac autonomic modulations among spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY), and Sprague-Dawley rats (SD) across sleep-wake cycles. Continuous power spectral analysis of electroencephalogram, electromyogram, and heart rate variability was performed in unanesthetized free moving rats during daytime sleep. Frequency-domain analysis of the stationary R-R intervals (RR) was performed to quantify the high-frequency power (HF), low-frequency power (LF)-to-HF ratio (LF/HF), and normalized LF (LF%) of heart rate variability. WKY and SD had similar mean arterial pressure, which is significantly lower than that of SHR during active waking, quiet sleep, and paradoxical sleep. Compared with WKY and SD, SHR had lower HF but similar RR, LF/HF, and LF% during active waking. During quiet sleep, SHR developed higher LF/HF and LF% in addition to lower HF. SHR ultimately exhibited significantly lower RR accompanied with higher LF/HF and LF% and lower HF during paradoxical sleep compared with WKY. We concluded that significant cardiac sympathovagal imbalance with an increased sympathetic modulation occurred in SHR during sleep, although it was less evident during waking.     

Dietary sodium intake and age in spontaneously hypertensive rats: effects on blood pressure and sympathetic activity

Spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) were placed on sodium restricted diets (9 and 17 mumol/g) or on a regular sodium diet (101 mumol/g) at 2, 4, 7, or 10 weeks of age, and continued until 16 weeks of age. Severe sodium restriction (9 mumol/g) initiated at 2 or 4 weeks of age prevented hypertension development in SHR and severely retarded growth. Hypertension development was attenuated when 9 mumol/g was initiated at 7 weeks of age, and was not affected when started at 10 weeks of age. Mean arterial pressure (MAP) in WKY receiving 9 mumol Na/g initiated at 2 and 4 weeks of age was below normal, but was not affected when this diet was given at 7 or 10 weeks of age. Less severe sodium restriction (17 mumol Na/g) resulted in a reduction in hypertension development when initiated at 2, 4, and 7 weeks of age, but not at 10 weeks of age. MAP was normal in WKY receiving 17 mumol Na/g at all ages of diet initiation. When the 9 or 17 mumol Na/g diet were initiated at 2, 4, and 7 weeks of age, the response of blood pressure to hexamethonium administration was blunted in SHR relative to both WKY receiving the same diet, and to control SHR receiving 101 mumol Na/g. We conclude that both WKY and SHR require a minimum amount of dietary sodium for normal growth and for the achievement of normal BP in WKY, and hypertension in SHR. This sodium requirement decreases with age. SHR and WKY exhibit similar sensitivities to sodium intake with respect to body weight, but the effects on BP are more pronounced in SHR. The BP lowering effects of dietary sodium restriction may be due to a blunting of the pressor effectiveness of the sympathetic nervous system.     

Platelet serotonin content and uptake in spontaneously hypertensive rats

Platelet serotonin (5-HT) content and uptake were studied in male SHR and WKY at various ages. Blood was withdrawn from the carotid artery under anesthesia and 5-HT levels determined from platelet rich plasma (PRP) using a HPLC technique coupled with an electrochemical detection method. Platelet 5-HT uptake was studied by incubating PRP at 37 degrees C for 10 sec with increasing concentrations of 3H-5HT. Lineweaver- Burk plots of 3H-5HT uptake were linear suggesting simple Michaelis- Menten uptake kinetics. The SHR had more platelets than age-matched controls and consequently a higher blood circulating pool of 5-HT. Nevertheless, the 5-HT platelet levels were similar to those of their age-matched rats. The 5 week-old SHR and WKY had greater numbers of platelets and higher 5-HT platelet levels than the older rats of both strains. The affinity constants (Km) and the maximal velocities (Vmax) of platelet 5-HT uptake did not differ significantly between the 12 week- and the 6 month-old SHR and WKY. These data suggest that the SHR do not show the same impairment in platelet 5-HT metabolism as observed in essential hypertension in man.     

Renal Na+-K+-ATPase in weanling and adult spontaneously hypertensive rats

The interrelationships among plasma renin activity (PRA, ng AI/ml plasma/hr), aldosterone concentration (ng%), and renal Na+-K+-ATPase activity (mumole PO4/mg protein/hr) were studied in 9 weanling normotensive spontaneously hypertensive rats (SHR), 9 adult hypertensive SHR, and 9 weanling and 9 adult normotensive Wistar-Kyoto rats (WKY). All groups were placed on a normal (0.4% sodium) diet. PRA and plasma aldosterone, measured in samples drawn from the ether-anesthetized rat, were higher in weanling SHR (15.2 +/- 2.0, 37 +/- 4.2) than in WKY. PRA measured in samples collected from a separate group of unanesthetized weanling SHR was also greater than in age-matched WKY. In adult SHR, PRA (6.1 +/- 0.9) and plasma aldosterone (20.0 +/- 2.7) were decreased. During the weanling period Na+-K+-ATPase activity in SHR was not only greater than in age-matched WKY but was also increased compared to adult normotensive and hypertensive rats (137 +/- 9 weanling SHR, 89 +/- 7 weanling WKY, 73 +/- 11 adult SHR, 84 +/- 17 adult WKY). Thus, during the weanling period the renin-angiotensin-aldosterone (R-A-A) system and renal Na+-K+-ATPase activity are activated in SHR. The elevation of Na+-K+-ATPase activity may be due to increased aldosterone levels. It was noted, however, that plasma aldosterone was similar in adult WKY and weanling SHR, while Na+-K+-ATPase activity was higher in SHR. These findings involving R-A-A and renal Na+-K+-ATPase activity prior to the elevation of blood pressure suggest that the kidneys may play a role in the initiation of hypertension in SHR.     

Effects of ovariectomy on indices of insulin resistance, hypertension, and cardiac energy metabolism in middle-aged spontaneously hypertensive rats (SHR).

Insulin resistance is a risk factor for coronary heart disease. The protection of young women from coronary events is sharply reduced with menopause. To assess the impact of menopause on glucose tolerance, insulin resistance, body weight gain, heart size, and cardiac energy metabolism, we studied 28-week-old female SHR and Wistar-Kyoto (WKY) rats, who were either ovariectomized (SHR(OVX) and WKY(OVX)) or sham-operated (SHR(SHAM) and WKY(SHAM)). Animals underwent blood-pressure measurement and an oral glucose tolerance test (OGTT). Hearts were weighed and assayed for metabolic enzyme activities. Female SHR were 33 % lighter and hypertensive (+ 36 mmHg), with 33 % larger hearts (when corrected for body weight differences) compared to WKY. Although ovariectomized animals of both strains were heavier overall than their sham-operated counterparts, when heart weights were corrected for body weight, both OVX strains had lighter hearts than both SHAM strains. Glucose and insulin responses during OGTT were similar between the four groups; however, free fatty acid (FFA) responses were approximately 50 % greater in SHR than WKY, although less in SHR(OVX) than SHR(SHAM). WKY(OVX) demonstrated 8 % lower ventricular hexokinase activity than WKY(SHAM), which may reflect reduced cardiac glucose utilization. We also noted 16 % higher citrate synthase activity in WKY hearts. In conclusion, the insulin resistance characteristic of younger SHR is blunted in middle-aged female rats, although FFA responses remain elevated. Ovariectomy did not alter in vivo glucose tolerance in this group; however, sex hormones may be important in maintaining normal heart size and the potential for cardiac glucose metabolism.     

Overexpression of non-functional LAT1/4F2hc in renal proximal tubular epithelial cells from the spontaneous hypertensive rat.

The present study examined the expression of type 1 L-amino acid transporter (LAT1) and its associated glycoprotein 4F2hc in freshly isolated renal proximal tubules and immortalized renal proximal tubular epithelial (PTE) cells from spontaneously hypertensive (SHR) and normotensive (WKY) rats. The study also examined the inward and outward transport of [(14)C]-L-leucine, the preferred substrate of LAT1. The abundance of LAT1 and 4F2hc was greater in SHR than in WKY, both in freshly isolated renal proximal tubules and immortalized renal proximal tubular cells. In the absence of extracellular Na(+) the BCH (2-aminobicyclo(2,2,1)-heptane-2-carboxylic acid)-sensitive [(14)C]-L-leucine uptake in SHR PTE cells was approximately 50% that observed in WKY PTE cells (77+/-4 vs 164+/-7 pmol/mg protein). In the absence of extracellular Na(+) the affinity of the transporter for the substrate in WKY PTE cells was 7.7-fold that in SHR cells, as evidenced by lower K(0.5) values. Gene silencing with a LAT1 siRNA and a 4F2hc siRNA significantly reduced LAT1 and 4F2hc expression, which was accompanied by a marked reduction in Na(+)-independent [(14)C]-L-leucine uptake in both SHR and WKY PTE cells. The spontaneous and L-leucine-stimulated outward transfer of [(14)C]-L-leucine was Na(+)-independent in both SHR and WKY PTE cells. The spontaneous [(14)C]-L-leucine efflux was higher in WKY than in SHR PTE cells and the potency of L-leucine to stimulate [(14)C]-L-leucine efflux in WKY (EC(50) = 9 microM) was greater than in SHR PTE cells (EC(50) = 41 microM). It is concluded that the SHR kidney overexpress LAT1/4F2hc units which display low affinity for L-leucine transport.     

Protein kinase C activity and reactivity to phorbol ester in vascular smooth muscle from spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY)

Protein kinase C (PKC) activity in aortic and renal arterial smooth muscle from SHR (20-23 wk male; mean arterial pressure = 178 mm Hg) and WKY (age/sex matched; mean arterial pressure = 126 mm Hg) was quantitated. Activity was greatest in the particulate fractions relative to the soluble fractions in all sources. The only difference between SHR and WKY was in the soluble fraction from SHR renal arteries, which had 2 fold more activity (255 pmol/mg/min) when compared with WKY (136 pmol/mg/min). This difference was not apparently related to force modulation, since the magnitude of isometric force development in renal arteries in response to phorbol 12,13-dibutyrate was not different between SHR and WKY. The magnitude of force developed in response to phorbol 12,13-dibutyrate and PKC activity in the particulate fraction was greatest in aorta vs. renal arteries in both WKY and SHR. These results suggest that regional vascular differences in the amount of PKC activity may exist which are not apparently related to a disease state (i.e., hypertension). These differences may be related to differential sensitivity to phorbol ester-mediated contractions in isolated smooth muscle.     

Upregulation of platelet (L)-arginine: nitric oxide pathway after exercise training in hypertension

We investigated whether physical exercise can affect platelet L-arginine?- nitric oxide pathway in spontaneously hypertensive rats (SHR). Sixteen male SHR and 16 Wistar Kyoto rats (WKY) were divided among exercise (EX) and sedentary (SED) groups. After 20?weeks of treadmill training, systolic blood pressure (mm?Hg) was significantly lower in exercised spontaneously hypertensive rats (SHR/EX; 138?± 8) than in sedentary spontaneously hypertensive rats (SHR/SED; 214?± 9). Exercise significantly increased platelet L-arginine transport (pmol L-arginine·(10(9) cells)(-1)·min(-1)), assessed by incubation with L-[(3)H]-arginine, in both WKY (SED, 0.196?± 0.054 compared with EX, 0.531?± 0.052) and SHR (SED, 0.346?± 0.076 compared with EX, 0.600?± 0.049). Nitric oxide synthase (NOS) activity (pmol L-citrulline·(10(8) cells)(-1)), measured by the conversion of L-[(3)H]-arginine to L-[(3)H]-citrulline, was significantly increased in SHR/EX (0.072?± 0.007) compared with SHR/SED (0.038?± 0.007), but no changes were observed in WKY. The iNOS and eNOS protein levels assessed by Western blot were not affected by exercise. This upregulation of the platelet L-arginine-NO pathway may attenuate the risk of thromboembolic events, supporting the role of exercise in hypertension management.