l-carnitine and its propionate: improvement of endothelial function in SHR through superoxide dismutase-dependent mechanisms

To clarify the mechanism underlying the antioxidant properties of l-carnitine (LC) and propionyl-l-carnitine (PLC) on spontaneously hypertensive (SHR) and normotensive WKY, animals were treated with either PLC or LC (200 mg kg(- 1)). Aorta was dissected and contraction to (R)-( - )-phenylephrine (Phe) and relaxation to carbachol (CCh) were assessed in the presence or not of the NO synthase (NOS) inhibitor, l-NAME. [image omitted] production was evaluated by lucigenin-enhanced chemiluminescence and its participation on relaxation was observed after incubation with superoxide dismutase (SOD) plus catalase. Protein expressions of eNOS, Cu/Zn-SOD and Mn-SOD were studied by western blot. Both LC and PLC treatments improved endothelial function of SHR through increasing NO participation and decreasing [image omitted] probably involving higher Cu/Zn-SOD expression. PLC treatment augmented eNOS expression in SHR. Surprisingly, LC increased [image omitted] produced by aorta from WKY and thus diminished NO and damaged endothelial function. Conversely, PLC did not affect CCh-induced relaxation in WKY. These results demonstrate that LC and PLC prevent endothelial dysfunction in SHR through an antioxidant effect.     

Exercise training improves aortic endothelium-dependent vasorelaxation and determinants of nitric oxide bioavailability in spontaneously hypertensive rats.

The present study examined in vitro vasomotor function and expression of enzymes controlling nitric oxide (NO) bioavailability in thoracic aorta of adult male normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) that either remained sedentary (Sed) or performed 6 wk of moderate aerobic exercise training (Ex). Training efficacy was confirmed by elevated maximal activities of both citrate synthase (P = 0.0024) and beta-hydroxyacyl-CoA dehydrogenase (P = 0.0073) in the white gastrocnemius skeletal muscle of Ex vs. Sed rats. Systolic blood pressure was elevated in SHR vs. WKY (P < 0.0001) but was not affected by Ex. Despite enhanced endothelium-dependent relaxation to 10(-8) M ACh in SHR vs. WKY (P = 0.0061), maximal endothelium-dependent relaxation to 10(-4) M ACh was blunted in Sed SHR (48 +/- 12%) vs. Sed WKY (84 +/- 6%, P = 0.0067). Maximal endothelium-dependent relaxation to 10(-4) M ACh was completely restored in Ex SHR (93 +/- 9%) vs. Sed SHR (P = 0.0011). N(omega)-nitro-l-arginine abolished endothelium-dependent relaxation in all groups (P 相似文献   

Hypertension alters the participation of contractile prostanoids and superoxide anions in lipopolysaccharide effects on small mesenteric arteries

The involvement of cyclooxygenase-2 (COX-2)-derived products and superoxide anion in the effect of lipopolysaccharide in noradrenaline (NA)-induced contraction was investigated in small mesenteric arteries (SMA) from normotensive, Wistar Kyoto (WKY), and spontaneously hypertensive (SHR) rats. In WKY, lipopolysaccharide (10 microg/ml, 1 and 5 h) only inhibited the NA response (0.1-30 microM) in the presence of dexamethasone (1 microM), indomethacin (10 microM), the selective COX-2 inhibitor, NS 398 (10 microM), and the TXA(2)/PGH(2) receptor antagonist, SQ 29,548 (10 microM) but not of superoxide dismutase (SOD, 100 U/ml). In SHR, lipopolysaccharide inhibited the NA response by itself; this inhibition was potentiated by dexamethasone, indomethacin, NS 398, SQ 29,548 and SOD. The effect of lipopolysaccharide plus indomethacin, NS 398 or SQ 29,548 was higher in SMA from WKY than SHR only after 1 h lipopolysaccharide incubation. N(G)-nitro-L-arginine methyl ester (100 microM) and endothelium removal abolished the indomethacin-induced potentiatory effect of lipopolysaccharide in both strains. Endothelium removal also abolished the SOD potentiatory effect in SMA from SHR. Lipopolysaccharide increases COX-2 expression to a similar level in both strains and iNOS expression in a greater extent in SHR; these increases were reduced by dexamethasone. These results indicate: 1) lipopolysaccharide induces the endothelial production of contractile prostanoids from COX-2 in SMA, probably to compensate the increase in NO from iNOS; 2) the production of prostanoids in the presence of lipopolysaccharide seems to be greater in normotensive than hypertensive rats only after lipopolysaccharide short incubation times; 3) endothelial production of O(2)(.-) contributes to counteract depression of NA contraction caused by lipopolysaccharide only in SHR.     

Hypertension alters role of iNOS, COX-2, and oxidative stress in bradykinin relaxation impairment after LPS in rat cerebral arteries

This study was performed to investigate the role of reactive oxygen species and inducible nitric oxide (NO) synthase (iNOS) and cyclooxygenase-2 (COX-2) metabolites in the lipopolysaccharide effect on bradykinin-induced relaxation in middle cerebral arteries from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). LPS exposure (10 microg/ml for 1-5 h) reduced bradykinin relaxation; this effect appeared earlier and was greater in arteries from SHR than WKY rats. LPS also reduced the relaxation to the NO donor diethylamine (DEA)-NO; however, LPS modified neither the bradykinin relaxation after inhibiting NO synthesis with N(G)-monomethyl-L-arginine (0.1 mM) nor endothelial NOS expression. In arteries from WKY rats, the respective iNOS and COX-2 inhibitors aminoguanidine (0.1 mM) and NS-398 (10 microM) and the superoxide anion scavenger SOD (100 U/ml) reduced the LPS effect on bradykinin relaxation; however, the thromboxane A(2) (TxA(2))PGH(2) receptor antagonist SQ-29548 (1 microM) and the H(2)O(2) scavenger catalase (1,000 U/ml) did not modify the LPS effect. In arteries from SHR, all of these drugs reduced the LPS effect. LPS exposure (5 h) increased superoxide anion levels in arteries from both strains and TxA(2) levels only in SHR. COX-2 expression rose to a similar level in arteries from both strains after 1 and 5 h of LPS incubation, whereas expression of Cu/Zn- and Mn-SOD only increased after 5 h. In conclusion, in segments from WKY rats, LPS reduced bradykinin-induced relaxation through increased production of NO (from iNOS) and superoxide anion. The greater LPS effect observed in arteries from SHR seems to be related to higher participation of reactive oxygen species and contractile prostanoids (probably TxA(2)).     

Effect of blood pressure on L-NAME-sensitive component of vasorelaxation in adult rats

The aim of this study was to investigate nitric oxide (NO) production and L-NAME-sensitive component of endothelium-dependent vasorelaxation in adult normotensive Wistar-Kyoto rats (WKY), borderline hypertensive rats (BHR) and spontaneously hypertensive rats (SHR). Blood pressure (BP) of WKY, BHR and SHR (determined by tail-cuff) was 111+/-3, 140+/-4 and 184+/-6 mm Hg, respectively. NO synthase activity (determined by conversion of [(3)H]-L-arginine) was significantly higher in the aorta of BHR and SHR vs. WKY and in the left ventricle of SHR vs. both BHR and WKY. L-NAME-sensitive component of endothelium-dependent relaxation was investigated in the preconstricted femoral arteries using the wire myograph during isometric conditions as a difference between acetylcholine-induced relaxation before and after acute N(G)-nitro-L-arginine methyl ester pre-treatment (L-NAME, 10(-5) mol/l). Acetylcholine-induced vasorelaxation of SHR was significantly greater than that in WKY. L-NAME-sensitive component of vasorelaxation in WKY, BHR and SHR was 20+/-3 %, 29+/-4 % (p<0.05 vs. WKY) and 37+/-3 % (p<0.05 vs. BHR), respectively. There was a significant positive correlation between BP and L-NAME-sensitive component of relaxation of the femoral artery. In conclusion, results suggest the absence of endothelial dysfunction in the femoral artery of adult borderline and spontaneously hypertensive rats and gradual elevation of L-NAME-sensitive component of vasorelaxation with increasing blood pressure.     

In SHR aorta, calcium ionophore A-23187 releases prostacyclin and thromboxane A2 as endothelium-derived contracting factors

In mature spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY), acetylcholine and the calcium ionophore A-23187 release endothelium-derived contracting factors (EDCFs), cyclooxygenase derivatives that activate thromboxane-endoperoxide (TP) receptors on vascular smooth muscle. The EDCFs released by acetylcholine are most likely prostacyclin and prostaglandin (PG)H(2), whereas those released by A-23187 remain to be identified. Isometric tension and the release of PGs were measured in rings of isolated aortas of WKY and SHR. A-23187 evoked the endothelium-dependent release of prostacyclin, thromboxane A(2), PGF(2alpha), PGE(2), and possibly PGH(2) (PGI(2) > thromboxane A(2) = PGF(2alpha) = PGE(2)). In SHR aortas, the release of prostacyclin and thromboxane A(2) was significantly larger in response to A-23187 than to acetylcholine. In response to the calcium ionophore, the release of thromboxane A(2) was significantly larger in aortas of SHR than in those of WKY. In both strains of rat, the inhibition of cyclooxygenase-1 prevented the release of PGs and the occurrence of endothelium-dependent contractions. Dazoxiben, the thromboxane synthase inhibitor, abolished the A-23187-dependent production of thromboxane A(2) and inhibited by approximately one-half the endothelium-dependent contractions. U-51605, an inhibitor of PGI synthase, reduced the release of prostacyclin elicited by A-23187 but induced a parallel increase in the production of PGE(2) and PGF(2alpha), suggestive of a PGH(2) spillover, which was associated with the enhancement of the endothelium-dependent contractions. These results indicate that in the aorta of SHR and WKY, the endothelium-dependent contractions elicited by A-23187 involve the release of thromboxane A(2) and prostacyclin with a most likely concomitant contribution of PGH(2).     

Increasing oxidative stress with molsidomine increases blood pressure in genetically hypertensive rats but not normotensive controls

Spontaneously hypertensive rats (SHR) have a higher level of oxidative stress and exhibit a greater depressor response to a superoxide scavenger, tempol, than normotensive Wistar-Kyoto rats (WKY). This study determined whether an increase in oxidative stress with a superoxide/NO donor, molsidomine, would amplify the blood pressure in SHR. Male SHR and WKY were given molsidomine (30 mg.kg(-1).day(-1)) or vehicle (0.01% ethanol) for 1 wk, and blood pressure, renal hemodynamics, nitrate and nitrite excretion (NOx), renal superoxide production, and expression of renal antioxidant enzymes, Mn- and Cu,Zn-SOD, catalase, and glutathione peroxidase (GPx), were measured. Renal superoxide and NOx were higher in control SHR than in WKY. Molsidomine increased superoxide by approximately 35% and NOx by 250% in both SHR and WKY. Mean arterial blood pressure (MAP) was also higher in control SHR than WKY. Molsidomine increased MAP by 14% and caused renal vasoconstriction in SHR but reduced MAP by 16%, with no effect on renal hemodynamics, in WKY. Renal expression of Mn- and Cu,Zn-SOD was not different between SHR and WKY, but expression of catalase and GPx were approximately 30% lower in kidney of SHR than WKY. The levels of Mn- and Cu,Zn-SOD were not increased with molsidomine in either WKY or SHR. Renal catalase and GPx expression was increased by 300-400% with molsidomine in WKY, but there was no effect in SHR. Increasing oxidative stress elevated blood pressure further in SHR but not WKY. WKY are likely protected because of higher bioavailable levels of NO and the ability to upregulate catalase and GPx.     

Antioxidant activity of propionyl-L-carnitine in liver and heart of spontaneously hypertensive rats

Oxidative stress plays an important role in arterial hypertension and propionyl-L-carnitine (PLC) has been found to protect cells from toxic reactive oxygen species. In this work, we have evaluated the antioxidant capacity of chronic PLC treatment in spontaneously hypertensive rats (SHR) by measuring the activity of antioxidant enzymes and the lipid peroxidation in liver and cardiac tissues. The activity of glutathione peroxidase was decreased in liver and cardiac tissues of SHR when compared with their normotensive controls, Wistar- Kyoto (WKY) rats, this alteration being prevented by PLC treatment. Glutathione reductase activity was increased in hypertensive rats and no effect was observed after the treatment. No significant changes in superoxide dismutase activity were observed among all experimental groups. Liver of hypertensive rats showed higher catalase activity than that of normotensive rats, and PLC enhanced this activity in both rat strains. Thiobarbituric acid reactive substances, determined as a measure of lipid peroxidation, were increased in SHR compared with WKY rats, and PLC treatment decreased these values not only in hypertensive rats but also in normotensive ones. The content of carnitine in serum, liver and heart was higher in PLC-treated rats, but PLC did not prevent the hypertension development in young SHR. In addition, triglyceride levels, which were lower in SHR than WKY rats, were reduced by chronic PLC treatment in both rat strains. These results demonstrate: i) the hypotriglyceridemic effect of PLC and ii) the antioxidant capacity of PLC in SHR and its beneficial use protecting tissues from hypertension-accompanying oxidative damage.     

Urinary levels of 2,3-dinor-6-oxo-PGF1 alpha: a reliable index of the production of PGI2 in the spontaneously hypertensive rat

The urinary levels of 2,3-dinor-6-oxo-PGF1 alpha (PGI2-M), a major metabolite of PGI2, are determined by the balance between the amount of PGI2 synthesized and the extent of its further metabolic oxidation. The purpose of the present study was to determine if the urinary excretion of PGI2-M can be used as a reliable index of the in vivo production of PGI2 in both normal Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). This involved the exclusion of differences in metabolism between these two strains of rats. In order to do so, we monitored the urinary excretion of PGI2-M during paired intravenous infusions of 6-oxo-PGF1 alpha (the stable product of the spontaneous hydrolysis of PGI2) in conscious, unrestrained SHR and WKY rats aged 12-15 weeks, in doses ranging from 250 to 700 ng. In one experiment, PGI2 was infused instead of 6-oxo-PGF1 alpha. The results of these experiments indicate that SHR and WKY rats are equal with regard to the transformation of 6-oxo-PGF1 alpha and PGI2 into PGI2-M. For both groups, there is a good correlation between the amount of 6-oxo-PGF1 alpha infused and the amount of PGI2-M excreted in urine. These observations confirm the validity of using the urinary levels of 2,3-dinor-6-oxo-PGF1 alpha as an index of PGI2 production in both WKY and SHR. In addition, they support the conclusions drawn from our previous studies, namely that SHR do not produce more PGI2 than WKY rats in vivo, contrary to the situation prevailing in vitro.     

NAD(P)H oxidase-derived peroxide mediates elevated basal and impaired flow-induced NO production in SHR mesenteric arteries in vivo

Nitric oxide (NO) and reactive oxygen species (ROS) have fundamentally important roles in the regulation of vascular tone and remodeling. Although arterial disease and endothelial dysfunction alter NO and ROS levels to impact vasodilation and vascular structure, direct measurements of these reactive species under in vivo conditions with flow alterations are unavailable. In this study, in vivo measurements of NO and H2O2 were made on mesenteric arteries to determine whether antioxidant therapies could restore normal NO production in spontaneously hypertensive rats (SHR). Flow was altered from approximately 50-200% of control in anesthetized Wistar-Kyoto rats (WKY) and SHR by selective placement of microvascular clamps on adjacent arteries while NO and H2O2 were directly measured with microelectrodes. Relative to WKY, SHR had significantly increased baseline NO and H2O2 concentrations (2,572 +/- 241 vs. 1,059 +/- 160 nM, P < 0.01; and 26 +/- 7 vs. 7 +/- 1 microM, P < 0.05, respectively). With flow elevation, H2O2 but not NO increased in SHR; NO but not H2O2 was elevated in WKY. Apocynin and polyethylene-glycolated catalase decreased baseline SHR NO and H2O2 to WKY levels and restored flow-mediated NO production. Suppression of NAD(P)H oxidase with gp91ds-tat decreased SHR H2O2 to WKY levels. Addition of topical H2O2 to increase peroxide to the basal concentration measured in SHR elevated WKY NO to levels observed in SHR. The results support the hypothesis that increased vascular peroxide in SHR is primarily derived from NAD(P)H oxidase and increases NO concentration to levels that cannot be further elevated with increased flow. Short-term and even acute administration of antioxidants are able to restore normal flow-mediated NO signaling in young SHR.     

Nitric Oxide in Systemic and Pulmonary Hypertension

Endothelium-derived nitric oxide (NO) is an important gas molecule in the regulation of vascular tone and arterial pressure. It has been considered that endothelial dysfunction with impairment of NO production contributes to a hypertensive state. Alternatively, long-term hypertension may affect the endothelial function, depress NO production, and thereby reduce the dilator action on vasculatures. There were many studies to support that endothelium-dependent vasodilatation was impaired in animals and humans with long-term hypertension. However, results of some reports were not always consistent with this consensus. Recent experiments in our laboratory revealed that an NO synthase inhibitor, N^G-nitro-L-arginine monomethyl ester (L-NAME) caused elevation of arterial pressure (AP) in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). The magnitude of AP increase following NO blockade with L-NAME was much higher in SHR than WKY. In other experiments with the use of arterial impedance analysis, we found that L-NAME slightly or little affected the pulsatile hemodynamics including characteristic impedance, wave reflection and ventricular work. Furthermore, these changes were not different between SHR and WKY. The increase in AP and total peripheral resistance (TPR) following NO blockade in SHR were significantly greater than those in WKY, despite higher resting values of AP and TPR in SHR. In connection with the results of other studies, we propose that heterogeneity with respect to the involvement of NO (impairment, no change or enhancement) in the development of hypertension may exist among animal species, hypertensive models and different organ vessels. Our study in SHR provide evidence to indicate that the effects of basal release of NO on the arterial pressure and peripheral resistance are not impaired, but enhanced in the hypertensive state. The increase in NO production may provide a compensatory mechanism to keep the blood pressure and peripheral resistance at lower levels. The phenomenon of enhanced NO release also occurs in certain type of pulmonary hypertension. We first hypothesized that a decrease in NO formation might be responsible for the pulmonary vasoconstriction during hypoxia. With the measurement of NO release in the pulmonary vein, we found that ventilatory hypoxia produced pulmonary hypertension accompanying an increase in NO production. Addition of NO inhibitor (L-NAME), blood or RBC into the perfusate attenuated or abolished the NO release, while potentiating pulmonary vasoconstriction. During hypoxia, the increased NO formation in the pulmonary circulation similarly exerts a compensatory mechanism to offset the degree of pulmonary vasoconstriction.     

Endothelium-dependent vasorelaxation to the AMPK activator AICAR is enhanced in aorta from hypertensive rats and is NO and EDCF dependent

Activation of AMP-activated protein kinase (AMPK) induces vasorelaxation in arteries from healthy animals, but the mechanisms coordinating this effect are unclear and the integrity of this response has not been investigated in dysfunctional arteries of hypertensive animals. Here we investigate the mechanisms of relaxation to the AMPK activator 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR) in isolated thoracic aorta rings from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Although AICAR generated dose-dependent (10(-6)-10(-2) M) relaxation in precontracted WKY and SHR aortic rings with (E(+)) or without (E(-)) endothelium, relaxation was enhanced in E(+) rings. Relaxation in SHR E(+) rings was also enhanced at low [AICAR] (10(-6) M) compared with that of WKY (57 ± 8% vs. 3 ± 2% relaxation in SHR vs. WKY E(+)), but was similar and near 100% in both groups at high [AICAR]. Pharmacological dissection showed that the mechanisms responsible for the endothelium-dependent component of relaxation across the dose range of AICAR are exclusively nitric oxide (NO) mediated in WKY rings, but partly NO dependent and partly cyclooxygenase (COX) dependent in SHR vessels. Further investigation revealed that ACh-stimulated COX-endothelium-derived contracting factors (EDCF)-mediated contractions were suppressed by AICAR, and this effect was reversed in the presence of the AMPK inhibitor Compound C in quiescent E(+) SHR aortic rings. Western blots demonstrated that P(Thr(172))-AMPK and P(Ser(79))-acetyl-CoA carboxylase (indexes of AMPK activation) were elevated in SHR versus WKY E(+) rings at low AICAR (～2-fold). Together these findings suggest that AMPK-mediated inhibition of EDCF-dependent contraction and elevated AMPK activation may contribute to the enhanced sensitivity of SHR E(+) rings to AICAR. These results demonstrate AMPK-mediated vasorelaxation is present and enhanced in arteries of SHR and suggest that activation of AMPK may be a potential strategy to improve vasomotor dysfunction by suppressing enhanced endoperoxide-mediated contraction and enhancing NO-mediated relaxation.     

Erectile dysfunction in spontaneously hypertensive rats: pathophysiological mechanisms

Hypertensive men have a higher prevalence of erectile dysfunction (ED) than the general population. Experimental evidence of ED in hypertensive animals is scarce. This study evaluates the erectile function of spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto rats (WKY) in vivo by the increase in intracavernosal pressure after electrical stimulation of the cavernous nerve (CN) and by isometric tension studies on corporal strips. Frequency-dependent erectile responses to CN stimulations were reduced in SHR. Phenylephrine induced lower corporal contractions in SHR although pD2 values were similar to WKY. Endothelium-dependent relaxations to ACh were impaired significantly in SHR, and indomethacin improved these relaxations in both WKY and SHR, the latter thus reaching values similar to WKY. Corporal relaxations to sodium nitroprusside were enhanced in SHR. Thus a dysfunctional alpha-adrenergic contraction of the corporal smooth muscle, an increased cyclooxygenase-dependent constrictor tone, and/or a defect in endothelium-dependent reactivity are associated with the altered erectile mechanisms in SHR. Drugs targeting endothelial dysfunction may delay the occurrence of ED as a complication of hypertension.     

Impaired UTP-induced relaxation in the carotid arteries of spontaneously hypertensive rats

Uridine 5′-triphosphate (UTP) has an important role as an extracellular signaling molecule that regulates inflammation, angiogenesis, and vascular tone. While chronic hypertension has been shown to promote alterations in arterial vascular tone regulation, carotid artery responses to UTP under hypertensive conditions have remained unclear. The present study investigated carotid artery responses to UTP in spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats (WKY). Accordingly, our results found that although UTP promotes concentration-dependent relaxation in isolated carotid artery segments from both SHR and WKY after pretreatment with phenylephrine, SHR exhibited significantly lower arterial relaxation responses compared with WKY. Moreover, UTP-induced relaxation was substantially reduced by endothelial denudation and by the nitric oxide (NO) synthase inhibitor N^G-nitro-L-arginine in both SHR and WKY. The difference in UTP-induced relaxation between both groups was abolished by the selective P2Y₂ receptor antagonist AR-C118925XX and the cyclooxygenase (COX) inhibitor indomethacin but not by the thromboxane-prostanoid receptor antagonist SQ29548. Furthermore, we detected the release of PGE₂, PGF_2α, and PGI₂ in the carotid arteries of SHR and WKY, both at baseline and in response to UTP. UTP administration also increased TXA₂ levels in WKY but not SHR. Overall, our results suggest that UTP-induced relaxation in carotid arteries is impaired in SHR perhaps due to impaired P2Y₂ receptor signaling, reductions in endothelial NO, and increases in the levels of COX-derived vasoconstrictor prostanoids.

     

Endothelium-derived relaxing factors in the kidney of spontaneously hypertensive rats

Acetylcholine (ACh)-induced vasodilation is mainly due to endothelium-derived nitric oxide (EDNO) and hyperpolarizing factor (EDHF). To explore the mechanisms underlying attenuated endothelium-dependent vasodilation in hypertensive arteries, we measured the EDNO released from isolated kidneys of spontaneously hypertensive rats (SHR) using a sensitive chemiluminescence assay system of NO. ACh-induced renal vasodilation was significantly smaller in SHR than in the normotensive control, Wistar-Kyoto rats (WKY). However, ACh-induced NO release did not differ between SHR and WKY (10⁻⁷ M: SHR +37 ± 2 [SE] vs. WKY +32 ± 4 fmol/min/g kidney). Perfusion with a 20 mEq/L high-K⁺ buffer, which is reported to inhibit action of EDHF, significantly reduced ACh-induced vasorelaxation in WKY but not in SHR, resulting in identical renal perfusion pressure in SHR and wKY under these conditions. These results indicate that attenuated ACh-induced vasorelaxation in the SHR kidney may be attributed to a decrease in EDHF rather than that in EDNO.     

L-carnitine attenuates oxidative stress in hypertensive rats

The present study aimed to investigate whether l-carnitine (LC) protects the vascular endothelium and tissues against oxidative damage in hypertension. Antioxidant enzyme activities, glutathione and lipid peroxidation were measured in the liver and heart of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. Nitrite and nitrate levels and total antioxidant status (TAS) were evaluated in plasma, and the expression of endothelial nitric oxide synthase (eNOS) and p22phox subunit of NAD(P)H oxidase was determined in aorta. Glutathione peroxidase activity was lower in SHR than in WKY rats, and LC increased this activity in SHR up to values close to those observed in normotensive animals. Glutathione reductase and catalase activities, which were higher in SHR, tended to increase after LC treatment. No differences were found in the activity of superoxide dismutase among any animal group. The ratio between reduced and oxidized glutathione and the levels of lipid peroxidation were respectively decreased and increased in hypertensive rats, and both parameters were normalized after the treatment. Similarly, LC was able to reverse the reduced plasma nitrite and nitrate levels and TAS observed in SHR. We found no alterations in the expression of aortic eNOS among any group; however, p22phox mRNA levels showed an increase in SHR that was reversed by LC. In conclusion, chronic administration of LC leads to an increase in hepatic and cardiac antioxidant defense and a reduction in the systemic oxidative process in SHR. Therefore, LC might increase NO availability in SHR aorta by a reduction in superoxide anion production.     

Effects of angiotensin II type 1 receptor blockade on the oxidative stress in spontaneously hypertensive rat tissues

The aim of this work was to investigate the production of oxidative damage in homogenized kidney, liver and brain of spontaneously hypertensive rats (SHR), as well as the involvement of angiotensin (Ang) II in this process. Groups of 12-week-old SHR and Wistar Kyoto rats (WKY) were given 10 mg/kg/day losartan in the drinking water during 14 days. Other groups of WKY and SHR without treatment were used as controls. The production of thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) and the activity of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (Gpx) were determined. No significant difference in TBARS was observed between untreated SHR or WKY rats; GSH content was lower in the liver but higher in the brain of SHR compared to WKY rats. In tissues from the SHR group, SOD and Gpx activities were reduced, whereas CAT activity was slightly increased in kidney. TBARS levels did not change in WKY rats after losartan administration, but were reduced in SHR liver and brain. Losartan treatment decreased GSH content in WKY kidney, but increased GSH in SHR liver. The activity of the antioxidant enzymes was not modified by losartan in WKY rats; however, their activities increased in tissues from treated SHR. The lower activity of antioxidant enzymes in tissues from hypertensive rats compared to those detected in normotensive controls, indicates oxidative stress production. Ang II seems to play no role in this process in normotensive animals, although AT1 receptor blockade in SHR enhances the enzymatic activity indicating that Ang II is implicated in oxidative stress generation in the hypertensive animals.     

Nitric oxide release from normal and dysfunctional endothelium.

The endothelium plays a critical role in maintaining vascular tone by releasing vasoconstrictor and vasodilator substances. Endothelium - derived nitric oxide (NO) is a vasodilator rapidly inactivated by superoxide (O2-) found in significant quantities. The porphyrinic sensor (0.5-8 microm diameter) and chemiluminescence methods were used to measure NO and (O2-) respectively. Effects of hypertension, low density lipoprotein (LDL), and heart preservation on the release of NO and O2- were delineated. In the single endothelial cell (rat aorta) NO concentration was the highest in the cell membrane decreasing exponentially with distance from cell, and becoming undetectable beyond 50 microm and 25 microm for normotensive (WKY) and hypertensive (SHR) rats respectively. The endothelium of SHR released 40% less NO (300+/-25 nmol L(-1)) than that of normotensive rats (500+20 nmol L(-1)), due to the higher production of O2- in SHR rats. An exponentially decreasing NO production (from 1.20 +/- 0.15 to 0.16 +/- 0.05 micromol (L-1)) and concomitant increase of O2- generation (from 10 +/- 0.3 to 300 +/- 25 nmol L(-1) were observed in left ventricle of stored (eight hours) rabbit heart. Native and oxidized low density lipoproteins (nLDL and oxLDL) inhibited NO generation and increased O2- production. The local depletion of the L-arginine substrate may disarrange the nitric oxide synthase, leading to production of O2- from oxygen.     

Maturation reveals a decrease in endothelium-dependent contraction induced by depolarization in the aorta of spontaneously hypertensive rats

The influence of the endothelium on aortic contractility to KCl 100 mM was studied during maturation and aging in normotensive Wistar and spontaneously hypertensive rats (SHR). In Wistar rats, there was no significant difference in maximal responses in the course of aging whether the endothelium was present (E+) or not (E-). A similar result was obtained in SHR E- rings. However, contraction was significantly higher in E+ rings of young (9 weeks) compared to adult and old SHR (18, 25, 36 and 72 weeks) (in mN/mm2: 34.8 +/- 3.1 versus 24.8 +/- 1.8, 16.0 +/- 2.5, 17.4 +/- 2.0 and 12.9 +/- 1.8, p<0.01). This increase remained significant in 18- compared to that of 25-, 36- and 72-week-old rats (p<0.01). No change appeared with age in noradrenaline-induced contractions of E+ rings neither in Wistar nor in SHR. A dose-dependent decrease in response to KCl was observed after an in vivo pretreatment of the young SHR with acetylsalicylic acid. Finally, blocking the TXA2/PGH2 receptor by addition of GR 32191B or ONO-3708 led to a decrease in the response of young SHR aortic rings to KCl. This study points out a decrease in the response of SHR aortic rings to a depolarizing agent during maturation. The enhanced contraction observed in young SHR seems to be the result of an increased participation of an endothelium-derived, cyclooxygenase-dependent contracting factor(s), most likely either TXA2 or PGH2. This factor might play a key role in the onset of hypertension in the spontaneously hypertensive strain.     

Alpha-lactorphin and beta-lactorphin improve arterial function in spontaneously hypertensive rats

alpha-lactorphin (Tyr-Gly-Leu-Phe) lowers blood pressure in conscious adult SHR. This tetrapeptide is originally released from milk protein alpha-lactalbumin by enzymatic hydrolysis. In order to evaluate the antihypertensive mechanisms of alpha-lactorphin, the effects of the tetrapeptide on vascular function were investigated in (30-35 weeks old) spontaneously hypertensive rats (SHR) with established hypertension and age-matched normotensive Wistar-Kyoto (WKY) rats in vitro. In addition, we studied the vascular effects of another structurally related tetrapeptide, beta-lactorphin (Tyr-Leu-Leu-Phe), which originates from milk protein beta-lactoglobulin. Endothelium-dependent relaxation to acetylcholine (ACh) was reduced in mesenteric arterial preparations of SHR as compared to those of WKY. In SHR, the ACh-induced relaxation was augmented by alpha-lactorphin or beta-lactorphin. The role of nitric oxide (NO) is suggested, since this improvement was abolished by the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Simultaneous potassium channel inhibitor tetraethylammonium (TEA) elicited no additional effect on the ACh-induced relaxation. The cyclooxygenase inhibitor diclofenac did not attenuate the augmented ACh relaxation induced by alpha-lactorphin or beta-lactorphin, suggesting that endothelial vasodilatory prostanoids were not involved in the effect of the tetrapeptides. Endothelium-independent relaxation to the NO donor sodium nitroprusside (SNP) was augmented in mesenteric arterial preparations of SHR by simultaneous beta-lactorphin. The tetrapeptides did not alter vascular responses in mesenteric arteries from WKY. In conclusion, both alpha-lactorphin and beta-lactorphin improved vascular relaxation in adult SHR in vitro. The beneficial effect of alpha-lactorphin was directed towards endothelial function, whereas beta-lactorphin also enhanced endothelium-independent relaxation.