Nitrate therapy in stable angina pectoris

Hotspot DNMT3A mutations in clonal hematopoiesis and acute myeloid leukemia sensitize cells to azacytidine via viral mimicry response

Somatic mutations in DNA methyltransferase 3A (DNMT3A) are among the most frequent alterations in clonal hematopoiesis (CH) and acute myeloid leukemia (AML), with a hotspot in exon 23 at arginine 882 (DNMT3A^R882). Here, we demonstrate that DNMT3A^R882H-dependent CH and AML cells are specifically susceptible to the hypomethylating agent azacytidine (AZA). Addition of AZA to chemotherapy prolonged AML survival solely in individuals with DNMT3A^R882 mutations, suggesting its potential as a predictive marker for AZA response. AML and CH mouse models confirmed AZA susceptibility specifically in DNMT3A^R882H-expressing cells. Hematopoietic stem cells (HSCs) and progenitor cells expressing DNMT3A^R882H exhibited cell autonomous viral mimicry response as a result of focal DNA hypomethylation at retrotransposon sequences. Administration of AZA boosted hypomethylation of retrotransposons specifically in DNMT3A^R882H-expressing cells and maintained elevated levels of canonical interferon-stimulated genes (ISGs), thus leading to suppressed protein translation and increased apoptosis.

Intermittent Nitrate Use and Risk of Hip Fracture

PURPOSE

Nitrates, commonly used antianginal medications, also have a beneficial effect on bone remodeling and bone density, particularly with intermittent use. However, their effect on fracture risk is not clear. We examined the relation of short-acting nitrate use (proxy for intermittent use) with the risk of hip fracture in a large cohort of older adults with ischemic heart disease.

METHODS

Participants aged 60 years or more with ischemic heart disease and without a history of hip fracture from The Health Improvement Network, an electronic medical records database in the United Kingdom, were included. The association of incident (new) use of short-acting nitrate formulations (nitroglycerin sublingual/spray/ointment or isosorbide dinitrate injection/sprays) with incident (new-onset) hip fracture risk was examined by plotting Kaplan-Maier curves and calculating hazard ratios using Cox proportional hazards regression models. Competing risk by death was analyzed in separate analyses.

RESULTS

Among 14,451 pairs of matched nitrate users and nonusers (mean age, 72 ± 7.6 years, 41% women for each cohort), 573 fractures occurred during follow-up (257 nitrate users; 316 nonusers). Hip fracture risk was 33% lower among short-acting nitrate users compared with nonusers (hazard ratio, 0.67; 95% confidence interval, 0.53-0.85; P = .0008). Competing risk analysis by death did not change effect estimates.

CONCLUSIONS

In this large population-based cohort of older adults with ischemic heart disease, we found a significant reduction in hip fracture risk with the use of short-acting nitrates (intermittent use). Future studies are warranted given the potential for nitrates to be potent, inexpensive, and readily available antiosteoporotic agents.

The influence of nitroglycerin on the proliferation of endothelial progenitor cells from peripheral blood of patients with coronary artery disease

Endothelial progenitor cells (EPCs) are associated with vascular repairing and progression of atherosclerotic lesion. It may lead to coronary artery disease (CAD) if circulating EPCs lose their function. Continuous nitroglycerin (NTG) therapy causes increased vascular oxidative stress and endothelial dysfunction. The aim of this study was to investigate the effects of NTG on the proliferation of human peripheral blood-derived EPCs. EPC cultures, collected from 60 CAD patients and cultured for 7-12 days, were treated with different concentrations of NTG (0.0, 0.3, 1.0, 2.0, 7.5, 15.0, and 20.0 mg/l) for 72 h, respectively. The cell counts and proliferative activities of EPC; the levels of vascular endothelial growth factor-A (VEGF-A), nitric oxide (NO) and peroxynitrite (ONOO(-)) in culture medium; and the level of reactive oxygen species (ROS) in adherent cells were measured. Compared with control (0.0 mg/l NTG), the cell number and proliferative activities of EPCs were increased when treated with 1.0 mg/l NTG and reached maximum level when NTG concentration was 7.5 mg/l. However, there was a significant reduction when treated with higher doses of NTG (≥15.0 mg/l). Meanwhile, VEGF-A expression reached its maximal expression with 7.5 mg/l NTG, but gradually declined by incubation with higher doses of NTG. There was a linear relationship between NO level and NTG concentration, but no changes of ONOO(-) and ROS levels were found when EPCs were incubated with 0.3-7.5 mg/l NTG. However, ONOO(-) and ROS levels were significantly increased when incubated with 15 and 20 mg/l NTG. Our data demonstrated that moderate dose of NTG may stimulate the proliferative activities of EPCs isolated from CAD patients.

Attenuation of acute lung inflammation and injury by whole body cooling in a rat heatstroke model

Whole body cooling is the current therapy of choice for heatstroke because the therapeutic agents are not available. In this study, we assessed the effects of whole body cooling on several indices of acute lung inflammation and injury which might occur during heatstroke. Anesthetized rats were randomized into the following groups and given (a) no treatment or (b) whole body cooling immediately after onset of heatstroke. As compared with the normothermic controls, the untreated heatstroke rats had higher levels of pleural exudates volume and polymorphonuclear cell numbers, lung myloperoxidase activity and inducible nitric oxide synthase expression, histologic lung injury score, and bronchoalveolar proinflammatory cytokines and glutamate, and PaCO2. In contrast, the values of mean arterial pressure, heart rate, PaO2, pH, and blood HCO3(-) were all significantly lower during heatstroke. The acute lung inflammation and injury and electrolyte imbalance that occurred during heatstroke were significantly reduced by whole body cooling. In conclusion, we identified heat-induced acute lung inflammation and injury and electrolyte imbalance could be ameliorated by whole body cooling.

Coronary artery spasm--clinical features, diagnosis, pathogenesis, and treatment

Coronary (artery) spasm plays an important role in the pathogenesis of ischemic heart disease, including stable angina, unstable angina, myocardial infarction, and sudden death. The prevalence of coronary spasm differs among populations, is higher in Japan and Korea than in the Western countries probably due to genetic as well as environmental factors. Coronary spasm occurs most often from midnight to early morning and is usually not induced by exercise in the daytime. The attacks of coronary spasm are associated with either ST segment elevation or depression, or negative U wave on ECG. Patients with multi-vessel coronary spasm may suffer from lethal arrhythmia, including advanced AV block, ventricular tachycardia or fibrillation, or even sudden death, and they are often resistant to conventional medical therapy including Ca-channel blockers (CCBs). Endothelial nitric oxide (NO) activity is reduced and markers of oxidative stress are elevated in patients with coronary spasm. Thrombogenesis is enhanced and plasma levels of hsCRP and P-selection are elevated in patients with coronary spasm. Thus, patients with coronary spasm have endothelial dysfunction and are suffering from a low-grade chronic inflammation. Polymorphisms of endothelial NO synthase, smoking, and low-grade inflammation are the most important risk factors for coronary spasm. Coronary spasm is a hyper-contraction of coronary smooth muscle triggered by an increase of intracellular Ca2+ in the presence of an increased Ca2+ sensitivity. It has been shown that RhoA/ROCK pathway is involved in Ca2+ sensitivity and that the reduced endothelial NO activity results in increased Ca2+ sensitivity through enhanced RhoA/ROCK pathway. Accordingly, it is possible that in addition to CCBs, RhoA/ROCK pathway blockers may prove to be useful for the treatment of coronary spasm.

Mitochondrial aldehyde dehydrogenase-2 (ALDH2) Glu504Lys polymorphism contributes to the variation in efficacy of sublingual nitroglycerin

Glyceryl trinitrate (GTN), also known as nitroglycerin, has been used to treat angina and heart failure for more than 130 years. Recently, it was shown that mitochondrial aldehyde dehydrogenase-2 (ALDH2) is responsible for formation of NO, the metabolite needed for GTN efficacy. In the present study, we show that the common G-to-A polymorphism in exon 12 of ALDH2--resulting in a Glu504Lys replacement that virtually eliminates ALDH2 activity in both heterozygotes and homozygotes--is associated with a lack of efficacy of sublingual GTN in Chinese subjects. We also show that the catalytic efficiency (Vmax/Km) of GTN metabolism of the Glu504 protein is approximately 10-fold higher than that of the Lys504 enzyme. We conclude that the presence of the Lys504 allele contributes in large part to the lack of an efficacious clinical response to nitroglycerin; we recommend that this genetic factor be considered when administering nitroglycerin to patients, especially Asians, 30-50% of whom possess the inactive ALDH2*2 mutant allele.

Modulation of prostaglandin biosynthesis by nitric oxide and nitric oxide donors

The biosynthesis and release of nitric oxide (NO) and prostaglandins (PGs) share a number of similarities. Two major forms of nitric-oxide synthase (NOS) and cyclooxygenase (COX) enzymes have been identified to date. Under normal circumstances, the constitutive isoforms of these enzymes (constitutive NOS and COX-1) are found in virtually all organs. Their presence accounts for the regulation of several important physiological effects (e.g. antiplatelet activity, vasodilation, and cytoprotection). On the other hand, in inflammatory setting, the inducible isoforms of these enzymes (inducible NOS and COX-2) are detected in a variety of cells, resulting in the production of large amounts of proinflammatory and cytotoxic NO and PGs. The release of NO and PGs by the inducible isoforms of NOS and COX has been associated with the pathological roles of these mediators in disease states as evidenced by the use of selective inhibitors. An important link between the NOS and COX pathways was made in 1993 by Salvemini and coworkers when they demonstrated that the enhanced release of PGs, which follows inflammatory mechanisms, was nearly entirely driven by NO. Such studies raised the possibility that COX enzymes represent important endogenous "receptor" targets for modulating the multifaceted roles of NO. Since then, numerous papers have been published extending the observation across various cellular systems and animal models of disease. Furthermore, other studies have highlighted the importance of such interaction in physiology as well as in the mechanism of action of drugs such as organic nitrates. More importantly, mechanistic studies of how NO switches on/off the PG/COX pathway have been undertaken and additional pathways through which NO modulates prostaglandin production unraveled. On the other hand, NO donors conjugated with COX inhibitors have recently found new interest in the understanding of NO/COX reciprocal interaction and potential clinical use. The purpose of this article is to cover the advances which have occurred over the years, and in particular, to summarize experimental data that outline how the discovery that NO modulates prostaglandin production has impacted and extended our understanding of these two systems in physiopathological events.

Effects of GW274150, a novel and selective inhibitor of iNOS activity, in acute lung inflammation

1. The aim of this study was to investigate the effect of GW274150, a novel, potent and selective inhibitor of inducible nitric oxide synthase (iNOS) activity in a model of lung injury induced by carrageenan administration in the rats. 2. Injection of carrageenan into the pleural cavity of rats elicited an acute inflammatory response characterized by: fluid accumulation in the pleural cavity which contained a large number of polymorphonuclear cells (PMNs) as well as an infiltration of PMNs in lung tissues and subsequent lipid peroxidation, and increased production of nitrite/nitrate (NO(x)), tumour necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta). 3. All parameters of inflammation were attenuated in a dose-dependent manner by GW274150 (2.5, 5 and 10 mg x kg(-1) injected i.p. 5 min before carrageenan). 4. Carrageenan induced an upregulation of the intracellular adhesion molecules-1 (ICAM-1), as well as nitrotyrosine and poly (ADP-ribose) (PAR) as determined by immunohistochemical analysis of lung tissues. 5. The degree of staining for the ICAM-1, nitrotyrosine and PAR was reduced by GW274150. These results clearly confirm that NO from iNOS plays a role in the development of the inflammatory response by altering key components of the inflammatory cascade. 6. GW274150 may offer a novel therapeutic approach for the management of various inflammatory diseases where NO and related radicals have been postulated to play a role.

In vitro skin permeation of Sinitrodil, a member of a new class of nitrovasodilator drugs

Clinical trials have shown the potential of benzoxazinones, a new class of organic nitrates, in cardiovascular therapy. In particular Sinitrodil possesses a coronary vascular selectivity greater than that of Nitroglycerin and isosorbide dinitrate. The objective of this study was a preliminary evaluation of the ability of these new organic nitrate derivatives to reach therapeutical steady-state plasma concentrations following a transdermal administration. In vitro permeation studies through human stratum corneum and epidermis have been conducted on two members of this class: Sinitrodil (ITF 296) and ITF 1129. Comparative studies have also been carried out with Nitroglycerin, Isosorbide dinitrate and Nicorandil. Two different fixed concentrations were tested: 0.08% w/v solution and saturated solution. Sinitrodil could be considered a good candidate for transdermal administration on the basis of the in vitro permeation results and of the known therapeutical plasma concentration.

Influence of Vasodilator Drugs on Perioperative Blood Pressure

Survey results are given of the incidence and the etiology of perioperative hypertension in patients sub jected to coronary artery surgery. Over the years, numer ous types of antihypertensives have been used for intravenous administration with the aim of preventing or treating perioperative hypertension. Nitrovasodilator compounds such as sodium nitroprusside and nitroglyc erin (NTG), a few calcium antagonists (nifedipine, nicar dipine and isradipine), the short-acting β-blocker esmo lol, clonidine, and the multifactorial compounds labetalol and ketanserin are discussed in detail. Perioperatively, there is an increasing level of plasma catecholamines, causing α-adrenoceptor stimulation. This indicates that α-adrenoceptor blockade with appropriate antagonists is a logical approach for the treatment of perioperative hypertension. For this reason, the multifactorial agent urapidil, which is an α-adrenoceptor blocker and a 5-HT1A agonist, is discussed extensively.

Effect of transdermal nitroglycerin or N-acetylcysteine, or both, in the long-term treatment of unstable angina pectoris

OBJECTIVES

This study was designed to evaluate whether the addition of transdermal nitroglycerin or oral N-acetylcysteine, or both, to conventional medical therapy improves the natural history of unstable angina pectoris.

BACKGROUND

Transdermal nitroglycerin is widely used to treat angina pectoris, but the development of tolerance is a major problem that may reduce its clinical efficacy. It has been suggested that the addition of N-acetylcysteine to nitroglycerin reverses the development of tolerance, potentiates the hemodynamic response to nitroglycerin and may improve in-hospital prognosis in unstable angina.

METHODS

We assessed the efficacy of adding transdermal nitroglycerin or oral N-acetylcysteine, or both, to conventional medical therapy in a randomized, double-blind, placebo-controlled trial involving 200 patients with unstable angina who were followed up for 4 months.

RESULTS

Outcome events--death, myocardial infarction or refractory angina requiring revascularization--occurred in 31% of patients receiving nitroglycerin, 42% of those receiving N-acetylcysteine, 13% of those receiving nitroglycerin plus N-acetylcysteine and 39% of those receiving placebo (p = 0.0052). Kaplan-Meier curves showed a higher probability (p < 0.01) of no failure of medical treatment in the group receiving both nitroglycerin and N-acetylcysteine than in those receiving placebo, N-acetylcysteine or nitroglycerin alone. The combination of nitroglycerin and N-acetylcysteine was associated with a high incidence of side effects (35%), mainly intolerable headache, which was almost twice as frequent as in patients receiving nitroglycerin alone.

CONCLUSIONS

The combination of nitroglycerin and N-acetylcysteine, associated with conventional medical therapy in the long-term treatment of patients with unstable angina, reduces the occurrence of outcome events. However, the high incidence of side effects limits the clinical applicability of this therapeutic strategy at least at the dosage used in the present study.

Nitric oxide-mediated cyclooxygenase activation. A key event in the antiplatelet effects of nitrovasodilators

We have evaluated the contributions of nitric oxide (NO) and prostacyclin (PGI2) in the in vivo antiplatelet effects of clinically useful nitrovasodilators. In rats, intravenous infusion of three NO donors, glyceryl trinitrate, sodium nitroprusside, or 3'-morpholinosydnonimine, the stable metabolite of molsidomine, released 6-keto PGF1alpha (the stable metabolite of PGI2) and inhibited ex vivo human platelet aggregation to adenosine diphosphate by at least 80%. In in vitro studies, glyceryl trinitrate, sodium nitroprusside, and 3'-morpholinosydnonimine, at clinically attainable concentrations, increased cyclooxygenase activity in endothelial cells (EC), which resulted in a four- to sixfold release of 6-keto PGF1alpha. Pretreatment of the EC with hemoglobin which binds to and inactivates the biological actions of NO, but not by methylene blue (MelB), attenuated the NO-mediated PGI2 from the EC by at least 70%. Release of 6-keto PGF1alpha by the NO donors increased the ability of these compounds to inhibit thrombin-induced human platelet aggregation by at least 10 times; this potentiation was inhibited by hemoglobin but not by MeB. MeB blocked the direct anti-platelet effect of the NO donors in the absence of EC. In summary, we have demonstrated that NO, directly as well as together with an NO-driven cyclooxygenase activation (and hence PGI2), release contributes to the marked anti-platelet effects observed after the in vivo administration of clinically used nitrovasodilators.

Effects of diuretic therapy on the development of tolerance to nitroglycerin and exercise capacity in patients with chronic stable angina

BACKGROUND

Therapy with diuretics has been reported to prevent the development of nitrate tolerance. Importantly, diuretics may have independent antianginal effects through their effects on intravascular volume. The present investigation was designed to determine whether diuretic therapy could prevent the development of tolerance to continuous transdermal nitroglycerin. The study was also designed to examine whether diuretic therapy has an independent antianginal effect.

METHODS AND RESULTS

Twelve patients with chronic stable angina were studied in a randomized, double-blind, crossover trial. Patients received diuretic (hydrochlorothiazide plus amiloride) or placebo for 14 to 20 days. During each double-blind treatment period, patients underwent treadmill exercise testing on three separate occasions. The first exercise testing was performed after 7 to 10 days of single-blind, placebo transdermal nitroglycerin therapy. Subsequently, exercise testing was repeated on the first day of active transdermal nitroglycerin therapy and following 7 to 10 days of continuous transdermal nitroglycerin application. Therapy with a diuretic was associated with an increase in exercise capacity but had no effect on nitroglycerin tolerance. During therapy with placebo transdermal nitroglycerin, diuretic therapy caused an increase in treadmill walking time to the development of moderate angina compared with placebo (371 +/- 26 versus 288 +/- 16 seconds, diuretic versus placebo, P < .01). Similar results were obtained during both acute and sustained nitroglycerin therapy.

CONCLUSIONS

The results of this study demonstrate that therapy with a diuretic has no effect on the development of tolerance to continuous transdermal nitroglycerin. Interestingly, diuretic therapy itself has important antianginal effects and improves exercise capacity in patients with stable angina.

Angina: an update for dentistry

Advances in medicine have dramatically altered the diagnosis and treatment of angina and the prognosis for patients with this condition. The authors review current medical practices and make recommendations for the dental management of patients.

Contemporary approaches in medical management of patients with stable coronary artery disease

CAD continues to be the principal cause of mortality in the United States, and the largest group of patients with CAD are those with stable angina. Among this group of patients, the most common manifestation of CAD is presence of transient episodes of myocardial ischemia. The presence of transient ischemia and not the severity of angina has been found to be associated with poor clinical outcome in patients with stable CAD. As part of a global treatment strategy for patients with stable CAD, changes in lifestyle and modification of coronary risk factors should be emphasized as an integral part of treatment. Conventional antianginal therapy is quite effective in controlling anginal attacks. Currently, several drugs and therapeutic strategies are available for the treatment of patients with angina (see Table 5). Nitrates are highly effective antianginal drugs with complex beneficial actions in patients with CAD, but their usefulness is limited by development of tolerance during long-term use. When clinically indicated, the use of nitrates should be supplemented with another longer-acting antianginal drug, such as a beta-blocker or a calcium channel blocker. Based on the available data, beta-blockers, when tolerated, seem to be the most effective antianginal drugs for most patients with stable CAD. Beta-blockers are also the most effective anti-ischemic drugs that reduce the magnitude of myocardial ischemia detected during routine daily activities. Calcium channel blockers are also effective vasodilators and good antianginal drugs. The clinician should become familiar with the different actions that this heterogeneous group of drugs has on the heart and vessels. This knowledge allows the clinician to choose the appropriate combination of different antianginal drugs for patients on an individualized basis. It is also critical to develop the treatment strategy by carefully taking into account other associated medical conditions that are frequently encountered in patients with CAD.

Intermittent transdermal nitroglycerin therapy. Decreased anginal threshold during the nitrate-free interval

BACKGROUND

Intermittent transdermal nitroglycerin therapy is effective in the treatment of stable angina and prevents the development of tolerance. Previous investigations have suggested that removal of nitroglycerin patches may be associated with a decrease in anginal threshold. This study examines the effect of nitroglycerin patch removal on anginal threshold in a group of patients with stable angina.

METHODS AND RESULTS

Twelve patients with stable angina were enrolled in a randomized, double-blind, placebo-controlled, crossover study. These patients had reproducible treadmill walking times and were taking no other long-acting antianginal medications or vasodilators. They received 0.8 mg/h transdermal nitroglycerin or wore a matching placebo patch for 5 to 7 days and then crossed over to the other treatment arm of the study. Transdermal nitroglycerin was applied at 8:00 PM and removed at 8:00 AM each day. On the last day of each treatment period, patients underwent treadmill exercise testing at 8:00 AM (before patch removal) and at 2, 4, and 6 hours after patch removal. The primary end point was the treadmill walking time until moderate angina (P2). Other end points included the treadmill walking time until onset of angina (P1), the amount of ST segment depression at P1 and P2, and treadmill walking time until the development of 1 mm ST depression. Heart rate, systolic blood pressure, and the rate-pressure product were determined at rest before exercise and at P1 and P2. At 8:00 AM P1 and P2 were not significantly affected by active nitroglycerin compared with placebo, indicating the development of tolerance. Removal of the active transdermal nitroglycerin patch was associated with a significant decrease in the time to P1 at 2, 4, and 6 hours after patch removal compared with placebo. There was also a decrease in the time to P2 after active patch removal that was statistically significant compared with placebo at 2 and 4 hours and was of borderline significance at 6 hours. There were no differences in heart rate, blood pressure, or amount of ST segment depression at either P1 or P2 after active compared with placebo patch removal.

CONCLUSIONS

In patients with stable angina pectoris, intermittent transdermal nitroglycerin therapy is associated with a decrease in anginal threshold for 4 to 6 hours after patch removal. Although the cause of this phenomenon remains uncertain, it may be due to counterregulatory responses that develop during nitroglycerin patch application.

Comparison of efficacy of nisoldipine, metoprolol, and isosorbide dinitrate in patients with stable exertional angina: a randomized, cross-over, placebo-controlled study

We evaluated the acute antianginal effect of oral nisoldipine (10 mg), metoprolol (40 mg), and long-acting isosorbide dinitrate (20 mg) in 15 patients with stable exertional angina. The patients performed symptom-limited treadmill exercise at 2 h after the administration of placebo (Placebo stages 1 and 2) and each of the active drugs. After Placebo stage 1, the patients were randomized for cross-over evaluation of the acute effect of a single oral dose of placebo (Placebo stage 2), nisoldipine, metoprolol, or long-acting isosorbide dinitrate. All 15 patients developed angina during all of exercise tests and their exercise tests were terminated at the onset of angina. The time until development of 0.1 mV ST segment depression was increased by all three drugs compared to placebo, and it was significantly longer with metoprolol than with isosorbide dinitrate. Similarly, the time to ceasing exercise because of angina was also prolonged by all three drugs. The exercise time was longer with nisoldipine and metoprolol compared to isosorbide dinitrate, but there was no significant difference between nisoldipine and metoprolol. In conclusion, metoprolol and nisoldipine more effectively prolonged exercise compared to long-acting isosorbide dinitrate in patients with stable exertional angina.

Comparison between felodipine and isosorbide mononitrate as adjunct to beta blockade in patients > 65 years of age with angina pectoris

Coronary artery disease is an increasingly common medical problem in the elderly, and relatively few studies investigating drug therapy focus on this population. To assess the efficacy and safety of the calcium channel blocker, felodipine, and isosorbide mononitrate (ISMN), as adjunct to optimal beta-blocker therapy in elderly patients, a placebo-controlled, double-blind study was conducted in 46 patients, aged between 65 and 80 years, with documented stress-induced angina pectoris and myocardial ischemia. With use of a latin-square design, with 3 periods of 4 weeks each, exercise testing was performed after each period. Felodipine, 5 mg once daily, significantly improved both time to ischemic threshold and pain threshold (p = 0.02 and p = 0.003, respectively, vs placebo), and tended to increase total exercise time (p = 0.06 vs placebo). In contrast, ISMN, 20 mg twice daily, did not significantly affect these parameters. Comparison of the 2 active treatment arms showed that, overall, felodipine was more effective than ISMN, with a statistically significant difference for time to ischemic threshold (p = 0.02). With regard to safety, felodipine was also better tolerated than ISMN, which led to more patients discontinuing study medication with ISMN (p < 0.05 between ISMN and felodipine). It is concluded that in elderly patients who are treated with optimal beta blockade, felodipine, but not ISMN, leads to an additional significant reduction in ischemic parameters during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of hyperventilation-induced attacks with infusion of B-type (brain) natriuretic peptide in patients with variant angina

B-type (brain) natriuretic peptide (BNP) forms a peptide family with A-type (atrial) natriuretic peptide (ANP), which is involved in the regulation of blood pressure and fluid volume. We have demonstrated that BNP is a novel cardiac hormone secreted predominantly from the ventricle and that plasma levels of BNP markedly increase in proportion to the severity of congestive heart failure. Spasm of a major coronary artery (coronary spasm) is the cause of variant angina and can be induced by hyperventilation. We examined whether BNP infusion suppresses coronary spasm in patients with variant angina. The effect of BNP infusion on anginal attacks induced by hyperventilation was studied in 11 patients with variant angina in whom the attacks were reproducibly induced by hyperventilation. This study was performed in the early morning on 3 consecutive days. Fourteen minutes after infusion of BNP was begun (day 2, 0.05 micrograms/kg/min) or saline (days 1 and 3), hyperventilation was started and continued for 6 minutes. Anginal attacks were induced in all 11 patients by hyperventilation on days 1 and 3, respectively. Anginal attacks were not induced in any patient on day 2 (BNP infusion). Fourteen minutes after BNP infusion was begun, plasma BNP levels increased from 23.7 +/- 6.7 pg/ml to peak levels of 2591 +/- 255 pg/ml (p < 0.01) and plasma ANP levels increased from 28.9 +/- 7.5 pg/ml to peak levels of 69.2 +/- 13.2 pg/ml. Five minutes after BNP infusion was finished, plasma levels of cyclic guanosine monophosphate (cGMP) increased from 20.3 +/- 7.4 pg/ml to peak levels of 63.5 +/- 13.7 pg/ml (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma arteriovenous cGMP difference as a useful indicator of nitrate tolerance in patients with heart failure

BACKGROUND

The present study was performed to evaluate the effects of nitroglycerin (GTN) on plasma arteriovenous cGMP production and to compare its hemodynamic effects in patients with congestive heart failure (CHF). We also estimated the potential clinical value of plasma arteriovenous cGMP production as an indicator of nitrate tolerance.

METHODS AND RESULTS

Plasma arterial and venous cGMP levels, atrial natriuretic peptide level, and hemodynamic parameters were measured before and after GTN infusion in 14 patients with CHF. Although the plasma levels of arterial cGMP and atrial natriuretic peptide decreased immediately after GTN, the plasma level of venous cGMP did not change. GTN infusion caused a dose-dependent increase in plasma arteriovenous cGMP production, and there was a positive correlation between the decrease of pulmonary capillary wedge pressure and the increase of plasma arteriovenous cGMP production immediately after GTN. Hemodynamic tolerance was observed after both 12 and 24 hours, when plasma arteriovenous GMP production was also attenuated.

CONCLUSIONS

These findings indicate that the plasma arteriovenous cGMP difference is a clinical indicator of vasodilatory action of GTN and a useful indicator of nitrate tolerance in patients with CHF.

Effects of continuous intravenous infusion of isosorbide dinitrate on development of tolerance to vasodilating action in human epicardial coronary arteries

This study was performed to determine the effects of long-term intravenous infusion on the coronary vasodilating actions of continuous intravenous and bolus intracoronary administration of isosorbide dinitrate (ISDN). With quantitative coronary angiography, the coronary diameter and the vasodilating response to intracoronary ISDN (1 mg) at angiographically normal segments were studied before and after intravenous administration of ISDN, 10 to 60 micrograms/min for 1 hour, 2 days, or 5 days. The vasodilating effects of intravenous ISDN were 72% +/- 13%, 65% +/- 21%, and 6% +/- 11% of the response to intracoronary ISDN in the baseline study in each group. Irrespective of the duration of intravenous infusion, subsequent intracoronary ISDN dilated coronary arteries to extent similar to that observed in each baseline study. In conclusion, significant coronary vasodilating effects of intravenous ISDN were observed after a 2-day infusion, whereas tolerance to the vasodilating effects apparently developed within 5 days of infusion. The vasodilating response to bolus intracoronary ISDN was preserved even when the vasodilating effects of intravenous ISDN were no longer present.

Risk of rebound phenomenon during nitrate withdrawal

Organic nitrates are first-line drugs in the therapy and prevention of angina. These compounds, are acutely effective yet some formulations demonstrate a rapid decline in effect with chronic use. In this review the mechanisms of development of nitrate tolerance and the different strategies to prevent it are considered. If frequent dosing, high dosages and long acting preparations giving constant 24 h plasma GTN levels are more likely to cause tolerance, nitrate-low periods seem to be effective in restoring the drug's efficacy. Intermittent therapy with GTN patches, an effective way to prevent tolerance, raises the problem of the rebound phenomenon during the removal period. Considerable variations in its occurrence have been reported and in this review the factors that may influence the incidence of the rebound are discussed. The dangers of rebound can be lessened by concomitant anti-anginal drugs or avoiding any abrupt decline in blood nitrate concentrations. The use of beta-blockers or calcium channel blockers during intermittent therapy with GTN patches and oral preparations of isosorbide dinitrate or isosorbide 5-mononitrate seem to be effective for this purpose.

Antithrombotic properties of transdermal nitroglycerin in stable angina pectoris

Nitroglycerin provides an external source of nitric oxide which stimulates guanylate cyclase and produces vasodilatation and inhibition of platelet function. The antithrombotic effects of intravenous nitroglycerin were recently documented in various experimental models and in patients with unstable angina. This protocol was designed to evaluate whether these effects could also be detected with transdermal nitroglycerin in patients with stable angina. In a randomized, double-blind, controlled parallel trial, 22 patients received transdermal nitroglycerin, 0.6 mg/hour (11 patients), or placebo (11 patients). Platelet aggregation to adenosine diphosphate (ADP) and to thrombin was measured in whole blood. Thrombus formation was assessed on porcine aortic media exposed to the patient's venous blood for 3 minutes at shear rates of 2,546 and 754 s-1. Platelet aggregation to ADP decreased from 7.7 +/- 0.8 to 5.3 +/- 0.8 ohms (p < 0.05) with nitroglycerin, and to thrombin from 15.6 +/- 1.2 to 12 +/- 1.2 ohms (p < 0.05). Thrombus size at the high-shear rate decreased from 2.8 +/- 0.7 to 1.0 +/- 0.3 microns 2 (p < 0.05), and at the low-shear rate from 2.5 +/- 0.5 to 1.0 +/- 0.2 microns 2 (p < 0.05). Placebo had no significant effect on platelet aggregation and platelet thrombus deposition. These parameters were all reduced by > or = 20% in 8 patients taking nitroglycerin but only in 3 patients taking placebo (p < 0.05). Transdermal nitroglycerin significantly inhibits platelet aggregation and mural thrombus formation in patients with angina pectoris.

Eccentric dosing with isosorbide-5-mononitrate in angina pectoris

In a placebo-controlled, parallel, double-blind study, 214 patients with stable angina were studied. Doses of 5, 10 and 20 mg of immediate-release isosorbide-5-mononitrate (IS-5-MN) or placebo were administered at 0800 and 1500 hours for a period of 3 weeks. On days 1 and 14, patients underwent exercise testing before, and 2 and 7 hours after both doses; on days 7 and 21, testing was performed 2 hours after morning dosing. Study variables included total exercise duration and time to moderate angina. On day 1, the active treatment groups showed improvement over the placebo group 2 and 7 hours after dose 1, and 2 hours after dose 2. Throughout the subsequent study period, each active treatment group was superior to placebo 2 hours after the first and second doses. Only the 20 mg dose increased exercise duration 7 hours after dosing, and this was observed after both doses 1 and 2 on day 14. There were fewer episodes of angina in patients receiving the 20 mg dose. There was no increase in nocturnal angina during eccentric dosing with IS-5-MN. In comparing exercise times throughout the study, tolerance did not develop during eccentric dosing. The morning exercise tests before tablet administration showed a progressive increase during the study period, with slightly greater improvement in patients receiving active therapy. This absence of a zero hour effect suggests that rebound does not occur during eccentric dosing with immediate-release IS-5-MN.

Nitrates and angina pectoris

This review discusses the mechanisms of action of the organic nitrates, nitrate tolerance, and the effects of nitrates in patients with stable angina pectoris. The nitrates are prodrugs that enter the vascular smooth muscle, where they are denitrated to form the active agent nitric oxide (NO). NO activates guanylate cyclase, which results in cyclic guanosine monophosphate (cGMP) production and vasodilation as a result of reuptake of calcium by the sarcoplasmic reticulum. NO is identical to endothelium-derived relaxing factor (EDRF), which induces vasodilation, inhibits platelet aggregation, reduces endothelium adhesion, and has anticoagulant and fibrinolytic effects. Thus, the nitrates may be more than vasodilators and, in addition to reducing ischemia, may affect the process of atherosclerosis. The vascular effects of nitrates are attenuated during sustained therapy. Although the basis for the phenomenon of nitrate tolerance is not completely understood, sulfhydryl depletion as well as neurohormonal activation and increased plasma volume may be involved. The administration of N-acetylcysteine, angiotensin-converting enzyme (ACE) inhibitors, or diuretics do not consistently prevent nitrate tolerance. At present, intermittent nitrate therapy is the only way to avoid nitrate tolerance. The intermittent administration of nitrates, however, cannot provide continuous therapeutic benefits, and thus monotherapy with nitrates is not suitable for many patients with stable angina pectoris.

Platelet cyclic GMP. A potentially useful indicator to evaluate the effects of nitroglycerin and nitrate tolerance

BACKGROUND

The present study was designed to investigate the intracellular production of cyclic GMP (cGMP) in platelets in response to nitroglycerin and to determine the potential clinical value of platelet cGMP as an indicator of the effects of nitroglycerin and nitrate tolerance.

METHODS AND RESULTS

Platelet cGMP levels and the diameters of the coronary arteries before and 2 minutes after intracoronary injection of 200 micrograms nitroglycerin were measured in 15 patients who had previously received nitrates (nitrates group) and in 16 who had not received any nitrates (no-nitrates group). Platelet cGMP levels increased significantly after nitroglycerin injection in the two groups, but plasma cGMP levels and plasma atrial natriuretic peptide levels did not change. The percent increase in platelet cGMP levels and the percent dilatation of the left anterior descending (LAD) and left circumflex (LCx) coronary arteries after nitroglycerin injection were higher in the no-nitrates group than in the nitrates group (platelet cGMP levels: artery, 74.2 +/- 18.3% versus 11.5 +/- 4.2%, P < .01; vein, 73.6 +/- 22.9% versus 9.0 +/- 3.1%, P < .01; coronary dilatation: LAD, 46.7 +/- 6.0% versus 9.9 +/- 2.5%, P < .01, LCx, 51.2 +/- 8.7% versus 6.1 +/- 3.0%, P < .01). The percent increase in platelet cGMP levels was significantly correlated with the percent dilatation of the coronary arteries (LAD: r = .90, P < .01; LCx: r = .92, P < .01) in the no-nitrates group and not in the nitrates group.

CONCLUSIONS

These results indicate that platelet cGMP can be used as an indicator for in situ evaluation of nitroglycerin effects and that patients who have received nitrates develop nitrate tolerance, which affects intracellular production of cGMP and vasodilation in the response to nitroglycerin.

Differences of intravenous nitroglycerin responses in left ventricular systolic and end-diastolic pressures and coronary artery diameters during long-term treatment with cutaneous nitroglycerin patches

The differences of intravenous nitroglycerin responses in left ventricular (LV) systolic and end-diastolic pressures and in coronary artery diameters (cross-tolerance) were investigated in patients receiving nitroglycerin patches. During diagnostic cardiac catheterization, graded doses of 50, 100, and 150 mcg of intravenous nitroglycerin were given. Left ventricular systolic and end-diastolic pressures and left coronary arteriograms were obtained during each dose. Twenty patients with coronary artery disease were studied. Before cardiac catheterization, 10 received nitroglycerin patch (patch group), and 10 did not (control group). In the control group, graded intravenous nitroglycerin doses of 50, 100, and 150 mcg caused decrease in LV systolic pressure of 18 +/- 7%, 20 +/- 5%, and 23 +/- 6%, respectively. In the patch group, the same intravenous nitroglycerin doses decreased LV systolic pressure by 12 +/- 6% (p < 0.05), 19 +/- 7% (NS), and 18 +/- 6% (p < 0.05), respectively, (p value: vs. control group). At the same intravenous nitroglycerin doses, LV end-diastolic pressures were decreased by 48 +/- 14%, 52 +/- 17%, and 56 +/- 9%, respectively, in the control group. However, there were no significant differences in LV end-diastolic pressure between the two groups for any of the three intravenous nitroglycerin doses. The same intravenous nitroglycerin doses caused increase in diameter of the left anterior descending coronary artery and circumflex coronary artery in the control group, which was attenuated significantly in the patch group. Tolerance may develop in LV systolic pressure and coronary artery diameters, whereas it may not develop in LV end-diastolic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Methylene blue inhibits the antithrombotic effect of nitroglycerin

OBJECTIVES

The aim of this study was to examine whether cyclic guanosine monophosphate (GMP) may be involved in the antithrombotic action of nitroglycerin.

BACKGROUND

Nitroglycerin has been shown to inhibit platelet function in vitro by stimulating prostacyclin or inhibiting thromboxane A2 production, or both. Nitroglycerin has also been shown to possess potent antithrombotic properties in vivo. However, the mechanism of this antithrombotic effect is unclear.

METHODS

Nitroglycerin was infused to produce a 10% decrease in mean arterial pressure in 27 normal pigs by exposing their circulating arterial blood to porcine aortic media in an ex vivo perfusion chamber. Eight pigs received an infusion of nitroglycerin alone; eight received an infusion of methylene blue, a guanylate cyclase inhibitor, followed by nitroglycerin infusion and five pigs received an infusion of nitroglycerin followed by methylene blue and subsequent infusion of cyclic GMP.

RESULTS

With nitroglycerin alone, quantitative autologous indium-111-labeled platelet deposition (x10(6) on the aortic media was decreased to 63.9 +/- 10.4% (p = 0.01) of the baseline control platelet deposition. Methylene blue given before nitroglycerin tended to increase platelet deposition relative to baseline and platelet deposition after nitroglycerin was 142 +/- 35% (p = NS) of baseline value. In pigs that received all three agents, nitroglycerin reduced platelet deposition to 42.3 +/- 12.2% of baseline value; this decrease was then attenuated by subsequent methylene blue infusion but was enhanced by cyclic GMP infusion to 16.4 +/- 3.8% of baseline value (p = 0.006 vs. baseline control and p = 0.02 versus methylene blue infusion).

CONCLUSIONS

Guanylate cyclase inhibition with methylene blue abolishes the antithrombotic effect of nitroglycerin, which can be enhanced by cyclic GMP.

Drug-patient interactions and their relevance in the treatment of heart failure

The effects of congestive heart failure (CHF) on drug disposition and elimination are many and varied. Indeed, the pharmacokinetics of many of the drugs used to treat CHF are significantly altered by the patient's underlying condition. Reduced gastric emptying in CHF delays absorption and decreases the peak plasma concentrations of furosemide, bumetanide, and digoxin. Moreover, drugs that have a high hepatic extraction ratio (organic nitrates, morphine, prazosin, and hydralazine) achieve higher than expected plasma concentrations in patients with CHF. In contrast, drugs requiring biotransformation to active forms, e.g., angiotensin-converting enzyme (ACE) inhibitors such as enalapril, perindopril, quinapril, and ramipril, generally have lower than expected plasma concentrations. Nevertheless, ACE inhibitors can impair renal function in CHF, leading to an actual increase in plasma concentrations. However, decreases in absorption and first-pass metabolism are often offset by reduced hepatic and renal clearance. The overall absorption of lisinopril may be reduced in some CHF patients; consequently, the onset of effect is delayed but is often more prolonged.

Role of nitrates in angina pectoris

Nitrates are used extensively for the treatment of angina pectoris. However, continuous therapy with either oral nitrates or nitroglycerin patches leads to rapid development of tolerance, with loss or diminution of antianginal and anti-ischemic effects. The only practical way to avoid the development of tolerance is to use intermittent daily therapy with nitrates. Nitroglycerin patches applied for 10-12 hours during the day increase exercise duration for 8-12 hours, but a rebound increase in anginal attacks during the nitrate-free interval may occur. Oral isosorbide-5-mononitrate, 20 mg twice a day, with the first dose administered in the morning and the second dose 7 hours later, increases exercise duration for at least 12 hours without the development of tolerance to either the morning or afternoon dose. This dosing regimen has been shown not to produce a rebound phenomenon during the periods of low nitrate levels at night and early hours of the morning. Isosorbide dinitrate (30 mg) prescribed at 7 AM and 1 PM does not produce tolerance to the 7 AM dose, but effects of the afternoon dose have not been evaluated. Recent data suggest that isosorbide dinitrate given 3 or 4 times daily produces tolerance and this dosing schedule is inadequate for antianginal prophylaxis. It should be recognized that intermittent oral or patch therapy with nitrates during the day leaves the patient unprotected at night and early hours of the morning. If this is of concern, additional therapy with another class of antianginal agent, preferably a long-acting beta blocker or a long-acting calcium antagonist should be instituted.

Metabolism of nitroglycerin by smooth muscle cells. Involvement of glutathione and glutathione S-transferase

Metabolism of nitroglycerin (GTN) in the vascular smooth muscle is required for the drug to be effective in the treatment of angina pectoris and congestive heart failure. The usefulness of GTN is limited by the development of tolerance to the drug. The metabolism of GTN was studied in its target tissue, vascular smooth muscle. Inorganic nitrite was produced by cultured smooth muscle cells when GTN was added to the culture dish. Nitrite production increased with increasing GTN concentration and with incubation time. The enzymatic nature of GTN metabolism to nitrite was assessed by enzyme inhibition studies. Indocyanine green, a non-substrate inhibitor of glutathione S-transferase, inhibited GTN metabolism by smooth muscle cells. Cellular glutathione is also involved in GTN metabolism by the smooth muscle cell. Pretreatment with phorone, a glutathione S-transferase substrate, depleted cellular glutathione and decreased nitrite production from GTN. Pretreatment with buthionine sulfoximine, inhibitor of gamma-glutamylcysteine synthetase, decreased intracellular glutathione and caused decreased GTN metabolism in smooth muscle cells. Removal of cysteine from the smooth muscle cell incubation medium in combination with buthionine sulfoximine pretreatment decreased GTN metabolism to a lower level than buthionine sulfoximine pretreatment alone. This study shows that glutathione S-transferase and glutathione are involved in GTN metabolism by cultured smooth muscle cells.

Plasma profile and haemodynamic tolerance to isosorbide-5-mononitrate in controlled-release form

1. Plasma concentrations and some haemodynamic parameters known to be affected by nitrates, were monitored in healthy volunteers who received three different dose regimens of isosorbide-5-mononitrate (5-ISMN) over 5 day study periods. 2. No haemodynamic tolerance was found in the 60 mg once-daily dose schedule which produced high plasma concentrations during the daytime but concentrations no greater than 100 ng ml-1 at night. In contrast, a dose regimen of 60 mg followed by 30 mg 12 h later and thereafter every 8 h until the fifth day induced complete haemodynamic tolerance. With this dose regimen the minimum plasma concentrations were never below 300 ng ml-1. A significant attenuation of haemodynamic effects was also found with the third dose regimen, 60 mg followed by 30 mg 6 h later for 5 days, which produced minimum plasma concentrations of between 100 ng ml-1 to 300 ng ml-1; the degree of attenuation rose as trough plasma concentrations increased. 3. In conclusion, 60 mg 5-ISMN in a controlled-release (Durules) preparation given once daily was the only dose regimen not inducing nitrate tolerance.

Fourth International Study of Infarct Survival: protocol for a large simple study of the effects of oral mononitrate, of oral captopril, and of intravenous magnesium. ISIS-4 collaborative group

The fundamental aim of the International Studies of Infarct Survival (ISIS) collaborative group is to assess reliably the balance of any benefits and risks for widely practicable treatments that might produce moderate but worthwhile mortality reductions in patients with suspected acute myocardial infarction. Substantial numbers of lives might be saved by such treatments, but benefits of the size that can realistically be expected may be reliably detected only by randomized trials involving some tens of thousands of patients. In order to recruit such numbers, ISIS involves almost no extra work for collaborators: hence, busy general hospitals--where the majority of acute myocardial infarction patients are actually treated--can take part easily. The ability of the ISIS trials to yield clear, reliable answers depends entirely on the collaboration of many doctors and nurses in the participating hospitals. For this reason, publication of the final results is in the names of all the collaborators. All patients, high risk as well as low risk, presenting within 24 hours of the onset of suspected acute myocardial infarction are eligible for ISIS-4, provided that the responsible physician does not initially consider there to be any clear indications for, or clear contraindications to, any one of the trial treatments--nitrate, angiotensin-converting enzyme inhibitor, or magnesium. Patients are randomized between 1 month of oral controlled-release mononitrate or placebo; between 1 month of oral captopril or placebo; and between 24 hours of intravenous magnesium or open control (i.e., no infusion). (Patients who are to be given intravenous or other non-trial nitrate for just a few days can still be entered). In this trial, 3 quite different treatments will each be evaluated. At first glance, this may appear to complicate the results, but in fact appropriate statistical analysis of this "factorial" design will allow all patients to contribute fully to assessment of the separate effects of each treatment (while also providing important information about the combined effects). Apart from giving the trial treatments, all other aspects of individual patient management are left entirely to the responsible physician to decide. For example, previous trials in suspected acute myocardial infarction have shown that, for many categories of patients, antiplatelet and fibrinolytic therapy can save lives. Hence, most collaborating doctors will wish to give antiplatelet therapy routinely and to start fibrinolytic therapy in many of their patients before randomizing them in ISIS-4.(ABSTRACT TRUNCATED AT 400 WORDS)

The antiplatelet effects of organic nitrates and related nitroso compounds in vitro and in vivo and their relevance to cardiovascular disorders

Organic nitrates, cornerstones of antianginal therapy, are believed to exert their principal anti-ischemic benefit by relaxing vascular smooth muscle. Recent evidence suggests that these compounds and related nitro(so) vasodilators are also potent platelet inhibitors. In view of the well recognized role of thrombotic events mediated by platelets in acute coronary syndromes, the antiplatelet effect of nitrates may also be of mechanistic importance in the treatment of these disorders. This review details the biochemical mechanism by which nitro(so) compounds inhibit platelet function and summarizes the in vitro and in vivo evidence that supports their antithrombotic effects.

Acute and chronic antianginal efficacy of continuous twenty-four-hour application of transdermal nitroglycerin. Steering Committee, Transdermal Nitroglycerin Cooperative Study

To resolve the controversies surrounding the antianginal use of chronic, continuous 24-hour transdermal nitroglycerin therapy, a double-blind, placebo-controlled, randomized, parallel-group study was designed. Eligible patients had chronic angina pectoris with symptom-limited, reproducible treadmill tests and were responsive to sublingual nitroglycerin (n = 562). Patients were randomly assigned to placebo or 1 of 7 doses of active treatment (15, 30, 45, 60, 75, 90 and 105 mg/24 hours). In the active drug groups, treatment was initiated with 15 mg/24 hours during the first week of double-blind dosing with subsequent weekly increases until the assigned dose was reached, after which the dose was held constant. Treadmill tests were performed 0, 4 and 24 hours after the initial double-blind patches were applied, after each titration step and after 8 weeks. At the end of double-blind therapy, a sublingual nitroglycerin exercise challenge was repeated. Exercise tolerance in patients using the active patch increased 34 seconds (p less than 0.05) over patients taking placebo 4 hours after the initial application of double-blind therapy, but there was no statistically significant difference in exercise time between placebo and active drug groups by 24 hours after the first application or for the remaining 8 weeks of the trial. Increasing the dose did not overcome the loss of effect. A partial attenuation of the response to a sublingual nitroglycerin challenge seen on exercise tolerance testing also occurred, with patients who received the highest dose showing the greatest attenuation. There were no differences in angina frequency among the groups, although in a post hoc analysis, patients with greater than 7 attacks per week had a reduction in anginal frequency of 6 to 7 attacks per week with active treatment versus 2 attacks per week with placebo. The study showed that (1) tolerance to the exercise effects of continuous transdermal nitroglycerin develops within 24 hours after application; and (2) increasing the dose does not overcome this tolerance. The observation that symptomatic improvement may occur in the absence of increases in exercise tolerance seems deserving of further study.

Long-term efficacy of continuous and intermittent use of transdermal nitroglycerin in stable angina pectoris

To assess efficacy of transdermal nitrate use, a randomized, placebo-controlled trial of continuous and intermittent use of nitroglycerin patches (10 mg/24 hours) was conducted in 127 patients with stable angina pectoris who discontinued exercise testing within 9 minutes because of angina. After a placebo run-in week, baseline (day 0) symptom-limited exercise testing was performed and repeated on day 1 and 14 before and after the administration of 0.5 mg of sublingual nitroglycerin. On day 0, total exercise duration was the same (within narrow limits) in all 3 groups and remained unchanged in the placebo group. On day 1, total exercise duration increased from 406 +/- 115 to 469 +/- 158 seconds (p less than 0.001) in the continuously treated group and from 396 +/- 105 to 475 +/- 171 seconds (p less than 0.001) in the intermittently treated group. In the intermittent group, exercise duration increased slightly to 483 +/- 140 seconds on day 14, and in the continuous group exercise duration decreased to 447 +/- 144 seconds. However, this decrease was not statistically significant. Similar treatment effects were seen for time to 1-mm ST depression. Sublingual nitroglycerin remained effective in all 3 groups and on all days. Eleven actively treated patients and 1 patient taking placebo discontinued the study because of headache. It is concluded that continuous use of transdermal nitroglycerin remains partially effective and intermittent therapy remains fully effective in improving long-term exercise capacity with acceptable adverse effects in patients with stable angina pectoris.

Biochemical and pharmacological interactions between nitroglycerin and thiols. Effects of thiol structure on nitric oxide generation and tolerance reversal

Co-administration of N-acetylcysteine (NAC) with nitroglycerin (NTG) has been shown to partially reverse nitrate tolerance and to potentiate the hypotensive effect of NTG in humans. However, a high clinical dose of NAC was required for this pharmacologic interaction resulting in the production of unwanted side-effects. Therefore, sulfhydryl compounds more active than NAC need to be identified if this interaction is to be exploited clinically. We previously suggested that the effect of sulfhydryl compounds on NTG may be mediated by the formation of S-nitrosothiol or nitric oxide (NO) extracellularly to the vascular smooth muscle cell (e.g. in plasma) (Fung et al., J. Pharmacol Exp Ther 245: 524-530, 1988). In an attempt to understand the structural features which govern this thiol-catalyzed NO generation from NTG, nineteen different aliphatic and ten aromatic sulfhydryl compounds were examined with respect to their catalytic activity to generate NO from NTG in plasma. Significantly enhanced production of NO was observed with most sulfhydryl compounds examined when compared to buffer control. Among the aliphatic thiols, only mercaptosuccinic acid was more potent than NAC (2x), whereas among the aromatic thiols, both thiosalicylic acid (TSA, 10x) and TSA-methyl ester (3x) were more potent than NAC. Comparative in vitro relaxation studies were carried out using isolated (and nitrate-tolerant) rat aortic rings with NTG/TSA and NTG/NAC, in the presence of 0.5% (v/v) plasma. Under these conditions, partial reversal of NTG tolerance could be achieved with TSA, but not with NAC. These data are consistent with the view that extracellular production of NO or S-nitrosothiol serves as a tolerance-reversing mechanism of thiols on NTG. TSA appears to be a more potent sulfhydryl compound than NAC in this biochemical and pharmacologic interaction.

Influence of intravenous administration set composition on the sorption of isosorbide dinitrate

The influence of the composition of administration sets on the sorption of isosorbide dinitrate was investigated in-vitro. Isosorbide dinitrate solutions (250 micrograms mL-1) in 0.9% NaCl or 10% glucose were stored in glass containers and administered at a flow rate of 20 mL h-1. The influence of the concentration of different plasticizers (di-ethylhexylphthalate, tri-ethylhexyltrimelitate) in polyvinylchloride tubings was determined. Polybutadiene tubings of different mol. wt coextruded laminates of these polybutadienes with PVC of different composition and a polyethylene tubing were evaluated. The higher the Shore hardness of the PVC tubing, the lower the sorption. The infusion fluid played an additional role only for the tubings with high Shore hardness (greater than 70). The sorption of isosorbide dinitrate to polybutadiene tubings of different mol. wt was less than 2.5% after 5 h and was comparable with the sorption to the polyethylene tubing. When polybutadiene/PVC laminates were used, the sorption increased significantly and was in most cases dependent on the Shore hardness of the PVC (higher Shore hardness gave lower sorptions) and on the mol. wt of the polybutadiene (lower mol. wt resulted in higher sorption). Sorption was not dependent on the type of PVC plasticizer.

Effects of sublingual nitroglycerin in patients receiving transdermal nitroglycerin for coronary artery disease: prevention of cross-tolerance

The systemic hemodynamic and coronary dilative responses to sublingual nitroglycerin were studied in patients receiving transdermal nitroglycerin. A total of 48 patients with coronary artery disease were divided into 4 groups: 12 patients receiving 1 tablet of sublingual nitroglycerin without transdermal nitroglycerin (Group 1), 12 patients receiving 1 tablet of sublingual nitroglycerin with 12-hour-daily intermittent therapy of transdermal nitroglycerin (Group 2), 12 patients receiving 1 tablet of sublingual nitroglycerin with continuous therapy of transdermal nitroglycerin with continuous therapy of transdermal nitroglycerin (Group 3), and 12 patients receiving 2 tablets of sublingual nitroglycerin with continuous therapy of transdermal nitroglycerin (Group 4). Before and during administration of sublingual nitroglycerin, aortic pressure, left ventricular pressure, and coronary artery diameter were examined at diagnostic cardiac catheterization in all patients. During sublingual nitroglycerin, the decreases of aortic systolic pressure and left ventricular end-diastolic pressure were greater in Group 1, 2, and 4 than in Group 3. Dilation of coronary arteries by sublingual nitroglycerin tended to be greater in Group 1, 2, and 4 than in Group 3. Thus, the effects of sublingual nitroglycerin for the relief of ischemia might be more prominent in patients with intermittent therapy of transdermal nitroglycerin than in those with continuous therapy. The increased dose of sublingual nitroglycerin for the relief of ischemia might be more effective in patients with continuous therapy of transdermal nitroglycerin.

Intravenous nitroglycerin infusion inhibits cyclic blood flow responses caused by periodic platelet thrombus formation in stenosed canine coronary arteries

BACKGROUND

Nitroglycerin and other clinically relevant organic nitrate derivatives have been shown to inhibit platelet aggregation in vitro. This antithrombotic effect of nitrates is potentiated by reduced thiol. To determine the potential relevance of this mechanism of action in vivo, we examined the effect of intravenous nitroglycerin infusion on periodic platelet thrombus formation in a canine model of coronary artery stenosis.

METHODS AND RESULTS

We used a canine model of coronary artery stenosis associated with cyclic reductions in coronary blood flow that have been shown to depend on periodic platelet thrombus formation. We quantified the frequency of cycles per 40-minute observation period and monitored the effect of a continuous infusion of intravenous nitroglycerin on the cycle frequency. The administration of 10-15 micrograms/kg/min nitroglycerin reduced cyclic platelet thrombus formation significantly and did so without a significant change in coronary artery blood flow. Pretreatment with the reduced thiol, N-acetylcysteine (100 mg/kg during 30 minutes), led to inhibition of cyclic platelet thrombus formation by intravenous nitroglycerin at doses that alone had no such effect (5 micrograms/kg/min).

CONCLUSION

These data suggest that one mechanism by which intravenous nitroglycerin improves ischemia in acute coronary artery disease syndromes may be by inhibition of platelet thrombus formation and may highlight the potential importance of reduced thiol in this mechanism.

[Vascular effects of adenosine-triphosphate]

This study assessed the effects of adenosine triphosphate (ATP) on systemic vascular resistances during the hypothermic cardiopulmonary bypass phase of cardiac surgery. Twenty patients scheduled for cardiac surgery were randomly divided into an ATP group (n = 10), and a placebo group (n = 10). Anaesthesia was similar for all the patients (diazepam, fentanyl and pancuronium). During the heart arrest phase, and as soon as the arterial pressure, the level in the venous return reservoir, and the pump flow rate had all been in steady state for 5 min, ATP or placebo was injected into the venous line of the oxygenator. Injection speed was doubled every three minutes, twice. The following ATP doses were administered: 0.012, 0.025 and 0.05 mg.kg-1.min-1. The level in the venous return reservoir was kept constant. Mean arterial pressure (MAP) and pump flow rate (DP) were assessed every half minute. Systemic vascular resistances were calculated with the relationship MAP/DP. Changes in vascular capacitance were directly proportional to changes in DP as the heart had been excluded, and all the blood returned to the pump, the blood volume being kept constant. MAP and DP remained unchanged in the placebo group. In the opposite ATP induced a dose-related systemic vasodilation: MAP decreased from 82.8 +/- 12.5 mmHg (control) to 66.0 +/- 14.8 mmHg, 59.8 +/- 10.6 mmHg, and 49.0 +/- 4.7 mmHg with 0.012, 0.025 and 0.05 mg.kg-1.min-1 ATP respectively. The MAP returned to preinfusion control levels when the ATP infusion was discontinued (90.0 +/- 17.8 mmHg). The DP, and therefore venous return, did not change, neither during ATP infusion, nor after its discontinuation.(ABSTRACT TRUNCATED AT 250 WORDS)