Nitroglycerin and long-acting nitrates

Axillary and subclavian venous spasm during pacemaker implantation - A case report and literature review

Key Clinical Message

Venous spasm is an important reason for complicated or failed implantations of cardiac implantable electronic devices. Prevention or risk reduction of venous spasm during cardiac implantable electronic device implantation may be achieved by ultrasound or fluoroscopic imaging prior to puncture, cephalic vein cut-down, sufficient pre- and perioperative hydration, nitroglycerin injection and effective sedation, and analgesia.

Abstract

This case report with literature review focuses on venous spasm as a potential cause for complicated implantations of cardiac implantable electronic devices. The case report is clinically relevant as it describes a progressive spasm affecting the axillary and the subclavian vein. A 66-year-old female complained of symptomatic atrial fibrillation (AF) and atypical atrial flutter despite interventional and medical treatment. As an ultimate treatment, she was scheduled for pacemaker implantation and atrioventricular node ablation. Several puncture attempts of the axillary vein failed. Despite venous blood aspiration, no guidewires could be advanced into the axillary vein. We performed a first venogram revealing significant spasm of the axillary vein. Another failed venous puncture occurred after change of access site to the subclavian vein. A second venogram displayed progression of the spasm, now affecting both the axillary and the subclavian veins. Normal saline perfusion was administered as well as intravenous isosorbide. Unfortunately, a repeated venogram after 15 min waiting time showed persistence of the spasm, still affecting both veins. The procedure was discontinued as the patient became uncomfortable. Venous spasm is an important reason for complicated or failed implantations of cardiac implantable electronic devices. Commonly used medical prevention and treatment are intravenous fluids and nitroglycerin. Prevention or risk reduction of venous spasm during cardiac implantable electronic device implantation may be achieved by ultrasound or fluoroscopic imaging prior to puncture, cephalic vein cut-down, sufficient pre- and perioperative hydration, nitroglycerin injection and effective sedation and analgesia.

Nitroglycerin trapping in melamine matrices

Melamine (Mel) was used as host matrix for liquid nitroglycerin (NG), to prepare Mel/NG solid powdered compounds containing up to 45 wt% of this explosive. The two preparation processes used for this purpose consisted in evaporating a solution of both components, either in ambient conditions or under reduced pressure by the Spray Flash-Evaporation (SFE) process. In Mel/NG materials, amorphous nitroglycerin is distributed in the crystallized melamine matrix as inclusions, which were found to be smaller in size in the material prepared by the SFE process. Mel/NG materials are not stable over time: they gradually lose the nitroglycerin they contain by evaporation.

Efficacy of prophylactic doses of intravenous nitroglycerin in preventing myocardial ischemia under general anesthesia: A systematic review and meta-analysis with trial sequential analysis

STUDY OBJECTIVE

To evaluate the efficacy of intravenous nitroglycerin (TNG) in preventing intraoperative myocardial ischemia (MI) under general anesthesia. Moreover, we analyzed the hemodynamic changes in heart rate (HR), mean blood pressure (MBP), and pulmonary capillary wedge pressure (PCWP) associated with TNG administration both before and after the induction of anesthesia.

DESIGN

Meta-analysis.

SETTING

Operating room, cardiac surgery or non-cardiac surgery, all surgeries were elective measurements. We performed a computerized search of articles on PubMed, Scopus, and the Cochrane Central Register of Controlled Trials. Meta-analysis was performed using Review Manager. The data from the individual trials were combined using a random-effects model to calculate either the pooled relative risk (RR) or the weighted mean difference (WMD) with 95% confidence interval (CI). We conducted trial sequential analysis (TSA). The primary outcome was the incidence of MI and the secondary outcomes were hemodynamic changes (HR, MBP, and PCWP).

MAIN RESULTS

Using electronic databases, we selected 10 trials with a total of 353 patients for our review. Prophylactic intravenous TNG did not significantly decrease the incidence of MI (RR=0.61; CI, 0.33 to 1.13; P=0.12; I²=55). TSA corrected the CI to 0.05 to 7.39 and showed that 9.5% of the required information size was achieved. In terms of hemodynamic changes, intravenous TNG significantly reduced MBP in comparison with the placebo (MBP pre-induction: WMD=-7.27; 95% CI -14.2 to -0.33; P=0.04; I²=97%; MBP post-induction: WMD=-5.13; 95% CI -9.17 to -1.09; P=0.01; I²=73%).

CONCLUSIONS

Our analyses showed that prophylactic intravenous TNG does not reduce the incidence of intraoperative MI. Moreover, TSA suggests that further studies are necessary to confirm the results (GRADE: very low). Prophylactic doses of intravenous TNG significantly reduced the MBP both pre and post anesthesia induction (GRADE: very low).

Effect of nitric oxide on spinal evoked potentials and survival rate in rats with decompression sickness

Nitric oxide (NO) releasing agents have, in experimental settings, been shown to decrease intravascular nitrogen bubble formation and to increase the survival rate during decompression sickness (DCS) from diving. The effect has been ascribed to a possible removal of preexisting micronuclei or an increased nitrogen washout on decompression through augmented blood flow rate. The present experiments were conducted to investigate whether a short- or long-acting NO donor [glycerol trinitrate (GTN) or isosorbide-5-mononitrate (ISMN), respectively] would offer the same protection against spinal cord DCS evaluated by means of spinal evoked potentials (SEPs). Anesthetized rats were decompressed from a 1-h hyperbaric air dive at 506.6 kPa (40 m of seawater) for 3 min and 17 s, and spinal cord conduction was studied by measurements of SEPs. Histological samples of the spinal cord were analyzed for lesions of DCS. In total, 58 rats were divided into 6 different treatment groups. The first three received either saline (group 1), 300 mg/kg iv ISMN (group 2), or 10 mg/kg ip GTN (group 3) before compression. The last three received either 300 mg/kg iv ISMN (group 4), 1 mg/kg iv GTN (group 5), or 75 μg/kg iv GTN (group 6) during the dive, before decompression. In all groups, decompression caused considerable intravascular bubble formation. The ISMN groups showed no difference compared with the control group, whereas the GTN groups showed a tendency toward faster SEP disappearance and shorter survival times. In conclusion, neither a short- nor long-acting NO donor had any protective effect against fatal DCS by intravenous bubble formation. This effect is most likely due to a fast ascent rate overriding the protective effects of NO, rather than the total inert tissue gas load.

Coronary vasodilation by the use of sublingual nitroglycerin using 64-slice dual-source coronary computed tomography angiography

BACKGROUND

Sublingual nitroglycerin capsules or spray is routinely used to treat anginal attacks and to maximally dilate the epicardial coronary arteries during coronary angiography. These dilated coronary vessels have an advantage, but increased heart rates were disadvantageous for coronary computed tomography angiography (CTA).

PURPOSE

The influence of applying nitroglycerin was analyzed regarding the coronary diameter, coronary luminal attenuation, evaluable number of coronary segments, heart rate (HR), HR variability, the optimal reconstruction phase, and image scoring of CTA in the same patients using a 64-slice dual-source CT.

METHODS AND SUBJECTS

Fifty-two patients with atypical chest pain underwent coronary CTA before and after the administration of sublingual nitroglycerin without heart rate control. The coronary diameter and luminal attenuation were measured on short-axial images in each coronary segment. The coronary vasodilation ratios (VRs) were calculated from the coronary diameters at the same location before and after the use of nitroglycerin. The local institutional review board approved this study and written informed consent was obtained from all the patients.

RESULTS

No significant differences were noted in the HR variability or optimal reconstruction phase, despite an increase in HR after the use of nitroglycerin. Nitroglycerin significantly enlarged the coronary artery diameter, and VRs of each coronary segment ranged from 7.54% to 22.26%. As compared with baseline coronary diameter, VRs of minor segments (16.91%) were significantly larger than those of major segments (11.35%), and the magnitude of VR correlated with the baseline coronary diameter (r=-0.48, p<0.001). Coronary luminal attenuation significantly increased due to additional administration of contrast material after the use of nitroglycerin (p<0.01), but no significant difference was noted in the image quality after the use of nitroglycerin.

CONCLUSION

Sublingual nitroglycerin significantly enlarged the coronary diameters, especially in peripheral small coronary arteries, and increased the evaluable number of coronary segments on coronary CTA.

Noninvasive assessment of coronary vasodilation using magnetic resonance angiography

OBJECTIVES

The purpose of this study was to investigate the use of coronary magnetic resonance angiography (MRA) for assessing human epicardial coronary artery vasodilation.

BACKGROUND

Coronary vasodilation plays a vital role in the human coronary circulation. Previous studies of epicardial coronary vasodilation have used invasive coronary angiography. Coronary MRA may provide an alternative noninvasive method to directly assess changes in coronary size.

METHODS

Thirty-two subjects were studied: 12 patients (age 55 +/- 18 years) and 20 healthy subjects (age 34 +/- 4 years). High-resolution multi-slice spiral coronary MRA (in-plane resolution of 0.52 to 0.75 mm) was performed before and after sublingual nitroglycerin (NTG). Quantitative analysis of coronary vasodilation was performed on cross-sectional images of the right coronary artery (RCA). A time-course analysis of coronary vasodilation was performed in a subset of eight subjects for 30 min after NTG. Signal-to-noise ratio was also measured on the in-plane RCA images.

RESULTS

Coronary MRA demonstrated a 23% increase in cross-sectional area after NTG (16.9 +/- 7.8 mm2 to 20.8 +/- 8.9 mm2, p <0.0001), with significant vasodilation between 3 and 15 min after NTG on time-course analysis. The MRA measurements had low interobserver variability (< or =5%) and good correlation with X-ray angiography (r=0.98). The magnitude of vasodilation correlated with baseline cross-sectional area (r=0.52, p=0.03) and age (r=0.40, p=0.019). Post-NTG images also demonstrated a 31% improvement in coronary signal-to-noise ratio (p = 0.002).

CONCLUSIONS

Nitroglycerin-enhanced coronary MRA can noninvasively measure coronary artery vasodilation and is a promising noninvasive technique to study coronary vasomotor function.

Intraportal administration of glyceryl trinitrate or nitroprusside exerts more systemic than intrahepatic effects in anaesthetised cirrhotic rats

BACKGROUND/AIMS

Increased intrahepatic vascular tone can be pharmacologically manipulated in isolated cirrhotic livers. Intrahepatic endothelial dysfunction may lead to a decreased production of the potent endogenous vasodilator nitric oxide in cirrhotic livers. The aims of the study were to determine whether portal pressure can be lowered in vivo by injecting nitric oxide donors glyceryl trinitrate or nitroprusside directly in the portal vein and whether this is related to a decrease in intrahepatic resistance.

METHODS

In anaesthetised CCl4 cirrhotic rats, intraportal doses of glyceryl trinitrate 0.5, 1 or 5 microg/kg/ min or nitroprusside 1, 5 or 10 microg/kg/min did not decrease portal pressure but only arterial pressure. Systemic and splanchnic haemodynamics were measured before and during 15 min intraportal infusion of glyceryl trinitrate 10 microg/kg/min or nitroprusside 20 microg/kg/min.

RESULTS

Glyceryl trinitrate decreased portal pressure from 14.0+/-1.1 to 11.8+/-1.4 mm Hg, splanchnic perfusion pressure from 102+/-10 to 74+/-5 mm Hg and portal sinusoidal flow from 2.11+/-0.38 to 1.70+/-0.35 ml/min/g liver (all p<0.05). Nitroprusside did not decrease portal pressure significantly but led to a reduction of the splanchnic perfusion pressure (104+/-9 to 66+/-7 mm Hg) and the portal sinusoidal flow (2.39+/-0.50 to 1.77+/-0.31 ml/min/g liver; all p<0.05). Portal sinusoidal resistance was not altered by either drug.

CONCLUSIONS

Intraportal infusion of nitric oxide donors decreased arterial pressure more than portal pressure. Portal sinusoidal resistance remained unaffected, but the liver parenchyma became less perfused with high doses. The systemic effects of nitric oxide donating drugs prevailed.

Effect of chronic nitrate treatment on retinal vessel caliber in open-angle glaucoma

PURPOSE

A recent report has suggested that nitrate therapy may delay the progression of glaucomatous damage. To investigate the mechanism that may mediate this effect, we sought to determine whether nitrate therapy is associated with retinal vasodilatation in patients with glaucoma.

METHODS

Retinal venous and arterial diameters were determined from color fundus photographs of the optic nerve head obtained during a retrospective study designed to investigate any potential effects of chronic nitrate treatment on the progression of glaucomatous pathology. Fourteen eyes of 14 patients who were receiving chronic nitrate therapy for systemic diseases unrelated to glaucoma were randomly selected. Vascular measurements were compared with those of 15 eyes of 15 control patients with glaucoma who did not receive any nitrate therapy.

RESULTS

In comparison with control patients, nitrate-treated patients showed significant average vasodilatation of 17% (P = .008) and 13% (P = .01) in the superior and inferior temporal retinal veins, respectively. A 5% increase in average retinal arterial diameter was also detected, but this was not statistically significant.

CONCLUSION

Chronic nitrate treatment is associated with retinal venous dilatation in patients with glaucoma. Although not assessed in this study, it is possible that a protective effect of nitrates may be mediated by a vasoactive effect leading to improved perfusion of the retina and perhaps the optic nerve head, in a similar fashion to what has been observed in the circulation of the heart. Additional studies of the effect of nitrates on the ocular circulation are needed, however, to support this speculation.

Short-term hemodynamic, anti-ischemic, and antianginal effects of pirsidomine, a new sydnonimine

Pirsidomine is a new sydnonimine compound in clinical development. As a prodrug, it is transformed into a nitric oxide-releasing metabolite in vivo. In animal tests there were no signs of tolerance with repeated administration. The short-term effects of 10, 20, and 40 mg of the drug on pulmonary hemodynamics and ischemic parameters were examined at rest and during exercise in a double-blind, randomized, placebo-controlled study. The study included 48 patients with documented coronary artery disease and exercise-induced ST-segment depression. Compared with the baseline test, there was a reduction of diastolic pulmonary artery pressure with pirsidomine at rest (placebo: -0.4 +/- 0.5 mm Hg; 10 mg: - 1.5 +/- 2.4 mm Hg; 20 mg: - 1.4 +/- 1.1 mm Hg; 40 mg: - 2.3 +/- 1.3 mm Hg [p < 0.05 ]) and at the highest comparable workload (placebo: -2.8 +/- 1.9 mm Hg; 10 mg: -7.3 +/- 6.8 mm Hg; 20 mg: -8.4 +/- 7.9 mm Hg [p <0.05]; 40 mg: -13.8 +/- 7.1 mm Hg [p <0.05]). ST-segment depression decreased at the highest comparable workload (placebo: -0.33 +/- 0.49 mm; 10 mg: -1.33 +/- 1.37 mm [p <0.05]; 20 mg: -1.33 +/- 0.83 mm [p <0.05]; 40 mg: -1.96 +/- 0.86 mm [p <0.05]) and total exercise time increased (placebo: 15 +/- 48 s; 10 mg: 98 +/- 126 s; 20 mg: 165 +/- 251 s [p <0.05]; 40 mg: 155 +/- 174 s [p <0.05]). Of 40 patients who complained of angina pectoris symptoms in the baseline test, 15 became free of angina pectoris with pirsidomine. Compared with placebo, blood pressure, heart rate during exercise, and cardiac output during exercise showed no significant change. Plasma concentration response relations of the metabolite revealed concentrations that caused a half-maximum effect of 6 ng/ml, 13 ng/ml, 20 ng/ml, and 28 ng/ml in reduction of ST-segment depression, reduction of diastolic pulmonary artery pressure, relief of angina pectoris symptoms, and an increase in exercise duration, respectively. Thus, pirsidomine is an effective anti-ischemic and antianginal agent. A significant preload reduction was obtained with plasma metabolite concentrations lower than those necessary to achieve a satisfactory antianginal effect.

Glyceryl trinitrate enhances the adenosine-induced inhibition of platelet responses: a mechanism potentially involved in the in vivo anti-aggregating effects of organic nitrates

1. The present study investigated the influence of the organic nitrate glyceryl trinitrate (GTN) on the anti-aggregating effects of adenosine. We determined the effects of adenosine, GTN and their combination on platelet responses in platelet-rich plasma and whole blood, and on intracellular levels of 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP). 2. Adenosine inhibited the in vitro platelet aggregation in response to different agonists in a dose-dependent way through an elevation of intraplatelet cAMP levels. Effective adenosine concentrations were higher than those detectable under physiological conditions, but very close to levels achieved during myocardial ischaemia or haemorrhagic shock. 3. GTN was able to decrease platelet responses influencing intraplatelet cGMP levels. Furthermore, the drug increased the inhibitory effects of adenosine and enhanced its effects on intraplatelet cAMP levels. 4. The present data provides further evidence that compounds that increase intraplatelet levels of cGMP and cAMP act synergistically on the inhibition of platelet aggregability through the influence of increased cGMP levels on cAMP accumulation. The interplay between GTN and adenosine in the inhibition of platelet function could be effective during nitrate administration in the treatment of acute myocardial ischaemia when blood adenosine levels are significantly increased.

Inhibitory effect of nitroglycerin and sodium nitroprusside on platelet activation across the coronary circulation in stable angina pectoris

This study assessed the inhibitory effect of nitroglycerin and sodium nitroprusside on platelet aggregation in a model of platelet activation across coronary circulation. Platelet aggregation is believed to contribute to the precipitation of acute ischemic syndromes. We previously showed that rapid atrial pacing in patients with stable coronary artery disease (CAD) causes platelet hyperaggregability during blood passage in coronary circulation. Because nitroglycerin and sodium nitroprusside have been shown to inhibit platelet aggregation, we examined the effect of these drugs on this model of platelet activation. During catheterization of 19 patients with CAD (> 50% diameter narrowing of epicardial coronary arteries), we measured platelet aggregation (using whole blood platelet aggregometry) on blood samples obtained simultaneously from the coronary sinus and aorta at rest, and 2 minutes after onset of rapid atrial pacing. This procedure was repeated during an intravenous infusion of either nitroglycerin (n = 9) or sodium nitroprusside (n = 10). There was no arteriovenous difference in platelet aggregation under resting conditions. Atrial pacing caused an increase in platelet aggregation in coronary sinus blood (+64 +/- 9%; p < 0.01), but not in arterial blood (15 +/- 12% decrease; p = NS). This increase was transient and returned toward baseline 10 minutes after termination of pacing. Although resting platelet aggregation was not affected by nitroglycerin or sodium nitroprusside, activation of platelets with atrial pacing across the coronary bed was stopped by pretreatment with therapeutic doses of nitroglycerin or sodium nitroprusside. When coronary blood flow increases in patients with CAD, platelets are activated and aggregate more easily. This activation can be blunted by pretreatment with nitroglycerin or sodium nitroprusside.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of forskolin and organic nitrate on aggregation and intracellular cyclic nucleotide content in human platelets

1. The present study investigated the effect of a combination between forskolin, a naturally occurring diterpene which directly activates adenylyl cyclase, and glyceryl trinitrate (GTN), which enhances intraplatelet cyclic guanosine monophosphate levels, on human platelet aggregation and intracellular content of cyclic nucleotides 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP). 2. Forskolin inhibited, in a dose-dependent way, platelet aggregation in response to collagen and adrenaline in platelet-rich plasma. In whole blood samples, forskolin inhibited collagen-stimulated aggregation. In presence of forskolin the intraplatelet cAMP levels were significantly increased. 3. GTN directly decreased the platelet response to collagen in whole blood samples (IC50 = 122 mumol/l) and it increased the intraplatelet levels of both cGMP and cAMP. 4. GTN at 20 and 40 mumol potentiated the inhibitory effects of forskolin on platelet aggregation in both platelet-rich plasma and whole blood. 5. Our results suggest a synergistic effect of the simultaneous increase of both cAMP and cGMP on the biochemical steps involved in the inhibition of the platelet response.

Phenomenon of nitrate tolerance

The phenomenon of nitrate tolerance has now been appreciated for almost a century, and our understanding of this process has greatly improved during the past 20 years. Therapeutic nitrates are now recognized as exogenous sources of nitric oxide (or nitrosothiols), which appears to be a primary mediator of natural vasodilatation. Nitrates have been clearly shown to have vasodilatory and antiplatelet effects, both of which diminish during continuous exposure. Nitrate tolerance has been documented with most nitrate preparations when the patient is given continuous nitrate therapy. Tolerance to nitrates may occur in any patient, regardless of underlying illness, medication dose, or serum concentration of NTG. The cause of this phenomenon is multifactorial; there appear to be both cellular and systemic processes involved. To date, no adjuvant pharmacologic intervention has conclusively demonstrated benefit in preventing, abating, or reversing nitrate tolerance. Interruption of nitrate exposure for as little as 8 to 12 hours does appear to be the best means of preventing or reversing tolerance. Nevertheless, some patients with objective tolerance continue to experience relief of symptoms. In addition, despite laboratory-documented cross-tolerance, patients receiving continuous nitrate therapy at usual clinical doses may continue to benefit from the hemodynamic and antianginal effects of SL NTG. Hence, nitrate tolerance is a real entity, but the clinical importance of this phenomenon remains controversial. Finally, further investigation will need to address quality-of-life issues and perhaps assess relief of ischemia by other means.

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.

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.

Transcutaneous nitroglycerin in the treatment of erectile dysfunction in spinal cord injured

We have tested the erectile effect of penile applicated nitroglycerin plasters (Transiderm-Nitro 10 mg/24 hours) in 17 spinal cord injured men, who had responded to intracavernous papaverine injections with erections sufficient for vaginal penetration. The nitroglycerin plasters were applied on the skin of the penile shaft and a positive response was obtained in 12 men. A total of 5 men reported an erectile response sufficient for vaginal penetration after using nitroglycerin plasters at home. All 5 preferred to continue with this noninvasive treatment compared to papaverine injections. Our results indicate that men with spinal cord injury who need doses larger than 15 mg papaverine to obtain erection sufficient for vaginal penetration will not achieve this with nitroglycerin plasters. We suggest that this noninvasive treatment should be tested on spinal cord injured men before injection therapy is initiated.

Investigation of a possible pharmacokinetic interaction between ibopamine and isosorbide-5-mononitrate

The possibility of a pharmacokinetic interaction between isosorbide-5-mononitrate (5-ISMN) and epinine, the active metabolite of ibopamine, has been investigated in 8 healthy male subjects given single doses of 200 mg ibopamine and 20 mg 5-ISMN, separately and together. The plasma 5-ISMN concentration-time profile was the same whether 5-ISMN was administered concomitantly with ibopamine or alone [AUC(o-t): 2.24 micrograms.ml-1.h after 5-ISMN alone, 2.16 micrograms.ml-1.h after 5-ISMN+ibopamine]. The plasma concentrations of total and free epinine and the urinary recovery of total epinine, homovanillic acid and dihydroxyphenylacetic acid, too, were not different when ibopamine was administered alone or concomitantly with 5-ISMN. The intake of ibopamine did not change the blood pressure and heart rate. The decrease in diastolic blood pressure induced by 5-ISMN was not influenced by concomitant intake of ibopamine. The observations suggest that in healthy volunteers there is no pharmacokinetic interaction between 5-ISMN and ibopamine.

No evidence of toxicity or carcinogenicity of pentaerythritol tetranitrate given in the diet to F344 rats and B6C3F1 mice for up to two years

Toxicology and carcinogenesis studies of pentaerythritol tetranitrate (PETN), an organic nitrate used in explosives and as a therapeutic agent for angina pectoris, were conducted by administering diets containing PETN,NF (National Formulary Grade, a 1:4 mixture of PETN and lactose) to both sexes of F344 rats and B6C3F1 mice in 14-day, 13-week and 2-year studies. PETN was found to be essentially non-toxic in 14-day and 13-week studies at dietary concentrations as high as 10,000 ppm; the weight gain of female rats was lower than that of controls at 5000 and 10,000 ppm in the 13-week study. In the 13-week studies, one in ten high-dose female rats had an adenoma of the Zymbal gland and one in ten high-dose female mice had a hepatocellular adenoma. Dietary concentrations chosen for the 2-year studies were 5000 and 10,000 ppm for male rats and male and female mice, and 1240 and 2500 ppm for female rats. In the 2-year studies, there were no adverse effects on survival or body weight gains in either sex of rats or mice. No neoplastic or non-neoplastic lesions were considered to be related clearly to PETN administration. Neoplasms of the Zymbal gland occurred at low incidences in PETN-exposed groups of both sexes of rats in the 2-year study.

Effects of nitroglycerin at therapeutic doses on platelet aggregation in unstable angina pectoris and acute myocardial infarction

The platelet aggregation response to adenosine diphosphate (ADP) and to thrombin was quantified in 10 patients, 5 with unstable angina pectoris and 5 with acute myocardial infarction, before, during and after a 45-minute infusion of nitroglycerin. An impedance aggregometer allowing rapid bedside studies in whole blood was used. The reproducibility of the methods was documented to be within 10%. Doses of nitroglycerin were titrated for a 10 mm Hg decrease in mean arterial blood pressure with mean doses being 1.2 +/- 0.2 (standard error of the mean) micrograms/kg/min. Nitroglycerin decreased the area under the aggregation curve induced by ADP from 43 +/- 3.6 to 30 +/- 6.3 cm2 (p = 0.007) and by thrombin from 8.9 +/- 1.7 to 4.1 +/- 0.9 cm2 (p = 0.003). Peak responses to ADP were decreased from 13.3 +/- 1 to 9.1 +/- 1.7 ohms (p = 0.005) and to thrombin from 9.3 +/- 2 to 5.0 +/- 1.2 ohms (p = 0.003). All patients had greater than or equal to 50% inhibition with 1 agent or the other and the inhibition was greater than 50% with each of the 2 aggregating agents in 6 patients. Analyses performed on blood withdrawn 15 minutes after the discontinuation of nitroglycerin showed a return to baseline before nitroglycerin results. When analyses were delayed and performed on blood preserved at room temperature for 30 minutes, no effect of nitroglycerin could be detected. Thus, bedside platelet aggregation studies document a significant and reversible effect of nitroglycerin at therapeutic doses on platelet function.

Nitroglycerin for portal hypertension. A controlled comparison of the hemodynamic effects of graded doses

Nitroglycerin is reportedly an effective treatment for portal hypertension. However, the effects of graded doses have not been examined. We administered nitroglycerin intravenously to 10 patients with alcoholic cirrhosis, beginning at 10 micrograms/min and doubling the dose every 10 min thereafter until mean arterial pressure fell 10-15 mmHg. We compared the response to that of 10 patients receiving a control infusion. The median infusion rate of nitroglycerin was 40 micrograms/min (range 10-160 micrograms/min). Nitroglycerin significantly reduced cardiac output as well as pulmonary artery, pulmonary capillary and mean arterial pressure. The overall effects of nitroglycerin on the hepatic venous pressure gradient and azygous (gastroesophageal collateral) blood flow were heterogeneous. However, the hepatic venous pressure gradient significantly increased in nitroglycerin-treated patients with high pulmonary capillary pressures (greater than or equal to 12 mmHg) compared to control patients with similar cardiac filling pressures at both median and maximum rates of infusion. Nitroglycerin is therefore not a uniformly effective treatment for portal hypertension. Cardiac filling pressure may be a determinant of the splanchnic hemodynamic response to nitroglycerin.

Failure of nitroglycerin and diltiazem to reduce platelet-mediated vasoconstriction in dogs with coronary artery stenosis and endothelial injury: further evidence for thromboxane A2 and serotonin as mediators of coronary artery vasoconstriction in vivo

This study was designed to test the efficacy of nitroglycerin and diltiazem in inhibiting in vivo platelet aggregation and reducing platelet-mediated vasoconstriction in a canine model of coronary artery stenosis and endothelial injury. Coronary artery diameter was measured in vivo by means of ultrasonic crystals sutured on the left anterior descending coronary artery (LAD) immediately distal to an external constrictor (LAD1), 1 cm below (LAD2), and on the left circumflex coronary artery. Coronary diameter was continuously measured before, during cyclic flow variations (progressive declines in blood flow followed by sudden restorations of flow due to recurrent intracoronary platelet aggregation), during cyclic flow variations and intravenous infusion of nitroglycerin (5 micrograms/kg per min) or diltiazem (15 micrograms/kg per min), and after cyclic flow variations were abolished by administration of LY53857, a serotonin receptor antagonist (n = 7), or SQ29548, a thromboxane A2 receptor antagonist (n = 7). During control cyclic flow variations, at the nadir of coronary flow (6% to 11% of the nonstenosed values), LAD1 cross-sectional area decreased by 43 +/- 8% and 44 +/- 3% in the two groups of dogs subsequently treated with LY53857 and SQ29548, respectively. Neither nitroglycerin nor diltiazem caused changes in cyclic flow variation frequency or severity. Furthermore, neither drug significantly reduced the vasoconstriction associated with cyclic flow variations, whereas they significantly increased circumflex artery cross-sectional area. In contrast, LY53857 and SQ29548 were very effective in abolishing cyclic flow variations and the coronary vasoconstriction related to them. Five additional dogs received an intracoronary infusion of nitroglycerin (21 +/- 5 micrograms/kg per min) and later diltiazem (15 micrograms/kg per min).(ABSTRACT TRUNCATED AT 250 WORDS)

The haemodynamic effects of sublingual nitroglycerin spray in severe left ventricular failure

The use of sublingual nitroglycerin spray has been studied in twenty patients referred to our Intensive Care Unit for further treatment of severe left ventricular failure. Within five minutes of spray administration significant falls in pulmonary artery occlusion pressure, mean arterial pressure, heart rate, right atrial pressure and systemic vascular resistance occurred. Similarly significant increases in cardiac index, stroke volume index and left ventricular stroke work index were found. These results show a considerable improvement in the haemodynamic parameters of invasively monitored patients and we believe that its administration undoubtedly "buys time" for the critically ill patient. However, we would caution against its routine use at present in view of the potential problem of hypotension, until further information is available.

Systemic and regional hemodynamic effects of isosorbide dinitrate in patients with liver cirrhosis and portal hypertension

In a group of 17 cirrhotic patients with portal hypertension, we have investigated the effects of 5 mg sublingual administration of isosorbide dinitrate (IDN) on central hemodynamics, on regional (hepatic and renal) hemodynamics and on blood gases. Fifteen min after drug administration, we observed a decrease in the right atrial mean pressure from 4 +/- 1 to 3 +/- 1 mmHg (mean +/- S.E.M., P less than 0.02) and of pulmonary arterial wedge pressure from 7 +/- 1 to 4 +/- 1 mmHg (P less than 0.001) with decreases of the cardiac index from 4.2 +/- 0.2 to 3.7 +/- 0.2 l/min/m2 (P less than 0.001) and the mean arterial pressure from 89 +/- 4 to 72 +/- 3 mmHg (P less than 0.001) and an increase in heart rate from 86 +/- 4 to 94 +/- 5 beats/min (P less than 0.001). Arterial PO2 decreased from 73 +/- 2 to 66 +/- 2 mmHg (P less than 0.001). As a consequence of both cardiac index and arterial PO2 reductions, O2 transport to the tissues was reduced from 602 +/- 32 to 518 +/- 26 ml/min.m2 (P less than 0.001). The hepatic venous pressure gradient decreased from 17 +/- 1 to 14 +/- 1 mmHg (P less than 0.001) and hepatic vein PO2 did not change. The hepatic blood flow (HBF) determined in 7 patients remained unchanged. Renal blood flow (RBF) determined in 5 patients decreased from 0.76 +/- 0.11 to 0.68 +/- 0.11 l/min (P less than 0.001). In conclusion, isosorbide dinitrate reduces portal hypertension in patients with liver cirrhosis without compromising hepatic perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Intravenous administration of isosorbide dinitrate attenuates the pressor response to laryngoscopy and tracheal intubation

In order to evaluate the effect of isosorbide dinitrate (ISDN), administered as a bolus intravenous injection, on the circulatory response to tracheal intubation, mean arterial pressure (MAP), and heart rate (HR) in response to laryngoscopy for 30 s followed by tracheal intubation were compared in patients not receiving ISDN (control) and receiving 40 micrograms/kg or 80 micrograms/kg of ISDN 45 s before starting laryngoscopy. Each group consisted of 10 patients undergoing elective surgery. Forty-five seconds after starting laryngoscopy, MAP was significantly (P less than 0.01) lower in patients receiving 80 micrograms/kg ISDN than in those receiving no or 40 micrograms/kg ISDN. HR increased to a similar extent in the three groups. These results indicate that a bolus injection of ISDN (80 micrograms/kg) is a simple, practical and highly effective means of attenuating the hypertensive response to direct laryngoscopy and tracheal intubation.

Oral nitroglycerin in angina pectoris--evaluation of effect by computerized exercise testing using two different doses

The antianginal effects of sustained-released oral nitroglycerin were evaluated in patients with chronic stable angina using a double-blind randomized protocol. Nineteen patients were inducted into the trial and 17 of these completed the study. Two doses of oral nitroglycerin were used; 2.6 mg and 6.5 mg given three times daily for a period of 2 weeks, the patients crossing over to the alternative dose at the end of each period. Evaluation of effect was carried out 2 hours after the morning dose using graded treadmill exercise testing with on-line computer analysis of the electrocardiogram (EKG) (CASE, Marquette Electronics, Inc.). Various exercise parameters were measured and the results compared to placebo values and between the two dosages. The aim was to demonstrate an antianginal effect and to look for a dose-response relationship and for attenuation of effect if any on continued administration. The mean +/- SEM exercise time on placebo was 6.7 +/- 0.6 min, increasing to 8.6 +/- 8 min (p less than 0.02) with 2.6 mg tds dosage and 8.4 +/- 0.7 min (p less than 0.01) with 6.5 mg tds of oral nitroglycerin. None of the other exercise-derived indices were altered significantly by oral nitroglycerin. Two patients were withdrawn because of severe headaches and both were receiving the higher dose. The data did not demonstrate any dose-response relationship but confirmed the anti-anginal efficacy of sustained action oral nitroglycerin. This efficacy did not show any significant attenuation of effect on continued administration, indicating a possible lack of development of tolerance.

Review: the pharmacological control of variceal bleeding

The haemodynamic effects and clinical uses of drugs used in the management of patients with oesophageal variceal bleeding are reviewed. Vasoconstrictor agents (vasopressin, teripressin) alone or in combination with nitrates continue to be used for acute bleeding episodes, while somatostatin is an alternative. Alpha- and beta-adrenergic blocking drugs and vasodilators which lead to a sustained decrease in portal pressure can be used for the prevention of bleeding episodes, but despite numerous studies the pharmacological treatment of variceal bleeding remains controversial.

Platelets, vasoconstriction, and nitroglycerin during arterial wall injury. A new antithrombotic role for an old drug

Endothelial injury in vivo is associated with platelet deposition and a localized platelet-dependent vasoconstrictive response. To assess the influence of nitroglycerin on platelets and vasoconstriction, quantitative 111In-labeled platelet deposition (no platelets x 10(6)/cm2) of the injured segment and the degree of angiographic vasoconstriction (percent diameter narrowing proximal and distal to the dilated segment) produced during injury by balloon angioplasty of the common carotid arteries were studied in heparinized normal pigs that were sacrificed immediately after the procedure. In deeply injured (injury extending through the internal elastic lamina) compared with mildly injured (deendothelialization only) arteries, there was both greater platelet deposition (63.8 vs. 6.9, p = 0.04) and more vasoconstriction (30% vs. 19%, p = 0.02). In the presence of deep arterial wall injury, nitroglycerin given intravenously at a dose sufficient to lower mean arterial pressure by 9 +/- 2% significantly decreased both platelet deposition (16.2 vs. 63.8, p less than 0.008) and the vasoconstrictive response (20 vs. 30%, p less than 0.02) relative to control. However, in the presence of mild arterial wall injury, nitroglycerin decreased vasoconstriction relative to control (10% vs. 19%, p less than 0.01) without causing a significant decrease in the already low level of platelet deposition (5.6 vs. 6.9, respectively; p = NS), suggesting a direct smooth muscle relaxant effect of nitroglycerin. This is the first reported in vivo effectiveness of nitroglycerin in the reduction of platelet deposition after deep arterial injury.

Emergency treatment of severe cardiogenic pulmonary edema with intravenous isosorbide-5-mononitrate

Intravenous isosorbide-5-mononitrate (IS-5-MN) was administered to 24 patients, mean age 73, with severe respiratory distress after pulmonary edema and acute left heart failure. The condition was due to ischemic cardiopathy in 18 patients (4 with acute myocardial infarctions), congestive cardiomyopathy in 3, hypertensive cardiopathy in 2, and mitral valvular disease in 1. Therapy consisted of an intravenous (i.v.) bolus dose of IS-5-MN, followed by a continuous infusion (mean 8 mg/hour over 24 hours) of i.v. furosemide and additional oxygen. Clinical data were recorded as well as blood gas values and repeated chest radiographs. All patients survived and improved markedly; only 6 needed mechanical ventilation. Most patients had fast respiratory relief, with no untoward reaction, except a brief decrease of blood pressure in a ventilated patient taking morphine. These data indicate that i.v. IS-5-MN is effective and safe for the management of severe acute cardiogenic pulmonary edema.

Bay K 8644-induced changes in the ECG pattern of the rat and their inhibition by antianginal drugs

1. The effects of intracarotid administration of Bay K 8644 on the ECG pattern along with their reversal by antianginal drugs were investigated in anaesthetized rats. 2. Intracarotid injections of Bay K 8644 (0.5-50.0 micrograms kg-1) produced a dose-related transient increase in systemic blood pressure. 3. The pressor response was accompanied by ST segment elevation (0.5-10.0 micrograms kg-1), ST segment depression concomitant with the occurrence of arrhythmias (20.0 micrograms kg-1), or A-V block (50.0 micrograms kg-1). 4. ST segment elevation reached its maximal value within 15 s and could be observed for 30-240 s. 5. The increase in blood pressure was immediate (within 5 s) and short lasting (30-120 s). After the initial increase it returned to control levels (0.5-20.0 micrograms kg-1) or dropped below (50.0 micrograms kg-1). 6. The ST segment elevation caused by 5.0 micrograms kg-1 Bay K 8644 (submaximal dose) was blocked by antianginal drugs (e.g. nitroglycerin, nifedipine and diltiazem) and by the peripheral benzodiazepine receptor antagonist PK 11195. However, the pressor response was not blocked by any of the drugs used. 7. ST segment elevation (or depression) induced by intracarotid administration of Bay K 8644 provides a useful tool for the evaluation of potential antianginal drugs.

In vivo induction and reversal of nitroglycerin tolerance in human coronary arteries

The mechanism by which tolerance to the clinical effects of organic nitrates develops has not been elucidated. This study was done to determine whether an intravenous infusion of nitroglycerin induces tolerance in the coronary vascular bed and whether such tolerance is reversed by the sulfhydryl-group donor N-acetylcysteine. We studied 19 subjects--17 with coronary artery disease and 2 without it--who had a mean age (+/- SD) of 54 +/- 9 years. Coronary sinus blood flow, which approximates blood flow to the left ventricle, was measured before and during intracoronary injections of nitroglycerin (10, 25, 50, and 100 micrograms). The patients then received a 24-hour intravenous infusion of saline (n = 7) or of nitroglycerin, 45 +/- 13 micrograms per minute (n = 12), after which the responses of coronary sinus flow to the same doses of intracoronary nitroglycerin used earlier were measured. In the seven patients given saline, the four doses of intracoronary nitroglycerin caused similar percentage increases in coronary sinus flow before and after the saline infusion. In the 12 patients given intravenous nitroglycerin, the four intracoronary doses caused percentage increases in coronary flow before the infusion of 30 +/- 9, 35 +/- 14, 41 +/- 12, and 52 +/- 15, respectively. After the infusion, the same doses of nitroglycerin caused smaller (P less than 0.05) percentage increases (16 +/- 6, 21 +/- 11, 23 +/- 12, and 27 +/- 11, respectively), indicating the development of partial tolerance. Subsequently, 7 of the 12 patients received N-acetylcysteine, after which intracoronary nitroglycerin caused percentage increases in coronary sinus flow similar to the values measured before the intravenous nitroglycerin was given (34 +/- 13, 32 +/- 8, 38 +/- 11, and 44 +/- 16, respectively). We conclude that the coronary vasodilator effect of nitroglycerin is attenuated by an intravenous infusion of nitroglycerin (that is, partial tolerance develops) and that tolerance to the agent can be reversed by administration of the sulfhydryl-group donor N-acetylcysteine. The mechanism by which N-acetylcysteine reverses tolerance will require further investigation.

Hemodynamic effects of intravenous isosorbide dinitrate and nitroglycerine in acute myocardial infarction and elevated pulmonary artery wedge pressure

We compared in a randomized fashion the hemodynamic effects of intravenous (IV) isosorbide dinitrate (ISDN) and nitroglycerine (NTG) in 45 patients with acute myocardial infarction and elevated pulmonary artery wedge pressure (Paw). Titration of ISDN dose to lower Paw greater than or equal to 25 percent resulted in a fall of this parameter from 32 +/- 8 to 24 +/- 5 mm Hg and was associated with a fall in mean blood pressure (96 +/- 15 to 90 +/- 14 mm Hg, p less than 0.05), systemic vascular resistance (1715 +/- 572 to 1548 +/- 414 dynes X s X cm-5, (p less than 0.05), pulmonary vascular resistance (182 +/- 106 to 154 +/- 78 dynes X s X cm-5, p less than 0.05) and mean right atrial pressure (11 +/- 4 to 7 +/- 4 mm Hg, p less than 0.05). In addition, ISDN significantly (p less than 0.05) increased cardiac index from 2.37 +/- 0.54 to 2.54 +/- 0.59 L/min/m2, stroke volume index from 28 +/- 8 to 31 +/- 8 ml/m2, and stroke work index from 28 +/- 11 to 31 +/- 12 g X m/m2. The ISDN dose ranged from 50 to 533 micrograms/min (mean +/- SD 326 +/- 176 micrograms/min) and could not be predicted from baseline hemodynamic values. A comparison between the effect of ISDN and NTG in doses producing comparable reduction in Paw showed similar hemodynamic changes. It was concluded that IV ISDN in patients with elevated mean pulmonary artery wedge pressure due to acute myocardial infarction results in a decrease in right and left ventricular preload and afterload and improvement of cardiac output and cardiac work. The effective dose ranges from 50 to 533 micrograms/min and cannot be predicted from baseline hemodynamic values. In doses producing comparable reduction in Paw, ISDN and NTG had similar hemodynamic effects.

Coronary vasodilation by nitrates is not mediated by the prostaglandin system: a quantitative cineangiographic study

The possible role of prostaglandins in mediating large coronary artery vasodilation by nitrates was investigated by quantitative magnification coronary angiography. The effects of aspirin (1 g systemically and 100 mg intracoronary) in preventing large coronary artery vasodilation induced by intracoronary isosorbide dinitrate was investigated in 16 patients. Of these, 5 received 0.3 mg (Group 1A) and 11 received 3 mg (Group 1B) intracoronary isosorbide dinitrate, before and 15 minutes after aspirin. Relative to control, 0.3 mg isosorbide dinitrate induced a 19 +/- 9% (mean +/- SD) (p less than 0.01) and 19.5 +/- 11% (p less than 0.01) increase in coronary diameter before and after aspirin, respectively (p = NS). Changes after 3 mg isosorbide were 23 +/- 12% (p less than 0.01) and 26.5 +/- 14% (p less than 0.01), respectively, before and after aspirin (p = NS). In 10 additional patients (Group 2), the effect of the same dose of aspirin on rest coronary artery tone was assessed: changes relative to control were 0.9 +/- 5.5% (p = NS) minutes after aspirin. The intracoronary administration of 3 mg isosorbide dinitrate produced a 24.7 +/- 11% increase in coronary diameter (p = NS versus pre- and postaspirin isosorbide in Group 1B). Urinary 6-ketoprostaglandin-F1 alpha values in urine samples collected in the 8 hours before and the 8 hours after the study in five patients in Group 1B and five patients of Group 2, revealed a 36 +/- 14% (mean +/- SD) reduction in excretion of prostacyclin (p less than 0.01). These data rule out a role for prostaglandins both in mediating dilation of large coronary arteries by nitrates and in affecting their vascular tone at rest.

Current perspectives in treatment of angina pectoris

The most appropriate treatment for a patient with angina pectoris depends on the underlying pathophysiologic process and whether any associated illness is present. Each patient's clinical history must be carefully reviewed so the hemodynamic process responsible for the clinical picture is understood. If symptoms are produced mostly by an increase in myocardial oxygen demand, efforts should be directed toward reducing the demand or improving coronary blood flow to meet the demand. If symptoms appear to occur secondary to vasospasm, treatment should be directed toward relief of spasm with potent vasodilating agents, such as calcium channel blockers. Most patients have a clinical picture consistent with mixed angina and may require combination therapy. Treatment of associated illnesses and the safety of pharmacologic agents used in their presence should be carefully considered. Finally, if treatment is to successfully reduce the incidence of serious cardiac events and prolong life, the goal of therapy should be relief of the total ischemic burden on the heart.

Comparison of transdermal nitrate and isosorbide dinitrate in chronic stable angina

The effects of transdermal nitrate (TN) (Transiderm-Nitro TTS, Geigy Pharmaceuticals, one 10 cm2 patch daily) and oral isosorbide dinitrate (ISDN) (Sorbitrate, Stuart Pharmaceuticals, 10 mg three times daily) were compared in a group of 20 patients with chronic stable angina pectoris. Treadmill exercise duration was prolonged from a median time of 365 s to 428 s after ISDN (P less than 0.05), but was unchanged after TN. The difference between the active treatments was not significant. Weekly consumption of glyceryl trinitrate (GTN) increased during treatment with TN from a median value of 5.5 to 6.3 (P less than 0.05). A decrease was observed after ISDN (7.8 to 3.9, P = NS), and the difference between the drugs was significant (P less than 0.01). Systolic arterial pressure was significantly lower during the ISDN than during the TN treatment period in both the supine (135 +/- 5 vs 128 +/- 5 mm Hg; P less than 0.05) and standing positions (134 +/- 5 vs 122 +/- 5 mm Hg; P less than 0.05). No change in weekly attack rate, the degree of ST depression at angina on treadmill testing, or the number of episodes of ST depression recorded during a 24 h period by Holter monitoring was observed after either drug. In this study, an antianginal effect was demonstrated for ISDN but not for TN. It is suggested that the dose of TN may have been inadequate to demonstrate such an effect, and further studies using a higher dose schedule will be required.

Pharmacokinetics of pentaerythritol tetranitrate following intra-arterial and oral dosing in the rat

The pharmacokinetics of pentaerythritol tetranitrate (2,2-bis(hydroxymethyl)-1,3-propanediol tetranitrate, 1) were studied in rats following a single intra-arterial or oral dose (2 mg/kg) of the 14C-labeled drug. Blood levels of the tetranitrate and its metabolites were determined using a thin-layer radiochromatographic procedure. The apparent systemic clearance of 1 was 0.61 +/- 0.16 L/min/kg (mean +/- SD, n = 6) which exceeded the value of normal cardiac output in rats. The steady-state volume of distribution was 4.2 +/- 1.1 L/kg (n = 6), and the elimination half-life was estimated at 5.8 +/- 0.6 min (n = 6). Blood levels of 1 were only detectable (higher than 4.0 ng/mL) in three of the six rats examined after the oral dose. The trinitrate derivative (2,2-bis(hydroxymethyl)-1,3-propanediol trinitrate, 2) the active metabolite of 1, was not detectable following oral dosing with the tetranitrate. The oral bioavailability of 1 was in the range of 0-8%. In spite of the low water solubility of 1 (i.e., 1 microgram/mL), a rather high fraction of the radioactive oral dose [25.7 +/- 10.3% (n = 4) versus 62.4 +/- 14.5% (n = 4) from the intra-arterial dose] was recovered in the urine. A significant portion of the intra-arterial dose (32.7 +/- 11.0%, n = 4) was eliminated in feces, indicating enterohepatic recycling of radioactivity. Analysis of the metabolite pattern in urine indicated extensive metabolism of 1, 2, and the dinitrate derivative 3 (2,2-bis(hydroxymethyl)-1,3-propanediol dinitrate). Less than 0.2% of the dose was recovered as unchanged drug and 2 following either route of administration.

Isosorbide dinitrate in experimental portal hypertension: a study of factors that modulate the hemodynamic response

Isosorbide dinitrate, a long-acting vasodilator, has been tested in human portal hypertension with conflicting results. In order to determine some of the factors that could affect the individual response to this drug, we infused isosorbide dinitrate at a low dose (10 to 25 micrograms per kg per min) and a high dose (100 micrograms per kg per min) to rats with portal vein stenosis. Under pentobarbital anesthesia, portal pressure was measured with an ileocolic vein catheter while cardiac output and regional blood flows were measured with the microsphere technique. At a dose that decreased arterial pressure by approximately 10%, cardiac output remained unchanged while portal vein inflow decreased significantly; portal pressure was not reduced (10.7 +/- 0.2 vs. 10.0 +/- 0.3 mm Hg), indicating a rise in portal vascular resistance. At a high dose of isosorbide dinitrate, arterial pressure and cardiac output fell markedly; portal pressure decreased only modestly (11.3 +/- 0.3 vs. 9.8 +/- 0.6 mm Hg, p less than 0.05), but portal flow was unchanged, indicating a reduction in portal vascular resistance. In addition, portal hypertensive rats received a constant i.v. infusion of N-acetyl-cysteine; the combination of the latter and isosorbide dinitrate markedly potentiated the effects on arterial pressure. Thus, the dose of the drug and the presence of cysteine-containing compounds appear to modulate the hemodynamic response to isosorbide dinitrate. Clinical testing with this drug should be undertaken with consideration of these factors.

Potentiation of nitroglycerin-induced coronary dilatation by N-acetylcysteine

Previous studies have suggested that (1) nitroglycerin causes vasodilatation by interacting with sulfhydryl groups in vascular smooth muscle, thereby activating guanylate cyclase and increasing the intracellular concentration of cyclic GMP, and (2) N-acetylcysteine, a source of sulfhydryl groups, potentiates the peripheral vasodilatory effect of nitroglycerin. This study was performed to explore the influence of N-acetylcysteine on nitroglycerin-induced coronary dilatation. In 18 patients (13 men and five women, 30 to 76 years old), coronary sinus blood flow (by thermodilution) was measured before and during intracoronary administration of nitroglycerin, 25 micrograms, both before and 5 min after a 15 min intravenous infusion of (1) 5% dextrose in water (n = 8, control) or (2) 100 mg/kg N-acetylcysteine (n = 10). Nitroglycerin caused no change in heart rate or systemic arterial pressure. In the control patients, coronary sinus blood flow behaved similarly during the two injections: it was 134 +/- 36 ml/min (mean +/- SD) before and 183 +/- 50 ml/min during injection No. 1 (average increase, 49 +/- 25 ml/min; average percent increase, 38 +/- 21%); and it was 131 +/- 34 ml/min before and 178 +/- 45 ml/min during injection No. 2 (average increase, 47 +/- 23 ml/min; average percent increase, 37 +/- 20%) (NS compared with injection 1). In the patients who received N-acetylcysteine, coronary sinus blood flow was 149 +/- 48 ml/min before and 191 +/- 54 ml/min during injection 1 (average increase, 42 +/- 15 ml/min; average percent increase, 30 +/- 12%) (NS compared with eight control values).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacology of the nitrates in angina pectoris

Nitrate therapy is the oldest treatment modality for angina pectoris. In addition to sublingual nitroglycerin, longer-acting preparations are available to provide angina prophylaxis. Nitrates work as venodilators and arterial dilators, and by these actions in patients with angina pectoris can reduce myocardial oxygen demands while maintaining or increasing coronary artery flow. On the cellular level, they may increase endothelial prostacyclin release to cause their vasodilating effects. Long-acting nitrates are available in sublingual, chewable, oral, buccal and topical forms. The topical forms include nitroglycerin paste and transcutaneous patches. Long-acting nitrates have a duration of action of 2 to 24 hours, depending on the preparation used. The transcutaneous patches, which provide the longest duration of activity, are being reexamined regarding long-term efficacy and drug tolerance. Nitrates are also available in an intravenous form and in a short-acting sublingual spray soon to be released. The safety of nitrates has been confirmed. Their hemodynamic and safety profiles allow them to be combined with calcium-channel blockers, beta-adrenergic blockers or both when trying to improve on the antianginal efficacy of single-drug therapy.

The effects of sublingually administered nitroglycerin on forearm vascular resistance in patients with heart failure and in normal subjects

This study examined the effects of sublingually administered nitroglycerin on forearm resistance vessels in normal subjects (n = 9) and in patients with congestive heart failure (n = 8). Forearm blood flow was measured with a strain-gauge plethysmograph and forearm vascular resistance was calculated. To assess the magnitude of reflex forearm vasoconstriction triggered by decreased central venous pressure after sublingual nitroglycerin, lower body negative pressure (LBNP) was applied to produce a comparable decrease in central venous pressure to that after nitroglycerin. The change in forearm vascular resistance during LBNP was compared with that after nitroglycerin. In normal subjects, LBNP increased but nitroglycerin did not change forearm vascular resistance. In patients with congestive heart failure neither nitroglycerin nor LBNP changed forearm vascular resistance. The direct vasodilator effect of nitroglycerin on forearm resistance vessels assessed by the difference between the change in forearm vascular resistance produced by nitroglycerin and that during LBNP tended to be less in patients with congestive heart failure than in normal subjects, which might have resulted from decreased vasodilator capacity of resistance vessels in patients with congestive heart failure. Changes in forearm vascular resistance with a cold pressor test were not different between normal subjects and patients with congestive heart failure. These data suggest that in normal subjects, nitroglycerin does not alter forearm vascular resistance because its dilator effect is offset by reflex vasoconstriction. In patients with congestive heart failure, reflex vasoconstriction is impaired but the direct vasodilator effect of nitroglycerin also tends to be reduced, so that as a net effect forearm vascular resistance is not altered.

Nitrates and endothelial prostacyclin production: studies in vitro

The hypothesis that nitrates evoke prostacyclin production by vascular endothelium has been reevaluated on cultured umbilical vein endothelial cells and in vascular fragments, both obtained from humans. Endothelial cell monolayers (passages 1 and 2) were washed free of culture medium and exposed for 3 to 5 min to buffer or nitroglycerin (NTG), isosorbide dinitrate (ISDN), or isosorbide-5-mononitrate (ISMN) over a range of concentrations (10(-9)M to 10(-6)M) encompassing those usually attained in vivo, with or without 25 microM sodium arachidonate. Basal prostacyclin production, measured by radioimmunoassay of the stable metabolite 6-keto-PGF1 alpha, depended on cell density in the endothelial monolayer (being higher in preconfluent cultures) and on incubation time. Basal prostacyclin, however, was not altered by incubation with NTG (3.3 +/- 2.0 pg/1000 cells without drug vs 3.9 +/- 3.8 pg/1000 cells with drug, mean +/- SD), ISDN (3.1 +/- 1.9 vs 3.1 +/- 2.2), or ISMN (2.0 +/- 0.9 vs 2.3 +/- 1.5) at 10(-7)M (all differences NS). Also, long-term incubation (2, 6, and 24 hr) with ISDN and ISMN did not alter prostacyclin production over control. Over a 30-fold increase (p less than .001) in prostacyclin production was obtained with arachidonate stimulation, but incubation with nitrates did not significantly modify the stimulated production. Saphenous vein, mesenteric artery, and atrial appendage fragments incubated at 37 degrees C for 20 min in a shaking water bath with a control buffer produced 27.8 +/- 13.9, 189.7 +/- 75.2, and 662.3 +/- 390.6 pg 6-keto-PGF1 alpha/mg tissue, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)