Central reactive oxygen species mediate cardiovascular effects of urotensin II in spontaneously hypertensive rats

Central urotensin II (UII) may participate in the regulation of cardiovascular functions by stimulating sympathy pathway. However, the central mechanism remained unknown. Recent studies have shown that brain reactive oxygen species (ROS) mediate the sympatho-excitatory effects. In the present study, we tested the hypothesis that ROS mediate central cardiovascular effects of UII. Experiments were conducted in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Immunocytochemistry, intracerebroventricular (icv) infusion and lucigenin-enhanced chemiluminescence assay were employed to detect UII receptor expression and ROS level, respectively. The following results were obtained: (1) Expressions of UII receptors of rostral ventrolateral medulla (RVLM) and nucleus tractus solitarii (NTS) were increased in SHR rats compared with WKY rats (P < 0.05). (2) UII (icv) significantly increased mean arterial pressure (MAP) (P < 0.05), and the effect of UII was significantly more pronounced in SHR rats than that in WKY rats (P < 0.05); (3) Tempol (a superoxide dismutase mimic) or Urantide (an antagonist of UII receptor) pretreatments eliminated the pressor effect of UII (P < 0.05) in SHR rats; (4) Brain superoxide level was increased in UII-treated SHR rats compared with that in cerebrospinal fluid (CSF)-treated SHR rats (P < 0.05). These results indicate that ROS mediate central cardiovascular effects of UII in SHR rats and provide evidence for a novel relationship between UII and ROS.     

Antihypertensive effect of low ethanol intake in spontaneously hypertensive rats

Light to moderate drinking in humans lowers the risk of coronary heart disease and may lower blood pressure. We examined the effect of chronic low daily alcohol consumption on blood pressure, platelet cytosolic free calcium [Ca²⁺]_i, tissue aldehyde conjugates and renal vascular changes in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). We also examined the effects of the same weekly amount of alcohol consumption over a one day period each week simulating weekend drinking in humans. Animals, age 7 weeks, were divided into six groups of six animals each and were treated as follows: WKY and SHR control, normal drinking water; WKY and SHR, 0.5% ethanol in drinking water; WKY and SHR, 3.5% ethanol in drinking water one day/week. After 14 weeks systolic blood pressure, platelet [Ca²⁺]_i, liver, kidney and aortic aldehyde conjugates were significantly higher (p < 0.05) in untreated SHRs as compared to untreated WKYs. Daily 0.5% ethanol consumption in SHRs significantly (p < 0.05) attenuated these changes and also attenuated smooth muscle cell hyperplasia and narrowing of the lumen in small arteries and arterioles of the kidney. WKY rats treated with 0.5% ethanol had lower aldehyde conjugates without any significant effect on blood pressure and platelet [Ca²⁺]_i as compared to WKY controls. Consumption of 3.5% ethanol one day/week did not affect blood pressure and associated changes in normotensive WKY rats or hypertensive SHRs as compared to their respective controls. These results suggest that chronic daily low ethanol intake lowers blood pressure in SHRs by lowering tissue aldehyde conjugates and cytosolic free calcium.     

Vasodilating effect of di-peptides in thoracic aortas from spontaneously hypertensive rats

In this study, we found that antihypertensive di-peptide Val-Tyr (VY) showed a vascular relaxation effect in KCl-induced contraction of thoracic aorta rings from 18-week-old spontaneously hypertensive rats among di-peptides of VY, Ile-Tyr, and Tyr-Val irrespective of their angiotensin I-converting enzyme inhibitory activity. The effect was endothelium-independent, and was closely associated with vascular responses in the vascular smooth muscle layer.     

Differential effect of losartan in female and male spontaneously hypertensive rats

We demonstrated that the decreased response to acetylcholine observed in aorta of male and female spontaneously hypertensive rats is corrected after sustained (15 days) reduction of blood pressure levels by losartan. In order to verify if the same occurs in resistance vessels, vascular diameter changes induced by topical application of acetylcholine and bradykinin (endothelium-dependent vasodilators) and sodium nitroprusside (endothelium-independent vasodilator) to mesenteric arterioles studied in vivo, in situ were determined in rats treated with losartan for 24 h (acute) or 15 days (chronic). Rats that presented similar reduction (in %) of the blood pressure levels after losartan treatment were chosen. Sodium nitroprusside induced similar responses in losartan-treated and untreated male or female SHR. Whereas in female SHR, losartan corrected the diminished arteriolar response to endothelium-dependent vasodilators after acute and chronic treatment, in male SHR this correction only occurred after chronic treatment. Thus, losartan corrected the endothelial dysfunction more easily in female than in male SHR and independently of the normalization or the magnitude of the reduction of the blood pressure levels. In an attempt to explain the difference, we evaluated the losartan effect on nitric-oxide synthase (NOS) activity and angiotensin II AT1 and AT2 receptor gene expression in these animals. In male and female SHR, NOS activity and AT1 receptor expression were not altered by acute or chronic treatment. On the other hand, AT2 receptor expression was augmented only in female SHR by these treatments. Therefore, augmented AT2 receptor expression, but not alteration of NOS activity or AT1 receptor expression, might explain the difference observed.     

Calpastatin level in spontaneously hypertensive rats

We studied calpastatin activity in erythrocytes of Milan hypertensive and prehypertensive rats, in their normotensive controls, in F1 and F2 hybrids, and in two inbred strains derived from F2, one hypertensive and the other normotensive. Our results show that the decrease in calpastatin activity observed in Milan hypertensive rats was not caused by hypertension, it was transmitted in a recessive way in heterozygous, and it was not correlated to hypertension.     

Interval bisection in spontaneously hypertensive rats

An interval bisection procedure was used to study time discrimination in spontaneously hypertensive rats (SHR), which have been proposed as an animal model for the attention deficit hyperactivity disorder (ADHD); Wistar Kyoto and Wistar rats were used as comparison groups. In this procedure, after subjects learn to make one response (S) following a short duration stimulus, and another (L) following a long duration stimulus, stimuli of intermediate durations are presented, and the percentage of L is calculated for each duration. A logistic function is fitted to these data, and different parameters that describe the time discrimination process are obtained. Four conditions, with different short and long durations (1-4, 2-8, 3-12, 4-16s) were used. The results indicate that time discrimination is not altered in SHR, given that no difference in any of the parameters obtained were significant. Given that temporal processing has been proposed as a fundamental factor in the development of the main symptoms of ADHD, and that deficits in time discrimination have been found in individuals with that disorder, the present results suggest the necessity of exploring time perception in SHR with other procedures and sensory modalities, in order to assess its validity as an animal model of ADHD.     

Antihypertensive effect of tryptic hydrolysate of milk casein in spontaneously hypertensive rats

1. Repeated oral administrations of tryptic hydrolysate of bovine milk casein (CEI) showed antihypertensive effect in spontaneously hypertensive rats. 2. Single oral administration of CEI antagonized the pressor response to angiotensin I. 3. Bovine milk casein hydrolysate inhibited the angiotensin I-converting enzyme (ACE) activity. Three peptides with ACE-inhibiting activity were isolated from CEI. 4. It is suggested that ACE-inhibiting peptides in the tryptic hydrolysate milk casein are absorbed from the intestinal tract and produce an antihypertensive effect.     

G-proteins in kidneys of spontaneously hypertensive rats

G(s alpha)-, total G(i alpha)- and G(q/11alpha)-protein concentrations were investigated by quantitative immunoblotting in membranes of total kidney, renal cortex and medulla as well as in cortical tubules and glomeruli of Spontaneously Hypertensive Rats (SHR) and normotensive Wistar Kyoto rats (WKY), aged 5 weeks, 3 or 8 months. We found that total kidney of 5 week old SHR possess less G(s alpha)-, G(i alpha)- and G(q/11alpha)-proteins than controls. For G(s alpha)-proteins, differences found in total kidney were mirrored both in cortex (tubules and glomeruli) and in medulla. Decreased G(i alpha)-concentrations were accompanied by lower tubular but higher glomerular levels, while medullar levels were also increased. Decreased G(q/11alpha)-concentrations were reflected in decreased glomerular and medullary concentrations. Kidneys of 3 month old SHR and WKY possessed similar concentrations of all G(alpha)-species. In 8 month old SHR similar G(i alpha)-, but decreased G(s alpha)-and G(q/11alpha)-concentrations were observed. The G(s alpha)-decrease was reflected in cortex and medulla, the G(q/11alpha)-decrease in the medulla. We conclude that the main strain-related differences in G(alpha)-concentrations are seen in prehypertensive SHR.     

Val-Glu-Pro对原发性高血压大鼠的体内降压作用

Val-Glu-Pro(VEP)是从钝顶螺旋藻(Spirulina platensis)中发现的一种血管紧张素转化酶(ACE)抑制肽.以原发性高血压大鼠(SHR)为模型,检测单次口服和一周间口服VEP的降压效果,并通过Real-timePCR和酶联免疫吸附法(ELISA)探索其对肾素-血管紧张素系统(RAS)主要成分在SHR大鼠肾脏和血清中的表达调控作用.结果表明:口服VEP的最低有效降压剂量为5mg/kg,加大剂量后表现出剂量效应,最低加权收缩压(WSBP)出现在口服后6h,最低加权舒张压(WDBP)出现在口服后4 h.在一周间口服试验中,10 mg/kg VEP处理组的WSBP在第5日显著低于负对照组.此外,口服VEP显著下调了SHR大鼠肾脏中肾素(renin)、ACE、血管紧张素Ⅱ(AngⅡ)类型1受体(AT1)的mRNA表达,并上调AngⅡ类型2受体(AT2)的mRNA表达,说明VEP的降压效果可能与对RAS系统的抑制作用相关,在高血压的预防和治疗中具有潜在的应用前景.     

Selective effect of tempol on renal medullary hemodynamics in spontaneously hypertensive rats

The present study assessed the short- and long-term effect of tempol, a membrane-permeable mimetic of superoxide dismutase, on renal medullary hemodynamics in spontaneously hypertensive rats (SHR). Tempol was given in the drinking water (1 mM) for 4 days or 7 wk (4-11 wk of age), and medullary blood flow (MBF) was measured over a wide range of renal arterial pressure by means of laser-Doppler flowmetry in anesthetized rats. In addition, the response of the medullary circulation to angiotensin II (5-50 ng x kg(-1) x min(-1) iv) was determined in SHR treated for 4 days with tempol. Compared with control SHR, short- and long-term treatment with tempol decreased arterial pressure by approximately 20 mmHg and increased MBF by 35-50% without altering total renal blood flow (RBF) or autoregulation of RBF. Angiotensin II decreased RBF and MBF dose dependently (approximately 30% at the highest dose) in control SHR. In SHR treated with tempol, angiotensin II decreased RBF (approximately 30% at the highest dose) but did not alter MBF significantly. These data indicate that the antihypertensive effect of short- and long-term administration of tempol in SHR is associated with a selective increase in MBF. Tempol also reduced the sensitivity of MBF to angiotensin II. Taken together, these data support the idea that tempol enhances vasodilator mechanisms of the medullary circulation, possibly by interacting with the nitric oxide system. Increased MBF and reduced sensitivity of MBF to angiotensin II may contribute to the antihypertensive action of tempol in SHR.     

Angiotensin-converting enzyme (kinase II) in pituitary gland of spontaneously hypertensive rats

Angiotensin-converting enzyme (ACE) (kinase II; dipeptidyl carboxypeptidase, EC 3.4.15.1) activity was measured in pituitary gland of young (4-week-old) and adult (18-week-old) male, spontaneously hypertensive rats (SHR) and in age-matched normotensive male Wistar-Kyoto (WKY) control rats. In the three lobes of the pituitary gland ACE activity was significantly higher in young than in adult animals, in both SH and WKY rats. In the anterior lobe, ACE activity was lower in SHR when compared to age-matched Wistar-Kyoto controls. In contrast, ACE activity in the intermediate lobe of the pituitary gland was higher in SHR, and in particular in young animals. The observed differences between young WKY and SH rats in both the intermediate and anterior lobes did not appear to be due to a modified affinity of ACE for the substrate hippuryl-His-Leu, but to alterations in ACE maximal velocity or number of available molecules. No differences in ACE activity were detected between SHR and WKY rats in the posterior lobe. Total protein content was higher in the intermediate lobe and lower in the posterior lobe of young SHR when compared to normotensive controls. The present results suggest the possibility for a role of pituitary ACE in spontaneous (genetic) hypertension in rats.     

Breathing pattern of spontaneously hypertensive rats

The trachea of rats anaesthetized with sodium pentobarbitone was cannulated and the air flow velocity and the pressure of the oesophagus were measured. In the spontaneously hypertensive rats the breathing frequency was higher, the tidal volume and the effective lung resistance were smaller than that of the normotensive Wistar rats. It seems that the neurohumoral control of respiration in SHR animals differs from that of normotensive rats.     

Tissue catecholamine concentrations in spontaneously hypertensive rats

Tissue concentrations of noradrenaline (NA), dopamine (DA) and adrenaline (A) were compared in spontaneously hypertensive (SHR) and normotensive (NCR) rats, aged 1, 3, 8, 14 and 24 weeks The organs analyzed included the brain, subdivided into prosencephalon and rhombencephalon, heart, adrenal glands and kidney. Brain catecholamines were significantly lower in SHR than in NCR, and the difference appeared already at the age of 3 weeks. Concomitant increase was found in the adrenal NA and A concentrations of the SHR. Concentration of NA in the heart decreased in the SHR following onset of hypertension. It is concluded that the diminished NA, DA and A concentrations in the brain as well as the augmented adrenal NA and A levels in the SHR may be causally related to the development of hypertension, while the heart NA level reflects the secondary, hypertension -- related changes.     

Renal microvasculature in spontaneously hypertensive rats.

The renal microvasculature was studied in normotensive rats and in rats with spontaneous hypertension. The microvascular pattern was normal in both groups of animals, suggesting normal renin secretion. This may or may not indicate a role for renin in the cause of spontaneous hypertension.     

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.     

Impaired angiotensin-induced drinking in spontaneously hypertensive rats

The drinking response during the 30 minutes following intracerebroventricular injection of angiotensin II (AII) (1 to 200 ng) was compared in male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto control rats (WK). SHR drank significantly less than WK at the 10, 50 and 100 ng doses. In contrast, responses to intracerebroventricular carbachol and intraperitoneal hypertonic saline were not different between SHR and WK. These agents are believed to induce drinking by mechanisms independent of angiotensin. Binding of I¹²⁵-labelled AII to particles prepared from the hypothalamus, thalamus, septum and midbrain (HTSM) region was measured in one month old male and two month old female SHR and their respective age matched WK controls. No differences were found in binding between SHR and WK of either sex. These data demonstrate an impairment of drinking responses in the SHR which seem to be specific for angiotensin. This finding supports the hypothesis that the CNS angiotensin system might be abnormal in these animals.     

Angiotensin stimulates respiration in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) have an activated brain angiotensin system. We hypothesized 1) that ventilation (V) would be greater in conscious SHR than in control Wistar-Kyoto (WKY) rats and 2) that intravenous infusion of the ANG II-receptor blocker saralasin would depress respiration in SHR, but not in WKY. Respiration and oxygen consumption (VO(2)) were measured in conscious aged-matched groups (n = 16) of adult female SHR and WKY. For protocol 1, rats were habituated to a plethysmograph and measurements obtained over 60-75 min. After installation of chronic intravenous catheters, protocol 2 consisted of 30 min of saline infusion ( approximately 14 microliter. kg(-1). min(-1)) followed by 40 min of saralasin (1.3 microgram. kg(-1). min(-1)). V, tidal volume (VT), inspiratory flow [VT/inspiratory time (TI)], breath expiratory time, and VO(2) were higher, and breath TI was lower in "continuously quiet" SHR. In SHR, but not in WKY rats, ANG II-receptor block decreased V, VT, and VT/TI and increased breath TI. During ANG II-receptor block, an average decrease in VO(2) in SHR was not significant. About one-half of the higher V in SHR appears to be accounted for by an ANG II mechanism acting either via peripheral arterial receptors or circumventricular organs.     

Antihypertensive effect of an extract of Passiflora edulis rind in spontaneously hypertensive rats

Orally administered methanol extract of Passiflora edulis rind (10 mg/kg or 50 mg/kg) or luteolin (50 mg/kg), which is one of consistent polyphenols of the extract, significantly lowered systolic blood pressure in spontaneously hypertensive rats (SHRs). Quantitative analysis by liquid chromatography tandem mass spectrometry (LC-MS/MS) showed that the extract contained 20 microg/g dry weight of luteolin and 41 microg/g dry weight of luteolin-6-C-glucoside. It also contained gamma-aminobutyric acid (GABA, 2.4 mg/g dry weight by LC-MS/MS or 4.4 mg/g dry weight by amino acid analysis) which has been reported to be an antihypertensive material. Since the extract contained a relatively high concentration of GABA, the antihypertensive effect of the extract in SHRs might be due mostly to the GABA-induced antihypertensive effect and partially to the vasodilatory effect of polyphenols including luteolin.     

Plasma concentrations of endothelin-1 in spontaneously hypertensive rats and DOCA-salt hypertensive rats

To investigate the possible involvement of endothelin-1 (ET-1), an endothelium-derived potent vasoconstrictor peptide, in the pathophysiology of hypertension, plasma ET-1 levels in 15-week-old spontaneously hypertensive rats (SHR) and DOCA-salt hypertensive rats were measured with a sandwich-type enzyme immunoassay. The vasocontractile effect of ET-1 in aortic helical preparations was significantly more sensitive in DOCA-salt hypertensive rats than in control sham-operated rats, but plasma levels of ET-1 did not differ between them. Plasma ET-1 levels in genetically hypertensive rats (SHR and stroke-prone SHR) were significantly lower than those in age-matched normotensive Wistar-Kyoto (WKY) rats. The plasma concentrations of big ET-1, a precursor of ET-1, in both SHR and SHR-SP were significantly lower than those of WKY, suggesting that the production of ET-1 is decreased in rats of genetic hypertension. Although the vascular reactivity to ET-1 increased in both DOCA-salt hypertensive and genetically hypertensive rats, present findings of the plasma ET-1 levels suggest that the role of ET-1 in the vascular control system may be different in DOCA-salt hypertensive rats and genetically hypertensive rats.