Pharmacology of nitroglycerin and long-acting nitrates

Hydrogel encapsulating gold nanoparticles for targeted delivery of nitroglycerin to reduce post-cardiac dysfunction inflammation by inhibiting the Wnt/β-catenin signaling pathway

The discovery of nitric oxide's role in biological processes like platelet function, vasodilation, cell permeability, and inflammation has advanced our understanding of organic nitrate therapy's hemodynamic and nonhemodynamic effects. Short-term use of organic nitrates prevents left ventricular enlargement and infarct expansion. However, information on their long-term impact on LV remodeling in post-acute cardiac dysfunction patients is limited. In this study, we utilized an innovative active hydrogel with gelatin (Gel)/polyethylene glycol (PEG)/polylactic acid (PLA) encapsulating gold nanoparticles (AuNPs)-based drug delivery system for the sustained release of nitroglycerin (NTG). Gel/PEG/PLA/NTG/AuNPs hydrogel-based system is a non-transplant surgical method that can adhere to the surface of the heart and deliver the drug directly to the epicardium. Cardiac dysfunction was induced by ligating the left anterior descending coronary artery. Echocardiograms were used to study the pre- and post-operative hemodynamics. Hematoxylin and eosin (H&E) and Masson's trichrome stain (MTS) staining revealed that the acute myocardial infarction (AMI) rats' group had irregularly shaped fibers and a lack of transverse striations, whereas Gel/PEG/PLA/NTG/AuNPs hydrogel group showed significant improvement. Rats in the Gel/PEG/PLA hydrogel group demonstrated marked vasodilation, compared to the AMI group. Mechanistically, we determined that hydrogel disrupts the initiation of post-cardiac dysfunction via inhibiting Wnt/β-catenin transcriptional activation. Hence, the Gel/PEG/PLA/NTG/AuNPs hydrogel group effectively protected against ischemic injury and inflammation in AMI, demonstrating a novel method for treating acute cardiac dysfunction.

Anaesthetic considerations for impacted fetal head at caesarean delivery: a focused review

BACKGROUND

Impacted fetal head occurs when the fetal head is deeply engaged within the maternal pelvis and difficult to deliver during caesarean delivery. In order to deliver the fetal head, additional surgical manoeuvres and/or pharmacological tocolysis are needed. The aim of this focused review is to outline the incidence, risk factors, management and complications of this obstetric emergency from the perspective of the anaesthetist.

METHODS

Databases were searched for free text headings and subject headings associated with different permutations of terms related to impacted fetal head and caesarean delivery.

RESULTS

Impacted fetal head has been estimated to occur in 1.5 % of elective caesarean deliveries and 2.9-18.4% of all emergency caesarean deliveries at any cervical dilatation. Risk factors include advanced cervical dilatation, labour augmentation with oxytocin, prolonged second stage of labour, fetal malposition and junior grade of operating obstetrician. If impacted fetal head occurs, the anaesthetist in conjunction with the multidisciplinary team should consider decreasing the height of the operating table, providing a step for the obstetrician to stand on, placing the patient in the head down position, providing pharmacological tocolysis with glyceryl trinitrate (or nitroglycerin), beta-2 adrenoreceptor agonists or volatile anaesthetic agents, and managing complications such as postpartum haemorrhage.

CONCLUSION

Impacted fetal head is an obstetric emergency that the anaesthetist should be familiar with and has a vital role in managing. We propose an algorithm for management that may serve as a clinical decision aid.

Impacted fetal head at cesarean delivery

PURPOSE

Impacted fetal head (IFH) can be defined as the deep engagement of the fetal head in the maternal pelvis at the time of cesarean delivery that leads to its difficult or impossible extraction with standard surgical maneuvers. In this narrative review, we aimed to ascertain its incidence, risk factors, management and complications from the perspective of the anesthesiologist as a multidisciplinary team member.

METHODS

Databases were searched from inception to 24 January 2023 for keywords and subject headings associated with IFH and cesarean delivery.

RESULTS

IFH has an incidence of 2.9-71.8 % in emergency cesarean section. Maternal risk factors are advanced cervical dilatation, second stage of labor and oxytocin augmentation. Anesthetic and obstetric risk factors include epidural analgesia and trial of instrumental delivery and junior obstetrician, respectively. Neonatal risk factors are fetal malposition, caput and molding. Current evidence indicates a lack of confidence in the management of IFH across the multidisciplinary team. Simple interventions in IFH include lowering the height or placing the operating table in the Trendelenburg position, providing a step for the obstetrician and administering pharmacological tocolysis. Maternal complications are postpartum hemorrhage and bladder injury while neonatal complications include hypoxic brain injury, skull fracture and death. Surgical complications are reviewed to remind the anesthesiologist to anticipate and prepare for potential problems and manage complications in a timely manner.

CONCLUSION

The anesthesiologist has a fundamental role in the facilitation of delivery in IFH. We have proposed an evidence based management algorithm which may be referred to in this emergency situation.

Molecular Mechanisms of Migraine: Nitric Oxide Synthase and Neuropeptides

Migraine is a common condition with disabling attacks that burdens people in the prime of their working lives. Despite years of research into migraine pathophysiology and therapeutics, much remains to be learned about the mechanisms at play in this complex neurovascular condition. Additionally, there remains a relative paucity of specific and targeted therapies available. Many sufferers remain underserved by currently available broad action preventive strategies, which are also complicated by poor tolerance and adverse effects. The development of preclinical migraine models in the laboratory, and the advances in human experimental migraine provocation, have led to the identification of key molecules likely involved in the molecular circuity of migraine, and have provided novel therapeutic targets. Importantly, the identification that vasoconstriction is neither necessary nor required for headache abortion has changed the landscape of migraine treatment and has broadened the therapy targets for patients with vascular risk factors or vascular disease. These targets include nitric oxide synthase (NOS) and several neuropeptides that are involved in migraine. The ability of NO donors and infusion of some of these peptides into humans to trigger typical migraine-like attacks has supported the development of targeted therapies against these molecules. Some of these, such as those targeting calcitonin gene-related peptide (CGRP), have already reached clinical practice and are displaying a positive outcome in migraineurs for the better by offering targeted efficacy without significant adverse effects. Others, such as those targeting pituitary adenylate cyclase activating polypeptide (PACAP), are showing promise and are likely to enter phase 3 clinical trials in the near future. Understanding these nitrergic and peptidergic mechanisms in migraine and their interactions is likely to lead to further therapeutic strategies for migraine in the future.

Regional cerebral perfusion during the premonitory phase of triggered migraine: A double-blind randomized placebo-controlled functional imaging study using pseudo-continuous arterial spin labeling

OBJECTIVE

To identify changes in regional cerebral blood flow (CBF) associated with premonitory symptoms (PS) of nitroglycerin (NTG)-triggered migraine attacks.

BACKGROUND

PS could provide insights into attack initiation and alterations in neuronal function prior to headache onset.

METHODS

We undertook a functional imaging study using a double-blind placebo-controlled randomized approach in patients with migraine who spontaneously experienced PS, and in whom PS and migraine-like headache could be induced by administration of NTG. All study visits took place in a dedicated clinical research facility housing a monitoring area with clinical beds next to a 3Tesla magnetic resonance imaging scanner. Fifty-three patients with migraine were enrolled; imaging on at least one triggered visit was obtained from 25 patients, with 21 patients completing the entire imaging protocol including a placebo visit. Whole brain CBF maps were acquired using 3D pseudo-continuous arterial spin labeling (3D pCASL).

RESULTS

The primary outcome was that patients with migraine not taking preventive treatment (n = 12) displayed significant increases in CBF in anterior cingulate cortex, caudate, midbrain, lentiform, amygdala and hippocampus (p < 0.05 family-wise error-corrected) during NTG-induced PS. A separate region of interest analysis revealed significant CBF increases in the region of the hypothalamus (p = 0.006, effect size 0.77). Post hoc analyses revealed significant reductions in CBF over the occipital cortices in participants with a history of migraine with underlying aura (n = 14).

CONCLUSIONS

We identified significant regional CBF changes associated with NTG-induced PS, consistent with other investigations and with novel findings, withstanding statistical comparison against placebo. These findings were not present in patients who continually took preventive medication. Additional findings were identified only in participants who experience migraine with aura. Understanding this biological and treatment-related heterogeneity is vital to evaluating functional imaging outcomes in migraine research.

Bioenzyme-responsive L-arginine-based carbon dots: the replenishment of nitric oxide for nonpharmaceutical therapy

Nitric oxide (NO) is a short-lived, bioactive gas that has been found to have affinitive effects on cardiovascular diseases as well as cancer biology, while NO deficiency may cause serious pathological responses. The existing chemically-synthesized NO donors have inevitable systemic toxicity and cannot be released adaptively. Hence, L-arginine, an endogenous NO precursor, merits investigation as a natural efficient NO donor. Herein, we designed amino acid-doped L-arginine CDs-based bioenzyme-responsive NO donors, which could adaptively replenish NO/ONOO^- in response to different microenvironments. Our results indicated the mechanism of the NO/ONOO^- supplementation of L-arginine-based CDs and their potential for nonpharmaceutical gas-involving theranostics for the first time.

Are some patient-perceived migraine triggers simply early manifestations of the attack?

OBJECTIVE

To study the agreement between self-reported trigger factors and early premonitory symptoms amongst a group of migraineurs in both spontaneous and pharmacologically provoked attacks.

METHODS

Fifty-three subjects with migraine with and without aura, with ≤ 22 headache days/month, with spontaneous premonitory symptoms associated with migraine attacks were recruited nationally. A detailed history was taken by a study investigator to confirm diagnosis and extended phenotyping was performed to identify patient-reported triggers for migraine attacks, premonitory symptom phenotype and headache characteristics, using a standardised physician-administered questionnaire. The same subjects were exposed to a 0.5 mcg/kg/min nitroglycerin infusion over 20 min, to determine if similar migraine symptoms could be triggered. The triggered attacks were phenotyped in the same way as spontaneous ones. Percentage agreement and Cohen's kappa measure of agreement were used to identify concordance between patient-reported triggers and the corresponding spontaneous and triggered premonitory symptoms. Percentage agreement of > 60% and/or a kappa value > 0.3 with P < 0.05 were considered significant.

RESULTS

There was statistically significant agreement between perception of light as a migraine trigger and spontaneous premonitory photophobia; perception of sound as a trigger and triggered premonitory phonophobia; skipping meals as a trigger and spontaneous premonitory food cravings; and food triggers and spontaneous premonitory food cravings. There was good agreement between stress and premonitory triggered mood change.

CONCLUSIONS

At least some patient-reported triggers, such as light, sound, foods and skipping meals, may represent early brain manifestations of the premonitory phase of the migraine attack.

Headache and non-headache symptoms provoked by nitroglycerin in migraineurs: A human pharmacological triggering study

Background

Studying a spontaneous migraine attack is challenging, particularly the earliest components. Nitroglycerin is a potent, reliable and reproducible migraine trigger of the entirety of the migraine attack, making its use experimentally attractive.

Methods

Fifty-three subjects with migraine with a history of spontaneous premonitory symptoms were exposed to a 0.5 mcg/kg/min nitroglycerin infusion. Eighty-three percent (n = 44) developed typical premonitory and headache symptomatology. Fifty-seven percent (n = 25) were invited back to further study visits, during which they were re-exposed to nitroglycerin or placebo infusion in a double-blind randomised design. The phenotype of premonitory symptoms and headache was captured and compared to spontaneous attacks and between triggered attacks using agreement analysis.

Results

More premonitory symptoms were triggered with nitroglycerin than placebo (mean symptom difference = 4, t₂₀ = 7.06, p < 0.001). The agreement in triggering for the most commonly reported premonitory symptoms (concentration difficulty and tiredness) was >66%. The retriggering agreement for all but one premonitory symptom was >60%. The agreement in timing to onset of premonitory symptoms was reliable across two triggered attacks. The agreement with spontaneous attacks and between attacks for headache and its associated symptoms, including laterality, was less reliable.

Conclusions

Nitroglycerin can reliably and reproducibly provoke premonitory symptomatology associated with migraine. This forms an ideal model to study the earliest manifestations of migraine attacks.

Acute Management of Hypertension Following Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is responsible for approximately 15% of strokes annually in the United States, with nearly 1 in 3 of these patients dying without ever leaving the hospital. Because this disproportionate mortality risk has been stagnant for nearly 3 decades, a main area of research has been focused on the optimal strategies to reduce mortality and improve functional outcomes. The acute hypertensive response following ICH has been shown to facilitate ICH expansion and is a strong predictor of mortality. Rapidly reducing blood pressure was once thought to induce cerebral ischemia, though has been found to be safe in certain patient populations. Clinicians must work quickly to determine whether specific patient populations may benefit from acute lowering of systolic blood pressure (SBP) following ICH. This review provides nurses with a summary of the available literature on blood pressure control following ICH. It focuses on intravenous and oral antihypertensive medications available in the United States that may be utilized to acutely lower SBP, as well as medications outside of the antihypertensive class used during the acute setting that may reduce SBP.

Brain activations in the premonitory phase of nitroglycerin-triggered migraine attacks

Our aim was identify brain areas involved in the premonitory phase of migraine using functional neuroimaging. To this end, we performed positron emission tomography scans with H2(15)O to measure cerebral blood flow as a marker of neuronal activity. We conducted positron emission tomography scans at baseline, in the premonitory phase without pain and during migraine headache in eight patients. We used glyceryl trinitrate (nitroglycerin) to trigger premonitory symptoms and migraine headache in patients with episodic migraine without aura who habitually experienced premonitory symptoms during spontaneous attacks. The main outcome was comparing the first premonitory scans in all patients to baseline scans in all patients. We found activations in the posterolateral hypothalamus, midbrain tegmental area, periaqueductal grey, dorsal pons and various cortical areas including occipital, temporal and prefrontal cortex. Brain activations, in particular of the hypothalamus, seen in the premonitory phase of glyceryl trinitrate-triggered migraine attacks can explain many of the premonitory symptoms and may provide some insight into why migraine is commonly activated by a change in homeostasis.

Optimal starting time of acquisition and feasibility of complementary administration of nitroglycerin with intravenous beta-blocker in multislice computed tomography

OBJECTIVES

We determined the optimal starting time of acquisition after sublingual nitroglycerin (NTG) administration and evaluated the effects on multislice computed tomographic (MSCT) images of a complementary administration of sublingual NTG with beta-blocker.

METHODS

Sixty patients who underwent MSCT coronary angiography (CA) were randomly divided into 2 groups as follows: 30 patients given an intravenous administration of beta-blocker (landiolol hydrochloride, mean dose of 0.032 mg/kg per minute; group B); and 30 patients given a coadministration of intravenous beta-blocker and sublingual NTG (0.3 mg; group N). Blood pressure and heart rate were recorded every 1 minute after NTG administration. In addition, the maximum diameters of the proximal and distal lesions in each coronary artery were measured, and the number of assessable segments was calculated.

RESULTS

Blood pressure significantly decreased and heart rate significantly increased 4 minutes after NTG administration. The number of assessable segments was significantly greater in group N than in group B. The maximum diameters of the distal lesions of the left anterior descending and left circumflex arteries and both proximal and distal lesions of the right coronary artery were significantly larger in group N than in group B.

CONCLUSIONS

It is advisable to obtain MSCT images after sublingual NTG administration because nitrates are always given during conventional CA and may prevent beta-blocker-induced coronary spasm. The optimal starting time for MSCT CA is approximately 3 minutes after sublingual NTG administration.

Sublingual nitroglycerin versus placebo as a tocolytic for external cephalic version: a randomized controlled trial in parous women

OBJECTIVE

The purpose of this study was to evaluate the efficacy of sublingual nitroglycerin as a tocolytic agent for external cephalic version in parous women.

STUDY DESIGN

A double-blinded randomized controlled trial was performed. Patients with parity of >or=1 at 36 to 40 weeks of gestation who were eligible for external cephalic version were included. Patients were randomized to receive either two sublingual sprays of 400 mug of nitroglycerin or two sprays of placebo 3 minutes before the trial of external cephalic version. Rates of successful external cephalic version and side effects were compared between groups.

RESULTS

Of 99 patients in the study, 50 patients received sublingual nitroglycerin, and 49 patients received placebo. There were no differences in maternal age, gestational age, estimated fetal weight, amniotic fluid index, and placental location between the two groups. The success rate of external cephalic version was 48% in the nitroglycerin group compared with 63% in the placebo group (P=.13). There was a higher incidence of headaches in the nitroglycerin group (42% vs 4%, P<.001).

CONCLUSION

Sublingual nitroglycerin was associated with a higher rate of headache and did not improve the rate of successful external cephalic version.

In vitro activation of soluble guanylyl cyclase and nitric oxide release: a comparison of NO donors and NO mimetics

Nitric oxide (NO) performs a central role in biological systems, binding to the heme site of soluble guanylyl cyclase (sGC), leading to enzyme activation and elevation of intracellular levels of cGMP. Organic nitrates, in particular, nitroglycerin (GTN), are clinically important nitrovasodilators that function as NO-mimetics in biological systems. Comparison of sGC activation data with electrochemically measured rates of NO release for genuine NO donors, NONOates and nitrosothiols, yields an excellent correlation between the EC(50) for sGC activation and the rate constant for NO release, k(NO). However, activation of sGC by GTN and the nitrates has very different characteristics, including the requirement for specific added thiols, for example, cysteine. The reaction of GTN with cysteine in anaerobic solution yields NO slowly, and NO release, measured by chemiluminescence detection, is quenched by added metal ion chelator. The generation of NO under aerobic conditions is 100-fold slower than the anaerobic reaction. Furthermore, NO release from the reaction of GTN with cysteine in phosphate buffer is too slow to account for sGC activation by GTN/cysteine. The slow rate of the chemical reaction to release NO suggests that nitrates can activate sGC by an NO-independent mechanism. In contrast to the genuine NO donors, GTN behaves as a partial agonist with respect to sGC activation, but in the presence of the allosteric sGC activator, YC-1, GTN exhibits full agonist activity.

Glyceryl trinitrate and acute uterine relaxation: a literature review

The use of nitro-vasodilators for achieving rapid uterine relaxation in the resolution of obstetric emergencies has been documented for nearly 120 years. Glyceryltrinitrate (GTN) is the most commonly used nitro-vasodilator for this purpose, with the presumed mechanism of action being via nitric oxide and cyclic guanosine monophosphate (cGMP) mediated processes. GTN is known to release nitric oxide to effect smooth muscle relaxation and some dose response data is available for its vasodilator activity. Human myometrium is known to synthesize and respond to nitric oxide, with changes in the production of and sensitivity to nitric oxide being subject to the cyclical and gestational state of the uterus. Experimental data on the efficacy of GTN in reliably producing uterine relaxation is conflicting and inconsistent. A total of 32 studies and case reports on the use of GTN in achieving rapid uterine relaxation have appeared in the English language literature. Case reports are subject to reporting bias and prospective randomized controlled trials are not without design flaws. Indications for the use of GTN in achieving rapid uterine relaxation cover the antepartum, intrapartum and postpartum periods. The safety of GTN during obstetric emergencies appears high, with no adverse maternal or neonatal outcomes. To establish the efficacy of GTN in reliably achieving uterine relaxation, well designed randomized controlled trials in labouring women are required.

Inhibition of human platelet aggregation by nitric oxide donor drugs: relative contribution of cGMP-independent mechanisms

Inhibition of platelet activation by nitric oxide (NO) is not exclusively cGMP-dependent. Here, we tested whether inhibition of platelet aggregation by structurally distinct NO donors is mediated by different mechanisms, partly determined by the site of NO release. Glyceryl trinitrate (GTN), sodium nitroprusside (SNP), S-nitrosoglutathione (GSNO), diethylamine diazeniumdiolate (DEA/NO), and a novel S-nitrosothiol, RIG200, were examined in ADP (8 microM)- and collagen (2.5 microgram/ml)-activated human platelet rich plasma. GTN was a poor inhibitor of aggregation whilst the other NO donors inhibited aggregation, irrespective of agonist. These effects were abolished by the NO scavenger, hemoglobin (Hb; 10 microM, P < 0.05, n = 6), except with high concentrations of DEA/NO, when NO concentrations exceeded the capacity of Hb. However, experiments with the soluble guanylate cyclase inhibitor, ODQ (100 microM), indicated that only SNP-mediated inhibition was exclusively cGMP-dependent. Furthermore, the cGMP-independent effects of S-nitrosothiols were distinct from those of DEA/NO, suggesting that different NO-related mediators (e.g., nitrosonium and peroxynitrite, respectively) are responsible for their actions.

Novel S-nitrosothiols do not engender vascular tolerance and remain effective in glyceryltrinitrate-tolerant rat femoral arteries

Organic nitrates, such as glyceryltrinitrate, are nitric oxide (NO) donor drugs that engender tolerance with long-term use. Here, we tested the hypothesis that our novel S-nitrosothiols, N-(S-nitroso-N-acetylpenicillamine)-2-amino-2-deoxy-1,3,4,6, tetra-O-acetyl-beta-D-glucopyranose (RIG200) and S-nitroso-N-valeryl-D-penicillamine (D-SNVP), do not induce vascular tolerance ex vivo. Femoral arteries from adult male Wistar rats were preconstricted with phenylephrine and perfused with the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME). Perfusion pressure was measured during 20 h treatment with supramaximal concentrations of NO donor (10 microM). Perfusion with glyceryltrinitrate caused a vasodilatation, which recovered over 2-20 h. In contrast, the S-nitrosothiols caused vasodilatations that were maintained throughout the 20 h perfusion period. Responses to S-nitrosothiols were partially reversed by the NO scavenger ferrohaemoglobin and fully reversed by the soluble guanylate cyclase inhibitor [1H-[1,2,4] oxadiazole [4,3-a]quinoxaline-1-one (ODQ). Glyceryltrinitrate-tolerant vessels were fully responsive to bolus injections of S-nitrosothiols. Resistance to tolerance is an attractive property of our novel compounds, particularly in view of their sustained activity in arteries with damaged endothelium.

Novel S-nitrosothiols do not engender vascular tolerance and remain effective in glyceryl trinitrate-tolerant rat femoral arteries

Organic nitrates, such as glyceryl trinitrate, are nitric oxide (NO) donor drugs that engender tolerance with long-term use. Here, we tested the hypothesis that our novel S-nitrosothiols, N-(S-nitroso-N-acetylpenicillamine)-2-amino-2-deoxy-1,3,4,6, tetra-O-acetyl-beta-D-glucopyranose (RIG200) and S-nitroso-N-valeryl-D-penicillamine (D-SNVP), do not induce vascular tolerance ex vivo. Femoral arteries from adult male Wistar rats were preconstricted with phenylephrine and perfused with the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME). Perfusion pressure was measured during 20-h treatment with supramaximal concentrations of NO donor (10 microM). Perfusion with glyceryltrinitrate caused a vasodilatation, which recovered over 2-20 h. In contrast, the S-nitrosothiols caused vasodilatations that were maintained throughout the 20-h perfusion period. Responses to S-nitrosothiols were partially reversed by the NO scavenger ferrohaemoglobin and fully reversed by the soluble guanylate cyclase inhibitor [1H-[1,2,4] oxadiazole [4,3-a]quinoxaline-1-one (ODQ). Glyceryltrinitrate-tolerant vessels were fully responsive to bolus injections of S-nitrosothiols. Resistance to tolerance is an attractive property of our novel compounds, particularly in view of their sustained activity in arteries with damaged endothelium.

The pharmacodynamics of sumatriptan in nitroglycerin-induced headache

Migraine is a common disorder that causes significant morbidity in those afflicted. Many novel antimigraine compounds are in clinical development, yet full characterization of each one's pharmacodynamic behavior is a formidable task due to the difficulty in studying a migraineur during an attack. Nitroglycerin (NTG) administration commonly causes a headache with some features similar to those of a migraine. As such, NTG has been used as a model of vascular headaches, including migraine. The pharmacodynamic effects of nitroglycerin and sumatriptan on middle cerebral artery blood flow velocity (MCAv) and headache scores were studied in 10 healthy male volunteers. An intravenous infusion of NTG titrated to 0.5 mcg/kg/min over 30 minutes resulted in a median reduction from baseline in MCAv of 27% (range: 16.4%-37.3%). Nine of the subjects developed a headache with a median verbal score of 3.5 of 10 (range: 0-5). Subjects received sumatriptan either 2 mg intravenously or 6 mg subcutaneously, which abated clinical headache in 9 of the 10 subjects (p = 0.030). A median sumatriptan-induced increase in MCAv of 21% (p = 0.054) suggested a constricting effect on the NTG-induced dilated MCA. A two-compartment pharmacokinetic/indirect-effects pharmacodynamic model was fit to the sumatriptan concentration and MCAv data using iterative two-stage analysis. This model was unbiased and fit the concentration (r2 = 0.98) and the MCAv (r2 = 0.79) data well. These results suggest that NTG-induced headache and the development of pharmacokinetic/pharmacodynamic models could serve as a useful method for exploring the mechanisms of abortive migraine drugs.

Regioselectivity of nitroglycerin denitration by flavoprotein nitroester reductases purified from two Pseudomonas species

Two species of Pseudomonas capable of utilizing nitroglycerin (NG) as a sole nitrogen source were isolated from NG-contaminated soil and identified as Pseudomonas putida II-B and P. fluorescens I-C. While 9 of 13 laboratory bacterial strains that presumably had no previous exposure to NG could degrade low concentrations of NG (0.44 mM), the natural isolates tolerated concentrations of NG that were toxic to the lab strains (1.76 mM and higher). Whole-cell studies revealed that the two natural isolates produced different mixtures of the isomers of dinitroglycerol (DNG) and mononitroglycerol (MNG). A monomeric, flavin mononucleotide-containing NG reductase was purified from each natural isolate. These enzymes catalyzed the NADPH-dependent denitration of NG, yielding nitrite. Apparent kinetic constants were determined for both reductases. The P. putida enzyme had a Km for NG of 52 +/- 4 microM, a Km for NADPH of 28 +/- 2 microM, and a Vmax of 124 +/- 6 microM x min(-1), while the P. fluorescens enzyme had a Km for NG of 110 +/- 10 microM, a Km for NADPH of 5 +/- 1 microM, and a Vmax of 110 +/- 11 microM x min(-1). Anaerobic titration experiments confirmed the stoichiometry of NADPH consumption, changes in flavin oxidation state, and multiple steps of nitrite removal from NG. The products formed during time-dependent denitration reactions were consistent with a single enzyme being responsible for the in vivo product distributions. Simulation of the product formation kinetics by numerical integration showed that the P. putida enzyme produced an approximately 2-fold molar excess of 1,2-DNG relative to 1,3-DNG. This result could be fortuitous or could possibly be consistent with a random removal of the first nitro group from either the terminal (C-1 and C-3) positions or middle (C-2) position. However, during the denitration of 1,2-DNG, a 1.3-fold selectivity for the C-1 nitro group was determined. Comparable simulations of the product distributions from the P. fluorescens enzyme showed that NG was denitrated with a 4.6-fold selectivity for the C-2 position. Furthermore, a 2.4-fold selectivity for removal of the nitro group from the C-2 position of 1,2-DNG was also determined. The MNG isomers were not effectively denitrated by either purified enzyme, which suggests a reason why NG could not be used as a sole carbon source by the isolated organisms.

Pharmacodynamic models of nitroglycerin-induced hemodynamic tolerance in experimental heart failure

Pharmacodynamic tolerance during continuous nitroglycerin (NTG) infusion is a significant limitation of nitrate therapy. The mechanism of this phenomenon is not well-understood but may involve physiologic compensation which involves vasoconstriction. We have obtained pharmacodynamic data on NTG-induced hemodynamic tolerance in a rat model of congestive heart failure (CHF), which we have shown to mimic human behavior toward NTG in vivo. In this report, we developed two mechanism-based pharmacokinetic/pharmacodynamic models to describe the time-dependent effects of NTG infusion on left ventricular end-diastolic pressures (LVEDP) in CHF rats and compared their abilities to describe the observed hemodynamic data. Both mathematical models introduced a counter-regulatory vasoconstrictive effect as a result of NTG-induced vasodilation and assumed the magnitude of this effect to be driven by the extent of the initial hemodynamic effect produced by NTG. The decay of this counter-regulatory effect was described by a first-order process in both models. A model that assumed vasoconstriction to develop via two sequential first-order processes was statistically superior in describing the data, when compared to one that assumed a single first-order process and a lag phase. Both models provided similar estimates of the half-life for the disappearance of the vasoconstriction (t1/2 of vasoconstriction: 128min vs. 182min, respectively), and both predicted rebound elevation of LVEDP after abrupt NTG withdrawal. These results are consistent with a counter-regulatory mechanism of NTG-induced hemodynamic tolerance and suggest that such an approach may be useful for modeling other tolerance phenomena as well.

Effect of apparent elimination half-life on nitroglycerin-induced hemodynamic rebound in experimental heart failure

Hemodynamic rebound after abrupt withdrawal may be an important consideration associated with nitroglycerin (NTG) monotherapy. This phenomenon may arise from unopposed neurohormonal vasoconstriction because of rapid elimination of NTG. The role of NTG pharmacokinetics in the development of hemodynamic rebound was examined using a rat model of congestive heart failure. NTG was infused for 90 min, then the dose was either abruptly stopped (n = 8) or gradually reduced by 20% every 20 min (n = 7). Abrupt withdrawal caused rebound elevations of left ventricular end-diastolic pressure (LVEDP) to about 25% above baseline values, at 30-60 min after drug termination (P < 0.01), but this was completely avoided by graded NTG withdrawal. A positive correlation was observed (P < 0.05) between the percentage reduction in LVEDP during infusion and the maximum percentage rebound in rats after abrupt withdrawal but not after graded withdrawal. These results suggest that NTG-induced hemodynamic rebound is related to its short biological half-life and that this phenomenon is consistent with a mechanism of neurohormonal compensation.

Effect of nitroglycerin ointment placement on headache and flushing in healthy subjects

The purpose of this study was to determine the effect of site of nitroglycerin ointment placement on headache and flushing in healthy subjects. Twenty-six subjects were given two doses of nitroglycerin ointment 3 hr apart in a randomly assigned arm-chest sequence or chest-arm sequence. Subject reports of headache and flushing using the visual analogue scale were recorded. There were no significant differences in headache or flushing based on the site or sequence of placement. Thus, the practice by nurses of routinely teaching patients to vary the site of nitroglycerin ointment placement to minimize side-effects must be questioned.

Nitrate therapy in the elderly

Changes in the heart and blood vessels with age alter the response of the cardiovascular system to pharmacologic agents. Nitrate plasma half-life is longer and volume of distribution is larger in older persons. Apparently, these pharmacokinetic differences in older persons lead to increased venous smooth muscle responsivity to nitrates which, in turn, leads to greater reductions in central venous and pulmonary arterial pressures after nitrate administration. This is probably the explanation for the greater frequency of nitrate-induced severe hypotension and bradycardia in elderly patients with myocardial infarction compared with younger patients. Clinicians should be cognizant of the changes in the cardiovascular system which occur with age that sensitize the elderly patient to the action of organic nitrates. Initial dosages of nitrates should accordingly be less than in younger patients.

Drug-related syncope

The records of 483 patients admitted to the emergency room because of syncope were reviewed. Forty-one patients were found to have drug-related syncope. Thirty-nine experienced syncope related to drugs administered for cardiovascular disease. The most frequently associated diseases were anginal syndrome (22 patients), hypertension (13 patients), and a history of myocardial infarction (6 patients). Thirty-eight patients experienced symptomatic orthostatic hypotension following drug taking (nitrates in 19 patients, beta blockers in 10 patients, nifedipine in 3 patients, prazosin and quinidine in 2 patients each, methyldopa and verapamil in 1 patient each). One patient developed complete heart block as a result of digoxin intoxication. Two patients developed the characteristic picture of anaphylactic reaction (1 with ampicillin, 1 with dipyrone). During one-year follow-up, without the offending medications, no further syncopal episodes were reported by these patients. We conclude that drug-related syncope was more common among our patients with syncope than had been reported previously. It is suggested that drug-related syncope should be taken into consideration in any patient with syncope who is treated by any of the above-mentioned drugs.

The role of nitrates, beta blockers, and calcium antagonists in stable angina pectoris

Numerous controlled studies have shown that nitrates, beta blockers, and calcium antagonists are effective in the treatment of stable angina pectoris. The pharmacokinetics, pharmacodynamics, and hemodynamic effects of these agents are different, and thus combination therapy offers additive improvement and also counterbalancing of the undesirable side effects of each drug. The choice of therapy depends on the severity of symptoms, associated diseases, compliance, side effects, and status of left ventricular function. The main mechanism of improvement is a decrease in myocardial oxygen consumption, though an increase in coronary blood flow is another potential reason for the use of calcium blockers. This review considers the properties of these drugs, their mechanism of action, and the results of randomized studies.

The effect of isosorbide dinitrate on the arterial vascular bed: a dose response study in dogs

Isosorbide dinitrate (ISDN) was infused stepwise intraarterially into the left hindlimb (5.7-364.8 micrograms/kg/min.) into six dogs. The mean local vascular resistance was decreased by 32% in the left hindlimb after a dose of up to 91.2 micrograms/kg/min. corresponding to a 1.6-fold increase in the left femoral artery blood flow, without significant changes in the control limb or central haemodynamics. The muscular blood flow in the adductor magnus muscle obtained by the Xenon washout technique remained unchanged in 6 of 7 other dogs at ISDN infusion rates of 91.2 micrograms/kg/min., indicating that the increase in femoral artery blood flow was not a consequence of increased muscular blood flow. The arterio-venous extraction fraction of radioactive microspheres was lower in the experimental leg during ISDN infusion when compared with the control leg, suggesting that AV-shunts are opened during ISDN infusion. In addition to the well-known effect on preload, the present results confirm that ISDN also acts on afterload. Thus, ISDN may be classified as a mixed agent acting on both pre- and afterload which is in agreement with some previous studies.

[Regional blood flow in congestive cardiac failure and inhibition of angiotensin converting enzyme]

In congestive cardiac failure myocardial deficiency is accompanied by neurohormonal dysfunction with reflex stimulation of the sympathetic nervous system and the renin-angiotensin-aldosterone system (RAAS). These two systems act synergistically, resulting in peripheral vasoconstriction with increased vascular resistance and therefore greater demand on left ventricular haemodynamics. The role of the RAAS is better understood when angiotensin-converting enzyme inhibitors (ACEI) are used. The vasodilatation produced by these inhibitors mostly affects those vascular beds that depend on the vasopressor effect of angiotensin II, and primarily the renal vascular system: glomerular filtration is improved, and sodium excretion is increased. The RAAS has little influence on the other regional blood flows, so that the administration of ACEI is not followed by cutaneous, muscular or visceral vasodilatation. However, the cerebral blood flow remains normal or even increases despite the fall in systemic arterial pressure, and the coronary output is preserved. Angiotensin-converting enzyme inhibitors produce a strong, though selective, vasodilatation without reflex tachycardia, benefiting primarily the kidneys. The resulting increase in sodium excretion contributes to the long-term effect of ACEI in the treatment of congestive cardiac failure.