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R Busse

Publications and source records attributed to R Busse.

At least 73 records · Page 4Linked to original sources
PubMed1999

Inhibition of the production of endothelium-derived hyperpolarizing factor by cannabinoid receptor agonists.

1. The endogenous cannabinoid, anandamide, has been reported to induce an 'endothelium-derived hyperpolarizing factor (EDHF)-like' relaxation in vitro. We therefore investigated the effects of cannabinoid CB1 receptor agonists; HU 210, delta9-tetrahydrocannabinol (delta9-THC) and anandamide, and a CB1 antagonist/inverse agonist, SR 141716A, on nitric oxide (NO) and EDHF-mediated relaxation in precontracted rings of porcine coronary, rabbit carotid and mesenteric arteries. 2. In rings of mesenteric artery HU 210 and delta9-THC induced endothelium- and cyclo-oxygenase-independent relaxations which were sensitive to SR 141716A. Anandamide (0.03-30 microM) induced a slowly developing, endothelium-independent relaxation which was abolished by diclofenac and was therefore mediated by cyclo-oxygenase product(s). None of the CB1 agonists tested affected the tone of precontracted rings of rabbit carotid or porcine coronary artery. 3. In endothelium-intact segments, HU 210, delta9-THC and anandamide did not affect NO-mediated responses but under conditions of continuous NO synthase/cyclo-oxygenase blockade, significantly inhibited acetylcholine and bradykinin-induced relaxations which are attributed to the production of EDHF. The effects of HU 210 and delta9-THC were not observed when experiments were performed in the presence of SR 141716A suggesting the involvement of the CB1 receptor. 4. In a patch clamp bioassay of EDHF production, HU 210 decreased the EDHF-mediated hyperpolarization of detector smooth muscle cells when applied to the donor segment but was without effect on the membrane potential of detector cells. The inhibition of EDHF production was unrelated to alterations in Ca2+ -signalling or cytochrome P450 activity. 5. These results suggest that the activation of endothelial CB1 receptors appears to be negatively coupled to the production of EDHF.

Animals↗
PubMed1999

Role of increased production of superoxide anions by NAD(P)H oxidase and xanthine oxidase in prolonged endotoxemia.

Superoxide anions (O2-) are supposedly involved in the pathogenesis of endothelial dysfunction. We investigated whether the enhanced formation of O2- is involved in the attenuation of endothelium-dependent relaxation induced by lipopolysaccharide (LPS). Rats were injected with LPS (10 mg/kg IP), the aorta was removed after 12 or 30 hours, and generation of O2-, H2O2, and ONOO- was measured using chemiluminescence assays. Protein tyrosine nitration and expression of xanthine oxidase (XO), NAD(P)H oxidase, and manganese superoxide dismutase were determined by Western or Northern blotting, and endothelium-dependent relaxation in aortic rings was studied. LPS treatment increased vascular O2- (from 35+/-2 cpm/ring at baseline to 166+/-21 cpm/ring at 12 hours and 225+/-16 cpm/ring at 30 hours) and H2O2 formation, which was partially sensitive to the NAD(P)H oxidase inhibitor diphenylene iodonium at both time points studied and to the XO inhibitor oxypurinol only 30 hours after LPS treatment. Expression of XO and NAD(P)H oxidase (p22phox, p67phox, and gp91phox) were increased by LPS in a time-dependent manner, as were protein tyrosine nitration and ONOO- formation. LPS also induced expression of the oxidative stress-sensitive protein manganese superoxide dismutase. Endothelium-dependent relaxation was impaired after LPS treatment and could not be restored by inhibition of inducible NO synthase. Inhibition of O2- with superoxide dismutase, oxypurinol, tiron, or the superoxide dismutase mimetic Mn(III)tetrakis(4-benzoic acid)porphyrin chloride did not restore but further deteriorated the relaxation of LPS-treated rings. In summary, treatment of rats with LPS enhances vascular expression of XO and NAD(P)H oxidase and increases formation of O2- and ONOO-. Because removal of O2- compromised rather than restored endothelium-dependent relaxation, a direct role of O2- in the induction of endothelial dysfunction is unlikely. Other mechanisms, such as prolonged protein tyrosine nitration by peroxynitrite (which is formed from NO and O2-) or downregulation of the NO effector pathway, are more likely to be involved.

Analysis of Variance↗
PubMed1999

Vascular endothelial growth factor activates nuclear factor-kappaB and induces monocyte chemoattractant protein-1 in bovine retinal endothelial cells.

Vascular endothelial growth factor (VEGF) has been suggested to play a role in the pathogenesis of diabetic vascular complications. In the present study, we investigated whether expression of monocyte chemoattractant protein-1 (MCP-1), a chemokine that has been proposed to recruit leukocytes to sites of inflammation, neovascularization, and vascular injury, can be modulated by VEGF in bovine retinal microvascular endothelial cells (BRECs). VEGF induced expression of MCP-1 mRNA in BRECs in a concentration- and time-dependent manner. Secretion of MCP-1 into the culture medium of BRECs treated with VEGF for 24 h was increased by 2.2-fold compared with the control. Inhibitors of transcription factor NF-kappaB, N-alpha-tosyl-L-lysine chloromethylketone (TLCK) and N-acetylcysteine (NAC), as well as an inhibitor of the extracellular signal-regulated kinase (ERK) pathway, PD 98059, attenuated VEGF-induced expression of MCP-1 mRNA. Using electrophoretic gel mobility shift assay, we observed that VEGF stimulated binding activity of NF-kappaB. VEGF-induced NF-kappaB activation was inhibited by TLCK and NAC, but not by PD 98059. Binding activity of transcription factor AP-1, which is suggested to regulate induction of the MCP-1 gene together with NF-kappaB, was also stimulated by VEGF. PD 98059 inhibited the VEGF-induced activation of AP-1. These results indicate that VEGF induces MCP-1 expression in BRECs most likely by activating NF-kappaB and AP-1 via ERK-independent and -dependent pathways. Activation of NF-kappaB and induction of MCP-1 by VEGF in microvascular endothelial cells may contribute to the development of diabetic vascular complications.

Acetylcysteine↗
PubMed1999

[Health technology assessment in the international context: where does Germany stand? For the "German Scientific Working Group Technology Assessment for Health care"].

The evaluation of medical technologies, Health Technology Assessment (HTA), is gaining more and more importance in Germany. Starting from a comprehensive definition of the term medical technology, this article first describes the development of HTA since the seventies as an instrument for improving decision-making in health policy. HTA is presented as a repetitive cycle of a sequence of steps starting with the prioritization of topics to be evaluated to the analysis of the impact of the results. Current trends in the further improvement of HTA methods are described, such as the formalization of the topic selection. The current situation in Germany is presented with regard to the regulation of licensing/market entry, coverage by the statutory health insurance, and the utilization of medical technologies. Finally, current activities in the field of HTA in Germany as well as the role of the German Scientific Working Group Technology Assessment for Health Care are discussed.

Guidelines as Topic↗
PubMed1999

Leptin induces oxidative stress in human endothelial cells.

Human umbilical vein endothelial cells (HUVEC) express functional receptors to leptin, the product of the ob gene. As human obesity is associated with atherosclerosis and hyperleptinemia, we investigated whether leptin, in addition to its angiogenic properties, exerts atherogenic effects through the generation of oxidative stress in endothelial cells. In HUVEC leptin increased the accumulation of reactive oxygen species (ROS), as assessed by the oxidation of 2', 7'- dichlorodihydrofluorescein, in a time- and concentration-dependent manner. In addition, leptin activated the NH2-terminal c-Jun kinase/stress-activated protein kinase pathway as demonstrated by enhanced JNK activity and AP-1 DNA binding. Both effects were sensitive to antioxidant treatment with N-acetylcysteine. NF-kappaB, another redox-sensitive transcription factor, was also activated by leptin stimulation in an oxidant-dependent manner. Finally, activation of both AP-1 and NF-kappaB was associated with an enhanced expression of the monocyte chemoattractant protein-1 in HUVEC. These findings demonstrate that ROS are second messengers involved in leptin-induced signaling in endothelial cells. Thus, chronic oxidative stress in endothelial cells under hyperleptinemia may activate atherogenic processes and contribute to the development of vascular pathology.

Arteriosclerosis↗
PubMed1999

Which factors determine the use of diagnostic imaging technologies for gastrointestinal complaints in general medical practice?

OBJECTIVE: Even though gastrointestinal complaints are among the most frequent reasons to contact general medical practitioners, little is known about the actual care of these patients, especially the use of diagnostic imaging technologies. METHODS: In a network of 57 family practitioners and 29 general internists in Lower Saxony, Germany, 1,217 contacts with patients with gastrointestinal diseases (16%, gastritis; 12%, gastroenteritis; 6%, cholelithiasis; 5% each, ulcus ventriculi and duodeni, and 14%, no final diagnosis) were documented. The effects of patient and physician/practice side factors on the use of ultrasonography and radiography were modeled using multivariate logistic regression. RESULTS: For ultrasonography, diagnosis and ownership of an ultrasound unit (odds ratio [OR] = 3.33) were highly significant predictors (p < .0001), followed by unknown diagnosis at beginning of contact (OR = 1.92; p = .0019), physician specialty (OR for internists = 1.89; p = .0025), and severity (p = .0085). For radiography, ownership of an ultrasound unit was the most significant factor (OR = 0.34; p < .0001), followed by severity (p < .0009), ownership of x-ray apparatus (OR = 2.56; p = .0025), physician specialty (OR for internists = 1.98; p = .0358), and unknown diagnosis at beginning of contact (OR = 1.79; p = .0451). Not significant were age and sex of patient and diagnosis for radiography. CONCLUSIONS: Physicians use diagnostic imaging technologies for patients with gastrointestinal complaints according to severity and knowledge about the diagnosis, but ownership of technology is the most predictive factor.

Adult↗
PubMed1999

Cardiac catheterization in Germany. Diffusion and utilization from 1984 to 1996.

OBJECTIVE: To describe the diffusion of cardiac catheterization technologies and time trends of their use according to setting and geographic region in Germany during a 13-year period. It is hypothesized that the cardiac catheterization technology has matured from an experimental state to a broadly accepted technology. METHODS: Data come from the annual survey of the German Society for Cardiovascular Research. All German cardiac catheterization units are requested to provide data on volume and type of catheterization procedures. Data are available from 1984 to 1996. Number and type of procedure, type of unit, diagnoses, and complications are all recorded. The overall response rate is 90%, on average. RESULTS: The total number of catheterization units was 324 in 1996, or an average of 3.69 units per 1 million population. In 1996, all of the East German Länder and districts were below average. Utilization of cardiac catheterization procedures increased exponentially during the study period. The number of angiographies rose from about 45,000 in 1984 to more than 450,000 in 1996; the number of angioplasties increased almost by a factor of 50 to 125,000 procedures in 1996. Inverse correlations between the rates per million population of either coronary angiographies or PTCAs and mortality rates from ischemic heart disease were observed at the level of the German Länder. CONCLUSION: Further studies taking patient characteristics, long-term outcomes, and other factors in account are necessary to clarify the large geographic variations and the negative relationship between utilization rates and coronary heart disease mortality found in this study.

Adult↗
PubMed1998

Hydralazine prevents endothelial dysfunction, but not the increase in superoxide production in nitric oxide-deficient hypertension.

Dilator responses, superoxide anion-production, endothelial nitric oxide (NO) synthase and soluble guanylyl cyclase expression were determined in aortic rings from Wistar rats treated for 5 weeks either with the NO synthase inhibitor NG-nitro-L-arginine-methylester (L-NAME), L-NAME plus hydralazine or placebo. In the L-NAME-treated group, acetylcholine-induced relaxation was significantly attenuated whereas it was nearly normal in the L-NAME/hydralazine group. This difference was even more pronounced following inhibition of the endogenous superoxide dismutase using diethyldithiocarbamate. Aortic superoxide production was significantly elevated in both L-NAME-treated groups and hydralazine had no acute effect on superoxide formation. Expression of endothelial NO synthase was similar in all three groups whereas the attenuated soluble guanylyl cyclase expression in rats treated with L-NAME was nearly normalised by concomitant hydralazine treatment. These results demonstrate that in NO-deficient hypertension hydralazine treatment improves vasodilator responses but not the increased superoxide production.

Acetylcholine↗
PubMed1998

Leptin, the product of Ob gene, promotes angiogenesis.

The adipocyte-derived cytokine leptin is thought to play a key role in the control of satiety and energy expenditure. Because adipogenesis and angiogenesis are tightly correlated during the fat mass development, we tested the hypothesis that leptin is able to modulate the growth of the vasculature. Experiments were performed using cultured human umbilical venous endothelial cells (HUVECs) and porcine aortic endothelial cells. The presence of 170-kDa endothelial leptin receptor (Ob-R) was assessed in HUVECs by Western blot analysis. Reverse transcriptase-polymerase chain reaction analysis using specific oligonucleotides for the short and long Ob-R forms further revealed the expression of both Ob-R transcripts in endothelial cells. Moreover, leptin evoked a time-dependent tyrosine phosphorylation of a number of endothelial proteins, the most prominent of which were the mitogen-activated protein kinases Erk1/2. Treatment of HUVECs with leptin led to a concentration-dependent increase in cell number that was maximal at 10 ng/mL leptin and equivalent to that elicited by vascular endothelial growth factor. This effect was associated with an enhanced formation of capillary-like tubes in an in vitro angiogenesis assay and neovascularization in an in vivo model of angiogenesis. These results indicate that leptin, via activation of the endothelial Ob-R, generates a growth signal involving a tyrosine kinase-dependent intracellular pathway and promotes angiogenic processes. We speculate that this leptin-mediated stimulation of angiogenesis might represent not only a key event in the settlement of obesity but also may contribute to the modulation of growth under physiological and pathophysiological conditions in other tissues.

Adipocytes↗
PubMed1998

Ca2+-independent activation of the endothelial nitric oxide synthase in response to tyrosine phosphatase inhibitors and fluid shear stress.

Fluid shear stress enhances NO formation via a Ca2+-independent tyrosine kinase inhibitor-sensitive pathway. In the present study, we investigated the effects of the protein tyrosine phosphatase inhibitor phenylarsine oxide and of fluid shear stress on endothelial NO production as well as on the membrane association and phosphorylation of the NO synthase (NOS) III. Phenylarsine oxide (10 micromol/L) induced an immediate and maintained NO-mediated relaxation of isolated rabbit carotid arteries, which was insensitive to the removal of extracellular Ca2+ and the calmodulin antagonist calmidazolium. This phenylarsine oxide-induced vasodilatation was unaffected by genistein but abrogated by the tyrosine kinase inhibitor erbstatin A. Incubation of native or cultured endothelial cells with phenylarsine oxide resulted in a time-dependent tyrosine phosphorylation of mainly Triton X-100-insoluble (cytoskeletal) proteins, along with a parallel change in the detergent solubility of NOS III, such that the enzyme was recovered in the cytoskeletal fraction. A similar, though slightly delayed, phenomenon was also observed after the application of fluid shear stress but not in response to any receptor-dependent agonist. Although Ca2+-independent NO formation was sensitive to erbstatin A, phenylarsine oxide treatment was associated with the tyrosine dephosphorylation of NOS III rather than its hyperphosphorylation. Proteins that also underwent redistribution in response to the tyrosine phosphatase inhibitor included paxillin, phospholipase C-gamma1, mitogen-activated protein kinase, and the tyrosine kinases Src and Fyn. We envisage that fluid shear stress and tyrosine phosphatase inhibitors may alter the conformation and/or protein coupling of NOS III, facilitating its interaction with specific phospholipids, proteins, and/or protein kinases that enhance/maintain its Ca2+-independent activation.

Analysis of Variance↗
PubMed1998

Pulsatile stretch in coronary arteries elicits release of endothelium-derived hyperpolarizing factor: a modulator of arterial compliance.

To date, the release of the endothelium-derived hyperpolarizing factor (EDHF) has been demonstrated only in response to receptor-dependent Ca2+-elevating agonists. Since endothelial cells in situ are continuously subjected to rhythmic distension, we investigated the effect of rhythmic stretch on the release of EDHF from isolated porcine coronary arteries. In the combined presence of diclofenac and N(G)-nitro-L-arginine (L-NNA), sinusoidal pressure oscillations (from 40 to 50 mm Hg, 4 minutes, 1.5 Hz) led to simultaneous oscillations in the external diameter of coronary artery segments, the amplitude of which were decreased by iberiotoxin and apamin and also by endothelial denudation. In order to directly demonstrate the release of EDHF, the intraluminal solution from endothelium-intact coronary segments exposed to pulsatile stretch was applied to detector rat aortic smooth muscle cells, the membrane potential of which was continuously measured using the patch-clamp technique. The hyperpolarization of detector cells induced by the intraluminal solution was proportional to the amplitude of the pressure oscillations applied to the donor artery and was attenuated by either preincubation of donor arteries with 17-octadecynoic acid or application of either tetrabutylammonium or iberiotoxin to detector cells. In contrast to the bradykinin-induced release of EDHF, the EDHF synthesized in response to pulsatile stretch did not exhibit any tachyphylaxis. These findings demonstrate for the first time that the synthesis of EDHF in coronary arteries can be mechanically stimulated by rhythmic vessel wall distension and suggest that the continuous release of EDHF may contribute to the adjustment of an adequate vascular compliance and to the control of coronary blood flow.

6-Ketoprostaglandin F1 alpha↗
PubMed1998

Inducible nitric oxide synthase (iNOS) in the human heart: expression and localization in congestive heart failure.

The inducible nitric oxide (NO) synthase (iNOS or NOS2) generates a prolonged release of large amounts of NO which may be cytotoxic and/or inhibit myocyte contractility. It has been suggested that this mechanism specifically contributes to heart failure caused by dilated cardiomyopathy (DCM). To test this hypothesis we compared the myocardial amount and localization of iNOS in myocardial biopsies from patients with heart failure caused by either DCM or ischemic heart disease (IHD). During heart transplantation, myocardial biopsies collected from the diseased heart after explantation were frozen in liquid nitrogen. Twenty-two patients in NYHA class III-IV were included (DCM: n = 8; IHD: n = 14). In each biopsy, iNOS expression was assessed using reverse transcription polymerase chain reaction (RT-PCR), and visualized by immunohistochemistry. iNOS was detected in all biopsies. Intriguingly, the amount of iNOS mRNA (shown as iNOS cDNA normalized to GADPH cDNA) did not differ significantly between the two groups (DCM 30 +/- 7; IHD 20 +/- 6, mean +/- S.E.M., P > 0.05). Similarly, no inter-group differences in the amount of iNOS protein (Western) were observed. iNOS was invariably located to vascular endothelial and smooth muscle cells. In addition, an iNOS reaction in relation to the myocyte membrane was found in 4 of the 22 patients. These four patients (two from each group) had significantly (P < 0.05) higher iNOS/GADPH ratios (54 +/- 20) than patients without myocyte membrane iNOS reaction (17 +/- 15). In conclusion, iNOS is expressed in the myocardium of all patients with heart failure caused by either DCM or IHD. iNOS is located primarily and invariably in the endothelium and vascular smooth muscle cells of the myocardial vasculature and its expression appears to be associated with the condition of heart failure per se rather than related to the heart failure etiology.

Adult↗
PubMed1998

Vasodilator dysfunction in aged spontaneously hypertensive rats: changes in NO synthase III and soluble guanylyl cyclase expression, and in superoxide anion production.

OBJECTIVE/METHODS: Genetic hypertension is associated with an apparent endothelial dysfunction and impaired endothelium-dependent vasodilatation in response to increased flow and receptor-dependent agonists. However, the link between impaired vasodilatation and nitric oxide (NO) synthase expression is still unclear. In the present study, dilator responses were determined in the aorta and coronary circulation of 16 month old spontaneously hypertensive (SHR) and Wistar Kyoto rats (WKY). Changes in vascular reactivity were compared with alterations in superoxide anion production as well as endothelial NO synthase (NOS III) and soluble guanylyl cyclase expression. RESULTS: In the isolated perfused heart both the bradykinin- and sodium nitroprusside-induced vasodilator responses were attenuated in SHR compared to WKY. Western blot analysis revealed a parallel reduction in NOS III expression in coronary microvascular endothelial cells from SHR. Superoxide anion production in aortae from SHR was markedly elevated over that of aortae from WKY, and was almost completely abolished by pretreatment with superoxide dismutase. Superoxide dismutase induced similar relaxations in phenylephrine-preconstricted aortic rings from both SHR and WKY, but failed to restore the attenuated acetylcholine- and sodium nitroprusside-induced relaxations in SHR. No difference in NOS III expression was detected in the aortae from either strain whereas soluble guanylyl cyclase expression was markedly decreased in SHR. CONCLUSIONS: These results demonstrate that NOS III expression in different tissues is differentially affected by hypertension. Moreover, although an elevated superoxide anion production is apparent in the aorta, a reduced soluble guanylyl cyclase expression appears to account for the observed vasodilator dysfunction in SHR.

Acetylcholine↗
PubMed1998

Thrombin receptor expression is increased by angiotensin II in cultured and native vascular smooth muscle cells.

OBJECTIVE: The factors involved in restenosis after balloon angioplasty are poorly characterized but the local concentration of the potent mitogens angiotensin II (AII) and thrombin is known to be increased at sites of vascular injury. We investigated the possibility of a synergistic interaction between AII and thrombin by studying the effects of AII on the expression of the thrombin receptor in rat aortic smooth muscle cells (VMSC). METHODS: Thrombin receptor mRNA expression was studied by Northern blot analysis and RT-PCR using total RNA extracted from VMSC or from endothelium-denuded rat aortae. As a measure of thrombin receptor protein expression, we assessed either the thrombin-stimulated release of 6-keto-prostaglandin F1 alpha from VMSC or the contraction of endothelium-denuded rat aortic rings. RESULTS: The thrombin receptor mRNA was expressed at a low level in both cultured and native VMSC. AII concentration- and time-dependently increased expression of thrombin receptor mRNA in VMSC and augmented the thrombin-induced release of 6-keto-prostaglandin F1 alpha as well as the thrombin induced contraction. Blockade of the angiotensin subtype 1 (AT1) receptor by EXP3174 or D8731 prevented the AII-mediated increase in thrombin receptor expression. The effect of AII on the increase in thrombin receptor mRNA expression was enhanced by the protein kinase C inhibitor Ro 31-8220, but was unaffected by prolonged incubation with phorbol myristate acetate or the tyrosine kinase inhibitors genistein and erbstatin A. CONCLUSION: These results demonstrate that AII enhances the expression of thrombin receptor in cultured and native VMSC. In cultured cells, this effect is mediated by the activation of the AT1 receptor subtype. This synergistic effect between AII and the thrombin receptor may promote the extensive proliferation of smooth muscle cells in response to vascular injury.

6-Ketoprostaglandin F1 alpha↗
PubMed1998

Characterization of NS 2028 as a specific inhibitor of soluble guanylyl cyclase.

1 The haeme-containing soluble guanylyl cyclase (alpha1beta1-heterodimer) is a major intracellular receptor and effector for nitric oxide (NO) and carbon monoxide (CO) and mediates many of their biological actions by increasing cyclic GMP. We have synthesized new oxadiazolo-benz-oxazins and have assessed their inhibitory actions on guanylyl cyclase activity in vitro, on the formation of cyclic GMP in cultured cells and on the NO-dependent relaxation of vascular and non-vascular smooth muscle. 2 Soluble guanylyl cyclase, purified to homogeneity from bovine lung, was inhibited by 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS 2028) in a concentration-dependent and irreversible manner (IC50 30 nM for basal and 200 nM for NO-stimulated enzyme activity). Evaluation of the inhibition kinetics according to Kitz & Wilson yielded a value of 8 nM for Ki, the equilibrium constant describing the initial reversible reaction between inhibitor and enzyme, and 0.2 min(-1) for the rate constant k3 of the subsequent irreversible inhibition. Inhibition was accompanied by a shift in the soret absorption maximum of the enzyme's haem cofactor from 430 to 390 nm. 3 S-nitroso-glutathione-enhanced soluble guanylyl cyclase activity in homogenates of mouse cerebellum was inhibited by NS 2028 (IC50 17 nM) and by 17 structural analogues in a similar manner, albeit with different potency, depending on the type of substitution at positions 1, 7 and 8 of the benzoxazin structure. Small electronegative ligands such as Br and Cl at position 7 or 8 increased and substitution of the oxygen at position 1 by -S-,- NH- or -CH2- decreased the inhibition. 4 In tissue slices prepared from mouse cerebellum, neuronal NO synthase-dependent activation of soluble guanylyl cyclase by the glutamate receptor agonist N-methyl-D-aspartate was inhibited by NS 2028 (IC50 20 nM) and by two of its analogues. Similarly, 3-morpholino-sydnonimine (SIN-1)-elicited formation of cyclic GMP in human cultured umbilical vein endothelial cells was inhibited by NS 2028 (IC50 30 nM). 5 In prostaglandin F2alpha-constricted, endothelium-intact porcine coronary arteries NS 2028 elicited a concentration-dependent increase (65%) in contractile tone (EC50 170 nM), which was abolished by removal of the endothelium. NS 2028 (1 microM) suppressed the relaxant response to nitroglycerin from 88.3+/-2.1 to 26.8+/-6.4% and induced a 9 fold rightward shift (EC50 15 microM) of the concentration-relaxation response curve to nitroglycerin. It abolished the relaxation to sodium nitroprusside (1 microM), but did not affect the vasorelaxation to the KATP channel opener cromakalim. Approximately 50% of the relaxant response to sodium nitroprusside was recovered after 2 h washout of NS 2028. 6 In phenylephrine-preconstricted, endothelium-denuded aorta of the rabbit NS 2028 (1 microM) did not affect relaxant responses to atrial natriuretic factor, an activator of particulate guanylyl cyclase, or forskolin, an activator of adenylyl cyclase. 7 NO-dependent relaxant responses in non-vascular smooth muscle were also inhibited by NS 2028. The nitroglycerin-induced relaxation of guinea-pig trachea preconstricted by histamine was fully inhibited by NS 2028 (1 microM), whereas the relaxations to terbutaline, theophylline and vasoactive intestinal polypeptide (VIP) were not affected. The relaxant responses to electrical field stimulation of non-adrenergic, non-cholinergic nerves in the same tissue were attenuated by 50% in the presence of NS 2028 (1 microM). 8 NS 2028 and its analogues, one of which is the previously characterized 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), appear to be potent and specific inhibitors of soluble guanylyl cyclase present in various cell types. Oxidation and/or a change in the coordination of the haeme-iron of guanylyl cyclase is a likely inhibitory mechanism.

Animals↗