Endogenous Nitric Oxide Release Research Articles

Ginsenosides stimulate endogenous production of nitric oxide in rat kidney

Ginsenosides (GS), saponins purified from Panax ginseng, increase renal blood flow in rats. Nitric oxide (NO) is thought to be the substance endogenously released by GS in preconstricted lungs and cultured endothelial cells. The present study aims to determine whether GS could stimulate endogenous release of NO in rat kidney and whether GS affected the activity of NO synthase in kidney tissues. The serum and urine levels of the stable NO metabolites, nitrite (NO 2) and nitrate (NO 3) and urinary cGMP levels were measured 8 hr after a single intraperitoneal injection of GS (200 mg/kg) into rats. The effects of the NO synthesis inhibitor, Nω-nitro-L-arginine methyl ester, and the NO precursor, L-arginine, on the GS-induced changes were also determined. The activity of NO synthase, as determined by conversion of [ 14C]-L-arginine to [ 14C]-L-citrulline, in whole kidney, glomeruli and cortical tubules was also investigated. A single injection of GS resulted in endogenous production of NO as reflected by increase in serum and urine levels of NO 2/NO 3 and urinary cGMP levels, which were inhibited by the addition of Nω-nitro-L-arginine methyl ester and restored by L-arginine. GS also stimulated the activity of NO synthase in whole kidney as well as glomeruli and cortical tubules, and this increase was significantly prevented by Nω-nitro-L-arginine methyl ester. It was concluded that stimulation in endogenous production of NO by GS may contribute to its antinephritic action and may play a protective role in the kidney.

Nitric oxide does not modulate myocardial contractility acutely in in situ canine hearts.

The study was designed to assess the influence of nitric oxide (NO) on myocardial contractility in vivo. The left anterior descending coronary artery (LAD) of 28 anesthetized, open-chest dogs was perfused with arterial blood via an extracorporeal circuit. In the LAD bed, segmental shortening (SS), an index of local myocardial contractility, was measured with ultrasonic crystals. Coronary blood flow (CBF) was measured by Doppler flow transducer and used to calculate myocardial oxygen consumption (MVO2). Studies were performed with coronary perfusion pressure (CPP) constant (n = 23) or with CBF constant (n = 5). Measurements were obtained 1) during intracoronary infusions of the NO donors sodium nitroprusside (SNP, 80 ng/min) and nitroglycerin (NTG, 40 micrograms/min) and of a stimulator of endogenous NO release, acetylcholine (ACh, 20 micrograms/min), and 2) after inhibition of basal NO synthase activity with either NG-nitro-L-arginine methyl ester (L-NAME, 300 micrograms/min ic for 15 min) or NG-monomethyl-L-arginine (L-NMMA 2mg/min ic for 15 min). Decreases in SS (-38%) and MVO2 (-42%) during intracoronary isoflurane infusion verified responsiveness of preparation to negative inotropic agents. With CPP constant, SNP, NTG, and ACh caused increases in CBF (177, 28, and 280%, respectively) with no changes in SS or MVO2. Neither L-NAME nor L-NMMA affected SS, MVO2, or CBF. With CBF constant, the SNP- and ACh-induced decreases in CPP were accompanied by no changes in SS. In conclusion, NO had no direct influence on myocardial contractility or oxygen demand under baseline conditions, or when its local concentration was increased acutely with SNP, NTG, or ACh. An augmented SS secondary to increased CBF per se, i.e., Gregg's phenomenon, did not obscure potential negative inotropic effects of SNP and ACh with CPP constant.

PGI 2 and nitric oxide involvement in the regulation of systemic and pulmonary basal vascular tone in the pig

In anesthetized, ventilated pigs we analyzed the involvement of nitric oxide (NO) and prostaglandins (PGs) in the regulation of systemic and pulmonary basal vascular tone. Endogenous release of NO was blocked by N G-nitro- l-arginine methyl ester ( l-NAME) and prostanoid biosynthesis by indomethacin. Blocking NO raised pulmonary and systemic arterial pressure and vascular resistances. These effects show that in the pig there is continuous release of minute amounts of NO. Blocking prostanoid biosynthesis did not affect the vasoconstrictor effect of l-NAME on the pulmonary vascular bed, but significantly strengthened the hypertensive effect of l-NAME on the systemic vascular bed. These data show that different mechanisms regulate pulmonary and systemic vascular tone. Administration of a stable analogue of PGI 2 to pigs pretreated with indomethacin reversed the systemic vasoconstrictor effect of l-NAME. In conclusion, our data show that NO especially modulates pulmonary vascular tone, while PGI 2 preferentially modulates systemic vascular tone.

NITRIC OXIDE MODULATION OF MICROVASCULAR RESPONSES IN THE DEOXYCORTICOSTERONE ACETATE-SALT HYPERTENSIVE RAT. 115

Previous studies in our laboratory have demonstrated that arteriolar dilations mediated by stimulation of endogenously release nitric oxide release are depressed during an established stage of hypertension in spontaneously hypertensive rat (SHR). In the present study, we assessed the response of small arterioles in the cremaster muscle of DOCA-Salt hypertensive rats to stimulation of endogenous NO release and the effects of NO blockade or constrictor sensitivity to topically applied norepinephrine. Microvascular responses were assessed during an early stage (1 week after induction) and late stage (4 weeks after induction) of hypertension using intravital microscopy. Exposure to increasing concentrations of acetylcholine(10-10 - 10-5 M) produced a dose-dependent dilation of arterioles (16 ± 1 μm). This dilation was abolished in the presence of a 10-4 M bath concentration of Nw-nitro-L-arginine methyl ester (L-NAME), a specific antagonist of nitric oxide (NO) synthesis. L-NAME also produced reductions in resting arteriolar diameters that were attenuated in DOCA-Salt rats. These result suggest that basal and stimulated release of endogenous NO in the microcirculation of DOCA-Salt rats is attenuated.Funded by a grant from the American Heart Association.

Nitric oxide and sympathoexcitatory cardiovascular neurons of the ventrolateral medulla in cats

In acute experiments on cats, the effects of injections of nitric oxide (NO) donors and an inhibitor of its synthesis into the sympathoexcitatory neuronal structures in the ventrolateral medulla (VLM) were studied to examine their effects on the peripheral mechanisms of the cardiovascular control. Unilateral injections of NO donors, nitroglycerine (1.3–5.2 nmol) or sodium nitroprusside (1.1–4.6 nmol) into the sites of the sympathoexcitatory neurons residing in the VLM induced the lowering of the systemic arterial pressure (SAP) in a dose-depended fashion. Two types of the hypotensive responses have been distinguished. In the first type responses, lowering of the SAP level was mainly due to a decrease in the peripheral vascular resistance (PVR), while the heart rate (HR) and stroke volume (SV) were only slightly reduced. In the second type responses, the drop in SAP level resulted mainly from a decrease in the HR and myocardial contractivity. These effects were induced by the limitation of the descending excitatory influences to the heart and vessels from the VLM sympathoexcitatory systems. An increase in the NO concentrations in the neuronal structures located 2.5–4.5 mm caudally to the trapezold bodies resulted in the first type responses, while that in the sites immediately adjacent to the caudal sympathoinhibitory area (0.5–1.5 mm rostrally to the XIIth cranial nerve roots) was associated with the second type of reactions. Stimulation of the endogenous NO release from the neurons after injections of L-arginine induced the same cardiovascular shifts as exogenic NO did, and attenuation of NO synthesis following injections of NO antagonist L-NMMA into the VLM neuronal structures evoked hemodynamic shifts of a reverse direction. Injections of NO donors inhibited the reflex responses induced by the activation of the carotid sinus receptors. Our data give further evidence for NO involvement in the inhibitory control of the cardiac activity and vascular tone through those VLM sympatoexcitatory neurons, which are involved in the system of central neurogenic cardiovascular control and the activity of which prevent the development of hypertension.

The role of endogenous nitric oxide in the response of coronary blood flow to tachycardia

The role of endogenous nitric oxide as mediator of flow-dependent dilation is well established. However, its role in the adaptation of coronary blood flow to tachycardia is less well defined. This study was designed to determine whether nitric oxide is a mediator in pacing-induced hyperaemia. Twenty pigs were instrumented for coronary blood flow, aortic pressure and atrial pacing measurements. Their heart rate was increased by 20 beats every 5 min. Coronary blood flow was measured basally and at each pacing interval before and after each of the following interventions: intracoronary saline infusion (n = 6), N omega-nitro-L-arginine methyl ester infusion (L-NAME, 20 micrograms/kg per min intracoronarily, n = 9) and infusion of L-NAME plus L-arginine (0.3 mg/kg per min intracoronarily, n = 5). The coronary peak flow increased with atrial pacing. The maximum increase in coronary blood flow with pacing was significantly reduced after infusion of L-NAME (159 +/- 33 versus 143 +/- 30%), whereas no change was observed in the saline group (163 +/- 28 versus 172 +/- 29%). However, it increased significantly in the group receiving L-NAME plus L-arginine (147 +/- 29 versus 182 +/- 40%). In the pig, the increase in coronary blood flow and therefore the vasodilation of the microvasculature that accompanies tachycardia depend, partly, on the release of endogenous nitric oxide.

Renal responses to intra-arterial administration of adrenomedullin in dogs.

The present study was undertaken to evaluate the renal responses to intra-arterial infusion (12.5 pmol.kg-1.min-1) for 30 min of adrenomedullin (ADM) in denervated kidneys of anesthetized dogs (n = 8). Total renal blood flow (RBF) was measured with an electromagnetic flow probe, and two single-fiber laser-Doppler needle flow probes were used to measure relative changes in cortical (CBF) and medullary blood flow (MBF). ADM administration resulted in decreases in renal vascular resistance (32.3 +/- 4.9 to 22.3 +/- 3.0 mmHg.ml-1.min.g) and increases in RBF (4.5 +/- 0.5 to 6.0 +/- 0.6 ml.min-1.g-1), CBF (33 +/- 1.3%, n = 41, and MBF (32 +/- 5.7%, n = 5) without changes in glomerular filtration rate. There were also substantial increases in urine flow (11.3 +/- 1.9 to 28 +/- 4.8 microliters.min-1.g-1), as well as in sodium excretion (1.8 +/- 0.2 to 4.2 +/- 0.6 microliter.min-1.g-1). After cessation of ADM infusion, partial recovery of these responses was observed within a 30-min period. Responses to ADM were attenuated during inhibition of nitric oxide (NO) synthesis by nitro-L-arginine (50 micrograms.kg-1.min-1). These findings indicate that renal vasodilator, diuretic, and natriuretic responses to ADM may be mediated by the release of endogenous NO and suggest that ADM could play a role in regulating water and electrolyte excretion by the kidney.

N‐NITRO‐L‐ARGININE AND INDOMETHACIN DO NOT AFFECT ENDOTHELIN‐INDUCED CONSTRICTION OF LARGE AND SMALL CORONARY ARTERIES IN THE ANAESTHETIZED GREYHOUND

1. The aim of this study was to investigate whether endothelin-1 (ET-1)-induced constriction of large and small coronary arteries in the anaesthetized greyhound is modulated by the endogenous release of nitric oxide or prostanoids. 2. ET-1 (1-100 ng/kg) and the alpha1-adrenoceptor agonist phenylephrine (0.5-2 mu g/kg), when injected directly into the circumflex coronary artery, caused dose-dependent decreases in epicardial coronary artery diameter and coronary vascular conductance without affecting systemic arterial pressure or the rate and force of cardiac contraction. 3. Inhibition of NO synthesis with N-nitro-L-arginine (NOLA, 5 mg/kg, i.c.) decreased coronary artery diameter, coronary conductance and heart rate and increased arterial pressure. The coronary vasoconstrictor response to ET-1 was unaffected by NOLA. By contrast, NOLA significantly increased the phenylephrine-induced constriction of the epicardial coronary artery but not the resistance vessels. 4. Indomethacin (5 mg/kg, i.v.), an inhibitor of cyclo-oxygenase, significantly decreased epicardial coronary artery diameter but did not affect coronary conductance. Indomethacin had no effect on the coronary vascular responses to ET-1 or phenylephrine. Combined treatment with NOLA plus indomethacin also failed to affect the coronary vasoconstrictor effects of ET-1. 5. Basal release of NO and vasodilator prostanoids modulated resting coronary vascular tone but did not influence the vasoconstrictor responses to endothelin in either large or small coronary arteries.

Mechanisms of vascular preservation by a novel NO donor following rat carotid artery intimal injury.

We studied the effects of a novel organic nitric oxide (NO) donor, 4-hydroxymethyl-furazan-3-carboxylic acid-2-oxide (CAS-1609), in a rat carotid artery intimal injury model. The NO donor, CAS-1609, or its non-NO-donating control compound, 4-hydroxymethyl-furazan-3-carboxylic acid (C-93-4845), was infused intravenously at 30 micrograms/day. Seven days after injury, carotid artery rings contracted only 56 +/- 6 mg to NG-nitro-L-arginine methyl ester in C-93-4845-treated rats, compared with 120 +/- 17 mg in CAS-1609-treated rats (P < 0.02), indicating a preservation of endogenous NO release. Improved responses to the endothelium-dependent dilator, acetylcholine, also occurred in injured arteries treated with CAS-1609. Morphometric analysis of injured carotid arteries given the inactive compound showed marked intimal thickening with an intimal-to-medial ratio (I/M) of 0.76 +/- 0.02, compared with a significantly lower I/M of 0.32 +/- 0.04 (P < 0.01) in injured carotid arteries given CAS-1609. Additionally, CAS-1609 was found to have a concentration-dependent stimulatory effect on cultured rat aortic endothelial cell proliferation (P < 0.01) but and inhibitory effect on platelet-derived growth factor-BB (10 ng/ml)-stimulated rat aortic smooth muscle cell proliferation (P < 0.01). This is the first study to demonstrate that NO plays a dual role in vascular cell proliferation, stimulating endothelial cells but inhibiting smooth muscle cell proliferation. This dual effect of NO on cell proliferation is associated with an in vivo reduction in neointimal thickening and an acceleration of endothelial recovery determined by both anatomic and functional methods.

Role of basal and stimulated release of nitric oxide in the regulation of radial artery caliber in humans.

Although it is well established that nitric oxide contributes to the regulation of resistance arterial tone in humans, its role at the level of large arteries is less clear. Therefore, we assessed in healthy volunteers the effect of local administration of the inhibitor of nitric oxide synthesis NG-monomethyl-L-arginine (L-NMMA) on basal radial artery diameter (transcutaneous A-mode echotracking) and radial blood flow (Doppler) as well as on the radial response to acetylcholine and the nitric oxide donor sodium nitroprusside. A catheter was inserted into the brachial artery for measurement of arterial pressure and infusion of L-NMMA (2, 4 and 8 mumol/min for 5 minutes, n = 11), acetylcholine (3, 30, 300 and 900 nmol/min for 3 minutes, n = 8), and nitroprusside (2.5, 5, 10, and 20 nmol/min for 3 minutes, n = 6). None of the treatments affected arterial blood pressure or heart rate. L-NMMA dose-dependently decreased radial blood flow (from 31 +/- 6 to 17 +/- 3 10(-3) L/min after 8 mumol/min, P < .01) but did not affect radial artery diameter (from 2.93 +/- 0.11 to 2.90 +/- 0.14 mm). Acetylcholine dose-dependently increased radial blood flow (154 +/- 43% after 900 nmol/min) and radial artery diameter (16 +/- 4%), and both effects were markedly reduced after L-NMMA (increase in radial blood flow and radial artery diameter: 22 +/- 20% and 3 +/- 2%, respectively; both P < .01 versus controls). Nitroprusside also dose-dependently increased radial artery diameter (14 +/- 4% after 20 nmol/min) but only moderately affected radial blood flow (47 +/- 21%).(ABSTRACT TRUNCATED AT 250 WORDS)

The role of nitric oxide and NO-donor agents in myocardial protection from surgical ischemic-reperfusion injury

The coronary vascular endothelium is injured by ischemia-reperfusion, which may facilitate the pathophysiological role played by neutrophils. Hearts undergoing coronary artery bypass surgery or other surgical procedures requiring cardiopulmonary bypass and elective cardioplegia undergo repetitive episodes of ischemia and reperfusion, which leads to endothelial injury as well as contractile dysfunction and morphological injury, despite the use of cardioprotective cardioplegic solutions and other strategies of myocardial protection. In cardiac surgery, as in coronary occlusion, endothelial injury seems to occur upon reperfusion with unmodified blood. Blood cardioplegia does not prevent this surgical ‘reperfusion injury’, but does prevent extension of endothelial injury during the period of hypothermic cardioplegic arrest (‘protected ischemia’). It is not known whether global cardioplegic ischemia in preoperatively injured hearts impairs the basal release of nitric oxide (NO) and hence obtunds this endogenous protective mechanism. However, enhancement of blood cardioplegia with the NO precursor, l-arginine, reduces postsurgical myocardial injury, suggesting that endogenous or basal release of NO participates in the modulation of ischemic-reperfusion injury. In addition, an NO-donor agent also protects the myocardium from surgical ischemic-reperfusion injury. Both cardioprotective strategies involve inhibition of neutrophil accumulation, consistent with the known inhibitory effects of NO on neutrophil adherence and neutrophil-mediated damage to the coronary endothelium. Therefore, NO-related therapy offers a new strategy to protect the myocardium, including the coronary endothelium, from surgically imposed ischemic-reperfusion injury.

915-79 Nitric Oxide is a Preferential Subendocardial Vasodilator

The effects of nitric oxide (NO) on myocardial blood flow (MBF) have been studied previously by observing responses to agents that stimulate or block endogenous NO release. To study the direct in vivo effects of endoluminally administered NO on transmural myocardial perfusion, we studied 4 anesthetized dogs using a new method for intracoronary NO administration. NO gas was bubbled through deoxygenated saline to achieve the saturation constant (2–3 mM). During ventricular pacing at 100 beats/min, the solution was infused into the left main coronary artery at doses of 0.2 and 16 μmol/min, Transmural myocardial perfusion and coronary blood flow were measured with radioactive microspheres after 2 minutes of infusion. Changes in MFB (ml/gm/min) induced from continuous NO infusion were compared to endothelially mediated NO release induced by intracoronary administration of acetylcholine (Ach 2,0 μmol/min) and non-NO mediated vasodilitation by intracoronary adenosine (AD 1.2 μmol/min). Results:BasalNO 0.2NO 16AchADMBF(mean)0.8 ± 0.031.4 ± 0.10*1.6 ± 0.08*1.6 ± 0.06*2.5 ± 0.11*ED MFB0.7 ± 0.031.4 ± 1.4*1.8 ± 0.12*1.8 ± 0.08*2.7 ± 0.13*EDIEP0.7 ± 0.021.0 ± 0.06*1.3 ± 0.07*1.2 ± 0.05*1.3 ± 0.07*mean ± sem*p &lt; 001 vs. basal ED/EP = endocardial to epicardial blood flow ratio mean ± sem p &lt; 001 vs. basal ED/EP = endocardial to epicardial blood flow ratio High dose NO (16 μmol/min) caused an increase in endocardial and total myocardial blood flow which was similar to that produced by acetylcholine. Nitric oxide causes dose dependent increases in myocardial blood flow and the endocardial to epicardial blood flow ratio. High dose endoluminal NO infusion causes changes in myocardial blood flow and transmural myocardial perfusion which are equivalent to that caused byendothelial derived NO, Moreover, whether administered exogenously or released endogenously, NO is a preferential sub-endocardial vasodilator.

Role of endogenous nitric oxide on PAF-induced vascular and respiratory effects

The role of endogenous nitric oxide (NO) on vascular and respiratory smooth muscle basal tone was evaluated in six anaesthetized, paralysed, mechanically ventilated pigs. The involvement of endogenous NO in PAF-induced shock and airway hyperresponsiveness was also studied. PAF (50 ng/kg, i.v.) was administered before and after pretreatment with NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg, i.v.), an NO synthesis inhibitor. PAF was also administered to three of these pigs after indomethacin infusion (3 mg/kg, i.v.). In normal pigs, L-NAME increased systemic and pulmonary vascular resistances, caused pulmonary hypertension and reduced cardiac output and stroke volume. The pulmonary vascular responses were correlated with the increase in static and dynamic lung elastances, without changing lung resistance. Inhibition of NO synthesis enhanced the PAF-dependent increase in total, intrinsic and viscoelastic lung resistances, without affecting lung elastances or cardiac activity. The systemic hypotensive effect of PAF was not abolished by pretreatment with L-NAME or indomethacin. This indicates that systemic hypotension is not correlated with the release of endogenous NO or prostacyclines. Indomethacin completely abolished the PAF-dependent respiratory effects.

Endothelium is a target organ of parathyroid secretions in genetic hypertensive rats.

We investigated the relationships between vascular endothelium and parathyroid function. Blood pressure (BP), circulating endothelins (ETs) and atrial natriuretic peptide (ANP), and BP responses to parathyroid hormone (PTH) and NG-nitro-L-arginine methyl ester (L-NAME) were measured in parathyroidectomized (PTx), PTx and fed a Ca2+ enriched diet (PTx-HCa) and sham SHR.22 weeks after surgery, BP was significantly decreased in PTx and PTx-HCa, plasma ETs levels were increased, whereas ANP levels were decreased. In anesthetized rats, BP increase induced by L-NAME was greater in PTx-HCa than in sham group, indicating increased endogenous nitric oxide release in hypoparathyroid rats. The hypotensive response to PTH remained unchanged. These data demonstrate that endothelium is activated in long-term hypoparathyroid SHR, reflecting an adaptative response to decreased BP.

Changes in pulmonary vascular tone during exercise. Effects of nitric oxide (NO) synthase inhibition, L-arginine infusion, and NO inhalation.

Nitric oxide (NO) is a potent endogenous vasodilator. Its role in the normal and stressed pulmonary circulation is unclear. To better understand the importance of endogenous NO in normal physiological responses, we studied the effects of altered NO availability on the change in pulmonary vascular tone that accompanies exercise. In paired studies we measured blood flow and pressures in the pulmonary circulation at rest and during treadmill exercise at a speed of 4 mph with and without (a) N omega-nitro-L-arginine, 20 mg/kg intravenously, a selective inhibitor of NO synthase; (b) L-arginine, 200 mg/kg intravenously, substrate for NO synthase; (c) combination of the inhibitor and substrate; and (d) inhalation of NO > 30 ppm, to determine if endogenous release of NO elicits maximal vasodilation. In addition, we sought to determine the site of NO effect in the pulmonary circulation by preconstriction with either U-44619 or hypoxia (fraction of inspired O2 = 0.12) using a distal wedged pulmonary catheter technique. NO synthase inhibition raised pulmonary vascular tone equally at rest and exercise. L-Arginine reversed the effects of NO synthase inhibition but had no independent effect. NO inhalation did not reduce pulmonary vascular tone at rest or enhance the usual reduction in pulmonary vascular resistance with exercise. The effect of NO synthase inhibition was in pulmonary vessels upstream from small veins, suggesting that endogenous NO dilates primarily small arteries and veins at rest. We conclude that, in sheep, endogenous NO has a basal vasodilator function that persists during, but is not enhanced by, exercise.

Effect of endogenous and inhaled nitric oxide on the ventilation-perfusion relationships in oleic-acid lung injury.

Previous investigations have shown that the ventilation-perfusion (VA/Q) mismatch caused by acute lung injury can be alleviated either by inducing vasodilation in ventilated lung units with inhaled nitric oxide (NO) or by inhibiting the synthesis of endogenous NO, which opposes hypoxic pulmonary vasoconstriction. To determine the effects of a combination of these interventions, we evaluated cardiopulmonary function and VA/Q distributions in 10 dogs with oleic acid-induced lung injury. Each animal received, in random order, zero or 40 ppm of NO in inspiratory gas, with and without intravenous infusion of NG-monomethyl-L-arginine (L-NMMA) (5 mg/kg/h). The multiple inert-gas elimination technique was used to estimate VA/Q distributions. Systemic L-NMMA administration alone did not affect VA/Q inequality and gas exchange, but increased pulmonary and systemic vascular resistance. Inhaled NO improved gas exchange by redistributing blood flow from shunt units to lung units with a nearly ideal VA/Q ratio, without affecting pulmonary or systemic vascular resistance. Improved VA/Q matching and gas exchange was most pronounced when NO was inhaled in the presence of systemic L-NMMA. Inhalation of NO reversed the pulmonary but not the systemic vasoconstriction caused by L-NMMA. These results suggest that endogenous NO release is not limited to hypoxic lung regions in animals with oleic acid-induced lung injury. Inhaled NO reversed L-NMMA-induced pulmonary vasoconstriction and improved VA/Q matching by selectively dilating the pulmonary vasculature in ventilated lung units.

Endogenous nitric oxide enhances prostaglandin production in a model of renal inflammation.

The interaction between nitric oxide (NO) and cyclooxygenase (COX) was studied in a rabbit model of renal inflammation, the ureteral obstructed hydronephrotic kidney (HNK). Ex vivo perfusion of the HNK but not the control kidney (e.g., unobstructed contralateral kidney, CLK), led to a time-dependent release of nitrite (NO2-), a breakdown product of NO. Stimulation of the HNK with bradykinin (BK) evoked a time-dependent increase in prostaglandin E2 (PGE2) production. NG-monomethyl-L-arginine (L-NMMA), which blocks the activity of both constitutive and inducible nitric oxide synthase (cNOS and iNOS), aminoguanidine, a recently described selective iNOS inhibitor, dexamethasone, or cycloheximide abolished the release of NO2- and attenuated the exaggerated BK-induced PGE2 production. This supports the existence of iNOS and COX-2 in the HNK. In the CLK, BK elicited release of both NO2- and PGE2 but this did not augment with time. L-NMMA but not aminoguanidine, dexamethasone, or cycloheximide attenuated NO2- and PGE2 release indicative of the presence of constitutive but not inducible NOS or COX. The current study suggests that the endogenous release of NO from cNOS in the CLK activates a constitutive COX resulting in optimal PGE2 release by BK. In addition, in the HNK, NO release from iNOS activates the induced COX resulting in markedly increased release of proinflammatory prostaglandin. The broader implication of this study is that the cyclooxygenase isozymes are potential receptor targets for nitric oxide.

Differential effects of inhaled nitric oxide on normoxic and hypoxic isolated in situ neonatal pig lungs perfused by extracorporeal membrane oxygenation

Inhaled nitric oxide (NO) is effective as a selective pulmonary vasodilator, but its effects on uninjured lungs subjected to normoxia and hypoxia have not been fully studied. The authors sought the response of pulmonary vascular resistance (PVR) to inhaled NO in piglet lungs devoid of ischemic injury in a model of reversible pulmonary hypertension. If the changes were dose-responsive, the authors asked whether the PVR changes were related to normoxia or hypoxia, and hypothesized that the change would be more pronounced for hypoxia than normoxia. In situ isolated piglet lungs were prepared by occlusive tracheostomy and ligation of the ductus arteriosus and aorta. Cannulae positioned in the left atrium and pulmonary artery were connected to a standard extracorporeal membrane oxygenation (ECMO) circuit, and flow was increased to approximate cardiac output. After stabilization, piglets (aged 5 to 14 days, weighing 3.2 to 6.4 kg) were divided into two groups of four each: normoxic (F io 2 0.30, normal PVR) and hypoxic (F io 2 0.07, increased PVR). NO was administered at 10 to 80 parts per million (ppm) in increments of 10 ppm, for 5 minutes at each concentration, with a return to baseline before each new dose. Flow, pulmonary arterial (PA) and left atrial (LA) pressures were continuously monitored, from which PVR was calculated (PVR = [P PA − P LA]/flow) and expressed as logΔPVR. Data were analyzed statistically by repeated measures of analysis of variance, comparing logΔPVR to baseline at each dose of NO, and comparing logΔPVR for normoxic and hypoxic lungs at each dose of NO. The authors found: (1) NO significantly decreased PVR at all doses in both normoxic and hypoxic piglet lungs ( P < .05). (2) Effects of NO were dose-dependent ( P < .05). (3) Normoxic piglet lungs showed a steady decline in PVR throughout the entire dose range. (4) Hypoxic piglet lungs had a rapid decrease in PVR, with maximum effect at 30 to 40 ppm. In conclusion: (1) This model allows reversible pulmonary hypertension in normal lungs, with physiological responses to hypoxia and NO. (2) NO reduces PVR even in normoxia; however, intrinsic endogenous NO release may account for the more attenuated response to inhaled NO. (3) The more exaggerated response to NO in hypoxia may result from increased sensitivity in the face of decreased endogenous release of NO.

Medical treatment of pulmonary hypertension in acute lung disease

A moderate pulmonary hypertension is a hallmark of experimental, as well as clinical, acute lung injury. Pulmonary hypertension in acute lung injury, appears to be caused primarily by a partially reversible increase in extra-alveolar vascular closing pressure, the latter being modulated by vasodilating products of the cyclooxygenase pathway of arachidonic acid metabolism, as well as by an endogenous release of nitric oxide. Gas exchange in acute lung injury is improved by increased pulmonary vascular tone. However it is also improved by inhaled nitric oxide, which increases perfusion to the better aerated lung areas. Whether pharmacological interventions aimed at the prevention of right ventricular failure in acute lung injury improve right ventriculo-vascular coupling sufficiently to exert a favourable influence on outcome, remains to be shown.

Halothane vasodilation and nitric oxide in rat pial vessels.

We investigated whether halothane (HAL), administered via cerebral cortical suffusion at concentrations of 1, 2, and 3%, could induce cerebral microvascular dilatation in vivo and whether the vasodilatory response was dependent on nitric oxide (NO) synthesis. The studies were performed using N2O/fentanyl-anesthetized, paralyzed, and mechanically ventilated rats. A closed cranial window and an intravital microscopy technique were employed. This system permitted the controlled delivery of various vasoactive agents in an artificial cerebrospinal fluid (aCSF) solution and the measurement of diameters of pial arterioles and venules. Each experiment included evaluations of (a) the direct smooth muscle relaxing action of NO, using sodium nitroprusside (SNP), and (b) the capacity for generation and release of endogenous NO, using adenosine diphosphate (ADP). Following confirmation of an intact NO-relaxing and generating capacity, HAL (in aCSF) was suffused at increasing concentrations. Nitric oxide synthase (NOS) inhibition was established with topical nitro-L-arginine (L-NA) or its methyl ester (L-NAME) and the above sequence repeated. The results for rats treated with L-NA (n = 5) or L-NAME (n = 5) were analyzed separately and as a combined group. No significant differences in vascular responses were observed when comparing the two groups. Initially, both SNP and ADP produced significant diameter increases (all groupings) in arterioles (14-28% change) and venules (14-25% change). For all groups, suffusions of 1 to 3% HAL produced arteriolar dilation, ranging from a 10 to 25% increase over baseline diameter. A statistically significant dose dependency was only observed with the combined data.(ABSTRACT TRUNCATED AT 250 WORDS)