Biomedical subjects

R Busse

Publications and source records attributed to R Busse.

At least 127 records · Page 7Linked to original sources

PubMed1996

Nitric oxide attenuates the release of endothelium-derived hyperpolarizing factor.

BACKGROUND: The contribution of the endothelium-derived hyperpolarizing factor (EDHF), proposed to be a cytochrome P450-derived metabolite of arachidonic acid, to endothelium-dependent dilatation under physiological conditions has yet to be established, because its effect can be detected only after inhibition of NO synthase and cyclooxygenase. The possibility that NO exerts a feedback inhibition on EDHF formation was studied in isolated perfused arterial segments. METHODS AND RESULTS: Under combined blockade of NO synthase and cyclooxygenase, the EDHF-mediated vasodilatation elicited by receptor-dependent agonists in rabbit carotid and porcine coronary arteries was significantly attenuated by the NO donors C87-3786 and CAS 1609. The endothelium-independent dilatation elicited by isoproterenol was not altered by either NO donor. In NG-nitro-L-arginine-treated carotid artery segments, C87-3786 significantly attenuated the acetylcholine-induced increase in 6-keto-prostaglandin F1 alpha release, which was taken as an index of arachidonic acid liberation. In parallel experiments using cultured human endothelial cells, C87-3786 attenuated the Ca2+ response to bradykinin. The release of EDHF from a luminally perfused porcine coronary artery was detected by recording the membrane potential of downstream-situated cultured rat aortic smooth muscle cells. The NO donor C87-3786 had no effect on the hyperpolarization elicited by preformed EDHF but markedly inhibited its release from bradykinin-stimulated donor segments. CONCLUSIONS: These findings indicate that under physiological conditions, the production of EDHF is damped by NO. Therefore, it follows that when NO synthesis is impaired, alleviation of this intrinsic inhibition may, at least in part, maintain endothelial vasodilator function.

6-Ketoprostaglandin F1 alpha↗

PubMed1996

In vivo nitrate tolerance is not associated with reduced bioconversion of nitroglycerin to nitric oxide.

BACKGROUND: In vitro data suggest that reduced bioconversion of nitroglycerin (NTG) to nitric oxide (NO) contributes to the development of vascular and hemodynamic tolerance to NTG. We examined the in vivo validity of this hypothesis by measuring NTG-derived NO formation by in vivo spin-trapping of NO in vascular tissues from nitrate-tolerant and -nontolerant rats. METHODS AND RESULTS: Five groups (n = 6 to 8 each) of conscious chronically catheterized rats received NTG (0.2 or 1 mg/h IV) for 72 hours (nitrate-tolerant groups). Four other groups received either NTG vehicle (placebo, for 72 hours) or were left untreated (control). Nitrate tolerance was substantiated by a reduced (55% to 85%) hypotensive response to NTG in vivo and a reduced relaxation to NTG in isolated aortic rings. NTG-derived NO formation in aorta, vena cava, heart, and liver was measured as NOFe(DETC)2 and NO-heme complexes formed in vivo during 35 minutes combined with ex vivo cryogenic electron spin resonance spectroscopy. NO formation was significantly (P < .05) increased in all tissues in nitrate-tolerant rats in an NTG dose-dependent manner. Furthermore, the amount of NO formed from a bolus dose of NTG (6.5 mg/kg over 20 minutes) was similar in nitrate-tolerant and -nontolerant rats. CONCLUSIONS: The results suggest that vascular and hemodynamic NTG tolerance occurs despite high and similar rates of NO formation by NTG in tolerant and nontolerant target tissues. This finding is compatible with the assumption that reduced biological activity of NO, rather than reduced bioconversion of NTG to NO, contributes to in vivo development of nitrate tolerance.

Animals↗

PubMed1996

Serotonin stimulates the expression of thrombin receptors in cultured vascular smooth muscle cells. Role of protein kinase C and protein tyrosine kinases.

BACKGROUND: Thrombin has been implicated in the development of intimal thickening after balloon angioplasty. The action of thrombin on vascular cells involves the proteolytic activation of G protein-coupled receptors that are subjected to rapid and irreversible homologous desensitization. Hence, the amount and availability of thrombin-activatable receptors play a determinant role in thrombin responsiveness. The possibility that the platelet-derived product serotonin (5-HT) regulates expression of the thrombin receptor was examined in cultured rat aortic vascular smooth muscle cells. METHODS AND RESULTS: Thrombin receptor expression was assessed at the mRNA level by Northern blot analysis and functionally by measurement of the release of 6-ketoprostaglandin F1 alpha. 5-HT significantly enhanced thrombin receptor mRNA levels in a time- and concentration-dependent manner, an effect that was abolished by 5-HT2 receptor antagonists and by inhibition of protein kinase C but only slightly affected by inhibitors of protein tyrosine kinases. Enhanced thrombin receptor mRNA levels after exposure to 5-HT were associated with an increase in the thrombin-induced release of 6-ketoprostaglandin F1 alpha. CONCLUSIONS: 5-HT stimulates the expression of thrombin receptors in vascular smooth muscle cells, probably via activation of 5-HT2 receptors and the subsequent activation of protein kinase C and possibly also protein tyrosine kinases. The upregulation of the synthesis of plasma membrane thrombin receptors by 5-HT released from aggregating platelets at sites of vascular injury may potentiate the mitogenic and constrictor actions of thrombin in the vascular wall.

6-Ketoprostaglandin F1 alpha↗

PubMed1996

Interdependence of calcium signaling and protein tyrosine phosphorylation in human endothelial cells.

The signal transduction cascade which initiates transmembraneous influx of Ca2+ into endothelial cells in response to the discharge of intracellular Ca2+ stores is thought to involve a step sensitive to tyrosine kinase inhibition. We investigated the interrelationship between Ca2+ signaling and protein tyrosine phosphorylation following cell stimulation with either the receptor-dependent agonist, bradykinin, or the protein-tyrosine phosphatase inhibitor, phenylarsine oxide. In cultured human endothelial cells phenylarsine oxide instigated a concentration-dependent increase in the intracellular concentration of free Ca2+ ([Ca2+]i). This increase in [Ca2+]i was not associated with the tyrosine phosphorylation of phospholipase C gamma, enhanced formation of inositol 1,4,5-trisphosphate, or the rapid depletion of intracellularly stored Ca2+ but was coincident with the enhanced and prolonged tyrosine phosphorylation of a number of cytoskeletal proteins. In bradykinin-stimulated cells the tyrosine phosphorylation of the same cytoskeletal proteins (most notably 85- and 100-kDa proteins) was transient when cells were stimulated in the presence of extracellular Ca2+, was maintained under Ca2+-free conditions, and was reversed following readdition of extracellular Ca2+. These data suggest that the tyrosine phosphorylation of 2 cytoskeletal proteins is determined by the level of Ca2+ present in intracellular stores thus indicating a critical role for tyrosine phosphorylation in the control of capacitative Ca2+ entry in endothelial cells.

Amino Acid Sequence↗

PubMed1996

Antioxidants differentially affect nuclear factor kappa B-mediated nitric oxide synthase expression in vascular smooth muscle cells.

Increased 'oxidative stress' resulting in the activation of nuclear factor kappa B (NF-kappa B) is thought to play a crucial role in the cytokine-mediated expression of the inducible isoform of nitric oxide synthase (iNOS) in different cell types. Therefore, the effects of four different antioxidants, carbocromen, chrysin, 3,4-dichloroisocoumarin (DCI) and N-acetylserotonin (NAS), on iNOS expression were investigated in vascular smooth muscle cells (VSMC). All antioxidants strongly reduced the phorbol ester-stimulating superoxide anion formation in native VSMC. Carbocromen (200 microM) and chrysin (50 microM) had no effect, while NAS (1 mM) abolished the increase in nitrine production and iNOS protein abundance in cultured VSMC exposed to interleukin-1 beta (IL-1 beta, 60 U/ml) or the adenyl cyclase activator forskolin (10 microM). DCI also revealed a marked inhibitory effect in IL-1 beta-stimulated VSMC, but was less effective in cells treated with forskolin. DCI, but not NAS, also suppressed the activation of NF-kappa B in VSMC exposed to IL-1 beta, while no significant NF-kappa B activation was detected in forskolin-treated cells. These findings demonstrate that antioxidants differentially affect iNOS expression in VSMC both at the transcriptional level by preventing the activation of NF-kappa B and at the post-transcriptional level, presumably by promoting iNOS mRNA or protein degradation. They also suggest that reactive oxygen intermediates do not play a role in the activation of NF-kappa B by IL-1 beta in VSMC, and that transcription factors other than NF-kappa B mediate the induction of iNOS expression by elevating the intracellular concentration of cyclic AMP.

Animals↗

PubMed1996

Potentiation of the biological efficacy of bradykinin by ACE inhibitors: a shift in the affinity of the B2 receptor?

We have recently demonstrated that the angiotensin I-converting enzyme (ACE) inhibitor ramiprilat augments the endothelium-dependent dilator response to bradykinin in the isolated perfused rat heart by an interaction at the B2 receptor level. We have now investigated whether this is an effect of the ACE inhibitor class of compounds by studying the bradykinin-induced vasoconstriction in isolated segments of the rabbit jugular vein. Among five different ACE inhibitors, moexiprilat and ramiprilat proved to be the most effective in potentiating the constrictor response to bradykinin. This effect was not mimicked by other protease inhibitors or the synthetic ACE substrate hippuryl-L-histidyl-L-leucine. The ACE inhibitors, on the other hand, failed to affect the constrictor or dilator responses elicited by other receptor-dependent agonists in this vascular model. These findings demonstrate that ACE inhibitors selectively potentiate the B2 receptor-mediated constrictor response to bradykinin in the rabbit jugular vein, possibly by increasing the affinity of the B2 receptor.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1996

Inhibition by antioxidants of nitric oxide synthase expression in murine macrophages: role of nuclear factor kappa B and interferon regulatory factor 1.

1. In view of the potential deleterious effects of high amounts of nitric oxide (NO) produced by the inducible isoform of NO synthase (iNOS) in inflammation, the prevention of the expression of this enzyme represents an important therapeutic goal. In cytokine-stimulated cells, activation of nuclear factor kappa B (NF-kappa B) is crucial for the increase in iNOS gene expression. Since NF-kappa B activation appears to involve a redox-sensitive step, we have investigated whether three structurally unrelated antioxidants, 5,7-dihydroxyflavone (chrysin), 3,4-dichloroisocoumarin (DCI) and N-acetyl 5-hydroxytryptamine (N-acetylserotonin, NAS), affect iNOS expression in cultured RAW 264.7 monocyte/macrophages stimulated with bacterial lipopolysaccharide (LPS, 140 ng ml-1) and interferon-gamma (IFN gamma, 5 u ml-1). 2. During a 6 h incubation period neither LPS nor IFN gamma alone exerted a significant effect but when combined, caused a prominent increase in nitrite formation, iNOS mRNA and protein abundance. Co-incubation with chrysin (50 microM), DCI (50 microM) or NAS (1 mM) markedly attenuated this increase in iNOS gene expression. 3. DCI, but not chrysin or NAS, prevented the activation of NF-kappa B in cells exposed to LPS plus IFN gamma for 30 min. In contrast, all three antioxidants significantly blunted the DNA-binding activity of interferon regulatory factor 1 (IRF-1), which mediates the synergistic effect of IFN gamma on iNOS gene expression in cells treated for 2 h with LPS plus IFN gamma. 4. DCI thus appears to inhibit iNOS gene expression at the transcriptional level by preventing the activation of both NF-kappa B and IRF-1. The inhibitory effect of DCI on NF-kappa B activation, however, does not seem to be related to its antioxidative properties, since DCI, unlike chrysin or NAS, is a potent serine protease inhibitor which stabilizes the inactive NF-kappa B complex by protecting the inhibitory I kappa B-alpha subunit from proteolytic degradation. 5. The virtually identical inhibitory effect of chrysin, DCI and NAS on the activation of IRF-1 points to a redox-sensitive step in the activation of this transcription factor, which in contrast to NF-kappa B requires de novo protein synthesis. 6. Since iNOS gene expression in human cells and tissues usually requires the combination of several cytokines, antioxidants such as chrysin and NAS which do not interfere with the activation of NF-kappa B may be of therapeutic value for selectively inhibiting the enhanced expression of this enzyme in inflammation.

Animals↗

PubMed1996

Effect of cyclic GMP-dependent vasodilators on the expression of inducible nitric oxide synthase in vascular smooth muscle cells: role of cyclic AMP.

1. In the present study we examined whether interleukin-1 beta (IL-1 beta) increases the activity of adenylyl cyclase in vascular smooth muscle cells and determined its role in the cytokine-induced expression of the inducible nitric oxide synthase (iNOS) and activation of nuclear transcription factor-kappa B (NF-kappa B). In addition the interaction between cyclic AMP- and cyclic GMP-elevating agonists on the IL-1 beta-stimulated expression of iNOS was examined. 2. Exposure of vascular smooth muscle cells to IL-1 beta stimulated the formation of cyclic AMP but not of cyclic GMP. The intracellular level of cyclic AMP reached a maximum within 1 h and then gradually declined over the next 5 h. This IL-1 beta (60 u ml-1)-stimulated formation of cyclic AMP was modest (about 3 fold at 60 u ml-1 for 1 h) compared to that evoked by isoprenaline (about 9 fold at 3 x 10(-6) M for 2 min). 3. The IL-1 beta (60 u ml-1 for 24 h)-stimulated accumulation of nitrite, which was taken as an index of NO production, was concentration-dependently increased by preferential inhibitors of cyclic AMP-dependent phosphodiesterases (rolipram and trequinsin). This effect was reproduced by a specific activator of the cyclic AMP-dependent protein kinase(s) A, Sp-8-CPT-cAMPS (10(-4) M) but was prevented by a specific inhibitor of cyclic AMP-dependent protein kinase(s) A, Rp-8-CPT-cAMPS (10(-4) M). These compounds alone [rolipram (10(-6) M), trequinsin (3 x 10(-6) M) and Sp-8-CPT-cAMPS (10(-4) M)] slightly but significantly increased the release of nitric oxide while Rp-8-CPT-cAMPS elicited no such effect. 4. Inducible NOS protein was expressed in IL-1 beta (30 u ml-1, 24 h)-stimulated smooth muscle cells as assessed by Western blot analysis. The level of iNOS protein was markedly increased in smooth muscle cells which had been exposed to IL-1 beta in combination with either rolipram (3 x 10(-6) M) or Sp-8-CPT-cAMPS (10(-4) M) but was reduced in those exposed to IL-1 beta and Rp-8-CPT-cAMPS (10(-4) M). A weak expression of iNOS protein was found in smooth muscle cells which had been exposed to either Sp-8-CPT-cAMPS or rolipram alone for 24 h while Rp-8-CPT-cAMPS elicited no such effect. 5. Exposure of smooth muscle cells to IL-1 beta (30 u ml-1) for 30 min increased the level of NF-kappa B-DNA complexes in nuclear extracts as detected by electrophoretic mobility shift assay. Similar levels of NF-kappa B-DNA complexes were found in cells which had been exposed to IL-1 beta in combination with either Sp-8-CPT-cAMPS (10(-4) M), trequinsin (10(-6) M) or rolipram (10(-6) M). None of the modulators alone affected the basal level of NF-kappa B binding activity. 6. NO-donors [sodium nitroprusside (SNP) 10(-4) M; dinitrosyl-iron-di-L-cysteine-complex (DNIC), 10(-4) M; 3-morpholino-sydnonimine (SIN-1), 10(-4) M] and atrial natriuretic factor (10(-6) M) significantly increased the IL-1 beta (30 or 60 u ml-1, 24 h)-stimulated expression of iNOS protein and activity as assessed indirectly by the conversion of oxyhaemoglobin to methaemoglobin. In the absence of IL-1 beta, SNP (10(-4) M, 24 h) but not the other cyclic GMP-dependent vasodilators caused a modest expression of iNOS protein. No such effect was found in smooth muscle cells exposed to SNP in combination with Rp-8-CPT-cAMPS (10(-4) M) while an increased level of iNOS protein was found in those exposed to SNP in combination with either Sp-8-CPT-cAMPS (10(-4) M) or rolipram (3 x 10(-6) M). 7. Exposure of vascular smooth muscle cells to either S-nitroso-L-cysteine (Cys-SNO, 10(-4) M), SNP (10(-4) M) or SIN-1 (10(-4) M) for 35 min affected minimally the basal activation of NF-kappa B but abolished that evoked by IL-1 beta (30 u ml-1 added during the last 30 min). However, addition of Cys-SNO following the stimulation with IL-1 beta (during the last 5 min of the 30 min exposure period) reduced the level of NF-kappa B-DNA complexes only slightly. 8. These data indicate that the cyclic AMP-dependent pathway plays a decisi

Animals↗

PubMed1996

Intracellular pH and tyrosine phosphorylation but not calcium determine shear stress-induced nitric oxide production in native endothelial cells.

Signalling pathways determining the shear stress-induced production of NO from endothelial cells in situ were investigated using a bioassay system in which shear stress was increased by inducing vasoconstriction in an endothelium-intact donor segment (rabbit iliac artery) while maintaining a constant luminal perfusion rate. Shear stress-induced NO production, as assessed by changes in the tone of a preconstricted endothelium-denuded detector ring, was biphasic and consisted of an initial transient (20- to 25-minute) Ca(2+)-dependent phase followed by a Ca(2+)-independent plateau phase, which was maintained as long as the donor segment remained constricted. Stretching the donor segments to their in vivo length abolished the initial phase without affecting the plateau phase of NO release. Inhibition of the Na(+)-H+ exchanger using HOE 694 elicited an intracellular acidification which attenuated shear stress-induced NO production. The specific protein kinase C inhibitor, Ro 31-8220, was without effect, whereas the unspecific inhibitors, staurosporine and calphostin C, abolished the shear stress-induced production of NO. Erbstatin A, a tyrosine kinase inhibitor, attenuated the shear stress-induced tyrosine phosphorylation of specific cellular proteins and abrogated the associated NO production. In summary, these data indicate that shear stress activates the NO synthase at basal levels of [Ca2+]i via a mechanotransduction cascade that involves tyrosine phosphorylation and can be modulated by changes in pHi. The apparent fundamental alteration of the endothelial NO synthase under shear stress that renders its maintained activation independent of an increase in [Ca2+]i is probably the consequence of a change in the enzyme microenvironment.

Animals↗

PubMed1996

Molecular responses of endothelial tissue to kinins.

The endothelial response to kinin stimulation is the result of a series of complex intracellular reactions involving changes in the intracellular concentration of free calcium ([Ca2+]i) and intracellular pH, enhanced phosphorylation of several proteins via the activation of at least four distinct families of protein kinases, and activation of membrane ion transport systems. Some of the more recent developments in this field suggest that endothelial tyrosine kinases and tyrosine phosphatases as well as serine/threonine phosphatases are also activated in response to bradykinin. In addition, the finding that the mitogen-activated protein kinase (MAP kinase) pathway was tyrosine phosphorylated, and presumably activated, in endothelial cells after an increase in [Ca2+]i has wideranging implications for these cells. Indeed, MAP kinase recognizes many different substrates in the cell, including growth factor receptors, microtubule-associated proteins, specific serine-threonine protein kinases, phospholipase A2, and transcription factors. Further recent studies of interest have underscored the role of endothelium-derived hyperpolarizing factor in addition to nitric oxide and prostacyclin in the coronary vasculature. Indeed, this mediator, which seems to be an endothelium-derived, cytochrome P450-derived metabolite of arachidonic acid, would now appear to represent a substantial constitutive component of the vasodilator response to bradykinin.

Animals↗

PubMed1996

[Family practice diagnosis of patients with venous diseases in relation to severity, diagnosis and practice facilities. Results of the ASAM study "Physician status and factor evaluation study of ambulatory patient management"].

Although venous diseases are very common and represent frequent reasons for consultations in general practices, little is known about the actual ambulatory care for these patients. In a sentinel network consisting of general practitioners, 385 contacts with patients suffering from venous diseases (64% with varicose veins, 24% with phlebitis and 11% with ulcers) were documented. In 9% of the cases, the functional disability was "severe". The diagnostic procedures included laboratory tests in 23%, ECG in 11%, Doppler sonography in 8% and X-ray or angiography in 5%. The frequency of these diagnostic procedures correlated significantly with the degree of severity. The probability of a Doppler sonography in practices with ultrasound equipment compared to practices without it, was-stratified for the degree of severity, the unequal distribution of diseases and the level of acquaintance with the patient-between 2.2 and 2.6 (p always < 0.05), the probability of laboratory tests between 2.4 and 2.6 (p always < 0.001). This significant dependence of diagnostic procedures from the available equipment calls for the introduction of diagnostic standards as measures of quality assurance even for so-called trivial diseases.

Adult↗

PubMed1996

[Problem-based learning in a social medicine course--a concept for improving learning achievement and practice relevance].

In many medical curricula around the world, problem-based learning (PBL), i.e. inductive, usually interdisciplinary learning based on real or constructed cases, has been shown to improve the acquisition of knowledge. Additionally, it is valued positively by students. On the other hand, lecturing is usually valued negatively. Teaching of epidemiology and social medicine is further handicapped by the fact that students consider it irrelevant. In 1994/95, one of 18 social medicine courses for fifth year medical students at Hannover Medical School was problem-based. The following "cases" were used: 1. rheumatic patient with various social medical problems (losing sick pay, receiving status as handicapped person, early retirement etc.), 2. cluster of patients with leukaemia in the surroundings of a nuclear power plant and 3. recent newspaper articles on the effects of the 1993 Health Care Reform Law (dentists refusing to treat patients because of a fixed budget, introduction of prepayment methods in hospital etc.). Evaluation by the students at the end of the course revealed that PBL is well accepted in social medicine. Students rated learning success, relevance of the subject compared to other disciplines and the ability to transfer the acquired knowledge into medical practice well above the traditional courses. Besides lectures, practical courses and seminars, PBL should therefore be used as a standard method of learning in undergraduate medical education.

Attitude of Health Personnel↗

PubMed1995

S-nitrosation of serum albumin by dinitrosyl-iron complex.

The objective of this study was to identify a potential mechanism for S-nitrosation of proteins. Therefore, we assessed S-nitrosation of bovine serum albumin by dinitrosyl-iron-di-L-cysteine complex [(NO)2Fe(L-cysteine)2], a compound similar to naturally occurring iron-nitrosyls. Within 5-10 min, (NO)2Fe(L-cysteine)2 generated paramagnetic albumin-bound dinitrosyl-iron complex and S-nitrosoalbumin in a ratio of 4:1. Although S-nitroso-L-cysteine was concomitantly formed in low amounts, its concentration was not sufficient to account for formation of S-nitrosoalbumin via a trans-S-nitrosation reaction. Low oxygen tension did not affect S-nitrosation by the dinitrosyl-iron complex thus excluding the involvement of oxygenated NOx-species in the nitrosation reaction. Blockade of albumin histidine residues by pyrocarbonate, which prevented formation of dinitrosyl-iron-albumin complex, did not inhibit S-nitrosation of albumin. Thus, S-nitrosation of albumin by (NO)2Fe(L-cysteine)2 can proceed by direct attack of a nitrosyl moiety on the protein thiolate, without previous binding of the iron. We conclude that protein-bound dinitrosyl-iron complexes detected in high concentrations in certain tissues provide a reservoir of S-nitrosating species, e.g. low molecular dinitrosyl iron complexes.

Animals↗

PubMed1995

In vivo spin trapping of glyceryl trinitrate-derived nitric oxide in rabbit blood vessels and organs.

BACKGROUND: The objectives of this study were (1) to assess glyceryl trinitrate (GTN)-derived nitric oxide (NO) formation in vascular tissues and organs of anesthetized rabbits in vivo, (2) to establish a correlation between tissue NO levels and a biological response, and (3) to verify biotransformation of GTN to NO by cytochrome P-450. METHODS AND RESULTS: NO was trapped in tissues in vivo as a stable paramagnetic mononitrosyl-iron-diethyldithiocarbamate complex [NOFe(DETC)2]. After removal of the tissues, NO was determined by cryogenic electron spin resonance spectroscopy. NO formation in vitro was assessed by spin trapping and by activation of soluble guanylyl cyclase. The GTN-elicited decrease in coronary perfusion pressure was monitored in isolated, constant-flow perfused rabbit hearts. NO was not detected in control tissues. In GTN-treated rabbits, NO formation was higher in organs than in vascular tissues and higher in venous than in arterial vessels. In isolated hearts, ventricular NO levels and decreases in coronary perfusion pressure achieved by GTN were closely correlated. Purified cytochrome P-450 catalyzed NO formation from GTN in a P-450-NADPH reductase- and NADPH-dependent fashion. CONCLUSIONS: Since GTN-derived NO formation in myocardial tissue correlates to the GTN-elicited vasodilator response, we conclude that GTN-derived NO detected in vivo correlates with the systemic effects of GTN. Therefore, the higher rate of NO formation detected in veins compared with arteries explains the preferential venodilator activity of GTN. High NO formation in cytochrome P-450-rich organs in vivo and efficient NO formation from GTN by cytochrome P-450 in vitro highlights the importance of this pathway for NO formation from GTN in the intact organism.

Animals↗

PubMed1995

Characterization of the stable L-arginine-derived relaxing factor released from cytokine-stimulated vascular smooth muscle cells as an NG-hydroxyl-L-arginine-nitric oxide adduct.

The nature of an L-arginine-derived relaxing factor released from vascular smooth muscle cells cultured on microcarrier beads and stimulated for 20 h with interleukin 1 beta was investigated. Unlike the unstable relaxation elicited by authentic nitric oxide (NO) in a cascade superfusion bioassay system, the effluate from vascular smooth muscle cells induced a stable relaxation that was susceptible to inhibition by oxyhemoglobin. Three putative endogenous NO carriers mimicked this stable relaxing effect: S-nitroso-L-cysteine, low molecular weight dinitrosyl-iron complexes (DNICs), and the adduct of NG-hydroxy-L-arginine (HOArg) with NO. Inactivation of S-nitroso-L-cysteine by Hg2+ ions or trapping of DNICs with agarose-bound bovine serum albumin abolished their relaxing effects, whereas that of the vascular smooth muscle cell effluate remained unaffected. In addition, neither S-nitrosothiols nor DNICs were detectable in the effluate from these cells, as judged by UV and electron spin resonance (ESR) spectroscopy. The HOArg-NO adduct was instantaneously generated upon reaction of HOArg with authentic NO under bioassay conditions. Its pharmacological profile was indistinguishable from that of the vascular smooth muscle cell effluate, as judged by comparative bioassay with different vascular and nonvascular smooth muscle preparations. Moreover, up to 100 nM HOArg was detected in the effluate from interleukin 1 beta-stimulated vascular smooth muscle cells, suggesting that sufficient amounts of HOArg are released from these cells to spontaneously generate the HOArg-NO adduct. This intercellular NO carrier probably accounts for the stable L-arginine-derived relaxing factor released from cytokine-stimulated vascular smooth muscle cells and also from other NO-producing cells, such as macrophages and neutrophils.

Acetylcholine↗

PubMed1995

Increase in serum NG-hydroxy-L-arginine in rats treated with bacterial lipopolysaccharide.

Aortic rings isolated from rats 4 h after an injection i.p. of 30 mg/kg Escherichia coli lipopolysaccharide showed a marked hyporeactivity to noradrenaline. This effect was paralleled by an increase in the level of nitrite/nitrate in the serum of lipopolysaccharide-treated rats, indicative of an enhanced nitric oxide (NO) synthase activity. Most important, however, the serum concentration of the NO synthase intermediate, NG-hydroxy-L-arginine, was also markedly elevated from 3.7 to 15.8 microM. Circulating NG-hydroxy-L-arginine may thus represent a sensitive and specific marker of NO synthase activity in vivo.

Amino Acid Oxidoreductases↗

PubMed1995

Inhibition of arginase by NG-hydroxy-L-arginine in alveolar macrophages: implications for the utilization of L-arginine for nitric oxide synthesis.

The hypothesis was investigated that the nitric oxide (NO) synthase intermediate, NG-hydroxy-L-arginine (HOArg), is an arginase inhibitor in rabbit or rat alveolar macrophages. Exogenously applied HOArg strongly inhibited the arginase activity present in these cells (IC50 > or = 15 microM), and attenuated L-[3H]arginine transport (IC50 > or = 500 microM) in rabbit alveolar macrophages. Moreover, up to 37 microM HOArg were detected in the conditioned medium, but not in the lysate, of rat alveolar macrophages exposed to bacterial lipopolysaccharide for 18 h. HOArg may thus be a potent endogenous arginase inhibitor in these cells which increases the availability of L-arginine for NO biosynthesis.

Amino Acid Oxidoreductases↗

PubMed1995

Kinin-mediated activation of endothelial no formation: possible role during myocardial ischemia.

Endothelial cells produce a variety of factors involved in the control of vascular tone, platelet activation and cell growth, one of the most important being nitric oxide (NO). Although continuously produced in response to fluid shear stress, the release of NO from these cells can be enhanced further by humoral stimuli, such as bradykinin. This is the result of a chain of complex intracellular events involving changes in Ca2+, pH and protein phosphorylation. Endothelial cells are also capable of synthesizing bradykinin from an endogenous source, the release of which is markedly enhanced under hypoxic conditions. The finding that ACE inhibitors promote the local accumulation of the peptide and increase its efficacy at the receptor level may partly explain the potent anti-ischemic and cardioprotective effects of these drugs.

Angiotensin-Converting Enzyme Inhibitors↗