L-arginine is the physiological precursor for the formation of nitric oxide in endothelium-dependent relaxation

Vasodilation in black Americans: attenuated nitric oxide-mediated responses

BACKGROUND

Attenuated vasodilation in response to the intra-arterial administration of the beta-adrenergic agonist isoproterenol (INN, isoprenaline), an endothelium-independent vasodilator, has previously been observed in normotensive black Americans. To determine whether this reflected a more generalized attenuation of responses to vasodilators, we compared forearm blood flow responses to the endothelium-dependent vasodilator methacholine and the endothelium-independent vasodilator sodium nitroprusside in young normotensive black men and white men.

METHODS

Forearm blood flow responses to the intra-arterial administration of isoproterenol (10 to 400 ng/min), methacholine (0.25 to 8 micrograms/min), and sodium nitroprusside (0.25 to 8 micrograms/min) were measured with use of venous occlusion plethysmography in 11 normotensive black men (mean +/- SE age, 30.5 +/- 2.2 years) and nine normotensive white men (mean age, 28.0 +/- 3.2 years).

RESULTS

Baseline characteristics, including baseline forearm blood flow, were similar in the black and the white subjects. Vasodilation in response to isoproterenol, sodium nitroprusside, and methacholine was significantly attenuated in black subjects, resulting respectively in a 3.7-fold, 3.6-fold, and 5.0-fold increase in forearm blood flow in black subjects and a 7.5-fold, 5.2-fold, and 6.9-fold increase in forearm blood flow in white subjects (ANOVA; isoproterenol, p < 0.0001; sodium nitroprusside, p < 0.0001; methacholine, p = 0.01).

CONCLUSIONS

Our finding of attenuated nitric oxide-mediated vasodilation in response to methacholine and sodium nitroprusside in healthy black American men suggests that attenuated vasodilation in black subjects is a relatively generalized phenomenon, resulting in attenuated responses to multiple vasodilators that act through different receptor- and nonreceptor-mediated mechanisms.

Determination and characterization of nitric oxide generation in mice by in vivo L-Band EPR spectroscopy

The authors have shown direct, real-time, in vivo measurement of nitric oxide (NO) in mice by using the water soluble metal chelator complex, N-methyl-D-glucamine dithiocarbamate (MGD), and Fe(II) as monitored by EPR at L-band. The three-line EPR spectrum from the product [(MGD)2-Fe(II)-NO] was observed noninvasively in lipopolysaccharide (LPS)-treated mice. The spectrum was markedly suppressed by the administration, before LPS injection, of phenyl N-tert-butyl nitrone (PBN), an inhibitor of the expression of induced nitric oxide synthase (iNOS). When 15N-arginine was administered to LPS-treated mice, a diagnostic EPR spectrum was observed, consisting of both three- and two-line EPR signals, due to (MGD)2-Fe(II)-14NO and (MGD)2-Fe(II)-15NO, respectively. The results strongly suggested that the NO detected in these experiments was synthesized by iNOS. In vivo EPR measurements of [(MGD)2-Fe(II)-NO] at several regions in the body (from the head to the tail) indicated that the NO was generated mostly in the upper abdomen near the liver. These observations were confirmed by ex vivo EPR measurements on isolated organs where higher NO levels were detected in vivo in the liver and kidney. The spectroscopic results, combined with the pharmacokinetic data, support the model that NO detected in LPS-treated mice was produced mainly in the liver, and that it did not reflect NO-adduct complex accumulated in the liver via the blood circulation.

Nitric oxide in respiratory failure in the newborn infant

Nitric oxide given as an inhalation (INO) is a novel selective pulmonary vasodilator without effects on the systemic circulation. Preliminary observations indicated that INO treatment was associated with improvements in oxygenation in near-term newborn infants with hypoxic respiratory failure and persistent pulmonary hypertension of the newborn (PPHN). Subsequently, at least eight prospective randomized controlled trials evaluating the use of INO in the near-term neonate with hypoxic respiratory failure have been presented or published. A meta-analysis of these trials has provided evidence that INO improves the PaO2 in the INO-treated infants by 52.8 mm Hg (weighted mean difference) compared with controls (95% CI, 38.2, 67.4), and significantly decreases the oxygenation index by 16.9 compared with controls (95% CI, -22.2, -11.6). The incidence of death or need for ECMO is significantly reduced by treatment with INO, relative risk 0.71 compared to control (95% CI, 0.57, 0.87), with the majority of the improvement observed in the reduction in the need for ECMO. A single study of infants with congenital diaphragmatic hernia (CDH) did not show a benefit for early INO therapy, with treated infants having a greater requirement for ECMO (P = .043). At present, there are no long-term evaluations of infants who have received INO as part of these prospective trials. INO improves oxygenation and reduces the need for ECMO in the near-term hypoxic neonate, but further research is required to evaluate the ultimate safety and benefit of this therapy.

Enhancement of nitric oxide production after arterial reconstruction in patients with arteriosclerosis obliterans

PURPOSE

Nitric oxide (NO) not only relaxes vascular smooth muscles, but it also reduces platelet adhesion and is itself a potent antiaggregatory substance. Experimental studies have shown that the release of NO is modulated by the blood flow. However, little clinical information is available about the effects of hemodynamic changes after arterial reconstruction on NO production. We therefore examined whether the plasma levels of nitrite (NO2-) and nitrate (NO3-) ions increased after arterial reconstruction in patients with arteriosclerosis obliterans (ASO).

METHODS

Blood samples were obtained from the femoral artery in seven patients who underwent arterial reconstruction and seven healthy individuals (control). NO2- and NO3- levels were measured using high-performance liquid chromatography before the operation and 1 hour and 14 days after the operation. In addition, the mean femoral artery blood flow and ankle-brachial pressure index (ABI) were also measured using a duplex and Doppler velocimeter both before and after the operations.

RESULTS

In the control subjects, the mean plasma NO2-, NO3-, and NOx (NO2- plus NO3-) levels in the femoral artery were 0.37 +/- 0.15 mumol/L, 45.6 +/- 10.8 mumol/L, and 46.0 +/- 10.9 mumol/L, respectively. Before the operation in the patients with ASO, the mean plasma NO3- (23.8 +/- 2.2 mumol/L) and NOx levels (24.0 +/- 2.3 mumol/L) were significantly lower than those in the control subjects, whereas the plasma NO2- levels (0.27 +/- 0.04 mumol/L) were comparable between the two groups. At 14 days after operation, the mean plasma NO3- and NOx levels in the femoral artery were significantly increased to 42.8 +/- 5.6 mumol/L and 43.4 +/- 5.6 mumol/L compared with those before the operation, whereas the mean plasma NO2- levels (0.50 +/- 0.05 mumol/L) changed significantly. The mean ABI and the mean flow rate before the operation were 0.32 +/- 0.07 and 344 +/- 145 ml/min, respectively. Both the ABI and the mean flow rate significantly increased to 1.04 +/- 0.06 and 627 +/- 141 ml/min after the operation.

CONCLUSIONS

In patients who have ASO, the mean plasma level of NO is significantly lower than that of healthy individuals. In patients with ASO, the mean blood flow increased significantly after arterial reconstruction. This hemodynamic improvement may thus enhance NO production and may also help to maintain the patency of the bypass graft or native artery.

Endogenous nitric oxide on arterial hemodynamics: a comparison between normotensive and hypertensive rats

Endogenous nitric oxide (NO) plays an important role in maintaining a vasodilator tone. In the present study, we compared the effects of NO blockade on the steady and pulsatile components of arterial hemodynamics between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto strain (WKY), 22-26 wk of age. In the first series of experiments, various doses (1-30 mg/kg i.v.) of N(G)-nitro-L-arginine methyl ester (L-NAME) were administered to block the NO release in anesthetized WKY and SHR. In both WKY and SHR, L-NAME caused a dose-dependent increase in arterial pressure (AP) with a decrease in heart rate (HR). The maximal effects of L-NAME on AP and HR occurred at a dose of 10 mg/kg. Both the AP increase and HR decrease were higher in SHR (AP, +38 +/- 4 mmHg; HR, -49 +/- 5 beats/min) than WKY (AP, +22 +/- 3 mmHg; HR, -33 +/- 5 beat/min). In other series, the technique of impedance spectral analysis was employed to investigate the effects of L-NAME (10 mg/kg i.v.) on the arterial hemodynamics. The aortic pressure and flow waves were recorded and subjected to Fourier transform for the analysis of impedance spectra. Both in WKY (n = 12) and in SHR (n = 12), L-NAME significantly increased AP and total peripheral resistance (TPR). The pulsatile and frequency-dependent hemodynamics including characteristic impedance, wave reflection, and ventricular work were only slightly altered. Despite higher resting values of AP and TPR in SHR (mean AP, 154 +/- 7 mmHg; mean TPR, 204 +/- 17 x 10(3) dyn x s x cm(-5)) than WKY (mean AP, 94 +/- 6 mmHg; mean TPR, 98 +/- 12 x 10(3) dyn x s x cm(-5)), the magnitudes of AP and TPR increments after NO blockade were significantly higher in SHR (AP, +37 +/- 3 mmHg; TPR, +124 +/- 16 x 10(3) dyn x s x cm(-5)) than in WKY (AP, +24 +/- 3 mmHg; TPR, +45 +/- 7 x 10(3) dyn x s x cm(-5)). The continuous formation of endogenous NO affects predominantly the AP and peripheral resistance in both WKY and SHR. The windkessel functions, such as impedance spectra, pulse-wave reflection, and ventricular work, are less affected after NO blockade. In addition, the effects of NO release on the AP and TPR appear to be enhanced in rats with established hypertension.

Inhibitory effect of a fullerene derivative, monomalonic acid C60, on nitric oxide-dependent relaxation of aortic smooth muscle

1. Effects of a fullerene C60 derivative, monomalonic acid C60 (MMA C60), on endothelium-containing or denuded aorta of rabbit, trachea and ileum of guinea pig, and stomach (fundus), vas deferens and uterus of rat were studied pharmacologically. 2. MMA C60 (10(-5) M) significantly reduced the maximum response of the relaxation induced by acetylcholine in endothelium-containing thoracic aorta of rabbit, and the acetylcholine-induced relaxation was recovered in the presence of superoxide dismutase (SOD, 250 units/ml). 3. Nitric oxide-generating agent, S-nitroso-N-acetylpenicillamine, caused the relaxation of aorta without endothelium in a concentration-dependent manner, and the concentration-response curve was shifted to the right in the presence of MMA C60. This inhibitory effect of the derivative was also masked in the presence of superoxide dismutase (SOD). 4. Sodium nitroprusside-induced relaxation was not affected by either MMA C60 or SOD. In the other tissues, this C60 derivative had no effect on the responses induced by any agonist. 5. These observations indicate that MMA C60 inhibits the endothelium-dependent relaxation induced by acetylcholine but does not affect the agonist-induced contractile response of smooth muscle.

Role of L-arginine, a substrate for nitric oxide-synthase, in gastroprotection and ulcer healing

Nitric oxide (NO) synthesized from L-arginine interacts with prostaglandins (PG) and sensory neuropeptides in the regulation of mucosal integrity, but the role of L-arginine, a substrate for NO-synthase, in gastroprotection and healing of chronic gastric ulcers has been little studied. In this study we compared the effects of intragastric (i.g.) and systemic (i.v.) administration of L-arginine or D-arginine on gastric secretion and acute gastric lesions provoked in rats by i.g. application of 100% ethanol, acidified aspirin (ASA), or the exposure to 3.5h of water immersion and restraint stress (WRS). In addition, the effects of L-arginine on ulcer healing and the formation of new vessels (angiogenesis) were determined, using monoclonal antibody (MAb E-9). L-arginine (10-200 mg/kg i.g.) failed to significantly affect gastric secretion but dose-dependently reduced the gastric lesions induced by 100% ethanol. ASA, and WRS, the doses inhibiting 50% of these lesions being 65, 94, and 72 mg/kg, respectively. This protection was accompanied by a significant rise in the gastric blood flow (GBF), whereas L-arginine given i.v. failed to affect the ethanol-lesions and the GBF. D-arginine or the NO-related amino acids--L-glutamine, L-citrulline, or L-ornithine--failed to significantly influence these lesions. Suppression of the generation of mucosal PG by indomethacin or capsaicin-denervation attenuated the protection and hyperemia induced by L-arginine. The inhibition of constitutive NO synthase by L-NNA had no significant effect on the protection afforded by L-arginine, but reduced the gastric hyperemia accompanying this protection. L-arginine (150 mg/kg per day, i.g.) accelerated the ulcer healing and increased GBF at the ulcer margin, and angiogenesis, whereas treatment with L-NNA had an opposite effect. L-arginine added to NG-nitro-L-arginine (L-NNA) restored the ulcer healing, hyperemia, and angiogenesis. We conclude that: (1) the protective activity of L-arginine involves gastric hyperemia mediated by NO and a mild irritant effect due to enhanced generation of endogenous PG, and (2) the ulcer healing properties of L-arginine depend upon its hyperemic and angiogenic actions, possibly involving NO.

Inhaled nitric oxide and hypoxic respiratory failure in infants with congenital diaphragmatic hernia. The Neonatal Inhaled Nitric Oxide Study Group (NINOS)

OBJECTIVE

We designed and conducted a randomized, double-masked, controlled multicenter study to determine whether inhaled nitric oxide (INO) in term and near-term infants with congenital diaphragmatic hernia (CDH) would reduce the occurrence of death and/or the initiation of extracorporeal membrane oxygenation (ECMO).

PATIENTS AND METHODS

Infants of 34 weeks gestation or more, <14 days of age with CDH, without known structural heart disease, requiring assisted ventilation for hypoxemic respiratory failure with two oxygenation indices (OIs) of 25 or more at least 15 minutes apart, were eligible for this trial. Infants were centrally randomized and then received masked treatment with 20 ppm NO or 100% oxygen as control. Infants with less than a full response to 20 ppm NO (increase in PaO2 > 20 Torr) after 30 minutes were evaluated at 80 ppm NO/control study gas.

RESULTS

The 28 control and 25 treated infants enrolled by the 13 participating centers were not significantly different at randomization for any of the measured variables including prerandomization therapies and initial OIs (45.8 +/- 16.3 for controls, 44.5 +/- 14.5 for INO). Death at <120 days of age or the need for ECMO occurred in 82% of control infants compared with 96% of INO infants (ns). Death occurred in 43% of controls and 48% of the INO group (ns), and ECMO treatment was used for 54% of control and 80% of INO-treated infants. There was no significant improvement in PaO2 (delta PaO2 7.8 +/- 19.8 vs 1.1 +/- 7.6 Torr, ns) nor significant reduction in OI (-2.7 +/- 23.4 vs 4.0 +/- 14.8, ns) associated with INO treatment. Mean peak nitrogen dioxide (NO2) concentration was 1.9 +/- 1.3 ppm and the mean peak methemoglobin was 1.6 +/- 0.8 mg/dL. No infant had study gas discontinued for toxicity. There were no differences between the control and INO groups for the occurrence of intracranial hemorrhage, specific grades of intracranial hemorrhage, periventricular leukomalacia, brain infarction, and pulmonary or gastrointestinal hemorrhages.

CONCLUSIONS

Although the immediate short-term improvements in oxygenation seen in some treated infants may be of benefit in stabilizing responding infants for transport and initiation of ECMO, we conclude that for term and near-term infants with CDH and hypoxemic respiratory failure unresponsive to conventional therapy, inhaled NO therapy as used in this trial did not reduce the need for ECMO or death.

Nitric oxide synthase inhibition in a spontaneously hypertensive rat model of diabetic nephropathy

1. To investigate the role of nitric oxide (NO) in diabetic nephropathy the effect of nitric oxide synthase (NOS) inhibition by NG-nitro-L-arginine methyl ester (L-NAME) was observed in a streptozotocin diabetic spontaneously hypertensive rat (SHR) model. 2. Two groups of SHR (n = 8) with streptozotocin-induced diabetes were studied. One group was given L-NAME 5 mg/kg bodyweight per day in the drinking water for 8 weeks while both groups received daily subcutaneous injections of Ultratard insulin. Creatinine clearance, urinary protein excretion, urinary nitrate concentration and systolic blood pressure were measured at fortnightly intervals. Rats were killed at 8 weeks and plasma angiotensin II (AngII) was measured by radioimmunoassay. 3. Renal function (endogenous creatinine clearance) remained stable in both groups. In the L-NAME group, however, there was a progressive increase in proteinuria that was highly significant at 6 weeks (22.1 +/- 2.9 compared with 6.5 +/- 0.7 mg/ 24 h per 100 g in control SHR diabetic rats P < 0.001). 4. Systolic blood pressure was significantly elevated in the L-NAME group throughout the study compared with the control group. 5. Plasma AngII was significantly elevated in the L-NAME group compared with controls (42.8 +/- 10.3 vs 15.1 +/- 1.9 pmol/L, respectively; P < 0.05). 6. Activation of the renin-angiotensin system may account, at least in part, for the resulting vasoconstrictor activity with chronic nitric oxide depletion.

Inhibitory effects of a fullerene derivative, dimalonic acid C60, on nitric oxide-induced relaxation of rabbit aorta

Dimalonic acid C60 (10(-5) M), a new fullerene derivative, produced an augmentation of phenylephrine-induced tone and reduced both the acetylcholine-induced maximum relaxation and the amplitude of substance P (10(-8) M)-induced relaxation in endothelium-containing thoracic aorta of rabbit; the acetylcholine- and substance P-induced relaxation was restored in the presence of superoxide dismutase (250 U/ml). Dimalonic acid C60 (10(-5) M) did not influence the phenylephrine-induced contractile response in the absence of endothelium, but the acetylcholine-induced relaxation was eliminated by removal of the endothelium. Superoxide anion generation, using hypoxanthine (1 mM)/xanthine oxidase (16 mU/ml), reduced the acetylcholine-induced relaxation and produced an augmentation of phenylephrine-induced tone in endothelium-containing strips; these effects were negated by the addition of superoxide dismutase (250 U/ml). A nitric oxide-generating agent, S-nitroso-N-acetylpenicillamine, caused relaxation of aorta without endothelium in a concentration-dependent manner, and the concentration-response curve was shifted to the right in the presence of dimalonic acid C60. This inhibitory effect of dimalonic acid C60 was also masked in the presence of superoxide dismutase. Sodium nitroprusside-induced relaxation was not affected by either dimalonic acid C60 or superoxide dismutase. These observations suggest that dimalonic acid C60 inhibits endothelium (nitric oxide)-dependent agonist-induced relaxation through the production of superoxide.

Determination of dimethylated arginines in human plasma by high-performance liquid chromatography

Using high-performance liquid chromatography (HPLC) with multigradient elution, N(G),N(G)-dimethyl-L-arginine (asymmetric-DMA, ADMA) and N(G),N'(G)-dimethyl-L-arginine (symmetric-DMA, SDMA) can be separated from human plasma samples. The dimethylarginine compounds in plasma, after extraction with a cation-exchange column, are converted to fluorescent derivatives with o-phthaldialdehyde (OPA) in an alkaline medium and the derivatives are separated simultaneously within 50 min on a reversed-phase column (Ultracarb 3 ODS(20)). The recoveries of ADMA and SDMA are over 80% and the method permits quantitative determination of dimethylated arginines at concentrations as low as 0.1 micromol/l in human plasma.

Role of endothelium and nitric oxide in histamine-induced responses in human cranial arteries and detection of mRNA encoding H1- and H2-receptors by RT-PCR

1. Histamine induces relaxation of human cranial arteries. Studies have revealed that the relaxant histamine H1-receptor predominates in human cerebral and the H2-receptor in temporal arteries, while H1- and H2-receptors are of equal importance in the middle meningeal artery. The purpose of the present study was to examine the role of the endothelium and nitric oxide in histamine-induced responses and to show the presence of mRNA encoding H1- and H2-receptors in human cranial arteries. 2. Electrophoresis of polymerase chain reaction (PCR) products from human cerebral, middle meningeal and temporal arteries, demonstrated products corresponding to mRNA encoding both H1- and H2-receptors in arteries with and without endothelium. The amplified PCR products were sequenced and showed 100% homology with the published sequences of these histamine receptors. 3. A sensitive in vitro system was used to study vasomotor responses to histamine. In precontracted cerebral, middle meningeal and temporal arteries with and without endothelium, histamine caused a concentration-dependent relaxation with Imax values between 87% and 81% and pIC50 values between 8.14 and 7.15. In arteries without endothelium the histamine-induced relaxation was significantly less potent (Imax values between 87% and 66% and pIC50 values between 7.01 and 6.67) than in cranial arteries with an intact endothelium. 4. This addition of histamine to arteries without endothelium and pretreated with the histamine H2-antagonist, cimetidine (10(-5) M), caused a concentration-dependent contraction of the cranial arteries with Emax values between 86% and 29% and pEC50 values between 7.53 and 6.77. This contraction was blocked by the histamine H1-receptor antagonist, mepyramine (10(-7) M), and even turned into a relaxation with Imax values between 84% and 14% and pIC50 values between 7.42 and 5.86. 5. The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 3 x 10(-5) M) significantly inhibited the relaxant response to histamine in cerebral and temporal arteries (pIC50 values between 7.43 and 7.13). The combined treatment with L-NAME (3 x 10(-5) M) and cimetidine (10(-5) M) caused a further displacement of the concentration-response curve (pIC50 values between 7.14 and 6.57) and decreased the maximum relaxant responses in all three cranial arteries (Imax values between 62% and 39%). 6. In conclusion, this is the first study which show mRNA encoding histamine H1- and H2-receptors in human cranial arteries. The results indicate that histamine-induced relaxation of human cranial arteries is partially mediated via an endothelial H1-receptor coupled to the production of nitric oxide and partially via a H2-receptor associated with the smooth muscle cells. In addition, there is evidence for a contractile H1-receptor in the smooth muscle cells in these arteries.

Effects of intraluminal or extraluminal endothelin on perfused rabbit basilar arteries

The authors investigated selective intra- and extraluminal effects of endothelin (ET) on perfused basilar and extracranial arteries and also studied the interaction between ET and extraluminal oxyhemoglobin (oxyHb). The basilar, mesenteric, and femoral arteries were isolated from 23 Japanese White rabbits. After isolation of the intra- and extraluminal sides of the preparation, 3 x 10(-10) to 3 x 10(-8) mol/L of ET was administered intra- or extraluminally. After extraluminal pretreatment with 10(-5) mol/L oxyHb, 10(-5) mol/L N(G)-monomethyl-L-arginine (L-NMMA), or 10(-6) mol/L indomethacin, 10(-10) to 10(-8) mol/L of ET was administered intra- or extraluminally. Arterial contraction was evaluated by measuring the increase in the perfusion pressure gradient with a differential pressure gauge. Both intra- and extraluminal ET (10(-9) to 3 x 10(-8) mol/L) showed potent and dose-dependent vasoconstricting effects on basilar arteries (p < 0.01). The effect of ET on the basilar arteries was significantly greater than on the femoral or mesenteric arteries (both p < 0.01). The effect of intraluminal ET was enhanced by extraluminal oxyHb (p < 0.05) and L-NMMA (p < 0.01), but not by extraluminal indomethacin. Extraluminal oxyHb did not potentiate the contraction induced by extraluminal ET. These results indicate that the sensitivity of the basilar artery to intraluminal ET is greater than that of the femoral or mesenteric artery. Endothelin may act as a potent vasoconstrictor intra- as well as extraluminally under conditions such as subarachnoid hemorrhage in which oxyHb is present in the extraluminal space and endothelium-derived relaxing factors are inhibited.

Potentiation of the relaxing action of isoproterenol by forskolin in rabbit aortic rings: the involvement of beta 2-adrenoceptors

1. Forskolin, an activator of adenylate cyclase, potentiated the relaxing response to isoproterenol in rabbit aortic rings precontracted by phenylephrine (PE). 2. The potentiating effect of forskolin was inhibited by propranolol, a beta-adrenoceptor inhibitor, but not by methylene blue, a guanylate cyclase inhibitor. 3. The relaxing response to terbutaline, a beta 2-adrenoceptor agonist, but not lower concentrations of dobutamine, a beta 1-adrenoceptor agonist, also was potentiated by forskolin. Forskolin, however, potentiated the relaxing response to high concentrations of dobutamine, which activates both beta 1- and beta 2-adrenoceptors. 4. Yohimbine, an alpha 2-adrenoceptor inhibitor, glyburide, an ATP-sensitive K+ channel inhibitor, iberiotoxin, a Ca(2+)-activated K+ channel inhibitor, or endothelium-removal failed to affect the potentiating effect of forskolin. 5. Dibutyryl cyclic AMP (cAmp) also potentiated the relaxing response to terbutaline. 6. These results suggest that in rabbit aortic rings forskolin causes the apparent potentiation of isoproterenol-induced relaxation by mainly affecting the relaxing response due to the activation of beta 2-adrenoceptors by the forskolin-induced increase in the level of cAMP.

Nitric oxide-endothelin-1 interaction in humans

Healthy men received NG-monomethyl-L-arginine (L-NMMA) intravenously to study cardiovascular and metabolic effects of nitric oxide synthase blockade and whether this alters the response to endothelin-1 (ET-1) infusion. Controls only received ET-1. L-NMMA effects were that heart rate (17%) cardiac output (17%), and splanchnic and renal blood flow (both 33%) fell promptly (all P < 0.01). Mean arterial blood pressure (6%), and systemic (28%) and pulmonary (40%) vascular resistance increased (P < 0.05 to 0.001). Arterial ET-1 levels (21%) increased due to a pulmonary net ET-1 release (P < 0.05 to 0.01). Splanchnic glucose output (SGO) fell (26%, P < 0.01). Arterial insulin and glucagon were unchanged. Subsequent ET-1 infusion caused no change in mean arterial pressure, heart rate, or cardiac output, as found in the present controls, or in splanchnic and renal blood flow or splanchnic glucose output as previously found with ET-1 (G. Ahlborg, E. Weitzberg, and J. M. Lundberg. J. Appl. Physiol. 79: 141-145, 1995). In conclusion, L-NMMA like ET-1, induces prolonged cardiovascular effects and suppresses SGO. L-NMMA causes pulmonary ET-1 release and blocks responses to ET-1 infusion. The results indicate that nitric oxide inhibits ET-1 production and thereby interacts with ET-1 regarding increase in vascular tone and reduction of SGO in humans.

The mechanism of the relaxing effect of ascorbic acid in guinea pig isolated tracheal muscle

1. The effect of ascorbic acid was studied in the guinea pig isolated tracheal muscle. 2. Ascorbic acid with relatively higher concentrations produced a dose-dependent relaxation in tracheal muscle submaximally precontracted with KCl, histamine, and carbachol. 3. Removing the epithelium did not significantly alter the relaxing effect of ascorbic acid in histamine- and KCl-precontracted strips. 4. The relaxing effect of ascorbic acid is stronger in carbachol-precontracted epithelium-denuded strips than in epithelium-intact strips. 5. Indomethacin, but not L-NAME, partially inhibited the relaxing effect of ascorbic acid. 6. These results indicate that the relaxation induced by ascorbic acid in guinea pig isolated tracheal muscle does not fully depend on the presence of epithelium but is partially mediated by the production of prostanoids from smooth muscle.

A possible role of endogenous inhibitor for nitric oxide synthesis in the bovine ciliary muscle

The present experiments were designed to investigate the possible role of endogenous methylarginine derivatives such as NG-monomethyl-L-arginine, asymmetrical NG,NG-dimethyl-L-arginine and symmetrical NG,N'G-dimethyl-L-arginine for the nitric oxide synthesis in the bovine ciliary muscle. The contents of asymmetrical NG,NG-dimethyl-L-arginine and symmetrical NG,N'G-dimethyl-L-arginine in the bovine ciliary muscle were determined to be 370.2 +/- 27.6 (n = 5) and 182.4 +/- 22.9 (n = 5) pmoles g-1 wet weight, respectively by means of the automated high-performance liquid chromatography. NG-Monomethyl-L-arginine was below the assay limits. On the basis of the total tissue water content (0.792 +/- 0.006 ml g-1 wet weight, n = 14), the concentrations of asymmetrical NG,NG-dimethyl-L-arginine and symmetrical NG,N'G-dimethyl-L-arginine were tentatively estimated to be (4.7 +/- 0.3) x 10(-7) M (n = 5) and (2.3 +/- 0.3) x 10(-7) M (n = 5), respectively. A23187 (10(-7)-3 x 10(-4) M) produced a concentration-dependent relaxation of the ciliary muscle strips which had been contracted with 10(-5) M carbachol. Authentic asymmetrical NG,NG-dimethyl-L-arginine (3 x 10(-6)-3 x 10(-4) M), but not symmetrical NG,N'G-dimethyl-L-arginine (3 x 10(-4) M), inhibited the 10(-6) M A23187-induced relaxation in a concentration-dependent manner. The inhibition with asymmetrical NG,NG-dimethyl-L-arginine (10(-4) M) was reversed by an addition of 3 x 10(-3) M L-arginine, but not by 3 x 10(-3) M D-arginine. The A23187 (10(-6) M)-induced relaxation was enhanced by 3 x 10(-3) M L-arginine or superoxide dismutase (50 U ml-1), whereas it was inhibited by carboxy-PTIO (3 x 10(-4) M), a scavenger of nitric oxide, or methylene blue (10(-5) M), an inhibitor of guanylate cyclase. The carbachol-induced contraction was enhanced by asymmetrical, NG,NG-dimethyl-L-arginine (10(-5) M) and inhibited by 3 x 10(-3) M L-arginine. Any effect of prostanoid formation during the A23187-induced relaxation was ruled out by using indomethacin (10(-5) M). Sodium nitroprusside (10(-5) M), a donor of nitric oxide, also produced a relaxation, which was inhibited by methylene blue (10(-5) M) or carboxy-PTIO (3 x 10(-4) M) and was augmented by superoxide dismutase (50 U ml-1), but unaffected by asymmetrical NG,NG-dimethyl-L-arginine (3 x 10(-4) M) or L-arginine (3 x 10(-3) M). These results lead us to speculate that the nitric oxide synthesized endogenously from L-arginine may play a role for mediating relaxation of the bovine ciliary muscle and that the endogenous asymmetrical NG,NG-dimethyl-L-arginine may be involved in inhibiting the biosynthesis of nitric oxide when there are increased intracellular concentrations of the methylarginine under certain circumstances.

Melatonin inhibits vasospastic action of hydrogen peroxide in human umbilical artery

We evaluated the antioxidant property of melatonin as it relates to the vasospastic effect of hydrogen peroxide (H2O2) on the human umbilical artery. Helical sections of umbilical arteries were obtained from healthy pregnant women who were delivered between weeks 37 and 39 of gestation. Changes in maximal potassium chloride (KCl)-induced tension were measured in arterial segments with intact endothelium. Segments were treated with H2O2 alone, or were pretreated either with an H2O2 scavenger (catalase, 2000 i.u.), a hydroxyl radical scavenger (mannitol, 10(-2) M), a nitric oxide-synthesis inhibitor (L-NG-monomethyl arginine, LNMA, 2 x 10(-4) M), or melatonin (10(-6) M to 10(-4) M). The effect of H2O2 (10(-4) M) on the relaxation induced by the calcium ionophore A23187 was also determined in arterial segments, with or without pretreatment with melatonin (10(-6) M, 10(-4) M). H2O2 (10(-6) M to 10(-4) M) potentiated vascular tension in a concentration-dependent manner (P < 0.0001). Pretreatment with LNMA significantly suppressed the vasospastic effect of H2O2 (P < 0.0001). Pretreatment with either catalase or mannitol significantly reduced the vasospastic effect of H2O2 (P < 0.005, P < 0.002, respectively). Melatonin also significantly reduced the vasospastic effect of H2O2 in a concentration-dependent manner (H2O2 10(-6) M, P < 0.0001 : H2O2 10(-5) M, P < 0.0001 : H2O2 10(-4) M, P < 0.00001). Pretreatment with H2O2 significantly inhibited the relaxation induced by the calcium ionophore A23187 (P < 0.005). Treatment with melatonin prior to exposure to H2O2 significantly restored the relaxation induced by A23187 (P < 0.005). Results suggest that H2O2 potentiates vascular tension in the human umbilical artery, perhaps by suppressing the endothelial synthesis of nitric oxide. Melatonin significantly suppressed the vasospastic effect of H2O2, possibly due to its ability to scavenge the hydroxyl radical.

Influence of basal release of nitric oxide on systolic and diastolic function of both ventricles

Nitric oxide is continuously released by coronary artery endothelium under basal conditions; it maintains vascular tone and regulates coronary blood flow. The objective of this study was to investigate the influence of this basal release of nitric oxide on right and left ventricular systolic and diastolic function. Isolated pig hearts perfused at a constant pressure with enriched autologous blood were used. Systolic and diastolic pressure-volume relationships of isovolumically contracting hearts were studied in the control setting and after addition of 1 mmol/L L-N(G)-monomethyl-arginine followed by 5 mmol/L L-arginine to the perfusate. Addition of L-N(G)-monomethyl-arginine caused an acute rise in coronary vascular resistance and a reduction in right and left ventricular systolic function as evaluated by the slope values of the pressure-volume curves, but had little effect on the diastolic function of either ventricle. L-Arginine restored the systolic function to the control level. This alteration in ventricular function was not a result of ischemia because myocardial oxygen consumption was not significantly affected by the acute increase in coronary vascular resistance induced by L-N(G)-monomethyl-arginine. We conclude that basal release of nitric oxide has no direct negative inotropic effect, but in fact plays an important role in preserving right and left ventricular systolic function and maintains the basal coronary vascular tone.

An arginine analog inhibits responses of both the endothelium and smooth muscle of canine in situ vein grafts

Increased shear, pressure, and oxygen tension in vein grafts may alter production of endothelium-derived vasoactive and anti-mitogenic factors such as nitric oxide which subsequently affect development of neointimal hyperplasia. This study was designed to determine whether or not nitric oxide mediates endothelium-dependent responses in femoral in situ vein grafts. Non-reversed, canine femoral vein grafts were placed bilaterally to bypass a ligated segment of the femoral artery in dogs. After 6 weeks, the grafts were removed, cut into rings, and suspended in organ chambers for measurement of isometric force. In some rings the endothelium was removed deliberately. In the presence of indomethacin, the synthetic analog of L-arginine, L-N(G)-monomethyl-arginine (10(-4) M; L-NMMA) did not cause a significant change in baseline tension of rings with endothelium. L-NMMA reduced only contractions of rings with endothelium to the alpha-adrenergic agonist UK 14,304. The analog also reduced maximal relaxations to the calcium-ionophore, A23187 in rings with endothelium. In addition, L-NMMA reduced relaxations of rings without endothelium to adenosine diphosphate by 35%. Positive immunostaining for nitric oxide synthase was present in both the myointima and media of histological sections of grafts. In conclusion, these results suggest that in situ vein grafts exhibit two unique properties which are unlike unoperated arteries or veins: (i) alpha2-adrenergic receptors may be coupled to the release of contractile endothelium-derived factors associated with production of nitric oxide: and (ii) nitric oxide may be released by the smooth muscle in response to purinergic stimulation. The presence of nitric oxide synthase throughout the wall of the graft may result in production of nitric oxide in response to adenosine diphosphate released by platelets and to circulating catecholamines.

Oxidant injury, nitric oxide and pulmonary vascular function: implications for the exercising horse

The athletic ability of the horse is facilitated by vital physiological adaptations to high-intensity exercise, including a thin (but strong) pulmonary blood-gas barrier, a large pulmonary functional reserve capacity and a consequent maximum oxygen uptake (VO2max) far higher than in other species. A high pulmonary artery pressure also serves to enhance pulmonary function, although stress failure of lung capillaries at high pulmonary transmural pressures, and the contribution of other factors which act in the exercising horse to increase pulmonary vascular tone, may lead to pathological or pathophysiological sequelae, such as exercise-induced pulmonary haemorrhage (EIPH). Reactive oxygen species (ROS) are an important component of the mammalian inflammatory response. They are released during tissue injury and form a necessary component of cellular defences against pathogens and disease processes. The effects of ROS are normally limited or neutralized by a multifactorial system of antioxidant defences, although excessive production and/or deficient antioxidant defences may expose healthy tissue to oxidant damage. In the lung, ROS can damage pulmonary structures both directly and by initiating the release of other inflammatory mediators, including proteases and eicosanoids. Vascular endothelial cells are particularly susceptible to ROS-induced oxidant injury in the lung, and both the destruction of the pulmonary blood-gas barrier and the action of vasoactive substances will increase pulmonary vascular resistance. Moreover, ROS can degrade endothelium-derived nitric oxide (NO), a major pulmonary vasodilator, thereby, with exercise, synergistically increasing the likelihood of stress failure of pulmonary capillaries, a contributing factor to EIPH. This review considers the implications for the exercising horse of oxidant injury, pulmonary vascular function and NO and the contribution of these factors to the pathogenesis of equine respiratory diseases.

Association of nitric oxide production by kidney proximal tubular cells in response to lipopolysaccharide and cytokines with cellular damage

Recent findings suggest that nitric oxide (NO) is an important biologic mediator which exerts a wide variety of effects on numerous physiological and pathophysiological processes. L-Arginine is oxidized to L-citrulline with concomitant NO production; as a result, nitrate and nitrite accumulates. This study was conducted to determine the potential NO production by proximal tubular cells (PTC) in response to bacterial lipopolysac-charides (LPS) and cytokines and to evaluate the cytotoxic effect associated with NO release. After a 7-day stimulation with LPS (100 micrograms/ml), interleukin-1 beta (IL-1 beta) (10 ng/ml), and tumor necrosis factor alpha (TNF-alpha) (10 ng/ml), the nitrate and nitrite levels were determined by a spectrophotometric method based on the Griess reaction. Moreover, alpha-methylglucopyranoside phosphate and lactate dehydrogenase release and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay served as indicators of sodium-dependent hexose transport integrity and cell death, respectively. IL-1 beta and TNF-alpha used alone or together or combined with LPS led to a significant generation of NO by PTC. Our results also demonstrate that NO induced by LPS and cytokines could inhibit sodium-dependent transport and could induce PTC damage.

Nitric oxide modulates human chorionic gonadotropin-induced ovulation in the rabbit

OBJECTIVE

To examine the potential role of the L-arginine:nitric oxide pathway in hCG-induced ovulation in the rabbit.

DESIGN

Randomized, controlled animal study.

SETTING

University research laboratory.

INTERVENTION(S)

Nitric oxide synthase, the enzyme that produces nitric oxide (NO), was immunohistochemically localized in the ovary. NG-nitro-L-arginine methyl ester (L-NAME), an analogue of L-arginine, which inhibits the enzyme NO synthase, and the inactive D-enantiomer were administered in vivo and/or in vitro via an isolated, perfused ovary preparation during the periovulatory period.

MAIN OUTCOME MEASURE(S)

Rate of follicular rupture (ovulatory efficiency).

RESULT(S)

Immunohistochemical staining for NO synthase was localized specifically to the granulosa cell layer of the follicle and the endothelium and adventitia of ovarian blood vessels. In vivo administration of L-NAME significantly reduced the percentage of large follicles that ovulated in response to hCG (treated 24.6%, control 68.1%). Similarly, exposure of the in vitro-perfused ovary to L-NAME significantly reduced follicular rupture (treated 32.8%, control 64.2%). In contrast, addition of an equimolar concentration of D-NAME to the perfusion medium had no significant effect on the rate of ovulation (treated 83.3%, control 61.3%).

CONCLUSION(S)

The stereospecific inhibition of follicular rupture by the arginine analogue suggests that NO production by the ovary is an important feature of the normal physiologic processes of the periovulatory period.

Endothelial stunning and myocyte recovery after reperfusion of jeopardized muscle: a role of L-arginine blood cardioplegia

Ischemia and reperfusion may damage myocytes and endothelium in jeopardized hearts. This study tested whether (1) endothelial dysfunction (reduced nitric oxide release) exists despite good contractile performance and (2) supplementation of blood cardioplegic solution with nitric oxide precursor L-arginine augments nitric oxide and restores endothelial function. Among 30 Yorkshire-Duroc pigs, 6 received standard glutamate/aspartate blood cardioplegic solution without global ischemia. Twenty-four underwent 20 minutes of 37 degrees C global ischemia. Six received normal blood reperfusion. In 18, the aortic clamp remained in place 30 more minutes and all received 3 infusions of blood cardioplegic solution. In 6, the blood cardioplegic solution was unaltered; in 6, the blood cardioplegic solution contained L-arginine (a nitric oxide precursor) at 2 mmol/L; in 6, the blood cardioplegic solution contained the nitric oxide synthase inhibitor L-nitro arginine methyl ester (L-NAME) at 1 mmol/L. Complete contractile and endothelial recovery occurred without ischemia. In jeopardized hearts, complete systolic recovery followed infusion of blood cardioplegic solution and of blood cardioplegic solution plus L-arginine. Conversely, contractility recovered approximately 40% after infusion of normal blood and blood cardioplegic solution plus L-NAME. Postischemic nitric oxide production fell 50% in the groups that received blood cardioplegic solution and blood cardioplegic solution plus L-NAME but was increased in the group that received blood cardioplegic solution L-arginine. In vivo endothelium-dependent vasodilator responses to acetylcholine recovered 75% +/- 5% of baseline in the blood cardioplegic solution plus L-arginine group, but less than 20% of baseline in other jeopardized hearts. Endothelium-independent smooth muscle responses to sodium nitroprusside were relatively unaltered. Myeloperoxidase activity (neutrophil accumulation) was similar in the blood cardioplegic solution (without ischemia) and blood cardioplegic solution plus L-arginine groups (0.01 +/- 0.002 vs 0.013 +/- 0.003 microgram/gm tissue). Myeloperoxidase activity was raised substantially to 0.033 +/- 0.002 microgram/gm after exposure to normal blood and to 0.025 +/- 0.003 microgram/gm after infusion of blood cardioplegic solution and was highest at 0.053 +/- 0.01 microgram/gm with exposure to blood cardioplegic solution plus L-NAME in jeopardized hearts. The discrepancy between contractile recovery and endothelial dysfunction in jeopardized muscle can be reversed by adding L-arginine to blood cardioplegic solution.

Effect of NG-monomethyl-L-arginine on the microcirculation of rat skin

1. The effects of NG-monomethyl-L-arginine (L-NMMA), a nitric oxide (NO) synthase inhibitor, on the microcirculation of rat dorsal skin were studied to examine the role of NO in the regulation of regional haemodynamics. 2. The blood volume in the skin microcirculation, which was continuously measured by reflectance spectrophotometry, was significantly decreased in response to L-NMMA (10 mg/kg bodyweight, i.v.), suggesting vasoconstriction, and the response continued for more than 20 min. In contrast, the increase in systemic blood pressure (BP) disappeared soon after administration of L-NMMA. 3. These results show that L-NMMA elicits long-lasting responses in the skin microcirculation, whereas the systemic BP rapidly recovers, suggesting a large contribution of the NO system to the regulation of rat skin microcirculation.

Maturation alters the pulmonary arterial response to hypoxia and inhaled nitric oxide in the presence of endothelial dysfunction

Surgical intervention in ever younger patients has led to a new appreciation of the unique physiology of the neonate. Specifically, newborn patients may respond very differently to hypoxic episodes and subsequent treatment with inhaled nitric oxide than older infants. In the current study, we examined differences in the pulmonary arterial response to hypoxia and inhaled nitric oxide in 48-hour-old (n = 8) and 14-day-old (n = 8) Yorkshire pigs in a model of nitric oxide synthase inhibition, as might be seen with endothelial dysfunction. Data were acquired after treatment with the nitric oxide synthase inhibitor N omega-nitro-L-arginine during hypoxia (inspired oxygen fraction = 0.10) and during inhalation of nitric oxide (100 ppm). Input mean impedance, reflecting distal arteriolar vasoconstriction, and characteristic impedance, reflecting proximal arterial geometry and distensibility, were calculated. The modulus of elasticity, a measure of the "stiffness" of the proximal vessels, was also calculated. Hypoxia caused a large increase in input mean impedance in both 48-hour-old and 14-day-old pigs (4826 +/- 272 versus 8744 +/- 488 dyne.cm.sec-5 and 3129 +/- 73 versus 6000 +/- 134 dyne.cm.sec-5, respectively; p = 0.0078). Characteristic impedance was not altered in the younger animals (1171 +/- 76 dyne.cm.sec-5) but increased in the older animals (419 +/- 15 versus 797 +/- 20 dyne.cm.sec-5. p = 0.0078). Older animals also experienced an increase in the modulus elasticity (1.92E06 +/- 3.2E05 versus 1.05E07 +/- 3.9E05 dyne/cm2, p = 0.0078). These data show that inhibited nitric oxide production, as might be seen in endothelial dysfunction, potentiates the profound hypoxic vasoconstriction observed at the level of the distal pulmonary arterioles in both neonatal and infant animals. In contrast, only older animals had a stiffening of the larger, more proximal vessels with hypoxia. In both age groups, inhaled nitric oxide effectively reduced the increases in impedance.

Nitric oxide (NO) modulates the neurogenic control of blood pressure in rats with chronic renal failure (CRF)

Increased sympathetic nervous system (SNS) activity plays a role in the genesis of hypertension in rats with chronic renal failure (CRF). Because nitric oxide (NO) modulates the activity of the SNS, a deficit of NO synthesis could be responsible for the increased SNS activity in these animals. In the present study, we evaluated the effects of L-arginine and L-NAME on blood pressure and SNS activity-in Sprague Dawley 5/6 nephrectomized or sham-operated rats. SNS activity was determined by measuring norepinephrine turnover rate in several brain nuclei involved in the regulation of blood pressure. In the same brain nuclei, we measured NO content and nitric oxide synthase (NOS) gene expression by semiquantitative measurements of NOS mRNA reverse transcription polymerase chain reaction. In CRF rats, norepinephrine turnover rate was increased in the posterior hypothalamic nuclei, locus coeruleus, paraventricular nuclei, and the rostral ventral medulla, whereas NOS mRNA gene expression and NO2/NO3 content were increased in all brain nuclei tested. L-NAME increased blood pressure and NE turnover rate in several brain nuclei of both control and 5/6 nephrectomized rats. In CRF rats, a significant relationship was present between the percent increment in NOS mRNA gene expression related to the renal failure, and the percent increase in norepinephrine turnover rate caused by L-NAME. This suggests that endogenous NO may partially inhibit the activity of the SNS in brain nuclei involved in the neurogenic regulation of blood pressure, and this inhibition is enhanced in CRF rats. In summary, the increase in SNS activity in the posterior hypothalamic nuclei and in the locus coeruleus of CRF rats is partially mitigated by increased local expression of NOS m-RNA.

Adaptation of myocardial blood flow to increased metabolic demand is not dependent on endothelial vasodilators in the rat heart

OBJECTIVE

To investigate the role of endothelial vasodilating factors in adaptation of myocardial blood flow to increased metabolic demands.

DESIGN

Alterations in the effects of endothelium dependent (acetylcholine) and independent (sodium nitroprusside) vasodilators and the beta 1 receptor agonist dobutamine were studied after inhibition of endothelium derived relaxing factor (EDRF) with L-NG-nitro-arginine methyl ester (L-NAME), prostanoid synthesis with indomethacin, and ATP sensitive potassium channels with glibenclamide.

EXPERIMENTAL ANIMALS

Female Wistar rats, in situ perfused heart.

MAIN OUTCOME MEASURES

Myocardial blood flow (H2 clearance); systolic fractional thickening (pulsed Doppler); mean arterial blood pressure.

RESULTS

L-NAME reduced myocardial blood flow by 58 (12)% (mean (SD), P < 0.001) and systolic thickening fraction (FT) by 36 (9)% (P < 0.05). These effects were significantly reversed by administration of L-arginine but not D-arginine. Pretreatment with L-NAME inhibited the increase in myocardial blood flow caused by acetylcholine (control: +42 (9)%; L-NAME: -29 (7)%, P < 0.001) but did not affect the increase in myocardial blood flow caused by sodium nitroprusside (control: +44 (5)%; L-NAME: +34 (10)%, NS). Pretreatment with L-NAME did not change the effect of dobutamine on myocardial blood flow (+61 (3)%) and FT (+32 (8)%) compared with baseline values (P < 0.001). Neither pretreatment with indomethacin nor with glibenclamide reduced the dobutamine induced increase in myocardial blood flow.

CONCLUSIONS

Inhibition of EDRF, prostanoid synthesis, and ATP sensitive potassium channels did not reduce the vasodilator reserve during increased metabolic demands induced by beta 1 adrenergic stimulation. Therefore, adaptation of myocardial blood flow to increased metabolic demands is independent of endothelial relaxing factors in the rat heart.

A tutorial on the diffusibility and reactivity of free nitric oxide

In this review, I consider the quantitative consequences of the diffusion of free NO in determining its biological actions. Several studies have measured the extent to which NO diffuses away from an NO-producing cell, and the distance of its diffusion is quite large, on the order of 100-200 microm. This wide diffusibility is consistent also with the high value for its diffusion constant, 3300 microm2/s. Mathematical simulations based on this wide diffusibility suggest that, within spatial limits of approximately 0.3-0.4 mm, the actions of free NO are dictated by the total number of NO-producing cells within this location as opposed to where the NO-producing cells are located within this space. These results suggest that the actions of NO are surprisingly long range and the diffusion of NO is an important determinant of its biological actions. Thus, the effects of NO on individual target cells may be determined more by each cell's preprogrammed characteristic response to NO than by proximity to an NO source. In addition, scavenging of NO by hemoglobin in blood vessels should represent a significant sink for its scavenging, posing difficulty for the postulate that only free NO functions as EDRF.

Control of cerebral and ocular blood flow autoregulation in neonates

Several factors have been implicated in the regulation of cerebral and ocular vasomotor tone in the newborn: the interrelationship between prostanoids, NO, and other vasoactive mediators remains a subject of interest and active investigation. Pharmacologic modulation may provide new treatment modalities for diseases of the newborn that are mostly hemodynamic and vascular in nature.

Importance of nitric oxide in the coronary artery at rest and during pacing in humans

OBJECTIVES

The purpose of this study was to investigate the role of endothelium-dependent vascular regulation in the human coronary circulation during rest and hyperemic states.

BACKGROUND

Evidence of the role of nitric oxide (NO) during metabolic demand is not consistent in animal and human coronary circulation.

METHODS

NG-Monomethyl-L-arginine (L-NMMA), a specific inhibitor of NO synthesis, was infused into the left anterior descending coronary artery at rest and during rapid atrial pacing in 18 subjects--9 with normal coronary arteries (control) and 9 with atherosclerotic coronary arteries. The diameter of the epicardial coronary artery was measured by quantitative coronary angiography. Vasodilation of the coronary microcirculation was assessed using an intracoronary Doppler FloWire.

RESULTS

Infusion of 25 mumol/min of L-NMMA reduced the diameter of the proximal and distal epicardial coronary artery segments by 8 +/- 2% (mean +/- SE) and 11 +/- 2%, respectively (p < 0.05) in the control subjects. The coronary blood flow (CBF) decreased by 33 +/- 13% during L-NMMA infusion. L-NMMA caused similar changes in the diameter of the distal epicardial segment and the CBF in patients with coronary artery disease. The proximal vessel diameter did not change significantly during infusion of L-NMMA. During pacing, infusion of L-NMMA caused the same changes in vessel diameter as before pacing in both groups, but did not affect CBF.

CONCLUSIONS

Our findings indicate that NO synthesis maintains basal vasomotor tone in both conduit and resistance vessels in the normal human coronary circulation. Although NO release was impaired in the large epicardial coronary arteries in patients with atherosclerosis, NO still regulated vascular tone in the small epicardial coronary arteries and arterioles. Our results suggest that vasodilation in arterioles during increased myocardial oxygen demand is mediated by metabolic or myogenic mechanisms, or both, rather than by endothelium-dependent production of NO.

Reperfusion Injury: Basic Concepts and Protection Strategies

Prolonged ischemia such as that following myocardial infarction or occurring during long-term coronary bypass procedures causes serious damage to the myocardium. Early reperfusion is an absolute prerequisite for the survival of ischemic tissue. However, reperfusion has been referred to as the "double edged sword" because reperfusing ischemic myocardium carries with it a component of injury known as reperfusion injury. Reperfusion injury includes a number of events, such as reperfusion arrhythmias, myocardial infarction, stunning, vascular damage, and endothelial dysfunction. The underlying mechanism of reperfusion injury is not entirely known, but the existing evidence suggests that oxygen free radicals generated during the first few minutes of reflow lead to damage of cellular membranes, intracellular calcium overload, and uncoupling of excitation-contraction coupling. Although controversial, free radical scavengers, in general, are highly effective in the attenuation of reperfusion injury in animal models. Newer endogenous protection strategies, which include ischemic and heat shock preconditioning, are known to reduce reperfusion injury following ischemia.

Attenuated central pressor response to nitric oxide synthesis inhibition in chronic renal failure rats

OBJECTIVES

Central and peripheral roles of nitric oxide (NO) in blood pressure regulation have been suggested. The present study was aimed at examining if the role of NO in blood pressure regulation is altered in chronic renal failure.

METHODS

Blood pressure responses to acute inhibition of NO were examined in 5/6 nephrectomized rats. Three weeks after the renal ablation, under thiopental (50 mg/kg, i.p.) anesthesia, an intracerebroventricular cannula was placed in the left lateral ventricle and the femoral vein was cannulated to serve as an infusion route. The arterial blood pressure was measured in the right femoral artery. NG-nito-L-arginine methyl ester (L-NAME) was infused (100 microgram/kg per min for 60 min either intracerebroventricularly or intravenously.

RESULTS

Chronic renal failure rats showed a significantly higher arterial pressure than the control rats (147 +/- 14 mmHg vs. 122 +/- 13 mmHg). Intracerebroventricular L-NAME did not affect the arterial pressure in chronic renal failure rats (0.5 +/- 4 mmHg increase from the basal), while it significantly increased the arterial pressure in normal rats (22 +/- 3 mmHg increases from the basal). Intravenous L-NAME increased the arterial pressure, the magnitude of which did not differ between the normal and chronic renal failure rats (24 +/- 3 vs. 16 +/- 3 mmHg increases from the basal).

CONCLUSION

These results indicate that the central role of NO in the regulation of blood pressure is altered in chronic renal failure.

Peroxynitrite: a two-faced metabolite of nitric oxide

The discovery that nitric oxide (NO) reacts with superoxide (O2.-) forming peroxynitrite (ONOO-) (1) and the proof that this reaction occurs in vivo (2,3) holds enormous implications for the understanding of free radicals in biological systems. Not only in mammalian defense mechanisms against microorganisms, but also in pathophysiology during overexposure of tissues to radicals or other highly reactive species. Peroxynitrite is a highly reactive compound with harmful effects on cells and could therefore be an important microbicidal compound. Furthermore, the reaction of superoxide with NO interferes with NO signalling mechanisms. NO is not only released in response to inflammatory agents by inflammatory cells, but is also an important messenger molecule in paracrine mechanisms and neurotransmission. Whether peroxynitrite formation is a negative side effect of NO and superoxide release, or a functional characteristic is yet to be determined, and will be discussed in this review.

Synthesis of nitric oxide by the haemocytes of the American horseshoe crab ( Limulus polyphemus )

Nitric oxide (NO) synthase, the enzyme responsible for the production of NO from L-arginine, is present in haemocytes of the American horseshoe crab ( Limulus polyphemus ). The synthesis of NO results in down-regulation of the aggregatory function of these cells in a manner similar to that previously described for mammalian platelets. These data indicate that formation of NO from L-arginine is a pathway of early evolutionary origin.

Long-term smoking impairs platelet-derived nitric oxide release

BACKGROUND

Long-term smoking impairs endothelium-dependent vasodilation, which is mediated by nitric oxide (NO). However, it is unknown whether long-term smoking impairs the platelet-derived NO release, which regulates platelet aggregation.

METHODS AND RESULTS

Platelet-derived electrical current induced by collagen was measured with an NO-selective electrode in 12 smokers and 11 nonsmokers. Collagen-induced intraplatelet cGMP and platelet aggregation was measured in smokers and nonsmokers. S-nitroso-N-acetyl-dl-penicillamine, a direct NO donor, dose dependently increased in electrical current (r = .99). Collagen induced platelet aggregation and dose dependently increased electrical current (r = .94). Collagen-induced electrical current and cGMP were significantly augmented by L-arginine, a precursor of NO, and attenuated by NG-monomethyl-L-arginine, an inhibitor of NO synthesis. Significant correlation was found between collagen-induced electrical current and cGMP (r = .73). These findings indicate that the change in electrical current reflects the NO release through the L-arginine-NO pathway in platelets. Collagen-induced electrical current (6.7 versus 13.8 pA; P < .001) and cGMP (1.2 versus 3.0 pmol/10(9) platelets; P < .005) were significantly lower in smokers than in nonsmokers. Although L-arginine increased cGMP levels in both smokers and nonsmokers, the level was still lower in smokers than in nonsmokers. The inhibitory effect of L-arginine on collagen-induced platelet aggregation was significantly lower in smokers than in nonsmokers (P < .05).

CONCLUSIONS

These findings provide evidence that platelet-derived NO release is significantly impaired in long-term smokers, resulting in the augmentation of platelet aggregability.

Nitric oxide mediates central activation of sympathetic outflow induced by interleukin-1 beta in rats

The excitatory mechanism of central sympathetic outflow induced by interleukin-1 beta was investigated in urethane-anesthetized rats. Intracerebroventricular administration of interleukin-1 beta induced a gradually developing elevation of plasma noradrenaline levels in a dose-dependent manner (50, 100 and 200 ng/animal), while the levels of adrenaline were not affected. The elevation of noradrenaline levels induced by interleukin-1 beta (100 ng/animal i.c.v.) was abolished by the following treatments with: (1) a chemical sympathectomizer, 6-hydroxydopamine (15 mg/kg i.v., 3 days before); (2) a prostaglandin synthesis inhibitor, indomethacin (500 micrograms/animal i.c.v.); (3) a nitric oxide synthase inhibitor, L-NG-nitroarginine methyl ester (100 micrograms plus 10 micrograms/min i.c.v.); and (4) a nitric oxide scavenger, oxyhemoglobin (32.3 micrograms plus 3.23 micrograms/min i.c.v.). In contrast to these results, D-NG-nitroarginine methyl ester, an inactive isomer of L-NG-nitroarginine methyl ester, and methemoglobin, a metabolite of oxyhemoglobin, were without effect. Furthermore, prostaglandin E2 (100 ng/animal i.c.v.) rapidly and markedly elevated the plasma level of noradrenaline but not adrenaline. This prostaglandin E2-induced elevation of plasma noradrenaline levels was not attenuated by L-NG-nitroarginine methyl ester (100 micrograms plus 10 micrograms/min i.c.v.). The present results suggest that nitric oxide is involved in the interleukin-1 beta-induced central activation of sympathetic outflow. Furthermore, there probably exists nitric oxide-linked prostaglandin-generating system in the brain.

Inhibition of nitric oxide synthase by antisense techniques: investigations of the roles of NO produced by murine macrophages

1. An antisense approach to block nitric oxide (NO) synthesis was developed, complementing the widely used chemical inhibitors and overcoming problems associated with their use in studying the roles of NO. 2. Murine macrophage cell lines (J774.2) were generated expressing a 500 bp sequence from inducible NO synthase (iNOS) in either the antisense or sense orientation, driven by the SV40 promoter/enhancer region. 3. Messenger RNA derived from the transfected sequences was detected by a specific cDNA probe. Cells expressing sense and antisense iNOS RNA were characterized further. 4. The antisense lines produced 22-97% less NO than the sense lines on stimulation with lipopolysaccharide (LPS) in the range 1 ng ml-1 - 10 micrograms ml-1, as determined by nitrite production. One antisense line in particular, A10, expressed substantially less iNOS protein on LPS stimulation as determined by western blot analysis. 5. Adhesion of the antisense line, A10, to cytokine-stimulated murine endothelial cells (sEnd.1 line) was significantly higher than adhesion of the sense lines. There was a negative correlation between the amount of NO produced, as determined by nitrite accumulation, and the level of adhesion of the transfected lines. This indicates and anti-adhesive role of NO, produced by macrophages during the 15 min of the assay, in adhesion to endothelial cells. 6. This novel approach allowed the roles of NO in adhesion to be investigated with the substantial advantage that the contribution of NO produced rapidly by activated macrophages could be studied separately from that produced in a continuous manner by endothelial cells. 7. These lines, and the extension of this approach, will be of great use in dissecting the contributions of NO produced by different cell types to its many potential functions.

Influence of nitric oxide on hypoglycemia--or angiotensin II-stimulated ACTH and GH secretion in normal men

In order to establish whether nitric oxide (NO) is involved in the regulation of ACTH and/or GH secretion, normal male subjects were treated i.v. with the NO-synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (40 micrograms/kg injected plus 50 micrograms/kg infused over 60 min) in basal conditions and/or during stimulation with insulin (0.15 IU/kg body weight in an i.v. bolus) to induce hypoglycemia (ITT) or ASP 1 ILE-5 angiotensin II (ANG II) (increasing doses of 4, 8 and 16 ng/kg/min, each dose for 20 min). The administration of L-NAME neither changed the basal secretion of ACTH and GH nor modified the hormonal responses to ANG II stimulation. Also the GH response during ITT remained unchanged in the presence of L-NAME. In contrast, the ACTH response to hypoglycemia was significantly higher when L-NAME was administered. These data suggest that in normal men NO has a negative effect on ACTH secretion, but not GH secretion, in response to hypoglycemia. Furthermore, our results argue against a role of NO in the control of basal and ANG II-stimulated ACTH and GH secretions.

High-performance liquid chromatographic assay for the quantitation of L-arginine in human plasma

L-Arginine is metabolized to nitric oxide by nitric oxide synthase, and abnormalities in nitric oxide production have been implicated in the pathogenesis of some diseases involving the vasculature. Thus, there has been interest in the effects of pharmacologic doses of L-arginine in patients with cardiovascular and renal diseases. To study the disposition of exogenous doses, an HPLC method was developed to analyze plasma samples for L-arginine. The assay involves precolumn derivatization of arginine with naphthalenedicarboxaldehyde and cyanide followed by HPLC with UV detection. Only a simple deproteinization of the plasma samples was required. The derivatized arginine was stable (less than 5% degradation in 20 h), facilitating batch sample processing and analysis in an autosampler. Calibration curves were generated in Ringer's lactate solution instead of plasma to correct for endogenous plasma L-arginine. Recovery in plasma, compared to Ringer's solution (n = 4), was 103%. Mean intraday assay precision (n = 6), expressed as coefficient of variation, was 3.4%. Interassay precision (n = 6) was 7%. The assay was applied for the quantitation of L-arginine in plasma samples from a normal subject who had been given a single oral (10 g) and a single intravenous dose (30 g) of exogenous L-arginine.

Endothelial cell injury in cardiovascular surgery: the pathophysiology of vasomotor dysfunction

Impaired vasomotor function has been suggested as playing a role in the pathophysiology of hypertension, diabetes, hypercholesterolemia, and atherosclerosis, all of which are common in cardiovascular surgery patients. In addition to chronic vasomotor dysfunction, alterations in vasomotor tone can result in acute arterial spasm, microcirculatory ischemia, and wide variations in systemic blood pressure. Changes in the health of the vascular endothelium may also impact the late patency of coronary artery bypass grafts, the progression of atherosclerosis in the native coronary circulation, and the long-term success of cardiac transplants. In the resting state the endothelium produces several substances that promote vascular relaxation and inhibition of platelet function, thus assuring the unhindered flow of blood through the capillaries. In response to injury, the endothelium loses some capacity to relax and also releases powerful vasoconstrictive agents. Attempting to understand the contributions that these substances play in the vasomotor dysfunction seen after cardiothoracic surgery is an area of active investigation.

Protective effect of NG-monomethyl-L-arginine against hypotension inducted by combined tumour necrosis factor-alpha and whole body hyperthermia in rats

We studied: (a) the adverse effects of tumour necrosis factor-alpha (TNF) given during whole body hyperthermia (WBH) on mean arterial pressure (MAP) and gut mucosa in anaesthetized rats; (b) the potential protective effect of NG-monomethyl-L-arginine (L-NMA), an inhibitor of nitric oxide synthase; and (c) the influence of L-NMA on the antitumour effect of the trimodality therapy, WBH + TNF + Carboplatin (CBDCA). In normothermic rats, TNF alone (10(5) or 10(6) U/kg) did not cause hypotension, but increased MAP (p < 0.05). L-NMA alone (5, 10 and 20 mg/kg) increased MAP moderately and dose-dependently (p < 0.05). WBH (41.5 degrees C for 2 h) increased MAP markedly (from 103 +/- 4 to 161 +/- 4 mm Hg). This increase in MAP was sustained throughout the hyperthermia, but was followed by a transient relative hypotension (MAP = 80 +/- mm Hg) on cessation of WBH and an eventual return to near baseline at 30 min post-WBH (MAP = 94 +/- 5 mm Hg). WBH + TNF (10(5) or 10(6) U/kg) initially increased MAP similarly to WBH alone. During the second hour of WBH, however, MAP decreased towards pre-treatment levels, and cessation of WBH was followed by sustained hypotension. This late hypotensive state was associated with a mortality during the early (first 2 h) post-WBH period of 17 and 100% at TNF dose of 10(5) and 10(6) U/kg TNF, respectively. L-NMA given to rats receiving WBH + TNF (10(6) U/kg) maintained MAP at levels similar to WBH alone during WBH treatment. L-NMA prevented the post-WBH hypotension, and extended the survival beyond the early (first 2 h) post-WBH period. No rat, however, receiving high dose TNF (10(6) U/kg) survived more than 12 h even with L-NMA (totally 40 mg/kg). WBH + TNF (10(5) and 10(6) U/kg) also produced marked histopathological injury to the gut mucosa at 2 h post-treatment. L-NMA substantially protected the gut from this injury. In rats bearing a transplantable fibrosarcoma, L-NMA did not decrease the antitumour effect consisting of WBH + TNF (10(5) U/kg) + CBDCA, while it decreased (p < 0.05) the general toxicity (weight loss, diarrhea and foot oedema) of this combination. We conclude that L-NMA may prevent or ameliorate the early toxicity but not the late lethal effects of WBH + high dose TNF (10(6) U/kg). Additionally, L-NMA reduces some of the toxicity of WBH + TNF (10(5) U/kg) + CBDCA without decreasing the antitumour effect of this trimodality therapy. Inhibitors of nitric oxide synthase such as L-NMA may provide a novel approach to overcoming the toxicity of TNF in combination with WBH.

Exercise-induced vasodilation in forearm circulation of normal subjects and patients with congestive heart failure: role of endothelium-derived nitric oxide

OBJECTIVES

This study was undertaken to investigate the role of endothelium-derived nitric oxide in the regulation of forearm blood flow during exercise in normal subjects and patients with congestive heart failure.

BACKGROUND

Nitric oxide-mediated vasodilation in response to muscarinic stimulation is impaired in the peripheral circulation of patients with congestive heart failure. Whether nitric oxide-mediated vasodilation during exercise is also impaired in patients with congestive heart failure is unknown.

METHODS

Forearm blood flows (ml/min per 100 ml) were determined during rhythmic hand grip exercise at 15%, 30% and 45% of maximal voluntary contraction by venous occlusion plethysmography before and after regional inhibition of nitric oxide synthesis with administration of L-NG-monomethylarginine (L-NMMA) in the brachial artery of 17 patients with congestive heart failure (mean age 49 years, mean left ventricular ejection fraction 0.22) and 10 age-matched normal subjects.

RESULTS

Before administration of L-NMMA in the brachial artery, forearm blood flows in patients with congestive heart failure during rhythmic hand grip exercise at 15%, 30% and 45% of maximal voluntary contraction were slightly but not significantly lower than that of normal subjects ([mean +/- SE] 6.8 +/- 1.0, 8.5 +/- 1.0 and 12.9 +/- 1.7 ml/min per 100 ml, respectively, in patients with congestive heart failure vs. 6.6 +/- 1.2, 11.6 +/- 1.9 and 16.2 +/- 1.9 ml/min per 100 ml, respectively, in normal subjects, p = NS). After administration of L-NMMA in the brachial artery, forearm blood flows in normal subjects significantly decreased by 10% to 21% during hand grip exercise but did not change during exercise in patients with congestive heart failure.

CONCLUSIONS

Regional inhibition of nitric oxide synthase with administration of L-NMMA in the brachial artery significantly decreased forearm blood flows during rhythmic hand grip exercise in normal subjects but not in patients with congestive heart failure. These findings suggest that nitric oxide-mediated vasodilation during submaximal exercise is impaired in the forearm circulation of patients with congestive heart failure.

Use-dependent loss of acetylcholine- and bradykinin-mediated vasodilation after nitric oxide synthase inhibition. Evidence for preformed stores of nitric oxide-containing factors in vascular endothelial cells

In the present study, we examined the possibility that the endothelium-dependent vasodilators acetylcholine and bradykinin release preformed pools of nitric oxide-containing factors. Successive injections of selected doses of acetylcholine (1.18 +/- 0.3 micrograms/kg IV) or bradykinin (5 micrograms/kg IV) caused reproducible hypotensive and vasodilator responses within sympathetically intact and sympathetically denervated hindlimbs of conscious rats. After administration of the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 25 mumol/kg IV), the first injection of acetylcholine or bradykinin produced pronounced depressor and vasodilator responses that, in the case of bradykinin, were greater than those observed before L-NAME administration. However, each successive injection of acetylcholine and bradykinin produced progressively smaller responses, such that the later injections elicited a markedly diminished hypotension and vasodilation. This "use-dependent" loss of endothelium-dependent vasodilation was not due to the diminished vasorelaxant potency of nitric oxide-containing factors because the vasodilator effects of the nitric oxide donor sodium nitroprusside (32 micrograms/kg IV) and the S-nitrosothiol compound S-nitro-socysteine (200 nmol/kg IV) were augmented in the presence of L-NAME. These results suggest that the use-dependent loss of the hemodynamic effects of acetylcholine and bradykinin in L-NAME-treated rats may be due to the release and subsequent depletion of a factor whose synthesis depends on the bioavailability of nitric oxide. Taken together, these results suggest that preformed pools of nitric oxide-containing factors exist within the endothelium of resistance vessels and that endothelium-dependent agonists exert their vasorelaxant effects at least in part by the mobilization of these performed pools.