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Biomedical subjects

M Kelm

Publications and source records attributed to M Kelm.

At least 55 records · Page 3Linked to original sources
PubMed1997

[Formation, therapy and prevention of false aneurysm of the femoral artery following diagnostic and interventional heart catheterization].

OBJECTIVE: As pseudoaneurysm of the femoral artery after catheter introduction is a frequent complication, its causes and therapeutic options were investigated in a large patient collective. PATIENTS AND METHODS: In a prospective study with colour-Doppler duplex sonography of 6928 patients after diagnostic and of 3764 after interventional cardiac catheterisation, pseudoaneurysms were diagnosed in 80 patients (0.75%), 46 after diagnostic (0.66%) and 34 after interventional (0.9%) catheterisation. RESULTS: The incidence was higher in women than men (1.33% vs 0.58%; P < 0.05). Anticoagulation after sheath removal was the leading risk factor (n = 55, 68.8%), especially after interventional coronary intervention 85.3 vs 56.5%, P < 0.05). Local compression under duplex sonography monitoring was undertaken in 69 patients (86.3%), achieving aneurysmal obliteration in 53 (76.8%). Spontaneous thrombosis occurred in 15 of the remaining 27 patients, and surgical closure became necessary in 12. CONCLUSIONS: These data indicate a risk profile for the occurrence of pseudoaneurysm after cardiac catheterisation which can be dealt with by preventive measures. Local compression under duplex sonographic monitoring was the treatment of choice with a high success rate and low incidence of complications.

Aged↗
PubMed1997

The nitric oxide/superoxide assay. Insights into the biological chemistry of the NO/O-2. interaction.

Nitric oxide (NO) is a widespread signaling molecule involved in the regulation of an impressive spectrum of diverse cellular functions. Superoxide anions (O-2) not only contribute to the localization of NO action by rapid inactivation, but also give rise to the formation of the potentially toxic species peroxynitrite (ONOO-) and other reactive nitrogen oxide species. The chemistry and biological effect of ONOO- depend on the relative rates of formation of NO and O-2. However, the simultaneous quantification of NO and O-2 has not been achieved yet due to their high rate of interaction, which is almost diffusion-controlled. A sensitive spectrophotometric assay was developed for the simultaneous quantification of NO and O-2 in aqueous solution that is based on the NO-induced oxidation of oxyhemoglobin (oxyHb) to methemoglobin and the O-2-mediated reduction of ferricytochrome c. Using a photodiode array photometer, spectral changes of either reaction were analyzed, and appropriate wavelengths were identified for the simultaneous monitoring of absorbance changes of the individual reactions. oxyHb oxidation was followed at 541.2 nm (isosbestic wavelength for the conversion of ferri- to ferrocytochrome c), and ferricytochrome c reduction was followed at 465 nm (wavelength at which absorbance changes during oxyHb to methemoglobin conversion were negligible), using 525 nm as the isosbestic point for both reactions. At final concentrations of 20 microM ferricytochrome c and 5 microM oxyHb, the molar extinction coefficients were determined to be epsilon465-525 = 7.3 mM-1 cm-1 and epsilon541.2-525 = 6.6 mM-1 cm-1, respectively. The rates of formation of either NO or O-2 determined with the combined assay were virtually identical to those measured with the classical oxyhemoglobin and cytochrome c assays, respectively. The assay was successfully adapted to either kinetic or end point determination in a cuvette or continuous on-line measurement of both radicals in a flow-through system. Maximal assay sensitivity was approximately 25 nM for NO and O-2. Cross-reactivity with ONOO- was controlled for by the presence of L-methionine. Generation of NO from the NO donor spermine diazeniumdiolate could be reliably quantified in the presence and absence of low, equimolar, and high flux rates of O-2. Likewise, O-2 enzymatically generated from hypoxanthine/xanthine oxidase could be specifically quantified with no difference in absolute rates in the presence or absence of concomitant NO generation at different flux rates. Nonenzymatic decomposition of 3-morpholinosydnonimine hydrochloride (100 microM) in phosphate buffer, pH 7.4 (37 degrees C), was found to be associated with almost stoichiometric production of NO and O-2 (1.24 microM NO/min and 1.12 microM O-2/min). Assay selectivity and applicability to biological systems were demonstrated in cultured endothelial cells and isolated aortic tissue using calcium ionophore and NADH for stimulation of NO and O-2 formation, respectively. Based on these data, a computer model was elaborated that successfully predicts the reaction of NO and O-2 with hemoprotein and may thus help to further elucidate these reactions. In conclusion, the nitric oxide/superoxide assay allows the specific, sensitive, and simultaneous detection of NO and O-2. The simulation model developed also allows the reliable prediction of the reaction between NO and O-2 as well as their kinetic interaction with other biomolecules. These new analytical tools will help to gain further insight into the physiological and pathophysiological significance of the formation of these radicals in cell homeostasis.

Cytochrome c Group↗
PubMed1997

[Intracoronary dipyridamole reduces the incidence of acute coronary vessel occlusion in percutaneous transluminal coronary angioplasty--a prospective randomized study].

Even in the era of coronary stenting, acute coronary artery occlusion continues to represent a significant limitation of percutaneous transluminal coronary angioplasty (PTCA). Despite application of heparin and aspirin, abrupt vessel closure still occurs in 2-8%, depending on the definition applied. Especially patients receiving PTCA for acute coronary syndromes are at high risk for abrupt vessel closure. The formation of an intracoronary thrombus plays a central role in the pathogenesis of abrupt vessel closure. Dipyridamole induces dilatation of coronary arteries and prevents platelet aggregation by a mechanism that differs from that of aspirin. The primary purpose of the study was to evaluate whether adjunctive local intracoronary therapy with dipyridamole could reduce the incidence of coronary artery occlusion following PTCA. Secondary endpoints were defined as myocardial infarction, necessity for bypass grafting, and death. In 939 PTCA procedures performed for stable angina and in 155 angioplasty procedures for acute coronary syndromes (unstable angina, acute myocardial infarction), patients were randomized to receive conventional pretreatment consisting of heparin 15,000 I.E. and aspirin 500 mg i.v. or additional intracoronary infusion of dipyridamole (0.5 mg/kg body weight). Dipyridamole was applied in 550 interventions (455 interventions in men, 95 interventions in women, age = 59.2 +/- 8.4; 74 emergency procedures); conventional pretreatment was performed in 544 interventions (444 interventions in men, 100 interventions in women, age 58.3 +/- 7.9; 81 emergency procedures). Intracoronary application of dipyridamole resulted in a significant reduction in the incidence of abrupt vessel closure following PTCA. This significant reduction was observed in patients presenting with stable ischemia as well as in patients receiving PTCA for acute coronary syndromes. Concerning secondary end points, intracoronary application of dipyridamole did not affect the need for bypass grafting or the incidence of death following PTCA. Intracoronary application of dipyridamole was associated with a reduction in the incidence of myocardial infarction following PTCA which, however, failed to reach significance.

Adult↗
PubMed1997

Nitric oxide induced contractile dysfunction is related to a reduction in myocardial energy generation.

OBJECTIVE: It has been suggested that nitric oxide (NO) is involved in the regulation of myocardial function in a variety of diseases such as dilated cardiomyopathy, myocarditis, heart transplant rejection, and septic shock. However, the underlying mechanism of NO mediated reduction of cardiac contractility has not been clearly established so far. Therefore, we studied the effects of authentic NO on left ventricular function and myocardial energy status in the isolated heart. METHODS: In 43 isolated perfused guinea pig hearts quantitative and kinetic changes in coronary flow (CF), left ventricular developed pressure (LVDP), the cardiac release of adenosine, lactate, cyclic GMP, and norepinephrine were measured during infusion of authentic NO. In parallel, myocardial phosphocreatine (PCr), ATP and the free energy change of ATP-hydrolysis (delta GATP) were measured using 31P nuclear magnetic resonance spectroscopy. RESULTS: At low concentrations (0.01 to 1.0 mumol/L) NO increased CF only; at higher concentrations (1 to 100 mumols/L) CF remained elevated and LVDP was significantly reduced. Onset and offset of changes in LVDP occurred always within 2 to 5 s after start and cessation of NO infusion. Contractile dysfunction was significantly correlated to a pronounced increase in adenosine formation (> 70-fold), a significant decrease in myocardial PCr (-78%), ATP (-25%) and a decrease in delta G(ATP) from -61.76 kJ/mol to -50.75 kJ/mol. This was paralleled by a significant decrease in myocardial oxygen consumption (-65%) and a tenfold increase in lactate production. Coronary vasodilation (NO: 0.001 to 1.0 mumol/L) significantly correlated with the increase in cGMP release, whereas at negative inotropic concentrations (NO: 10 to 100 mumols/L) a clear quantitative and kinetic dissociation between NO-induced changes in cGMP and LVDP was observed. Contractile dysfunction was not related to cardiac release of norepinephrine. CONCLUSIONS: In the isolated heart NO can potently depress myocardial energy generation thus being an effective modulator of cardiac contractility. This effect of NO may be of pathophysiological significance in cardiac muscle disorders in vivo.

Adenosine↗
PubMed1997

[Coronary vasomotion in coronary heart disease--significance of epicardial and microcirculatory vessels for myocardial perfusion].

The most important function of the coronary vasculature is the effective regulation of coronary blood flow according to the metabolic needs of the myocardium. Under physiological conditions, coronary blood flow is regulated by a balance of vasoconstricting and -dilating components which can be differentiated with regard to the site (macro- vs. microcirculation), compartment (endothelium vs. vascular smooth muscle), and mechanism of action (receptor dependent vs. independent). This balance includes on the one hand the ability of the coronary circulation to maintain a relatively constant blood flow at any given oxygen demand irrespective of perfusion pressure (coronary autoregulation). On the other hand, coronary blood flow can be increased rapidly and effectively several-fold when myocardial oxygen demand increases. Previous investigations have demonstrated that the coronary endothelium plays a key role in the development of arteriosclerotic vascular lesions. In the time course of arteriosclerosis, functional alterations in endothelium dependent vasodilatation alterations are already present before angiographically demonstrable morphologic lesions. In the present manuscript, the diagnostic methods used to assess clinically the coronary macro- and microcirculation with regard to endothelium and smooth muscle dependent vasomotion are reviewed. In addition, present pharmacotherapeutic strategies to improve myocardial perfusion in coronary artery disease are discussed.

Animals↗
PubMed1997

[Significance of coronary thrombosis for chronic myocardial ischemia].

Apart from the relevance of disorders of lipid metabolism for the clinical and morphological progression of coronary artery disease, coronary thrombosis has received increasing attention in recent years. It is undoubtedly the decisive factor in the pathogenesis of acute coronary syndromes, which is underlined by the therapeutic success of various antithrombotic interventions. Furthermore coronary thrombosis is regarded to be a key factor for morphological disease progression also in stable coronary syndromes, which eventually may lead to critical limitation of myocardial perfusion. This is caused by the formation of subclinical coronary thrombi, which either undergo endogenous lysis or become morphologically fixed as they are incorporated into the plaque. Besides local factors, systemic disturbances of hemostasis and endogenous thrombolysis are of relevance. The concept of thrombotic progression of coronary thrombosis is supported by data on the reduction of morphological disease progression or antiischemic effectiveness of anti-thrombotic interventions like aspirin, low-molecular weight heparin and low-dose intermittent urokinase therapy. Percutaneous transluminal coronary angioplasty results in deep mechanical injury of the vessel wall, which is accompanied by secondary coronary thrombosis in the majority of the cases, not necessarily leading to abrupt vessel closure. Particularly, dilatation of primary thrombus as it has been described as the substrate of the culprit lesion in unstable coronary syndromes, promotes release of thrombin and activation of platelets, which in turn furthers the proliferative processes in the pathogenesis of restenosis. Even though data on the reduction of the rate of restenosis by the use of platelet aggregation inhibitors like aspirin, ticlopidin and dipyridamole have not consistently supported this concept, the EPIC. Study has shown that even in patients with stable angina pectoris clinical restenosis rate may be reduced by a platelet-IIb/IIIa-antagonist.

Angina Pectoris↗
PubMed1997

Impairment of adenosine-induced dilation of forearm resistance arteries in patients with arterial hypertension.

BACKGROUND: Adenosine is a potent mediator of arteriolar tone in particular during ischemia, hypoxia, and exercise. Functional disturbance of this dilatory pathway may be highly significant for the pathophysiology and pathogenesis of arterial hypertension. PATIENTS AND METHODS: Forearm blood flow (FBF) was quantified by venous occlusion plethysmography following intra-arterial infusion of adenosine at increasing doses in 13 patients with arterial hypertension (HT) and 12 age-matched normotensive controls (NT). Hyperemic peak flow was measured following 3 minutes of non-flow ischemia. RESULTS: FBF at rest was comparable in both groups and was dose-dependently increased by adenosine in both groups. In patients with HT adenosine-induced vasodilation was significantly impaired over the entire dose-response curve compared with NT (6.0 mumol/min: 14.5 +/- 1.0 versus 8.6 +/- 0.9 ml.min-1.100 ml-1 of tissue, p < 0.01). Maximum forearm blood flow during reactive hyperemia was also profoundly impaired in the hypertensive patients (-38%, p < 0.01). In the overall group of normotensive and hypertensive subjects, flow responses to adenosine were i) significantly correlated with peak flow (adenosine 2.0 mumol/min: r = 0.79, p < 0.001), and total flow during reactive hyperemia and ii) inversely related to the magnitude of arterial blood pressure. CONCLUSIONS: The study reported presents first evidence that adenosine-dependent dilation of forearm resistance arteries is impaired in patients with arterial hypertension. This vascular dysfunction is associated with the impairment of ischemia-induced reactive hyperemia which in turn may contribute to progressive end-organ damage in arterial hypertension.

Adenosine↗
PubMed1996

Determination of nitrite in human blood by combination of a specific sample preparation with high-performance anion-exchange chromatography and electrochemical detection.

All photometric or HPLC methods described to date have been unable to detect nitrite, a reliable marker of NO synthase activity, in human blood because of its rapid metabolism within the erythrocytes. We now elaborate on method to prevent nitrite degradation during sample preparation which in combination with high-performance anion-exchange chromatography and electrochemical detection allows a sensitive measurement of nitrite. A linear current response in the concentration range of 10-1000 nmol/l nitrite was observed yielding a correlation coefficient of 0.99. In addition, the combination of the electrochemical with a UV detector allowed us to simultaneously quantify nitrate within one analytical run, which is the end product of NO/nitrite metabolism. Basal levels for nitrate and nitrite in human blood were determined with 25 +/- 4 mumol/l and 578 +/- 116 nmol/l (n = 8), respectively and thus were in the same concentration range as expected from NO measurement in saline perfused isolated organs or cultured endothelial cells. Therefore, the presented method may be used to assess activity of endothelial constitutive NO synthase in humans under physiological and pathophysiological conditions.

Biomarkers↗
PubMed1996

Characterisation of left ventricular relaxation in the isolated guinea pig heart.

The time constant of left ventricular pressure fall, tau, has frequently been used as a measure of myocardial relaxation in the blood-perfused, ejecting heart. The aim of the present study was to characterise tau in relation to beta-adrenergic activation, coronary perfusion pressure and flow as well as cardiac oxygen supply and demand in the isolated, isovolumically beating heart. Therefore, tau was analysed from digitised left ventricular pressure data in a total of 23 guinea pig hearts perfused with saline at constant pressure (60 cmH2O). The coronary venous adenosine concentration ([ADO]) served as an index of myocardial oxygenation. Isoprenaline (0.4-3.2 nmol l-1) decreased and propranolol (3-9 mumol l-1) increased tau dose-dependently (linear regression tau vs lg([isoprenaline]), r = 0.74; tau vs. lg([propranolol]), r = 0.66, both P < 0.05). During graded reductions in cardiac oxygen supply from 96.1 +/- 12.6 (SEM) to 44.4 +/- 4.4 microliters min-1 g-1, tau was prolonged from 61.5 +/- 12.7 to 109.9 +/- 22.6 ms while left ventricular developed pressure (LVDP) decreased from 90.7 +/- 7.2 to 40.7 +/- 5.1 mmHg. In parallel, [ADO] increased from 23.7 +/- 9.1 to 58.0 +/- 19.1 pmol ml-1 (P < 0.05). Increasing oxygen supply to 165.4 +/- 32.4 microliters min-1 g-1 augmented LVDP to 102.7 +/- 7.3 mmHg but did not change tau or [ADO]. There was a dual response of tau to changes in cardiac oxygen supply or demand. As long as oxygen supply and demand matched, tau remained constant. However, when the oxygen supply was less than 100 microliters min-1 g-1, left ventricular relaxation was prolonged in parallel to the reduction in oxygen supply. In addition, a close relationship was observed between [ADO] as an indicator of myocardial oxygenation and tau (Spearman correlation, r = 0.99, P < 0.005). We conclude that the time constant of left ventricular pressure fall, tau, sensitively reflects myocardial relaxation in the isolated, isovolumically beating guinea pig heart. Moreover, in this model left ventricular relaxation is not influenced by alterations in coronary perfusion pressure or flow as long as cardiac oxygen demand is matched by an adequate supply. Rather relaxation is strictly coupled to myocardial oxygenation as reflected by coronary venous adenosine concentrations.

Animals↗
PubMed1996

Impaired effectiveness of nitric oxide-donors in resistance arteries of patients with arterial hypertension.

OBJECTIVE: To assess the dilatory effectiveness of nitric oxide donors in resistance arteries of patients with arterial hypertension in comparison with that in those of normotensive controls. BACKGROUND: Endothelium-dependent vasodilation has been demonstrated to be impaired in arterial hypertension. Besides disturbances in endothelial nitric oxide production a reduced vasodilatory effectiveness of nitric oxide might contribute to this phenomenon of endothelial dysfunction. We therefore investigated the dilatory responsiveness of resistance arteries to exogenous nitric oxide by means of administration of the nitric oxide donors glycerol trinitrate (GTN), isosorbide dinitrate (ISDN) and sodium nitroprusside (SNP) in hypertensive patients. METHODS: Forearm blood flow was measured by venous occlusion plethysmography at rest and during intra-arterial infusion of nitric oxide donors at increasing doses in 11 patients with arterial hypertension and in 10 age-matched normotensive controls. RESULTS: Forearm blood flow at rest was comparable in the two groups and was dose-dependently increased by administration of either nitric oxide donor. In patients with arterial hypertension, blood flow responses to infusions of organic nitrates were significantly impaired over the entire dose-response curve compared with those of normotensive controls (220 nmol/min GTN 13.1 +/- 1.3 and 8.6 +/- 0.3 ml/min per 100 ml tissue; 212 nmol/min ISDN 9.9 +/- 0.7 and 5.8 +/- 1.0 ml/min per 100 ml tissue). Blood flow responses to infusion of the nitric oxide donor SNP were also profoundly impaired in the hypertensive patients, the extent of which impairment equalled that found with the organic nitrates. Within the entire set of normotensive and hypertensive subjects, maximal flow responses to either nitric oxide donor were inversely correlated with mean arterial blood pressure. CONCLUSIONS: Dilation of resistance arteries in response to infusion of nitric oxide donors is impaired in hypertensive patients and the degree of this impairment depends critically on the severity of arterial hypertension. The reduced effectiveness of nitric oxide appears to be independent of the class of nitric oxide donor and thus of the mode of intravascular nitric oxide generation. These findings are likely to have important implications not only for our understanding of the pathophysiological mechanisms of endothelial dysfunction but also for nitric oxide donor therapy in arterial hypertension.

Adult↗
PubMed1996

Left ventricular mass is linked to cardiac noradrenaline in normotensive and hypertensive patients.

BACKGROUND: Left ventricular hypertrophy constitutes a powerful independent risk factor for heart failure, sudden death and ventricular dysrhythmia. Experimental data suggest that, apart from increased cardiac work load, noradrenaline may be one of the factors triggering myocardial hypertrophy. OBJECTIVE: To test the hypothesis that the extent of left ventricular hypertrophy is coupled to cardiac noradrenaline independently from the magnitude of arterial blood pressure. PATIENTS AND METHODS: Following exclusion of coronary artery disease by cardiac catheterization, cardiac noradrenaline release was measured in relation to left ventricular mass in 25 patients with arterial hypertension (HT), of whom five had left ventricular hypertrophy (HT + LVH) and 20 had normal left ventricular mass (HT - LVH), seven normotensive patients with hypertrophic cardiomyopathy (HCM) and a normotensive control group (n = 7). Noradrenaline was measured in arterial and coronary venous plasma using high-performance liquid chromatography. Coronary blood flow was quantified using the gas chromatographic argon method. Indices of left ventricular mass were calculated from the end-diastolic thicknesses of the interventricular septum and the posterior wall determined by echocardiography. RESULTS: The coronary venous plasma concentration of noradrenaline was significantly higher in HT - LVH, HT + LVH and HCM than it was in normotensives. Whereas in normotensives there was a net uptake of noradrenaline (17 +/- 10 pmol/min) across the coronary circulation, a net release of noradrenaline was observed in HT - LVH (69 +/- 26 pmol/min), in HT + LVH (121 +/- 55 pmol/min) and in HCM (341 +/- 96 pmol/min). In a multivariate linear regression analysis model, left ventricular mass correlated significantly with the net noradrenaline release rate (r = 0.64, P < 0.001), whereas arterial blood pressure as an additional independent variable did not correlate with left ventricular mass. CONCLUSION: The present data demonstrate that an increased left ventricular mass in normotensive and in hypertensive patients is closely coupled to an increased cardiac sympathetic activity, supporting the need for additional studies to determine whether adjunctive sympatholytic therapy is beneficial in patients with left ventricular hypertrophy and increased cardiac noradrenaline release.

Cardiac Catheterization↗
PubMed1996

Evidence for a multifactorial process involved in the impaired flow response to nitric oxide in hypertensive patients with endothelial dysfunction.

The assessment of endothelial function in hypertensive patients receiving acetylcholine has revealed conflicting results. Whether an impaired flow response to acetylcholine is explained solely by a diminished endothelial synthesis of nitric oxide (NO) remains unclear as yet. In the present study, we tested the hypothesis that mechanisms other than reduced NO synthesis contribute to the hypertension-associated impairment of endothelium-dependent vasodilation. Therefore, the dilatory response to endogenous and exogenous NO was measured in resistance arteries and cutaneous microvessels in the forearm circulation of 12 normotensive individuals and 17 hypertensive patients. In addition, the overall dilatory capacity was assessed by peak flow during reactive hyperemia after 3 minutes of ischemia. Forearm blood flow was quantified by venous occlusion plethysmography at rest, during application of the NO donor sodium nitroprusside, and during stimulation of endogenous NO synthesis by acetylcholine and bradykinin. Blood flow velocity in the cutaneous microvasculature was measured with laser-Doppler flowmetry in parallel. Resting forearm flow was comparable in both groups (3.1 +/- 0.2 and 3.4 +/- 0.2 mL.min-1.100mL-1 tissue), whereas blood pressure and thus peripheral vascular resistance was significantly elevated in hypertensive compared with normotensive subjects. Hyperemic peak flow was significantly blunted in hypertensive patients. Sodium nitroprusside, acetylcholine, and bradykinin increased flow in a dose-dependent manner to a comparable extent in the control group (13.3 +/- 0.8, 13.6 +/- 1.3, and 14.6 +/- 0.7 mL.min-1.100mL-1 tissue, respectively). In contrast, in hypertensive patients maximum increase in resting flow was significantly reduced (sodium nitroprusside, -36%; acetylcholine, -44%; and bradykinin, -56%). The flow response after stimulation of endogenous NO synthesis by bradykinin was significantly more blunted compared with that of exogenous NO after application of sodium nitroprusside. In the cutaneous microvasculature, bradykinin-induced increases in blood flow velocity were selectively impaired in hypertensive patients, whereas flow response to acetylcholine was preserved. Thus, we conclude that in arterial hypertension endothelium-dependent, NO-mediated dilation of resistance arteries and cutaneous microvessels of the forearm vasculature is heterogeneously impaired, depending on the type of endothelial receptor stimulated. Furthermore, the present data suggest that in hypertensive patients the impairment of NO-dependent dilation of resistance arteries is caused by at least three different mechanisms: (1) a reduced endothelial synthesis of NO due to either a disturbed signal-transduction pathway and/or a reduced activity of NO synthase, (2) an accelerated NO degradation within the vessel wall, and (3) alterations in the vessel architecture resulting in an overall reduced dilatory capacity of resistance arteries.

Female↗
PubMed1996

Selective impairment of nitric oxide dependent vasodilation in young adults with hypercholesterolaemia.

OBJECTIVE: To investigate comparatively flow response of resistance arteries to exogenous and endogenous nitric oxide in young adults with high serum cholesterol. BACKGROUND: Impaired vascular effectiveness of endogenous and exogenous nitric oxide may be considered to unmask impairment of its anti-atherogenic properties. It may thus represent a valuable early diagnostic index for these young adults at high risk for developing atherosclerosis. METHODS: In 10 patients with elevated plasma levels of low-density lipoprotein (high cholesterol group, age 34 +/- 5 year; (mean +/- SEM) level of low-density lipoprotein 5.2 +/- 0.5 mmol/l) and 12 age-matched control individuals (control group, 34 +/- 3 years; level of low-density lipoprotein < 3.9 mmol/l), forearm blood flow was measured by venous occlusion plethysmography at rest, during reactive hyperaemia after 3 min no-flow ischaemia, and during local intra-arterial infusions of acetylcholine, bradykinin, sodium nitroprusside and adenosine in increasing doses. RESULTS: In both groups resting forearm blood flow was similar and was dose-dependently increased by each vasodilator. In the hypercholesterolaemic patients compared with control subjects maximal forearm blood flow was significantly impaired after stimulation of endogenous nitric oxide synthesis by acetylcholine and bradykinin and during infusion of the nitric oxide donor sodium nitroprusside (acetylcholine: -19%, bradykinin: -29%, sodium nitroprusside: -24% versus control individuals; P < 0.05). In contrast, adenosine-dependent vasodilation and peak flow during reactive hyperaemia were similar in both groups. CONCLUSION: Excess of low-density lipoprotein cholesterol leads to selective impairment of nitric oxide-dependent vasodilation even in young adults, whereas adenylylcyclase-dependent vasodilation of vascular smooth muscle and maximal dilatory capacity are preserved. In view of the anti-atherogenic properties of nitric oxide, it appears highly desirable to detect this selective vascular dysfunction early in these young adults at high risk of developing atherosclerotic lesions.

Acetylcholine↗
PubMed1995

Transport of L-arginine in arginine-deprived endothelial cells.

In vascular endothelium, L-arginine (ARG) plays a crucial role as a substrate for various metabolic pathways, one of which is the synthesis of bioregulatory nitric oxide. Transport of ARG across the cell membrane determines intracellular substrate availability. Membranous transport in turn may be dependent on the extra-to-intracellular gradient in ARG concentration. To test this hypothesis ARG transport was characterized in control and ARG-deprived endothelial cells (EC). Within a two-hour deprivation period a decrease of more than 50% in intracellular ARG concentration was observed. Initial uptake rates for ARG revealed no significant differences between ARG-deprived and control EC (30.0 +/- 2.7 vs. 30.6 +/- 2.1 pmol*(mg protein*min)-1). Two distinct ARG transporter components were observed dependent on extracellular ARG concentration. No significant differences between ARG-deprived and control EC were found with respect to the kinetics of these ARG transporter components. The present data suggest that in this model the transport rate of ARG into EC is not directly dependent on the intracellular ARG concentration. Thus, a feedback loop between intracellular ARG concentration and ARG transporters as a critical determinant for endothelial ARG-dependent pathways such as NO-synthesis appears highly unlikely.

Animals↗
PubMed1995

Human endothelial cells bioactivate organic nitrates to nitric oxide: implications for the reinforcement of endothelial defence mechanisms.

Although in therapeutic use for more than a century, the mode of cellular action of organic nitrates remains incompletely understood. Despite ample experimental evidence from animal studies to show that nitrates are metabolized to NO in the vascular smooth muscle, direct demonstration of such an activity in human vascular cells is still lacking. Moreover, the role of the endothelium in modulating the pharmacodynamic action of nitrates is far from clear. We therefore aimed to investigate whether or not human endothelial cells are capable of bioactivating these drugs to NO and whether the amounts generated are sufficient to elicit any biological effects. Using cultured human umbilical vein endothelial cells (HUVECs) as an established model system a combination of three different methods was used to address this issue: (1) quantification of NO formation upon endothelial nitrate metabolism using the oxyhaemoglobin technique; (2) evaluation of the second messenger response using radioimmunoassay for cGMP; and (3) assessment of mechanism and extent of potentiation of the anti-aggregatory effect of nitrates in the presence of endothelial cells as a relevant bioassay. We now show that superfusion of cultured human endothelial cells on microcarrier beads with either glyceryl trinitrate (GTN) or isosorbide dinitrate (ISDN; both at 0.1-100 mumol L-1) results in a concentration-dependent formation of NO. NO generation from isosorbide 5-mononitrate (IS-5-N) was below the detection limit. The amounts of NO produced (maximally 2.97 +/- 0.98 pmoles NO min-1 x mg protein with 100 mumol L-1 GTN; n = 8) were similar to those elicited upon challenge of the cells with 100 nM bradykinin. NO formation from either organic nitrate was accompanied, in a concentration-dependent and methylene blue-inhibitable manner, by stimulation of endothelial soluble guanylyl cyclase with consequent increases in the intracellular level of cGMP (maximally 32-fold over basal levels with ISDN), a significant portion of which was released into the extracellular space. Upon continuous 30 min superfusion or repeated application of high concentrations of GTN (100 mumol L-1) nitrate bioactivation to NO was subject to partial tachyphylaxis. Co-incubation of washed human platelets with HUVECs potentiated the anti-aggregatory action of nitrates in a cell number dependent and oxyhaemoglobin-sensitive manner and this effect, too, was accompanied by increases in intraplatelet cGMP levels. The potentiating effect was largely inhibited after blockade of sulfhydryl groups by pre-incubation of HUVECs with N-ethylmaleimide and completely abrogated after pretreatment of cells with the tissue fixative glutaraldehyde. These results demonstrate that human endothelial cells are capable of bioactivating organic nitrates to NO by an enzymatic, apparently thiol-sensitive pathway, in quantities sufficient to influence endothelial and platelet function. Besides the well known vasorelaxant action of organic nitrates, which is mainly due to their metabolism in the smooth muscle compartment, these drugs may therefore be endowed with a hitherto underestimated potential to directly influence endothelial functions via the NO/cGMP pathway. Through specific bioactivation in the endothelium itself organic nitrates can thus mimic and reinforce protective functions normally served by a functional endothelium such as the modulation of blood cell/vessel wall interactions and inhibition of cell proliferation.

Biotransformation↗
PubMed1995

Role of nitric oxide in the regulation of coronary vascular tone in hearts from hypertensive rats. Maintenance of nitric oxide-forming capacity and increased basal production of nitric oxide.

In arterial hypertension, coronary flow reserve, expressed by the difference between autoregulated and maximal coronary flow, is frequently impaired. Previous experimental and clinical investigations using acetylcholine as a stimulus for the production of endothelium-derived relaxing factor suggested that an impaired endothelium-dependent vasodilation, presumably caused by a decreased formation of nitric oxide (NO), may account for this microvascular dysfunction. However, so far no study has been performed that quantifies the formation of NO within the coronary circulation of hypertensive hearts to assess its role in setting coronary vascular tone in the hypertensive heart. We therefore quantified NO formation within the coronary circulation of constant flow-perfused, isolated hearts from spontaneously hypertensive rats (SHR, 16th to 26th week), as a model for hypertensive heart disease, and from the normotensive control strain (Wistar-Kyoto, WKY) using the oxyhemoglobin technique. Coronary perfusion pressure and vascular resistance were almost 30% higher in SHR compared with WKY hearts. Intracoronarily applied NO decreased coronary vascular resistance by maximally 45% of resting values in a concentration-dependent manner in both groups. The bradykinin-induced decrease in coronary vascular resistance and the parallel increase in NO release were comparable in SHR and WKY hearts and fell within the vasodilator range of exogenously applied NO. Moreover, basal release of NO normalized to heart wet weight was 50% higher in SHR compared with WKY hearts. Rates of basal NO release were correlated inversely with changes in coronary perfusion pressure and vascular resistance in both groups (r = -.85 and -.84, respectively, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗