Nitric Oxide Precursor L-arginine Research Articles

Effect of l-arginine cardioplegia on recovery of neonatal lamb hearts after 2 hours of cold ischemia

Despite hypothermia and cardioplegia, myocardial ischemia followed by reperfusion results in both ventricular and endothelial dysfunction. The endothelial dysfunction is characterized by a reduced response to acetylcholine, which implies a reduced ability of the endothelium to release nitric oxide after hypothermic ischemia and reperfusion. We have previously demonstrated that infusion of the nitric oxide precursor L-arginine only during reperfusion after hypothermic ischemia significantly improves the recovery of ventricular function and results in an increased vasodilator response to the infusion of acetylcholine. In contrast, other investigators have found that nitric oxide has deleterious effects during postischemic reperfusion. In the current experiments we have further examined the role of endothelial production of nitric oxide by adding 10 mmol/L L-arginine to cardioplegia in isolated, blood-perfused neonatal lamb hearts having 2 hours of cold cardioplegic ischemia. In another group 10 mmol/L D-arginine, an inactive enantiomer of L-arginine, was added to the cardioplegia. Controls received only cardioplegia (dextrose-potassium). At 30 minutes of reperfusion, the L-arginine group showed a significantly improved recovery in left ventricular systolic function (maximum developed pressure, developed pressure at a constant balloon volume [V10] resulting in an end-diastolic pressure of 10 mm Hg before ischemia, positive maximum dP/dt, and dP/dt at V10), diastolic function (negative maximum dP/dt and end-diastolic pressure at V10), coronary blood flow, endothelial function (assessed by the coronary vascular resistance response to acetylcholine), and myocardial oxygen consumption compared with the control group (p < 0.05). There were no significant differences in the recovery of any variables between the D-arginine and control groups. These results suggest that provision of more substrate for the endothelial production of nitric oxide during ischemia has an important salutary effect on the recovery of postischemic myocardial and endothelial function and provide further evidence for an important role for the endothelial production of nitric oxide in the response to hypothermic ischemia and reperfusion in the neonatal lamb heart.

Role of NO mechanism in cardiovascular effects of diaspirin cross-linked hemoglobin in anesthetized rats.

The role of nitric oxide (NO) in the cardiovascular actions of diaspirin cross-linked hemoglobin (DCLHb) was studied in anesthetized rats. The regional circulatory and systemic hemodynamic effects of DCLHb (400 mg/kg iv) were studied using a radioactive microsphere technique in control (untreated) and L-arginine (a NO precursor) pretreated rats. DCLHb produced a significant increase in blood pressure (75%), cardiac output (42%), stroke volume (36%), and total peripheral resistance (45%), without affecting heart rate, when administered to control rats. L-Arginine pretreatment significantly attenuated DCLHb-induced systemic hemodynamic effects. DCLHb-induced increase in blood flow to the skin and spleen was completely blocked, and that to the heart was partially blocked, by L-arginine pretreatment, suggesting that cardiovascular actions induced by DCLHb could be antagonized by the NO precursor L-arginine. The NO synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) produced significant increases in regional vascular resistance, leading to a decrease in blood flow to all the organs except the heart, where an increase in blood flow and a decrease in vascular resistance was observed. DCLHb, when administered in L-NAME-pretreated rats, accentuated the decrease in blood flow to the gastrointestinal system, spleen, mesentery and pancreas, skin, and musculoskeletal system. These studies provide evidence that the NO precursor L-arginine can attenuate the effects of DCLHb and that DCLHb can potentiate the effect of the NOS inhibitor L-NAME. The role of NO in the mechanism of action of DCLHb was further studied by estimating plasma guanosine 3',5'-cyclic monophosphate (cGMP) in control, DCLHb-treated, L-NAME-treated, and L-NAME followed by DCLHb-treated rats. DCLHb and L-NAME significantly decreased the concentration of circulating cGMP in blood plasma. L-NAME pretreatment potentiated DCLHb-induced decrease in cGMP levels. Because the formation of cGMP is stimulated by NO, these studies provide additional evidence for the involvement of NO in the mechanism of action of DCLHb. It is concluded that NO plays an important role in the cardiovascular effects of DCLHb.

Bombesin-induced contractions of guinea pig lung strips are modulated by endogenous nitric oxide.

We have investigated the effects of a nitric oxide (NO) biosynthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) on the bombesin-evoked contraction of guinea pig parenchymal lung strips. The bombesin-induced contractions of lung strips were significantly increased after L-NAME (300 micro)) pre-treatment. The maximal response was increased (P < 0.01) by 37% after L-NAME treatment when compared with the control group. The pD2 value was not influenced by L-NAME pre-treatment. The enhancement of the bombesin-induced contraction caused by L-NAME was reversed by addition of an excess of the NO precursor L-arginine (600 microM) but not by the addition of its inactive enantiomer D-arginine (600 microM). Like L-NAME, methylene blue (1 microM), an agent that inhibits the soluble guanylyl cyclase activated by NO, significantly increased (P < 0.01) the maximal contraction induced by bombesin (183 +/- 16 mg) when compared with the control group (141 +/- 15 mg). When tested against other agonist-induced contractions, L-NAME did not change the responsiveness of parenchymal lung strips to bradykinin or carbachol but significantly increased lung contraction induced by histamine. NO synthesis inhibition resulted in a pronounced increase in the bombesin-induced contraction of guinea-pig lung strips. Our results suggest that bombesin contributes to NO synthesis and release which then acts to reduce the contraction of the lungstrip in response to bombesin.

Supplemental l-arginine during cardioplegic arrest and reperfusion avoids regional postischemic injury

Unenhanced hypothermic cardioplegia does not prevent postischemic endothelial and contractile dysfunction in hearts subjected to antecedent regional or global ischemia. This study tested the hypothesis that supplementing blood cardioplegic solution and reperfusion with the nitric oxide precursor l-arginine would preserve endothelial function, reduce infarct size, and reverse postcardioplegia regional contractile dysfunction by the L-arginine-nitric oxide pathway. In 23 anesthetized dogs, the left anterior descending coronary artery was ligated for 90 minutes, after which total bypass was established for surgical “revascularization.” In 10 dogs, unsupplemented multidose hypothermic blood cardioplegic solution was administered for a total of 60 minutes of cardioplegic arrest. In eight dogs, L-arginine was given intravenously (4 mg/kg per minute) and in blood cardioplegic solution (10 mmol) during arrest. In five dogs, the nitric oxide synthesis blocker N ω-nitro-L-arginine (1 mmol) was used to block the L-arginine–nitric oxide pathway during cardioplegia and reperfusion. Infarct size (triphenyltetrazolium chloride) as percent of the area at risk was significantly reduced by L-arginine compared with blood cardioplegic solution (28.2% ± 4.1% versus 40.5% ± 3.5%) and was reversed by N ω-nitro-L-arginine to 68.9% ± 3.0% ( p < 0.05). Postischemic regional segmental work in millimeters of mercury per millimeter (sonomicrometry) was significantly better with l-arginine (92 ± 15) versus blood cardioplegic solution (28 ± 3) and N ω-nitro-L-arginine (26 ± 6). Segmental diastolic stiffness was significantly lower with L-arginine (0.46 ± 0.06) compared with blood cardioplegic solution (1.10 ± 0.11) and was significantly greater with N ω-nitro- l-arginine (2.70 ± 0.43). In ischemic-reperfused left anterior descending coronary arterial vascular rings, maximum relaxation response to acetylcholine, the stimulator of endothelial nitric oxide, was depressed in the blood cardioplegic solution group (77% ± 4%) and was significantly reversed by L-arginine (92% ± 3%). Smooth muscle function was unaffected in all groups. We conclude that cardioplegic solution supplemented with L-arginine reduces infarct size, preserves postischemic systolic and diastolic regional function, and prevents arterial endothelial dysfunction via the L-arginine–nitric oxide pathway. (J T HORAC C ARDIOVASC S URG 1995;110:302-14)

Augmentation of Microvascular Nitric Oxide Improves Myocardial Performance Following Global Ischemia

Hearts exposed to global myocardial ischemia associated with cardiac surgery often suffer postischemic endothelial and contractile dysfunction related to antecedent regional or global ischemia. Our studies tested the hypothesis that supplementing blood cardioplegia and reperfusion with the nitric oxide (NO) precursor L-arginine or the NO donor SPM-5185 would preserve endothelial function, reduce infarct size, and reverse postcardioplegia regional contractile dysfunction or global dysfunction. In the first study involving 23 anesthetized dogs undergoing regional ischemia, supplementation of blood cardioplegia with L-arginine: (1) reduced infarct size; (2) improved postischemic regional segmental work and diastolic stiffness; (3) attenuated neutrophil accumulation in the area at risk; and (4) improved postischemic depressed coronary artery endothelial function. The NO synthase inhibitor N-nitro-L-arginine (L-NA) reversed these protective effects. In another experiment involving 18 anesthetized dogs undergoing normothermic global ischemia, hearts treated with blood cardioplegia supplemented with the NO donor SPM-5185 demonstrated better postischemic coronary artery endothelial function, lowered myeloperoxidase activity in the ischemic-reperfused myocardium, and significantly improved global ventricular function in the group receiving high-dose SPM-5185. We conclude that the inclusion of L-arginine or high-dose NO donor SPM-5185 in blood cardioplegia improves postischemic ventricular performance and endothelial function in ischemically injured hearts, possibly by inhibition of neutrophil-mediated damage via the L-arginine-NO pathway.

Angiotensin-(1-7) and nitric oxide interaction in renovascular hypertension.

New studies suggest that vasodilator systems may play an important role in restraining the rise in peripheral vascular resistance associated with the evolution of arterial hypertension. We characterized in conscious dogs the hemodynamic and hormonal effects of 4 weeks of feeding either the nitric oxide synthase inhibitor N omega-nitro-L-arginine (3 mg.kg-1.d-1) or the nitric oxide precursor L-arginine (0.3 mg.kg-1.d-1) during the evolution of two-kidney, one clip hypertension. Inhibition of nitric oxide production elicited a form of hypertension more severe than that produced in placebo-fed two-kidney, one clip dogs. The higher levels of blood pressure were accompanied by lower levels of plasma renin activity and lower angiotensin II concentrations. During the chronic phase of renovascular hypertension, the fall in blood pressure produced by acute systemic injections of lisinopril or losartan was significantly reduced in dogs given the nitric oxide inhibitor. In contrast, chronic administration of L-arginine had no effect on the magnitude of hypertension or on the increases in renin activity and hyperangiotensinemia associated with the evolution of renal hypertension. Likewise, the fall in blood pressure produced by pharmacological blockade of angiotensin II was not different from that recorded in untreated renal hypertensive dogs. The vasodilator component of the blood pressure response due to intravenous injections of angiotensin-(1-7) (1 to 100 nmol/kg) was augmented in both untreated and L-arginine-treated two-kidney, one clip hypertensive dogs, but was significantly attenuated in hypertensive dogs fed the nitric oxide synthase inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of hippocampal nitric oxide in memory retention in rats

The present study investigated the role of hippocampal nitric oxide (NO) in memory retention of an inhibitory avoidance learning task in rats. The anatomical locus was aimed at the dentate gyrus (DG). Results indicated that intra-DG administration of a NO generator, sodium nitroprusside (SNP), at moderate doses enhanced retention performance in a dose-response fashion in rats. SNP at higher doses, on the other hand, impaired memory retention. Intra-DG injection of a NO inhibitor, L- N G -monomethylarginine ( l-MeArg), impaired retention performance at moderate doses. Coadministration of a NO precursor l-arginine (2.9 and 7.2 μg) reversed the memory-impairing effect of l-MeArg. An in vitro ADP-ribosylation experiment showed five protein bands with molecular weights around 118, 94, 54, 43, and 39 kDa that were labeled. The labeling intensity of these proteins decreased as the concentration of in vivo SNP increased. These results suggest that hippocampal NO plays a facilitatory role in the memory process of an inhibitory avoidance learning task in rats.

953-36 L-Arginine Administration Improves Left Ventricular Performance in Neonatal Lambs Following Cardiopulmonary Bypass and Two Hours of Global Hypothermic Ischemia

Prior studies in isolated neonatal lamb hearts showed that the nitric oxide precursor L-Arginine (L-ARG), infused during reperfusion (rep) improved left ventricular (LV) function and coronary blood flow (CBF) after hypothermic ischemia. We evaluated the effects of L-ARG in an in situmodel of cardiopulmonary bypass (CPS) and hypothermic circulatory arrest (HCA) in 13 neonatal lambs with LV micromanometers and LV free wall sonomicrometry crystals. Before CPB, hemodynamics and LV regional preload recruitable stroke work (RPRSW) were recorded. Coronary blood flow (CBF) was determined with microspheres. Animals were cooled to 15°C prior to 2 hrs HCA. Group LARG (n = 6) received an infusion of L-ARG calculated to achieve a plasma concentration of 3 mM during the first 15 min of rep on CPS. Group CON (n = 7) received 0.2 mg/kg phentolamine at rep, according to the clinical protocol of this institution. Animals were weaned from CPB and data obtained for 3 hrs. No intergroup differences were seen in heart rate, systemic vascular resistance, cardiac output, or left atrial pressure at baseline or during rep. (p &gt; 005) CBF at 1 and 2 hrs rep was not different between the two groups (p &gt; 0.05). Rep RPRSW data are expressed as mean % recovery of baseline.Group1 hr2 hrs3 hrsCON65.563.552L-ARG80*81.7*84**p &lt; 0.05 p &lt; 0.05 Increased nitric oxide production during early rep improves recovery of the immature myocardium following CPS and HCA. Techniques such as this may have application in clinical cardiac surgery.

Virus-induced airway hyperresponsiveness in guinea pigs is related to a deficiency in nitric oxide.

Intratracheal inoculation of parainfluenza type 3 virus to guinea pigs induces a marked increase in airway responsiveness in vivo and in vitro. In spontaneously breathing anesthetized guinea pigs inhalation of an aerosol containing the nitric oxide (NO) precursor L-arginine (2.0 mM) completely prevented the virus-induced airway hyperresponsiveness to histamine. In addition, perfusion of L-arginine (200 microM) or the direct NO-donor S-nitroso-N-acetyl-penicillamine (SNAP, 1 microM) through the lumen of tracheal tubes from infected animals prevented the increase in airway responsiveness to histamine or the cholinoceptor agonist methacholine. The NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 120 microM) did not further increase the virus-induced airway hyperresponsiveness. In additional experiments, NO was measured with an Iso-NO nitric oxide meter and sensor. Stimulation of control tissues in vitro with histamine (10(-3) M) resulted in a contraction with a simultaneous release of NO (44.5 +/- 5.4 nM). The release of NO was markedly reduced by 75% (P < 0.01, 11.4 +/- 3.1 nM) in tracheas from virus-infected animals that demonstrated enhanced contractile responses. Preincubation of tissues from virus-treated guinea pigs with L-arginine (200 microM) completely prevented the enhanced contraction and simultaneously returned the NO production to control values (51.2 +/- 3.4 nM). An NO deficiency might be causally related to the development of airway hyperresponsiveness after a viral respiratory infection.

&lt;i&gt;L&lt;/i&gt;-Arginine Supplementation Antagonizes the Effects of Angiotensin II and Endothelin 1 on Mesangial Cell Proliferation

Proliferation of mesangial cells (MC) is regarded as a precursor to the development of glomerulosclerosis and may be mediated by mitogenic vasoconstrictors such as angiotensin II (ANG-II) and endothelin 1 (ET-1). Dietary supplementation with the nitric oxide (NO) precursor L-arginine has been shown in in vivo models to suppress the development of glomerulosclerosis. We undertook the present study to determine whether L-arginine supplementation in vitro could modulate the mitogenic effects of ANG-II and ET-1 on MC. MC showed significantly greater incorporation of [3H]thymidine compared to control when incubated with 10-6M ANG-II and 10-8M ET-1. Supplementing media with L-arginine to achieve a 10-fold increase in concentration to 4 mM was found to significantly antagonize the mitogenic effect of these agents on MC, an effect that was attenuated by both the NO synthase inhibitor NG-monomethyl-L-arginine as well as the guanylate cyclase inhibitor methylene blue, suggesting that the effect of L-arginine is mediated via cyclic GMP generation. The direct NO generator sodium nitroprusside at 10-5M was also found to suppress MC [3H]thymidine incorporation under ANG-II and ET-1 stimulation, an effect that was also attenuated by coincubation with methylene blue. The protein kinase G inhibitor Rp-8-Br-cGMPS was also found to attenuate the antiproliferative effect of L-arginine. These data suggest that L-arginine supplementation can attenuate the proliferative effect of mitogens such as ANG-II and ET-1 on MC proliferation by a mechanism that appears to require NO and cGMP generation. These findings may in part account for the observed ability of L-arginine supplementation to retard the development of glomerulosclerosis.

Role of nitric oxide in modulating neurotransmitter release from rat striatum

The effect of the nitric oxide synthase inhibitor N-nitro- l-arginine methyl ester (L-NAME) on the basal and stimulation-evoked release of dopamine (DA) and acetylcholine (ACh) was investigated in rat striatum. The experiments were carried out in isolated superfused striatal slices, loaded with either [ 3H]-dopamine or [ 3H]-choline. We have found that L-NAME reduced the elecrical field stimulation-evoked release of DA, while its enantiomer N-nitro-D-arginine methyl ester (D-NAME) was ineffective. In the presence of the nitric oxide (NO) precursor l-arginine L-NAME failed to influence DA release. Furthermore, treatment with the N-methyl- d-aspartate (NMDA) receptor antagonist MK-801 completely reversed the effect of L-NAME on striatal DA release. In contrast, L-NAME had no effect on either the basal or the stimulation-evoked ACh release in any experimental conditions studied. Our data indicate that endogenously produced NO is involved in the modulation of striatal DA, but not in ACh release. Furthermore, it seems likely that the modulatory effect of NO is linked to activation of presynaptic NMDA receptors located on the striatal dopaminergic nerve terminals.

Lung preservation with euro-collins, University of Wisconsin, wallwork, and low-potassium-dextran solutions

Using isolated rat lungs, we compared prevention of ischemia-reperfusion injury provided by flushing the lungs with modified Euro-Collins solution (EC), University of Wisconsin solution (UW), low-potassium-dextran solution (LPD), or Wallwork solution (WA). After 4 hours' and 6 hours' cold ischemia, reperfusion injury was assessed on the basis of changes in filtration coefficients ( K fc ) and pressure-flow curves, characterized by the slope of the curves (incremental resistance) and the extrapolation of this slope to zero flow (pulmonary pressure intercept [Ppi]). After 4 hours, K fc and Ppi were higher with EC than with UW, LPD, and WA, and the incremental resistance was higher with EC and UW. After 6 hours, K fc and incremental resistance Ppi were higher with LPD than with WA. Because ischemia-reperfusion injury is associated with decreased endothelial synthesis of prostacyclin and nitric oxide, we tested whether the addition of prostacyclin or the nitric oxide precursor l-arginine to WA would improve preservation. The K fc and Ppi were lower with both treatments. In conclusion, ischemiareperfusion injury was best prevented by using WA. The favorable effect of prostacyclin or l-arginine emphasizes the role played by endothelial dysfunction in ischemia-reperfusion injury.

Enhanced endothelial adhesiveness in hypercholesterolemia is attenuated by L-arginine.

We have shown that chronic administration of the nitric oxide (NO) precursor L-arginine normalizes NO-dependent vasodilation and markedly inhibits atherogenesis in a hypercholesterolemic rabbit model. We hypothesized that this antiatherogenic effect is due to modulation of endothelial adhesiveness by endothelium-derived NO. New Zealand White rabbits were fed normal chow (Cont), a high-cholesterol diet (Chol), a high-cholesterol diet supplemented with L-arginine (Arg), or a normal diet supplemented with the NO synthase antagonist L-nitroarginine (L-NA) for 2 weeks. In additional studies, some animals receiving L-NA were also treated with hydralazine to normalize blood pressure. After 2 weeks, thoracic aortas were harvested, opened longitudinally, and placed in a culture dish with the endothelial surface exposed to medium containing WEHI 78/24 cells, a monocytoid cell line. After incubation with the monocytoid cells for 30 minutes on a rocking platform, the aortic segments were washed repeatedly to remove nonadherent cells and adherent cells counted by epifluorescent microscopy. Monocytoid cell binding to aortic endothelium was significantly increased in Chol (P < .001 versus Cont); binding was markedly reduced in arginine-fed hypercholesterolemic animals (P < .05, Arg versus Chol). Monocytoid cell binding to aortic endothelium was also significantly increased in L-NA (P < .05); hydralazine normalized blood pressure but did not reduce monocytoid cell binding. To confirm that alterations in NO activity modulate endothelial cell-monocyte interaction, the release of nitrogen oxides (NOx) by thoracic aortas was assessed by a chemiluminescent technique. The concentration of NOx in the conditioned medium from segments of Arg thoracic aortas was significantly greater than that from Cont aortas, whereas that from L-NA aortas was significantly less. Hypercholesterolemia enhances the adhesiveness of aortic endothelium for monocytes; this effect is attenuated by dietary L-arginine. Conversely, inhibition of NO synthesis enhances monocyte binding. The results suggest that endothelium-derived NO plays an important role in regulating the endothelial adhesiveness for monocytes. Alterations in NO activity may play a critical role in atherogenesis.

Major Role of Nitric Oxide in the Mediation of Regional CO2 Responsiveness of the Cerebral and Spinal Cord Vessels of the Cat

The role of nitric oxide (NO) in the mediation of cerebrovascular CO2 responsiveness was studied in 10 distinct brain and spinal cord regions of the anesthetized, ventilated, temperature-controlled, normoxic cat. Regional CBF was measured with 15-micron radiolabeled microspheres in hypocapnic, normocapnic, and hypercapnic conditions. CO2 responsiveness of each region was determined from the equation of the best-fit regression lines to the obtained flow values. The effect of altered endothelial and/or neuronal NO synthesis on CO2 responsiveness was studied following either selective blockade of the NO synthase enzyme by N omega-nitro-L-arginine methyl ester (L-NAME; 3 or 30 mg/kg i.v.) or simultaneous administration of L-NAME (3 mg/kg i.v.) and a large dose of the NO precursor L-arginine (30 mg/kg i.v.). Blockade of NO synthesis by 30 mg/kg L-NAME resulted in a significant reduction of the steady-state regional blood flow values and in an almost complete abolition of the CO2 sensitivity in each region studied. Changes of the basal flow values as well as the reduction of the regional CO2 sensitivity were dose dependent. Hypothalamic, sensorimotor cortical, and cerebellar regions were the areas most sensitive to the NO blockade. Impaired CO2 responsiveness following NO synthase inhibition, however, was reversed in these regions by simultaneous administration of a large dose of intravenously injected L-arginine. These findings suggest a major role of nitric oxide in the mediation of regional cerebrovascular CO2 responsiveness in cats.

L-arginine restores cholesterol-attenuated microvascular responses in the rat cremaster.

The role of L-arginine in the reversal of cholesterol-induced endothelial dysfunction was studied in the cremaster muscle microcirculation. In vivo television microscopy was used to measure microvascular diameters and macromolecular leakage. Male Sprague-Dawley rats were fed either a normal chow diet or a diet supplemented with 1% cholesterol and 0.5% cholic acid for 3 weeks prior to in vivo experimentation. The cholesterol diet caused a decreased third-order arteriole dilator response to both acetylcholine and serotonin. This decreased responsiveness occurred in the presence of a higher plasma concentration of L-arginine and an increased ratio of L-arginine to its metabolite L-citrulline. The attenuation to both agonists was reversed by intravenous infusion of the nitric oxide precursor L-arginine (30-mg/kg bolus and 10-mg/kg/min continuous infusion). The cholesterol diet also decreased the postcapillary macromolecular leakage response to serotonin, and again this effect was reversed by L-arginine infusion. D-Arginine infusion had no restorative effect with either agonist in the cholesterol animals. Further experimentation with the nitric oxide production inhibitor N omega-nitro-L-arginine methyl ester demonstrated an inhibition of aretriolar dilation to acetylcholine, but there was no inhibition of dilation or macromolecular leakage to serotonin. Thus, it is probable that serotonin-induced leakage as well as dilation was not caused by stimulation of nitric oxide. These results suggest that L-arginine restores both nitric oxide-dependent and -independent dilation as well as macromolecular leakage in cholesterol-fed rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide increases dopamine and serotonin release in the medial preoptic area.

Nitric oxide (NO) is becoming recognized as an important intercellular messenger in the brain. The present experiment used microdialysis to examine the potential role of NO in the regulation of dopamine (DA) and serotonin (5-HT) release in the medial preoptic area (MPOA) of freely moving male rats. The NO precursor L-arginine (L-Arg, 100 microM), administered into the MPOA via the dialysis probe, increased extracellular levels of DA, 5-HT, and the major metabolites of DA. These increases were blocked by the coadministration of the NO synthase inhibitor N-monomethyl L-arginine (NMMA, 400 microM). The inactive isomer D-arginine (100 microM) was ineffective, and NMMA by itself decreased DA below baseline levels. Thus, NO may modulate the release of DA and 5-HT in the MPOA.

Inhibition of endothelial derived relaxing factor (EDRF) aggravates ischemic acute renal failure in anesthetized rats.

The relative importance of endothelial derived relaxing factor (EDRF)/nitric oxide (NO) in maintaining kidney function in normal condition and in acute renal failure (ARF) were evaluated in inactin anesthetized rats. ARF was induced by unilateral occlusion of the left renal artery (40 min) followed by reperfusion, with the contralateral kidney serving as normal control. This protocol resulted in marked reductions in renal plasma flow (RPF), glomerular filtration rate (GFR) and increases in fractional sodium excretion (FENa) and urinary protein excretion in the post-ischemic kidney in comparison to the contralateral normal kidney. Administration of the nitric oxide (NO) synthase inhibitor NG--monomethyl-L-arginine (0.25 mg/kg per min, L-NMMA) exacerbated the ischemia-induced changes in renal functions as reflected by further reductions in urine flow (V), GFR, marked sodium wasting and renal edema. Pretreatment of the animals with NO precursor L-arginine (2.5 mg/kg per min, L-Arg) abolished the detrimental effects of L-NMMA in ARF. In contrast, D-Arginine (2.5 mg/kg per min, D-Arg) failed to reverse the detrimental effects of L-NMMA. Infusion of L-Arg alone also resulted in improvements in RPF and GFR in the ischemic kidney. The results of the present study suggest that the function of the ischemic kidney is sustained by EDRF/NO and is thus more sensitive to NO synthase inhibition.

Nitric Oxide Synthesis Inhibitors Induce Airway Hyperresponsiveness in the Guinea PigIn VivoandIn Vitro: Role of the Epithelium

The administration by aerosol of the nitric oxide (NO) synthesis inhibitors, N omega-nitro-L-arginine methyl ester (L-NAME) or Ng-monomethyl-L-arginine (L-NMMA), to spontaneously breathing anesthetized guinea pigs resulted in a significant enhancement of lung resistance (RL) after increasing intravenous doses of histamine. The maximal response was increased (p < 0.01) by 126% (L-NAME) and 282% (L-NMMA) compared with the control groups. This effect was inhibited by giving an aerosol of the NO precursor L-arginine (L-Arg) but not by its inactive enantiomer D-arginine (D-Arg). Perfusion through the lumen of guinea pig tracheal tubes in vitro with nitric oxide synthesis inhibitors (120 microM) resulted in a significant increase in basal tone, suggesting a role for NO in the maintenance of basal tone. In addition, the histamine concentration-response curve was significantly shifted upward: the maximal response was increased (p < 0.01) by 335% (L-NAME) and 250% (L-NMMA) compared with the control group. This effect was concentration dependently inhibited by coincubation with L-Arg (120, 200, and 400 microM), but not with D-Arg (200 microM). Furthermore, removal of the epithelium resulted in an upward shift in the histamine concentration-response curve: the maximal response was increased by 185%. However, incubation with L-NAME did not further increase tracheal responsiveness to histamine, but addition of L-Arg (360 microM), when a plateau was reached, relaxed the tissues to control values. Nitric oxide synthesis inhibition did not change the responsiveness of intact tissues in vitro after intraluminal stimulation with leukotriene D4, serotonin, or the cholinergic agonist arecoline.(ABSTRACT TRUNCATED AT 250 WORDS)

Paradoxical facilitation of pilocarpine-induced seizures in the mouse by MK-801 and the nitric oxide synthesis inhibitor L-NAME

The sensitivity of pilocarpine-induced seizures to NMDA receptor blockade with MK-801, or to inhibition of synthesis of the second messenger nitric oxide (NO) with N ω- nitro- L-arginine methyl ester ( L-NAME), was studied in mice. The NO precursor L-arginine (100–500 mg/kg, IP) and L-NAME (1–125 mg/kg, IP) had no overt effects on animals' behaviour by themselves, while MK-801 (0.1–0.8 mg/kg, IP) caused motor excitability at low doses and sedation and paraplegia at high ones. Contrary to expectation, MK-801 and L-NAME failed to protect mice against limbic motor seizures induced by pilocarpine (400 mg/ kg, IP), and L-arginine was not proconvulsant in mice challenged with a threshold convulsant dose of the cholinomimetic (100 mg/kg, IP). Surprisingly, both MK-801 and L-NAME were found to be proconvulsant when injected in conjunction with 100 mg/kg pilocarpine, and in both cases this convulsant action synergised with that produced by the dopamine D 1 agonist SK&F38393 (10 mg/kg, IP). Concomitant administration of L-arginine (500 mg/kg) prevented the convulsant effect of 5 mg/kg L-NAME but was ineffective against 25 mg/kg L-NAME and MK-801. It is concluded that glutamate, acting through the NMDA receptor and NO production, normally suppresses epileptogenesis in the mouse pilocarpine model of limbic epilepsy.

Nitric oxide modulates the release of corticotropin-releasing hormone from the rat hypothalamus in vitro

There is now considerable evidence that nitric oxide (NO) is an important neuroregulatory agent, but there has been very little investigation of the possible role of NO in neuroendocrine mechanisms. We have previously shown that acute rat hypothalamic explants can be used to study the regulation of hypothalamic neuropeptide release, and we have now utilised this experimental approach to investigate the putative involvement of NO in the control of the principal corticotropin-releasing hormone, CRH. We studied the direct effects of the NO precursor l-arginine ( l-ARG), as well as the NO donors molsidomine and sodium nitroprusside, on both the basal and stimulated release of CRH; the stimuli used were non-specific depolarisation with potassium chloride (KCl) and the specific cytokine, interleukin-1β (IL-1β; 100 U/ml). l-ARG was tested in each experimental condition with and without contemporaneous addition of its competitive antagonist N G-monomethyl- l-arginine ( l-NMMA). IL-1β-induced CRH release was also investigated in the presence of d-arginine ( d-ARG), which is not active as a precursor to NO, and ferrous hemoglobin (Hb), a substance which is a potent inactivator of NO. None of the NO precursors ( l-ARG, molsidomine, sodium nitroprusside) or antagonist ( l-NMMA or Hb) was able to affect basal CRH release. However, l-ARG 10 and 100 μM were found to significantly inhibit the release of CRH induced by 40 mM KCl; CRH fell to 45% of its stimulated level at the higher dose of l-ARG. This effect was attenuated in the presence of l-NMMA at a ten-fold higher dose. Equally, molsidomine dose-dependently attenuated both 28 mM and 40 mM KCl-induced CRH release. A significant inhibitory effect on KCl 40 mM-induced CRH secretion was also shown by 100 μM and 10 μM sodium nitroprusside. The cytokine IL-1β 100 U/ml significantly stimulated the release of hypothalamic CRH compared to control incubation vials; this stimulation was significantly prevented by both 100 μM and 10 μM l-ARG. The CRH response to IL-1β was, however, fully restored by the addition of either l-NMMA or 10 μM Hb. Both sodium nitroprusside 1 μM and molsidomine 100 μM also significantly inhibited IL-1β-induced CRH release, while the addition of 10 μM Hb was found to antagonize both molsidomine and sodium nitroprusside effects. The l-ARG stereoisomer, d-ARG, was without effect on IL-1β-induced CRH secretion. Thus, NO appears to directly and specifically inhibit the stimulated release of CRH from rat hypothalamic explants in vitro, while leaving basal CRH secretion unaffected. These findings are the first direct evidence that NO may be involved in neuroendocrine regulation, most specifically, that it may modulate the release of a hypothalamic neurohormone. The blockade of the effect of IL-1β by NO also suggests that certain neuroendocrine-immune interactions may be modulated by NO.