Absence of vascular tolerance in conductance vessels after 48 hours of intravenous nitroglycerin in patients with coronary artery disease

Radial artery diameter: a comprehensive systematic review of anatomy

AIMS

The objective of this systematic review is to determine with the highest accuracy the average radial artery (RA) diameter overall and in certain subgroups. The aim of this study is to provide assistance in the development of fitting transradial devices, an increasingly popular intervention.

METHODS

Several databases were used to extract appropriate studies highlighting RA diameter. Databases used in the generation of this study were Ovid EBM Reviews, Ovid Embase, Ovid Medline, Scopus and Web of Science Core Collection. RA diameter was determined overall, in males versus females, adults only, adults+children, in the presence of comorbidities, and finally RA diameter in the context of various vasodilators.

RESULTS

A total of 71 studies were included. The average RA diameter overall was determined to be 2.62±0.15 mm in children+adults and 2.70±0.15 mm in adults only. In comparison to an RA diameter of 2.68±0.24 mm in adult males, the diameter was found to be 2.27±0.27 mm in adult females (p=0.028). As for comorbidities, the mean RA diameter in adult patients with hypertension and congestive heart failure was 2.72±0.37 mm and 2.80±0.25 mm, respectively. Finally, the mean RA diameter with nitrate and angiotensin-converting enzyme (ACE) inhibitor use was 2.97±0.53 mm and 2.82±0.29 mm respectively. For comparison, the average outer diameter of a 5 French introducer sheath is 2.29 mm and a 6 French introducer sheath is 2.62 mm.

CONCLUSIONS

The findings presented in this study will help determine the most appropriate transradial device to use in several different populations in the context of vasodilator usage or the absence thereof.

Paradoxical normoxia-dependent selective actions of inorganic nitrite in human muscular conduit arteries and related selective actions on central blood pressures

BACKGROUND

Inorganic nitrite dilates small resistance arterioles via hypoxia-facilitated reduction to vasodilating nitric oxide. The effects of nitrite in human conduit arteries have not been investigated. In contrast to nitrite, organic nitrates are established selective dilators of conduit arteries.

METHODS AND RESULTS

We examined the effects of local and systemic administration of sodium nitrite on the radial artery (a muscular conduit artery), forearm resistance vessels (forearm blood flow), and systemic hemodynamics in healthy male volunteers (n=43). Intrabrachial sodium nitrite (8.7 μmol/min) increased radial artery diameter by a median of 28.0% (25th and 75th percentiles, 25.7% and 40.1%; P<0.001). Nitrite (0.087-87 μmol/min) displayed conduit artery selectivity similar to that of glyceryl trinitrate (0.013-4.4 nmol/min) over resistance arterioles. Nitrite dose-dependently increased local cGMP production at the dose of 2.6 μmol/min by 1.1 pmol·min(-1)·100 mL(-1) tissue (95% confidence interval, 0.5-1.8). Nitrite-induced radial artery dilation was enhanced by administration of acetazolamide (oral or intra-arterial) and oral raloxifene (P=0.0248, P<0.0001, and P=0.0006, respectively) but was inhibited under hypoxia (P<0.0001) and hyperoxia (P=0.0006) compared with normoxia. Systemic intravenous administration of sodium nitrite (8.7 μmol/min) dilated the radial artery by 10.7% (95% confidence interval, 6.8-14.7) and reduced central systolic blood pressure by 11.6 mm Hg (95% confidence interval, 2.4-20.7), augmentation index, and pulse wave velocity without changing peripheral blood pressure.

CONCLUSIONS

Nitrite selectively dilates conduit arteries at supraphysiological and near-physiological concentrations via a normoxia-dependent mechanism that is associated with cGMP production and is enhanced by acetazolamide and raloxifene. The selective central blood pressure-lowering effects of nitrite have therapeutic potential to reduce cardiovascular events.

Nitroglycerin headache and nitroglycerin-induced primary headaches from 1846 and onwards: a historical overview and an update

Nitroglycerin (NTG) (glyceryl trinitrate) was synthesized by the Italian chemist Ascanio Sobrero in Paris in 1846. A very unstable explosive, Alfred Nobel while working on explosives, combined it with Kiselguhr and patented it as dynamite in 1867. NTG was introduced in 1879 in medicine in the treatment of angina pectoris by the English doctor William Murrell. NTG-induced headache was quickly recognized as an important adverse event both in the industrial use of NTG, where it was used to produce dynamite, as well as in the use of NTG as drug. This review traces the evolution of our understanding of NTG headache.

Nitric oxide-induced headache may arise from extracerebral arteries as judged from tolerance to isosorbide-5-mononitrate

Long-term exposure to organic nitrates influences different sections of the vascular bed heterogeneously. Continuous dosage of nitrates leads to the development of tolerance both to the vascular effects and to the unwanted adverse effect, headache. Human data on the development of tolerance in different cranial arteries over more than 24 h are lacking. We compared the vascular changes of the middle cerebral, superficial temporal and radial arteries during oral administration of isosorbide-5-mononitrate (5-ISMN) 30 mg three times daily for 7 days in 11 healthy subjects in a double-blind, randomised, placebo controlled cross-over design. Blood velocity in the middle cerebral artery was measured with transcranial Doppler and the diameters of the temporal and radial arteries were measured with high frequency ultrasound. Headache recordings were compared to the observed vascular changes over time. Tolerance was complete within 24 h in the middle cerebral artery whilst in the superficial temporal and the radial arteries, tolerance was only partial and developed much more slowly, i.e. after 7 days correlating with the disappearance of NO-induced headache. The present study thus demonstrated the important differences in the time profiles of appearance of nitrate tolerance in arteries of different vascular beds in man. If vasodilatation is the cause of NO-induced headache the results point to extracerebral arteries as the locus of nociception. Due to a variety of other possible pain-inducing effects of nitric oxide our results do not exclude cerebral arteries.

Nitrite anion: the key intermediate in alkyl nitrates degradative mechanism

Alkyl nitrates are metabolized in vitro to yield nitric oxide, and thiol groups have long been considered necessary cofactors. Here, we report evidence that no reaction between thiols and alkyl nitrates takes place in vitro, but stronger reducing agents, such as iron(II) derivatives, are necessary; alkoxy radicals and nitrite anions are the reaction intermediates. The latter, in slightly acidic conditions, can nitrosate thiols to the corresponding S-nitrosothiols, the real NO releasers.

Implications of chronic heart failure on peripheral vasculature and skeletal muscle before and after exercise training

The pathophysiology of chronic heart failure (CHF) is typically conceptualized in terms of cardiac dysfunction. However, alterations in peripheral blood flow and intrinsic skeletal muscle properties are also now recognized as mechanisms for exercise intolerance that can be modified by therapeutic exercise. This overview focuses on blood delivery, oxygen extraction and utilization that result from heart failure. Related features of inflammation, changes in skeletal muscle signaling pathways, and vulnerability to skeletal muscle atrophy are discussed. Specific focus is given to the ways in which perfusion and skeletal muscle properties affect exercise intolerance and how peripheral improvements following exercise training increase aerobic capacity. We also identify gaps in the literature that may constitute priorities for further investigation.

Explaining the phenomenon of nitrate tolerance

During the last century, nitroglycerin has been the most commonly used antiischemic and antianginal agent. Unfortunately, after continuous application, its therapeutic efficacy rapidly vanishes. Neurohormonal activation of vasoconstrictor signals and intravascular volume expansion constitute early counter-regulatory responses (pseudotolerance), whereas long-term treatment induces intrinsic vascular changes, eg, a loss of nitrovasodilator-responsiveness (vascular tolerance). This is caused by increased vascular superoxide production and a supersensitivity to vasoconstrictors secondary to a tonic activation of protein kinase C. NADPH oxidase(s) and uncoupled endothelial nitric oxide synthase have been proposed as superoxide sources. Superoxide and vascular NO rapidly form peroxynitrite, which aggravates tolerance by promoting NO synthase uncoupling and inhibition of soluble guanylyl cyclase and prostacyclin synthase. This oxidative stress concept may explain why radical scavengers and substances, which reduce oxidative stress indirectly, are able to relieve tolerance and endothelial dysfunction. Recent work has defined a new tolerance mechanism, ie, an inhibition of mitochondrial aldehyde dehydrogenase, the enzyme that accomplishes bioactivation of nitroglycerin, and has identified mitochondria as an additional source of reactive oxygen species. Nitroglycerin-induced reactive oxygen species inhibit the bioactivation of nitroglycerin by thiol oxidation of aldehyde dehydrogenase. Both mechanisms, increased oxidative stress and impaired bioactivation of nitroglycerin, can be joined to provide a new concept for nitroglycerin tolerance and cross-tolerance. The consequences of these processes for the nitroglycerin downstream targets soluble guanylyl cyclase, cGMP-dependent protein kinase, cGMP-degrading phosphodiesterases, and toxic side effects contributing to endothelial dysfunction, such as inhibition of prostacyclin synthase, are discussed in this review.

Continuous Therapy with Nitroglycerin Impairs Endothelium-Dependent Vasodilation but Does Not Cause Tolerance in Conductance Arteries

We investigated in healthy humans whether continuous therapy with organic nitrates impairs conduit artery responses to nitroglycerin (GTN) as well as its effects on endothelium-dependent vasodilation. Sixteen young male volunteers were randomized to continuous treatment with either transdermal GTN (0.6 mg/h/24 hrs for 6 days) or no therapy. Endothelium-dependent (flow-mediated) dilatation (FMD) and endothelium-independent (GTN-mediated) dilatation (GMD) of the brachial artery were evaluated before randomization (session 1), after six days of transdermal GTN treatment (session 2), and three hours after withdrawal of transdermal GTN (session 3). In the GTN group, on session 1, 0.4 mg sublingual GTN increased resting brachial artery diameter from 0.40 +/- 0.03 to 0.45 +/- 0.03 cm (P < 0.01). At the time of session 2, this GTN-mediated vasodilation remained unchanged at baseline (0.47 +/- 0.04 cm), with no further significant dilatation in response to either stimulus. On session 3, three hours after patch removal, baseline brachial artery diameter and GMD returned to pretreatment values, but FMD remained blunted (session 1: 8.7 +/- 2.5; session 3: 4.1 +/- 1.7%, P < 0.05). There was no change in these variables in the control group. Our data demonstrate that continuous GTN therapy impairs endothelium-dependent vasodilation in conduit arteries yet does not induce nitrate tolerance.

Endothelial modulation and tolerance development in the vasorelaxant responses to nitrate of rabbit aorta

We investigated the endothelial modulations in nitrate tolerance in isolated rabbit aorta. Nitrate tolerance was induced by a 72-h treatment with transdermal nitroglycerin (NTG, 0.4 mg/h) in conscious rabbits, which was verified by a 20-fold increase in the EC50 values [NTG tolerance (6.1 +/- 0.8) x 10(-7) M vs control (3.0 +/- 0.6) x 10(-8) M]. The relaxations to NTG in tolerant and nontolerant aortic strips were enhanced when their endothelia were denuded [E(-)]. In the presence of endothelium [E(+)], NTG-tolerant vessels were not tolerant to acetylcholine (ACh), which can release endothelial nitric oxide (NO), exogenous NO or 8-bromo (Br)-cGMP. In NTG-tolerant and nontolerant vessels with endothelium, concentration-response curves for NO were the same as those in endothelium-absent tolerant vessels. In both NTG-tolerant and nontolerant vessels, treatment with superoxide dismutase (SOD, 20 units/ml), an O2-. scavenger, unaffected the responses to NTG reduced in the presence of endothelium, but treatment with NG-nitro-L-arginine methyl ester (L-NAME, 10(-4) M), an NO synthase (NOS) inhibitor, reversed these reductions. Thus, our data did not indicate that an increased endothelial superoxide O2-. production contributes to nitrate tolerance. Our study suggested that (i) an impaired biotransformation process from NTG to NO is responsible for the occurrence of nitrate tolerance and (ii) vascular response to NTG enhanced by endothelial removal is related to blocked endothelial NO release.

Attenuation of nitrate tolerance and oxidative stress by an angiotensin II receptor blocker in patients with coronary spastic angina

BACKGROUND

Nitrates are widely used to treat coronary artery disease, but their therapeutic value is compromised by the rapid development of tolerance. Recently, the renin-angiotensin system has been suggested to play an important role in the development of nitrate tolerance.

METHODS AND RESULTS

Sixty-four patients with coronary spastic angina were investigated to clarify the effect of angiotensin II type 1 receptor blocker (ARB) therapy on nitrate tolerance. Transdermal nitroglycerin (10 mg/d) and an ARB (candesartan, 8 mg/d) were administered to 21 patients (GTN+ARB group) for 3 days, whereas transdermal nitroglycerin and placebo were administered to 19 patients (GTN group). Another 18 patients were treated with placebo skin patches and placebo tablets for 3 days (control group). The brachial artery response to incremental doses of intravenous nitroglycerin (0.01, 0.1, and 1.0 micro;g/kg) was measured by ultrasound before and after transdermal nitroglycerin therapy. Before treatment, the arterial diameter was increased by nitroglycerin injection in each group. After treatment, the increase of arterial diameter was significantly suppressed in the GTN group but not in the control or GTN+ARB groups. The plasma level of thioredoxin (a marker of oxidative stress) was increased in the GTN group after treatment (P<0.01) but not in the control or GTN+ARB groups.

CONCLUSIONS

An ARB suppressed the development of nitrate tolerance during transdermal nitroglycerin therapy. These results suggest that increased oxidative stress induced by activation of angiotensin II may play an important role in the development of nitrate tolerance.

Sonic vibrational analysis provides continuous measurement of arterial properties

OBJECTIVE

We describe a new technology for measuring artery mechanical properties, called Sonic Vibrational Analysis (SVA). We utilize SVA to study the changes in radial artery smooth muscle tone caused by intravenous infusion of vasoactive agents.

METHODS

Six healthy volunteers were monitored with a radial intra-arterial catheter and an SVA sensor during progressively increasing doses of nitroglycerin (NTG), phenylephrine, sodium nitroprusside (SNP), dobutamine, and nicardipine. In SVA, the propagation velocity of an audio-frequency vibration is measured over a short segment of the radial artery. The measurement has sufficient temporal resolution to track the continuous changes in arterial properties that occur due to the natural blood pressure pulse.

RESULTS

Coupled with the measurement of radial blood pressure, SVA allowed determination of the physiological/mechanical state of the artery within a single cardiac cycle. NTG, SNP, and phenylephrine caused significant changes in both blood pressure and the physiological state of the radial artery. Nicardipine and dobutamine altered blood pressure without change in the state of the radial artery.

CONCLUSIONS

The current results are consistent with previous studies of the effects of vasoactive agents on the radial artery. SVA is non-invasive, continuous, localized to a well-defined section of artery, and suitable for the collection of large volumes of time-resolved data in a laboratory or clinical setting.

Nitrate tolerance, rebound, and their clinical relevance in stable angina pectoris, unstable angina, and heart failure

Vascular tolerance develops rapidly in isolated vascular strips exposed to millimolar concentrations of nitroglycerin. Several mechanisms, including depletion of sulfhydryl groups, reduced biotransformation of nitrates to NO or nitrosothiols, oxygen free radical injury, and downregulation of a membrane-bound enzyme or a nitrate receptor, have been proposed, but the exact mechanism responsible for in-vitro tolerance remains unknown. In-vivo tolerance of the beneficial effects of nitrates on hemodynamics, myocardial ischemia, and exercise performance develops rapidly. It has been suggested, but remains to be proven, that development of venous tolerance and not arterial tolerance is responsible for the attenuation of nitrate effects during long-term nitrate therapy. Several mechanisms, including neurohormonal activation, depletion of sulfhdryl groups, and the shift of fluid from the extravascular to intravascular compartment have been implicated. However, the use of agents to counteract these mechanisms (ACE inhibitors, sulfhydryl donors, diuretics) has produced conflicting results. Thus, at present the mechanism responsible for in vivo tolerance to nitrates remains unknown. Both in vitro and in vivo vascular tolerance to nitrates can be prevented or minimized by providing nitrate-free or low-nitrate intervals. However, during nitrate-free periods, rebound phenomena (rest angina in patients with ischemic heart disease or a deterioration in exercise performance prior to the renewal of the morning dose in patients with stable angina) remain a clinical concern. When treating patients with stable angina pectoris, it must be recognized that none of the nitrate preparations or formulations can provide round-the-clock antianginal or antiischemic prophylaxis. In these patients, beneficial antianginal and antiischemic effects of nitrates for 10-14 hours during the daytime can be maintained by using formulations and dosing regimens that avoid or minimize the development of tolerance (standard formulation of isosorbide-5-mononitrate, 20 mg in the morning and 7 hours later; slow-release formulation of isosorbide-5-mononitrate, 120-240 mg once a day; or nitroglycerin patch delivering 0.6 nitroglycerin per hour for 10-12 hours each day). Only the patch on and off treatment is associated with nitrate rebound. Although intermittent nitrate therapy is not associated with the development of tolerance, this strategy cannot be recommended for treating unstable angina because rebound angina during nitrate-free periods complicates clinical decision making. In the acute phase of unstable angina, continuous treatment with intravenous nitroglycerin is recommended because it permits rapid up- or down-titration. Tolerance towards antianginal and antiischemic effects does develop in a substantial number of patients with 24 hours, but this can be overridden by dose escalation and restoration of the therapeutic effectiveness of nitroglycerin. Tolerance towards the beneficial effects of nitrates on hemodynamics and on exercise performance also develops rapidly during continuous or long-term nitrate therapy, and for these reasons nitrates are not used as first-line therapy to treat chronic heart failure. In combination with hydralazine, high-dose isosorbide dinitrate (30-40 mg four times a day) improves survival, but this combination therapy is inferior to ACE inhibitors.

New insights into mechanisms underlying nitrate tolerance

The hemodynamic and anti-ischemic efficacy of organic nitrates is rapidly blunted due to the development of nitrate tolerance. The mechanisms underlying this phenomenon remain poorly understood and likely involve several independent factors. More recent experimental observations suggest that tolerance may be the consequence of intrinsic abnormalities of the vasculature, including enhanced vascular superoxide and endothelin production. Superoxide anions degrade nitric oxide derived from nitroglycerin, whereas autocrine-produced endothelin within vascular smooth muscle sensitizes the vasculature to circulating neurohormones, such as catecholamines and angiotensin II, all of which may compromise the vasodilator potency of nitroglycerin. Interestingly, these vascular consequences of in vivo nitroglycerin treatment can be mimicked by incubating cultured endothelial and smooth muscle cells with angiotensin II. Further, nitrate tolerance and rebound following sudden cessation of prolonged nitroglycerin therapy can be prevented by concomitant treatment with high-dose angiotensin-converting enzyme inhibition or angiotensin-I receptor blockade. These data strongly suggest that increased circulating levels of angiotensin II, which are encountered during in vivo nitroglycerin treatment, initiate cellular events that ultimately attenuate the nitroglycerin vasodilator effects during prolonged treatment periods.

Explaining fatigue in congestive heart failure

Fatigue is a prominent symptom in patients with chronic heart failure, limiting physical activity and impairing quality of life. Although the underlying mechanisms are not clearly identified, alterations associated with peripheral adaptation in heart failure appear to play an important role, including a variably impaired peripheral perfusion during exercise, reduced oxidative capacity of skeletal muscle, impaired muscle strength, and possibly reflex mechanisms associated with alterations in the metabolism of skeletal muscle. Exercise training can, in part, reverse these peripheral alterations, improve exercise capacity, and alleviate fatigue.