Dietary vitamin C supplementation decreases blood pressure in DOCA-salt hypertensive male Sprague Dawley rats and this is associated with increased liver oxidative stress

The effects of a vitamin C supplemented diet on blood pressure, body and liver weights, liver antioxidant status, iron and copper levels were investigated in DOCA-salt treated and untreated Sprague-Dawley (SD) male rats after 8 weeks of treatment. Vitamin C supplementation had no effect on blood pressure in SD rats but induced a significant decrease in blood pressure in DOCA-salt treated rats, the decrease being more efficient at 50 mg/kg of vitamin C than at 500 mg/kg. Hepatic lipid peroxidation and iron levels were significantly increased in DOCA-salt hypertensive rats whereas total hepatic antioxidant capacity (HAC), glutathione peroxidase (GSH-Px) and catalase (CAT) activities were decreased. Vitamin C supplementation did not affect the overall antioxidant defences of control SD rat livers. In contrast, vitamin C supplementation accentuated the DOCA-salt induced accumulation of liver iron and lipid peroxidation. This occurred without any notable aggravation in the antioxidant deficiency of vitamin C supplemented DOCA-salt treated rat livers. Our data suggest that DOCA-salt treatment induces an accumulation of iron in rat livers which is responsible for the prooxidant effect of vitamin C. The normalization of blood pressure in DOCA-salt treated rats by vitamin C supplementation appears thus independent from liver antioxidant status.     

Mechanism of the anti-hypertensive property of the naturally occurring phenolic,malabaricone C in DOCA-salt rats

In this study, we studied whether chronic oral administration of the natural antioxidant, malabaricone C (mal C) can reduce blood pressure (BP) and attenuate cardio-vascular remodeling in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The dose of mal C for its anti-hypertensive action was optimized by measuring the systolic BP (SBP). DOCA-salt rats showed very high SBP, associated with organ hypertrophy, collagen depositions, and inflammatory infiltrations in cardiac and aortic sections, reduced plasma total antioxidant status and NO level, and increased levels of TBARS, PGI2 as well as vasoconstrictors (AVP, Big ET, and ET-1). DOCA-salt also reduced smooth muscle- and endothelium-dependent vascular relaxation in rats. Mal C reversed all these changes of the DOCA-salt rats and improved their vascular reactivity. Mal C exerts anti-hypertensive property in DOCA-salt rats by reducing oxidative stress and organ hypertrophy, and improving endothelial and vascular functions. Given that mal C has appreciable natural abundance and is non-toxic to rodents, further studies would help in establishing its medicinal potential against hypertension.     

Effect of angiotensin II on energetics,glucose metabolism and cytosolic NADH/NAD and NADPH/NADP redox in vascular smooth muscle

We investigated the potential of chronic administration of an oral daily dose (10 mg/kg) of the dietary flavonoid quercetin to prevent hypertension and oxidative stress induced by deoxycorticosterone acetate (DOCA)-salt in rats. We have compared its effects to those produced by the well-known anti-hypertensive drug verapamil, administered orally (20 mg/kg/day). Quercetin and verapamil treatments reduced systolic blood pressure of DOCA-salt rats in approximately 67.6 and 63.3% respectively, producing no effect in control animals. Both drugs reduced significantly hepatic and renal hypertrophy induced by DOCA-salt administration, while only quercetin prevented cardiac hypertrophy. Decreased endothelium-dependent relaxation to acetylcholine of aortic rings from DOCA-salt-treated rats was improved by quercetin, but verapamil only enhanced it in the presence of superoxide dismutase (SOD) plus catalase. Increased plasma and heart thiobarbituric acid reactive substances (TBARS) and total glutathione (GSH) levels in liver and heart, decreased liver glutathione peroxidase (GPX) and liver and kidney glutathione transferase (GST) activities were observed in DOCA-salt-treated rats compared to the control animals. The antihypertensive effect of quercetin was accompanied by normalisation of plasma TBARS values, improvement of the antioxidant defences system in heart and liver, restoring total GSH levels in both organs and altered liver GST and GPX activities, and improving kidney GST activity. Verapamil treatment only restored GSH levels in heart, having no effect on other alterations induced by DOCA-salt chronic administration in the antioxidant defences analysed. In conclusion, quercetin shows both antihypertensive and antioxidant properties in this model of mineralocorticoid hypertension, while verapamil exhibits only antihypertensive effects.     

Effects of chronic quercetin treatment on hepatic oxidative status of spontaneously hypertensive rats

The effects of chronic administration of an oral daily dose of quercetin (10 mg Kg^–1), the most abundant dietary flavonoid, were investigated on hepatic oxidative status in spontaneously hypertensive rats and normotensive Wistar Kyoto rats. Decreased liver glutathione peroxidase activity, increased liver total glutathione levels and increased both hepatic and plasmatic malondialdehyde concentrations were observed in spontaneously hypertensive rats when compared to Wistar Kyoto rats. In spontaneously hypertensive rats, treatment with quercetin for 5 weeks reduced blood pressure, increased glutathione peroxidase activity and reduced both plasma and hepatic malondialdehyde levels. However, none of these effects were observed in Wistar Kyoto rats. In conclusion, quercetin shows both antihypertensive and antioxidant properties in this model of genetic hypertension.     

Effects of Melothriamaderaspatana leaf extract on antioxidant status in sham-operated and uninephrectomized DOCA-salt hypertensive rats

The present study was designed to investigate the antihypertensive and antioxidant effect of Melothria maderaspatana leaf extract (MME) on sham-operated and DOCA-salt (deoxycorticosterone acetate) induced hypertensive rats. Administration of DOCA-salt significantly increased the systolic (from 127 to 212 mm Hg) and diastolic (from 91 to 174 mm Hg) blood pressure compared to sham-operated control rats, while treatment with MME significantly reduced the systolic (from 212 to 135 mm Hg) and diastolic (from 174 to 96 mm Hg) blood pressure compared to hypertensive control. In DOCA-salt rats, the plasma and tissue concentration of thiobarbituric acid reactive substances (TBARS) and lipid hydroperoxide (LOOH) significantly increased and administration of MME significantly reduced these parameters towards the levels in sham-operated control. In hypertensive rats, activities of the enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) and levels of non-enzymatic antioxidants such as vitamin C, vitamin E and reduced glutathione (GSH) decreased significantly in the plasma and tissues. Administration of MME returned the enzymatic and non-enzymatic antioxidants towards sham-operated control. MME shows both antihypertensive and antioxidant properties in DOCA-salt hypertensive rats and, among the three different doses tested, 200 mg/kg caused the maximum effect.     

Possible role of an endogenous opioid in the antihypertensive action of propranolol in spontaneously hypertensive rats

The effect on systolic blood pressure and heart rate of the acute and chronic intraperitoneal (i.p.) administration of d- and dl-propranolol was investigated on unanesthetised spontaneously hypertensive rats. The effect of naloxone on the propranolol induced hypotension was also studied to test the hypothesis that the antihypertensive effect of propranolol involves the release of an endogenous opiate. On i.p. administration, 3 mg/kg d-propranolol was inactive; 3 and 30 mg/kg dl-propranolol decreased blood pressure and heart rate in a dose-dependent manner. When the rats were pretreated with 2 mg/kg naloxone i.p., the effect of propranolol on the blood pressure was nearly completely abolished, while that on the heart rate was only partially blocked. Chronic administration of dl-propranolol (30 mg/kg b.i.d.) to spontaneously hypertensive rats from the age of 6 weeks (prehypertensive phase) for 29 days prevented the development of hypertension while the rats treated with physiological saline for 29 days (control group) developed hypertension. Naloxone (2 mg/kg i.p.) administered on the 29th day to chronically treated rats induced a reversal of the propranolol action on systolic blood pressure and heart rate, i.e., blood pressure and heart rate increased. Naloxone had no such effect in the control group. We suggest that the release of an endogenous opioid contributes to the acute and chronic antihypertensive action of i.p. propranolol in spontaneously hypertensive rats and that the secretion of endogenous opioids participating in the control of cardiovascular functions is influenced by adrenergic mechanisms.     

Evolution of liver antioxidant status and iron implication during the development of deoxycorticosterone-saline hypertension in rats

Hypertension is known to be associated with an oxidative stress resulting from an imbalance of antioxidant defense mechanisms in various tissues. The purpose of this study was to investigate the relationship between the increase of arterial blood pressure, measured during the gradual development of experimental hypertension in deoxycorticosterone (DOCA)-salt-treated rats, and an early imbalance of liver antioxidant status. The levels of liver oxidant/antioxidant markers and iron were studied during the induction of hypertension in 3-, 6-, and 8-wk DOCA-salt-treated Sprague-Dawley rats. Hepatic antioxidant defenses were decreased as early as 3 wk of hypertensive treatment: the decrease of peroxidase-reductase-transferase and catalase activities was associated with a significant increase of thiobarbituric acid reactive substances (TBARS) levels. Liver oxidative stress increased until 6 wk, and remained stable at 8 wk of DOCA-salt treatment. Concurrently, liver iron levels were increased at 6 wk and returned to normal values after 8 wk of hypertensive treatment. Iron seems to be an inductor of liver oxidative stress and responsible for the persistent oxidative stress, most likely through secondary free-radical release. Thus, our data (1) confirm that hypertension in DOCA-salt-treated rats might be a free-radical-dependent disease where hepatic oxidant/antioxidant imbalance is obviously involved from the beginning of blood pressure elevation and (2) suggest that the use of suitable iron chelators might reverse liver oxidative stress associated with the increase of blood pressure.     

Polyphenols restore endothelial function in DOCA-salt hypertension: role of endothelin-1 and NADPH oxidase

Red wine polyphenols (RWPs) have been reported to exert beneficial effects in preventing cardiovascular diseases, such as hypertension. We studied the effects of chronic treatment with RWPs and apocynin, an inhibitor of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, on blood pressure, endothelial function, and oxidative status in deoxycorticosterone acetate (DOCA)-salt-induced hypertension. Rats were administered RWPs (40 mg/kg) or apocynin (33 microg/kg) daily by gavage for 5 weeks. Plasma catechin levels were detected only after RWP treatment. RWPs and apocynin prevented both the increase in systolic blood pressure and the proteinuria induced by DOCA-salt. Plasma malonyldialdehyde levels, urinary iso-prostaglandin F(2alpha) excretion, aortic superoxide production, and aortic NADPH oxidase activity were found to be increased in animals of the DOCA group. RWP and apocynin treatments reduced these parameters in DOCA-salt rats, having no effect on control rats. However, only RWPs reduced the increase in plasma endothelin-1 (ET-1) levels and aortic p22(phox) gene overexpression found in DOCA-salt animals. RWPs and apocynin also improved the blunted endothelium-dependent relaxation response to acetylcholine in noradrenaline-precontracted aortic rings. All these results suggest that chronic treatment with RWPs prevents hypertension and vascular dysfunction. RWPs prevent vascular oxidative stress by inhibiting NADPH oxidase activity and/or by reducing ET-1 release.     

Systemic antioxidant properties of L-carnitine in two different models of arterial hypertension

In spite of a wide range of drugs being available in the market, treatment of arterial hypertension still remains a challenge, and new therapeutic strategies could be developed in order to improve the rate of success in controlling this disease. Since oxidative stress has gained importance in the last few years as one of the mechanisms involved in the origin and development of hypertension, and considering that L-carnitine (LC) is a useful compound in different pathologies characterized by increased oxidative status, the aim of the present study was to investigate the systemic antioxidant effect of LC and its correlation to blood pressure in two experimental models of hypertension: (1) spontaneously hypertensive rats (SHR) and (2) rats with hypertension induced by N^ω-nitro-L-arginine methyl ester (L-NAME). Treatment with captopril was also performed in SHR in order to compare the antioxidant and antihypertensive effects of LC and captopril. The antioxidant defense capacity, in terms of antioxidant enzyme activity, glutathione system availability and plasma total antioxidant capacity, was measured in both animal models with or without an oral, chronic treatment with LC. All the antioxidant parameters studied were diminished in SHR and in L-NAME-treated animals, an alteration that was in general reversed after treatments with LC and captopril. In addition, LC produced a significant but not complete reduction of systolic and diastolic blood pressure levels in these two models of hypertension, whereas captopril was able to normalize blood pressure. Both LC and captopril prevented the reduction in nitric oxide (NO) levels observed in hypertensive animals. This suggests a decrease in the systemic oxidative stress and a higher availability of NO induced by LC in a similar way to captopril’s effects, which could be relevant in the management of arterial hypertension eventually.     

Antioxidant status,lipid peroxidation,mixed function oxidase and UDP-glucuronyl transferase activities in livers from control and DOCA salt-hypertensive male Sprague Dawley rats

The effects of DOCA-salt hypertensive treatment on hepatic glutathione-dependent defense system, antioxidant enzymes, lipid peroxidation, mixed function oxidase and UDP-glucuronyl transferase activities were investigated in male Sprague Dawley rats.Compared with controls, DOCA-salt hypertensive rats had lower body weights (linked to liver hypertrophy). Mixed function oxidase and p-nitrophenol-UGT activities were not affected by the treatment but a significant lower rate of the glucuronoconjugation rate of bilirubin (p < 0.001) was observed in DOCA-salt hypertensive rats. While cytosolic glutathione contents and glutathione reductase activity were not affected, glutathione peroxidase (p < 0.001), glutathione transferase (p < 0.001) and catalase (p < 0.01) activities were decreased and associated with higher malondialdehyde contents (p < 0.001) in treated rats. The imbalance in liver antioxidant status (increasing generation of cellular radical species), associated with increases in lipid peroxidation, suggests that oxidative stress might be directly related to arterial hypertension in DOCA-salt treated male Sprague Dawley rats.     

Age-dependent DOCA-salt hypertension in Brattleboro rats: the role of vasopressin

The age-dependent participation of endogenous vasopressin (VP) during the development of DOCA-salt hypertension was studied in young (28-day-old) and adult (75-day-old) Brattleboro rats. VP-deficient homozygous (DI) rats were compared to heterozygous (non-DI) littermates which do synthetize VP. Six weeks of DOCA-salt treatment did not increase blood pressure (BP) in adult DI rats. On the other hand, in young DI animals there was a significant rise of systolic and mean arterial pressure accompanied by the hypertrophy of the left ventricle. This moderate DOCA-salt hypertension of young DI rats contrasted with severe hypertension of young non-DI rats. Increased BP response of young VP-deficient DOCA-salt treated rats was independent of the saline intake or blood volume expansion which were similar in young hypertensive and adult normotensive DI animals. It could be concluded that vasopressin is not essential for the induction of DOCA-salt hypertension in young rats even if VP is responsible for the magnitude of BP elevation. In contrast to young animals vasopressin is very important for the development of DOCA-salt hypertension in adult rats.     

Increased reactive oxygen species contributes to kidney injury in mineralocorticoid hypertensive rats.

Hypertension is associated with increased reactive oxygen species (ROS). Renal ROS production and their effects on renal function have never been investigated in mineralocorticoid hypertensive rats. In this study we hypothesized that increased ROS production in kidneys from deoxycorticosterone (DOCA)-salt rats contributes to adverse renal morphological changes and impaired renal function in DOCA-salt hypertensive rats. We also determined whether ROS-induced renal injury was dependent on blood pressure. DOCA-salt hypertensive rats exhibited a marked increase in blood pressure, renal ROS production, glomerular and tubular lesions, and microalbuminuria compared to sham rats. Treatment of DOCA-salt hypertensive rats with apocynin for 28 days resulted in attenuation of systolic blood pressure and improvement of renal morphology. Renal superoxide level in DOCA-salt rats was 215% of sham-operated rats and it was significantly decreased to 140% with apocynin treatment. Urinary protein level was decreased from 27 +/- 3 mg/day in DOCA-salt hypertensive rats to 9 +/- 2 mg/day. 28 days of Vitamin E treatment also reduced renal injury in regard to urinary protein level and renal morphology but had no effect on blood pressure in DOCA-salt rats. Increased urinary 8-isoprostane, a marker for oxidative stress, in DOCA-salt hypertensive rats (55 +/- 8 ng/day) was diminished by vitamin E treatment (24 +/- 6 ng/day). These data suggest that renal injury characteristic of mineralocorticoid hypertension is associated with oxidative stress and is partly independent of blood pressure.     

Magnesium supplementation and deoxycorticosterone acetate--salt hypertension: effect on arterial mechanical properties and on activity of endothelin-1

The aim of this study was to show whether the decrease in blood pressure induced by Mg supplementation in deoxycorticosterone acetate - salt (DOCA-salt) hypertensive rats is associated with mechanical modifications of blood vessels and (or) changes in tissular production and (or) vasoconstrictor activity to endothelin-1. DOCA-salt treatment increased blood pressure, media thickness, cross-sectional area, and lumen diameter of carotid arteries. Distensibility and incremental elastic modulus versus stress were not altered in carotid arteries, suggesting that the DOCA-salt vessel wall adapts structurally to preserve its blood pressure buffering capacity. Magnesium supplementation attenuated DOCA-salt hypertension. In comparison with normotensive rats, systolic, mean, and pulse pressures were higher whereas diastolic pressure was not different in Mg-supplemented DOCA-salt rats. Magnesium supplementation did not significantly modify the elastic parameters of carotid arteries. In resistance mesenteric arteries, DOCA-salt hypertension induces an inward hypertrophic remodeling. Magnesium supplementation attenuates wall hypertrophy and increases lumen diameter to the normotensive diameter, suggesting a decrease in peripheral resistance. Magnesium supplementation normalizes the altered vasoconstrictor activity of endothelin-1 in mesenteric arteries and attenuates endothelin-1 overproduction in kidney, left ventricle, and aorta of DOCA-salt rats. These findings suggest that Mg supplementation prevents blood pressure elevation by attenuating peripheral resistance and by decreasing hypertrophic effect of endothelin-1 via inhibition of endothelin-1 production.     

Chronic effect of prazosin and yohimbine on the renal epinephrine content of DOCA-sodium and SHR-hypertensive rats

The chronic effect of two alpha-adrenergic receptor blockers, prazosin and yohimbine, on the renal noradrenaline (NA) content was investigated in two models of hypertensive rats, the DOCA-salt and the spontaneously hypertensive rats (SHR). In DOCA-salt rats an inversal relation exists between the level of blood pressure and renal NA content in all groups studied, except those treated with yohimbine and prazosin plus yohimbine. In SHR rats a decreased renal NA content has been detected with respect to their normotensive Wistar-Kyoto (WKY) rat controls. The administration of prazosin and/or yohimbine did not alter the renal NA content of the SHR rats, while on the contrary these agents produced an elevation of these levels in kidneys from normotensive WKY rats. These results suggest that the alpha-selective blocker agents used, demonstrate a different effect on the renal NA content in the two models of hypertension studied.     

Central neurotransmitter receptors in hypertensive rats

Muscarinic cholinergic ([³H]QNB), α₁ ? ([³H]WB-4101), and α₂ ? ([³H]clonidine) adrenergic ligand binding was measured in various regions of the brains of adult normotensive, spontaneously hypertensive, and DOCA-salt hypertensive rats. There was a 66% increase in the number of α₁-adrenergic receptors in hypothalamus of the spontaneously hypertensive rats as compared to normotensive controls, with no change in the K_d value. There were no other differences in the spontaneously hypertensive rats and none in the DOCA-salt model. α₁-Adrenergic binding was elevated in hypothalamus of spontaneously hypertensive rats 4–20 weeks of age even though blood pressure in the 4-week old animals was not at hypertensive levels (i.e., <150 mmHg). Treatment of adult spontaneously hypertensive rats with clonidine HCl significantly reduced blood pressure but failed to alter the binding of [³H]WB-4101 in hypothalamus. Thus, it appears that the enhanced number of α₁-adrenergic receptors in hypothalamus of spontaneously hypertensive rats is neither a consequence of the increased blood pressure, nor a phenomenon common to all models of hypertension.     

Prostacyclin synthase and phospholipases in the vascular wall of experimental hypertensive rats

To reveal the role of enzymes involved in PGI2 synthesis for vascular PGI2 generation in experimental hypertensive models, we defined PGI2 synthase and phospholipases activities in the aortic wall of two different experimental hypertensive rats, e.g. spontaneously hypertensive rats (SHR) and desoxycorticosterone acetate (DOCA)-salt hypertensive rats. In the stage of established hypertension both of the hypertensive models had a significantly large capacity of the vascular wall to produce PGI2, as compared to respective control rats. PGI2 synthase activities in the vascular wall were significantly increased by 27% for SHR and by 80% for DOCA-salt hypertensive rats. Moreover, the enzymatic activities were closely related to the blood pressure values for both of the models. On the other hand, phospholipase C or phospholipase A2 activities were increased or unchanged in SHR, respectively, whereas both of the phospholipases were significantly decreased in DOCA-salt hypertensive rats. Thus, it is indicated that PGI2 synthase is partly responsible for the increased PGI2 generation in the vascular wall of SHR and DOCA-salt hypertensive rats, and that vascular phospholipase C is playing a more important role in providing arachidonate for PGI2 synthesis in SHR.     

Exercise intensities modulate cognitive function in spontaneously hypertensive rats through oxidative mediated synaptic plasticity in hippocampus

Oxidative damage in the brain may lead to cognitive impairments. There was considerable debate regarding the beneficial effects of physical exercise on cognitive functions because exercise protocols have varied widely across studies. We investigated whether different exercise intensities alter performance on cognitive tasks. The experiment was performed on spontaneously hypertensive rats (6 months at the established phase of hypertension) distributed into 3 groups: sedentary, low-intensity exercise and high-intensity exercise. Systolic blood pressure measurements confirmed hypertension in spontaneously hypertensive rats. In comparison to normotensive Wistar-Kyoto rats, sedentary spontaneously hypertensive rats had similar escape latencies and a similar preference for the correct quadrant in the probe trial. Compared to the sedentary group, the low-intensity exercise group had significantly better improvements in spatial memory assessed by Morris water maze. Low-intensity exercise was associated with attenuated reactive oxygen species, as measured by dihydroethidine fluorescence and nitrotyrosine staining in the dentate gyrus of the hippocampus. This was coupled with increased numbers of neurons and dendritic spines as well as a significant upregulation of synaptic density. In contrast, the beneficial effects of low-intensity exercise are abolished in high-intensity exercise as shown by increased free radical levels and an impairment in spatial memory. We concluded that exercise is an effective strategy to improve spatial memory in spontaneously hypertensive rats even at an established phase of hypertension. Low-intensity exercise exhibited better improvement on cognitive deficits than high-intensity exercise by attenuating free radical levels and improving downstream synaptic plasticity.     

Effect of an exercise regimen on development of hypertension in rats

The possibility that a forced exercise regimen might prevent the development of hypertension induced in rats both by renal encapsulation and chronic administration of deoxycorticosterone acetate (DOCA) and NaCl has been studied. In renal hypertensive rats, forced exercise at 0.4 to 1.25 miles/day, 7 days/wk for 16-22 wk failed to prevent the development of hypertension and cardiomegaly and reduced renal concentrating ability accompanying the hypertension. In DOCA-treated rats (10 mg/wk), forced exercise at 0.4 and 0.8 mile/day, 7 days/wk for 16 wk also failed to prevent both the development of hypertension and cardiomegaly. A review of data of others reveals that exercise may delay the development of hypertension in both Dahl salt-sensitive and spontaneously hypertensive (SHR) rats and may modestly reduce the maximal level of pressure attained. Of the four models of hypertension studied to date in rats, the Dahl salt-sensitive strain appears to be the one that responded best to exercise, although blood pressure eventually reached that of sedentary controls.     

Complete dissociation of DOCA-salt hypertension and red cell ion transport alterations.

Our previous study revealed major ion transport alterations that resulted in a pronounced elevation of red cell Na+ content in DOCA-salt treated homozygous vasopressin-deficient (DI) Brattleboro rats in which only a moderate increase of systolic blood pressure occurred. In contrast, no changes of red cell Na+ content were observed in heterozygous vasopressin-secreting (non-DI) Brattleboro rats with a severe DOCA-salt hypertension. Using a chronic supplementation of DI rats with an antidiuretic agonist dDAVP (1-desamino-8-D-arginine vasopressin) we did not demonstrate any significant changes of red cell ion transport in dDAVP-treated DI rats with a fully developed DOCA-salt hypertension. The absence of ion transport alterations seems to be mainly due to dDAVP-induced correction of altered K+ metabolism seen in DOCA-salt treated DI animals. It can be concluded that DOCA-salt hypertension can develop even without red cell ion transport alterations which are usually caused by cell K+ depletion.