Exercise conditioning attenuates the hypertensive effects of nitric oxide synthase inhibitor in rat

Many individuals with cardiovascular diseases undergo periodic exercise conditioning with or with out medication. Therefore, this study investigated the interaction of exercise training and chronic nitric oxide synthase (NOS) inhibitor (Nitro-L-Arginine Methyl Ester, L-NAME) treatment on blood pressure and its correlation with aortic nitric oxide (NO), antioxidant defense system and oxidative stress parameters in rats. Fisher 344 rats were divided into four groups: (1) sedentary control, (2) exercise training (ET) for 8 weeks, (3) L-NAME (10 mg/kg, subcutaneous for 8 weeks) and (4) ET + L-NAME. Blood pressure (BP) was monitored weekly for 8 weeks with tail-cuff method. The animals were sacrificed 24 h after last treatments and thoracic aortic rings were isolated and analyzed. Exercise conditioning resulted in a significant increase in respiratory exchange ratio (RER), aortic NO production, NO synthase activity and inducible iNOS protein expression. Training significantly enhanced aortic GSH levels, GSH/GSSG ratio and up-regulation of aortic CuZn-SOD, Mn-SOD, catalase (CAT) glutathione peroxidase (GSH-Px) activity and protein expression and significantly decreased aortic lipid peroxidation. Chronic L-NAME administration resulted in a significant depletion of aortic NO, NOS activity, endothelial (eNOS) and iNOS protein expression, GSH level, GSH/GSSG ratio, down-regulation of aortic antioxidant enzyme activities and protein expressions. Aortic xanthine oxidase (XO) activity significantly increased with increased lipid peroxidation and protein oxidation after L-NAME administration. The biochemical changes were accompanied by increased in BP. Interaction of training and chronic NOS inhibitor treatment resulted in normalization of BP and aortic antioxidant enzyme activity and protein expression, up-regulation of aortic GSH/GSSG ratio, NO levels, Mn-SOD protein expression, depletion of GSSG, protein oxidation and lipid peroxidation. The data suggest that training attenuated the oxidative injury caused by chronic NOS inhibitor treatment by up-regulating the NO and antioxidant systems and lowering the BP in rats.     

The time-dependent effect of Provinols on brain NO synthase activity in L-NAME-induced hypertension

Red wine polyphenols have been reported to possess beneficial properties for preventing cardiovascular diseases but their neuroprotective effects during chronic L-NAME treatment have not been elucidated. The aim of this study was to analyze a time course of Provinols effects on brain NO synthase activity and oxidative damage in L-NAME-induced hypertension. Male Wistar rats, 12 weeks old, were divided into six groups: control groups, groups treated with N(G)-nitro-L-arginine methyl ester (L-NAME, 40 mg/kg/day) for 4 or 7 weeks and groups receiving Provinols (40 mg/kg/day) plus L-NAME for 4 or 7 weeks. At the end of the treatment, marker of membrane oxidative damage - conjugated dienes (CD) in the brain and NO synthase activity in the cerebral cortex, cerebellum and brainstem were determined. L-NAME treatment for 4 or 7 weeks led to the increase in blood pressure, elevation of CD concentration and decrease of NO synthase activity in the brain parts investigated. Provinols partially prevented blood pressure rise and elevation of CD concentration. Comparing to the L-NAME treated group, Provinols increased NO synthase activity after 4 weeks of treatment. However, the prolonged Provinols treatment for 7 weeks had no effect on NO synthase activity decreased by L-NAME treatment. In conclusion, Provinols partially prevents L-NAME induced hypertension via the different mechanisms depending on the duration of treatment. Prevention of oxidative damage in the brain with modulating effect on NO synthase activity is suggested.     

Effect of oral magnesium supplementation on experimental pre-eclampsia induced by prolonged blockade of nitric oxide synthesis in pregnant rats

Nitric oxide inhibitor L-NAME when given alone caused a significant rise in both systolic and diastolic pressure, an increase in 24 hr urinary protein excretion and reduction in weight of the litter as compared to control group. Supplementation of MgSO4 at lower dose (250 mg/kg) did not inhibit this pre-eclamptic effect of L-NAME; but in higher doses (500 and 750 mg/kg), it inhibited the pre-eclamptic action of L-NAME. The results suggest that administration of MgSO4 improves the foetal outcome and significantly prevents the development of symptoms of pre-eclampsia like hypertension and proteinuria.     

Chronic low-dose L-NAME treatment increases nitric oxide production and vasorelaxation in normotensive rats

N(G)-nitro-L-arginine methyl ester (L-NAME) is a non-specific nitric oxide (NO) synthase inhibitor, commonly used for the induction of NO-deficient hypertension. The aim of this study was to investigate the effect of chronic low-dose administration of L-NAME on NO production, vascular function and structure of the heart and selected arteries of rats. Adult male Wistar rats were treated with L-NAME in the dose of approximately 1.5 mg/kg/day in drinking water for 8 weeks. Basal blood pressure (BP) of rats (determined by tail-cuff) was 112+/-3 mm Hg. The low-dose administration of L-NAME significantly elevated BP measured on the third and sixth week of treatment vs. controls by approximately 9 % and 12 %, respectively. After this period, BP of L-NAME-treated rats returned to the control values. The relative left ventricular mass, heart fibrosis and collagen III/collagen I ratio were not affected by L-NAME. Similarly, there were no alterations in the cross-sectional area and wall thickness/diameter ratio of the aorta and the femoral artery of L-NAME-treated rats. NO synthase activity (determined by conversion of [(3)H]-L-arginine to [(3)H]-L-citrulline) was not altered in the hypothalamus of L-NAME-treated rats. Interestingly, chronic low-dose L-NAME treatment significantly elevated NO synthase activity in the left ventricle and aorta, increased endothelium-dependent acetylcholine-induced vasorelaxation and reduced serotonin-induced vasoconstriction of the femoral artery. The data suggest that chronic low-dose L-NAME treatment can increase NO production and vasorelaxation in normotensive rats without negative structural changes in the cardiovascular system.     

Blood pressure relationship to nitric oxide, lipid peroxidation, renal function, and renal blood flow in rats exposed to low lead levels

The results of experiments designed to show that inhibition of nitric oxide production in rats exposed to low lead levels increases vascular resistance, decreases renal blood flow and glomerular function, and enhances oxidative stress. Forty-five adult male Sprague-Dawley rats were divided into four groups. Group A was used as controls and consisted of rats that received no treatment; group B acted as NO-inhibited controls by receiving L-NAME (N(G)-nitro-l-arginine methyl ester) as the NO inhibitor; group C was injected intraperitoneally with 8 mg/kg lead acetate for 2 wk; and group D receiving lead acetate plus L-NAME. Compared to healthy controls, significant elevation of the mean (p<0.01), systolic (p<0.04), and diastolic (p<0.01) blood pressures was found in the lead-treated rats. The renal blood flow was 1550+/-468 blood per unit (bpu) in the controls, 488+/-220 bpu in the L-NAME controls, 1050+/-458 bpu in the lead-treated group, and 878+/-487 bpu in the Pb plus L-NAME group. Low-level lead exposure did not change the urinary flow rate, creatinine clearance, and the creatinine, potassium, phosphorus, glucose, and protein excretion in 24-h urine. In the lead plus NO-inhibited rats, a significant decrease in sodium ion excretion was observed (p<0.01). The NO levels of the lead exposed, L-NAME-treated controls, and L-NAME plus lead-exposed groups are significantly lower compared to untreated controls: p<0.002, p<0.001, and p<0.01, respectively. When compared to untreated controls, the plasma malondialdehyde levels were not significantly different in the lead exposed, lead plus L-NAME, and L-NAME control groups. These results suggest that lead-induced hypertension might be related to a decrease of NO and consequent vasoconstriction, rather than to a decrease of renal blood flow or to decreases in renal sodium.     

Endotoxaemia in rats: role of NO, PAF and TXA2 in pulmonary neutrophil sequestration and hyperlactataemia.

OBJECTIVE AND DESIGN: The involvement of PAF, TXA2 and NO in LPS-induced pulmonary neutrophil sequestration an hyperlactataemia was studied in conscious rats. As pharmacological tools WEB 2170 (PAF receptor antagonist, 20 mg/kg), camongarel (inhibitor of TXA2 synthase, 30 mg/kg), N(G)-nitro L-arginine methyl ester (L-NAME -- non-selective nitric oxide synthase inhibitor, 30 mg/kg) were used. METHODS: Plasma lactate and NO2-/NO3- levels as well as myeloperoxidase (MPO) activity in lung tissue were measured one and five hours after administration of LPS (4 mg/kg(-1)). RESULTS: LPS induced a twofold increase in plasma lactate levels and nearly 10-fold increase in plasma NO2-/NO3- levels five but not one hour after LPS administration. However, LPS-induced increase in pulmonary MPO activity was seen at both time intervals. Neither WEB 2170 nor camonagrel changed one or five hours responses to LPS (lactate, NO2-/NO3-, MPO). L-NAME potentiated LPS-induced rise in MPO activity in the lung and this potentiation was not affected by WEB 2170 or camonagrel. L-NAME supressed plasma NO2-/NO3- response and substantially potentiated plasma lactate response to LPS and both effects were partially reversed by WEB 2170 or camonagrel. CONCLUSIONS: In summary, we demonstrated that PAF and TXA 2 play a role in overproduction of lactate during endotoxaemia in NO-deficient rats. However, these lipids do not mediate endotoxin-induced sequestration of neutrophils in the lung.     

Urinary excretion of 8-hydroxydeoxyguanosine and malondialdehyde after high dose radiochemotherapy preceding stem cell transplantation

The urinary excretion of the hydroxylated DNA base 8-hydroxydeoxyguanosine (8-OHdG) and the lipid peroxidation product malondialdehyde (MDA) was monitored in 11 patients with hematological malignancies undergoing total body irradiation and high-dose chemotherapy preceding bone marrow transplantation. Nine patients showed a prompt increase in urinary 8-OHdG (8-25 times the initial baseline level) on days 0-7 after irradiation onset; the excretion then decreased during the aplastic period and increased again when engraftment took place (in 7 patients). A significant positive correlation was found between urinary 8-OHdG and whole blood leukocyte count, both on day 5 (p =.04, r =.72) and on day 22 (p =.009, r =.80) after irradiation onset. One patient who lacked the first peak of 8-OHdG excretion showed low blood leukocyte counts (less than 2 x 10(9)/l) before therapy onset; this patient, however, later had a successful engraftment and then also showed considerable increases in both 8-OHdG excretion and leukocyte count. These observations suggest leukocytes play a part in the excretion of 8-OHdG after conditioning therapy preceding bone marrow transplantation. As opposed to the biphasic 8-OHdG excretion, the excretion of MDA showed a single peak appearing on days 11-19 after radiochemotherapy onset, i.e., during the period in which the patients suffered from cytopenia, mucositis, and other side effects of the treatment. It is suggested, therefore, that these clinical manifestations are associated with increased lipid peroxidation. Altogether, these findings illustrate the utility of serial urinary samples for monitoring oxidative stress due to conditioning therapy in clinical practice. They also demonstrate that different oxidative stress markers may behave quite differently regarding their appearance in the urine after whole-body oxidative stress.     

Physical conditioning modulates rat cardiac vascular endothelial growth factor gene expression in nitric oxide-deficient hypertension

Many individuals with cardiac diseases undergo periodic physical conditioning with or without medication to improve cardiovascular health. Therefore, this study investigated the interaction of physical training and chronic nitric oxide synthase (NOS) inhibitor (nitro-L-arginine methyl ester, L-NAME) treatment on blood pressure (BP), cardiac vascular endothelial factor (VEGF) gene expression, and nitric oxide (NO) systems in rats. Fisher 344 rats were divided into four groups and treated as follows: (1) sedentary control, (2) exercise training (ET) for 8 weeks, (3) L-NAME (10mg/kg, s.c. for 8 weeks), and (4) ET+L-NAME. BP was monitored with tail-cuff method. The animals were sacrificed 24h after last treatments and hearts were isolated and analyzed. Physical conditioning significantly increased respiratory exchange ratio, cardiac NO levels, NOS activity, endothelial eNOS, and inducible iNOS protein expression as well as VEGF gene expression. Training also caused depletion of cardiac malondialdehyde (MDA) levels indicating the beneficial effects of the training. Chronic L-NAME administration resulted in a depletion of cardiac NO level, NOS activity, and eNOS, nNOS, and iNOS protein expressions, as well as VEGF gene expression (2-fold increase in VEGF mRNA). Chronic L-NAME administration also enhanced cardiac MDA levels indicating cardiac oxidative injury. These biochemical changes were accompanied by increases in BP after L-NAME administration. Interaction of training and NOS inhibitor treatment resulted in normalization of BP and up-regulation of cardiac VEGF gene expression. The data suggest that physical conditioning attenuated the oxidative injury caused by chronic NOS inhibition by up-regulating the cardiac VEGF and NO levels and lowering the BP in rats.     

Longitudinal study of urinary 8-hydroxy-2'-deoxyguanosine excretion in healthy adults

Numerous studies have investigated the urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a biomarker for the assessment of oxidative DNA damage in humans. In this study, we performed six consecutive series of measurement of urinary levels of 8-OHdG in 68 healthy probands, in order to provide information on the intra- and inter-individual variability of 8-OHdG and to estimate the influence of smoking, age, sex, body weight and body mass index (BMI) on the excretion of 8-OHdG. The intraindividual coefficient of variation (CV) of urinary 8-OHdG/24h ranged from 0.18 to 1.06 (mean CV=0.48). Women excreted significantly lower amounts of 8-OHdG/24h than men, but the difference lost its significance when the body weight or urinary creatinine were used as covariates. By multiple linear regression analysis significant correlations between the mean individual levels of 8-OHdG/24h excretion and urinary creatinine (r_p = 0.61), and cotinine (r_p = 0.27) have been observed, whereas no statistically significant effect of age, body weight and BMI was found. The 8-OHdG/creatinine ratio was found to be significantly increased in 23 smokers (1.95 ± 0.40 μmol/mol) opposed to 45 non-smoking probands (1.62 ± 0.50 μmol/mol), which is in good agreement with previously published data. No effect of passive smoking on the excretion of 8-OHdG was found. From our data we conclude that the intraindividual variability of urinary 8-OHdG excretion has been underestimated so far, indicating that values of 8-OHdG measured by single spot monitoring are not representative for individual base levels.     

Pulmonary vascular iNOS induction participates in the onset of chronic hypoxic pulmonary hypertension

Pathogenesis of hypoxic pulmonary hypertension is initiated by oxidative injury to the pulmonary vascular wall. Because nitric oxide (NO) can contribute to oxidative stress and because the inducible isoform of NO synthase (iNOS) is often upregulated in association with tissue injury, we hypothesized that iNOS-derived NO participates in the pulmonary vascular wall injury at the onset of hypoxic pulmonary hypertension. An effective and selective dose of an iNOS inhibitor, L-N6-(1-iminoethyl)lysine (L-NIL), for chronic peroral treatment was first determined (8 mg/l in drinking water) by measuring exhaled NO concentration and systemic arterial pressure after LPS injection under ketamine+xylazine anesthesia. A separate batch of rats was then exposed to hypoxia (10% O2) and given L-NIL or a nonselective inhibitor of all NO synthases, N(G)-nitro-L-arginine methyl ester (L-NAME, 500 mg/l), in drinking water. Both inhibitors, applied just before and during 1-wk hypoxia, equally reduced pulmonary arterial pressure (PAP) measured under ketamine+xylazine anesthesia. If hypoxia continued for 2 more wk after L-NIL treatment was discontinued, PAP was still lower than in untreated hypoxic controls. Immunostaining of lung vessels showed negligible iNOS presence in control rats, striking iNOS expression after 4 days of hypoxia, and return of iNOS immunostaining toward normally low levels after 20 days of hypoxia. Lung NO production, measured as NO concentration in exhaled air, was markedly elevated as early as on the first day of hypoxia. We conclude that transient iNOS induction in the pulmonary vascular wall at the beginning of chronic hypoxia participates in the pathogenesis of pulmonary hypertension.     

Inhibition of nitric oxide production rescues LPS-induced fetal abortion in mice.

In this report, we examined the involvement of the cytokines tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, interleukin (IL)-4, and IL-10 as well as nitric oxide (NO) in the lipopolysaccharide (LPS)-induced experimental abortion model in BALB/c mice. Although in vivo administration of LPS in pregnant mice showed a 72% decrease of serum IL-10, no significant difference in serum TNF-alpha, IFN-gamma, and IL-4 levels, compared to controls, could be detected. At the same time, a correlation of fetal abortion and maternal splenomegaly with an important increase of NO synthesis in the serum was obtained. Simultaneous administration of LPS and aminoguanidine (AG; an inhibitor to NO synthase) rescued the LPS-induced fetal abortion, reduced maternal spleen weight to physiological levels, and decreased serum NO concentration to control levels. In vitro experiments showed that LPS directly induced NO production in primary placental cells and the TPOPHO-1 trophoblast cell line by stimulating the inducible isoform of NO synthase, which ultimately could be blocked by the NO synthase inhibitors AG and L-NAME. The results indicate that LPS, despite its beneficial involvement in intracellular infections, participates in inflammatory/autoimmune damage during pregnancy, leading to embryotoxicity, which is closely linked to the NO pathway.     

Systemic arterial pressure response to two weeks of Tempol therapy in SHR: involvement of NO, the RAS, and oxidative stress

The roles of nitric oxide (NO) and plasma renin activity (PRA) in the depressor response to chronic administration of Tempol in spontaneously hypertensive rats (SHR) are not clear. The present study was done to determine the effect of 2 wk of Tempol treatment on blood pressure [mean arterial pressure (MAP)], oxidative stress, and PRA in the presence or absence of chronic NO synthase inhibition. SHR were divided into four groups: control, Tempol (1 mmol/l) alone, nitro-L-arginine methyl ester (L-NAME, 4.5 mg x g(-1).day(-1)) alone, and Tempol + L-NAME or 2 wk. With Tempol, MAP decreased by 22%: 191 +/- 3 and 162 +/- 21 mmHg for control and Tempol, respectively (P < 0.05). L-NAME increased MAP by 16% (222 +/- 2 mmHg, P < 0.01), and L-NAME + Tempol abolished the depressor response to Tempol (215 +/- 3 mmHg, P < 0.01). PRA was not affected by Tempol but was increased slightly with L-NAME alone and 4.4-fold with L-NAME + Tempol. Urinary nitrate/nitrite increased with Tempol and decreased with L-NAME and L-NAME + Tempol. Tempol significantly reduced oxidative stress in the presence and absence of L-NAME. In conclusion, in SHR, Tempol administration for 2 wk reduces oxidative stress in the presence or absence of NO, but in the absence of NO, Tempol is unable to reduce MAP. Therefore, NO, but not changes in PRA, plays a major role in the blood pressure-lowering effects of Tempol. These data suggest that, in hypertensive individuals with endothelial damage and chronic NO deficiency, antioxidants may be able to reduce oxidative stress but not blood pressure.     

L-NAME-induced protein remodeling and fibrosis in the rat heart

The aim of the present study was to determine whether NO deficiency itself or rather the elevation of systolic blood pressure is responsible for the protein and structural remodeling of the heart during hypertension induced by long-term treatment by nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Three groups of rats were investigated. The first group served as control. In the second group L-NAME was given in the dose of 20 mg/kg/day in the drinking water and in the third group L-NAME was given in the dose of 40 mg/kg/day during 4 weeks. While L-NAME treatment in both doses caused essentially the same increase in systolic blood pressure (SBP), NO synthase activity and cGMP concentration in the left ventricle decreased by 17% and 13%, respectively in the 20 mg/kg/day L-NAME group and by 69% and 27%, respectively in the 40 mg/kg/day L-NAME group. The protein profile of the left ventricle in both L-NAME groups was characterized by an increased concentration of metabolic proteins. Nevertheless, a significant increase in the concentration of pepsin-soluble collagenous proteins and the concentration of hydroxyproline in pepsin-insoluble collagenous proteins was found only in the group receiving 40 mg/kg/day L-NAME. The morphometric evaluation revealed a significant increase in myocardial fibrosis in both L-NAME groups. However, this was more pronounced in the 40 mg/kg/day L-NAME group. It is concluded that NO deficiency resulted in significant enhancement of fibrotic tissue growth in proportion to the administered L-NAME dose, while SBP was increased similarly in both L-NAME groups. Thus, NO deficiency rather than hemodynamic changes appears to be crucially involved in collagenous protein and fibrotic tissue changes of the left ventricle in hypertension induced by L-NAME.     

Nitric oxide synthase inhibition does not affect the exercise-induced arterial hypoxemia in Thoroughbred horses.

Because sensitivity of equine pulmonary vasculature to endogenous as well as exogenous nitric oxide (NO) has been demonstrated, we examined whether endogenous NO production plays a role in exercise-induced arterial hypoxemia. We hypothesized that inhibition of NO synthase may alter the distribution of ventilation-perfusion mismatching, which may affect the exercise-induced arterial hypoxemia. Arterial blood-gas variables were examined in seven healthy, sound Thoroughbred horses at rest and during incremental exercise protocol leading to galloping at maximal heart rate without (control; placebo = saline) and with N(omega)-nitro-L-arginine methyl ester (L-NAME) administration (20 mg/kg iv). The experiments were carried out in random order, 7 days apart. At rest, L-NAME administration caused systemic hypertension, pulmonary hypertension, and bradycardia. During 120 s of galloping at maximal heart rate, significant arterial hypoxemia, desaturation of hemoglobin, hypercapnia, hyperthermia, and acidosis occurred in the control as well as in NO synthase inhibition experiments. However, statistically significant differences between the treatments were not found. In both treatments, exercise caused a significant rise in hemoglobin concentration, but the increment was significantly attenuated in the NO synthase inhibition experiments, and, therefore, arterial O(2) content (Ca(O(2))) increased to significantly lower values. These data suggest that, whereas L-NAME administration does not affect pulmonary gas exchange in exercising horses, it may affect splenic contraction, which via an attenuation of the rise in hemoglobin concentration and Ca(O(2)) may limit performance at higher workloads.     

Urinary excretion of 8-hydroxy-2'-deoxyguanosine measured by high-performance liquid chromatography with electrochemical detection

There is good evidence that oxidative DNA damage permanently occurs in living cells. The oxidative DNA damage product 8-hydroxy-2'-deoxyguanosine (8-OHdG) is one of the predominant forms of radical-induced lesions to DNA, and has therefore been widely used as a biomarker for oxidative stress, either in cellular DNA or as DNA repair product in urine. In this paper we describe the use of a high-performance liquid chromatographic procedure with electrochemical detection for the measurement of urinary 8-OHdG. Our study has addressed the questions (i) of baseline urinary levels of 8-OHdG in spot urine and 24-h urine, (ii) of inter- and intra-individual variation of this biomarker, and (iii) of confounding factors for the excretion of 8-OHdG. No significant difference between the mean group levels of 8-OHdG/creatinine in spot urine (2.03+/-1.21 micromol/mol, n=148) and in 24-h urine (1.86+/-1.09 micromol/mol, n=67) was observed. However, when only 24-h urine was used for analysis, 8-OHdG was found to be statistically significantly higher in smokers. By multiple linear regression analysis, urinary creatinine was identified as the only predictor of 8-OHdG/24 h (r(p)=0.33, P=0.007). High intra-individual coefficients of variation of 8-OHdG/24 h were observed in two healthy subjects over a period of 10 consecutive days (37 and 57%, respectively), indicating that the intra-individual fluctuation of urinary 8-OHdG has so far been underestimated. Therefore, we suggest that single values of 8-OHdG should be considered with caution, in particular in small study groups and when spot urine is used.     

Antioxidant treatment normalizes nitric oxide production, renal sodium handling and blood pressure in experimental hyperleptinemia

Recent studies suggest that adipose tissue hormone, leptin, is involved in the pathogenesis of arterial hypertension. However, the mechanism of hypertensive effect of leptin is incompletely understood. We investigated whether antioxidant treatment could prevent leptin-induced hypertension. Hyperleptinemia was induced in male Wistar rats by administration of exogenous leptin (0.25 mg/kg twice daily s.c. for 7 days) and separate groups were simultaneously treated with superoxide scavenger, tempol, or NAD(P)H oxidase inhibitor, apocynin (2 mM in the drinking water). After 7 days, systolic blood pressure was 20.6% higher in leptin-treated than in control animals. Both tempol and apocynin prevented leptin-induced increase in blood pressure. Plasma concentration and urinary excretion of 8-isoprostanes increased in leptin-treated rats by 66.9% and 67.7%, respectively. The level of lipid peroxidation products, malonyldialdehyde + 4-hydroxyalkenals (MDA+4-HNE), was 60.3% higher in the renal cortex and 48.1% higher in the renal medulla of leptin-treated animals. Aconitase activity decreased in these regions of the kidney following leptin administration by 44.8% and 45.1%, respectively. Leptin increased nitrotyrosine concentration in plasma and renal tissue. Urinary excretion of nitric oxide metabolites (NO(x)) was 57.4% lower and cyclic GMP excretion was 32.0% lower in leptin-treated than in control group. Leptin decreased absolute and fractional sodium excretion by 44.5% and 44.7%, respectively. Co-treatment with either tempol or apocynin normalized 8-isoprostanes, MDA+4-HNE, aconitase activity, nitrotyrosine, as well as urinary excretion of NO(x), cGMP and sodium in rats receiving leptin. These results indicate that oxidative stress-induced NO deficiency is involved in the pathogenesis of leptin-induced hypertension.     

Influence of renal denervation on renal effects of acute nitric oxide and ETA/ETB receptor inhibition in conscious normotensive rats.

The role of renal nerves in the effects of concomitant NO synthase and non-selective ET(A/)ET(B) receptor inhibition on renal function was investigated in conscious normotensive Wistar rats. NO synthase inhibition alone (10 mg/kg b. w. i.v. L-NAME) in sham-operated rats with intact renal nerves induced an increase in systolic, diastolic and mean arterial pressure, urine flow rate, sodium, chloride and calcium excretion (p<0.05). The effect of L-NAME was markedly reduced by bosentan (10 mg/kg b.w. i.v.) and the values of urine flow rate, sodium, chloride and calcium excretions returned to control level (p<0.05). L-NAME administration one week after a bilateral renal denervation increased blood pressure to a similar extent as in sham-operated rats but decreased urine flow rate (p<0.05) and did not change electrolyte excretion. ET(A/)ET(B) receptor inhibition with bosentan during NO synthase inhibition in the renal denervated rats did not produce changes in urine flow rate or electrolyte excretion. NO synthase inhibition as well as concurrent NO synthase and ET(A/)ET(B) receptor inhibition did not change clearance of inulin or paraaminohippuric acid in sham-operated or renal denervated rats. These results indicate that renal sympathetic nerves play an important modulatory role in NO and endothelin induced effects on renal excretory function.     

Role of extracellular signal-regulated kinases (ERK) in leptin-induced hypertension

We investigated if extracellular signal-regulated kinases (ERK) and oxidative stress are involved in the pathogenesis of arterial hypertension induced by chronic leptin administration in the rat. Leptin was administered at a dose of 0.25 mg/kg twice daily s.c. for 4 or 8 days. Blood pressure (BP) was higher in leptin-treated than in control animals from the third day of the experiment. The superoxide dismutase (SOD) mimetic, tempol, normalized BP in leptin-treated rats on days 6, 7 and 8, whereas the ERK inhibitor, PD98059, exerted a hypotensive effect on days 3 through 6. Leptin increased ERK phosphorylation level in renal and aortic tissues more markedly after 4 than after 8 days of treatment. In addition, leptin reduced urinary Na(+) excretion and increased renal Na(+),K(+)-ATPase activity, and these effects were abolished on days 4 and 8 by PD98059 and tempol, respectively. The levels of NO metabolites and cGMP were reduced in animals receiving leptin for 8 days. Markers of oxidative stress (H(2)O(2) and lipid peroxidation products) were elevated to a greater extent after 4 than after 8 days of leptin treatment. In contrast, nitrotyrosine, a marker of protein nitration by peroxynitrite, was higher in animals receiving leptin for 8 days. NADPH oxidase inhibitor, apocynin, prevented leptin's effect on BP, ERK, Na(+),K(+)-ATPase/Na(+) excretion and NO formation at all time points. SOD activity was reduced, whereas glutathione peroxidase (GPx) activity was increased in the group treated with leptin for 8 days. These data indicate that: (1) ERK, activated by oxidative stress, is involved only in the early phase of leptin-induced BP elevation, (2) the later phase of leptin-induced hypertension is characterized by excessive NO inactivation by superoxide, (3) the time-dependent shift from ERK to O(2)(-)-NO dependent mechanism may be associated with reduced SOD/GPx ratio, which favors formation of O(2)(-) instead of H(2)O(2).     

肾髓质诱导型一氧化氮合酶在动脉血压调控中的作用

本文通过慢性血液动力学实验,观察了肾髓质局部输入诱导型一氧化酶（ｉＮＯＳ）抑制剂ＡＧ（ａｍｉｎｏｇｕａｎｉｄｉｎｅ）对Ｄａｈｌ盐敏感大鼠（ＤＳ）、Ｄａｈｌ盐抵抗大鼠（ＤＲ）及ＳＤ（Ｓｐｒａｇｕｅ Ｄａｗｌｅｙ）大鼠动脉血压的影响,并测定了一氧化氮（ＮＯ）代谢终产物ＮＯ２及ＮＯ３含量（ＵＮＯＸ）、ｉＮＯＳ活性、肾功能以及血浆肾素活性（ＰＲＡ）。结果表明：ＡＧ能明显放大高盐（８％）引起的ＤＳ及ＳＤ大鼠