Biosynthesis of nitric oxide from L-arginine. A pathway for the regulation of cell function and communication

Substrate-dependent regulation of intracellular amino acid concentrations in cultured bovine aortic endothelial cells

Amino acid deprivation induces adaptive changes in amino acid transport and the intracellular amino acid pool in cultured cells. In this study intracellular amino acid levels were determined in cultured bovine aortic endothelial cells (EC) deprived of L-arginine or total amino acids for 1, 3, 6 and 24 h. Amino acid concentrations were analyzed by reverse phase HPLC after precolumn derivatisation. Under normal culture conditions levels of L-arginine L-citrulline, total essential and non-essential amino acids were 840 +/- 90 microM, 150 +/- 40 microM, 11.4 +/- 0.9 mM and 53.3 +/- 3.4 mM (n = 9), respectively. In EC deprived of L-arginine or all amino acids for 24 h L-arginine and L-citrulline levels were 200 microM and 50 microM, and 670 microM and 100 microM Deprivation of L-arginine or total amino acids induced rapid (1 h) decreases (30 - 50%) in the levels of other cationic (lysine, ornithine) and essential branched-chain (valine, isoleucine, leucine) and aromatic (phenylalanine, tryptophan) amino acids. L-glutamine was reduced markedly in EC deprived of total amino acids for 1 h - 6 h but actually increased 3-fold in EC deprived of L-arginine for 6 h or 24 h. Arginine deprivation resulted in a rapid decrease in the total intracellular amino acid pool, however concentrations were restored after 24 h. Increased amino acid transport and/or reduced protein synthesis may account for the restoration of amino acid levels in EC deprived of L-arginine. The sustained reduction in the free amino acid pool of EC deprived of all amino acids may reflect utilization of intracellular amino acids for protein synthesis.

Cloned murine T lymphocytes synthesize a molecule with the biological characteristics of nitric oxide

Recently, activated neutrophils and macrophages have been shown to synthesize nitric oxide (NO) exclusively from L-arginine. We searched for the presence of this pathway in murine T cell clones. Using a platelet aggregation bioassay sensitive to NO, we demonstrate that IL2-stimulated CTLL and HT2 cells inhibit platelet aggregation, whereas unstimulated lymphocytes do not. This action can be inhibited by the specific NO synthase competitor NG-mono-methyl arginine, and only the L form of arginine or its analogue L-homoarginine are capable of providing substrate for NO synthesis.

Protective effect of S-nitroso-N-acetyl-penicillamine in endotoxin-induced acute intestinal damage in the rat

Macroscopic jejunal damage and plasma leakage induced within 15 min by E. coli lipopolysaccharide (LPS 50 mg kg-1 i.v.) in the rat was enhanced by the inhibitor of nitric oxide (NO) formation, NG-monomethyl-L-arginine (L-NMMA 50 mg kg-1 i.v.). The nitro-vasodilator, S-nitroso-N-acetyl-penicillamine (SNAP; 10 micrograms kg-1 min-1 i.v.), which generates NO, attenuated both LPS-induced intestinal damage and the enhancement of such damage and plasma leakage produced by L-NMMA. Endogenous NO may thus have a protective role in the intestinal vasculature that can be mimicked by generators of NO.

Rabbit brain contains an endogenous inhibitor of endothelium-dependent relaxation

1. Supernatants prepared from the rabbit brain, lung and liver caused an endothelium-dependent and volume-related contraction of the phenylephrine-pretreated rabbit aorta and inhibited relaxation due to acetylcholine (ACh). 2. Perfusion in situ of the rabbit lung or liver with Krebs solution substantially reduced or removed the endothelium-dependent inhibitor. Spectrophotometric analysis revealed the presence of substantial amounts of haemoglobin (1.8-2.1 microM) in these organ supernatants. 3. Supernatants prepared from the Krebs-perfused rabbit brain retained the ability to contract the phenylephrine-pretreated rabbit aorta and to inhibit relaxation due to ACh and substance P (SP). Rabbit brain supernatant did not reduce the vasodilator effect of sodium nitroprusside (NP) or nitric oxide (NO). 4. Rabbit brain supernatant contained low (less than 0.35 microM) concentrations of haemoglobin. 5. The inhibitory effect of rabbit brain supernatant was reversed by L-arginine (500 microM) but not D-arginine (500 microM). 6. The inhibitor of endothelium-dependent vasodilatation present in rabbit brain was not removed by dialysis (24 h, 4 degrees C) but was partially precipitated by ammonium sulphate (30% w/v). 7. Rabbit brain contains an endogenous inhibitor of vascular NO biosynthesis. The identity of this inhibitor is not known although it seems likely to be a large peptide or protein.

Glomeruli synthesize nitrite in experimental nephrotoxic nephritis

Activated macrophages synthesize nitric oxide (NO) from L-arginine. In culture, the major stable end product is nitrite (NO2). Activated macrophages accumulate in glomeruli and are responsible for injury in experimental immune complex glomerulonephritis. We examined NO2- production by isolated glomeruli and urinary NO2- in accelerated nephrotoxic nephritis in the rat. Normal glomeruli did not produce NO2- spontaneously or when stimulated with lipopolysaccharide (LPS) (1 microgram/ml) or A23187 (2 microgram/ml). Cultured mesangial cells at first or seventh passage did not produce NO2- spontaneously or when stimulated. Nephritic glomeruli spontaneously produced NO2 at all times studied; this production was maximal at 24 hours after induction of glomerulonephritis (158.4 +/- 8.4 nmol/48 hr/ml, N = 3). The production of NO2- was inhibited 75 to 100% by NG-monomethyl-L-arginine (L-NMMA), and this inhibition was reversed by L-arginine, indicating NO2- production from L-arginine via NO. The production of NO2- was increased by LPS (1 microgram/ml) at 2, 7 and 21 days. NO2- was undetectable in normal rat urine; however, it was present in urine of rats with glomerulonephritis (Day 0 to 1:8161 +/- 2605 nmol/24 hr. N = 12). The production of NO in nephritic glomeruli may have implications for both the mechanism of glomerular injury and glomerular hemodynamics.

Endogenous nitric oxide as a probable modulator of pulmonary circulation and hypoxic pressor response in vivo

The objective of this study was to investigate the role of endogenous nitric oxide, formed from L-arginine, in the regulation of pulmonary circulation in vivo, with special reference to the hypoxic pressor response. In artificially ventilated open-chest rabbits, pulmonary vascular resistance at normoxic ventilation (FIO2 = 21%) was 78 +/- 16 cmH2O ml-1 min 1000-1 (mRUL). Hypoxic ventilation (FIO2 = 10%) increased pulmonary vascular resistance to 117 +/- 17 mRUL. N omega-nitro-L-arginine methylester (L-NAME), an inhibitor of nitric oxide synthase, increased pulmonary vascular resistance at normoxic ventilation to 192 +/- 28 mRUL and during hypoxic ventilation to 462 +/- 80 mRUL. During N omega-nitro-L-arginine methylester infusion there was also an increase in mean arterial blood pressure as well as a decrease in cardiac output that was even more pronounced during hypoxic ventilation. L-arginine reversed the effect of N omega-nitro-L-arginine methylester on pulmonary vascular resistance at normoxic ventilation to 140 +/- 26 mRUL and at hypoxic ventilation to 239 +/- 42 mRUL. In spontaneously breathing closed-chest rabbits, N omega-nitro-L-arginine methylester evoked a marked decrease in arterial PO2 and increases in respiration frequency and central venous pressure, while blood pH, PCO2 and base excess remained unchanged. Taken together these findings indicate that endogenous nitric oxide, formed from L-arginine, might be a regulator of ventilation-perfusion matching at normoxic ventilation, and that nitric oxide acts as an endogenous modulator of the hypoxic pressor response.

Expression of cellular effector functions and production of reactive nitrogen intermediates: a comparative study including T lymphocytes, T-like cells, neutrophil granulocytes, and mononuclear phagocytes

The ability of various cell types to secrete reactive nitrogen intermediates (RNI) upon functional activation was comparatively assessed. Neither in T lymphocyte clones mediating MHC class I or class II antigen-restricted killing via alpha/beta T cell receptor (TcR) or MHC-unrestricted killing via gamma/delta TcR, nor in peripheral blood mononuclear cells expressing natural killer or lymphokine-activated killer activity, target cell lysis was associated with detectable RNI production. Also, activated neutrophil granulocytes did not secrete RNI. In contrast, bone marrow-derived mononuclear phagocytes, activated to express tumoricidal activity, secreted marked RNI activity.

Mono-L-arginine-containing compounds dilate piglet pial arterioles via an endothelium-derived relaxing factor-like substance

We determined the effects of mono-L-arginine-containing compounds on pial arterioles of anesthetized piglets. A closed cranial window was implanted, and the diameter of one pial arteriole was determined by intravital microscopy. Diameter was determined during application of artificial cerebrospinal fluid containing no drugs and during application of 10(-5), 10(-4), 10(-3), and 10(-2) M L-arginine (ARG), L-arginine ethyl ester (AEE), N alpha-benzoyl-L-arginine (NBA), N alpha-benzoyl-L-arginine ester ethyl (BAEE), and L-citrulline (CIT). Initial diameters were 100-200 microns. All of these compounds dilated arterioles, but the threshold concentration needed to elicit dilation varied: 10(-5) M for NBA (n = 5), 10(-3) M for AEE (n = 9) and BAEE (n = 6), and 10(-2) M for ARG (n = 6) and CIT (n = 4). Maximal responses were 15 +/- 8% for CIT, 17 +/- 4% for ARG, 19 +/- 8% for BAEE, 28 +/- 5% for NBA, and 27 +/- 6% for AEE. Indomethacin pretreatment (5 mg/kg i.v.) did not change arteriolar responses to AEE, NBA, and BAEE. However, coadministration of methylene blue (0.5 x 10(-4) M or 0.5 x 10(-3) M) abolished dilation to 10(-3) M AEE or BAEE and attenuated dilation to 10(-5) M NBA. In addition, coadministration of hemoglobin (0.4 x 10(-4) M) abolished dilation to AEE, BAEE, or NBA. Last, intravenous (5 mg/kg) and coadministration (10(-3) M) of NG-methyl-L-arginine blocked dilation to NBA or AEE. We conclude that mono-L-arginine-containing compounds produce pial arteriolar dilation in piglets, possibly involving an endothelium-derived relaxing factor.

Reoxygenation injury and antioxidant protection: a tale of two paradoxes

Under certain circumstances, added antioxidants can protect tissues against reoxygenation injury after ischemia. Yet reperfusing blood carries many antioxidants with it. The implications of this "antioxidant paradox" are discussed.

Endotoxin-induced impairment of vasopressor and vasodepressor responses in the pithed rat

1. Effects of E. coli endotoxin on vascular responsiveness to a variety of agents were compared with those of the calcium channel blocking drug nicardipine in pithed rats. 2. Infusion of endotoxin (250 micrograms kg-1 h-1) produced a fall in mean arterial blood pressure (8 mmHg). A similar fall (11 mmHg) was seen in rats receiving nicardipine (1.0 mg kg-1). 3. Endotoxin impaired responsiveness to vasopressin, phenylephrine and cirazoline, producing a shift to the right in the dose-response curves without any change in the maximum response. Responsiveness to 5-hydroxytryptamine (5-HT) and to the alpha 2-adrenoceptor agonists clonidine and BHT 933, was also impaired with a marked reduction in their maximum responses. The dose-response curve to the pressor effects of endothelin was not significantly modified. 4. Nicardipine produced a similar pattern of impairment of responsiveness to these agents to that produced by endotoxin. However, nicardipine also shifted the pressor dose-response curve to endothelin to the right with no significant alteration in its maximum response. 5. The pressor responses to endothelin and to 5-HT were, respectively, preceded and followed by dose-dependent depressor responses, which were markedly reduced by endotoxin and nicardipine. 6. The concomitant infusion of arginine vasopressin (0.64 iu kg-1 h-1) prevented endotoxin-induced hypotension and also prevented the impairment in responsiveness to cirazoline and to BHT 933. 7. The similarity of the pattern of impaired pressor responsiveness (except in relation to endothelin) and depressor responsiveness produced by endotoxin and nicardipine may be consistent with a common mechanism of action.

Modulation of autonomic neuroeffector transmission by nitric oxide in guinea pig ileum

NG-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide synthesis, markedly enhanced tonic ("hump") responses to transmural stimulation in guinea pig ileum longitudinal muscle. The enhancement of the hump responses was probably due to a prejunctional effect on substance P-like neurotransmission, since the action of L-NMMA was exerted also in the presence of atropine, and since responses to substance P, a mimic of nerve stimulation, were unaffected by L-NMMA as were cholinergic twitch responses and the overflow of [3H]choline. Further in support, the hump responses were blocked by the substance P antagonist Spantide. All effects of L-NMMA were stereospecifically reversed by L-arginine. Endogenous nitric oxide thus selectively modulates peptidergic neurotransmission in the gut.

Induction of nitric oxide synthase by cytokines in vascular smooth muscle cells

We investigated the mechanisms by which cytokines lead to a diminished responsiveness of vascular smooth muscle to vasoconstrictors. The attenuation of noradrenaline-induced contraction by 6 to 24 h incubations with the cytokines, tumor necrosis factor and interleukin-1, in endothelium-denuded rabbit aorta was associated with an increase in intracellular cyclic GMP level. This increase was abolished by the stereoselective inhibitor of nitric oxide-synthase, NG-nitro-L-arginine and by cycloheximide. Formation of nitric oxide was detected in the cytosol of cytokine-treated native and cultured smooth muscle cells by activation of purified soluble guanylate cyclase, and depended on tetrahydrobiopterin, but not on Ca2(+)-calmodulin. The results indicate that cytokines induce a nitric oxide-synthase of the macrophage-type in vascular smooth muscle.

Anti-inflammatory glucocorticoids inhibit the induction by endotoxin of nitric oxide synthase in the lung, liver and aorta of the rat

The induction by endotoxin of Ca2(+)-independent nitric oxide (NO) synthase in the lung and liver of the rat was prevented by the glucocorticoids dexamethasone and cortisol but not by progesterone. The activity of the constitutive Ca2(+)-dependent NO synthase in the brain and the aorta was not affected by treatment with either endotoxin or glucocorticoids. In the aorta a Ca2(+)-independent NO synthase was also found following endotoxin treatment of rats, and this induction was likewise prevented by dexamethasone. The Ca2(+)-dependent NO synthase in the aorta was located in the vascular endothelium, whereas the Ca2(+)-independent enzyme was predominantly located in the vascular smooth muscle layer. Inhibition of induction of the Ca2(+)-independent NO synthase in vivo may underlie some of the physiological and pharmacological effects of the anti-inflammatory glucocorticoids.

Non-adrenergic non-cholinergic relaxation mediated by nitric oxide in the canine ileocolonic junction

The nature of the inhibitory non-adrenergic non-cholinergic (NANC) neurotransmitter was studied in circular muscle strips of the canine terminal ileum and ileocolonic junction. Nitric oxide (NO) induced tetrodotoxin-resistant NANC relaxation, similar to that induced by electrical stimulation or acetylcholine (ACh). Incubation with the stereospecific inhibitors of NO biosynthesis, NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine (L-NNA), resulted in an increase of basal tension in the ileocolonic junction which was partly reversed by L-arginine but not by D-arginine. Moreover, L-NMMA and L-NNA, but not D-NMMA, concentration dependently inhibited the NANC relaxation in response to electrical stimulation and ACh, but not that in response to NO or nitroglycerin. This inhibitory effect was reversed by L-arginine but not by D-arginine. Hemoglobin reduced the NANC relaxation in response to electrical stimulation, ACh and nitroglycerin, and abolished the responses to NO. Our results suggest that NO or a NO releasing substance mediates the NANC relaxation in the canine terminal ileum and ileocolonic junction.

Role of endothelium-derived nitric oxide in the regulation of tonus in large-bore arterial resistance vessels, arterioles and veins in cat skeletal muscle

The role of endothelium-derived nitric oxide in the regulation of vascular resistance (tonus) in cat skeletal muscle was studied with the use of NG-monomethyl-L-arginine (L-NMMA), a specific inhibitor of nitric oxide formation from L-arginine. The study was performed with a whole-organ technique which permits simultaneous, continuous and quantitative recordings of resistance reactions in the whole vascular bed (RT) and in its three consecutive sections: large-bore arterial resistance vessels (greater than 25 microns; Ra,prox), small arterioles (less than 25 microns; Ra,micro) and veins (Rv). NG-monomethyl-L-arginine (3-100 mg kg-1 tissue, i.a.) induced a dose-dependent increase in resistance that was preferentially, but not selectively, confined to the large-bore arterial resistance vessels. At a maximally effective dose (100 mg kg-1), the nitric oxide inhibitor caused a marked constriction, within 5 min, on average increasing RT by 99%, Ra,prox by 138%, Ra,micro by 18% and Rv by 23%. The constrictor response to NG-monomethyl-L-arginine was long-lasting but disappeared gradually over a period of about 1 h. However, it could be abruptly abolished by excess L-arginine (300 mg kg-1, i.a.). The vasodilator response (RT) to acetylcholine was significantly attenuated in the presence of NG-monomethyl-L-arginine compared with the control response. The results suggested that nitric oxide formation from L-arginine by the vascular endothelium plays a fundamental role in the regulation of vascular resistance (tone) in vivo, with its main site of action located in the large-bore arterial resistance vessels.

Regional and cardiac haemodynamic responses to glyceryl trinitrate, acetylcholine, bradykinin and endothelin-1 in conscious rats: effects of NG-nitro-L-arginine methyl ester

1. Conscious Long Evans rats, chronically instrumented for cardiovascular measurements, were challenged with i.v. bolus doses of glyceryl trinitrate (40 nmol kg-1), acetylcholine (1.2 nmol kg-1), bradykinin (3.2 nmol kg-1), or endothelin-1 (0.25 nmol kg-1). Under control conditions these doses produced similar falls in mean arterial blood pressure (glyceryl trinitrate, -20 +/- 3 mmHg; acetylcholine, -24 +/- 2 mmHg: bradykinin, -21 +/- 3 mmHg; endothelin-1, -25 +/- 3 mmHg), associated with renal, mesenteric and hindquarters vasodilatations (except for endothelin-1 which caused mesenteric vasoconstriction). 2. In the presence of NG-nitro-L-arginine methyl ester (L-NAME, 10 mgkg-1), a potent inhibitor of nitric oxide biosynthesis and endothelium-dependent vasorelaxation in vitro, the hypotensive responses to glyceryl trinitrate, acetylcholine, and endothelin-1 were increased, although that to bradykinin was not. However, comparing the differences between the response to glyceryl trinitrate and that to any other agonist in the absence and presence of L-NAME showed that there were relative attenuations of the hypotensive responses to bradykinin and endothelin-1, but not to acetylcholine, in the presence of L-NAME. 3. This comparative analysis showed that the renal and hindquarters vasodilator responses to bradykinin and endothelin-1 were attenuated in the presence of L-NAME, but the renal, mesenteric and hindquarters vasodilator responses to acetylcholine were not. However, when L-NAME was administered in the presence of pentolinium, captopril and the vasopressin V1-receptor antagonist, d(CH2)5[Tyr-(Et)]DAVP, (to abolish baroreflex and neurohumoral mechanisms), there was attenuation of the renal and mesenteric vasodilator effects of acetylcholine relative to those seen with glyceryl trinitrate. Under those conditions only the renal vasodilator effects of bradykinin and endothelin-1 were attenuated. 4. In separate experiments in conscious Long Evans rats, direct measurement of cardiac haemodynamics showed that the hypotensive responses to glyceryl trinitrate, acetylcholine, bradykinin and endothelin-l were entirely attributable to rises in total peripheral conductance since both in the absence and presence of L-NAME there were no reductions in cardiac index in response to these substances. 5. The results indicate that measurement of systemic arterial blood pressure alone in conscious rats does not permit reliable quantitation of the influence of L-NAME on regional vasodilator responses to glyceryl trinitrate, acetylcholine, bradykinin or endothelin-1. Furthermore, these substances exert effects in different vascular beds that may be differentially influenced by baroreflex mechanisms, neurohumoral mechanisms, or both. Moreover, except in the case of the renal vasodilator response to endothelin-1 (which was abolished in the presence of L-NAME), even when L-NAME caused attenuation of the vasodilator effects of acetylcholine or bradykinin (relative to glyceryl trinitrate), substantial responses remained. It is feasible that such responses in vivo are nitric oxide-independent.

Endothelin and a Ca2+ ionophore raise cyclic GMP levels in a neuronal cell line via formation of nitric oxide

1. The vasoconstrictor peptide endothelin-1 caused a fast, transient rise in guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels in a neuronal cell line (mouse neuroblastoma x rat glioma hybrid cells 108CC15). The mechanism of activation of guanylate cyclase by endothelin-1 was investigated. The endothelin-1-induced rise depended on the release of internal Ca2+. 2. The stimulation of cyclic GMP synthesis induced by endothelin-1 was suppressed after preincubating the cells in medium containing haemoglobin (IC50 3 microM). Similarly, pretreatment of the cells with the L-arginine analogues, L-canavanine (IC50 60 microM) or NG-monomethyl-L-arginine (IC50 2.5 microM), inhibited the cyclic GMP response to endothelin-1. Therefore, endothelin-1 activates guanylate cyclase most probably via formation of nitric oxide, which is released from L-arginine. 3. The Ca2+ ionophore ionomycin induced a transient rise in cyclic GMP levels, which was also suppressed by preincubation in the presence of either haemoglobin or the L-arginine analogues L-canavanine or NG-monomethyl-L-arginine. Therefore, we conclude that ionomycin can activate guanylate cyclase by a mechanism involving nitric oxide formation, similar to that induced by endothelin-1. 4. The alkaloid veratridine, which activates Na+ channels and also causes influx of Ca2+ induced a transient rise of cyclic GMP levels in the neuronal cell line. This stimulation was blocked by pretreating the cells with L-canavanine, NG-monomethyl-L-arginine or haemoglobin. 5. Loading the cells with the Ca2+ chelator BAPTA suppresed the cyclic GMP response to application of endothelin-1, ionomycin, or veratridine. Thus, in the neuronal cell line a rise in cytosolic Ca2 + activity seems to be sufficient to stimulate the nitric oxide forming enzyme which synthesizes the activator of soluble guanylate cyclase.

Serotonin stimulates both cytosolic and membrane-bound guanylate cyclase in NG108-15 cells

The cyclic GMP (cGMP) content was rapidly (greater than 30 s) increased by serotonin [5-hydroxytryptamine (5-HT)] (EC50 = 10 microM), and the increase lasted for greater than 10 min in NG108-15 cells. The 5-HT-induced elevation of cGMP level (EC50 = 10 microM) at 20 s ("fast" elevation) was inhibited by ICS 205-930 or MDL 72,222 and by Ca2+ deficiency in the reaction medium but not by organic Ca2+ antagonists. The 5-HT effect at 10 min ("slow" elevation) was not inhibited by several antagonists for 5-HT receptors of the 1A, 1B, 1C, 1D, 2, and 3 subtypes and was independent from external Ca2+ concentration. The fast and slow effects of 5-HT were similar to the effects of bradykinin and atrial natriuretic peptide (ANP), respectively, in aspects of both Ca2+ dependency and time course of the effects. Bradykinin transiently stimulated formation of inositol phosphates as well as accumulation of cGMP, a finding suggesting that intracellular Ca2+ is involved in bradykinin-induced cGMP accumulation as shown in the fast response to 5-HT. ANP, an activator of membrane-associated guanylate cyclase (mGC), slowly (approximately 60 s) increased the cGMP content (EC50 = 10 nM), a result lasting for greater than 10 min, and the effects were independent from external Ca2+, as shown in the slow response to 5-HT. 5-HT and ANP did not induce formation of inositol phosphates.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional and cardiac haemodynamic effects of NG-nitro-L-arginine methyl ester in conscious, Long Evans rats

1. Regional haemodynamic responses to i.v. bolus doses (0.1-10.0 mg kg-1) of NG-nitro-L-arginine methyl ester (L-NAME) were measured in conscious, Long Evans rats (n = 8) chronically instrumented with renal, mesenteric and hindquarters pulsed Doppler flow probes and intravascular catheters. 2. L-NAME caused dose-dependent pressor effects associated with renal, mesenteric and hindquarters vasoconstrictions. The mesenteric vascular bed showed earlier onset with more rapid, and greater, maximum vasoconstrictions than the renal or hindquarters vascular beds; however, the hindquarters vasoconstriction was more persistent. D-NAME was without significant effects (n = 2). 3. Primed infusion of L-arginine (100 mg kg-1 bolus followed by 100 mg kg-1 h-1 infusion), starting 10 min after an i.v. bolus injection of L-NAME (10 mg kg-1), caused significant reversal of the pressor responses, and renal and mesenteric vasoconstrictions, but not of the hindquarters vasoconstriction. Primed infusions of L-arginine (100 mg kg-1, 100 mg kg-1 h-1) starting 5 min after L-NAME (1 mg kg-1) additionally caused some reversal of the hindquarters vasoconstriction, but this effect was transient. 4. Primed infusion of L-arginine (100 mg kg-1, 100 mg kg-1 h-1) starting 30 min before i.v. bolus injection of L-NAME (10 mg kg-1) caused significant attenuation of the pressor effects and the renal and mesenteric vasoconstrictions but not of the hindquarters vasoconstriction. 5. In a separate group of rats (n = 8) chronically instrumented with thoracic aortic electromagnetic flow probes for the measurement of cardiac haemodynamics, i.v. bolus injection of L-NAME (10mgkg-1) produced significant reductions in total peripheral conductance, cardiac output, stroke volume, peak thoracic aortic flow and the maximum rate of rise of aortic flow; these were coincident with the maximum pressor and vasoconstrictor effects. 6. These results, collectively, are consistent with L-NAME interfering with L-arginine-nitric oxide pathways that have important influences on regional vascular conductances in vivo. The pressor effect resulting from L-NAME-induced vasoconstrictions is offset by a substantial reduction in cardiac function that may depend on direct and/or indirect effects of L-NAME on the heart.

Cultured astrocytoma cells inhibit platelet aggregation by releasing a nitric oxide-like factor

Cultured astrocytoma cells were tested for their ability to generate a nitric-oxide like factor using platelet aggregation as a bioassay. Incubation of astrocytoma cells with human washed platelets resulted in an inhibition of thrombin-induced platelet aggregation which was proportional to the number of astrocytoma cells added. The inhibition was potentiated by superoxide dismutase (SOD) and prevented by oxyhaemoglobin (oxyHb). The inhibitory activity of astrocytoma cells was also prevented by the NO biosynthesis inhibitor NG-monomethyl-L-arginine (MeArg), an effect reversed by co-incubation with L-arginine (L-Arg) but not D-arginine (D-Arg). These results demonstrate that astrocytoma cells release, independent of added agonist, a factor with the same pharmacological profile as NO, which is likely to be derived from L-arginine.

Mechanisms of macrophage-mediated tumor cell killing: a comparative analysis of the roles of reactive nitrogen intermediates and tumor necrosis factor

The roles of tumor necrosis factor (TNF alpha) and reactive nitrogen intermediates (RNI) as effectors of macrophage-mediated tumor cell killing were investigated in a variety of tumor cell lines. Three TNF alpha-sensitive tumor targets were also susceptible to resting bone-marrow-derived mononuclear phagocytes (BMMP). This macrophage lytic activity was markedly diminished or even abolished by anti-TNF alpha, indicating that TNF alpha is the major effector of macrophage-mediated killing of these targets. The other 21 tumor cell lines examined were resistant to TNF alpha but, in their large majority, were more or less susceptible to killing by interferon gamma (IFN gamma)- and Corynebacterium parvum (CP)-activated BMMP. Among the various analogues of L-arginine used to assess the role of L-arginine-derived RNI as mediators of macrophage tumoricidal activity, NG-monomethyl-L-arginine (NMMA) was most efficient in suppressing RNI secretion by activated macrophages. In some macrophage tumor-cell combinations, NMMA inhibited both the generation of RNI and the expression of tumoricidal activity in a dose-dependent manner, suggesting a central role for RNI as effectors. In other combinations, NMMA in concentrations that abolished secretion of RNI either affected tumor-cell killing only after its induction by IFN gamma, or not at all. The findings not only support the thesis that macrophages posses various means of coping with tumor cells but also suggest that the mechanism becoming operative is determined predominantly by the pathway of macrophage activation and the properties of the tumor-cell type.

Characterization of the L-arginine:nitric oxide pathway in human platelets

1. The activation of the L-arginine: nitric oxide (NO) pathway during aggregation of human platelets by adenosine 5'-diphosphate (ADP), arachidonic acid, thrombin and the calcium ionophore A23187 and its inhibition by NG-monomethyl-L-arginine (L-NMMA), NG-nitro-L-arginine methyl ester (L-NAME) and N-iminoethyl-L-ornithine (L-NIO) were studied. The inhibition of the cytosolic platelet NO synthase by these compounds was also examined. 2. Platelet aggregation induced by ADP (1-10 microM) and arachidonic acid (0.1-10 microM), but not that induced by thrombin (1-30 mu ml-1) or A23187 (1-10 nM), was inhibited by L-, but not D-arginine (1-30 microM). However, in the presence of a subthreshold concentration of prostacyclin (0.1 nM) or of M & B 22948 (1 microM), a selective inhibitor of guanosine 3':5'-cyclic monophosphate (cyclic GMP) phosphodiesterase, L-arginine caused concentration-dependent inhibition of aggregation induced by all of these aggregating agents. 3. L-NMMA, L-NAME and L-NIO (all at 1-30 microM), but not their D-enantiomers, enhanced to the same extent platelet aggregation induced by ADP, arachidonic acid and thrombin without affecting that induced by A23187. 4. In the presence of 300 microM L-arginine, the NO synthase in platelet cytosol was inhibited by L-NMMA, L-NAME and L-NIO with IC50s of 74 +/- 9, 79 +/- 8 and 8.5 +/- 1.5 microM (n = 3), respectively. 5. These results indicate that the L-arginine: NO pathway in human platelets plays a role in the modulation of platelet aggregation.

Incubation with endotoxin activates the L-arginine pathway in vascular tissue

Rat aortic rings incubated with a low dose of endotoxin (100 ng ml-1) for 5 h exhibited depressed reactivity to norepinephrine (NE) which was independent of the presence of endothelium. An inhibitor of nitric oxide synthesis from L-arginine NGmonomethyl-L-arginine (300 microM), but not the inactive D-enantiomer, restored the contractile response of endotoxin-treated rings to control. The effect of NGmonomethyl-L-arginine was reversed by L-arginine (1 mM). In the absence of NGmonomethyl-L-arginine, L- but not D-arginine relaxed endotoxin-treated rings but was without effect on control tissues. This response was reversed following inhibition of guanylate cyclase by methylene blue (3 microM). In addition, tissue cyclic GMP content was 10 times greater in endotoxin-treated compared to control tissue. These data indicate that endotoxin can act directly on vascular tissue to induce a hyporeactivity to NE which is secondary to the activation of the L-arginine pathway and subsequent activation of soluble guanylate cyclase.

Regional haemodynamic changes during oral ingestion of NG-monomethyl-L-arginine or NG-nitro-L-arginine methyl ester in conscious Brattleboro rats

Homozygous Brattleboro (i.e. vasopressin-deficient) rats were chronically instrumented with pulsed Doppler probes and intravascular catheters to permit continuous monitoring of regional haemodynamics. Over a 9 h period, rats drinking water showed no systematic changes in heart rate or mean arterial blood pressure although renal, mesenteric and hindquarters vascular conductances fell. These changes showed diurnal rhythms, probably related to the nocturnal habits of rats. In separate groups of animals spontaneous oral ingestion of NG-monomethyl-L-arginine (L-NMMA; 1 mg ml-1) or NG-nitro-L-arginine methyl ester (L-NAME; 0.1 mg ml-1) caused marked hypertension but no significant bradycardia. Compared to control animals, rats drinking L-NMMA for 9 h showed significantly greater mesenteric and hindquarters vasoconstrictions, and rats drinking L-NAME showed greater vasoconstrictions in all 3 vascular beds.

Induction and activity of NO synthase in bone-marrow-derived macrophages are independent of Ca2+

The aim of the present study was to analyse whether an increase in the intracellular free Ca2+ concentration ([Ca2+]i) plays a role as a signal mediating synthesis of nitric oxide (NO) in bone-marrow-derived macrophages, either by stimulating induction of NO synthase or by regulating the activity of the enzyme. Therefore we compared the effects of various synthetic analogues of bacterial lipopeptide and of lipopolysaccharide (LPS) on NO production (assessed as nitrite formation during an incubation for 24 h) and on [Ca2+]i [measured with the fluorescent probe indo-1 (1-[2-amino-5-(6-carboxyindol-2-yl)phenoxy]-2- 2-(2'-amino-5'-methylphenoxy)ethane-NNN'N'-tetra-acetic acid)]. Strongly dissociating effects were evoked on nitrite formation and on [Ca2+]i by the stimuli. LPS was preferentially effective on nitrite formation, whereas the Ca2+ ionophore ionomycin and AlF3 induced increases only in [Ca2+]i. The lipopeptides N-palmitoyl-(S)-[2,3-bis(palmitoyloxy)-(2RS)- propyl]-(R)-cysteinylalanylglycine, N-palmitoyl-(S)-[2,3-bis(palmitoyloxy)- (2RS)-propyl]-(R)-cysteinylseryl-lysyl-lysyl-lysine and (S)-(1,2- dicarboxyhexadecyl)ethyl-N-palmitoylcysteinylseryl-lysyl-lys yl-lysine stimulated both parameters, but the maximal effects on nitrite formation and the shape of the dose-response curves did not parallel the effects on [Ca2+]i. Reduction of extracellular Ca2+ with EGTA significantly inhibited increases in [Ca2+]i, but did not change nitrite formation. Furthermore, NO synthesis in the cytosolic fraction of stimulated macrophages was not affected by Ca2+ over the concentration range 10 nM-2 microM. We conclude that increases in [Ca2+]i are not required for NO production in bone-marrow-derived macrophages. Thus the cellular regulation of NO production strikingly differs from that in the vascular endothelium, brain and adrenal gland.

Vascular smooth muscle influences the release of endothelium-derived relaxing factor

Conditioned medium was collected from vascular smooth-muscle cells grown in culture to determine if these cells synthesize vasoactive substances. The medium caused a short-acting endothelium-independent constriction of rat aorta, followed by a prolonged, endothelium-dependent relaxation. This relaxation was mediated through the release of endothelium-derived relaxing factor (EDRF) as it was abolished by the addition of methylene blue (5 x 10(-6) M), haemoglobin (10(-6) M) or methyl arginine, but was not affected by indomethacin (10(-5) M). Smooth-muscle medium stimulated the production of EDRF from both rat and rabbit thoracic aortic rings as well as from cultured bovine pulmonary artery endothelial cells. The prolonged stimulation of EDRF by smooth-muscle medium was not mimicked by known physiological stimuli to EDRF release; EDRF-stimulating activity was not affected when smooth-muscle cells were grown in the presence of indomethacin (10(-5) M), although serum in the medium was required. The EDRF-stimulating substance(s) in the smooth-muscle medium was heat stable and associated with a high molecular mass (30,000 greater than Mr greater than 3500) water-soluble species that is as yet unidentified.

Nanomolar N(G)-nitroarginine inhibits NMDA-induced cyclic GMP formation in rat cerebellum

The very large increases in cyclic GMP levels that occur in cerebellar slices in response to N-methyl-D-aspartate (NMDA) receptor agonists result from the synthesis of the guanylate cyclase activator, nitric oxide, from L-arginine. We show that an arginine analogue, L-NG-nitroarginine, inhibits the cyclic GMP response to NMDA in an arginine-sensitive manner. There were two components to the inhibition, IC50 values being 6 and 600 nM. L-NG-nitroarginine is most potent inhibitor of nitric oxide synthesis in the brain described so far. The dual-component inhibition may reflect the presence of two nitric oxide synthase enzymes which differ markedly in their sensitivity to this compound.

L-NG-nitro-arginine and its methyl ester are potent inhibitors of non-adrenergic, non-cholinergic transmission in the rat anococcygeus

1. The effects of L-NG-nitro-arginine (L-NOARG) and some other arginine analogues on non-adrenergic, non-cholinergic (NANC) relaxations of the rat anococcygeus muscle were investigated. 2. L-NOARG (5-200 microM) produced concentration-related inhibition of the NANC response; 100 microM L-NOARG produced 90% inhibition. 3. L-Arginine (5-200 microM) produced a concentration-related reversal of the inhibitory effect of 20 microM L-NOARG; a five fold excess of L-arginine (100 microM) was required to obtain the maximum reversal of 90%. D-Arginine (100 microM) produced no such reversal, but significant reversal was produced by L-citrulline, L-arginine-L-aspartate, L-homoarginine and L-arginine-methyl-ester (all at 100 microM). 4. L-NG-nitro-arginine-methyl-ester (L-NAME; 5-200 microM) also reduced NANC relaxations, with a potency similar to that of L-NOARG; both L-NOARG and L-NAME were some ten times more potent than L-NG-monomethyl-arginine (L-NMMA). Like L-NOARG, the effects of L-NAME (20 microM) were reversed by 100 microM L- but not D-arginine. 5. Neither L-NOARG nor L-NAME (both 20 microM) affected submaximal relaxations induced by 10 microM sodium nitroprusside or 20 microM hydroxylamine. 6. D-NOARG, L-NG-tosyl-arginine and L-N alpha-(t-butyl-oxycarbonyl)-NG-nitro-arginine (all at 100 microM) had no effect on NANC relaxations. 7. Thus, in the rat anococcygeus, L-NOARG and L-NAME are more potent than L-NMMA as prejunctional inhibitors of NANC transmission. The reversibility of the effect of L-NOARG by arginine analogues suggests that the NANC system of the anococcygeus shows similarities to the endogenous nitrate system recently described in the brain.

Inhibition of nitric oxide synthase blocks N-methyl-D-aspartate-, quisqualate-, kainate-, harmaline-, and pentylenetetrazole-dependent increases in cerebellar cyclic GMP in vivo

The synthesis of nitric oxide by brain slices has been demonstrated in several laboratories. In addition, in vitro studies have demonstrated stimulation of nitric oxide synthesis by excitatory amino acid receptor agonists. These data have led to the hypothesis that this readily diffusible "intercellular messenger molecule" acts to generate a cascade effect by activating guanylate cyclase in several cell types and thereby augment levels of the second messenger cyclic GMP (cGMP). Therefore, we evaluated this hypothesis in vivo, by testing the actions of the nitric oxide synthase inhibitor N-mono-methyl-L-arginine (NMMA) on elevations in level of mouse cerebellar cGMP generated by excitatory amino acid receptor agonists. The stimulatory effects of D-serine, quisqualate, and kainate were all found to be antagonized by this enzyme inhibitor. In addition, NMMA antagonized the increases in cerebellar cGMP level elicited by harmaline and pentylenetetrazole, pharmacological agents that augment endogenous excitatory amino acid transmission. Our data are, therefore, the first in vivo demonstration that nitric oxide is an important "messenger molecule" in the cerebellum, mediating the actions of kainate, quisqualate, and N-methyl-D-aspartate receptor agonists on guanylate cyclase. These data are consistent with previous in vitro findings with kainate and N-methyl-D-aspartate.

An L-arginine/nitric oxide pathway present in human platelets regulates aggregation

Aggregation of human washed platelets with collagen is accompanied by a concentration-dependent increase in cyclic GMP but not cyclic AMP. NG-Monomethyl-L-arginine (L-MeArg), a selective inhibitor of nitric oxide (NO) synthesis from L-arginine, reduces this increase and enhances aggregation. L-Arginine, which has no effect on the basal levels of cyclic GMP, augments the increase in this nucleotide induced by collagen and also inhibits aggregation. Both of these effects of L-arginine are attenuated by L-MeArg. The anti-aggregatory action of L-arginine is potentiated by prostacyclin and by M&B22948, a selective inhibitor of the cyclic GMP phosphodiesterase, but not by HL725, a selective inhibitor of the cyclic AMP phosphodiesterase. L-Arginine also inhibits platelet aggregation in whole blood in a similar manner, although the concentrations required are considerably higher. L-Arginine stimulates the soluble guanylate cyclase and increases cyclic GMP in platelet cytosol. This stimulation is dependent on NADPH and Ca2+ and is associated with the formation of NO. Both the formation of NO and the stimulation of the soluble guanylate cyclase induced by L-arginine are enantiomer specific and abolished by L-MeArg. Thus, human platelets contain an NO synthase which is activated when platelets are stimulated. The consequent generation of NO modulates platelet reactivity by increasing cyclic GMP. Changes in the activity of this pathway in platelets may have physiological, pathophysiological, and therapeutic significance.

Kinetic characteristics of nitric oxide synthase from rat brain

The relationship between the rate of synthesis of nitric oxide (NO) and guanylate cyclase stimulation was used to characterize the kinetics of the NO synthase from rat forebrain and of some inhibitors of this enzyme. The NO synthase had an absolute requirement for L-arginine and NADPH and did not require any other cofactors. The enzyme had a Vmax. of 42 pmol of NO formed.min-1.mg of protein-1 and a Km for L-arginine of 8.4 microM. Three analogues of L-arginine, namely NG-monomethyl-L-arginine, NG-nitro-L-arginine and NG-iminoethyl-L-ornithine inhibited the brain NO synthase. All three compounds were competitive inhibitors of the enzyme with Ki values of 0.7, 0.4 and 1.2 microM respectively.

Haem-dependent activation of guanylate cyclase and cyclic GMP formation by endogenous nitric oxide: a unique transduction mechanism for transcellular signaling

The interaction between nitric oxide (NO) synthesized in one cell and the haem group of cytosolic guanylate cyclase located in target cells to form NO-haem-guanylate cyclase represents a unique signal transduction mechanism that links extracellular stimuli to the synthesis of cyclic GMP in nearby target cells. Autacoids, neurotransmitters, and macrophage- and neutrophil-activating factors interact with selective extracellular receptors to trigger formation of NO from L-arginine. NO may be viewed as a second messenger. The NO diffuses into adjacent target cells and causes haem-dependent activation of guanylate cyclase, thereby stimulating cyclic GMP accumulation. Guanylate cyclase-bound haem serves as a transducer in transferring the signal from NO to guanylate cyclase. Cyclic GMP acts as a third messenger in causing vascular smooth muscle relaxation, inhibition of platelet aggregation and adhesion, and modulation of macrophage, neutrophil, and other phagocytic cell functions. The unique physical and chemical properties of NO allow it to function as an intercellular modulator within a localized environment. This intercellular or transcellular signaling mechanism involving a common signal transduction mechanism permits the rapid initiation of localized complementary cellular functions leading to increased local blood flow, inhibition of local thrombosis, and modulation of phagocytosis and cytotoxicity.

Endogenous nitric oxide as a modulator of rabbit skeletal muscle microcirculation in vivo

1. Intravital microscopy of rabbit tenuissimus muscle microvasculature was used for in vivo studies of the role of endogenous nitric oxide (NO) in local vascular control. Derivatives of arginine were applied topically in order to modulate the formation of NO from L-arginine. 2. L-NG-monomethylarginine (L-NMMA) (10-100 microM), but not D-NG-monomethylarginine (D-NMMA), dose-dependently reduced microvascular diameters. The vasoconstriction induced by L-NMMA (100 microM) was prevented by pretreatment with L-arginine (1 mM) but not with D-arginine (1 mM). Intravenous infusions of L-arginine (300 mg kg-1) reversed the effect of L-NMMA (100 microM). L-Arginine or D-arginine applied topically at 1 mM per se had no effect on microvascular diameters. 3. Vasodilatation by acetylcholine (0.03-3 microM) was significantly inhibited by L-NMMA (100 microM), whereas vasodilatation by adenosine (0.1-100 microM) or sodium nitroprusside (100 nM) was not affected. 4. The hyperaemic response after tenuissimus muscle contractions induced by motor nerve stimulation was unaffected by the presence of L-NMMA (100 microM). 5. Aggregates of platelets and white blood cells were seen in venules during superfusion with L-NMMA (100 microM), but not with D-NMMA (100 microM). 6. Our results suggest that endogenous NO formed from L-arginine is a modulator of microvascular tone and platelet and white cell-vessel wall interaction in vivo. Nitric oxide does not, however, appear to play a role in the mediation of functional hyperaemia in this tissue.

Purification of soluble guanylyl cyclase from bovine lung by a new immunoaffinity chromatographic method

Soluble guanylyl cyclase was purified from bovine lung by an immunoaffinity chromatographic method using IgG fractions of antisera against a synthetic peptide of the C-terminus of the 70-kDa subunit of the enzyme. After anion-exchange chromatography, the enzyme was bound to an immunoaffinity column and was eluted with the synthetic peptide. This method allowed the convenient isolation of 2 mg of apparently homogeneous enzyme from 40 g cytosolic proteins. The enzyme had an apparent molecular mass of about 150 kDa and consisted of two subunits (70 kDa and 73 kDa) as determined by gel permeation fast protein liquid chromatography and SDS/PAGE. The basal activities determined in the presence of Mg2+ and Mn2+ were 10-20 nmol.min-1.mg-1 and 80-100 nmol.min-1.mg-1, respectively. The enzyme exhibited an ultraviolet-visible absorption spectrum typical for hemoproteins, with a Soret band at 430 nm. The purified enzyme was stimulated by NO-containing compounds. Maximal enzyme activities measured in the presence of sodium nitroprusside were 1.2-2.4 mumol.min-1.mg-1 (half-maximal effect of sodium nitroprusside at 1.3-1.9 microM) and 0.9-1.8 mumol.min-1.mg-1 (half-maximal effect at 0.28-0.41 microM sodium nitroprusside) in the presence of Mg2+ and Mn2+, respectively. The method developed for the large-scale purification of soluble guanylyl cyclase by immunoaffinity chromatography, using synthetic peptides for the elution of the enzyme, appears to be superior to previously described methods. As antibodies against synthetic peptides corresponding to deduced amino acid sequences of the respective protein are easily obtained, the described method may be suitable for a convenient large-scale purification of various proteins.

Nitric oxide as an inhibitory non-adrenergic non-cholinergic neurotransmitter

Inhibitory non-adrenergic non-cholinergic (NANC) nerves are thought to be important in the autonomic innervation of the gastrointestinal tract and other organ systems. The nature of their neurotransmitter is still debated. Speculation that nitric oxide (NO), formed from L-arginine in neuronal structures and other cells, could act as a neurotransmitter, is not yet supported by demonstration of its release upon nerve stimulation. Using a superfusion bioassay, we report the release of a vasorelaxant factor upon stimulation of the NANC nerves in the canine ileocolonic junction. Several pieces of evidence, including the selectivity of the bioassay tissues, chemical instability, inactivation by superoxide anion and haemoglobin, inhibition by NG-nitro-L-arginine (L-NNA) and potentiation by L-arginine all indicated that NO accounted for the biological activity of this transferable NANC factor.

Effects of indomethacin on the regional haemodynamic responses to low doses of endothelins and sarafotoxin

1. Regional haemodynamic responses to i.v. bolus injections of low doses (4 pmol and 40 pmol) of endothelin-1, -2, -3 and sarafotoxin-S6b were assessed in conscious, Long Evans rats in the absence and presence of indomethacin. 2. Both doses of endothelin-3 and sarafotoxin-S6b caused early renal vasodilatations that were not affected by indomethacin. Endothelin-1 caused an initial renal vasodilatation only in the presence of indomethacin, indicating that this peptide produced concurrent release of cyclo-oxygenase products that caused renal vasoconstriction. Neither dose of endothelin-2 produced an increase in renal conductance. 3. The 4 pmol dose of all four peptides caused mesenteric vasoconstrictions only. With the 40 pmol dose of the peptides, none caused early mesenteric vasoconstriction except in the presence of indomethacin. Thus, in this vascular bed the primary vasoconstrictor effects of the peptides (seen with the 4 pmol dose) were offset, following the 40 pmol dose, by release of vasodilator cyclo-oxygenase products. Indomethacin alone caused significant vasoconstriction only in the mesenteric vascular bed, indicating that in this region of the circulation, vasodilator prostanoids might be involved also in the tonic control of vascular conductance. 4. All four peptides at both doses caused early hindquarters vasodilatation. However, only the initial hypotensive and hindquarters vasodilator effects of the 40 pmol dose of sarafotoxin-S6b were attenuated by indomethacin. Under these conditions the hindquarters vasodilator effects of sarafotoxin-S6b were similar to those of the other peptides, indicating that the more marked effects of sarafotoxin-S6b in the absence of indomethacin were contributed to by vasodilator cyclo-oxygenase products in the hindquarters.

Control of regional blood flow by endothelium-derived nitric oxide

The regional hemodynamic consequences of inhibiting vascular endothelial nitric oxide generation with NG-monomethyl-L-arginine (L-NMMA) were studied in conscious Long-Evans rats. Experiments were carried out in groups of chronically instrumented rats with intravascular catheters and pulsed Doppler probes to monitor regional blood flow. L-NMMA (0.3-300 mg/kg) caused a dose-dependent, long-lasting (5-90 minutes), and enantiomerically specific increase in mean blood pressure and also caused bradycardia. The increase in blood pressure was accompanied by a dose-dependent and long-lasting vasoconstriction in the internal carotid, mesenteric, renal, and hindquarters vascular beds that could be attenuated, in a concentration-dependent manner, by L-arginine but not by D-arginine. In contrast, L-arginine did not affect the pressor or vasoconstrictor effects of vasopressin. These results indicate that nitric oxide production by vascular endothelial cells contributes to the maintenance of blood pressure and to the control of the resting tone of different vascular beds in the conscious rat.

Inhibition of endothelial nitric oxide biosynthesis by N-nitro-L-arginine

1. The actions of N-nitro-L-arginine (NOLA) on the release of nitric oxide (NO) from arterial endothelial cells was studied in rat isolated thoracic aortic rings and by bioassay of NO derived from cultured bovine aortic endothelial cells. 2. NOLA (3-10 mumol/L) caused concentration-dependent inhibition of acetylcholine-induced relaxation of phenylephrine-contracted rat aortic rings, which is dependent on the release of NO from the endothelium. The inhibitory actions of NOLA could be prevented by pre- and co-incubation with L-arginine (1 mmol/L). 3. Endothelium-independent relaxation induced by sodium nitroprusside was not affected by NOLA. 4. The release of NO from bovine aortic endothelial cells, induced by bradykinin (10 nmol/L), was detected by bioassay on pre-contracted rabbit aortic strips. NOLA (1-3 mumol/L, given through the cell column) reduced or abolished the release of NO, but did not affect relaxations of the bioassay tissues induced by glyceryl trinitrate or authentic NO. 5. These data indicate that NOLA potently inhibits the biosynthesis of NO from L-arginine, and thus prevents its release from arterial endothelial cells. It may be a useful pharmacological tool for probing the significance of NO biosynthesis in cardiovascular function.

Effect of N alpha-benzoyl-L-arginine ethyl ester on coronary perfusion pressure in isolated guinea pig heart

N alpha-Benzoyl-L-arginine ethyl ester (BAEE) when compared to L-arginine significantly decreased coronary perfusion pressure of isolated guinea pig heart in a dose dependent and reproducible manner. This effect of BAEE was antagonized by haemoglobin and N-monomethyl L-arginine, both inhibitors of endothelium dependent relaxation. These results support the notion that the mechanism of relaxation elicited by BAEE is due to the generation endothelium dependent relaxing factor (EDRF) like agents.

L-NG-monomethyl arginine and L-NG-nitro arginine inhibit non-adrenergic, non-cholinergic relaxation of the mouse anococcygeus muscle

1. The effects of L-NG-monomethyl arginine (L-NMMA) and L-NG-nitro arginine (L-NOARG) on non-adrenergic, non-cholinergic (NANC) relaxations of the mouse anococcygeus were investigated. 2. L-NMMA (10-200 microM) produced a concentration-related inhibition of the NANC response; the inhibitory effect of 50 microM L-NMMA was completely reversed by L-arginine but not D-arginine (both 100 microM). 3. L-NOARG (1-50 microM) also produced a concentration-related inhibition of the NANC response and was some 30-50 times more potent than L-NMMA; again, the effects of 10 microM L-NOARG were reversed by 100 microM L-, but not D-, arginine. By itself 100 microM L-arginine did not relax the tissue, but did cause a slight potentiation of the NANC response. 4. Sodium nitroprusside (0.01-10 microM), hydroxylamine (0.1-100 microM), sodium azide (1-100 microM) and nitric oxide (3-120 microM) all relaxed carbachol-induced tone; relaxations to submaximal concentrations of these nitrovasodilators were unaffected by either 50 microM L-NMMA or 10 microM L-NOARG. 5. L-NOARG 10 microM did not inhibit, but rather potentiated, contractions of the mouse anococcygeus due to stimulation of its sympathetic nerves. 6. The inhibitory effects of 10 microM L-NOARG on NANC relaxations were reversed by L-arginine (by 131%), L-citrulline (by 75%), L-arginine methyl ester (by 46%) and L-homoarginine (by 22%), but were unaffected by a variety of other amino acids and their derivatives (all at 100 microM). 7. The results provide strong evidence that NANC relaxations of the mouse anococcygeus are mediated by an endogenous nitrate material, probably derived from L-arginine, and confirm that L-NOARG provides a very useful and potent drug for the investigation of endogenous nitrate function.

L-NG-nitro arginine (L-NOARG), a novel, L-arginine-reversible inhibitor of endothelium-dependent vasodilatation in vitro

1. The effect of L-NG-nitro arginine (L-NOARG) was compared with that of L-NG-monomethyl arginine (L-NMMA) on vasodilatation of the isolated aorta of the rabbit and perfused mesentery of the rat in response to acetylcholine (ACh) and sodium nitroprusside (NP). 2. L-NOARG (1.5-100 microM) and L-NMMA (3-100 microM) produced concentration-related contraction of the rabbit aorta precontracted with phenylephrine (700-900 nM). Similarly, L-NOARG (10-200 microM) and L-NMMA (30-100 microM) elevated perfusion pressure of the noradrenaline (NA, 0.6-2.5 mM)-preconstricted rat mesentery preparation. 3. L-NOARG (1.5-100 microM) and L-NMMA (3-100 microM) caused concentration-related inhibition of the vasodilator effect of ACh (0.01-1.0 microM) on the rabbit aorta without influencing responses to NP (0.03-0.5 microM). L-NOARG methyl ester (30 microM) also inhibited ACh-induced vasorelaxation with similar potency to NOARG. L-arginine (30-150 microM) but not D-arginine (100 microM) caused graded reversal of the inhibitory effect of both L-NOARG (15 microM) and L-NMMA (30 microM). Complete reversal of the effect of both inhibitors was achieved with 150 microM L-arginine. L-Alanine (50 microM), L-arginosuccinic acid (5 microM), L-citrulline (50 microM), L-methionine (50 microM) and L-ornithine (50 microM) failed to reverse the inhibitory effect of L-NOARG (15 microM). 4. L-NOARG (10-200 microM) and L-NMMA (30-100 microM) inhibited the vasodilator effect of ACh (0.006-18.0 nmol) in the rat mesentery without affecting vasodilatation due to NP (1.1-11.1 nmol). L-Arginine (100 microM) but not D-arginine (100 microM) produced partial reversal of the effect of L-NOARG (30 microM) and L-NMMA (30 microM). 5. L- and D-N'-butyloxycarbonyl No-nitro arginine (100 microM) produced modest (approximately 20%) inhibition of the effect of ACh on the rabbit aorta; this effect was not reversible with L-arginine (100 microM). L-Namonocarbobenzoxy arginine (L-NMCA, 5O microM), L-N-NG-dicarbobenzoxy arginine (L-NDCA, 5 microM) and L-NG-tosyl arginine (50 microM) were inactive. 6. These results identify L-NOARG as a potent, L-arginine reversible inhibitor of endothelium-dependent vasodilatation. The available data suggests that L-NOARG, like L-NMMA, inhibits endothelial nitric oxide (NO) biosynthesis.