A multi-centre retrospective study of Nocardia speciation and antimicrobial susceptibility in Queensland, Australia

The study aims to characterise the species identification and antimicrobial susceptibility testing (AST) results of Nocardial isolates from adult patients across major public hospitals in Queensland, Australia, over a 15-year period. A multi-centre retrospective observational study of Nocardia sp. isolates was conducted from 7 major public hospitals in Queensland, Australia, over a 15-year period. Clinical samples from patients aged ≥ 18 years that isolated Nocardia sp. were included. Demographic and clinical data were collected, along with species identification and AST results. Overall, 484 Nocardia sp. were isolated. Most patients were male (297, 61%) with a mean (IQR) age of 60 (51-75) and a median (IQR) Charlson Comorbidity Index of 4 (2-6). Of these, 239 (49%) patients were immunosuppressed. Organisms were most frequently isolated from sputum (174, 36%), and superficial swabs (102, 21%). Patients presented with pulmonary infections (165, 35%) and superficial skin and soft tissue infections (87, 18%) most commonly. One hundred (21%) isolates were deemed pulmonary colonisation and were not treated. Of the speciated organisms, N. nova complex was the most common (93, 19%), followed by N. farcinica complex (79, 16%). Organisms were reliably susceptible to linezolid (240/245, 98%), amikacin (455/470, 97%), and trimethoprim/sulfamethoxazole (459/476, 96%), but less so to imipenem (243/472, 51%) and ceftriaxone (261/448, 58%). This is the largest Australian description of Nocardia sp. to date. Given antimicrobials are often commenced prior to AST results and sometimes even speciation, characterisation of local species and antibiogram data is important to guide empiric choices and local guidelines.

Reporting guidelines and journal quality in otolaryngology

OBJECTIVES

Journals increasingly use reporting guidelines to standardise research papers, partly to improve quality. Although defining journal quality is difficult, various calculated metrics are used. This study investigates guideline adoption by otolaryngology journals and whether a relationship exists between this and journal quality.

DESIGN, SETTING, PARTICIPANTS

Retrospective MEDLINE database review for English language, Index Medicus, journals of interest to otolaryngologists (October 2013).

MAIN OUTCOME MEASURES

The resulting journals were examined for the number of guidelines endorsed and then tabulated against surrogate measures of journal quality (Impact factor, Eigenfactor, SCImago, Source-Normalised rank). The primary outcome measure was the number of recognised reporting guidelines endorsed per journal. This was then correlated against journal quality scores. For comparison, a further small sample correlation was performed with 6 randomly selected and 6 high-profile clinical non-otolaryngology journals.

RESULTS

37 otolaryngology journals were identified. Number of guidelines used and quality scores were not normally distributed. Mean guideline usage was 1.0 for otolaryngology journals, 1.5 for randomly selected, and 5.5 for the high-profile journals. Only 18/37 (49%) otolaryngology journals endorsed any guidelines, compared with 11/12 non-otolaryngology journals. Within otolaryngology, Eigenfactor positively correlated with guideline use (r = 0.4, n = 44, p < 0.01) otherwise no correlation was found between guideline endorsement and journal quality.

CONCLUSIONS

Reporting guideline endorsement within otolaryngology journals is low. Although it might be expected that use of reporting guidelines improved quality, this is not reflected in the derived quality scores in otolaryngology. This may reflect low levels of use/enforcement, that quality indicators are inherently flawed, or that generalised guidelines are not always appropriate or valued by editors.

Diagnosis and prognosis of chest pain with normal coronary arteriograms

Ninety-eight patients previously investigated for suspected angina but shown to have normal coronary arteriograms were reviewed. The prognosis for like expectancy was excellent but 76% were still symptomatic after average follow up of three years. 41% of those re-evaluated were still thought to be describing cardiac-like pain. Full re-investigation showed coronary artery spasm or other causes of myocardial ischemia to be rare whereas oesophageal spasm was a common cause of the pain.

Endothelial function is impaired in fit young adults of low birth weight

OBJECTIVE

Non-insulin-dependent diabetes, hypertension and ischaemic heart disease, with insulin resistance, are associated with low birth weight (the 'Small Baby Syndrome'). Common to these adult clinical conditions is endothelial dysfunction. We tested the hypothesis that endothelial dysfunction could precede their development in those of low birth weight.

METHODS

Endothelial function was measured by ultrasonic 'wall-tracking' of flow-related brachial artery dilatation in fit 19-20 year old subjects randomly selected (blind to the investigators throughout the study) from low (< 2.5 kg) and normal (3.0-3.8 kg) birth weight subjects in the 1975-7 cohort of the Cardiff Births Survey and with no known cause for endothelial dysfunction.

RESULTS

Flow-related dilatation was impaired in low birth weight relative to normal birth weight subjects (median 0.04 mm [1.5%] [n = 22] cf. 0.11 mm [4.1%] [n = 17], p < 0.05; 0.04 mm [1.5%] [n = 15] cf. 0.12 mm [4.4%] [n = 12], p < 0.05 after exclusion of inadvertently included ever-smokers).

CONCLUSION

The findings suggest that endothelial dysfunction is a consequence of foetal malnutrition, consistent with contributing to the clinical features of the 'Small Baby Syndrome' in later adult life.

Syndrome X and endothelial dysfunction

OBJECTIVE

Syndrome X (angina, normal coronary arteriogram and positive exercise test) remains an enigma with unexplained features and apparent conflicts of evidence. The present study addressed whether (i) the Syndrome is characterised by generalised flow-related endothelial dysfunction, (ii) myocardial thallium201 defects reflect myocardial or microvascular dysfunction, (iii) endothelial dysfunction and its consequences can be improved by oral L-arginine.

METHODS

Flow-mediated brachial artery dilatation was measured by ultrasonic 'wall-tracking' in 7 Syndrome X patients, further characterised as having thallium201 defects and no known cause of endothelial dysfunction, and a normal control group. Syndrome X patients entered a 4-week randomised double-blind placebo-controlled cross-over trial of oral L-arginine (7 g twice daily), with brachial artery studies, exercise tests and technetium99 tetrafosmin scans.

RESULTS

Flow-mediated dilatation was absent in Syndrome X vs. normal. Stress technetium99 tetrafosmin and thallium201 scans showed similar defects. Flow-mediated dilatation, symptom-limited exercise duration and peak oxygen consumption (VO2max) were increased but rate-pressure-product (RPP) and radionuclide defects were unchanged after L-arginine vs. placebo.

CONCLUSIONS

The study supports coronary microvascular rather than myocardial dysfunction and shows loss of flow-mediated dilatation in systemic arteries. Oral L-arginine improved flow-mediated dilatation, exercise capacity and VO2max (by ca. 17%) despite unchanged RPP. The findings support generalised endothelial dysfunction. The arginine effects imply NO-mediated improvement of skeletal muscle perfusion suggesting improved homogeneity of microvascular distribution.

The cardiac endothelium: cardioactive mediators

Endothelial cells within the heart release a number of substances that modulate myocardial contractile function. These agents include nitric oxide, endothelin, prostanoids, adenylpurines, and other substances that have so far been characterized only in bioassay studies. A notable feature of many of these agents is that they influence contractile behavior predominantly by modifying cardiac myofilament properties rather than altering cytosolic Ca2+ transients. A consequence of this subcellular action is often a disproportionate effect on myocardial relaxation and diastolic tone. The paracrine modulation of cardiac myocyte function by endothelial cell factors is likely to be an important mechanism contributing to the overall regulation of cardiac contractile function, both physiologically and in pathological states.

Flosequinan in chronic heart failure: how is exercise capacity improved?

OBJECTIVE

Diuretics, angiotensin converting enzyme inhibitors and digoxin have become "standard" triple therapy for many patients with chronic cardiac failure. Flosequinan increases exercise duration and improves symptoms when added to standard triple therapy. Despite intensive study, the clinical pharmacology of flosequinan remains uncertain.

SETTING

The University Hospital of Wales, a Regional Cardiac Centre.

PATIENTS

Twenty four patients with chronic heart failure who remained symptomatic despite standard therapy including ACE inhibitors.

METHODS

A double-blind placebo-controlled parallel group study of 100 mg daily of flosequinan. We measured changes in exercise duration using cardiorespiratory exercise testing and changes in large artery distensibility using Doppler ultrasound.

RESULTS

Exercise duration after 8 weeks flosequinan treatment was significantly greater than following placebo treatment. The flosequinan-related increase in exercise duration (+14%) was associated with a significant reduction in VE/VCO2 slope (-16%). Brachial-radial pulse wave velocities were unaltered by flosequinan treatment.

CONCLUSIONS

Our results confirm that flosequinan improves exercise duration in patients with chronic heart failure. They suggest that this observed beneficial effect is independent of any change in large artery distensibility and that in the presence of ACE inhibitors, this improvement may be independent of any vasodilating action of flosequinan. Although this study confirms the beneficial symptomatic effects of flosequinan in chronic cardiac failure, clinical trials have subsequently demonstrated an overall increase in mortality in patients treated with 100 mg flosequinan daily. This has resulted in the withdrawal of flosequinan from routine clinical use.

Impaired matching of perfusion and ventilation in heart failure detected by 133xenon

In severe chronic heart failure (CHF) the ventilatory cost of CO2 elimination during exercise (VE/VCO2) is increased, suggesting ventilation/perfusion (V/Q) mismatch. The relationship of exercise VE/VCO2 regression slope m to deadspace ventilation was studied in 15 patients with CHF who underwent cardiopulmonary exercise testing and arterial blood gas monitoring. Regional lung ventilation and perfusion was studied, using 133xenon, at rest and peak exercise in a further group of 10 CHF patients and in five normal subjects. VE/VCO2 slope m correlated well with deadspace ventilation at peak exercise in the 15 patients with CHF. We therefore used exercise VE/VCO2 slope m to categorize CHF patients undergoing 133xenon imaging into groups with increased (slope m > 36) or normal (slope m < 36) exercise deadspace ventilation. In normals, resting V/Q determined by 133xenon showed a gravitational gradient, which improved on exercise as a result of relative increases and of relative reductions in regional perfusion; no significant changes in regional ventilation distribution were detected. In patients with CHF who had normal slope m (n = 5), rest and exercise V/Q were similar to the normal subjects. In CHF patients with increased slope m (n = 5) however, the resting gravitational gradient of V/Q was lost, and there were no significant changes in relative perfusion distribution on exercise. These findings suggest that the increased ventilatory cost of CO2 elimination found in certain patients with CHF is related to inability to coordinate and optimise the relative distribution of lung perfusion with respect to ventilation during exercise.

Endothelial control of arterial distensibility is impaired in chronic heart failure

BACKGROUND

Vascular tone is a determinant of conduit artery distensibility. The aim of this study was to establish whether endothelium-derived relaxing factor (EDRF) influences the distensibility of conduit arteries and whether endothelium-mediated increases in distensibility are impaired in chronic heart failure (CHF).

METHODS AND RESULTS

Conduit artery distensibility was measured by two methods in healthy subjects and in nine patients with CHF caused by dilated cardiomyopathy. In the first method, pulse-wave velocity (PWV) was measured in the right common iliac artery at rest and during local infusions of acetylcholine (10(-7) to 10(-5) mol/L) or adenosine (2 x 10(-7) to 2 x 10(-5) mol/L), with correction for systemic effects. Acetylcholine induced concentration-dependent local reductions of PWV in healthy subjects (-5%, -15%, and -26%) but not in CHF patients (3%, 1%, -4%, P < .01), whereas adenosine induced similar reductions of PWV in healthy subjects and CHF patients. In the second method, brachial artery diameter, blood flow, and blood pressure were measured noninvasively by high-resolution ultrasound, continuous-wave Doppler, and photoplethysmography during reactive hyperemia in the hand and after sublingual glyceryl trinitrate (GTN, 400 micrograms). Hyperemic flow, similar in healthy subjects and CHF patients, was associated with increases in diameter and distensibility in healthy subjects (8.8% and 18.4%, respectively) but not in CHF patients (0.3% and -4.5%), whereas GTN induced similar effects in healthy subjects and CHF patients.

CONCLUSIONS

These data indicate that conduit artery distensibility is increased by acetylcholine and increased blood flow in healthy subjects but not in CHF patients, whereas the effects of adenosine and GTN on distensibility are preserved in CHF patients. This implies that EDRF-mediated increases in distensibility are impaired in CHF patients, thus adding to cardiac work.

Endothelial control of myocardial function

The newly described phenomenon of endothelial control of myocardial contraction is reviewed. Endothelium both from endocardium and from coronary microvessels releases an unidentified contraction-prolonging agent and can be stimulated to release a contraction-abbreviating agent which is nitric oxide which elevates myocardial cyclic GMP content: these act by increasing and decreasing contractile protein sensitivity to cytosolic calcium respectively. The phenomenon has been confirmed in vitro and in vivo, with physiological and potential pathophysiological and pharmacological consequences for cardiac pump function.

Effects of the correction of renal anaemia by erythropoietin on physiological changes during exercise

The effects of treating the anaemia of end-stage renal failure with erythropoietin were studied in nine dialysis patients. The increase in haemoglobin concentration (by 59% from 7.0 +/- 1.2 to 11.1 +/- 1.1 g dl-1) was associated with increases in exercise duration (by 41%) and maximum oxygen consumption (by 34%). Treatment reduced resting heart rate but did not significantly alter heart rate at maximum exercise, nor resting or exercise blood pressure. Resting arterial potassium concentrations were slightly increased after treatment, but they increased similarly in relation to minute ventilation during exercise. Lactic acidaemia developed during exercise at both levels of haemoglobin, and was accompanied by similar reductions in arterial pH and bicarbonate levels but constant PaO2 and PaCO2. Ventilation was coupled to the metabolic rate of carbon dioxide production, ventilatory dead-space and arterial PCO2 before and after treatment of anaemia, the ventilatory requirement for carbon dioxide elimination being unchanged. Treatment of anaemia did not alter resting arterial lactate concentration; the concentration of lactate at maximum exercise was increased slightly following treatment but this increase did not reach statistical significance. The rate of increase in arterial lactate concentration as a function of oxygen consumption, assessed both with respect to the 'lactate threshold' and 'lactate slope index', was significantly delayed by treatment. Treatment of anaemia also delayed the 'anaerobic threshold', and there was good correlation between lactate and anaerobic thresholds. Treatment of renal anaemia by erythropoietin thus results in improved tissue oxygen supply during exercise, reflected by delay in the onset of lactic acidaemia.

The ventilatory cost of exercise compared in chronic heart failure and chronic renal anaemia

The cardiorespiratory responses to maximal treadmill exercise were compared in matched groups of patients with chronic renal anaemia or treated chronic heart failure, and in normal controls. Exercise capacity was similarly reduced in both patient groups compared to normal controls, the raised respiratory exchange ratio at peak exercise implying anaerobic metabolism due to limited oxygen delivery in heart failure and limited oxygen carrying capacity in anaemia. Minute ventilation (VE) was related linearly to minute CO2 production (VCO2) in all subjects (each r > 0.92) from all three groups. The slope of the VE/VCO2 relationship was normal in anaemia but steeper in heart failure, reflecting ventilation/perfusion mismatching in chronic heart failure.

Hyperinsulinaemia and microvascular angina ("syndrome X")

Glucose and insulin responses to a glucose load in 11 patients with angina attributed to microvascular coronary dysfunction were compared with those in 11 healthy subjects matched for age, sex, and body mass. Stimulated hyperinsulinaemia was demonstrated in the microvascular angina group. The findings suggest a role for increased concentrations of insulin in coronary microvascular dysfunction.

Syndrome X and hyperventilation

The cardiorespiratory responses to exercise and forced hyperventilation were measured in 17 unselected patients with syndrome X (angina, positive exercise test, normal coronary arteriogram, no other cardiovascular disease) and compared with those in 15 healthy subjects. Forced hyperventilation produced hypocapnia and metabolic alkalosis but no chest pain or electrocardiographic change. Patients with syndrome X showed reduced maximum oxygen consumption with an increased respiratory exchange ratio at peak exercise, confirming that exercise was limited by skeletal muscle perfusion--and thus that the increase in cardiac output with exercise is limited in syndrome X as in heart failure. Arterial carbon dioxide tension (PCO2) homoeostasis during exercise was normal but the ventilatory cost of carbon dioxide excretion was increased in syndrome X (as in heart failure). End tidal PCO2 measurements correlated only poorly with arterial PCO2 in individual patients with syndrome X, providing a possible explanation for previous reports, based on end tidal PCO2 of inappropriate hyperventilation. Patients with syndrome X did not show inappropriate hyperventilation but they did show hyperventilation that was appropriate to maintain normal arterial PCO2 in the face of reduced cardiac reserve.

Effects of 8-bromo-cyclic GMP on contraction and on inotropic response of ferret cardiac muscle

The effects of guanosine 3':5'-cyclic monophosphate (cGMP) on cardiac contraction are not established. Using isolated electrically-stimulated ferret papillary muscle at 29 degrees C, 2.0 mM calcium we investigated the effects of 8-Bromo-cGMP on (a) basal contraction for comparison with the effects of reduction in extracellular calcium or of reduction in resting muscle length; (b) contraction of preparations stimulated by isoprenaline, the dihydropyridine calcium agonist Bay K8644 or post-extrasystolic potentiation. 8-Bromo-cGMP (0.1 mM) induced a small significant reduction in isometric twitch tension (TT) (7%), isotonic shortening (PS) (6%) and in twitch duration, but had no effect on maximum unloaded shortening velocity (Vmax) or rate of tension development (+dT/dt). Reduction in muscle length induced a similar immediate effect on contraction. Reduction of extracellular calcium (2.0 mM to 1.25 mM) reduced TT by 24% and PS by 14% as well as Vmax (19%) and +dT/dt (29%), but did not alter twitch duration. Bay K8644 (0.01 to 10 microM) produced increases in TT, +dT/dt, PS and twitch duration each of which was significantly reduced in the presence of 8-Bromo-cGMP (0.1 mM). 8-Bromo-cGMP had no effect on the responses to isoprenaline 1 nM to 100 microM--which increased TT, +dT/dt and PS but markedly reduced twitch duration--nor on post-extrasystolic potentiation which increased TT and +dT/dt but slightly reduced twitch duration. These results show that 8-Bromo-cGMP induces changes similar to the immediate effects of reduction in resting muscle length, and reduces the positive inotropic effects of Bay K8644 but not those of isoprenaline or post-extrasystolic potentiation.

Acute haemodynamic effects of intravenous infusion of adenosine in conscious man

The acute haemodynamic effects of intravenous infusion of adenosine, a dilator of most vascular beds, were studied in 16 patients (seven with coronary artery disease, nine with normal coronary arteries) undergoing cardiac catheterization for investigation of chest pain. At the lowest dose used (4.3 mg min-1) adenosine increased minute ventilation by 44% (P less than 0.01, n = 11) and reduced pulmonary vascular resistance by 20% (P less than 0.05) without causing other significant haemodynamic changes. Symptoms, including chest discomfort in 14 patients and dyspnoea in 11, limited the maximum dose to 8.5 +/- 2.3 mg min-1 (mean +/- SD, 108 +/- 24 micrograms kg-1 min-1). At this dose, adenosine reduced pulmonary and systemic vascular resistance (by 38% and 34%, respectively) and increased heart rate (by 34%), stroke index (by 12%) and cardiac index (by 52%). Systemic blood pressure and right atrial pressure did not change. Unexpectedly, adenosine increased left ventricular end-diastolic pressure (LVEDP) (from 5 +/- 6 to 14 +/- 10 mmHg, n = 8), pulmonary capillary wedge pressure (from 3 +/- 2 to 10 +/- 5 mmHg, n = 16) and consequently mean pulmonary artery pressure (from 10 +/- 2 to 16 +/- 5 mmHg). Minute ventilation increased by 84% (n = 11), resulting in hypocapnia (PCO2: 31 +/- 3 mmHg, n = 8) and alkalosis (pH: 7.46 +/- 0.02, n = 8). Oxygen consumption was unchanged during the infusion, but increased by 21% 5 min post infusion. All effects were similar in patients with and without coronary artery disease. Adenosine therefore causes pulmonary and systemic vasodilation and respiratory stimulation. Symptoms and an increase in LVEDP of uncertain cause, which occur with high doses, may limit the use of adenosine as a systemic vasodilator in conscious subjects. However at lower doses adenosine causes selective pulmonary vasodilation which merits further study.

Chronic administration of N-acetylcysteine fails to prevent nitrate tolerance in patients with stable angina pectoris

1. Reduced availability of sulphydryl groups in vascular smooth muscle cells may contribute to the development of tolerance to the action of the organic nitrovasodilators. 2. Eight patients with stable angina were treated with 10 mg of transdermal glyceryl trinitrate per 24 h, together with 400 mg N-acetylcysteine, a sulphydryl group donor, or matching placebo three times daily in a double-blind randomised crossover manner for two periods of 4 days with intervening washout period of 3 days off these drugs. Other therapy remained unaltered during the study. 3. Blood pressure, heart rate and symptom-limited treadmill walking time were measured in the pre-treatment control state and 4 h after starting treatment on day 1 and day 4 of each glyceryl trinitrate treatment period. 4. The changes seen on day 1 were attenuated by day 4 to an equal extent in N-acetylcysteine and placebo treatment periods. 5. These results suggest that chronic oral administration of N-acetylcysteine fails to prevent the development of tolerance to the anti-anginal or haemodynamic effects of glyceryl trinitrate.

Does endocardium modulate myocardial contractile performance?

It is now clear that the endocardium releases at least two agents which exert opposing effects on myocardial contraction. One appears to be endothelium-derived relaxing factor (EDRF), as in vascular endothelium, but the identity of the other is unknown. The mechanism by which these agents exert their characteristic but opposing effects on the duration of contraction likewise remains unknown. It is unlike that of other inotropic interventions and merits further investigation. Alterations in the time of onset of relaxation have important implications for diastolic filling.

Calcific aortic stenosis in twins: a clue to its pathogenesis?

A pair of identical twins presented almost simultaneously at age 62 years with calcific aortic stenosis requiring surgery, one with bicuspid and one with tricuspid aortic valve. This suggests that bicuspid morphology may perhaps not be the cause, but may be a genetically linked marker of an inherited predisposition to calcific stenosis.

EDRF and the regulation of vascular tone

Vascular endothelium is now known to produce a vasodilator agent, known as endothelium derived relaxing factor (EDRF) and recently shown to be nitric oxide. It acts locally on subjacent vascular smooth muscle by stimulating soluble guanylate cyclase to increase cyclic GMP levels and so reduce cytosolic free calcium. EDRF activity varies widely between different artery types and can be stimulated by various pharmacological agents and by flow. Studies in the intact vascular bed of the buffer-perfused rabbit ear show that EDRF activity is high in resistance vessels (particularly those of ca. 150 microns diameter), that EDRF is responsible for a 4th power relationship of diameter to flow in response to acute changes in flow (so limiting pressure gradients needed to increase flow rate), and that basal EDRF activity maintains geometric similarity of vessel diameters (implying that the spatial distribution of flow remains constant at different flow rates).

N-acetylcysteine fails to attenuate haemodynamic tolerance to glyceryl trinitrate in healthy volunteers

1. The effects of chronic dosing with N-acetylcysteine (NAC), on nitrate-induced haemodynamic changes during the acute and chronic treatment of healthy volunteers with glyceryl trinitrate (GTN) patches (Transiderm nitro) has been investigated. 2. Seven volunteers were treated in a double-blind randomised crossover manner for two periods of 4 days with 20 mg of transdermal GTN/24 h together with NAC (200 mg three times daily) or matching placebo. There was a washout period of greater than 3 days between treatment periods. 3. Haemodynamic measurements (blood pressure (BP); heart rate (HR] at rest and following maximal treadmill exercise were performed before treatment and 4 h after starting treatment on days 1 and 4. 4. Significant haemodynamic changes as evidenced by a fall in BP and rise in HR, were seen on day 1 in both the NAC and placebo phases. By day 4 the haemodynamic changes had returned towards the pre-treatment values during both the NAC and placebo phases suggesting the development of tolerance in both treatment groups. 5. These findings suggest that concurrent administration of NAC fails to prevent the development of tolerance to GTN.

Syndrome X

The problem of anginalike chest pain with normal coronary arteriographic findings is briefly reviewed. This common clinical presentation (ca. 20% of patients investigated by coronary arteriography) is usually due to noncardiac causes (e.g., thoracic root or esophageal pain) but may represent myocardial ischemia attributable to reduced coronary dilator capacity downstream from the epicardial vessels and of unknown pathogenesis--Syndrome X (? less than 0.1% of such patients).

Vascular endothelium in ischemic heart disease: possible role for endothelium-derived relaxing factor

The nature, mechanism of action, and roles of endothelium-derived relaxant factor (EDRF) are reviewed, particularly in relation to the coordination of vascular behavior in response to changes in flow, coronary spasm, and platelet aggregation. Vascular endothelium performs a multiplicity of roles. It is an active sieve for macromolecules and leukocytes, a negatively charged "lubricant" for passage of negatively charged red cells and platelets, and a factory for Von Willebrand factor, glycoaminoglycans, and plasminogen activator and its inhibitor. It is also a processing plant that metabolizes adenosine nucleotides to adenosine and activates angiotensin. Endothelium also produces prostacyclin and endothelium-derived relaxant factor, which act synergistically and through different pathways to the common ends of relaxing vascular smooth muscle and inhibiting platelet aggregation. Most recently it has been shown to also produce a constrictor agent called endothelin, a peptide whose structure has now been elucidated. This review will concentrate on EDRF, the recently discovered vasodilator agent that is continuously released by all vascular endothelium. It would be premature to define the role of EDRF in ischemic heart disease. It may, however, be timely to consider the ways in which EDRF might be relevant, based on a review of what is at present known.

Glyceryl trinitrate and platelet aggregation: effects of N-acetyl-cysteine

The concentration range of GTN causing inhibition of platelet aggregation in vitro is much higher than the plasma concentrations achieved clinically. This action is potentiated by the sulphydryl donor N-acetylcysteine. We have investigated the effects of GTN given with and without N-acetylcysteine on ex vivo platelet aggregation in man. In a double-blind randomised crossover trial eight healthy volunteers were treated with 20 mg of transdermal GTN/24 h, together with N-acetylcysteine 200 mg three times daily or matching placebo. Platelet aggregation, measured ex vivo by whole blood impedance aggregometry in response to adenosine diphosphate, was not significantly altered by GTN acutely or after 4 days' treatment with or without N-acetylcysteine. Platelet cyclic guanosine monophosphate levels were not significantly altered by GTN either in the absence or presence of N-acetylcysteine. This result implies that previously reported beneficial effects of GTN in myocardial infarction or unstable angina are unlikely to be attributable to direct pharmacological inhibition of platelet aggregation.

Inotropic effects of endothelin in ferret ventricular myocardium

The characteristics of the inotropic response to endothelin were studied in isolated ferret papillary muscle preparations. Endothelin (0.1-10 nM) induced concentration-dependent positive inotropic effects. At 10 nM, isometric tension increased by 17%, maximum rate of tension development by 18%, maximum velocity of unloaded shortening by 23% and peak isotonic shortening by 11%. Time to peak isometric tension and half isometric relaxation time were unaltered by endothelin. This pattern of change is similar to that of elevating extracellular calcium concentration.

The role of EDRF in flow distribution: a microangiographic study of the rabbit isolated ear

A microangiographic technique was used to study the influence of endothelium-derived relaxing factor (EDRF) on vasomotor control mechanisms in resistance vessels of intact buffer-perfused rabbit ear. Selective inhibition of EDRF activity by hemoglobin unmasked an intrinsic ("myogenic") constrictor response to sudden increases in flow rate. EDRF activity was greatest in arteries in which calculated shear stress and hydraulic resistance were maximal, namely the central ear artery and its first generation of branch arteries: these are proximal "feed" vessels (150-700 microns internal diameter) in this bed. The findings are consistent with enhancement of EDRF release by the physical stimulus of shear stress in resistance vessels as previously demonstrated in conduit vessels-a phenomenon which is likely to exert a major influence on flow in vascular networks. EDRF activity thus reduced perfusion pressure and power losses, particularly in highly constricted preparations. Shear-induced release of EDRF may provide an integrating link between flow and arterial topography by optimizing perfusion characteristics over a wide range of flow rates.

Post-infarction ventricular septal defect: the importance of right ventricular coronary perfusion in determining surgical outcome

Mortality from a post-infarction ventricular septal defect (VSD) can be reduced by surgery, selection for which would be helped by knowledge of factors affecting the postoperative prognosis. We reviewed our 9-year experience (1978-1987) of 40 surgically treated patients, comparing preoperative characteristics in those who died postoperatively (n = 15, 37%) and those who survived (n = 25, 63%), all still alive. Sex, age, infarct size as assessed by peak serum creatine kinase values, left ventricular end-diastolic pressure and pulmonary/systemic flow ratio (2.9 +/- 0.2 vs 3.1 +/- 0.3) were similar. Survivors had a lower incidence of inferior infarct than those who died (6, 24% vs 9, 60%, P less than 0.05), a lower incidence of cardiogenic shock (7, 28% vs 10, 67%, P less than 0.05), less elevation of right ventricular end-diastolic pressure (10.1 +/- 0.9 vs 14.7 +/- 1.0 mm Hg, P less than 0.01) and less impairment of right ventricular coronary supply as determined by a coronary angiography-derived myocardial score (0.9 +/- 0.3 vs 4.7 +/- 0.7, P less than 0.001). The data suggest that right ventricular coronary perfusion influences prognosis. The proposed angiographic score may help to identify preoperatively those patients most likely to benefit from surgery.

Effects of enalapril on myocardial noradrenaline overflow during exercise in patients with chronic heart failure

The effects of the angiotensin converting enzyme inhibitor enalapril on myocardial sympathetic tone, as represented by noradrenaline overflow, were studied in 14 men with congestive heart failure (mean ejection fraction 20%) in a double blind crossover comparison with placebo. Arterial and coronary sinus catecholamine concentrations and oxygen content, and coronary sinus blood flow, were measured at rest and during peak symptom limited upright exercise on a bicycle ergometer. There were no significant changes four hours after the first dose of enalapril, but after six weeks of treatment (10-20 mg/day) enalapril reduced myocardial overflow of noradrenaline at peak exercise. The external workload (exercise duration) increased from baseline values after both placebo and enalapril, and there was no difference between placebo and enalapril at six weeks. Heart work, however, was lower after enalapril: stroke work index was reduced at rest and the double product was lower at peak exercise. The reduction in maximal myocardial oxygen consumption after enalapril did not reach statistical significance. Coronary sinus adrenaline concentrations after enalapril and after placebo were not significantly different. The long term reduction of myocardial sympathetic activity on exercise may represent a significant benefit from angiotensin converting enzyme inhibition in heart failure and may reflect a reduced cardiac workload.

Endothelium-derived relaxing factor

This article reviews what is known of endothelium-derived relaxing factor and its possible physiologic and pathophysiologic roles. This relaxing factor is now thought to be nitric oxide or a ready source of it. It acts as an endogenous nitrovasodilator, stimulating soluble guanylate cyclase to increase cyclic guanosine monophosphate (GMP) levels in vascular smooth muscle and platelets, with consequent relaxant and anti-aggregatory effects (predominantly when stimulated through receptor-operated channels). Its actions are thus synergistic with those of cyclic adenosine monophosphate (AMP)-mediated stimulation (for example, adenosine, prostacyclin). Endothelium-derived relaxing factor is unstable and is thought to act only very locally in vivo. Its release is continuous in the basal state and is stimulated by a number of neuropeptides and by agents released during platelet activation and thrombosis--with large differences in activity among different vessels. Endothelium-derived relaxing factor activity is also flow related, thereby coordinating vasomotor behavior in an intact vascular tree in response to changes in flow. Endothelium-derived relaxing factor activity is reduced in several pathologic states, including atherosclerosis.

In vivo EDRF activity influences platelet function

The administration of carbachol to rabbits to stimulate the release of endothelium derived relaxing factor (EDRF) results in inhibition of platelet aggregation and elevation of platelet cyclic GMP content. These effects are reversed by simultaneous administration of the EDRF inhibitors methylene blue or haemoglobin. The data provide the first direct biochemical evidence of in vivo EDRF activity.

Endothelium-derived relaxing factor and nitroprusside compared in noradrenaline- and K+-contracted rabbit and rat aortae

1. The effects of endothelium-derived relaxing factor (EDRF) (as stimulated by acetylcholine in the presence of endothelium), sodium nitroprusside and 8-bromocyclic GMP on mechanical relaxation, calcium (45Ca) influx and cyclic GMP levels were studied in isolated rabbit aortic preparations pre-contracted either by noradrenaline or by high (120 mM) extracellular potassium. 2. The results confirmed a relatively greater effect of these three interventions on mechanical relaxation and on reducing calcium influx in noradrenaline-contracted than in potassium-contracted preparations. 3. The increase in cyclic GMP levels induced by sodium nitroprusside, contrary to previous reports, was no greater in noradrenaline-stimulated preparations than in potassium-stimulated preparations, a finding confirmed in rat aortic preparations, and relaxation was not associated with a significant reduction of calcium influx in the potassium-stimulated preparations. 4. Cyclic GMP-mediated relaxation of potassium contraction thus appears to be due to actions of cyclic GMP other than on calcium influx. 5. These findings suggest that cyclic GMP reduces calcium influx more through receptor-operated channels than through voltage-operated channels. 6. The endothelium-dependent acetylcholine-induced elevation of cyclic GMP was reduced both by noradrenaline and by high extracellular potassium, possibly by altering release or activity of EDRF. 7. The sensitivity of the soluble guanylate cyclase system to stimulation by EDRF and nitrovasodilators appears to be greater in rat than rabbit aortic preparations.

Evidence that inhibitory factor extracted from bovine retractor penis is nitrite, whose acid-activated derivative is stabilized nitric oxide

1. Unactivated extracts of bovine retractor penis (BRP) contains 3-7 microM nitrite. Acid-activation of these extracts at pH 2 for 10 min followed by neutralization generates the active form of inhibitory factor (IF; assayed by its vasodilator action on rabbit aorta), and is associated with partial loss of nitrite. 2. Increasing the time of acid-activation at pH 2 from 10 to 60 min with intermittent vortex mixing generates greater vasodilator activity and increases nitrite loss. 3. When acid-activated and neutralized extracts are incubated at 37 degrees C or 30 min or boiled for 5 min, vasodilator activity is lost and nitrite content increased. Reactivation of these samples at pH 2 for 10 min followed by neutralization leads to partial recoveries of vasodilator activity with loss in nitrite content. 4. Addition of sodium nitrite to BRP extracts increases acid-activatable vasodilator activity pro rata. 5. Acid-activation of aqueous sodium nitrite solutions results in less loss of nitrite and generation of less vasodilator activity than BRP extracts. Vasodilatation is only transient and is rapidly abolished on neutralization, whereas responses to acid-activated BRP extracts are more prolonged and activity is stable on ice. 6. Bovine aortic endothelial cells yield vasodilator activity that is indistinguishable from that isolated from BRP. It is activated by acid, stable on ice, abolished by boiling or by haemoglobin, and appears to be due to the generation of nitric oxide (NO) from nitrite. 7. The data provide confirmatory evidence that nitrite in BRP extracts is IF, that acid-activation of BRP extracts yields NO which is responsible for its vasodilator action, and that inactivation occurs by decay of NO to nitrite and nitrate. They further suggest that BRP extracts contain a NO-stabilizing agent which favours conversion of nitrite to NO. 8. The finding that bovine aortic endothelial cells yield an agent indistinguishable from IF suggests that nitrite in endothelial cells may likewise be the precursor of endothelium-derived relaxing factor (EDRF), itself identified as NO.

A randomized cross-over study of enalapril in congestive heart failure: haemodynamic and hormonal effects during rest and exercise

We performed a randomized double-blind placebo controlled cross-over study of enalapril in 16 patients with chronic congestive heart failure, to assess haemodynamic and hormonal effects at rest and on exercise. Acute effects were measured 4 h after enalapril 10 mg, and chronic effects after 6 weeks treatment with enalapril 10-20 mg per day. Exercise tolerance, assessed by the duration of a maximal bicycle ergometer test, was not altered by enalapril. Mean blood pressure was reduced after enalapril, at rest and on exercise, acutely by 7% and 8% respectively, and chronically by 14% and 16%. Systemic vascular resistance was reduced by 16% at rest both acutely (NS) and chronically (p less than 0.05). The resting pulmonary capillary wedge pressure was reduced by 28% with chronic treatment. In the acute study, total body oxygen consumption on exercise was 26% higher after enalapril. Chronically, resting oxygen consumption was reduced by 13% after enalapril, with mixed venous oxygen saturation increasing by 16%. In the acute study enalapril increased plasma renin activity at rest and on exercise by 181% and by 189%, and reduced aldosterone by 49% (NS) and 39% (p less than 0.05), and these effects were sustained after 6 weeks. Enalapril increased antidiuretic hormone concentrations at rest acutely by 73% (NS) and chronically by 34% (p less than 0.05) but not on exercise; the increase in the acute study correlated with plasma enalaprilat levels (r = 0.66, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-derived relaxing factor and atriopeptin II elevate cyclic GMP levels in pig aortic endothelial cells

1. Two directly-acting stimulants of soluble guanylate cyclase, glyceryl trinitrate (0.1 microM) and sodium azide (10 microM), and a receptor-mediated stimulant of particulate guanylate cyclase, atriopeptin II (10 nM), each elevated the cyclic GMP content of primary cultures of pig aortic endothelial cells without affecting the cyclic AMP content. 2. Two receptor-mediated stimulants of adenylate cyclase, glucagon (1 microM) and isoprenaline (10 microM), had no effect on the cyclic AMP or cyclic GMP content of these cells, but the directly acting stimulant, forskolin (30 microM), induced a small increase in cyclic AMP content. 3. Three agents that release endothelium-derived relaxing factor (EDRF); bradykinin (0.1 microM), ATP (10 microM) and ionophore A23187 (0.1 microM), each markedly elevated the cyclic GMP content of pig aortic endothelial cells, but acetylcholine (1 microM) had no effect. None of these agents had any effect on cyclic AMP content. 4. Two agents that potentiate the actions of EDRF; M & B 22948 (100 microM) and superoxide dismutase (30 units ml-1), each elevated the cyclic GMP content of pig aortic endothelial cells without affecting the cyclic AMP content. Pretreating cells with catalase (100 units ml-1) did not affect the rise in cyclic GMP content induced by superoxide dismutase (30 units ml-1). 5. Pretreatment of pig aortic endothelial cells with haemoglobin (10 microM) reduced the resting content of cyclic GMP and blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 microM), sodium azide (10 microM), bradykinin (0.1 microM), ATP (10 microM), ionophore A23187 (0.1 microM), M & B 22948 (100 microM) and superoxide dismutase (30 units ml-1), but not that induced by atriopeptin II (10 nM). 6. Pretreatment of pig aortic endothelial cells with an inhibitor of soluble guanylate cyclase, methylene blue (20 microM), had no effect on the resting content of cyclic GMP. Methylene blue (20 microM) blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 microM), M & B22948 (100 microM) and bradykinin (0.1 microM), but not that induced by atriopeptin II (10 nM). 7. The data show that soluble guanylate cyclase, particulate guanylate cyclase and adenylate cyclase are present in pig aortic endothelial cells. They further suggest that EDRF, produced spontaneously or in response to vasoactive agents, elevates endothelial cyclic GMP content by stimulating soluble guanylate cyclase. It is possible that this may serve as a feedback loop by which the endothelial cell modulates EDRF production.

A report and review of recurrent left atrial myxoma: not always such 'a benign tumor'

We report a patient whose left atrial myxoma recurred three times and review 28 other reports of recurrent myxoma. Inadequate resection and multifocal growth appear to be two separate causes for recurrence.