Dermal dendritic melanocytic proliferations: an update

Dermal dendritic melanocytic proliferations are a broad group of congenital and acquired melanocytic lesions characterized by the presence of dermal spindled and dendritic cells resembling melanocytes migrating from the neural crest to the epidermis. Historically, they were subdivided into dermal melanocytoses (naevus of Ota, Ito, Mongolian spot and related conditions), blue naevi and malignant blue naevi. The purpose of this review is to provide an update on recent developments in the field with emphasis on new entities and their differential diagnosis.

Morphological analysis of nevoid melanoma: a study of 20 cases with a review of the literature

Nevoid melanoma is a rare variant of melanoma characterized by deceptive morphologic features reminiscent of a benign melanocytic nevus. Twenty (13 nodular, 7 verrucous) nevoid melanomas were reviewed with the goal of identifying the predominant architectural patterns, cytologic features, and prognostic indicators. Although at scanning magnification, many lesions showed a strong resemblance to banal compound or dermal nevi, careful inspection in all cases demonstrated subtle pleomorphism and impaired maturation with depth, invariably accompanied by multiple dermal mitoses. Four tumors recurred and three metastasized, with subsequent death of the patients. Follow-up information for a period of at least 3 years was available in eight cases. In this group, mortality was 37.5%, the metastasis rate was 37.5%, and the local recurrence rate was 75%, with an average tumor thickness of 2.5 mm. We conclude that nevoid melanoma may be distinguished from a benign melanocytic nevus by a high index of suspicion, a careful analysis of architecture, and attention to cytologic features. Our data and a review of the literature do not support the notion that nevoid melanoma has a better prognosis than ordinary melanoma.

Massive myocardial necrosis in thrombotic thrombocytopenic purpura: a case report and review of the literature

Thrombotic thrombocytopenic purpura (TTP) is an uncommon syndrome resulting from diffuse occlusion of small arterioles and capillaries by hyaline microthrombi. It is characterized by fever, thrombocytopenic purpura, microangiopathic hemolytic anemia, and neurologic and renal dysfunction. While cardiac pathology in TTP is commonly seen at autopsy, clinical cardiac dysfunction is rare and typically results from conduction system involvement. While 3% to 8% of patients with TTP report chest pain on admission, reports of fatal ventricular pump failure are extremely rare. We now report a case of TTP resulting in death from widespread myocardial necrosis. This patient presented with elevated cardiac enzymes and electrocardiographic disturbances that mimicked viral myocarditis, as well as a profound thrombocytopenia. Such a case may represent the extreme of a distribution of cardiac involvement in TTP or the consequence of an unidentified autoimmune process capable of precipitating severe myocardial TTP.

Roles of IL-1 and TNF in the decreased ileal muscle contractility induced by lipopolysaccharide

Gastrointestinal stasis during sepsis may be associated with gastrointestinal smooth muscle dysfunction. Endotoxin [lipopolysaccharide (LPS)] impairs smooth muscle contraction, in part through inducible nitric oxide synthase (NOS II) and enhanced nitric oxide production. We studied the roles of tumor necrosis factor-alpha (TNF) and interleukin-1 (IL-1) in this process by using TNF binding protein (TNFbp) and IL-1 receptor antagonist (IL-1ra). Rats were treated with TNFbp and IL-1ra, or their vehicles, 1 h before receiving LPS or saline. At 5 h after LPS, contractility was measured in strips of ileal longitudinal smooth muscle, and NOS II activity was measured in full-thickness segments of ileum. LPS decreased maximum stress (mean +/- SE) from 508 +/- 55 (control) to 355 +/- 33 g/cm2 (P < 0.05). Pretreatment with TNFbp plus IL-1ra prevented the LPS-induced decrease. Separate studies of TNFbp alone or IL-1ra alone indicated that, at the doses and timing used, TNFbp was more effective. LPS also increased NOS II activity by >10-fold (P < 0.01) over control. This increase was prevented by TNFbp plus IL-1ra (P = not significant vs. control). We conclude that the LPS-induced increase in NOS II activity and the decrease in ileal muscle contractility are mediated by TNF and IL-1.

Transcriptional regulation of endothelial nitric-oxide synthase by lysophosphatidylcholine

We have shown that lysophosphatidylcholine (lyso-PC) increases endothelial nitric-oxide synthase (eNOS) expression at the transcriptional level (Zembowicz, A., Tang, J.-L., and Wu, K. K. (1995) J. Biol. Chem. 270, 17006-17010). To elucidate the mechanism by which lyso-PC increases the eNOS transcription, we identified Sp1 sites at -104 to -90 and PEA3 sites at -40 to -24 as being involved in lyso-PC-induced promoter activity. Site-directed mutagenesis of Sp1 sites resulted in a marked reduction of basal and lyso-PC-induced activity whereas PEA3 site mutation abrogated response to lyso-PC. Band shift assays revealed that lyso-PC augmented Sp1 binding activity. Pretreatment of cells or nuclear extracts with okadaic acid reduced the Sp1 binding activity. Furthermore, okadaic acid treatment abrogated the lyso-PC induced promoter augmentation. Lyso-PC increased the nuclear extract protein phosphatase 2A (PP2A) activity, which was suppressed by okadaic acid treatment. These results suggest that lyso-PC up-regulates eNOS transcription by a PP2A-dependent increase in Sp1 binding activity.

Decreased ileal muscle contractility and increased NOS II expression induced by lipopolysaccharide

This study was designed to determine if an increase in nitric oxide synthase (NOS) activity induced by lipopolysaccharide (LPS) is associated with increases in NOS II protein and mRNA abundance and with altered ileal longitudinal muscle contractility. Strips of muscle taken from LPS-treated, but not control, animals exhibited reduced in vitro contractility when L-arginine was a component of the physiological salt solution. This reduction was reversed by N omega-nitro-L-arginine (L-NNA), a competitive inhibitor of NOS. Full-thickness segments of jejunum, ileum, and colon taken 5 h after LPS injection exhibited increased NOS activity, NOS II immunoreactivity, and NOS II mRNA abundance. Increased NOS II immunoreactivity and mRNA abundance also were detected in ileal muscle strips taken from LPS-treated animals. These data confirm the reported effects of LPS on intestinal NOS activity and indicate that it can be attributed, at least in part, to an increase in NOS II mRNA and protein abundance. Furthermore, the data suggest that an LPS-induced increase in NOS II may lead to a decrease in ileal muscle contractility.

Nitric oxide donors induce extrusion of cyclic GMP from isolated human blood platelets by a mechanism which may be modulated by prostaglandins

In the presence of 3-isobutyl-methylxanthine (IBMX), induction of cyclic 3',5'-guanosine monophosphate (GMP) production in human washed platelets (HWP) by nitric oxide donors (NOD) is followed by its accumulation in the surrounding medium in a time- and concentration-dependent manner. Thirty minutes incubation of HWP with 3-morpholino-sydonimine (SIN-1, 10 microM) at 37 degrees C resulted in a 4.6-fold increase of cyclic GMP in platelets, whereas in the extracellular medium the increase was 17.6-fold. Similar results were obtained when other NOD such as S-nitroso-N-acetylpenicyllamine (SNAP) and 3-(2-methoxy-5-chlorophenyl)oxatriazol-5-imine (GEA 3184) and the selective phosphodiesterase inhibitor, zaprinast (M&B 22948, 10 microM), were used. Probenecid (1-300 microM), an inhibitor of organic anion transport, or ouabain (1-300 microM), an inhibitor of Na+/K+ adenine triphosphate (ATP)-ase had no effect on cyclic GMP production or extrusion after stimulation with SIN-1. Significantly prostaglandin A1 (PGA1) and prostaglandin D2 (PGD2) inhibited the efflux of cyclic GMP from platelets induced by SNAP (10 microM) in a concentration-dependent fashion, with an IC50 of 63 +/- 16 and 143 +/- 17 microM, respectively. These studies suggest that the extrusion of cyclic GMP from human platelets after activation of soluble guanylate cyclase by NOD may contribute to the control of cyclic GMP levels in platelets with potential physiological and therapeutic consequences.

Induction of cyclooxygenase-2 in human umbilical vein endothelial cells by lysophosphatidylcholine

Lysophosphatidylcholine (lysoPC), a component of atherogenic lipoproteins and atherosclerotic lesions, has been recently suggested to play a role in atherogenesis. LysoPC is known to induce several endothelial genes involved in leukocyte recruitment, mitogenesis, and inflammation. Cyclooxygenases (prostaglandin H2 synthases) are rate-limiting enzymes involved in the endothelial synthesis of prostacyclin, an antiplatelet, vasorelaxant, and vasoprotective molecule. We investigated the effect of lysoPC on the endothelial expression of cyclooxygenases. Our results demonstrate that, in cultured human umbilical vein endothelial cells, lysoPC induces cyclooxygenase-2 mRNA and protein levels. Increased expression of cyclooxygenase-2 is accompanied by the enhancement of both basal- and calcium ionophore A23187-induced synthesis of prostacyclin. Nuclear runoff experiments demonstrated an increased rate of transcription of the cyclooxygenase-2 gene by lysoPC. In contrast, lysoPC did not affect the expression of constitutive cyclooxygenase-1. Our results suggest that the induction of endothelial cyclooxygenase-2 by lysoPC may be an important vasoprotective mechanism that limits progression of atherosclerotic lesions and promotes their regression.

Role of Sp1 in transcriptional activation of human nitric oxide synthase type III gene

Endothelial nitric oxide synthase (eNOS or NOS-III) is constitutively expressed. To elucidate the mechanism by which the basal expression of NOS-III gene is activated, we constructed in a luciferase vector, pXP1, serial 5'-deletion mutants of a 1.3-kb 5'-flanking fragment and transiently expressed them in cultured human endothelial cells. The promotor activity was detected in the -198/+22 region which contains several putative Sp1 binding sites. DNase I footprinting assays coupled with gel shift assays revealed the GC box(-104/-90) to be the Sp1 binding site. Site-directed mutation of 4 crucial bases in this site reduced the promotor activity by > 90%. These findings provide strong evidence that binding of Sp1 or closely related protein to this site is required for the activation of basal NOS-III transcription.

Transcriptional induction of endothelial nitric oxide synthase type III by lysophosphatidylcholine

Endothelial synthesis of NO is catalyzed by constitutive NO synthase type III (NOS-III). NOS-III has been thought to be regulated mainly at the level of enzyme activity by intracellular calcium. We report that in human umbilical vein endothelial cells lysophosphatidylcholine (lyso-PC), a component of atherogenic lipoproteins and atherosclerotic lesions, increases NOS-III mRNA and protein levels. This leads to the augmentation of NOS-III activity and the enhancement of antiplatelet properties of endothelial cells. Importantly, nuclear run-off experiments demonstrate a transcriptional mechanism of regulation of NOS-III expression by lysophosphatidylcholine. As endothelium-derived NO appears to be an anti-atherogenic molecule, induction of NOS-III by lyso-PC may be a protective response that limits the progress of the atherosclerotic lesion and promotes its regression.

Carboxyebselen a potent and selective inhibitor of endothelial nitric oxide synthase

Ebselen (Ebs) a glutathione peroxidase like agent has been recently described as an inhibitor of nitric oxide synthase (NOS). Presently, we report that carboxyebselen (HOOC-Ebs), a hydrophyllic derivative of Ebs inhibits NOS present in enzymatic preparations from bovine endothelium, porcine cerebella, and murine spleen, however, it is both more potent and more selective for the constitutive endothelial NOS than Ebs. Unlike Ebs, HOOC-Ebs (0.1-30 microM) causes a concentration-dependent endothelium-independent relaxations of rings of rabbit aorta. The mechanism of this relaxation remains unknown and it is attenuated by glutathione (GSH, 30-300 microM) and N-acetyl-L-cysteine (NAC, 30-300 microM). The vasorelaxant activity of acetylcholine (Ach, 0.1-1 microM) in aortic rings exposed to low concentrations of HOOC-Ebs (0.1-1 microM) or rings exposed to 10 microM HOOC-Ebs after their pretreatment with GSH or NAC (30-300 microM) remained unchanged. The lack of activity of HOOC-Ebs as a NOS inhibitor in intact endothelial cells contrasts the effectiveness of Ebs in this respect.

Inhibition of endothelial nitric oxide synthase by ebselen. Prevention by thiols suggests the inactivation by ebselen of a critical thiol essential for the catalytic activity of nitric oxide synthase

NO synthase (NOS) is a unique P-450-type enzyme containing both a reductase and a heme domain on a single polypeptide. We show that ebselen [Ebs, 2-phenyl-1,2-benzisoselenazol-3-(2H) one], a nontoxic selenoorganic compound known to break a cysteine thiolate/Fe bond of some of P-450 enzymes, is a relatively selective inhibitor of endothelial isoform of NOS. In rings of rabbit aorta, Ebs irreversibly blocked both the basal as well as acetylcholine- or calcium ionophore A23187-stimulated release of nitric oxide with an IC50 of 6 microM. In homogenates of bovine aortic endothelial cells, Ebs inhibited the activity of NOS, assayed by monitoring conversion of L-[2,3-3H]arginine to L-[2,3-3H]citrulline, with an IC50 of 8.5 microM. The inhibitory action of Ebs was prevented by glutathione, N-acetyl-L-cysteine or dithiothreitol (30-500 microM). The prevention by thiols of Ebs-induced inhibition of NOS suggests that these are competing with a thiol group of NOS that is essential for the catalytic activity of the enzyme. The consequence of the presence of thiols is the "trapping" of Ebs in the form of inactive selenyl sulfides. Consistent with the proposed mechanism of action of Ebs is lack of activity of diselenide of Ebs, which also demonstrates that the action of Ebs is independent of its glutathione peroxidase-like activity. In comparison to endothelial preparations, IC50 values of Ebs for inhibition of soluble isoforms of NOS present in homogenates of porcine cerebellum and of spleens obtained from lipopolysaccharide-treated rats were more than 30-fold higher.

Involvement of nitric oxide in the endothelium-dependent relaxation induced by hydrogen peroxide in the rabbit aorta

1. The effects of hydrogen peroxide (H2O2, 0.1-1 mM) on the tone of the rings of rabbit aorta precontracted with phenylephrine (0.2-0.3 microM) were studied. 2. H2O2 induced a concentration-dependent relaxation of both the intact and endothelium-denuded rings. However, in the presence of intact endothelium, H2O2-induced responses were 2-3 fold larger than in its absence, demonstrating the existence of endothelium-independent and endothelium-dependent components of the vasorelaxant action of H2O2. 3. The endothelium-dependent component of H2O2-induced relaxation was prevented by NG-nitro-L-arginine methyl ester (L-NAME, 30 microM) or NG-monomethyl-L-arginine (300 microM), inhibitors of nitric oxide synthase (NOS), in a manner that was reversible by L-, but not by D-arginine (2mM). The inhibitors of NOS did not affect the responses of denuded rings. 4. Methylene blue (10 microM), an inhibitor of soluble guanylate cyclase, blocked H2O2-induced relaxation of both the intact and denuded rings. 5. H2O2 (1 mM) enhanced the efflux of cyclic GMP from both the endothelium-intact and denuded rings. The effect of H2O2 was 4 fold greater in the presence of intact endothelium and this endothelium-dependent component was abolished after the inhibition of NOS by L-NAME (30 microM). 6. In contrast to the effects of H2O2, the vasorelaxant action of stable organic peroxides, tert-butyl hydroperoxide or cumene hydroperoxide, did not have an endothelium-dependent component. Moreover, they did not potentiate the efflux of cyclic GMP from the rings of rabbit aorta. 7. Exogenous donors of NO, specifically, 3-morpholinosydnonimine (SIN-1), glyceryl trinitrate or sodium nitroprusside were used to decrease the tone of denuded rings to the level induced by endogenous NO released from intact endothelium. This procedure did not influence the vasorelaxant activity of H202, showing that H202 does not potentiate the vasorelaxant action of NO within the smooth muscle.8. Thus, H202-induced relaxation in the rabbit aorta has both endothelium-dependent and independent components. The endothelium-dependent component of the relaxant action of H202 is due to enhanced endothelial synthesis of NO.

NG-hydroxy-L-arginine and hydroxyguanidine potentiate the biological activity of endothelium-derived relaxing factor released from the rabbit aorta

We investigated the effects of NG-hydroxy-L-arginine (L-HOArg) and hydroxyguanidine (HOG) on the synthesis and vasorelaxant activity of endothelium-derived relaxing factor (NO) released from the rabbit aortic endothelium. Both L-HOArg (10 microM) and HOG (10 microM) equally potentiated the vasorelaxant activity of NO released by Ach (0.1 or 0.3 microM) from the luminally perfused rabbit aorta and bioassayed using the superfused strips of the endothelium-denuded rabbit aorta. This potentiation was caused by the generation of a more stable vasodilator during the chemical reaction of L-HOArg or HOG with NO and it was abolished by NG-nitro-L-arginine methyl ester (L-NO2Arg, 10 microM). In contrast, in organ baths, L-HOArg (10 microM) or HOG (10 microM) did not affect the relaxations of intact rabbit aortic rings induced by Ach (0.01-1 microM). At concentrations higher than 10 microM, both L-HOArg and HOG were endothelium-independent vasorelaxants. However, L-HOArg (100 microM) prevented the inhibition by L-NO2Arg (10 microM) of Ach-induced relaxations of bathed aortic rings which indicates that L-HOArg is still a substrate for the NO synthase in the endothelium of the rabbit aorta.

Potentiation of the vasorelaxant activity of nitric oxide by hydroxyguanidine: implications for the nature of endothelium-derived relaxing factor

1. We recently demonstrated that NG-hydroxy-L-arginine (L-HOArg) is a substrate for the constitutive nitric oxide (NO) synthase present in bovine aortic endothelial cells cultured on microcarrier beads (EC). Furthermore, L-HOArg reacts chemically with NO released from these cells to form a potent and more stable vasodilator. This is most likely through a reaction with the hydroxyguanidino group. 2. Here, we studied the interaction of a simpler molecule, hydroxyguanidine (HOG) with NO. 3. HOG (10 microM), like L-HOArg (10 microM) or NG-hydroxy-D-arginine (D-HOArg, 10 microM), potentiated and stabilized the relaxant activity of authentic NO. 4. When NO was bubbled through the solution of HOG, a new compound was formed. It had similar physicochemical properties to those of the previously described L-HOArg/NO adduct. It was also a potent vasodilator and its action was inhibited by oxyhaemoglobin (10 microM), indicating formation of a NO-containing substance. 5. Moreover, HOG (10 microM) was not a substrate for the constitutive NO synthase present in the microsomal fraction of EC and did not affect the flow-induced or bradykinin-stimulated generation of prostacyclin, as measured by 6-keto-PGF1 alpha. 6. We also studied the effect of HOG on the endothelium-derived relaxing factor (EDRF) released from the column of EC. HOG (10 microM) potentiated and stabilized the relaxations of rabbit aortic strips induced by EDRF released by bradykinin (5-20 pmol) or ADP (5-10 nmol). These relaxations were inhibited by NG-nitro-L-arginine methyl ester (L-NAME, 10 microM) and L-arginine (L-Arg, 1 mM) reversed the inhibitory effects of L-NAME. 7. HOG (10 iM) augmented the basal (flow-induced) EC-dependent relaxations which were also inhibited by L-NAME (10 1M) and the effects of L-NOArg were reversed by L-Arg (1 mM).8. Thus, the hydroxyguanidino moiety of L-HOArg is involved in the reaction with NO. Moreover, the comparable reaction of the hydroxyguanidino compounds with NO on the one hand and with flowinduced and agonist-triggered EDRF on the other, strongly supports their common identity.

Modulation of the pharmacological actions of nitrovasodilators by methylene blue and pyocyanin

1. In superfused precontracted strips of rabbit aorta, methylene blue (MeB) or pyocyanin (Pyo, 1-hydroxy-5-methyl phenazinum betaine) at concentrations of 1-10 microM inhibited relaxations induced by endothelium-derived relaxing factor (EDRF), glyceryl trinitrate (GTN), S-nitroso-N-acetyl-penicillamine (SNAP) or 3-morpholino-sydnonimine (SIN-1). However, the vasorelaxant actions of sodium nitroprusside (NaNP) or sodium nitrite (NaNO2) were enhanced by MeB or Pyo. Oxyhaemoglobin (HbO2, 1 microM) inhibited the activities of EDRF and all of the nitrovasodilators studied. Vascular preparations were not relaxed by Pyo unless pretreated with NaNP (0.05-10 microM). 2. In bathed, precontracted rings of rabbit aorta, Pyo (10 microM) produced a shift to the left of the cumulative concentration-response curve for NaNP (0.01-10 microM). The rise in guanosine-3':5'-cyclic monophosphate (cyclic GMP) content of aortic tissue was also enhanced. 3. The vasorelaxant potency of NaNP (30 microM) at pH 5-8 and at 37 degrees C remained unchanged over 2.5 h while a solution of SNAP (30 microM) progressively lost its biological activity over 60 min. The in vitro degradation of the biological activity of SNAP was accelerated by MeB (150 microM) or Pyo (150 microM), whereas the vasorelaxant potency NaNP (30 microM) was doubled when incubated with MeB or Pyo. 4. In human platelet-rich plasma, MeB or Pyo (0.3-3.0 microM) uncovered an anti-aggregatory action of subthreshold concentrations of NaNP (4-8 microM). This was abrogated by HbO2 (10 microM).5. We conclude that MeB or Pyo differ from HbO2 in their mode of interaction with nitrovasodilators.HbO2 scavenges nitric oxide that is released from all types of nitrovasodilators. MeB and Pyo exert a similar action towards organic nitrovasodilators (e.g. SNAP, SIN-1). However, the pharmacological actions of inorganic nitrovasodilators (e.g. NaNP or NaNO2) are potentiated by MeB and Pyo owing to facilitation of the intracellular release of nitric oxide from the inorganic nitrovasodilators.

Induction of nitric oxide synthase activity by toxic shock syndrome toxin 1 in a macrophage-monocyte cell line

Toxic shock syndrome toxin 1 (TSST-1) is a Mr 22,000 protein produced by Staphylococcus aureus. It is thought to be the cause of toxic shock syndrome. We investigated the hypothesis that TSST-1 induces nitric oxide (NO) synthase and that the NO formed may be involved in the pathogenesis of toxic shock syndrome. We used the murine monocyte-macrophage cell line J744.2 that responds to TSST-1 and also expresses NO synthase activity upon immunological stimulation. J774.2 macrophages stimulated with TSST-1 (10-100 nM) generated nitrite, a breakdown product of NO, and induced concentration-dependent elevations of cGMP in the pig kidney epithelial cell line (LLC-PK1). This latter effect was due to the generation of L-arginine-derived NO for it was (i) abolished by oxyhemoglobin (10 microM), a scavenger of NO, or by methylene blue (10 microM), an inhibitor of NO-activated guanylate cyclase; (ii) potentiated by superoxide dismutase (100 units/ml), which prolongs the life of NO; (iii) inhibited by NG-monomethyl-L-arginine (0.3 mM), an inhibitor of NO synthase; (iv) significantly decreased when L-arginine (0.4 mM) in the medium was replaced by D-arginine (0.4 mM). Moreover, TSST-1 (100 nM) enhanced the activity of cytosolic NO synthase in J774.2 cells. Hydrocortisone (1 microM) but not indomethacin (5 micrograms/ml) or salicylic acid (5 micrograms/ml) prevented the generation of NO2- and the increases in cGMP levels in LLC-PK1 cells induced by J774.2 cells stimulated with TSST-1. The effects of hydrocortisone were partially reversed by coincubation with RU 486 (1 microM), an antagonist of glucocorticoid receptors. Thus, TSST-1 and perhaps other exotoxins produced by Gram-positive bacteria induce NO synthase and the increased NO formation may contribute to toxic shock syndrome and possibly to changes in the immune responses that accompany infection.

Mechanisms of the endothelium-dependent relaxation induced by NG-hydroxy-L-arginine

There are three mechanisms by which NG-hydroxy-L-arginine (L-HOArg) induces endothelium-dependent relaxations. L-HOArg is a substrate for the constitutive nitric oxide (NO) synthase present in endothelial cells (ECs). It reacts with NO released from EC to form a potent and more stable vasodilator. Moreover, it induces a relatively stable, EC-dependent relaxation that is not blocked by the inhibitors of NO synthesis. Subsequently, we have investigated the effects of hydroxyguanidine (HOG) on the biological activity of endothelium-derived relaxing factor (EDRF). HOG potentiated the relaxant responses of rabbit aortic strips to EDRF released from EC by adenosine diphosphate (ADP) or bradykinin as well as those induced by authentic NO. Importantly, it was not a substrate for NO synthesis and it did not affect the generation of prostacyclin by ECs. Thus, the effects of HOG were due to the chemical reaction of HOG with NO released from ECs and the formation of a more stable vasodilator. Moreover, HOG augmented not only agonist-triggered, but also flow-induced, EC-dependent relaxation and both effects of HOG were abolished by NG-nitro-L-arginine methyl ester (L-NO2-Arg). In contrast, the EC-dependent relaxation induced by L-HOArg was not inhibited by L-NO2Arg. Moreover, it was not affected by the removal of extracellular Ca2+, but was blocked by oxyhemoglobin and potentiated by superoxide dismutase. These results demonstrate the involvement of the hydroxyguanidino moiety of L-HOArg in its reaction with NO. Moreover, they strongly support the notion that nitrix oxide mediates both the agonist-triggered and flow-induced endothelium-dependent relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitroxergic nerves mediate vagally induced relaxation in the isolated stomach of the guinea pig

Here we show that the relaxation induced by stimulation of the vagus nerve in the presence of cholinergic (muscarinic) and adrenergic blockade in the isolated stomach of the guinea pig is mediated by nitric oxide (NO). This is substantiated by inhibition of vagal relaxation by NG-monomethyl-L-arginine, an inhibitor of NO synthesis. The effect of NG-monomethyl-L-arginine was partially reversed by coincubation with L-arginine but not with D-arginine. NO activates soluble guanylate cyclase, and relaxation of the stomach induced by vagal stimulation was prevented by an inhibitor of soluble guanylate cyclase, methylene blue, further supporting our conclusions. The relaxant effect of vagal stimulation was also ablated by hexamethonium, an inhibitor of ganglionic nicotinic receptors, thereby showing that ganglionic transmission did not rely on NO, through its release from preganglionic neurons. However, hexamethonium did not inhibit the gastric relaxation brought about by increasing the intragastric pressure, which is also mediated by NO as previously described by us. The selective inhibition by hexamethonium of only the vagally mediated relaxation but not of the pressure-induced relaxation of the stomach indicates the existence of at least two separate neuronal pathways able to generate NO and bring about gastric accommodation of food or fluid.

Nitric oxide and another potent vasodilator are formed from NG-hydroxy-L-arginine by cultured endothelial cells

The hypothesis was investigated that NG-hydroxy-L-arginine (L-HOArg) is an intermediate in the biosynthesis of nitric oxide (.NO) from L-arginine (L-Arg) by the constitutive .NO synthase (NOS) present in endothelial cells (ECs). When infused through a column of bovine aortic ECs on beads, either L-HOArg or D-HOArg (1-10 microM) substantially potentiated relaxations of the bioassay tissues to .NO released from the cells by ADP or bradykinin, and this effect was abolished by coinfusions of NG-nitro-L-arginine (L-NO2Arg) methyl ester (10 microM) or NG-monomethyl-L-arginine (L-MeArg; 30 microM). Both L-HOArg and D-HOArg, irrespective of the presence of ECs, also potentiated relaxations induced by authentic .NO, but not glyceryl trinitrate. This was due to a rapid chemical reaction of either isomer with .NO, resulting in the formation of a potent and more stable vasodilator. When infusions of L-HOArg (3 microM) were consequently made in the presence of D-HOArg (10 microM), the L-isomer no longer had any effect on relaxations induced by authentic .NO, but significantly increased the stimulated release of .NO from the column of ECs. The conclusion that L-HOArg is a substrate for the constitutive NOS in cultured ECs was strongly supported by the L-NO2Arg-sensitive conversion of L-HOArg, but not D-HOArg, to .NO by NOS preparations from these cells. Interestingly, cultured ECs produced from L-HOArg (greater than or equal to 3 microM), but not D-HOArg, a stable vasodilator, the effects of which were inhibited by oxyhemoglobin (0.3-3 microM). However, the formation of this substance was not prevented by L-NO2Arg methyl ester (10 microM) or L-MeArg (10-100 microM), suggesting an enzymatic pathway different from NOS.

Human polymorphonuclear leukocytes generate and degrade endothelin-1 by two distinct neutral proteases

Human polymorphonuclear leukocytes (PMNs, 4 x 10(6)/ml) converted human big endothelin (bET) to an endothelin-1 (ET-1)-like contractile factor, as assessed by bioassay. The formation of this ET-1-like activity from bET was partially inhibited by phosphoramidon (54 micrograms/ml), but not by pepstatin-A (1 microgram/ml), epoxysuccinyl-L-leucylamido(guanidino)butane (E-64, 10 micrograms/ml) or phenylmethylsulfonyl fluoride (PMSF, 25 micrograms/ml). In addition, nonactivated PMNs converted [125I]bET to [125I]ET-1, thus confirming the bioassay results. Incubation of ET-1 with fMLP-activated PMNs or cell-free supernatants from activated PMNs resulted in the loss of its contractile activity, and this loss of activity was paralleled by the metabolism of [125I]ET-1. The metabolism of [125I]ET-1 by PMNs or leukocyte cathepsin G (5 micrograms/ml) was prevented by PMSF (25 micrograms/ml), but not by phosphoramidon (54 micrograms/ml) or pepstatin-A (1 microgram/ml). Thus, PMNs can form ET-1 from bET via a neutral protease and degrade ET-1 via a serine protease, an observation that may have important pathophysiologic implications in disease states associated with PMN infiltration.