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Biomedical subjects

Allan D Struthers

Publications and source records attributed to Allan D Struthers.

At least 37 records · Page 2Linked to original sources
PubMed2004

Aldosterone-induced vasculopathy.

Aldosterone antagonists reduce mortality in chronic heart failure (CHF). An obvious question to ask is how do they do this. The prevailing hypothesis is that most of the adverse effects of aldosterone stem from its ability to produce a vasculopathy. This vasculopathy is characterised by a reduction in vascular nitric oxide and may be produced by aldosterone's ability to generate superoxide radicals which degrade endogenous NO. The consequences of this "aldosterone-induced vasculopathy" are that it produces tissue ischaemia/infarction and injury, which then repairs itself by producing fibrosis. "Aldosterone-induced vasculopathy" may be the main mechanism why aldosterone promotes widespread tissue injury and ultimately cardiac death.

Aldosterone↗
PubMed2004

Effects of exogenous and endogenous natriuretic peptides on forearm vascular function in chronic heart failure.

OBJECTIVE: Natriuretic peptides (NPs) reduce central venous pressure in patients with chronic heart failure (cHF) despite attenuation of arterial, renal, and humoral effects. This suggests a preserved venodilator response. This study had 4 aims: to compare the venodilator effects of human NPs in patients with cHF; to assess the contribution of basal ANP and BNP levels to regulation of forearm vascular volume (FVV); to test the hypothesis that venous ANP responsiveness is preserved in cHF; and to assess the involvement of endothelial nitric oxide-synthase (eNOS) in NP-induced vascular effects. METHODS AND RESULTS: Venous and arterial forearm vascular responses to incremental intra-arterial doses of ANP, Urodilatin, BNP, CNP, or the ANP receptor antagonist A71915 were studied in 53 patients and 11 controls. ANP receptor antagonism reduced FVV by 4.4%+/-1.2% (P<0.05). The forearm blood flow (FBF) response to ANP was significantly blunted in patients versus controls (P<0.01), whereas FVV increased similarly in both groups (maximum 14.7% and 13.4%, both P<0.001). The eNOS blockade reduced ANP-induced FBF changes in controls but not in patients (P<0.05), whereas similar reductions in FVV changes were seen in groups (both P<0.001). CONCLUSIONS: In cHF venous, but not arterial, ANP responsiveness is preserved. Arterial endothelial dysfunction may contribute to NP resistance.

Adult↗
PubMed2004

Review of aldosterone- and angiotensin II-induced target organ damage and prevention.

Aldosterone is well recognized as a cause of sodium reabsorption, water retention, and potassium and magnesium loss; however, it also produces a variety of other actions that lead to progressive target organ damage in the heart, vasculature, and kidneys. Aldosterone interacts with mineralocorticoid receptors to promote endothelial dysfunction, facilitate thrombosis, reduce vascular compliance, impair baroreceptor function, and cause myocardial and vascular fibrosis. Although angiotensin II has been considered the major mediator of cardiovascular damage, increasing evidence suggests that aldosterone may mediate and exacerbate the damaging effects of angiotensin II. While angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers reduce plasma aldosterone levels initially, aldosterone rebound, or 'escape' may occur during long-term therapy. Therefore, aldosterone blockade is required to reduce the risk of progressive target organ damage in patients with hypertension and heart failure. This may be achieved nonselectively with spironolactone or with use of the selective aldosterone blocker eplerenone. While both agents have been demonstrated to be effective antihypertensive agents, eplerenone may produce improved target organ protection as witnessed in a variety of clinical settings, without the antiandrogenic and progestational effects commonly observed with spironolactone.

Aldosterone↗
PubMed2004

What is the optimal serum potassium level in cardiovascular patients?

Humans are prone to sodium overload and potassium depletion. This electrolyte imbalance is important in the pathogenesis of cardiovascular disease and sudden cardiac death. Avoiding hypokalemia is beneficial in several cardiovascular disease states including acute myocardial infarction, heart failure, and hypertension. The evidence highlighting the importance of potassium homeostasis in cardiovascular disease and possible mechanisms explaining potassium's benefits are reviewed. Targets for serum potassium concentration are suggested.

Cardiovascular Diseases↗
PubMed2004

Aldosterone in heart failure: pathophysiology and treatment.

Aldosterone produces adverse effects on the vasculature (endothelial dysfunction) and on the myocardium (myocardial fibrosis). These effects have adverse clinical consequences that result in increases in deaths caused by sudden death and by progressive heart failure. The Randomized Aldactone Evaluation Study and the Eplerenone Post-acute Myocardial Infarction Heart Failure Efficacy and Survival Study show this clearly. Aldosterone blockade should become a regular third neuroendocrine-blocking drug in patients with chronic heart failure.

Aldosterone↗
PubMed2004

The clinical implications of aldosterone escape in congestive heart failure.

Angiotensin converting enzyme (ACE) inhibitor therapy does not reliably suppress aldosterone production, and 'aldosterone escape' occurs in up to 40% of patients with congestive heart failure (CHF). Aldosterone levels correlate with the risk of cardiovascular events. Aldosterone adversely affects the risk of cardiovascular events via mineralocorticoid receptors in the heart, blood vessels and other sites. Notably, aldosterone contributes to endothelial dysfunction and attenuates endothelium-dependent vasodilatation, at least partly by reducing nitric oxide bioavailability. Aldosterone also promotes myocardial fibrosis and cardiac remodelling by enhancing collagen synthesis, resulting in increased myocardial stiffness and increased left ventricular mass. These mechanisms mediated by aldosterone contribute to increased risk of ventricular arrhythmias and sudden cardiac death. Two major prospective trials, including one in which patients routinely received ACE inhibitor and beta blocker therapy, have shown that the use of an aldosterone blocker significantly reduces all-cause mortality, sudden cardiovascular death and hospitalisation in patients with acute or chronic left ventricular dysfunction or CHF. Inhibition of aldosterone's effect on mineralocorticoid receptors should now be considered standard therapy in these patient populations.

Aldosterone↗
PubMed2004

How much echo left ventricular hypertrophy would be missed in diabetics by applying the Losartan Intervention For Endpoint Reduction electrocardiogram criteria to select patients for angiotensin receptor blockade?

OBJECTIVE: The Losartan Intervention For Endpoint Reduction (LIFE) study demonstrated a clear mortality benefit in treating hypertensive patients with electrocardiogram (ECG) evidence of left ventricular hypertrophy (LVH) with losartan rather than atenolol. Previous studies have also shown that identifying and treating echo LVH is associated with prognostic benefits in hypertensive subjects, and is independent of the presence of ECG LVH. We sought to determine how many cases of echo LVH would be missed by applying the ECG criteria for LVH used in the LIFE study. DESIGN: A prospective study of 219 patients with type 2 diabetes recruited from the hospital diabetic clinic. METHODS: Fifteen ECG criteria were assessed on each subject and compared with the presence or absence of LVH on echocardiography. RESULTS: All the proposed ECG criteria are poor at identifying echo LVH in people with diabetes. CONCLUSION: Using ECG LVH to select patients for angiotensin receptor blockade would lead to many diabetics with echo LVH missing out on the benefits of treatment. This assumes that the benefits seen in the LIFE study would also occur if the LIFE strategy were extended to echo LVH patients as well as to ECG LVH patients.

Aged↗
PubMed2004

Furosemide responsiveness, non-adherence and resistance during the chronic treatment of heart failure: a longitudinal study.

BACKGROUND AND METHODS: Loop diuretic therapy is an essential part of chronic systolic heart failure (CH)F management, yet response to treatment can be variable. We analysed diuretic responsiveness in 39 stable patients with CHF in the community over 2 years. We measured serum ACE as a marker of adherence to ACE inhibitor therapy and urinary furosemide as a marker of diuretic adherence and action. Patients' clinical outcome was stable and not hospitalized (Group 0); alive but hospitalized (Group 1); or dead during follow up (Group 2). RESULTS: Prescribed furosemide dose was variable (range 20-370 mg generally once daily) and progressive dose increments were common. Failed furosemide adherence (defined as < 10% of a dose excreted in 24 h urine where normal average excretion = 50% of an oral dose) during static prescribed dosing was infrequent relative to all days of therapy; yet was equally common across all outcome groups. Furosemide non-adherence appeared to be independent of non-adherence with ACE inhibitor (as marked by serum ACE activity > 20 U l(-1)) treatment. Furosemide responsiveness (mm of sodium excreted per mg furosemide in urine) showed no relationship to prescribed dose and paradoxically tended to rise in patients with higher basal aldosterone concentrations. Furosemide responsiveness fell by outcome class despite increased dose. Within-patient responsiveness remained relatively constant although highly variable between individuals. CONCLUSIONS: Furosemide responsiveness varied greatly between individuals but was constant within an individual. Non-adherence with furosemide was less common among those who died and appeared to occur at different time points from non-adherence with ACE inhibitor treatment, which was slightly more common in all outcome groups. Patients who died were prescribed higher furosemide doses and had greater furosemide excretion yet had similar sodium excretion. The main factor in response to chronic furosemide therapy was intrarenal diuretic resistance. Gross non-adherence was less important.

Administration, Oral↗
PubMed2004

Tolerability of spironolactone in patients with chronic heart failure -- a cautionary message.

AIM: To assess how well heart failure patients tolerate spironolactone in routine clinical practice. DESIGN: Retrospective analysis of 226 patients attending a specialist heart failure clinic. RESULTS: One hundred and thirty of 226 (57.5%) patients tried spironolactone at least once. Forty-four of 130 (33.8%) discontinued spironolactone due to side-effects after a mean of 11.1 months; 59/141 (41.8%) trials of spironolactone resulted in at least one side-effect; therapy was stopped in 30/141 (21.3%) trials due to raised potassium or creatinine. Significant risk factors for raised potassium/creatinine were age and baseline potassium level. CONCLUSIONS: Potentially serious side-effects are common despite appropriate use of spironolactone.

Age Factors↗
PubMed2004

The role of aldosterone in heart failure and the clinical benefits of aldosterone blockade.

Aldosterone has a variety of detrimental effects on the heart and vasculature and is increasingly recognized as an important target in chronic heart failure, as illustrated by the Randomized Aldactone Evaluation Study. In this article, the evidence supporting the cardiovascular effects of aldosterone in humans and the proven benefits of aldosterone-receptor antagonists in heart failure shall be discussed.

Aldosterone↗
PubMed2004

Tonic levels of angiotensin II reduce tonic levels of vascular nitric oxide even in salt-replete man.

INTRODUCTION: Losartan improves stimulated endothelial function in patients with cardiovascular disease, but there are no data to establish whether losartan has this effect in normal man. Furthermore, whether losartan improves basal nitric oxide (NO) activity is controversial. We therefore examined whether treatment with losartan improved basal NO activity in normal, salt-replete man. If so, this would imply that tonic levels of angiotensin II (Ang II) reduce tonic basal levels of NO, even in salt-replete normal man. METHODS: We performed a randomised, placebo-controlled, double-blind crossover study in 24 healthy volunteers, comparing losartan 50 mg daily for one month versus placebo. Brachial artery endothelial function was assessed by bilateral venous occlusion plethysmography, measuring the response to intra-arterial infusions of the endothelial-dependent and endothelial-independent vasodilators, acetylcholine and sodium nitroprusside respectively and the endothelial-dependent vasoconstrictor NG-monomethyl-L-arginine. Results were analysed by multiple analysis of variance and statistical significance was taken as a p value of <or= 0.05. RESULTS: Losartan significantly increased the vasoconstriction in response to NG-monomethyl-L-arginine (-37+2% vs. -32+2%, losartan vs. placebo; p=0.05). Losartan improved the vasodilatation response to acetylcholine; however, this result did not reach significance (214+20% vs. 174+20%, losartan vs. placebo; p=0.15). Losartan did not affect the response to nitroprusside (172+15% vs. 176+16%, losartan vs. placebo; p=0.84). There was no significant difference in blood pressure between the two study days. CONCLUSIONS: Losartan improves basal NO bioactivity in healthy salt-replete volunteers. Even in salt-replete man, basal Ang II levels exert a tonic effect, which reduces basal NO.

Acetylcholine↗
PubMed2004

Aldosterone blockade in heart failure.

Aldosterone plays a key role in the pathophysiology of heart failure. Angiotensin converting enzyme inhibitors and angiotensin II receptor blockers may not suppress aldosterone production in the long term. This allows aldosterone to exert its effects on myocardial fibrosis and cardiac remodelling, endothelial function, electrolytes and baroreceptor response. The Randomized Aldactone Evaluation Study (RALES) tested spironolactone against placebo in patients with severe heart failure. The study found a 30% reduction in the risk of death among patients treated with spironolactone and a 31% reduction in the risk of death from cardiac causes. Patients in the spironolactone group had significantly lower risks of death from progression of heart failure and sudden cardiac death. The Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study (EPHESUS) investigated the effects of eplerenone against placebo in patients with myocardial infarction complicated by left ventricular dysfunction. Compared to placebo, the relative risk of death from any cause was 0.85 in eplerenone-treated patients, and the relative risk of death or hospitalisation for cardiovascular events was 0.87. The reduction in the risk of sudden death from cardiac causes was statistically significant. In conclusion, aldosterone blockade should form part of optimal therapy for patients with heart failure.

Cardiac Output, Low↗
PubMed2004

Statin therapy increases vascular sensitivity to angiotensin II in hypercholesterolaemic patients.

UNLABELLED: Cross-talk between various cardiovascular risk factors has been suggested by a number of studies. This study examines the interaction between hypercholesterolaemia and the renin-angiotensin system in vivo in man. METHODS: We performed a randomised, placebo-controlled, double-blind crossover study on 40 hypercholesterolaemic patients, comparing cholesterol-lowering therapy with a statin for six months versus placebo. Brachial artery function was assessed by bilateral venous occlusion plethysmography using intra-arterial infusions of the endothelial-dependent vasoconstrictors, angiotensin I (Ang I) and angiotensin II (Ang II), to measure vascular angiotensin-converting enzyme (ACE) and Ang II receptor response respectively. The endothelial-independent vasoconstrictor, noradrenaline, was used as a control vasoconstrictor. Results were analysed by multiple analysis of variance and statistical significance was taken as a p value <0.05. RESULTS: Cholesterol-lowering treatment with a statin significantly reduced the mean total cholesterol level to 5.71 mmol/L vs. 7.57 mmol/L on placebo (p<0.0001). Hypercholesterolaemia significantly increased the vasoconstriction response to noradrenaline (placebo versus statin treatment; p=0.046). In hypercholesterolaemia, there was a strong trend towards a reduction in the vasoconstriction response to Ang I (placebo versus statin treatment; p=0.089). In hypercholesterolaemia, the vasoconstriction response to Ang II was significantly reduced (placebo versus statin treatment; p=0.01). CONCLUSIONS: Our in vivo results show that, unlike some other previous work, hypercholesterolaemia is associated with down-regulation of the vasoconstrictor response to Ang II and that statin therapy up-regulates the local vasoconstrictor response to Ang II. The possibility now arises that, in man, statins alter the balance between AT(1)-receptors and AT(2)-receptors.

Angiotensin I↗
PubMed2003

Atrial natriuretic peptide regulates regional vascular volume and venous tone in humans.

OBJECTIVE: To date, the contribution of basal atrial natriuretic peptide (ANP) levels to resting vascular function in humans is unknown. In the present study we sought to investigate the role of ANP in regulating regional vascular volume and venous tone in healthy subjects. METHODS AND RESULTS: We used radionuclide plethysmography to examine the effects of ANP and the ANP-receptor antagonist A71915 on forearm vascular volume. Creating pressure/volume relations, we determined changes in vascular volume, compliance, and tone. Performing dose-ranging studies, we additionally assessed the potency and specificity of A71915 in the forearm resistance vasculature. Equilibrium blood pool scintigraphy was then used to assess the effects of systemic administration of A71915 on regional intestinal vascular volume. Infusion of ANP increased forearm vascular volume in a dose-dependent manner (maximum 20%; P<0.001), exerting a maximum venodilating effect at plasma levels similar to that seen in heart failure. A71915 increased venous tone, thereby decreasing vascular volume by 9.6+/-1.1%, P<0.001 (forearm), and 2.6+/-0.5%, P=0.01 (intestinal beds). At an infusion ratio of 50:1, A71915 almost completely abolished the effects of ANP on forearm blood flow. CONCLUSIONS: ANP locally regulates regional vascular volume and tone without affecting compliance.

Adult↗
PubMed2003

Myocardial production of C-type natriuretic peptide in chronic heart failure.

BACKGROUND: C-type natriuretic peptide (CNP) is a vasodilator produced by the vascular endothelium. It shares structural and physiological properties with the cardiac hormones atrial natriuretic peptide and brain natriuretic peptide (BNP), but little is known about its pathophysiological role in chronic heart failure (CHF). We assessed the hypothesis that CNP is produced by the heart in patients with CHF. METHODS AND RESULTS: Myocardial CNP production was determined (difference in plasma levels between the aortic root and coronary sinus [CS]) in 9 patients undergoing right and left heart catheterization as part of their CHF assessment (all male, age 59+/-9 years; New York Heart Association class 2.2+/-0.1; left ventricular ejection fraction 29+/-5%; creatinine 105+/-8 micro mol/L [all values mean+/-SEM]). BNP, established as originating from myocardium, was assessed from the same samples as a positive control. Analyses were performed by a blinded operator using a standard competitive radioimmunoassay kit (Peninsula Laboratories, Bachem Ltd UK). A step-up (29%) in plasma CNP concentration was found from the aorta to the CS (3.55+/-1.53 versus 4.59+/-1.54 pg/mL, respectively; P=0.035). The mean increase in CNP was 0.90+/-0.35 pg/mL (range 0.05 to 2.80 pg/mL). BNP levels increased by 57% from aorta to CS (86.0+/-20.5 versus 135.0+/-42.2 pg/mL; P=0.01). CS CNP levels correlated with mean pulmonary capillary wedge pressure (r=0.82, P=0.007). CONCLUSIONS: We have shown that CNP is produced by the heart in patients with CHF. Although further evaluation is required to define its full pathophysiological role in this condition, CNP may represent an important new local mediator in the heart.

Aged↗
PubMed2003

Exercise training as a therapy for chronic heart failure: can older people benefit?

Despite recent advances in pharmacological therapy, chronic heart failure remains a major cause of morbidity and mortality in older people. Studies of exercise training in younger, carefully selected patients with heart failure have shown improvements in symptoms and exercise capacity and in many pathophysiological aspects of heart failure, including skeletal myopathy, ergoreceptor function, heart rate variability, endothelial function, and cytokine expression. Data on mortality and hospitalization are lacking, and effects on everyday activity, depression, and quality of life are unclear. Exercise therapy for patients with heart failure appears to be safe and has the potential to improve function and quality of life in older people with heart failure. To realize these potential benefits, exercise programs that are suitable for older, frail people need to be established and tested in an older, frail, unselected population with comorbidities.

Aged↗