Andrew H. Henderson

Endothelium‐derived relaxing factor inhibits in vitro platelet aggregation

1 We studied the effects of endothelium‐derived relaxing factor (EDRF), bovine retractor penis muscle inhibitory factor and sodium nitroprusside, three stimulants of guanylate cyclase, on the in vitro aggregation of washed human platelets. 2 Platelet aggregation induced either by collagen or by the thromboxane A2 analogue U46619 was inhibited by all three agents. 3 The anti‐aggregatory effect of each agent was inhibited by haemoglobin. 4 The anti‐aggregatory effect of EDRF was potentiated by superoxide dismutase. 5 These findings are discussed in relation to a potential role for EDRF in haemostasis.

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.

St Cyres lecture. Endothelium in control.

Clinical science has evolved since the days of Sir Thomas Lewis, who gave the St Cyres lecture in 1931 and whose eponymous chair I occupy. It involves still the penetration of astute clinical observation, but has come increasingly to embrace the elucidation of underlying mechanisms in the more controlled conditions of the laboratory. Its compass is being stretched by the reductionism of molecular and cell biology, but these exciting developments do not exonerate us from the ever daunting task of seeking to understand the coordinated behaviour of the whole. Perhaps biomathematics will give new impetus to our efforts to discern form in the noise. Never was there greater need for cross-talk between the different scientific disciplines and between scientists and clinicians. The greatest growth area in cardiovascular science over recent years must surely be in the role of endothelium. Not only is there a lot of it-equivalent in mass to five normal hearts and in area to half a dozen tennis courts per standard 70 kg man-but it is coming to be recognised as a cardiovascular endocrine organ in its own right, occupying a critically strategic interface between blood and body, and subserving a multitude of regulatory roles. These range from acting as a selective permeability barrier, through vasomotor control, proand antithrombotic mechanisms and regulation of vascular growth, to metabolic and immunological activity. We here consider just one-namely the production of endothelium derived relaxing factor (EDRF), a powerful vasodilator substance released from the endothelium of all blood vessels of all species studied.

Rehabilitation after myocardial infarction trial (RAMIT): multi-centre randomised controlled trial of comprehensive cardiac rehabilitation in patients following acute myocardial infarction

Background It is widely believed that cardiac rehabilitation following acute myocardial infarction (MI) reduces mortality by approximately 20%. This belief is based on systematic reviews and meta-analyses of mostly small trials undertaken many years ago. Clinical management has been transformed in the past 30–40 years and the findings of historical trials may have little relevance now. Objectives The principal objective was to determine the effect of cardiac rehabilitation, as currently provided, on mortality, morbidity and health-related quality of life in patients following MI. The secondary objectives included seeking programmes that may be more effective and characteristics of patients who may benefit more. Design, setting, patients, outcome measures A multi-centre randomised controlled trial in representative hospitals in England and Wales compared 1813 patients referred to comprehensive cardiac rehabilitation programmes or discharged to ‘usual care’ (without referral to rehabilitation). The primary outcome measure was all-cause mortality at 2 years. The secondary measures were morbidity, health service use, health-related quality of life, psychological general well-being and lifestyle cardiovascular risk factors at 1 year. Patient entry ran from 1997 to 2000, follow-up of secondary outcomes to 2001 and of vital status to 2006. A parallel study compared 331 patients in matched ‘elective’ rehabilitation and ‘elective’ usual care (without rehabilitation) hospitals. Results There were no significant differences between patients referred to rehabilitation and controls in mortality at 2 years (RR 0.98, 95% CI 0.74 to 1.30) or after 7–9 years (0.99, 95% CI 0.85 to 1.15), cardiac events, seven of eight domains of the health-related quality of life scale (‘Short Form 36’, SF36) or the psychological general well-being scale. Rehabilitation patients reported slightly less physical activity. No differences between groups were reported in perceived overall quality of cardiac aftercare. Data from the ‘elective’ hospitals comparison concurred with these findings. Conclusion In this trial, comprehensive rehabilitation following MI had no important effect on mortality, cardiac or psychological morbidity, risk factors, health-related quality of life or activity. This finding is consistent with systematic reviews of all trials reported since 1983. The value of cardiac rehabilitation as practised in the UK is open to question.

Endothelium and inelastic arteries: an early marker of vascular dysfunction in non-insulin dependent diabetes.

Atheroma is the main cause of mortality and morbidity in patients with non-insulin dependent diabetes mellitus. Endothelial dysfunction underlies atheroma formation. Flow mediated vasodilatation is a measure of endothelial function as well as a determinant of arterial distensibility,1 measurements of which have not previously been reported in patients with non-insulin dependent diabetes. We studied 12 symptom free, non-smoking, healthy patients (six men) with well controlled non-insulin dependent diabetes diabnosed 1-7 (mean 3.8) years previously (mean age 50 (SD 9) years, body mass index 26.9 (4.8) kg/m2, serum cholesterol concentration 5.8 (0.5) mmol/l). Patients with known causes of endothelial dysfunction were excluded. All patients had insulin resistance with basal hyperinsulinaemia,2 no biochemical evidence of renal impairment, and no microalbuminuria. A group of 12 normal non-smoking subjects was matched for sex, age, body mass index, blood …

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 μm) and sodium azide (10 μm), 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 μm) and isoprenaline (10 μm), had no effect on the cyclic AMP or cyclic GMP content of these cells, but the directly acting stimulant, forskolin (30 μm), induced a small increase in cyclic AMP content. 3 Three agents that release endothelium‐derived relaxing factor (EDRF); bradykinin (0.1 μm), ATP (10 μm) and ionophore A23187 (0.1 μm), each markedly elevated the cyclic GMP content of pig aortic endothelial cells, but acetylcholine (1 μm) 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 μm) 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 μm) reduced the resting content of cyclic GMP and blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 μm), sodium azide (10 μm), bradykinin (0.1 μm) ATP (10 μm), ionophore A23187 (0.1 μm), M & B 22948 (100 μm) 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 μm), had no effect on the resting content of cyclic GMP. Methylene blue (20 μm) blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 μm), M & B 22948 (100 μm) and bradykinin (0.1 μm), 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.

Evidence that cyclic guanosine monophosphate (cGMP) mediates endothelium-dependent relaxation.

The mechanism of action of endothelium-derived relaxant factor (EDRF) was studied using aortic strip preparations of the rabbit and a bioassay system of a rabbit coronary artery perfused in series with an intact aorta. Methylene blue (an inhibitor of guanylate cyclase) inhibited, and 2-O-propoxyphenyl-8-azapurine-6-one (MB22948, an inhibitor of cGMP phosphodiesterase) potentiated the vascular effects of EDRF whether these were due to its basal or to stimulated release. Infusion of these agents at different sites in the bioassay indicated that they act pharmacologically at the smooth muscle level and not on release of EDRF or by chemical interaction with EDRF. The data are consistent with the hypothesis that EDRF-induced relaxation is mediated by elevation of smooth muscle cGMP levels.

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.

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.

Endothelium-derived relaxing factor.

Abstract 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 guanvlate 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, prostacyelin). Endothelium-derived relaxing factor is unstable and is thought lo 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.