Systemic Nitric Oxide Synthase Research Articles

Systemic NOS inhibition reduces contracting muscle oxygenation more in intact female than male rats

Females respond to baroreceptor stimulation with enhanced modulation of heart rate (HR) to regulate blood pressure and also express greater reliance on nitric oxide (NO) for vascular control compared to males. Sex differences in muscle oxygenation consequent to central hemodynamic challenge induced by systemic NO synthase (NOS) inhibition are unknown. We tested the hypotheses that systemic NOS inhibition would induce lower contracting skeletal muscle oxygenation in females compared to males. The spinotrapezius of Sprague-Dawley rats (females (♀) = 9, males (♂) = 9) was surgically exposed and contracted by electrical stimulation (180s, 1 Hz, ~6 V) under pentobarbital sodium anesthesia. Oxyphor G4 was injected into the muscle and phosphorescence quenching was used to measure the interstitial PO2 (PO2is, determined by O2 delivery-to-utilization matching) under control (Krebs-Henseleit solution) and after intra-arterial infusion of nitro-l-arginine methyl ester (l-NAME; NOS blockade; 10 mg kg−1). At rest, females showed a greater PO2is increase (ΔPO2is/ΔMAP) and HR (ΔHR/ΔMAP) reduction than males in response to the elevated MAP induced by systemic NOS inhibition (both p < 0.05). Following l-NAME, during the contracting steady-state, females exhibited lower PO2is than males (♂: 17.1 ± 1.4 vs ♀: 10.8 ± 1.4 mmHg, p < 0.05). The rate pressure product was lower in females than males (♂: 482 ± 14 vs ♀: 392 ± 29, p < 0.05) and correlated with the steady-state PO2is (r = 0.66, p < 0.05). These results support that females express greater reductions in HR than males in response to l-NAME-induced elevation of MAP via the baroreceptor reflex and provide new insights on how central hemodynamics affect skeletal muscle oxygenation in a sex-specific manner.

Chronic inhibition of nitric oxide synthase modulates calcium handling in rat heart 1.

Systemic infusion of nitric oxide synthase (NOS) inhibitors increases peripheral vascular resistance due to inhibition of endothelial NOS leading to the activation of the arterial baroreceptor mechanisms and inhibition of central sympathetic outflow. In the current study, we explored that systemic NOS blockage activates protein kinase A (PKA)-mediated signaling pathway through maintained cGMP-dependent protein kinase (PKG) activation. Rats were treated with 3 different concentrations of N(ω)-nitro-l-arginine methyl ester (L-NAME) for 14 days. Systemic L-NAME treatment induced a dose-dependent increase in blood pressure and increased mRNA levels of atrial natriuretic peptide (ANP) and phosphorylation levels of p44/42 MAPK without any change in cardiac mass. The cardiac cGMP levels and PKG-mediated phosphorylation of vasodilator-stimulated phosphoprotein (VASP) (Ser239) did not alter in any group. At the highest dose of treatment (100 mg/kg per day), PKA-mediated phosphorylations of VASP (Ser157) and troponin I (TnI) (Ser23/24) were enhanced significantly indicating the increase in PKA activation in response to chronic NOS blockage. Alterations in both phosphorylated phospholamban (Ser16/Thr17) and sarcoplasmic/endoplasmic Ca2+-ATPase (SERCA2) levels can increase cytosolic Ca2+ load and impair Ca2+ handling. Our data suggest that the increased PKA activation in response to chronic NOS blockage appears to be responsible for cardiac abnormalities that occur due to prolonged L-NAME treatment.

Renal Soluble Guanylate Cyclase Is Downregulated in Sunitinib-Induced Hypertension.

BackgroundThe tyrosine kinase inhibitor sunitinib causes hypertension associated with reduced nitric oxide (NO) availability, elevated renal vascular resistance, and decreased fractional sodium excretion. We tested whether (1) nitrate supplementation mitigates sunitinib‐induced hypertension and NO contributes less to renal vascular resistance as well as fractional sodium excretion regulation in sunitinib‐treated rats than in controls; and (2) renal soluble guanylate cyclase (sGC) is downregulated and sGC activation lowers arterial pressure in rats with sunitinib‐induced hypertension.Methods and ResultsArterial pressure responses to nitrate supplementation and the effects of systemic and intrarenal NO synthase (NOS) inhibition on renal hemodynamics and fractional sodium excretion were assessed in sunitinib‐treated rats and controls. Renal NOS and sGC mRNA as well as protein abundances were determined by quantitative polymerase chain reaction and Western blot. The effect of the sGC activator cinaciguat on arterial pressure was investigated in sunitinib‐treated rats. Nitrate supplementation did not mitigate sunitinib‐induced hypertension. Endothelium‐dependent reductions in renal vascular resistance were similar in control and sunitinib‐treated animals without and with systemic NOS inhibition. Selective intrarenal NOS inhibition lowered renal medullary blood flow in control but not in sunitinib‐treated rats without significant effects on fractional sodium excretion. Renal cortical sGC mRNA and sGC α1‐subunit protein abundance were less in sunitinib‐treated rats than in controls, and cinaciguat effectively lowered arterial pressure by 15‐20 mm Hg in sunitinib‐treated rats.ConclusionsRenal cortical sGC is downregulated in the presence of intact endothelium‐dependent renal vascular resistance regulation in developing sunitinib‐induced hypertension. This suggests that sGC downregulation occurs outside the renal vasculature, increases renal sodium retention, and contributes to nitrate resistance of sunitinib‐induced hypertension.

Effect of nebivolol on renal nitric oxide availability and tubular function in patients with essential hypertension.

Nebivolol is a selective β1 -receptor antagonist with vasodilating properties. In patients with essential hypertension, we tested the hypothesis that nebivolol increases systemic and renal nitric oxide (NO) availability using L-N(G) -monomethyl arginine (L-NMMA) as an inhibitor of NO production. In a randomized, placebo-controlled, crossover study, patients with essential hypertension were treated with nebivolol for five days, along with a standardized diet and fluid intake. We examined the acute effects of systemic NO synthase inhibition with L-NMMA on brachial blood pressure (bBP), pulse wave velocity (PWV) and central blood pressure (cBP) estimated by applanation tonometry, glomerular filtration rate (GFR), fractional excretion of sodium (FENa ), urinary excretion of both aquaporin-2 (u-AQP2) and epithelial sodium channels (u-ENaCγ ), and plasma concentrations of nitrate/nitrite (p-NOx ) and vasoactive hormones after five days' treatment with placebo and nebivolol. Nebivolol significantly reduced PWV, bBP, cBP and plasma renin, angiotensin II and aldosterone concentrations. The renal parameters, p-NOx and plasma arginine vasopressin concentration were not changed by nebivolol. There was no difference between nebivolol and placebo in the response to L-NMMA, with LMMA inducing a similar increase in PWV, bBP and cBP and a similar decrease in GFR, uAQP2 and u-ENaCγ and FENa [mean change -0.62% (95% confidence interval {CI} -0.40 to -0.84) during placebo vs. -0.57% (95% CI -0.46 to -0.68; P = 0.564) during nebivolol treatment]. Vasoactive hormones were changed to a similar extend by L-NMMA during administration of nebivolol and placebo. Nebivolol did not change p-NOx , and inhibition of NO synthesis induced the same response in blood pressure, GFR, renal tubular function and vasoactive hormones during nebivolol and placebo. Thus, the data did not support the hypothesis that nebivolol changes vascular and renal NO availability in patients with essential hypertension.

Pharmacological inhibition of nitric oxide synthase increases sympathetic nerve activity in healthy humans

Animal studies have indicated that nitric oxide (NO) is a key signaling molecule involved in the tonic restraint of central sympathetic outflow from the brainstem. Extension of these findings to humans has been difficult since experimental systemic NO synthase (NOS) inhibition rapidly increases blood pressure (BP) from the removal of endothelial‐dependent vasodilation and activates an arterial baroreflex‐mediated sympathoinhibitory response. Thus, to overcome this confounding inhibitory influence of the baroreflex we measured skin SNA, which is not under baroreceptor control. Seven healthy subjects (26 ± 3 yr) were studied before, during and 90 minutes after a 60 minute intravenous infusion of the NOS inhibitor NG‐nitro‐L‐arginine methyl ester (L‐NAME; 4mg/kg). Skin SNA and BP were continuously measured. Mean BP was increased from baseline at the end of the L‐NAME infusion (Δ15 ± 2 mmHg; P&lt;0.05) and remained elevated at 90 minutes post infusion (Δ16 ± 1 mmHg; P&lt;0.05). Similarly, skin SNA was elevated at the end of the L‐NAME infusion (ΔTotal Area 133 ± 59 au; P&lt;0.05) and this increase was maintained at 90 minutes post infusion (ΔTotal Area 209 ± 70 au; P&lt;0.05). Importantly, skin SNA remained unchanged during time control experiments. These preliminary findings suggest that pharmacological inhibition of NOS increases SNA and supports a role of NO in central sympathetic control in humans. Supported by NIH DK076636.

Contribution of Endothelial Nitric Oxide to Blood Pressure in Humans

HomeHypertensionVol. 49, No. 5Contribution of Endothelial Nitric Oxide to Blood Pressure in Humans Free AccessLetterPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessLetterPDF/EPUBContribution of Endothelial Nitric Oxide to Blood Pressure in Humans Markus P. Schlaich Roland E. Schmieder Markus P. SchlaichMarkus P. Schlaich Baker Heart Research Institute, Melbourne, Victoria, Australia Search for more papers by this author Roland E. SchmiederRoland E. Schmieder Department of Nephrology and Hypertension, University of Erlangen-Nuernberg, Erlangen, Germany Search for more papers by this author Originally published5 Mar 2007https://doi.org/10.1161/HYPERTENSIONAHA.107.087536Hypertension. 2007;49:e29Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: March 5, 2007: Previous Version 1 To the Editor:Assessment and dissection of the various components contributing to the complex regulation of blood pressure control is a challenging task, particularly so in humans. Gamboa et al1 are to be complemented on a perceptive and sophisticated study design in their approach to assess the contribution of endothelial-derived NO to blood pressure in humans. Inducing autonomic blockade by infusion of the ganglion blocker trimetaphan to eliminate baroreflex mechanisms, in concert with systemic inhibition of NO synthase, using NG-monomethyl-l-arginine, allowed them to estimate the contribution of endothelium-derived NO to blood pressure in healthy humans, pinning it down to an effect in the magnitude of ≈30 mm Hg. In accordance, the NG-monomethyl-l-arginine–induced increase in blood pressure during autonomic blockade was blunted in smokers assumed to be characterized by impaired NO availability.In a series of experiments using similar methodologies and systemic NO synthase blockade, we have investigated the role of endothelium-derived NO in another circulatory bed known to be strictly controlled by a variety of components, including the sympathetic nervous system, namely, the renal vasculature. In the absence of autonomic blockade, we could not detect any differences in NG-monomethyl-l-arginine–induced changes in systemic blood pressure or renal plasma flow between healthy control subjects and age-matched patients with hypertension,2 diabetes,3 or smokers,4 despite proven impairment of endothelium- dependent vasodilation in the forearm in some of these patients. However, common to all of these pathologic conditions was a substantial and significant augmentation of endothelium-dependent increases in renal plasm flow during concomitant infusion of the antioxidant vitamin C, particularly in smokers, thereby highlighting the profound impact of the abundance of reactive oxygen species on circulatory control, at least in the renal vascular bed in these populations. The absence of differences in response to blockade of endothelial NO synthase by NG-monomethyl-l-arginine and the similar blood pressure levels compared with control subjects could be the result of other mechanisms compensating for impaired endothelial NO availability, such as alterations in other endothelium-derived factors or in regulation of sympathetic nervous system activity. Extrapolating these findings to the data presented by Gamboa et al,1 one could expect that additional introduction of antioxidant measures in their smokers would have helped to further identify and unmask the contribution of oxidative stress as a cause for the impairment of endothelium-derived NO availability. One aspect that has been neglected in the discussion but certainly needs to be taken into account is the potential influence of activation of the renin–angiotensin system, known to interfere with the sympathetic nervous system, as well as the l-arginin/NO pathway, particularly through nicotinamide-adenine dinucleotide phosphate oxidase-dependent production of oxygen-free radicals, both on a central and peripheral level.5DisclosuresNone.1 Gamboa A, Shibao C, Diedrich A, Choi L, Pohar B, Jordan J, Paranjape S, Farley G, Biaggioni I. Contribution of endothelial nitric oxide to blood pressure in humans. Hypertension. 2007; 49: 170–177.LinkGoogle Scholar2 Jacobi J, Schneider MP, John S, Schmieder RE. Impact of NO-synthase inhibition on renal hemodynamics in normotensive and hypertensive subjects. J Hypertens. 2002; 20: 525–530.CrossrefMedlineGoogle Scholar3 Delles C, Schneider MP, Oehmer S, Fleischmann I, Fleischmann EF, Schmieder RE. Increased response of renal perfusion to the antioxidant vitamin C in type 2 diabetes. Nephrol Dial Transplant. 2004; 19: 2513–2518.CrossrefMedlineGoogle Scholar4 Schneider MP, Klingbeil AU, Delles C, Schmidt BM, John S, Schmieder RE. Vitamin C augments the renal response to L-arginine in smokers. Nephrol Dial Transplant. 2003; 18: 1512–1517.CrossrefMedlineGoogle Scholar5 Ramchandra R, Barrett CJ, Malpas SC. Nitric oxide and sympathetic nerve activity in the control of blood pressure. Clin Exp Pharmacol Physiol. 2005; 32: 440–446.CrossrefMedlineGoogle Scholar Previous Back to top Next FiguresReferencesRelatedDetailsCited ByGamboa A and Biaggioni I (2007) Response to Contribution of Endothelial Nitric Oxide to Blood Pressure in Humans, Hypertension, 49:5, (e30-e30), Online publication date: 1-May-2007. May 2007Vol 49, Issue 5 Advertisement Article InformationMetrics https://doi.org/10.1161/HYPERTENSIONAHA.107.087536PMID: 17339534 Originally publishedMarch 5, 2007 PDF download Advertisement SubjectsAutonomic Nervous SystemEndothelium/Vascular Type/Nitric Oxide

Effect of Systemic Nitric Oxide Synthase Inhibition on Arterial Stiffness in Humans

Stiffening of large elastic arteries impairs the buffering function of the arterial system and contributes to cardiovascular disease. The aim of this study was to determine whether endothelium-derived nitric oxide (NO) modulates the stiffness of large elastic arteries in humans. Seven apparently healthy adults (60+/-3 years, 2 males and 5 females) underwent systemic alpha-adrenergic blockade (phentolamine) and systemic NO synthase inhibition using NG-monomethyl-L-arginine (L-NMMA) in sequence. Phentolamine was given first to isolate contribution of NO to arterial stiffness by preventing reflex changes in sympathetic tone that result from systemic NO synthase inhibition, and also to compare arterial stiffness at a similar mean arterial pressure. Mean arterial blood pressure decreased (p<0.05) after phentolamine infusion but returned to baseline levels after L-NMMA infusion. The carotid beta-stiffness index (via simultaneous ultrasound and applanation tonometry on the common carotid artery) did not change after the restraint of systemic alpha-adrenergic nerve activity (9.8+/-1.2 vs. 9.1+/-1.1 U) but increased (p<0.05) after NO synthase inhibition (12.6+/-2.0 U). These results suggest that NO appears to modulate central arterial stiffness in humans.

Compromised Aortic Vasoreactivity in Male Estrogen Receptor-α-Deficient Mice during Acute Lipopolysaccharide-Induced Inflammation

Activation of the estrogen receptor-alpha (ERalpha) mediates the vasculoprotective effects of estrogen, in part, through modulating nitric oxide (NO) production and vasodilation. Whereas inflammation is accompanied by altered vascular reactivity and underlies the pathogenesis of vascular disease, the role of the ERalpha in the vascular responses associated with acute systemic inflammation remains poorly characterized. Contractile and relaxation responses of isolated aortic segments were investigated 12 h after ip injection of saline or lipopolysaccharide (LPS, 10 mg/kg) in male wild-type (ERalpha(+/+)) and ERalpha-deficient (ERalpha(-/-)) mice. As previously observed, LPS-injected ERalpha(+/+) mice displayed reduced contractile responses to phenylephrine and enhanced vasodilation in response to acetylcholine. In contrast, aortic tissues from LPS-injected ERalpha(-/-) mice displayed enhanced contractile responses and reduced sensitivity to acetylcholine- and sodium nitroprusside-induced vasodilation. LPS treatment in ERalpha(+/+) and ERalpha(-/-) mice resulted in similar increased levels of systemic NO production and inducible NO synthase expression in the vascular wall. However, expression of mRNA and protein for endothelial NOS and soluble guanylate cyclase (alpha- and beta-subunits) were significantly reduced in aortic tissues from LPS-treated ERalpha(-/-) animals, possibly accounting for reduced endothelial NO production and reduced smooth muscle responses to NO. These findings represent new evidence of the functional role of ERalpha in the male vasculature and suggest that during acute LPS-induced inflammatory responses, the ERalpha mediates the sustained expression of the molecular machinery essential for endothelial NO synthesis (i.e. endothelial NOS) and the vascular responses to NO (i.e. soluble guanylate cyclase).

Mild increases in portal pressure upregulate vascular endothelial growth factor and endothelial nitric oxide synthase in the intestinal microcirculatory bed, leading to a hyperdynamic state

Increased nitric oxide (NO) is the main factor leading to the hyperdynamic circulation associated with advanced portal hypertension (PHT), but the initial mechanisms and the magnitude of increase in portal pressure required to trigger NO production are not known. We addressed these issues by studying systemic and splanchnic hemodynamics and endothelial NO synthase (eNOS) and VEGF expression in rats with different degrees of portal hypertension. Portal vein ligation (PVL) performed over needles of three different calibers (16-, 18-, and 20-gauge) yielded different degrees of PHT and portosystemic shunting. Compared with sham rats, all three groups of PVL rats exhibited features of hyperdynamic circulation. Rats with minimal portal hypertension (PVL with a 16-gauge needle) showed an early increase in VEGF and eNOS expression selectively at the jejunum. Immunofluorescence showed that VEGF expression was located in highly vascularized areas of the mucosa. Inhibition of VEGF signaling markedly attenuated the increase in eNOS expression. In conclusion, mild increases in portal pressure are enough to upregulate eNOS at the intestinal microcirculation, and this occurs, at least in part, through VEGF upregulation.

Relationship between muscle sympathetic nerve activity and systemic hemodynamics during nitric oxide synthase inhibition in humans

Large interindividual differences exist in resting sympathetic nerve activity (SNA) among normotensive humans with similar arterial pressure (AP). We recently showed inverse relationships of resting SNA with cardiac output (CO) and vascular adrenergic responsiveness that appear to balance the influence of differences in SNA on blood pressure. In the present study, we tested whether nitric oxide (NO)-mediated vasodilation has a role in this balance by evaluating hemodynamic responses to systemic NO synthase (NOS) inhibition in individuals with low and high resting muscle SNA (MSNA). We measured MSNA via peroneal microneurography, CO via acetylene uptake and AP directly, at baseline and during increasing systemic doses of the NOS inhibitor NG-monomethyl-L-arginine (L-NMMA). Baseline MSNA ranged from 9 to 38 bursts/min (13 to 68 bursts/100 heartbeats). L-NMMA caused dose-dependent increases in AP and total peripheral resistance and reflex decreases in CO and MSNA. Increases in AP with L-NMMA were greater in individuals with high baseline MSNA (PANOVA<0.05). For example, after 8.5 mg/kg of L-NMMA, in the low MSNA subgroup (n=6, 28+/-4 bursts/100 heartbeats), AP increased 9+/-1 mmHg, whereas in the high-MSNA subgroup (n=6, 58+/-3 bursts/100 heartbeats), AP increased 15+/-2 mmHg (P<0.01). The high-MSNA subgroup had lower baseline CO and smaller decreases in CO with L-NMMA, but changes in total peripheral resistance were not different between groups. We conclude that differences in CO among individuals with varying sympathetic traffic have important hemodynamic implications during disruption of NO-mediated vasodilation.

Summary: Systemic Effects of Inhaled Nitric Oxide

Many effects of inhaled nitric oxide (NO) are not explained by the convention that NO activates pulmonary guanylate cyclase or is inactivated by ferrous deoxy- or oxyheme. Inhaled NO can affect blood flow to a variety of systemic vascular beds, particularly under conditions of ischemia/reperfusion. It affects leukocyte adhesion and rolling in the systemic periphery. Inhaled NO therapy can overcome the systemic effects of NO synthase inhibition. In many cases, these systemic-NO synthase-mimetic effects of inhaled NO seem to involve reactions of NO with circulating proteins followed by transport of NO equivalents from the lung to the systemic periphery. The NO transfer biology associated with inhaled NO therapy is rich with therapeutic possibilities. In this article, many of the whole-animal studies regarding the systemic effects of inhaled NO are reviewed in the context of this emerging understanding of the complexities of NO biochemistry.

Endothelium-derived hyperpolarizing factor-mediated renal vasodilatory response is impaired during acute and chronic hyperhomocysteinemia.

Endothelial dysfunction is an early event in the development of vascular complications in hyperhomocysteinemia. Endothelial cells release a number of vasodilators, including NO and prostacyclin. Several lines of evidence have indicated the existence of a third vasodilator pathway, mediated by endothelium-derived hyperpolarizing factor (EDHF). EDHF is a major determinant of vascular tone in small resistance vessels. The influence of hyperhomocysteinemia on EDHF is unknown. The present in vivo study evaluates the integrity of the EDHF pathway in the renal microcirculation of rats with acute and chronic hyperhomocysteinemia. EDHF-mediated vasodilation was evaluated as the renal blood flow (RBF) response to intrarenal acetylcholine during systemic NO synthase and cyclooxygenase inhibition. Acute hyperhomocysteinemia induced by intravenous homocysteine did not affect EDHF-mediated vasodilation. In contrast, intravenous methionine with subsequent hyperhomocysteinemia impaired the EDHF-mediated RBF response. When the methionine infusion was preceded by adenosine periodate oxidized to prevent the cleavage of S-adenosylhomocysteine to homocysteine and adenosine, a similar impairment of EDHF was observed, but with normal homocysteine levels. Animals with chronic hyperhomocysteinemia induced by a high-methionine, low-B vitamin diet during 8 weeks had a severely depressed EDHF-mediated vasodilation compared with those on a standard diet. Endothelium-independent vasodilation to deta-NONOate and pinacidil was not affected in acute and chronic hyperhomocysteinemia, demonstrating intact vascular smooth muscle reactivity. EDHF-dependent responses are impaired in the kidney of hyperhomocysteinemic rats. Because EDHF is a major regulator of vascular function in small vessels, these findings have important implications for the development of microangiopathy in hyperhomocysteinemia.

Effect of intravenous L‐NMMA on nitric oxide production in collagenous colitis

Background: Nitric oxide (NO) is greatly increased in the colon of patients with inflammatory bowel disease of different aetiology, including collagenous colitis. In man, NO can be generated from NO synthases as well as from non‐enzymatic sources. The source of the NO found in luminal intestinal gas has not been exactly pinpointed. We investigated the effect of the NO synthase inhibitor L‐NMMA on intestinal concentrations of NO in patients with clinically active collagenous colitis. In addition, we measured NO levels from the respiratory tract. Methods: Ten patients with active collagenous colitis were studied. NO levels were measured from the respiratory tract and in the rectum before and after i.v. administration of L‐NMMA (7.5 mg/kg) using a chemiluminescence method. Results: Airway NO release decreased markedly, and mean arterial blood pressure increased in all patients following L‐NMMA treatment. Basal rectal NO levels were high (median >10 000 ppb) and decreased markedly in 5 patients after L‐NMMA. In contrast, NO levels remained completely unchanged or even increased in the other 5 patients. Conclusion: Rectal levels of NO are greatly increased in patients with symptomatic collagenous colitis. Intravenous administration of an NO synthase inhibitor reduced rectal NO only in half of the patients despite clear evidence of effective systemic NO synthase inhibition. This could indicate alternative NOS‐independent sources of intestinal NO in this disease.

Hypertension induced by nitric oxide synthase inhibition activates the atrial natriuretic peptide (ANP) system

We assessed the effect of nitric oxide (NO) synthase inhibition on plasma atrial natriuretic peptide (ANP) concentration and content in some brain structures [neurohypophysis (NH), adenohypophysis (AH), medial basal hypothalamus (MHB) and olfactory bulb (OB)] in rats before and after blood volume expansion (BVE). Male Wistar rats were injected i.p. with N ϖ-nitro- l-arginine ( l-NNA), 25 mg/kg of body weight, 40 min before the experiment (acute treatment) or l-NNA at a dose of 25 mg/kg body weight, twice a day, for 4 days (chronic treatment). The acute treatment caused an increase in the blood pressure and plasma ANP concentration in rats under basal conditions and after BVE. A decrease in ANP content was observed in the OB and NH, whereas no significant changes were found in the AH or MBH. In chronically treated rats, we also found an increase in blood pressure and in plasma ANP concentration under basal conditions and after BVE. The ANP content increased in the OB, NH and AH. These results indicate that systemic NO synthase inhibition increases ANP concentration in plasma and in areas of the central nervous system. We hypothesize that ANP participates in the hypertension-induced by NO synthesis blockade acting by baroreceptors input to the brain to stimulate ANP release and synthesis that reduces NO prival hypertension.

Does nitric oxide buffer arterial blood pressure variability in humans?

Animal studies suggest that nitric oxide (NO) plays an important role in buffering short-term arterial pressure variability, but data from humans addressing this hypothesis are scarce. We evaluated the effects of NO synthase (NOS) inhibition on arterial blood pressure (BP) variability in eight healthy subjects in the supine position and during 60 degrees head-up tilt (HUT). Systemic NOS was blocked by intravenous infusion of N(G)-monomethyl-L-arginine (L-NMMA). Electrocardiogram and beat-by-beat BP in the finger (Finapres) were recorded continuously for 6 min, and brachial cuff BP was recorded before and after L-NMMA in each body position. BP and R-R variability and their transfer functions were quantified by power spectral analysis in the low-frequency (LF; 0.05-0.15 Hz) and high-frequency (HF; 0.15-0.35 Hz) ranges. L-NMMA infusion increased supine BP (systolic, 109 +/- 4 vs. 122 +/- 3 mmHg, P = 0.03; diastolic, 68 +/- 2 vs. 78 +/- 3 mmHg, P = 0.002), but it did not affect supine R-R interval or BP variability. Before L-NMMA, HUT decreased HF R-R variability (P = 0.03), decreased transfer function gain (LF, 12 +/- 2 vs. 5 +/- 1 ms/mmHg, P = 0.007; HF, 18 +/- 3 vs. 3 +/- 1 ms/mmHg, P = 0.002), and increased LF BP variability (P < 0.0001). After L-NMMA, HUT resulted in similar changes in BP and R-R variability compared with tilt without L-NMMA. Increased supine BP after L-NMMA with no effect on BP variability during HUT suggests that tonic release of NO is important for systemic vascular tone and thus steady-state arterial pressure, but NO does not buffer dynamic BP oscillations in humans.

Changes in short-term potentiation of hypoglossal activity by modulators of nitric oxide production in the rabbit

Stimulation of the superior laryngeal nerve (SLN) causes a potentiation of hypoglossal nerve activity persisting after cessation of stimulation. The mechanism of this phenomenon is uncertain. We investigated a potential role of the nitric oxide (NO) pathway in modulation of the after-effects of SLN stimulation on phrenic and hypoglossal activity in rabbits. L-Arginine, a substrate for NO synthesis and NG-Nitro-L-Arginine (L-NNA) an inhibitor of NO synthase (NOS), were administered systemically. L-Arginine and L-NNA alone caused small changes in respiratory activity. During pre-treatment with NO precursor the amplitude and duration of hypoglossal potentiation evoked by SLN stimulation were reduced. Systemic NO synthase inhibition partially reversed these effects of L-Arginine. The results showed that interference with NO production by NO substrate and NOS inhibitor modulates the effects of SLN stimulation on hypoglossal activity. Nitric oxide might be a negative modulator of the transmission of short-term potentiation (STP) in ypoglossal activity.

The Renal and Systemic Hemodynamic Effects of a Nitric Oxide-Synthase Inhibitor Are Reversed by a Selective EndothelinA Receptor Antagonist in Men

There is evidence for an interaction between nitric oxide (NO) and endothelin (ET) at the level of the renal vasculature. We hypothesized that acute renal effects of systemic NO synthase inhibition (NG-monomethyl-l-arginine, L-NMMA) may be blunted by coadministration of a specific ETA receptor antagonist (BQ-123) in healthy humans. Fifteen healthy young male subjects participated in this randomized, double-blind, placebo-controlled 3-way crossover study. These sodium-repleted volunteers received L-NMMA alone, or BQ-123 alone, or L-NMMA with a subsequent coinfusion of BQ-123. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were determined with the PAH and inulin clearance method, respectively. Mean arterial pressure (MAP) and pulse rate were measured noninvasively at baseline and every 15 min after the start of the study period. L-NMMA alone reduced RPF (−22%, P < 0.001) and GFR (−8%, P < 0.009) and increased MAP (+10%, P < 0.001). BQ-123 alone did not affect these parameters. However, coinfusion of BQ-123 blunted the effects of L-NMMA on RPF (P < 0.001), GFR (P < 0.001), and MAP (P = 0.006). Peripheral and renal hemodynamic effects of acute systemic NO synthase inhibition are at least partially reversed by ETA receptor blockade with BQ-123. This indicates a functional antagonism between specific ETA receptor antagonist and NO synthase inhibitors at the level of the renal vasculature.

Effects of the Nitric Oxide Synthase Inhibitor NG-Nitro-L-Arginine Methyl Ester (L-NAME) on Antropyloroduodenal Motility and Appetite in Response to Intraduodenal Lipid Infusion in Humans

Background: Studies in animals indicate that endogenous nitric oxide (NO) is an important inhibitory neurotransmitter in the gastrointestinal tract and that it modulates food intake. We evaluate the role of NO mechanisms in mediating the effects of small intestinal nutrients on antropyloroduodenal motility and appetite in humans. Methods: On 2 separate days, 8 healthy adult men received intravenous L-NAME 180 µg/kg/h or 0.9% saline (0-150 min); between 30 min and 120 min, an intraduodenal lipid infusion (2 kcal/min) was administered, and at 120 min subjects were offered a buffet meal (120-150 min). Antropyloroduodenal pressures were measured with a sleeve/sidehole manometric assembly. During the infusions, perceptions of hunger and fullness were assessed with visual analog questionnaires and amount and macronutrient content of food consumed at the buffet meal were quantified. Blood pressure and heart rate were monitored at regular intervals. Results: Intraduodenal lipid infusion was associated with increases in fullness (P < 0.05) and in frequency of isolated pyloric pressure waves (P < 0.05) and basal pyloric pressure (P < 0.05); and decreases in hunger (P < 0.05) and in frequency of antral (P < 0.05) and duodenal (P < 0.05) pressure waves. L-NAME increased diastolic blood pressure (P = 0.08) and decreased heart rate (P < 0.05), but had no effect on antropyloroduodenal pressures or food intake. Conclusions: Intravenous administration of the systemic NO synthase inhibitor, L-NAME, in a dose that affects cardiovascular function in healthy humans does not modify the antropyloroduodenal motor and appetite responses to intraduodenal lipid infusion.

Nitric oxide, an important regulator of perfusion-contraction matching in conscious pigs.

We examined whether nitric oxide (NO) inhibition during moderate reduction in coronary blood flow (CBF) would affect perfusion-contraction matching. Coronary stenosis (CS) was induced in conscious pigs, which resulted in a stable 39 +/- 1% reduction in CBF for 1.5 h. Ischemic zone wall thickening (IZWT) decreased by an average of 56 +/- 2% during CS from 2.7 +/- 0.2 mm. After reperfusion, myocardial stunning was observed, but this recovered without evidence of necrosis. After recovery and subsequent administration of systemic NO synthase inhibition (N(omega)-nitro-L-arginine, 25 mg. kg(-1). day(-1) x 3 days), CS for 1.5 h reduced CBF similarly but decreased IZWT significantly more, P < 0.05, by 89 +/- 5%. Myocardial stunning, i.e., the decrease in IZWT at 12 h post-CS, was more severe (-65 +/- 5% vs. -21 +/- 3%), P < 0.05. Furthermore, CS during NO synthase inhibition resulted in multifocal subendocardial areas of necrosis in the area at risk. These data suggest that in the intact, conscious pig, NO inhibition prevents perfusion-contraction matching, resulting in intensification of post-ischemic stunning and development of subendocardial necrosis.

The effects of chronic nitric oxide synthase suppression on glioma pathophysiology

Nitric oxide synthase (NOS) is strongly expressed in glioma and has an important role in tumour blood flow (TBF) regulation. Whether manipulation of NOS function within a tumour can have any therapeutic effect is unknown. This study therefore evaluated the pathophysiological effects of chronic systemic NOS inhibition on experimental rodent glioma blood flow, growth and necrosis.To determine the duration and pathophysiological effects of systemic NOS inhibition, Ng-nitroL-arginine methyl ester (L-NAME) was given to rats bearing C6 glioma acutely (single dose i.v., 30 mg kg) or for either 4 or 7 days (i.p. 75 mg kg day) prior to study.TBF and local cerebral blood flow (LCBF) were measured using C14-iodoantipyrine quantitative autoradiography. Tumour volume, tumoural necrosis and tumoural NOS were measured using conventional neuropathology and immunocytochemistry.Acute and 4-day L-NAME administration produced significant TBF reductions (‘;48 and ‘;39%, respectively) with less marked changes in LCBF (‘;35 and ‘;15%, respectively). Seven-day L-NAME administration reduced tumour volume ( p =0.12), increased tumoural necrosis ( p <0.05), but immunohistochemistry showed no difference in tumoural NOS expression. These results confirm that NOS has a significant role in the pathophysiology of experimental glioma, and that in this glioma model the effects of chronic systemic NOS inhibition are, for the period under study, predominately anti-tumoural. Whether chronic NOS inhibition is useful as an adjunct in glioma therapy or provides the opportunity for novel therapeutic approaches requires further study.