Chronic and acute effects of different antihypertensive drugs on femoral artery relaxation of L-NAME hypertensive rats

We aimed to compare the effects of chronic and acute administration of structurally different antihypertensives, diuretics - indapamide and hydrochlorothiazide, ACE inhibitor - captopril and indapamide+captopril combination on endothelium-dependent relaxation of femoral artery isolated from nitric oxide (NO)-deficient rats. In the chronic experiment, femoral artery was isolated from Wistar rats receiving L-NAME (40 mg/kg/day) solely or with indapamide (1 mg/kg/day), hydrochlorothiazide (10 mg/kg/day), captopril (10 mg/kg/day), and indapamide+captopril combination for seven weeks. In the acute in vitro experiment, the incubation medium with femoral artery isolated from L-NAME-hypertensive rats was supplemented with investigated antihypertensives in the same concentration 10(-4) mol/l. Interestingly, chronic L-NAME treatment did not cause a reduction of vasorelaxation. Indapamide+captopril elevated relaxation above the control level and completely prevented blood pressure increase induced by L-NAME. Acute incubation with captopril only or indapamide+captopril improved relaxation of femoral artery isolated from L-NAME-hypertensive rats, while the incubation with all antihypertensives increased vasorelaxation of femoral artery isolated from control Wistar rats. In conclusion, NO might be involved in the indapamide- and hydrochlorothiazide-induced improvement of vasorelaxation, while different vasorelaxing factors (prostacyclin, EDHF) contribute to the captopril-induced improvement of vasorelaxation. During the chronic treatment additive and synergic effects of indapamide and captopril may contribute to the prevention of hypertension and increase of vasorelaxation.     

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.     

Vascular effects of red wine polyphenols in chronic stress-exposed Wistar-Kyoto rats

Present study investigated the effect of red wine polyphenolic compounds (Provinols) on blood pressure (BP), nitric oxide synthase (NOS) activity and vascular function in Wistar-Kyoto (WKY) rats exposed to chronic social stress produced by crowding. Adult male rats were divided into four groups: control (480 cm(2)/rat), Provinols-treated (20 mg/kg/day, 480 cm(2)/rat), crowded (200 cm(2)/rat) and crowded treated with Provinols (20 mg/kg/day, 200 cm(2)/rat) for 8 weeks. No differences in BP were observed among the groups at the end of experiment, however, reduced BP was observed in Provinols-treated rats after 3 weeks of treatment. NOS activity in the aorta was significantly elevated in crowded rats, while Provinols alone had no effect on nitric oxide (NO) production. Acetylcholine-induced relaxation of the femoral artery was significantly improved in stressed and Provinols-treated rats vs. control, without significant changes in their noradrenaline-induced vasoconstriction. Interestingly, Provinols blunted the elevation of NO production and vasorelaxation during crowding. Increased endothelium-dependent vasorelaxation and NO synthesis in crowded rats may represent the adaptation mechanisms, resulting in unaltered blood pressure in stress-exposed normotensive rats. This study further demonstrated that elevated release of NO during chronic stress may be prevented by Provinols. Thus, Provinols might maintain equilibrium between endothelium-derived vasoconstrictor and vasodilator factors in stress.     

Nitric oxide-compromised hypertension: facts and enigmas

NO concentration in the femoral artery and femoral vein of anesthetized dogs was found to be 154.2+/-5.6 nM and 90.0+/-12 nM, respectively. Inhibition of NO synthase (NOS) slightly decreased the basal NO concentration in femoral artery from 154.2+/-5.6 to 137.2+/-3.3 nM. Acetylcholine-induced increase in NO concentration was slightly but still significantly attenuated, suggesting that very probably L-NAME did not inhibit all sources of nitric oxide (NO). Local NOS inhibition in the posterior hypothalamus dose-dependently increased systemic blood pressure (BP) in rats. Short-term general NOS inhibition in anesthetized dogs increased diastolic BP but not systolic BP. The heart rate after one-hour down-fluctuation returned to initial values. Proteosynthesis in the myocardium and both branches of the left coronary artery increased, but this was not supported by polyamines, since the activity of ornithine decarboxylase declined. Long-term general NOS inhibition elicited a sustained BP increase, a decrease in heart rate, cardiac hypertrophy and an increase in wall thickness of the coronary and carotid artery. The results indicate that NO deficiency itself plays a role in proteosynthesis and cardiac hypertrophy, in spite of relatively small increase in diastolic blood pressure and no change in systolic blood pressure, at least after an acute L-NAME administration. The hypotension response to acetylcholine and bradykinin studied in anesthetized NO-compromised rats, was unexpectedly enhanced. The elucidation of this paradoxical phenomenon will require further experiments.     

Effect of nitric oxide inhibition on blood pressure and corticosterone responses in adult rats neonatally treated with glutamate

The role of nitric oxide (NO) in the regulation of blood pressure and hypothalamic-pituitary-adrenal function of adult rats treated with monosodium glutamate (MSG) during the neonatal period was investigated. Blood pressure and the heart rate were registered by a computerized system of direct blood pressure measurement through an indwelling cannula in the femoral artery. The inhibition of the activity of NO synthase by acute injection of Nomega-nitro-L-argininemethylester (L-NAME, 30 mg/kg, i.v.) to control rats produced a rise of blood pressure and a fall of heart rate. Both responses were reduced in MSG-treated rats. Repeated administration of L-NAME (50 mg/kg, i.p, two times daily for 4 days) increased BP in both groups of animals. Corticosterone concentrations in the plasma were significantly increased in response to repeated L-NAME administration in MSG-treated rats, while ACTH levels were similar in both groups of animals. These data suggest that some of the cardiovascular and endocrine changes in rats treated with MSG may be due to the abnormal function of the NO system.     

Crowding-induced alterations in vascular system of Wistar-Kyoto rats: role of nitric oxide

The aim of this study was to determine the effect of chronic crowding on the cardiovascular system of Wistar-Kyoto (WKY) rats. Rats were randomly divided into the control (480 cm(2) per rat) or crowded (200 cm(2) per rat) group for eight weeks. Body weight, blood pressure (BP), heart rate and plasma nitrate/nitrite levels of the crowded rats were not different from controls at the end of the experiment. Plasma corticosterone exhibited an increasing trend (5.7+/-1.8 vs. 12.6+/-3.7 ng/ml, p=0.08) while blood glucose was significantly reduced in the crowded rats in comparison with the controls. Nitric oxide (NO) synthase activity and nitrate/nitrite levels of the crowded rats were significantly elevated in the aorta by 80 % and 20 %, respectively, but unchanged in the left ventricle. Moreover, acetylcholine-induced relaxation was significantly increased in the crowded rats in both the femoral artery (61+/-5 % vs. 76+/-5 %, p<0.001) and mesenteric artery (51+/-6 % vs. 72+/-7 %, p<0.001). In conclusion, results suggest that chronic crowding may increase vasorelaxation and vascular NO production in normotensive rats. This may be considered as an adapting mechanism preventing the development of the stress-related elevation of BP. Additionally, results also suggest caution in the housing of rats because an inappropriate crowding may affect results of the experiment significantly.     

Endothelial dysfunction and arterial pressure regulation during early diabetes in mice: roles for nitric oxide and endothelium-derived hyperpolarizing factor

We determined whether nitric oxide (NO) counters the development of hypertension at the onset of diabetes in mice, whether this is dependent on endothelial NO synthase (eNOS), and whether non-NO endothelium-dependent vasodilator mechanisms are altered in diabetes in mice. Male mice were instrumented for chronic measurement of mean arterial pressure (MAP). In wild-type mice, MAP was greater after 5 wk of N(omega)-nitro-L-arginine methyl ester (L-NAME; 100 mg x kg(-1) x day(-1) in drinking water; 97 +/- 3 mmHg) than after vehicle treatment (88 +/- 3 mmHg). MAP was also elevated in eNOS null mice (113 +/- 4 mmHg). Seven days after streptozotocin treatment (200 mg/kg iv) MAP was further increased in L-NAME-treated mice (108 +/- 5 mmHg) but not in vehicle-treated mice (88 +/- 3 mmHg) nor eNOS null mice (104 +/- 3 mmHg). In wild-type mice, maximal vasorelaxation of mesenteric arteries to acetylcholine was not altered by chronic L-NAME or induction of diabetes but was reduced by 42 +/- 6% in L-NAME-treated diabetic mice. Furthermore, the relative roles of NO and endothelium-derived hyperpolarizing factor (EDHF) in acetylcholine-induced vasorelaxation were altered; the EDHF component was enhanced by L-NAME and blunted by diabetes. These data suggest that NO protects against the development of hypertension during early-stage diabetes in mice, even in the absence of eNOS. Furthermore, in mesenteric arteries, diabetes is associated with reduced EDHF function, with an apparent compensatory increase in NO function. Thus, prior inhibition of NOS results in endothelial dysfunction in early diabetes, since the diabetes-induced reduction in EDHF function cannot be compensated by increases in NO production.     

Effects of Cudrania tricuspidata water extract on blood pressure and renal functions in NO-dependent hypertension

A pharmacological inhibition of nitric oxide synthase (NOS) in rats for 4-6 weeks produces renal vasoconstriction, renal dysfunction, and severe hypertension. The present study was aimed at investigating whether Cudrania tricuspidata (C. tricuspidata) water extract ameliorates N(G)-Nitro-L-arginine methylester (L-NAME)-induced hypertension. Treatment of L-NAME (60 mg/L drinking water, 4 weeks) causes a sustained increase in systolic blood pressure (SBP). The concentration of plasma NO metabolites and NO/cGMP productions in the vascular tissues of the L-NAME-treated group were significantly reduced as compared with those in the control. C. tricuspidata water extract blocked increase of SBP in the L-NAME-treated group and restored SBP to normal level. Futhermore, C. tricuspidata water extract was able to preserve the vascular NO/cGMP production and plasma NO metabolites concentration. However, there are no changes in the expression of ecNOS and iNOS of thoracic aorta among the rats of control, L-NAME-treated group, and L-NAME and C. tricuspidata water extract co-treated group. The urinary sodium level, urine volume, and creatinine clearance were significantly higher in rats co-treated with C. tricuspidata water extract and L-NAME than in L-NAME-treated group. Taken together, these results suggest that C tricuspidata water extract prevents the increase of SBP in the L-NAME-induced hypertension that may have been caused by enhanced generation of vascular NO/cGMP.     

Renal effects of acute nitric oxide and ET(A)/ET(B) receptor inhibition in conscious spontaneously hypertensive rats

The aim of the present study was to investigate the effects of endogenous endothelin on renal excretory function in spontaneously hypertensive rats (SHR) after inhibition of NO synthesis. The effects of non-selective ET(A)/ET(B) receptor blockade on L-NAME-induced changes in renal excretory function and blood pressure (BP) were investigated in conscious, SHR and normotensive Wistar rats with implanted catheters in the bladder for urine collection, in the femoral artery for BP registration and in the femoral vein for L-NAME and bosentan administration. L-NAME increased systolic, mean and diastolic BP, diuresis, sodium and chloride excretion (p < 0.01) in both normotensive and hypertensive rats but bosentan returned the values of diuresis, sodium and chloride excretion to control level without any changes in BP in normotensive rats. In SHR the effects of L-NAME were reduced after bosentan (p < 0.05) but the values of diuresis, sodium and chloride excretion still remained statistically significant as compared to control level despite the fact that bosentan lowered mean and diastolic BP increased due to L-NAME administration. Endogenous endothelins participate in a different manner in the rise of BP and in the changes in renal excretory function that develops after L-NAME-induced NO synthase inhibition in normotensive rats and in SHR.     

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.     

Organization of collagen bundles during tendon healing in rats treated with L-NAME

The Achilles tendon can support high tension forces and may experience lesions. The damaged tissue does not regenerate completely, with the organization and mechanical properties of the repaired tendon being inferior to those of a healthy tendon. Nitric oxide (NO) plays an important role in wound repair. We have examined the structural reorganization and repair in Achilles tendon after injury in rats treated with the NO synthase inhibitor L-NAME. The right Achilles tendon of male Wistar rats was partially transected. One group of rats was treated with L-NAME (~300 mg/kg per day, given in drinking water) for 4 days prior to tendon sectioning and throughout the post-operative period. Control rats received water without L-NAME. The tendons were excised at 7, 14, and 21 days post-injury and used to quantify hydroxyproline and for mechanical tests. Tendons were also processed for histomorphological analysis by polarized light microscopy, which showed that the collagen fibers were disorganized by day 7 in non-treated and L-NAME-treated rats. In non-treated rats, the organization of the extracellular matrix was more homogeneous by days 14 and 21 compared with day 7, although this homogeneity was less than that in normal tendon. In contrast, in injured tendons from L-NAME-treated rats, the collagen fibers were still disorganized on day 21. Tendons from treated rats had more hydroxyproline but lower mechanical properties compared with those from non-treated rats. Thus, NO modulates tendon healing, with a reduction in NO biosynthesis delaying reorganization of the extracellular matrix, especially collagen. T.C.T. and W.R.N were supported by studentships from CAPES, and S.H. was supported by a research fellowship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).     

Histamine-induced relaxation in pulmonary artery of normotensive and hypertensive rats: relative contribution of prostanoids, nitric oxide and hyperpolarization

The aim of this study was to determine the relative contribution of nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and prostanoids in histamine-induced relaxation of isolated pulmonary artery from normotensive and hypertensive rats. The hypertension was induced by oral administration of NO synthase inhibitor N(G)-nitro-L-arginine methylester (L-NAME, 50 mg/kg/day) to normotensive rats for 8 weeks. In phenylephrine-precontracted arterial rings the histamine-induced relaxation was significantly reduced in L-NAME-treated rats compared to the controls. Indomethacin (cyclooxygenase inhibitor) and glibenclamide (ATP-sensitive K+-channel blocker) did not inhibit the relaxation response in either control or hypertensive rats. On the other hand, tetraethylammonium (TEA), a K+-channel blocker with a broad specificity, significantly reduced histamine-induced relaxation in the pulmonary artery from both groups examined. The TEA-resistant relaxation was completely abolished by additional administration of L-NAME to the incubation medium. The results indicate that histamine-induced relaxation of the pulmonary artery in both normotensive and hypertensive rats is mediated mainly by nitric oxide, whereas EDHF seems to play a minor role.     

Effects of chronic N(omega)-nitro-L-arginine methyl ester administration on glucose tolerance and skeletal muscle glucose transport in the rat.

It has been suggested that nitric oxide (NO) is a key regulator of carbohydrate metabolism in skeletal muscle. The present study was undertaken to examine the effects of chronic in vivo competitive antagonism of NO synthase (NOS) by the administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) in the drinking water (1 mg/ml) for 14 days on glucose tolerance and skeletal muscle glucose transport in rats. Oral glucose tolerance tests (OGTT) revealed an impaired glucose tolerance in the L-NAME-treated rats as reflected by the area under the glucose curve (4675 +/- 514 mg% x 120 min (control) vs 6653 +/- 571 mg% x 120 min (L-NAME treated); P < 0.03). While a large rise in plasma insulin concentration was present in the control rats (0.87 +/- 0.34 ng/ml, P < 0.001) during the first 15 min of the OGTT, rises in plasma insulin concentration were absent in the L-NAME-treated rats (0.18 +/- 0.13 ng/ml, P = NS). Intravenous glucose tolerance tests confirmed an impaired insulin secretion in the L-NAME-treated rats. In contrast, insulin-stimulated 2-deoxyglucose transport was enhanced (P < 0.03) by chronic NOS inhibition (5.29 +/- 0.83 nmol/g/min) compared to control rats (2.21 +/- 0.90 nmol/g/min). Plasma sodium concentrations were lower and plasma potassium concentrations were higher in the L-NAME-treated group, indicating an impaired electrolyte status. We conclude that chronic in vivo administration of a NOS inhibitor, while not impairing basal parameters of carbohydrate metabolism, may manifest different responses than acute exposure to the same agent in vitro.     

Efficiency of NO donors in substituting impaired endogenous NO production: a functional and morphological study

Two exogenous NO donors were used to act as substitutes for impaired endogenous nitric oxide (NO) production due to inhibition of NO synthase in rats. Six weeks' lasting inhibition of NO synthase by NG-nitro-L-arginine methyl ester (L-NAME) induced stabilized hypertension. Simultaneously administered isosorbide-5-mononitrate did not prevent the development of hypertension. Molsidomine, administered concomitantly with L-NAME, significantly attenuated the BP increase. However, BP was still found to be moderately increased compared to the initial values. Remarkable alterations in the geometry of the aorta, carotid and coronary artery found in NO-deficient hypertension were prevented in rats administered L-NAME plus molsidomine at the same time. In spite of 6 weeks' lasting inhibition of NOS, the NOS activators acetylcholine and bradykinin induced BP decrease; the maximum hypotensive value did not differ from the values recorded in the controls or in animals treated with L-NAME plus molsidomine. Notably enough, the hypotension was similar to that found in rats administered L-NAME alone for six weeks. After NO synthase inhibition, Isosorbide-5-mononitrate does not substitute and molsidomine substitute only partially the impaired endogenous NO production.     

Vascular function and nitric oxide production in chronic social-stress-exposed rats with various family history of hypertension.

The study investigated the effect of chronic crowding stress on vascular function and nitric oxide (NO) production in rats with various family history of hypertension. Wistar (W), wBHR (offspring of W dams and spontaneously hypertensive sires), sBHR (offspring of spontaneously hypertensive dams and W sires) and spontaneously hypertensive rats (SHR) were used. Twelve-week-old males were divided into the control or crowded group for eight weeks. Basal blood pressure (BP, determined by tail-cuff plethysmography) of W, wBHR, sBHR and SHR rats was 112 +/- 3, 129 +/- 2, 135 +/- 2 and 187 +/- 3 mmHg, respectively. Crowding increased BP and reduced aortic NO synthase activity only in sBHR and SHR rats, without alterations in hypothalamic NO production. Acetylcholine-induced vasorelaxation of the femoral artery of stress-exposed rats was improved in W, unaltered in wBHR and sBHR and reduced in SHR. Crowding reduced serotonin-induced vasoconstriction in W and wBHR rats but had no effect in sBHR and SHR rats. In conclusion, the results suggest that crowded offspring of normotensive mothers were able to modify their vascular function in order to maintain BP at normal levels. On the other hand, offspring of hypertensive mothers were unable of effective adaptation of vascular function in stressful conditions resulting in gradual development of hypertension.     

Effect of chronic lithium administration on endothelium-dependent relaxation of rat mesenteric bed: role of nitric oxide

The mechanism of action of lithium, an effective treatment for bipolar disease, is still unknown. In this study, the mesenteric vascular beds of control rats and rats that were chronically treated with lithium were prepared by the McGregor method, and the mesenteric vascular bed vasorelaxation responses were examined. NADPH-diaphorase histochemistry was used to determine the activity of NOS (nitric oxide synthase) in mesenteric vascular beds. We demonstrated that ACh-induced vasorelaxation increased in the mesenteric vascular bed of rats treated with lithium. Acute No-nitro-L-arginine methyl ester (L-NAME) administration in the medium blocked ACh-induced vasorelaxation in the control group more effectively than in lithium-treated rats, while the vasorelaxant response to sodium nitroprusside, a NO donor, was not different between lithium-treated and control groups. Acute aminoguanidine administration blocked ACh-induced vasorelaxation of lithium-treated rats, but had no effect in the control rats. Furthermore, NOS activity, determined by NADPH-diaphorase staining, was significantly greater in the mesenteric vascular beds from chronic lithium-treated rats than in those from control rats. These data suggest that the enhanced ACh-induced endothelium-derived vasorelaxation in rat mesenteric bed from chronic lithium-treated rats might be associated with increased NOS activity, likely via iNOS. Simultaneous acute L-NAME and indomethacin administration suggests the possible upregulation of EDHF (endothelium-derived hyperpolarizing factor) in lithium-treated rats.     

The role of the hypothalamic nitric oxide in the pressor responses elicited by acute environmental stress in awake rats

We quantitatively investigated the change in nitric oxide (NO) in the hypothalamic paraventricular nucleus (PVN) and its effect on cardiovascular regulation during shaker stress (SS) using brain microdialysis in awake rats. Male Wistar rats were fed either N(G)-nitro-L-arginine methyl ester (L-NAME, 0.7 g/L) or tap water for 2 weeks. Two days after implantation of an arterial catheter and guide shaft, a microdialysis probe was placed to perfuse the PVN with degassed Ringer solution at 2 microl/min in awake normotensive Wistar (CONTROL) and chronic L-NAME-treated hypertensive rats. After the rat was placed in a plastic cage set on a shaker, the blood pressure and heart rate was monitored and 10-min SS was loaded at a frequency of 200 cycles/min. Dialysate samples were analyzed by NO analyzer (based on the Griess reaction) every 10 min, and NOx (NO(2)(-) + NO(3)(-)) was measured. Plasma NOx was also measured before and after SS. Pressor responses elicited by SS were significantly greater in L-NAME-treated rats than in the CONTROL. Although NOx in the PVN dialysate were increased by SS in the CONTROL, these responses were attenuated in chronic L-NAME-treated rats. Resting plasma NOx were higher in the CONTROL than in L-NAME-treated rats. SS elicited no difference between two groups in plasma NOx. These results indicated that NO within the PVN, but not in systemic circulation, may play a role on the attenuation of the pressor responses elicited by SS. The dysfunction of NO release within the PVN may, in part, play a role in the exaggerated pressor responses in acute environmental 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.     

Oxidative injury due to chronic nitric oxide synthase inhibition in rat: effect of regular exercise on the heart

Many individuals with cardiac diseases undergo periodic physical conditioning with or without medication. 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), heart rate (HR) and cardiac oxidant/antioxidant systems in rats. Fisher 344 rats were divided into four groups and treated as follows: (1) sedentary control (SC), (2) exercise training (ET) for 8 weeks, (3) L-NAME (10 mg/kg, s.c. for 8 weeks) and (4) ET+L-NAME. BP and HR were monitored with tail-cuff method. The animals were sacrificed 24 h after last treatments and hearts were isolated and analyzed. Physical conditioning significantly increased respiratory exchange ratio (RER), cardiac nitric oxide (NO) levels, NOS activity and endothelial (eNOS) and inducible (iNOS) protein expression. Training significantly enhanced cardiac glutathione (GSH) levels, GSH/GSSG ratio and up-regulation of cardiac copper/zinc-superoxide dismutase (CuZn-SOD), manganese (Mn)-SOD, catalase (CAT), glutathione peroxidase (GSH-Px) activity and protein expression. Training also caused depletion of cardiac malondialdehyde (MDA) and protein carbonyls. Chronic L-NAME administration resulted in depletion of cardiac NO level, NOS activity, eNOS, nNOS and iNOS protein expression, GSH/GSSG ratio and down-regulation of cardiac CuZn-SOD, Mn-SOD, CAT, GSH-PX, glutathione-S-transferase (GST) activity and protein expression. Chronic L-NAME administration enhanced cardiac xanthine oxidase (XO) activity, MDA levels and protein carbonyls. These biochemical changes were accompanied by increases in BP and HR after L-NAME administration. Interaction of training and NOS inhibitor treatment resulted in normalization of BP, HR and up-regulation of cardiac antioxidant defense system. The data suggest that physical conditioning attenuated the oxidative injury caused by chronic NOS inhibition by up-regulating the cardiac antioxidant defense system and lowering the BP and HR in rats.     

Hepatic morphological alterations,glycogen content and cytochrome P450 activities in rats treated chronically with N<Superscript>ω</Superscript>-nitro-L-arginine methyl ester (L-NAME)

Chronic treatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) biosynthesis, results in hypertension mediated partly by enhanced angiotensin-I-converting enzyme (ACE) activity. We examined the influence of L-NAME on rat liver morphology, on hepatic glycogen, cholesterol, and triglyceride content, and on the activities of the cytochrome P450 isoforms CYP1A1/2, CYP2B1/2, CYP2C11, and CYP2E1. Male Wistar rats were treated with L-NAME (20 mg/rat per day via drinking water) for 2, 4, and 8 weeks, and their livers were then removed for analysis. Enzymatic induction was produced by treating rats with phenobarbital (to induce CYP2B1/2), beta-naphthoflavone (to induce CYP1A1/2), or pyrazole (to induce CYP2E1). L-NAME significantly elevated blood pressure; this was reversed by concomitant treatment with enalapril (ACE inhibitor) or losartan (angiotensin II AT(1) receptor antagonist). L-NAME caused vascular hypertrophy in hepatic arteries, with perivascular and interstitial fibrosis involving collagen deposition. Hepatic glycogen content also significantly increased. L-NAME did not affect fasting glucose levels but significantly reduced insulin levels and increased the insulin sensitivity of rats, based on an intraperitoneal glucose tolerance test. Immunoblotting experiments indicated enhanced phosphorylation of protein kinase B and of glycogen synthase kinase 3. All these changes were reversed by concomitant treatment with enalapril or losartan. L-NAME had no effect on hepatic cholesterol or triglyceride content or on the basal or drug-induced activities and protein expression of the cytochrome P450 isoforms. Thus, the chronic inhibition of NO biosynthesis produced hepatic morphological alterations and changes in glycogen metabolism mediated by the renin-angiotensin system. The increase in hepatic glycogen content probably resulted from enhanced glycogen synthase activity following the inhibition of glycogen synthase kinase 3 by phosphorylation.