Biomedical subjects

J R Vane

Publications and source records attributed to J R Vane.

At least 127 records · Page 7Linked to original sources

PubMed1992

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.

Acetylcholine↗

PubMed1992

Endogenous endothelium-derived relaxing factor opposes hypoxic pulmonary vasoconstriction and supports blood flow to hypoxic alveoli in anesthetized rabbits.

Agents that inhibit nitric oxide synthesis augment hypoxic pulmonary vasoconstriction. In an animal model of unilateral alveolar hypoxia, we investigated the hypothesis that endogenous endothelium-derived relaxing factor/nitric oxide opposes hypoxic pulmonary vasoconstriction and supports blood flow to hypoxic alveoli, resulting in a reduction in arterial oxygen tension (PO2). In pentobarbital-anesthetized rabbits, unilateral alveolar hypoxia was produced by ventilation of one lung with 100% oxygen and the other with 100% nitrogen (O2/N2). NG-Nitro-L-arginine methyl ester (0.03 followed by 1.0 mg/kg i.v.) resulted in dose-dependent decreases in the percent of pulmonary blood flow to the N2-ventilated lung and increases in arterial PO2. L-Arginine (1 mg.kg-1.min-1 i.v.) prevented the NG-nitro-L-arginine methyl ester-induced redistribution of blood flow away from hypoxic alveoli and improvement in arterial PO2. Indomethacin (5 mg/kg i.v.) administered during O2/N2 ventilation resulted in a reduction in the percentage of total blood flow to the hypoxic lung and an increase in arterial PO2. However, NG-nitro-L-arginine methyl ester administered in the presence of indomethacin caused additional diversion of blood flow away from the hypoxic lung. The magnitude of the changes suggests that the endothelium-derived relaxing factor/nitric oxide system has the capacity to make a greater contribution than products of cyclooxygenase-mediated arachidonic acid metabolism in supporting blood flow to hypoxic alveoli in the rabbit.

Animals↗

PubMed1992

The two-step conversion of big endothelin 1 to endothelin 1 and degradation of endothelin 1 by subcellular fractions from human polymorphonuclear leukocytes.

The metabolism of big endothelin 1 (bET) and endothelin 1 (ET-1) by subcellular fractions from human polymorphonuclear leukocytes (PMNs) was investigated by bioassay and reversed-phase high-performance liquid chromatography. More than 80% of endothelin-converting activity was recovered from the cytosolic fraction, which in addition to ET-1 generated other peptides from bET. The processing of bET to all its metabolites including ET-1 was prevented by the serine protease inhibitor 3,4-dichloroisocoumarin (DCI; 50 microM) or the elastase inhibitor ONO-5046 (100 microM) but not by phenylmethylsulfonyl fluoride (PMSF; 143 microM), another serine protease inhibitor. Paradoxically, human leukocyte elastase, despite generating a bET fragmentation pattern similar to that of PMN cytosol, produced very little ET-1. However, subsequent treatment of the elastase-derived metabolites of bET with PMN cytosol in the presence of ONO-5046 dramatically increased the amount of ET-1 formed. The generation of ET-1 following this intervention was inhibited by DCI. The PMN membrane preparation degraded ET-1 to a major metabolite, similar to that produced from ET-1 by elastase, and several minor products, paralleled by a loss of its smooth muscle contracting activity. The degradation of ET-1 by PMN microsomes was prevented by DCI, PMSF, or ONO-5046. Our results suggest that an elastase-initiated serine protease cascade is responsible for the sequential conversion of bET to ET-1 by the PMN cytosol. Elastase also partly accounts for the ET-metabolizing properties of PMN microsomes.

Animals↗

PubMed1992

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.

Amino Acid Oxidoreductases↗

PubMed1992

Characterization of serine protease-derived metabolites of big endothelin in the cytosolic fraction from human polymorphonuclear leukocytes.

We have characterized by bioassay and reversed-phase high-performance liquid chromatography analysis (rp-HPLC) the conversion of human big endothelin-1 (bET-1) to endothelin-1 (ET-1) by the cytosolic fraction from human polymorphonuclear leukocytes (PMNs). Either the general serine protease inhibitor 3,4-dichloroisocoumarin (DCI; 50 microM) or the selective elastase inhibitor ONO-5046 (100 microM) blocked the formation of ET-1 from bET-1. Interestingly, human leukocyte elastase formed some of the same products from bET-1 as the PMN cytosol, but generated negligible amounts of ET-1. However, coincubation of the elastase-derived fragments of bET-1 with the PMN cytosol in the presence of ONO-5046 resulted in a 17-fold increase in the formation of ET-1, indicating that an elastase-derived intermediate of bET-1 was subsequently cleaved by a soluble protease(s) to form mature ET-1. We have identified by electrospray-mass spectrometry (ESMS) analysis this intermediate as bET-1(1-22). Analysis of bET-1 digestion by human leukocyte cathepsin G revealed the formation of a biologically active metabolite chromatographically distinct from ET-1, identified as bET-1(1-31) by ESMS. These findings indicate the presence of complex enzyme systems in human PMNs capable of activating bET-1.

Cathepsin G↗

PubMed1992

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)

Amino Acid Oxidoreductases↗

PubMed1992

Characterization of a microsomal calcium-dependent nitric oxide synthase in activated J774.2 monocyte/macrophages.

The nitric oxide (NO) synthase activity present in murine J774.2 monocyte/macrophages was characterized in terms of its intracellular localization, substrate specificity, and Ca2+ dependency. Traces of constitutive NO synthase activity were found in the microsomal fraction from noninduced J774.2 cells, whereas no NO synthase activity was detected in the cytosol. After 24 h in the presence of bacterial lipopolysaccharide and mouse interferon, NO synthase activity was substantially increased in both fractions with 51-60% of the total activity present in the cytosol. These activities, however, were clearly different, for the microsomal enzyme was Ca2+ dependent, whereas the cytosolic NO synthase was not. Moreover, NG-hydroxy-L-arginine (L-HOArg), L-homo-arginine, and several L-arginine (L-Arg)-containing dipeptides could replace L-Arg as substrates for the Ca(2+)-independent NO synthase, whereas the Ca(2+)-dependent enzyme accepted only L-Arg, L-HOArg, or L-Arg-L-Arg as substrates. Thus, a microsomal Ca(2+)-dependent NO synthase is induced in J774.2 monocyte/macrophages with a substrate specificity different from the inducible Ca(2+)-independent NO synthase as well as the constitutive NO synthase in, for example, endothelial cells. Irrespective of their intracellular localization, therefore, at least three isoforms of NO synthase exist, all of which can accommodate substrates different from L-Arg in size, charge, and hydrophobicity.

Amino Acid Oxidoreductases↗

PubMed1992

NG-hydroxy-L-arginine prevents the haemodynamic effects of nitric oxide synthesis inhibition in the anaesthetized rat.

1. We have investigated the effects of L-hydroxy-L-arginine (L-HOArg), an intermediate in the biosynthesis of nitric oxide (NO) from L-arginine (L-Arg), on the haemodynamic effects (systemic blood pressure and renal blood flow) of the NO synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) in the anaesthetized rat. 2. L-Arg or L-HOArg (3 mg kg-1 min-1), but not D-arginine (D-Arg) or NG-hydroxy-D-arginine (D-HOArg), elicited a slight but significant increase in total renal blood flow (RBF) of 11 +/- 2% and 11 +/- 1%. Since mean arterial blood pressure (MAP) did not change this dose of L-Arg or L-HOArg resulted in a reduced renal vascular resistance (RVR) of the same magnitude. 3. Bolus injections of L-NAME, at 0.3 or 1 mg kg-1 i.v., produced a significant fall in RBF of 11 +/- 2% and 32 +/- 5% and an increase in MAP of 7 +/- 3 mmHg and 22 +/- 5 mmHg, respectively. Consequently, RVR was elevated by 21 +/- 5% and 52 +/- 10%. 4. L-Arg or L-HOArg (3 mg kg-1 min-1) reduced the L-NAME-induced (0.3 or 1 mg kg-1) falls in RBF and increases in RVR by more than 65%. Neither D-Arg nor D-HOArg (3 mg kg-1 min-1) had any significant effect on the changes in RBF or RVR induced by L-NAME. 5. L-Arg or L-HOArg (3 mg kg-' min-') attenuated the pressor effect of L-NAME (3 mg kg-') by 73% and 64%, respectively, while neither the D-isomer of arginine nor hydroxyarginine had any effect.6. These results demonstrate that L-HOArg antagonizes the haemodynamic effects of NO-biosynthesis inhibition in vivo, thus supporting the hypothesis that L-HOArg is an intermediate in the formation of NO from L-Arg.

Animals↗

PubMed1992

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.

Amino Acid Oxidoreductases↗

PubMed1992

Different patterns of release of endothelium-derived relaxing factor and prostacyclin.

1. Release of endothelium derived relaxing factor (EDRF) and prostacyclin (PGI2) from endothelial cells (EC) cultured from bovine aortae was measured by bioassay and radioimmunoassay, respectively, during infusions (10 min) of bradykinin (BK), adenosine diphosphate (ADP), arachidonic acid (AA), alkaline buffers and the free-bases (FB) of L-arginine or D-arginine. Release of EDRF from the luminally perfused rabbit aorta was also measured during infusions (10 min) of acetylcholine (ACh), substance P and ADP. 2. Bradykinin (10 or 30 nM) infused through the column of EC induced release of both EDRF and PGI2, neither of which was maintained for the duration of the infusion. 3. ADP (1.6 or 4 microM) infused through the column of EC induced release of a EDRF which was maintained for the duration of the infusion and a release of PGI2 which lasted for a much shorter period. 4. Arachidonic acid (30 or 90 microM) infused through the column of EC caused a sustained release of EDRF and PGI2, both of which outlasted the infusion of AA. 5. L-Arginine FB, D-arginine FB or alkaline buffer infused through the column of EC released EDRF, but only small amounts of PGI2. The release of EDRF outlasted the period of infusion and was due to an increase in the pH of the Krebs solution perfusing the EC. 6. Infusions of ACh (0.25-1 microM) or ADP (4-16 microM) caused a sustained release of EDRF from the luminally-perfused rabbit aorta, whereas infusion of substance P (3.3-10 microM) caused only a transient release of EDRF. 7. These results show that distinct patterns of EDRF release exist to different agonists in both cultured and in situ EC, and that EDRF and PGI2 do not necessarily follow the same time course of release. Furthermore, sustained release of EDRF does not require the constant infusion of the precursor, L-arginine, whereas sustained release of PGI2 only occurs when AA, the precursor of PGI2, is present in the extracellular medium.

Acetylcholine↗

PubMed1992

The actions of endothelins-1 and -3 on the vascular and capsular smooth muscle of the isolated blood perfused spleen of the dog.

1. Endothelin-1 (ET-1), endothelin-3 (ET-3) and noradrenaline (NA) were administered as intra-arterial bolus injections into the isolated, blood-perfused spleen of the dog to assess agonist properties and relative molar potencies on the vascular and capsular smooth muscle. 2. An initial small vasodilatation was observed occasionally at low doses (1.0-10 pmol) of ET-1. 3. ET-1, ET-3 and NA all caused graded increases in splenic arterial vascular resistance. The molar ED50 for the splenic vasoconstrictor response to ET-1 was significantly less (P less than 0.001) than that to ET-3; both peptides were significantly more potent as vasoconstrictor agents than NA. The maximum increase in splenic arterial vascular resistance was not significantly different for either ET-1, ET-3 or NA. 4. The time course of the splenic vasoconstrictor response to ET-1 was significantly (P less than 0.01) longer than that to equieffective doses of ET-3 or NA. 5. The splenic vasoconstrictor responses to ET-1 and ET-3 were accompanied by reductions in spleen volume. The rank order of molar potency in causing splenic capsular contraction was ET-1 greater than ET-3 greater than NA. The maximum reduction in splenic volume was significantly greater for NA than for either ET-1 or ET-3. The two peptides (ET-1, ET-3) were equiefficacious in contracting splenic capsular smooth muscle. 6. The high molar potency of ET-1 as a splenic arterial vasoconstrictor, over 1,700 times more potent than NA, suggests that it may play an important local role in the control of splenic haemodynamics.

Animals↗

PubMed1992

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.

Animals↗

PubMed1992

Comparison of the release of vasoactive factors from venous and arterial bovine cultured endothelial cells.

The release of endothelium-derived relaxing factor (EDRF), prostacyclin (PGI2), and endothelin-1 (ET-1) was measured from endothelial cells (EC) cultured from either bovine vena cava (BVCEC) or bovine aorta (BAEC). EDRF release was determined by using the superfusion bioassay technique, whereas ET-1 and PGI2 were measured by specific radioimmunoassays. Bradykinin (BK) (0.05-30 pmol) given through columns of venous or arterial EC induced a dose-dependent release of EDRF. BK (0.05 pmol) evoked a release of EDRF from venous EC that was similar to the effect of a dose of 1 pmol from arterial EC. As with BAEC, infusions of NG-monomethyl-L-arginine (30 microM) caused an inhibition of EDRF release from BVCEC that was partially reversed by coinfusions of L-arginine (L-Arg; 100 microM). BK also induced a dose-dependent release of PGI2 from BVCEC. BVCEC and BAEC produced PGI2 in equivalent amounts when arachidonic acid (9.2 and 32 pmol) was added to the Krebs' solution perfusing the cells. BVCEC and BAEC released detectable amounts of ET-1 (0.4 +/- 0.1 and 0.9 +/- 0.3 ng/mL, respectively), over a 4-h period, and the release of ET-1 was increased approximately twofold by coincubations with thrombin (0.05-1 U/mL). These findings demonstrate that venous EC have a similar capacity to arterial EC to release vasoactive factors, thus supporting the hypothesis that veins have a functional endothelium that may modulate venous tone and platelet function.

Amino Acids↗

PubMed1992

Role of intracellular thiols in release of EDRF from cultured endothelial cells.

The availability of intracellular reduced thiols, such as L-cysteine or glutathione (GSH), may be critically important for the biosynthesis of endothelium-derived relaxing factor (EDRF). We have, therefore, investigated the effects of various sulfhydryl (SH) reagents, such as 1-chloro-2,4-dinitrobenzene (CDNB), diamide, 2,2'-dithiodipyridine (DTDP), or N-ethyl-maleimide (NEM), on the release of EDRF from cultured endothelial cells. None of the SH reagents tested affected the flow-induced EDRF release, but DTDP and NEM inhibited the release of EDRF stimulated by ADP, ionomycin, or poly-L-lysine. In contrast, NG-nitro-L-arginine methyl ester, an inhibitor of EDRF biosynthesis, blocked both the flow- and agonist-induced release of EDRF. Although NEM substantially potentiated the flow-induced release of prostacyclin (PGI2), probably due to a blockade of the reacylation of arachidonic acid, it inhibited the stimulated release of PGI2, whereas diamide did not significantly affect either release. Like CDNB or diamide, NEM, but not DTDP, caused a significant decrease in endothelial GSH. In contrast, both NEM and DTDP, but not CDNB or diamide, inhibited the ADP-induced mobilization of intracellular calcium, suggesting that they act on specific target proteins involved in endothelial cell calcium homeostasis rather than intracellular free SH groups. Moreover, the selective inhibition by these two SH reagents of the stimulated release of EDRF implies that a fundamental regulatory difference exists between agonist- and flow-induced EDRF biosynthesis.

Adenosine Diphosphate↗

PubMed1992

The role of chemical mediators released by the endothelium in the control of the cardiovascular system.

The vascular endothelium is much more than just a lining for blood vessels. It inactivates many mediators and produces a host of active substances. The production of these substances is modulated by interactions between the endothelial cells and white blood cells, platelets or constituents of plasma. The endothelial cells can be activated by amines, peptides, proteins, nucleotides, arachidonic acid and its metabolites, as well as by physical changes such as pulse pressure. This activation of endothelial cells is often mediated by specific receptors which respond in a variety of ways including the generation of prostacyclin and endothelium-derived relaxing factor (EDRF). Both of these mediators inhibit platelet aggregation and cause vascular dilatation, prostacyclin through increasing cyclic AMP, and EDRF through increasing cyclic GMP. EDRF has been identified as nitric oxide (NO) derived from the guanidino group of L-arginine. Inhibitors of NO formation cause a strong increase in blood pressure, showing that under normal conditions there is a constant formation of NO to dilate the vasculature. Endothelin is another agent made by endothelial cells; characterized and synthesized in 1988, it is the most potent vasoconstrictor so far discovered. Three endothelin isomers have been identified; paradoxically, ET-1 strongly releases both prostacyclin and NO, thus modulating its own vasoconstrictor activities.

Animals↗

PubMed1992

Secretory functions of the vascular endothelium.

The endothelial cells which line the blood vessels as a monolayer exert a remarkable control over the vascular system. Indeed, the endothelium can be regarded as a highly active metabolic and endocrine organ in its own right. On the hand, vasoactive substances such as serotonin and bradykinin are inactivated and on the other the cells can enzymatically produce the vasoconstrictor, angiotensin II and secrete endothelin-1 ((ET-1). Perhaps more importantly, the cells also produce two unstable vasodilator substances, which potently inhibit platelet clumping: prostacyclin and endothelium-derived relaxing factor (EDRF) which has been identified as nitric oxide (NO; 1). Both substances seem well designated as local hormones, released to influence adjacent cells. The endothelial cell, therefore, exerts control over the cardiovascular system by elaborating dilator substances as well as vasconstrictors.

Endothelins↗

PubMed1991

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.

Animals↗

PubMed1991

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.

Animals↗