NG-methylarginine, an inhibitor of endothelium-derived nitric oxide synthesis, is a potent pressor agent in the guinea pig: does nitric oxide regulate blood pressure in vivo?

The impact of L-arginine-nitric oxide metabolism on ischemia/reperfusion injury

Several experimental studies have revealed that the administration of L-arginine can reduce ischemia/reperfusion injury to skeletal muscle, kidney, liver, heart and brain. Moreover, the administration of L-arginine can cause protective hemodynamic alterations. However, in situations with a stimulated inducible NOS, the administration of large amounts of L-arginine may be hazardous for the patients.

Measurement of changes in cerebral blood volume in spontaneously hypertensive rats following L-arginine infusion using dynamic susceptibility contrast MRI

To understand whether the NO-dependent vasodilator L-arginine was effective upon a chronically hypertensive cerebral capillary endothelium, dynamic susceptibility contrast MRI was used to measure the relative cerebral blood volume (rCBV) changes in nonischemic spontaneously hypertensive rats (SHRs). rCBV was measured in 11 rats at 4.7 T using fast gradient echo imaging with intravenous injection of Gd-DTPA. Images were acquired before, immediately after, and up to 90 min after the infusion of 300 mg/kg L-arginine (n = 7) or of an equivalent volume of saline (n = 4). L-arginine increased rCBV in cortex beginning 10 min after infusion and reached significance after 30 min (P < 0.01), reached a peak of 1.24 +/- 0.06 (mean +/- SEM) times pre-injection level after 50 min, and was sustained throughout the 90 min observation period. In contrast, the rCBV in the deeper gray matter (striatum) showed no statistically significant change over the 90 min observation period. While this is consistent with previous studies showing that L-arginine infusion can directly modulate vascular tone and cerebral hemodynamics, it demonstrates that the effect is present only in cortex, and that it can occur also in the setting of a disturbed capillary endothelium.

Prolonged effect of a novel S-nitrosated glyco-amino acid in endothelium-denuded rat femoral arteries: potential as a slow release nitric oxide donor drug

1. The vasodilator properties of a novel S-nitrosated glyco-amino acid (RIG200) were investigated in isolated rat femoral arteries and compared with those of the parent S-nitrosothiol compound, S-nitroso-N-acetylpenicillamine (SNAP). 2. Spectrophotometric analysis revealed that 2.5 mM solutions of RIG200 decomposed more slowly (half-life (t1/2) = 216.2 +/- 26.7 min) than SNAP (t1/2 = 37.2 +/- 13.8 min) in Krebs buffer at 24 degrees C. Furthermore, the rate of decomposition of SNAP, but not of RIG200, was significantly reduced by the Cu(I) chelator, neocuproine. We concluded that the relative stability of RIG200 is due, at least in part, to its resistance to trace Cu(I)-catalyzed decomposition. Nitric oxide (NO) generation from SNAP and RIG200 was confirmed by use of an NO electrode. 3. Experiments to investigate the vasodilator effects of RIG200 were carried out on isolated femoral arteries taken from adult male Wistar rats (400-550 g). Lengths of artery (7-8 mm long) were cannulated, dissected free and perfused at constant flow rate (0.6 ml min-1) with Krebs buffer. Vessels were precontracted with phenylephrine (10.2 +/- 0.3 microM) and developed pressures of 91.8 +/- 4 mmHg, detected upstream by a differential pressure transducer. 4. Concentration-dependent vasodilator responses to bolus injections of SNAP or RIG200 (10 microliters; 10(-8)-10(-3) M) made into the perfusate of endothelium-intact vessels were transient, recovering the preinjection pressure in < 20 min. 5. Responses to equivalent bolus injections of SNAP in endothelium-denuded vessels were also transient but those in response to concentrations of RIG200 > 10(-5) M were sustained. Responses to 10(-3) M RIG200 were sustained for periods > 4 h. Sustained vasodilatation was reversed by the NO scavenger, ferrohaemoglobin (10 microM) but was unaffected by the NO synthase inhibitor, N omega-nitro-L-arginine methyl ester (200 microM), indicating involvement of NO from a source other than NO synthase. 6. We suggest that a possible explanation for the prolonged effect of RIG200 is retention of the compound by the vascular wall, facilitated by endothelial denudation. Slow decomposition of RIG200 in situ would release sufficient NO to maintain a 'vasodilator tone' which persists for more than 4 h. Selective retention by damaged vessels could have important therapeutic implications with regard to targeted delivery of NO, restoring protection to areas deprived of endogenous NO, whilst avoiding unwanted hypotension.

Design of nitric oxide synthase inhibitors and their use to reverse hypotension associated with cancer immunotherapy

It is now just 10 years since it was first appreciated that NO is endogenously synthesized in mammals. In this period, two constitutive and one inducible isoform of NOS have been isolated, sequenced, and characterized with respect to their protein chemistry and catalytic mechanism. A wide variety of NOS inhibitors, most targeted to the arginine binding site in the oxygenase domain, have been synthesized and used to elucidate the physiological and pathophysiological roles of NO. It is now clear that NO is involved in signal transduction (e.g., in neurotransmission and blood pressure homeostasis), and that these roles are mediated by low concentrations of NO synthesized by nNOS or eNOS. The NO receptor is the heme cofactor of soluble isoform of guanylyl cyclase. Higher amounts of NO, typically but not always synthesized by iNOS, are often cytotoxic. At a minimum, high concentrations of NO derange the signal transduction pathways normally served by nNOS or eNOS. In addition, NO or its nitrosative products (RSNO, N2O3, or ONOO-) inhibit or damage cellular constituents, interfering with DNA synthesis, energy metabolism, and the structural integrity of the cell. Such cytotoxicity can be beneficial to the host if pathogens or tumor cells are destroyed, but is detrimental to the host if it results in inappropriate inflammation, hypotension, or immunosuppression. Therapeutic utility of NOS inhibitors has been demonstrated in sepsis and cytokine-induced hypotension; additional applications are being identified in a treatment of inflammatory and autoimmune disorders.

ATP-induced cochlear blood flow changes involve the nitric oxide pathway

Although control mechanisms of cochlear blood flow (CBF) have been intensively studied since laser Doppler flowmetry was introduced for CBF measurement in animals and humans, the role of adenosine 5'-triphosphate (ATP) in CBF regulation is not known. Since ATP is a potent vasoactive agent in other organs, the aim of this study is to examine ATP-induced changes in CBF and to test whether the nitric oxide pathway is involved in ATP-induced CBF changes. The anterior inferior cerebellar artery (AICA) of anesthetized pigmented guinea pigs was exposed, and ATP was perfused into the AICA. For CBF measurement, the bulla was opened and the 0.7 mm laser probe of a Perimed PF2B flowmeter was positioned on the basal turn of the cochlea. AICA perfusion of an ATP solution caused dose-dependent transient CBF increases. The maximum CBF increase induced was 220% of the baseline. In some animals, CBF showed a dual effect; a transient decrease followed by a longer-lasting increase. The perfusions of sodium nitroprusside (SNP) also resulted in dose-dependent CBF changes. The intravenous application of N(omega)-nitro-L-arginine methyl ester (L-NAME) significantly attenuated ATP-induced CBF increases, and enhanced ATP-induced decreases, but did not affect SNP-induced CBF changes. The ATP-induced CBF responses indicate that ATP plays a role in CBF regulation. The biphasic characteristic of the ATP-induced CBF change suggests the involvement of both P2x- and P2y-subtype purinoceptors. That L-NAME caused attenuation of the ATP-induced CBF increase implies that the ATP-induced CBF increase is mediated by the release of endothelium-derived relaxing factor, nitric oxide, following activation of endothelial P2y-purinoceptors in the cochlear vascular bed and/or cochlear supplying vessels.

Response of normoxic pulmonary arteries of the rat in the resting and contracted state to NO synthase blockade

1. The pulmonary vasculature is normally in a low resting state of tone. It has been hypothesized that this basal tone is actively maintained by the continuous release of a vasodilator in the resting state. However, evidence for basal release of nitric oxide (NO) is inconclusive. 2. We studied the release of NO in arteries from the pulmonary circulation of male Wistar-Kyoto rats by examining the effects of the L-arginine analogue NG-nitro-L-arginine methyl ester (L-NAME) on resting pulmonary arteries and on vessels pre-contracted with prostaglandin F2(alpha) (PGF2 alpha). 3. Rats (n = 21) were killed by an overdose with pentobarbitone. Pulmonary arteries were dissected (mean internal diameter 459 +/- 11 microns) and mounted in a small vessel wire myograph. Resting tensions were to set to stimulate transmural pressures of 17.5 mmHg. 4. L-NAME (100 microM) was found to produce a contraction of 0.64 +/- 0.09 mN mm-1 in resting pulmonary arteries when added alone to the myograph bath. This contraction was not produced following removal of the endothelium. Vessel contraction to PGF(2 alpha) (100 microM) was found to be significantly greater when carried out in the presence of L-NAME (100 microM) -1.37 +/- 0.15 mN mm-1 compared with 1.96 +/- 0.17 mN mm-1. Dilation following acetylcholine (ACh) (1 microM) was abolished in the presence of L-NAME (100 microM). 5. Rat pulmonary artery contraction in response to the addition of L-NAME and the absence of contraction upon removal of the endothelium provides supportive evidence of the active release of nitric oxide for the maintenance of resting tone.

Prolonged reduction of high blood pressure with human nitric oxide synthase gene delivery

Endothelium-derived nitric oxide (NO) in peripheral vessels has been shown to modulate vascular resistance and blood pressure. We explored the effect of a continuous supply of human endothelial NO synthase (eNOS) on the blood pressure of spontaneously hypertensive rats (SHR) by somatic gene delivery. A DNA construct containing the human eNOS gene fused to the cytomegalovirus promoter/enhancer was injected into SHR through the tail vein. A single injection of the naked eNOS plasmid DNA caused a significant reduction of systemic blood pressure for 5 to 6 weeks in SHR, and the effect continued for up to 10 to 12 weeks after a second injection. The differences were significant from 2 to 12 weeks postinjections (n=6, P<.01). In a separate experiment, L-arginine, the substrate of eNOS, was supplied in drinking water at a concentration of 7.5 g/L for 11 weeks after eNOS gene delivery. A maximal blood pressure reduction of 21 mm Hg in SHR was observed with eNOS DNA compared with that of control SHR injected with vector DNA (181.9+/-1.46 versus 202.7+/-2.79 mm Hg, mean+/-SEM, n=6, P<.01). Human eNOS gene delivery induces significant increases in urinary and aortic cGMP levels and urinary and serum nitrite/nitrate content (P<.05), while no significant differences in body weight, heart rate, water intake, food consumption, or urine excretion were observed. These results indicate that somatic delivery of the human eNOS gene induces a prolonged reduction of high blood pressure and raises the potential of using eNOS gene therapy for hypertension and cardiovascular diseases.

GTP cyclohydrolase I mRNA induction and tetrahydrobiopterin synthesis in human endothelial cells

The key role of tetrahydrobiopterin (BH4) in the synthesis of nitric oxide by human umbilical vein endothelial cells (HUVEC) has been demonstrated. We characterized the induction of BH4 synthesis in a cell line (ECV) derived from HUVEC and primary HUVEC. A significant induction of guanosine triphosphate cyclohydrolase I (GTPCH) mRNA was observed in response to TNF, IL-1beta, and IFNgamma in ECV and HUVEC. The induction of GTPCH mRNA was abolished by actinomycin D. The cytokines led to an increased accumulation of BH4 in ECV. This effect was prevented by 2,4-diamino-6-hydroxypyrimidine, a selective inhibitor of GTPCH, as well as by actinomycin D and by cycloheximide. Results provide evidence for an increase in GTPCH activity and in BH4 levels in response to immunostimulants in human endothelial cells.

HLA-DR–Mediated Signals for Hematopoiesis and Induction of Apoptosis Involve But Are Not Limited to a Nitric Oxide Pathway

Cross-linking of major histocompatibility complex (MHC) class II antigens by anti-HLA-DR monoclonal antibody (MoAb; H81.9; IgG2a) results in inhibition of hematopoiesis in canine and human models. Inhibition of hematopoiesis is associated with apoptosis in a proportion of marrow cells. Since in murine macrophages class II cross-linking triggers nitric oxide (NO) production, and NO is thought to affect regulation of hematopoiesis, we investigated whether NO was involved in our models. In murine J774 monocytes/macrophages, MoAb H81.9 did induce NO. NO production was blocked by NG-monomethyl-L-arginine (NMMA), an inhibitor of NO synthase (NOS), and by the antioxidant N-acetylcysteine (NAC). In human and canine long-term marrow cultures (LTMCs) and in enriched marrow monocytes, however, no measurable increase in NO production was noted after H81.9 exposure. Nevertheless, NAC protected LTMCs against H81.9 induced inhibition of hematopoiesis. Therefore, we determined the effect of an exogenous NO donator, sin-1 (3-morpholinosydnonimine), on canine and human LTMCs and on apoptosis. Sin-1 at concentrations ≥100 μg/mL inhibited LTMCs and induced apoptosis; at low concentrations (1 μg/mL), however, sin-1 stimulated the generation of colony-forming unit granulocyte-macrophage. Combined treatment with sin-1 at 100 μg/mL and MoAb H81.9 resulted in profound inhibition of hematopoiesis in both canine and human LTMCs, and had an additive effect on apoptosis. At 1 μg/mL sin-1 counteracted the effect of H81.9 on hematopoiesis. The effect of sin-1 on apoptosis and hematopoiesis in LTMC was largely prevented by NAC. These results are consistent with the hypothesis that HLA-DR mediated apoptosis and inhibition of hematopoiesis involve oxidative stress. However, the biphasic response of hematopoiesis to sin-1 suggests a complex regulatory network possibly related to differences in NO sensitivity of distinct subpopulations of cells. Signals in addition to NO appear to be involved in the effect of anti-HLA-DR MoAb on hematopoiesis.

The sympathetic nervous system is involved in the maintenance but not initiation of the hypertension induced by N(omega)-nitro-L-arginine methyl ester

Studies in anesthetized animals have advanced the theory that there is an important neurogenic component to the hypertension caused by pharmacological inhibition of nitric oxide, but studies in conscious animals have produced conflicting evidence for and against this theory. To try to reconcile the seemingly contradictory data, we hypothesized that the neurogenic component of this hypertension is time dependent such that the sympathetic nervous system is involved primarily in the maintenance, rather than the initiation, of the hypertension. We measured intra-arterial pressure in conscious, unrestrained rats with and without guanethidine-induced sympathectomy during varying durations of intravenous N(omega)-nitro-L-arginine methyl ester (L-NAME). The major new finding is that sympathectomy had no effect on the hypertensive response to bolus injections of L-NAME but in the same rats it produced a greater than 50% attenuation in the hypertension seen after 6 days of continuous L-NAME (change in mean arterial pressure, 23+/-4 versus 55+/-4 mm Hg, P<.01, sympathectomy versus control). Using 8-hour infusions of L-NAME, we found that 60 minutes was the minimum time required for detecting a sympathectomy-sensitive component of L-NAME-induced hypertension. Furthermore, we demonstrate that the magnitude of this component increases further between 8 hours to 6 days of continuous L-NAME: it accounted for only 18% of the total hypertensive response at 8 hours but 61% after 6 days. From these experiments, we conclude that the importance of the sympathetic system in the pathogenesis of L-NAME-induced hypertension accrues slowly over hours and days, and thus its importance can be overlooked by focusing on the initial phase of the hypertension.

HLA-DR–Mediated Signals for Hematopoiesis and Induction of Apoptosis Involve But Are Not Limited to a Nitric Oxide Pathway

Cross-linking of major histocompatibility complex (MHC) class II antigens by anti-HLA-DR monoclonal antibody (MoAb; H81.9; IgG2a) results in inhibition of hematopoiesis in canine and human models. Inhibition of hematopoiesis is associated with apoptosis in a proportion of marrow cells. Since in murine macrophages class II cross-linking triggers nitric oxide (NO) production, and NO is thought to affect regulation of hematopoiesis, we investigated whether NO was involved in our models. In murine J774 monocytes/macrophages, MoAb H81.9 did induce NO. NO production was blocked by NG-monomethyl-L-arginine (NMMA), an inhibitor of NO synthase (NOS), and by the antioxidant N-acetylcysteine (NAC). In human and canine long-term marrow cultures (LTMCs) and in enriched marrow monocytes, however, no measurable increase in NO production was noted after H81.9 exposure. Nevertheless, NAC protected LTMCs against H81.9 induced inhibition of hematopoiesis. Therefore, we determined the effect of an exogenous NO donator, sin-1 (3-morpholinosydnonimine), on canine and human LTMCs and on apoptosis. Sin-1 at concentrations ≥100 μg/mL inhibited LTMCs and induced apoptosis; at low concentrations (1 μg/mL), however, sin-1 stimulated the generation of colony-forming unit granulocyte-macrophage. Combined treatment with sin-1 at 100 μg/mL and MoAb H81.9 resulted in profound inhibition of hematopoiesis in both canine and human LTMCs, and had an additive effect on apoptosis. At 1 μg/mL sin-1 counteracted the effect of H81.9 on hematopoiesis. The effect of sin-1 on apoptosis and hematopoiesis in LTMC was largely prevented by NAC. These results are consistent with the hypothesis that HLA-DR mediated apoptosis and inhibition of hematopoiesis involve oxidative stress. However, the biphasic response of hematopoiesis to sin-1 suggests a complex regulatory network possibly related to differences in NO sensitivity of distinct subpopulations of cells. Signals in addition to NO appear to be involved in the effect of anti-HLA-DR MoAb on hematopoiesis.

Measurements of total plasma nitrite and nitrate in pediatric patients with the systemic inflammatory response syndrome

OBJECTIVES

The systemic inflammatory response syndrome (SIRS) is typified by the presence of fever, hemodynamic changes, and end organ dysfunction. Endothelial cell activation leads to overproduction of nitric oxide, which results in sustained vasodilation and hypotension. This study was undertaken to determine the sensitivity, specificity, and positive and negative predictive values of plasma nitrite/nitrate measurements in identifying patients with clinical characteristics of SIRS, as defined by criteria based on physician diagnosis.

DESIGN

Prospective cohort study with consecutive sampling of patients.

SETTING

Tertiary, multidisciplinary, pediatric intensive care unit (ICU) at Children's Hospital of Wisconsin.

PATIENTS

Patients were divided into five groups. There were 16 pediatric controls undergoing elective surgery and 177 pediatric ICU patients without and 46 pediatric ICU patients with physician-diagnosed sepsis, septic shock, SIRS, or sepsis syndrome documented in the medical record (all considered physician-diagnosed sepsis). The 223 pediatric ICU patients included 195 pediatric ICU patients not meeting and 28 pediatric ICU patients meeting predetermined physiologic criteria for SIRS (considered criteria-based sepsis).

INTERVENTIONS

Blood samples were obtained for quantitative nitrite/nitrate analysis at the time of admission to the pediatric ICU and daily until discharge.

MEASUREMENTS AND MAIN RESULTS

Mean plasma nitrite/nitrate concentrations in the controls were 34.5 +/- 12 microM (95th percentile 54 microM). In pediatric ICU patients without and with physician-diagnosed sepsis, mean plasma nitrite/nitrate concentrations were 39 +/- 24 microM (p > .05 compared with controls) and 127 +/- 91 microM (p < .0001 compared with both controls and patients without physician-diagnosed sepsis), respectively. In pediatric ICU patients without and with criteria-based sepsis, the mean total plasma nitrite/nitrate concentrations were 56 +/- 59 microM (p = .008 compared with controls) and 80 +/- 64 microM (p = .003 compared with patients without criteria-based sepsis), respectively. The ability of plasma nitrite/nitrate > 54 microM to identify patients with physician-diagnosed sepsis is characterized as follows: 87% sensitivity, 77% specificity, 50% positive predictive value, and 96% negative predictive value. The ability of plasma nitrite/nitrate > 54 microM to identify patients with criteria-based sepsis is characterized as follows: 61% sensitivity, 68% specificity, 21% positive predictive value, and 92% negative predictive value.

CONCLUSIONS

Clinical diagnosis of SIRS is strongly associated with increased total plasma nitrite/nitrate concentrations in pediatric patients in the pediatric ICU. Many patients with increased nitrite/nitrate concentrations have inflammation without having a clinical diagnosis of SIRS. Our data suggest that increased plasma nitrite/nitrate concentrations are the standard for identifying patients with inflammation in the pediatric ICU.

Improvement of cardiac output and liver blood flow and reduction of pulmonary vascular resistance by intravenous infusion of L-arginine during the early reperfusion period in pig liver transplantation

BACKGROUND

The release of liver arginase after orthotopic liver transplantation (OLT) causes a deficiency of L-arginine and nitrite in the plasma. This deficiency is possibly related to pulmonary hypertension and reduced hepatic blood flow, which are commonly observed in the immediate reperfusion period. The aim of this study was to evaluate the impact of L-arginine supplementation on metabolic and hemodynamic parameters during liver reperfusion after OLT in pigs.

METHODS

Thirteen pig OLTs (control group, n=6; arginine group, n=7) were performed by a standard technique. Cold ischemic time was 20 hr. L-Arginine was infused at a dosage of 500 mg/kg body weight into the donor pigs (30 min before liver explantation) and also into the recipients (over a period of 3 hr from the beginning of the reperfusion period). At the end of the experimental study, the pigs were killed with an overdose of potassium.

RESULTS

In the control group, liver revascularization increased plasma arginase concentrations (+615%) and reduced plasma levels of L-arginine (-87%), nitrite (-82%), and nitrate (-53%). Infusion of L-arginine increased plasma levels of L-arginine from 94+/-21 micromol/L to 1674+/-252 micromol/L (P<0.001), L-ornithine from 46+/-8 micromol/L to 2215+/-465 micromol/L (P<0.001), and L-citrulline from 58+/-8 micromol/L to 116+/-34 micromol/L (P<0.001), but had no effect on plasma levels of nitrite and nitrate. Administration of L-arginine in the donor pigs did not produce any systemic or organ-specific hemodynamic alterations. Infusion of L-arginine into the recipient pigs improved cardiac performance (increase in heart rate [+61%, P=0.017] and cardiac index [+53%, P=0.005], reduction in pulmonary capillary wedge pressure [-54%, P=0.014]). Moreover L-arginine infusion increased oxygen consumption (+65%, P=0.003), reduced pulmonary vascular resistance index (P=0.001), stimulated portal venous blood flow (P=0.014), and elevated body temperature during the reperfusion period (P=0.007).

CONCLUSIONS

From these data, we conclude that the infusion of L-arginine during OLT improves the hemodynamic performance of the heart, lung, and liver.

Roles of nitric oxide and adenosine in the regulation of coronary conductance in the basal state and during reactive hyperemia

Nitric oxide (NO) and adenosine are important mediators in the regulation of coronary vascular tone and are released into the interstitium from the vascular endothelium and myocardium, respectively. The roles of these autacoids in the regulation of coronary flow in the basal and reactive hyperemic states were examined in Langendorff rabbit hearts perfused with oxygenated Krebs-Henseleit solution at 37 degrees C and 110 mmHg pressure. Instantaneous perfusion pressure-flow relationships were analyzed to derive coronary conductance both in the basal state and during the early phase of reperfusion (hyperemic state). N omega-nitro-L-arginine methyl ester (L-NAME) at increasing concentrations (10(-6) to 10(-4) mol/L) (n = 7) and 8-phenyltheophylline (8-PT) at increasing concentrations (10(-9) to 10(-6) mol/L) (n = 7) were applied to assess the role of NO and adenosine, respectively. L-NAME dose-dependently reduced the coronary conductance in both the basal and early hyperemic states, while 8-PT dose-dependently reduced conductance only in the hyperemic state. Changes in conductance during the early hyperemic phase correlated well with changes in the debt repayment ratio for either L-NAME (r = 0.94) or 8-PT (r = 0.99). These data suggest that a flow-related NO release mechanism regulates the coronary conductance in both the basal and hyperemic states while the metabolic regulation of adenosine release plays a role in the presence of ischemia.

Quinapril prevents hypertension and enhanced vascular reactivity in nitroarginine-treated rats

Long-term inhibition of nitric oxide synthase (NOS) by substituted arginine analogues has previously been shown to induce systemic hypertension in several animal species; however, the precise mechanisms for the elevated blood pressure remain unclear. We hypothesized that a portion of the hypertensive response to arginine analogues was due to direct inhibition of endothelial NOS and resultant functional alterations in the vasculature that contribute to elevated systemic resistance. Adult Sprague-Dawley rats were treated for 2 weeks with an arginine analogue, N omega Nitro-L-arginine (L-NNA), alone or in combination with the angiotensin converting enzyme (ACE) inhibitor quinapril. Next, thoracic aortas were removed, cut into rings and suspended in isolated tissue baths for measurement of contractile force in response to vasoactive drugs. Our results showed that oral L-NNA treatment significantly elevated systolic blood pressure in rats that was completely prevented by quinapril. Furthermore, L-NNA treatment increased endothelium-dependent and -independent contractility and attenuated endothelium-dependent vasodilation in the thoracic aorta. These functional alterations were also attenuated by quinapril treatment. Therefore, long-term L-NNA-induced hypertension in rats is associated with enhanced vascular reactivity due both to direct inhibition of endothelial NOS and to stimulation of the renin-angiotensin system.

Inhibition of endothelial cell amino acid transport System y+ by arginine analogs that inhibit nitric oxide synthase

A variety of N omega-monosubstituted L-arginine analogs are established inhibitors of nitric oxide synthase; in all cases, initial binding is competitive with the substrate L-arginine. The efficacy of such compounds in vivo will depend on their transport into the relevant nitric oxide synthase-containing cells; in fact, inhibition may actually be augmented if cellular uptake of L-arginine is also blocked by the analogs. Because vascular endothelial cells synthesize vasoactive nitric oxide under both physiological and pathophysiological conditions, we have performed inhibition analyses with novel arginine analogs to determine the substrate specificity of the primary L-arginine transport system. Na(+)-independent System y+, present in porcine pulmonary artery endothelial cells. As reported by others, no Na(+)-independent System bo,+ activity was detectable. For System y+. Dixon plots suggest competitive inhibition and apparent Ki values, which ranged between 0.1 and 0.8 mM, estimated for each inhibitor. Some influence of amino acid side chain structure could be detected, but in general, the data establish that this transport system accepts a broad range of arginine derivatives. Loading the cells with individual arginine analogs resulted in trans-stimulation of arginine uptake suggesting that they serve as substrates of System y+ as well as inhibitors. These results indicate that plasma membrane transport is unlikely to be a limiting factor in drug development for nitric oxide synthase inhibitors.

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.

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.

Endothelium-independent relaxation of aortic rings by the nitric oxide synthase inhibitor diphenyleneiodonium

1. The flavoprotein binder diphenyleneiodonium (DPI) is a potent, irreversible inhibitor of nitric oxide synthase (NOS), but produces only a transient pressor response following systemic administration to animals, despite evidence of persistent NOS inhibition. To characterize further the effects of DPI on vascular tone, isometric tension was recorded from rat isolated aortic rings mounted between steel wires in an organ bath. 2. The NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 1 mM) initiated an additional contraction of prostaglandin F2 alpha-preconstricted rings with endothelium which was sustained throughout the period of L-NAME exposure (+234 +/- 39% at 15 min). In contrast, addition of DPI (5 microM) to rings with endothelium produced a transient initial contraction (+111 +/- 27% at 2 min) followed by a more sustained relaxation (-27 +/- 19% at 15 min, P < 0.001 vs L-NAME). 3. The contraction to DPI was also observed in rings without endothelium, was abolished by L-NAME pretreatment, and was unaffected by the alpha-adrenoreceptor inhibitor prazosin. Relaxation in response to DPI was not inhibited by endothelium removal or by pretreatment with either L-NAME or with the ATP-sensitive potassium channel blocker glibenclamide. 4. The endothelium-independent relaxation to DPI was inhibited at 23 degrees C and its time course was delayed by pretreatment with the guanylate cyclase inhibitor methylene blue. 5. Thus, in addition to a transient initial contraction due to NOS inhibition, DPI produces an endothelium-independent, temperature-dependent relaxation which appears in part due to activation of guanylate cyclase. This relaxant effect of DPI may explain the transient nature of its pressor effect in vivo despite sustained NOS inhibition.

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.

The effects of high dose NG-nitro-L-arginine-methyl ester on myocardial blood flow and left ventricular function in dogs

PURPOSE

Nitric oxide (NO) synthase inhibition has been reported to cause elevation in mean arterial pressure (MAP) and a decrease in cardiac index (CI), the cause of which is not completely understood. It has been shown that increased concentrations of NO synthase inhibitors cause a further drop in cardiac output without a corresponding increase in arterial pressure, prompting the conclusion that NO inhibition results in direct myocardial depression. However, myocardial ischemia was not completely ruled out as a cause for myocardial dysfunction in these studies. The purpose of this study was to examine the effects of 30 mg/kg of the NO synthase inhibitor NG-nitro-L-arginine-methyl ester (L-NAME) to those of 300 mg/kg and assess the effects on coronary ischemia and myocardial function.

MATERIALS AND METHODS

Eight anesthetized dogs underwent median sternotomy and pericardiectomy. L-NAME 30 mg/kg was administered and the effects were recorded at 5, 15, and 30 minutes. Thereafter, 300 mg/kg was administered and the effects were observed for 5, 15, and 30 minutes. We measured MAP, heart rate (HR), CI, left ventricle (LV) and systolic and diastolic pressures, the first derivative of LV pressure (dP/dt), left anterior descending artery blood flow, regional LV contraction, gas tensions, and lactates. A coronary sinus catheter allowed for measurements of coronary sinus pressure, lactate, and gas tensions. Stroke volume, percent myocardial shortening (dL/dt) myocardial oxygen consumption, and net lactate myocardial production were calculated.

RESULTS

Whereas 30 mg/kg had minimal effects on coronary blood flow and LV function, 300 mg/kg resulted in profound hypotension, drop in CI, and acidocsis.

CONCLUSIONS

L-NAME at 30 mg/kg caused a rise in MAP and systemic vascular resistance; however, it had no effect on ventricular function. High dose NO synthase inhibition causes myocardial depression not related to increased afterload, coronary vasoconstriction, or myocardial ischemia.

Elevated blood pressures in mice lacking endothelial nitric oxide synthase

Nitric oxide produced in endothelial cells affects vascular tone. To investigate the role of endothelial nitric oxide synthase (eNOS) in blood pressure regulation, we have generated mice heterozygous (+/-) or homozygous (-/-) for disruption of the eNOS gene. Immunohistochemical staining with anti-eNOS antibodies showed reduced amounts of eNOS protein in +/- mice and absence of eNOS protein in -/- mutant mice. Male or female mice of all three eNOS genotypes were indistinguishable in general appearance and histology, except that -/- mice had lower body weights than +/+ or +/- mice. Blood pressures tended to be increased (by approximately 4 mmHg) in +/- mice compared with +/+, while -/- mice had a significant increase in pressure compared with +/+ mice (approximately 18 mmHg) or +/- mice (approximately 14 mmHg). Plasma renin concentration in the -/- mice was nearly twice that of +/+ mice, although kidney renin mRNA was modestly decreased in the -/- mice. Heart rates in the -/- mice were significantly lower than in +/- or +/+ mice. Appropriate genetic controls show that these phenotypes in F2 mice are due to the eNOS mutation and are not due to sequences that might differ between the two parental strains (129 and C57BL/6J) and are linked either to the eNOS locus or to an unlinked chromosomal region containing the renin locus. Thus eNOS is essential for maintenance of normal blood pressures and heart rates. Comparisons between the current eNOS mutant mice and previously generated inducible nitric oxide synthase mutants showed that homozygous mutants for the latter differ in having unaltered blood pressures and heart rates; both are susceptible to lipopolysaccharide-induced death.

Cardiovascular effects of an ultra-short-acting nitric oxide-releasing compound, zwitterionic diamine/NO adduct, in dogs

BACKGROUND

This study was conducted to clarify the cardiovascular effects of a new NO-releasing compound, NOC-7, and to compare it with other nitrovasodilators, sodium nitroprusside (SNP) and nitroglycerin, in dogs anesthetized with pentobarbital.

METHODS AND RESULTS

A bolus injection of NOC-7 decreased mean aortic blood pressure in a dose-dependent manner. The onset was rapid and the recovery quick. Continuous infusion of NOC-7 decreased mean aortic pressure from 115 +/- 3.9 to 84 +/- 2.9 mm Hg and infusion of SNP, from 118 +/- 3.8 to 87 +/- 3.1 mm Hg. The optimum doses of NOC-7 and SNP were determined to be 2.73 +/- 0.77 and 11.5 +/- 6.1 micrograms.kg-1.min-1, respectively. During infusion of NOC-7, heart rate and cardiac output were increased (P < .05), pulmonary artery pressure was not changed, and systemic and pulmonary vascular resistances were decreased (P < .05). Electromagnetic flowmetry showed that portal venous and internal carotid arterial blood flow were increased (P < .05) and that hepatic and renal arterial blood flows were not changed. These hemodynamic changes during NOC-7 infusion were similar to those with SNP. The plasma level of NO2-/NO3 did not change, but methemoglobin increased slightly (P < .05). Comparison between hypotensive responses before and after a 3.5-hour infusion of NOC-7 or nitroglycerin showed that acute tolerance developed to nitroglycerin but not to NOC-7.

CONCLUSIONS

The results indicate that NOC-7 may be useful as an ultra-short-acting nitrovasodilator that has no major adverse effect or tolerance.

Flow dependence of nitric oxide-mediated pressure change in rat mesenteric beds with different tonus

To investigate the flow-dependent contribution of basally released nitric oxide (NO) to vascular perfusion pressure, we compared the effects of a NO synthesis inhibitor on the pressure changes in some models of rate mesenteric vascular beds. Spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats (13-14-weeks-old) were used. The perfusion pressure at each flow rate was slightly higher in the SHR bed than in the WKY bed when no contractile compounds were applied. NG-Monomethyl-L-arginine (L-NMMA) significantly increased the pressure in WKY at flow rates more than 5 ml/min (8.9 mm Hg at 7 ml/min). L-NMMA increased the pressure in SHR at flow rates of 2-7 ml/min (40.2 mm Hg at 7 ml/min). L-NMMA markedly increased the pressure at each flow rate in both beds which methoxamine (30 microM) had constricted. The effects of L-NMMA were concentration-dependent, and were blocked by L-arginine. Therefore, basal NO release appears to contribute to the vasolidating tone although flow dependence of the effect is different in the absence or presence of an exogeneous tone in both hypertensive and normotensive rats.

Neural mechanism of pressor action of nitric oxide synthase inhibitor in anesthetized monkeys

Intravenous injection of NG-nitro-L-arginine (L-NA), a nitric oxide synthase inhibitor, elevated mean blood pressure by 29.0 +/- 4.9 mm Hg and decreased heart rate by 40.7 +/- 5.6 beats per minute in anesthetized Japanese monkeys (n = 6), whereas NG-nitro-D-arginine was without effect. After pretreatment with pentolinium, the magnitude of the pressure elevation by L-NA was significantly less than that after pretreatment with phentol-amine. The reduced blood pressure by either of the pretreatment drugs was compensated to control levels by a continuous infusion of angiotensin II before L-NA administration. Isolated monkey distal mesenteric arteries (150 to 200 microns OD) without endothelium responded to nerve stimulation by nicotine with a contraction, which was abolished by prazosin alone or in combination with alpha, beta-methylene ATP. In the strips thus treated and contracted with prostaglandin F2 alpha, nicotine caused a relaxation that L-NA abolished. L-NA but not NG-nitro-D-arginine reversed the inhibition. Histochemical staining of NADPH diaphorase, considered to be identical to nitric oxide synthase in neuronal tissues, demonstrated that positively stained nerve fibers were consistently present in the adventitia of monkey distal mesenteric arteries and arterioles. These results strongly suggest that nitroxidergic vasodilator nerves innervate peripheral small arteries and arterioles in the monkey and that these nerves participate in the regulation of systemic blood pressure. High blood pressure caused by nitric oxide synthase inhibitors is associated with an elimination of nitroxidergic nerve function together with an impairment of the basal release of nitric oxide from the endothelium.

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.

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.

Use-dependent loss of active sympathetic neurogenic vasodilation after nitric oxide synthase inhibition in conscious rats. Evidence for the presence of preformed stores of nitric oxide-containing factors

In this study, we examined whether air-jet stress-induced active sympathetic hindlimb vasodilation in conscious rats involves the release of preformed stores of nitric oxide-containing factors. We determined the effects of repeated episodes of air-jet stress (six episodes given 5 minutes apart) on mean arterial pressure and vascular resistances in the mesenteric bed and intact and sympathetically denervated hindlimb beds of conscious rats treated with saline or the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 25 mumol/kg IV). In saline-treated rats, air-jet stress produced alerting behavior, minor changes in blood pressure, pronounced mesenteric vaso-constriction, and immediate and marked vasodilation in the sympathetically intact hindlimb but a minor vasodilation in the sympathetically denervated hindlimb. Each air-jet stress produced virtually identical responses. In L-NAME-treated rats, the first air-jet stress produced vasodilator responses in the sympathetically intact and sympathetically denervated hindlimbs that were similar to those in the saline-treated rats. However, each subsequent air-jet stress produced progressively smaller vasodilator responses in the sympathetically intact but not the sympathetically denervated hindlimb. There was no loss of air-jet stress-induced alerting behavior or mesenteric vasoconstriction, suggesting that L-NAME did not interfere with the central processing of the air-jet or the resultant changes in autonomic nerve activity. The progressive diminution of air-jet stress-induced vasodilation in the intact hindlimb of L-NAME-treated rats may be due to the use-dependent depletion of preformed stores of nitric oxide-containing factors that cannot be replenished in the absence of nitric oxide synthesis.

Inhibition of nitric oxide synthase by 1-(2-trifluoromethylphenyl) imidazole (TRIM) in vitro: antinociceptive and cardiovascular effects

1. The ability of a range of substituted imidazole compounds to inhibit mouse cerebellar neuronal nitric oxide synthase (nNOS), bovine aortic endothelial NOS (eNOS) and inducible NOS (iNOS) from lungs of endotoxin-pretreated rats was investigated. In each case the substrate (L-arginine) concentration employed was 120 nM. 2. 1-(2-Trifluoromethylphenyl) imidazole (TRIM) was a relatively potent inhibitor of nNOS and iNOS (IC50S of 28.2 microM and 27.0 microM respectively) but was a relatively weak inhibitor of eNOS (IC50, 1057.5 microM). The parent compound, imidazole, was a weak inhibitor of all three NOS isoforms (IC50S: nNOS, 290.6 microM; eNOS, 101.3 microM; iNOS, 616.0 microM). Substitution of imidazole with a phenyl group to yield I-phenylimidazole (PI) resulted in an isoform non-selective increase in inhibitory potency (IC50S: nNOS, 72.1 microM; eNOS, 86.9 microM; iNOS, 53.9 microM). Further substitution of the attached phenyl group resulted in an increase in nNOS and a decrease in eNOS inhibitory potency as in TRIM, 1-chlorophenylimidazole (CPI; IC50S: nNOS, 43.4 microM; eNOS, 392.3 microM; iNOS, 786.5 microM) and 1-(2,3,5,6-tetrafluorophenyl) imidazole (TETRA-FPI; IC50S; nNOS, 56.3 microM; eNOS, 559.6 microM; iNOS, 202.4 microM). 3. The ability of TRIM to inhibit mouse cerebellar nNOS activity in vitro was influenced by the concentration of L-arginine (0.12-10.0 microM) in the incubation medium. When mouse cerebellar nNOS was used as enzyme source a double reciprocal (Lineweaver-Burk) plot in the presence/absence of TRIM (50 microM) revealed a competitive inhibitory profile. The K(m) for L-arginine and the Ki for TRIM calculated from these data were 2.4 microM and 21.7 microM, respectively. The ability of TRIM to inhibit mouse cerebellar nNOS activity in vitro was unaffected by varying the time of exposure of the enzyme to TRIM from 0-60 min at 0 degree C. 4. TRIM exhibits potent antinociceptive activity in the mouse as evidenced by inhibition of acetic acid induced abdominal constrictions. The ED50 for TRIM following i.p. administration was 20 mg kg-1 (94.5 mumol kg-1). The antinociceptive effect of TRIM was reversed by pretreatment of animals with L-arginine (50 mg kg-1, i.p.) and was not accompanied by sedation, motor ataxia or behavioural changes (rearing, crossing, circling, dipping) as assessed by use of a box maze procedure. 5. L-NG nitro arginine methyl ester (L-NAME, 20 mg kg-1, i.v.) but not TRIM (0.5-20 mg kg-1, i.v.) increased mean arterial blood pressure (MAP) in the urethane-anaesthetized rat. 6. L-NAME (100 microM) potentiated the contractile response of the rabbit isolated aorta to phenylephrine (ED50; 0.084 +/- 0.01 microM in the presence and 0.25 +/- 0.05 microM in the absence of L-NAME; maximum response, 7.7 +/- 0.4 g in the presence and 5.6 +/- 0.5 g in the absence of L-NAME, n = 6, (P < 0.05) whilst TRIM (1-100 microM) was without effect. L-NAME (100 microM) but not TRIM (1-100 microM) also reduced carbachol-induced relaxation of the phenylephrine-precontracted rabbit aorta preparation. 7. L-NAME (50 microM) potentiated the vasoconstrictor effect of bolus-injected noradrenaline (10-1000 nmol) and reduced the vasodilator effect of carbachol (10 microM) added to the Krebs reservoir in the rat perfused mesentery preparation. L-NAME (50 microM) also reduced nitric oxide (NO) release (measured by chemiluminescence of nitrite in the Krebs perfusate) in response to noradrenaline (100 nmol; 53.8 +/- 4.0 pmol ml-1 in the presence and 84.8 +/- 8.0 pmol ml-1 in the absence of L-NAME, n = 15, P < 0.05) and carbachol (10 microM; 63.9 +/- 5.0 pmol ml-1 in the presence and 154.0 +/- 9.0 pmol ml-1 in the absence of L-NAME, n = 15, P < 0.05). TRIM (50 microM) did not affect either the vasoconstrictor response to noradrenaline or the vasodilator response to carbachol or the accompanying release of NO from the perfused rat mesentery.

Coronary and systemic hemodynamic effects of sustained inhibition of nitric oxide synthesis in conscious dogs. Evidence for cross talk between nitric oxide and cyclooxygenase in coronary vessels

Sustained inhibition of NO synthesis (N omega-nitro-L-arginine [L-NNA], 20 mg.kg-1.d-1, 7 days) was investigated at rest and during exercise in conscious dogs. At rest, L-NNA did not alter mean arterial blood pressure but markedly increased total peripheral resistance (+73 +/- 14%, P < .01). Exaggerated hypertension was observed during exercise (+132 +/- 5 mm Hg after L-NNA versus +113 +/- 5 mm Hg before L-NNA, P < .01). L-NNA decreased the resting coronary artery diameter by 6 +/- 1% and suppressed its exercise-induced dilation but had no effect on coronary blood flow and resistance. L-NNA decreased flow repayment volumes during reactive hyperemia, but corresponding flow debt volumes remained unchanged. The cyclooxygenase inhibitor diclofenac (10 mg/kg) had no effect on reactive hyperemia parameters before L-NNA but reduced flow repayment volumes, durations, and corresponding debt-to-repayment ratios in L-NNA-treated dogs (all P < .05). In vitro, indomethacin blunted the residual relaxation to bradykinin of large coronary arteries taken from L-NNA-treated, but not from control, dogs. Bradykinin-induced increase in 6-ketoprostaglandin F1 alpha production was greater in coronary arteries taken from L-NNA-treated dogs (+ 179 +/- 41 pg/mm2) than from control dogs (+ 66 +/- 18 pg/mm2) (P < .05). These results indicate that (1) NO is of major importance in the control of systemic but not coronary resistance vessels at rest and during exercise, and (2) after L-NNA, the cyclooxygenase pathway is involved in myocardial reactive hyperemia and in the residual relaxation to bradykinin of isolated coronary arteries. Thus, in conscious dogs, the cyclooxygenase pathway might act as a protective mechanism of the coronary circulation when endothelial nitric oxide synthesis is altered.

Downregulation of nitrovasodilator-induced cyclic GMP accumulation in cells exposed to endotoxin or interleukin-1 beta

1. Induction of nitric oxide synthase (iNOS) results in overproduction of nitric oxide (NO), which may be a principal cause of the massive vasodilatation and hypotension observed in septic shock. Since NO-induced vasorelaxation is mediated via the soluble isoform of guanylate cyclase (sGC), the regulation of sGC activity during shock is of obvious importance, but yet poorly understood. The aim of the present study was to investigate the activation of sGC by sodium nitroprusside (SNP) before and after exposure of rat aortic smooth muscle cells to endotoxin (LPS) or interleukin-1 beta (IL-1 beta). 2. Exposure of rat aortic smooth muscle cells to SNP (10 microM) elicited up to 200 fold increases in cyclic GMP. This effect was attenuated by 30-70% in IL-1 beta- or LPS-pretreated cells, in a pretreatment time-and IL-1 beta- or LPS-concentration-dependent manner. When, however, cells were exposed to IL-1 beta or LPS and then stimulated with the particulate guanylate cyclase activator, atriopeptin II, no reduction in cyclic GMP accumulation was observed. 3. Pretreatment of rats with LPS (5 mg kg-1, i.v.) for 6 h led to a decrease in aortic ring SNP-induced cyclic GMP accumulation. 4. The IL-1 beta-induced reduction in SNP-stimulated cyclic GMP accumulation in cultured cells was dependent on NO production, as arginine depletion abolished the downregulation of cyclic GMP accumulation in response to SNP. 5. Reverse-transcriptase-polymerase chain reaction analysis revealed that the ratio of steady state mRNA for the alpha, subunit of sGC to glyceraldehyde phosphate dehydrogenase was decreased in LPS- or IL-1 beta-treated cells, as compared to vehicle-treated cells. 6. Protein levels of the alpha 1 sGC subunit remained unaltered upon exposure to LPS or IL-1 beta, suggesting that the early decreased cyclic GMP accumulation in IL-1 beta- or LPS-pretreated cells was probably due to reduced sGC activation. Thus, the observed decreased responsiveness of sGC to NO stimulation following cytokine or LPS challenge may represent an important homeostatic mechanism to offset the extensive vasodilatation seen in sepsis.

Intrathecal infusion of the nitric oxide synthase inhibitor N-methyl L-arginine after experimental spinal cord injury in guinea pigs

The potential role of nitric oxide (NO) production in secondary pathologic processes that follow spinal cord injury was examined in a guinea pig model that shows secondary loss of function for at least 3 days after trauma. Lateral compression injury of the lower thoracic cord was performed under ketamine/xylazine/acepromazine anesthesia. A fine polyethylene cannula was inserted through an incision in the dura rostral to the injury and run along the dorsal subdural space to the lesion level. The tube was connected to an osmotic pump delivering 1 microL/h of a 10 mM solution of either N-methyl-L-arginine or N-methyl-D-arginine in normal saline (pH 7.2). N-Methyl-L-arginine blocks both constitutive and inducible forms of NO synthase (NOS), present in neurons and inflammatory cells, respectively: N-methyl-D-arginine is the inactive stereoisomer. Two groups of 10 animals were used. Behavioral analysis and somatosensory evoked potential measurements were performed daily for 3 days, then the animals were fixed and survival of white matter at the center of the injury was evaluated, using toluidine-blue stained, 1 microns plastic sections. No significant difference was found between treated and control groups in degree or rate of secondary loss of spinal cord function or in the cross-sectional area of surviving white matter. These data do not support the hypothesis that local NO production by phagocytes, neurons, or other cells plays a significant role in secondary pathology of injury in this model.

The heart rate after inhibition of nitric oxide release in the anaesthetized dog

1. The effect of nitric oxide (NO) inhibition on heart rate was studied in anaesthetized vagotomized dogs. 2. The effect of changes of baroreceptor stimulation was prevented using an arterial pressure reservoir. 3. After NO-inhibitor (Nitro-L-arginine), heart rate decreased by 8% in spite of an unchanged pressure. 4. When upstream pressure was increased by constriction of the descending aorta, heart rate decreased by 4% before and after inhibition. Owing to the vagotomy this decrease was attributed to a sympathetic tone reduction following baroreceptor stimulation. 5. The results show that NO-inhibition reduces heart rate independently of an increased baroreceptor stimulation and does not reduce the basal sympathetic control on the sinus-atrial node.

Stimulation of lumbar sympathetic nerves may produce hindlimb vasodilation via the release of pre-formed stores of nitrosyl factors

The physiological activation of lumbar sympathetic nerves by air-jet stress produces a hindlimb vasodilation in conscious rats. Although the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester markedly reduces the duration of this air-jet stress-induced vasodilation, it does not prevent the initial fall in resistance. These data suggest that the vasodilation is initiated by the release of an as yet unidentified factor, whereas the vasodilation is sustained by the release of nitric oxide or newly synthesized nitrosyl factors such as S-nitrosothiols. At present, the possibility that neurogenic vasodilation may be initiated by the release of pre-formed pools of nitrosyl factors from storage sites within the hindlimb vasculature has not been addressed. We reasoned that if nitrosyl factors do exist in storage pools, then we should be able to demonstrate a "use-dependent" loss of vasodilation after nitric oxide synthesis inhibition which would be the result of a gradual depletion of the releasable pools of these nitrosyl factors. In the present study, we examined the effects of repeated episodes of direct electrical stimulation of the lumbar sympathetic chain on ipsilateral hindlimb vascular resistance in pentobarbital-anesthetized rats prior to and following administration of the nitric oxide synthesis inhibitors N(G)-nitro-L-arginine methyl ester (10, 25 or 100 mumol/kg i.v.) or N(G)-nitro-L-arginine (50 mumol/kg i.v.). Three episodes of electrical stimulation of 3.2 +/- 0.4 V (20 Hz, 5 ms duration, 5 ms delay for 10 s given 5 min apart) produced pronounced and reproducible reductions in hindlimb vascular resistance in the ipsilateral hindlimb (-56 +/- 5%, -55 +/- 5% and -53 +/- 6%, respectively), but no changes in mean arterial pressure. Three episodes of electrical stimulation at 4.8 +/- 0.4 V also caused reproducible decreases in hindlimb resistance (-59 +/- 7%, -61 +/- 9% and -64 +/- 12%) and minor but reproducible decreases in blood pressure. The vasodilation produced by the first electrical stimulation at 3.2 +/- 0.4 V was completely abolished by a 25 mumol/kg dose of N(G)-nitro-L-arginine methyl ester (-11 +/- 9%). The initial episode of electrical stimulation at 4.8 +/- 0.4 V produced a pronounced fall in ipsilateral hindlimb resistance in the N(G)-nitro-L-arginine methyl ester-treated animals whereas the second and third stimulations produced progressively smaller vasodilations (-55 +/- 4%, -34 +/- 3% and -19 +/- 2%, respectively). The 10 mumol/kg dose of N(G)-nitro-L-arginine methyl ester was not effective whereas the 100 mumol/kg dose produced similar effects as the 25 mumol/kg dose. The 50 mumol/kg dose of N(G)-nitro-L-arginine produced similar effects as the higher doses of N(G)-nitro-L-arginine methyl ester. Those results suggest that lower intensity electrical stimulation of the lumbar sympathetic nerves produces vasodilation via the release of nitric oxide or newly synthesized nitrosyl factors such as S-nitrosothiols. In contrast, the vasodilation produced by higher intensity electrical stimulation may involve the mobilization and release of pre-formed pools of nitrosyl factors which undergo a "use-dependent" depletion in the absence of nitric oxide synthesis. These pre-formed pools of nitrosyl factors may exist within the sympathetic nerves themselves. In addition, they may be stored within the vascular endothelium and released by neurogenically-derived neurotransmitters/neuromodulators.

The hypotensive effect of L-arginine is associated with increased expired nitric oxide in humans

Endothelial metabolism of L-arginine to L-citrulline and the potent vasodilator, nitric oxide (NO), is important in the regulation of vascular tone and resting BP. L-arginine improves abnormal endothelium-dependent vasodilation in the setting of hypercholesterolemia and has a vasodilatory effect in normal vessels, effects presumed to be mediated through increased endogenous NO production, although this has not been established by direct measurement of NO. In a randomized, placebo-controlled, crossover trial, 10 healthy male subjects received a 30-min infusion of 0.5 g/kg L-arginine hydrochloride. Subjects underwent continuous monitoring of BP and heart rate (HR) as well as intermittent determination of mixed expired NO concentration and plasma L-arginine and L-citrulline levels. Infusion of L-arginine produced a significant fall in mean BP with a peak effect of -9.3 +/- 0.9% (p<0.005). The hemodynamic effects of L-arginine were associated with an increase in mixed expired NO concentration (FeNO) of 55 +/- 15% (p<0.005) from 15 +/- 2 to 21 +/- 3 parts per billion (ppb) and an increase in the rate of pulmonary NO excretion of 118 +/- 45% (p<0.005), as well as a rise in plasma L-citrulline from 25 +/- 4 to 46 +/- 5 micromol/l (p<0.005). There was a significant correlation between the hypotensive response to L-arginine and the increase in expired NO (r=-0.68, p<0.05). The hypotensive effect of L-arginine in humans appears to be mediated, at least in part, by NO synthase metabolism of L-arginine and increased endogenous NO production as indicated both by increased plasma L-citrulline and by increased expired NO.

Changes in angiotensin II metabolism contribute to the increased pressor response to angiotensin after chronic treatment with L-NAME in the spontaneously hypertensive rat

1. Administration of nitric oxide (NO) synthase inhibitors, such as L-NAME, is associated with an increase in blood pressure and an increase in pressor responsiveness to infused angiotensin II (AngII). The present study was designed to investigate the contribution of changes in the metabolism of AngII to the enhanced pressor response to AngII in the spontaneously hypertensive rat (SHR; 14 weeks old) chronically treated with L-NAME. 2. Group I rats received L-NAME for 7 days (5 mg/kg per day) in their drinking water. Group II rats received water only. On day 7, rats were anaesthetized and metabolic clearance studies were performed. AngII concentrations in plasma and infusate were measured by radioimmunoassay. 3. Urinary NO2 was unchanged after L-NAME treatment, while NO3 decreased compared with control. Mean arterial pressure (MAP) was higher in the L-NAME treated rats than in control. After 30 min infusion of AngII, MAP increased significantly in both groups, although the increase was larger in L-NAME-treated than control rats. The metabolic clearance rate of AngII was significantly lower in L-NAME-treated rats than in the control group. 4. We conclude that chronic NO synthase inhibitors, such as L-NAME, cause a decrease in the rate at which AngII is metabolized. This decrease, in combination with the increase in the number of vascular AngII receptors, may account for the reported increase in pressor responsiveness to infused AngII.

A study of angiotensin II receptors after chronic inhibition of nitric oxide synthase in the spontaneously hypertensive rat

1. Nitric oxide (NO) synthase inhibition, induces a sustained increase in blood pressure and amplifies the pressor response to infused angiotensin II (AngII). This study was designed to investigate the contribution of AngII receptors in the elevated blood pressure and enhanced pressor response to AngII in the spontaneously hypertensive rat (SHR) chronically treated with N(G)-nitro-L-arginine-methyl ester (L-NAME). 2. Two groups of 13 week old female SHR were housed four to a box. Group I rats received L-NAME for 7 days (2.5 mg/kg per day) in their drinking water. Group II rats received water only. Blood pressure was monitored daily by tail-cuff plethysmography. Plasma AngII was measured by radioimmunoassay. Aortic and uterine receptor binding was determined by saturation analysis using [125I]-Sar8, Ile1)AngII. Data was analysed using the computer program LIGAND. 3. Mean systolic blood pressure was significantly elevated in rats treated with L-NAME compared with the control group. Plasma AngII concentration was slightly decreased in rats treated L-NAME compared with control. Densities of both aortic and uterine AngII receptors increased significantly following NO synthase inhibition. Receptor affinity in the aorta decreased in the L-NAME group compared with control. However, uterine AngII receptor affinity was unchanged. 4. We conclude that the increased blood pressure and enhanced pressor responsiveness that occurs with chronic inhibition of NO synthesis may result partly from increased vascular AngII receptor expression.

Vasodilator responses of rat isolated tail artery enhanced by oxygen- dependent, photochemical release of nitric oxide from iron-sulphur-nitrosyls

1. The vasodilator properties and photochemical decomposition of two synthetic iron-sulphur-nitrosyl clusters (cluster A: [Fe4S4(NO)4], tetranitrosyl-tetra-mu 3-sulphido-tetrahedro-tetrairon; and B:[Fe4S3 (NO)7]-1, heptanitrosyl-tri-mu 3-thioxotetraferrate(-1)) have been investigated. Experiments were carried out on isolated, internally-perfused segments of rat tail artery. 2. Bolus injections (10 microliters) of A or B ( > 0.25 mM) delivered into the internal perfusate generated sustained (or S-type) vasodilator responses, characterized by a persistent plateau of reduced tone due to NO released from clusters which enter and become trapped within endothelial cells. Clusters were therefore irradiated with visible laser light (lambda = 457.9 or 514.5 nm) either (a) in solution, while passing through a glass tube en route to the artery; or (b) when retained within the endothelium, by illuminating the artery directly during the plateau of an S-type response. Irradiation produced an additional vasodilator response, the magnitude of which depended upon wavelength and laser beam energy. 3. The nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (100 microM), had no effect on light-induced vasodilator responses. However, they were (a) blocked entirely by adding oxyhaemoglobin (5 microM) to the internal perfusate; and (b) greatly enhanced by the enzyme superoxide dismutase (150 u ml-1). 4. Photolysis of cluster B was measured by absorption spectroscopy and by detecting NO released with an electrochemical sensor. The photochemical reaction was found to be oxygen-dependent. The half-time for inactivation of cluster-derived NO was measured by interposing different lengths of tubing (i.e. time delays) between the photolysis tube and NO sensor. The steady-state probe current decayed exponentially with increasing delay time, with a t 1/2 of 21 s. The amplitudes of vasodilator responses of the tail artery also decreased exponentially by increasing the time delay (t 1/2 = 58 s). Superoxide dismutase (150 u ml-1) prevented this from happening, showing that "inactivation' of cluster-derived NO was caused by reaction with superoxide anions formed during photolysis. 5. We conclude that potentiation of vasodilator responses to iron-sulphur-nitrosyl clusters by visible light is due to an oxygen-dependent photochemical reaction which accelerates the release of ligated nitrosyl groups as free NO. Based on our measurements, we estimate that ca 100 pM NO is sufficient to produce a just-detectable additional vasodilatation and that the ED50 dose is ca 3.7 nM.

Effects of nitric oxide synthase inhibition on the cardiovascular response to low output shock

OBJECTIVE

To study the role of nitric oxide in the cardiovascular response to a model of a low output syndrome.

DESIGN

Prospective animal study.

SETTING

Animal research laboratory.

SUBJECTS

Sheep anesthetized with pentobarbital, mechanically ventilated, and monitored with pulmonary arterial and peripheral arterial catheters.

INTERVENTIONS

A low output state was induced by inflating a balloon-tip catheter placed in the right atrium. Cardiac index was maintained at 1 L/min/m2 throughout the experiment in three groups of sheep: a) control (n=6) b)LNNA group (pretreated with the nitric oxide synthase inhibitor N omega-nitro-L-arginine [LNNA, 100 mg/kg, iv bolus, n=6); and c) dexamethasone group (pretreated with dexamethasone (6 mg/kg, intravenous bolus, n=6). Dexamethasone is an inhibitor of the induction of nitric oxide synthase. LNNA or dexamethasone were administered 15 mins before inducing the low output state.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic and oxygen transport variables, and plasma lactate and pyruvate concentrations, were measured at baseline and during the next 3 hrs. For a comparable decrease in cardiac index and oxygen delivery in all groups, the LNNA group had less hypotension and a more marked increase in systemic vascular resistance as compared with the control group. Oxygen consumption and oxygen extraction were higher in the LNNA group as compared with the control group at 30 and 60 mins. Plasma lactate concentration increased significantly less in the LNNA group than in the control and the dexamethasone groups during the observation period.

CONCLUSIONS

Inhibition of nitric oxide synthesis during a severe low output state in sheep is associated with a better hemodynamic response, as evidenced by a greater vasoconstriction, and signs of less marked tissue hypoxia. It is likely that inhibition of nitric oxide synthesis in this model leads to an imbalance between the tonic relaxing action of nitric oxide and the influences of vasoconstrictor agents.

Vasodilation by intrathecal lipopolysaccharide of the cerebral arteries after subarachnoid haemorrhage in dogs

To investigate the influence of inducible nitric oxide synthase on cerebral arteries after subarachnoid haemorrhage (SAH) in vivo, lipopolysaccharide (LPS), a major inducer of inducible nitric oxide synthase, was injected intracisternally into control and SAH model dogs. Intracisternal injection of LPS (0.5 mg) produced a long-lasting, submaximal vasodilation of the basilar artery of control dogs on angiography. This effect became significant at 4 hours after LPS injection and plateaued after 6 hours. This vasodilation was reduced by N(G)-monomethyl-L-arginine. Vasopressin slightly suppressed the vasodilation, while bradykinin increased it. The concentration of L-arginine in CSF decreased after LPS injection, while that of L-citrulline increased. In cytokines, the concentration of tumour necrosis factor-alpha; (TNF-alpha;) in CSF increased transiently at 4 hours after LPS injection, while interleukin-1 beta, interleukin-6, interferon-gamma, did not change. These data suggest that vasodilation by LPS is mainly due to nitric oxide predominantly synthesized by an inducible nitric oxide synthase, proximally induced by TNF-alpha. Our data make it unlikely that SAH itself induces the inducible nitric oxide synthase in vascular tissue, since isolated endothelium-denuded basilar artery from SAH model dogs did not respond to L-arginine. In SAH model dogs, the degree of vasodilation by LPS differed with the severity of vasospasm. Vasodilation was much greater in mild than in severe vasospasm in dogs, and was increased by superoxide dismutase. These findings suggest that the induction of inducible nitric oxide synthase or its activity may be less effective in severe vasospasm.

L-arginine prevents corticotropin-induced increases in blood pressure in the rat

In this study we examined whether L-arginine treatment could prevent corticotropin (ACTH)-induced increases in blood pressure in the Sprague-Dawley rat. Sixty rats were randomly divided into six groups (n = 10): sham injection, ACTH injection (0.5 mg/kg per day in divided doses), L-arginine (0.6%) in food plus sham injection, L-arginine plus ACTH treatment, D-arginine (0.6%) in food plus sham injection, and D-arginine plus ACTH. Systolic pressure, water intake, urine volume, body weight, plasma and urinary electrolytes, and serum corticosterone concentrations were measured. ACTH increased systolic pressure (from 127 +/- 2 to 165 +/- 6 mm Hg, P < .001), water intake, and urine volume and decreased body weight body weight. L-Arginine reduced ACTH-induced blood pressure rises (130 +/- 3 mm Hg, P < .001) but had no effect on blood pressure in sham-treated rats. D-Arginine did not affect blood pressure in sham-treated rats, and systolic pressure in D-arginine+ACTH-treated rats was similar to that of ACTH-treated rats. L-Arginine decreased serum corticosterone concentrations in sham-treated rats (424 +/- 42 versus 238 +/- 25 ng/mL, P < .01), but D-arginine had no effect. However, both drugs decreased serum corticosterone concentrations in ACTH-treated rats (1071 +/- 117 versus 739 +/- 95 and 695 +/- 72 ng/mL for L- and D-arginine, respectively; both P < .05). As L-arginine but not D-arginine prevented ACTH-induced increases in blood pressure in Sprague-Dawley rats and both L- and D-arginine reduced serum corticosterone concentrations in ACTH-treated rats, the effects of L-arginine in preventing ACTH-induced hypertension were not simply a consequence of decreased corticosterone secretion.

Establishment of permanent human endothelial cells achieved by transfection with SV40 large T antigen that retain typical phenotypical and functional characteristics

The plasmid pMK16 containing-SV40 replicated origin defective gene was efficiently introduced into early-passage human umbilical vein endothelial cells (HUVEC) using positively charged liposomes. The resulting cell line acquired an almost infinite lifespan, was morphologically unchanged, expressed SV40-antigen, and coexpressed von Willebrand factor (vWF), tissue plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1), angiotensin conversion enzyme (ACE), and endothelin converting enzyme (ECE). In addition, these are the first immortalized human endothelial cells, to our knowledge, that biosynthesized and secreted interleukins (IL-1 beta and IL-6) in both a constitutive and regulated fashion and endothelin-1 (ET-1), the most potent vasoactive peptide, which has been suggested to be implicated in the pathogenesis of hypertension. Interestingly enough, both of the immortalized cells and the early-passage HUVEC from which the immortalized cells were obtained biosynthesized and secreted the same levels of ET-1 suggesting full maintenance of its biosynthetic pathway including the presence of active ECE, which cleaves big endothelin-1 (big-ET-1) to ET-1 and regulation factors. Moreover, the immortalized cells retained the ability to express the functional specific amino acid Na(+)-independent system Y+ transporter, which mediates L-arginine transport into endothelial cells from which endothelium-derived relaxing factor (EDRF, nitric oxide) is formed via the action of nitric oxide-synthase. Obtaining these immortalized human endothelial cells without alteration of the differentiated characteristics constitutes a useful model: (a) to study ET-1 secretion, gene regulation, and human ECE, which may be an important therapeutic target in disease conditions in which ET-1 is to be implicated; (b) to study L-arginine transport, which is a key step in the formation of EDRF; (c) to study IL-1 beta and IL-6 secretions, and gene regulations; (d) to substitute large quantities of HUVEC; and, finally, (e) to reproduce, starting with different primary endothelial cells both from human and animal origin.

Reduction of nitric oxide with L-/NG-monomethyl arginine in interleukin-2 and anti-CD3 monoclonal antibody combination therapy

We evaluated nitric oxide induction in antitumor therapy consisting of anti-CD3 monoclonal antibody (anti-CD3) and interleukin-2 (IL-2), then determined the effect of nitric oxide reduction with L-N(G)-monomethyl arginine (LNMA) on the therapeutic methods. Female C57BL/6 mice, MCA102 (a non immunogenic, NK-resistant murine fibrosarcoma cell line), and 145-2C11 (hamster anti-murine-CD3 mAb) were utilized in an experimental hepatic metastasis model developed by injecting a tumor cell suspension into the spleen of mice. A marked increase in serum NO2 (-) + NO1 was observed at 19 hours after anti-CD3 (10 μ, IV) and additional IL-2 administrations (40 × 10(1) U, twice, If) induced a further increase. The NO2, + NO3- elevation in spot urine in the combination therapy was not suppressed with LNMA at a dose of 100 μg/h but was significantly lowered at 300 μg/h. The efficacy of the anti-CD3 + IL-2 therapy was not diminished by LNMA administration either at 100 μg/h or at 300 μg/h.

Involvement of neurohumoral factors in the pressor mechanism of NG-nitro-L-arginine

The mechanism of the NG-nitro-L-arginine (L-NNA)-induced pressor response was examined in pentobarbital-anesthetized dogs. The pressor effect of L-NNA (50 mg/kg, i.v.) was significantly and equally diminished by pretreatment with either hexamethonium (25 mg/kg, i.v.) or phentolamine (5 mg/kg, i.v.). The intracisternal administration of L-NNA (1 mg/kg), which did not cause changes in cardiovascular parameters when administered systemically, produced a significant pressor response and tachycardia. Furthermore, significant suppression of L-NNA-induced pressor responses was observed after treatment of dogs with captopril (5 mg/kg, i.v.) or a non-peptide angiotensin II receptor antagonist, losartan (10 mg/kg, i.v.), or bilateral occlusion of renal veins. The inhibitory effects of hexamethonium and losartan were additive. These results suggest that, in addition to vasoconstriction due to the inhibition of endothelial nitric oxide production, increased activity of the sympathetic nervous and renin-angiotensin systems contributes significantly to the development of pressor responses produced by the intravenous injection of L-NNA in anesthetized dogs.

Inhaled nitric oxide for children with congenital heart disease and pulmonary hypertension

BACKGROUND

Endothelium-derived nitric oxide (NO) is a potent vasodilator and a major mediator of pulmonary vascular tone.

METHODS

Five infants underwent a trial of inhaled NO with hemodynamic monitoring in the operating room after atrioventricular canal repair. An additional 15 patients with congenital heart disease and refractory pulmonary hypertension were treated with inhaled NO for 1 day to 10 days postoperatively.

RESULTS

In the 5 infants with atrioventricular canal, corrective surgical intervention and conventional therapy (hyperventilation, inspired oxygen fraction of 0.80, and inotropic agents) lowered mean pulmonary artery pressure from 49.5 +/- 10.5 to 20.0 +/- 2.2 mm Hg (p < 0.001). Adding inhaled NO further decreased mean pulmonary artery pressure to 18.0 +/- 2.8 mm Hg (p = not significant). Inhaled NO had no effect on ventricular function curves (inflow occlusion) in this group. In the 15 patients with refractory postoperative pulmonary hypertension, 11 had a favorable response to inhaled NO, with a decrease in mean pulmonary artery pressure from 30.9 +/- 5.8 to 23.1 +/- 5.4 mm Hg (p < 0.01) in 8 patients with pulmonary artery catheters.

CONCLUSIONS

These studies demonstrate that inhaled NO has minimal beneficial effect on pulmonary artery pressure or cardiac output in infants after repair of atrioventricular canal. Inhaled NO is effective in decreasing PAP postoperatively in select patients with congenital heart disease and pulmonary hypertension refractory to conventional therapeutic modalities.