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

Association of natriuretic peptides and receptor activity with cardio-metabolic health at middle age

Natriuretic peptides (NP) have multiple actions benefitting cardiovascular and metabolic health. Although many of these are mediated by Guanylyl Cyclase (GC) receptors NPR1 and NPR2, their role and relative importance in vivo is unclear. The intracellular mediator of NPR1 and NPR2, cGMP, circulates in plasma and can be used to examine relationships between receptor activity and tissue responses targeted by NPs. Plasma cGMP was measured in 348 participants previously recruited in a multidisciplinary community study (CHALICE) at age 50 years at a single centre. Associations between bio-active NPs and bio-inactive aminoterminal products with cGMP, and of cGMP with tissue response, were analysed using linear regression. Mediation of associations by NPs was assessed by Causal Mediation Analysis (CMA). ANP's contribution to cGMP far exceed those of other NPs. Modelling across three components (demographics, NPs and cardiovascular function) shows that ANP and CNP are independent and positive predictors of cGMP. Counter intuitively, findings from CMA imply that in specific tissues, NPR1 responds more to BNP stimulation than ANP. Collectively these findings align with longer tissue half-life of BNP, and direct further therapeutic interventions towards extending tissue activity of ANP and CNP.

A new biomarker of cardiac resynchronization therapy response: cGMP to mature BNP ratio

BACKGROUND

Biomarkers that can predict cardiac resynchronization therapy (CRT) response have not yet been identified. The purpose of this study was to assess whether individual measurements of four brain/B-type natriuretic peptide (BNP) forms, coupled with cyclic guanosine monophosphate (cGMP) might contribute to the prediction of echocardiographic CRT responders.

METHODS

A BNP precursor (proBNP) and total BNP (= proBNP + mature BNP) were measured with newly developed kits, while an N-terminal fragment of proBNP (NT-proBNP) and cGMP were measured with commercial kits on the day before CRT implantation. Estimated mature BNP (emBNP = total BNP-proBNP), and the ratio of cGMP to each BNP form, as well as the concentrations of three other BNP forms, were prospectively investigated for their capability in predicting a response to CRT. A CRT responder was defined as an improvement in left ventricular ejection fraction >10% and/or a reduction in left ventricular end-systolic volume >15% at 6-month follow-up.

RESULTS

Out of 77 patients, 46 (60%) were categorized as CRT responders. Among the measurement parameters, only the highest quartile of the cGMP to emBNP ratio was an independent predictor of CRT responders (odds ratio 4.87, 95% confidence interval 1.25-18.89, p = 0.02). The cGMP to emBNP ratio was associated with the cumulative events of heart failure hospitalization within one year following CRT implantation (log-rank p = 0.029).

CONCLUSIONS

The cGMP to emBNP ratio could be utilized as a predictive biomarker of CRT responders. (Clinical Study on Responder Prediction in Cardiac Resynchronization Therapy Using Individual Molecular Measurement of Natriuretic Peptide: UMIN R000038927).

Heart is the Target Organ of Endogenous Cardiac Natriuretic Peptides

This study aimed to evaluate whether the heart is the target organ of endogenous atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in patients with heart failure (HF) with reduced ejection fraction (HFrEF).We measured the plasma levels of cyclic guanosine monophosphate (cGMP), which is a second messenger of ANP and BNP, in the aortic root (AO) and coronary sinus (CS) in 237 patients with HFrEF. Plasma levels of cGMP were significantly higher in the CS than those in the AO in 237 patients with HFrEF (10.0 ± 4.5 versus 10.5 ± 4.3 pmoL/mL, P < 0.0001) and were significantly higher in the CS than those in the AO (8.0 ± 3.6 versus 8.9 ± 3.8 pmoL/mL, P < 0.0001) in mild HF patients (New York Heart Association (NYHA) II, n = 114), but there was no difference in plasma cGMP between the AO and the CS (11.9 ± 4.4 versus 11.9 ± 4.3 pmoL/mL, NS) in severe HF patients (NYHA III-IV, n = 123). In mild HF patients, log (ANP + BNP) in the AO was an independent predictor of (CS-AO) cGMP among hemodynamics and nitrate therapy. There was a significant correlation between log [(CS-AO) ANP + (CS-AO) BNP] and (CS-AO) cGMP (r = 0.455, P < 0.0001) in mild HF patients.These findings indicate that cGMP is produced from the failing heart and that the heart is the target organ of endogenous ANP and BNP in patients with HFrEF. In severe HF patients, cGMP production may be attenuated because of the downregulation of biological receptors and/or increased cGMP degradation in the failing heart.

Sickle cell disease subjects and mouse models have elevated nitrite and cGMP levels in blood compartments

The hypothesis of decreased nitric oxide (NO) bioavailability in sickle cell disease (SCD) proposes that multiple factors leading to decreased NO production and increased consumption contributes to vaso-occlusion, pulmonary hypertension, and pain. The anion nitrite is central to NO physiology as it is an end product of NO metabolism and serves as a reservoir for NO formation. However, there is little data on nitrite levels in SCD patients and its relationship to pain phenotype. We measured nitrite in SCD subjects and examined its relationship to SCD pain. In SCD subjects, median whole blood, red blood cell and plasma nitrite levels were higher than in controls, and were not associated with pain burden. Similarly, Townes and BERK homozygous SCD mice had elevated blood nitrite. Additionally, in red blood cells and plasma from SCD subjects and in blood and kidney from Townes homozygous mice, levels of cyclic guanosine monophosphate (cGMP) were higher compared to controls. In vitro, hemoglobin concentration, rather than sickle hemoglobin, was responsible for nitrite metabolism rate. In vivo, inhibition of NO synthases and xanthine oxidoreductase decreased nitrite levels in homozygotes but not in control mice. Long-term nitrite treatment in SCD mice further elevated blood nitrite and cGMP, worsened anemia, decreased platelets, and did not change pain response. These data suggest that SCD in humans and animals is associated with increased nitrite/NO availability, which is unrelated to pain phenotype. These findings might explain why multiple clinical trials aimed at increasing NO availability in SCD patients failed to improve pain outcomes.

Urinary cGMP predicts major adverse renal events in patients with mild renal impairment and/or diabetes mellitus before exposure to contrast medium

BACKGROUND

The use of iodine-based contrast agents entails the risk of contrast induced nephropathy (CIN). Radiocontrast agents elicit the third most common cause of nephropathy among hospitalized patients, accounting for 11-12% of cases. CIN is connected with clinically significant consequences, including increased morbidity, prolonged hospitalization, increased risk of complications, potential need for dialysis, and increased mortality rate. The number of in-hospital examinations using iodine-based contrast media has been significantly increasing over the last decade. In order to protect patients from possible complications of such examinations, new biomarkers are needed that are able to predict a risk of contrast-induced nephropathy. Urinary and plasma cyclic guanosine monophosphate (cGMP) concentrations are influenced by renal function. Urinary cGMP is primarily of renal cellular origin. Therefore, we assessed if urinary cGMP concentration may predict major adverse renal events (MARE) after contrast media exposure during coronary angiography.

METHODS

Urine samples were prospectively collected from non-randomized consecutive patients with either diabetes or preexisting impaired kidney function receiving intra-arterial contrast medium (CM) for emergent or elective coronary angiography at the Charité Campus Mitte, University Hospital Berlin. Urinary cGMP concentration in spot urine was analyzed 24 hours after CM exposure. Patients were followed up over 90 days for occurrence of death, initiation of dialysis, doubling of plasma creatinine concentration or MARE.

RESULTS

In total, 289 consecutive patients were included into the study. Urine cGMP/creatinine ratio 24 hours before CM exposure expressed as mean±SD was predictive for the need of dialysis (no dialysis: 89.77±92.85 μM/mM, n = 277; need for dialysis: 140.3±82.90 μM/mM, n = 12, p = 0.008), death (no death during follow-up: 90.60±92.50 μM/mM, n = 280; death during follow-up: 169.88±81.52 μM/mM, n = 9; p = 0.002), and the composite endpoint MARE (no MARE: 86.02±93.17 μM/mM, n = 271; MARE: 146.64±74.68 μM/mM, n = 18, p<0.001) during the follow-up of 90 days after contrast media application. cGMP/creatinine ratio stayed significantly increased at values exceeding 120 μM/mM in patients who developed MARE, required dialysis or died.

CONCLUSIONS

Urinary cGMP/creatinine ratio ≥ 120 μM/mM before CM exposure is a promising biomarker for the need of dialysis and all-cause mortality 90 days after CM exposure in patients with preexisting renal impairment or diabetes.

Platelet inhibitory effects of juices from Pachyrhizus erosus L. root and Psidium guajava L. fruit: a randomized controlled trial in healthy volunteers

Background

The purpose of this study is to investigate cardiovascular benefits of juices obtained from two commonly consumed fruits in Thailand, Pachyrhizus erosus, L. (yam bean) and Psidium guajava, L. (guava), by examining their acute cardiovascular effects in healthy volunteers. Possible involvements of the dietary nitrate on their effects were investigated as well.

Method

Thirty healthy volunteers were randomly divided into three groups of 10 subjects per group and each group was allocated to drink 500 ml of freshly prepared yam bean root juice, guava fruit juice, or water. Systemic nitrate and nitrite concentrations, heart rate, systolic and diastolic blood pressure, serum K⁺ concentrations, ex vivo platelet aggregation, and plasma cGMP concentrations were monitored at the baseline and at various time points after the intake of juices or water. Data were compared by repeated measures ANOVA.

Results

Following the ingestion of both yam bean root juice and guava fruit juice, collagen-induced but not ADP-induced platelet aggregation was attenuated. Ingestion of yam bean root juice increased systemic nitrate and nitrite concentrations whereby elevated nitrite concentrations correlated with the extent of inhibiting collagen-induced platelet aggregation. In addition, positive correlation between systemic nitrite and plasma cGMP concentrations and negative correlation between plasma cGMP concentrations and the extent of collagen-induced platelet aggregation were revealed. Nevertheless, yam bean root juice reduced only diastolic blood pressure while guava fruit juice reduced heart rate, systolic and diastolic blood pressure.

Conclusion

The present study has illustrated, for the first time, acute inhibitory effects of yam bean root juice and guava fruit juice on ex vivo collagen-induced platelet aggregation in healthy subjects. Dietary nitrate was shown to underlie the effect of yam bean root juice but not that of guava fruit juice. Following yam bean root juice ingestion, systemic nitrate apparently converts to nitrite and further to NO which may attenuate platelet responses to collagen stimulation. Cardiovascular benefits of juices from yam bean root and guava fruit are noteworthy in term of the cardiovascular health-promoting approach.

Trial registration

Randomized controlled trial TCTR20150228001.

M-atrial natriuretic peptide and nitroglycerin in a canine model of experimental acute hypertensive heart failure: differential actions of 2 cGMP activating therapeutics

Background

Systemic hypertension is a common characteristic in acute heart failure (HF). This increasingly recognized phenotype is commonly associated with renal dysfunction and there is an unmet need for renal enhancing therapies. In a canine model of HF and acute vasoconstrictive hypertension we characterized and compared the cardiorenal actions of M‐atrial natriuretic peptide (M‐ANP), a novel particulate guanylyl cyclase (pGC) activator, and nitroglycerin, a soluble guanylyl cyclase (sGC) activator.

Methods and Results

HF was induced by rapid RV pacing (180 beats per minute) for 10 days. On day 11, hypertension was induced by continuous angiotensin II infusion. We characterized the cardiorenal and humoral actions prior to, during, and following intravenous M‐ANP (n=7), nitroglycerin (n=7), and vehicle (n=7) infusion. Mean arterial pressure (MAP) was reduced by M‐ANP (139±4 to 118±3 mm Hg, P<0.05) and nitroglycerin (137±3 to 116±4 mm Hg, P<0.05); similar findings were recorded for pulmonary wedge pressure (PCWP) with M‐ANP (12±2 to 6±2 mm Hg, P<0.05) and nitroglycerin (12±1 to 6±1 mm Hg, P<0.05). M‐ANP enhanced renal function with significant increases (P<0.05) in glomerular filtration rate (38±4 to 53±5 mL/min), renal blood flow (132±18 to 236±23 mL/min), and natriuresis (11±4 to 689±37 mEq/min) and also inhibited aldosterone activation (32±3 to 23±2 ng/dL, P<0.05), whereas nitroglycerin had no significant (P>0.05) effects on these renal parameters or aldosterone activation.

Conclusions

Our results advance the differential cardiorenal actions of pGC (M‐ANP) and sGC (nitroglycerin) mediated cGMP activation. These distinct renal and aldosterone modulating actions make M‐ANP an attractive therapeutic for HF with concomitant hypertension, where renal protection is a key therapeutic goal.

Alterations in adipocytokines and cGMP homeostasis in morbid obesity patients reverse after bariatric surgery

OBJECTIVE

Obesity-associated nonalcoholic fatty liver disease (NAFLD), covering from simple steatosis to nonalcoholic steatohepatitis (NASH), is a common cause of chronic liver disease. Aberrant production of adipocytokines seems to play a main role in most obesity-associated disorders. Changes in adipocytokines in obesity could be mediated by alterations in cyclic GMP (cGMP) homeostasis. The aims of this work were: (1) to study the role of altered cGMP homeostasis in altered adipocytokines in morbid obesity, (2) to assess whether these alterations are different in simple steatosis or NASH, and (3) to assess whether these changes reverse in obese patients after bariatric surgery.

DESIGN AND METHODS

In 47 patients with morbid obesity and 45 control subjects, the levels in blood of adipocytokines, cGMP, nitric oxide (NO) metabolites, and atrial natriuretic peptide (ANP) were studied. Whether weight loss after a bariatric surgery reverses the changes in these parameters was evaluated.

RESULTS

NO metabolites and leptin increase (and adiponectin decreases) similarly in patients with steatosis or NASH, suggesting that these changes are due to morbid obesity and not to liver disease. Inflammation and cGMP homeostasis are affected both by morbid obesity and by liver disease. The increases in interleukin 6 (IL-6), interleukin 18 (IL-18), plasma cGMP, ANP, and the decrease in cGMP in lymphocytes are stronger in patients with NASH than with steatosis. All these changes reverse completely after bariatric surgery and weight loss, except IL-18.

CONCLUSION

Altered cGMP homeostasis seems to contribute more than inflammation to changes in leptin and adiponectin in morbid obesity.

The cyclic guanosine monophosphate/B-type natriuretic peptide ratio and mortality in advanced heart failure

AIMS

Attenuation of the effects of natriuretic peptides has been demonstrated in animal models but studies in humans are scarce, particularly concerning renal attenuation. We investigated the attenuation of B-type natriuretic peptide (BNP) in chronic advanced heart failure (HF).

METHODS AND RESULTS

We included 62 outpatients with HF and severe left ventricular systolic dysfunction. Cases had at least one hospital admission or emergency department visit for acute HF in the previous year and were in NYHA class III/IV despite optimized therapy. The individual age- and sex-matched controls were symptomatically controlled (NYHA I and II). We collected 24 h urine and a blood sample from all patients. Plasma BNP and plasma (pcGMP) and urine cyclic guanosine monophosphate (ucGMP) were measured. Patients were followed for 3 months for hospital admission or all-cause death. ucGMP to plasma BNP (ucGMP/BNP) ratio was attenuated in cases vs. controls [median (IQR): 8354 (4293-16,456) vs. 12,693 (6896-22,851)]. There were no differences in pcGMP to BNP (pcGMP/BNP) ratio or urine cGMP excretion. Patients with worse outcome had lower pcGMP/BNP [260 (86-344) vs. 381 (244-728) in patients without adverse outcome events] and lower ucGMP/BNP [4146 (2207-9363) vs. 10,922 (7495-19,971)].

CONCLUSION

Renal NP's second messenger production is attenuated in advanced HF. Patients with worse outcome have lower ucGMP/BNP and pcGMP/BNP ratios.

Simultaneous assessment of endothelial function, nitric oxide synthase activity, nitric oxide-mediated signaling, and oxidative stress in individuals with and without hypercholesterolemia

BACKGROUND

Endothelial function is impaired in hypercholesterolemia and atherosclerosis. Based on mostly indirect evidence, this impairment is attributed to reduced synthesis or impaired biological activity of endothelium-derived nitric oxide (NO). It was the aim of this study to directly estimate and compare whole-body NO production in normo- and hypercholesterolemia by applying a nonradioactive stable isotope dilution technique in vivo.

METHODS

We enrolled 12 normocholesterolemic and 24 hypercholesterolemic volunteers who were all clinically healthy. To assess whole-body NO synthesis, we intravenously administered l-[guanidino-((15)N(2))]-arginine and determined the urinary excretion of (15)N-labeled nitrate, the specific end product of NO oxidation in humans, by use of gas chromatography-mass spectrometry. In addition, we measured flow-mediated vasodilation (FMD) of the brachial artery, expression of endothelial NOS (eNOS) in platelets, plasma concentration of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA), and urinary excretion of 8-isoprostaglandin F(2alpha) (8-iso-PGF(2alpha)).

RESULTS

After infusion of l-[guanidino-((15)N(2))]-arginine, cumulative excretion of (15)N-labeled-nitrate during 48 h was 40% [95% CI 15%-66%] lower in hypercholesterolemic than normocholesterolemic volunteers [mean 9.2 (SE 0.8) micromol vs 15.4 (2.3) micromol/l, P = 0.003]. FMD was on average 36% [4%-67%] lower in hypercholesterolemic than normocholesterolemic volunteers [6.3 (4.0)% vs 9.4 (4.6)%, P = 0.027]. Normalized expression of NOS protein in platelets was also significantly lower in hypercholesterolemic volunteers, whereas there were no significant differences in plasma ADMA concentration or urinary excretion of 8-iso-PGF(2alpha) between the 2 groups.

CONCLUSIONS

This study provides direct evidence for a decreased whole body NO synthesis rate in healthy people with hypercholesterolemia.

Lack of alteration of endogenous nitric oxide pathway during prolonged nitric oxide inhalation in intensive care unit patients

OBJECTIVE

To compare hemodynamic and gasometric variables and the plasma concentrations of nitric oxide metabolites (cyclic guanosine monophosphate and nitrate and nitrite), endothelin-1, and renin-angiotensin metabolites before and after the start of nitric oxide inhalation, after prolonged nitric oxide inhalation, and before and after nitric oxide withdrawal.

DESIGN

Prospective study.

SETTING

Surgical intensive care unit, university hospital.

SUBJECTS

Patients with acute lung injury and right ventricular failure.

INTERVENTIONS

Nitric oxide inhalation (10-12 ppm) during a median of 2.9 days (12 hrs to 6.5 days).

MEASUREMENTS AND MAIN RESULTS

The pulmonary vasodilator effects of inhaled nitric oxide improved arterial oxygenation in patients with acute lung injury (p < .05) and reduced right atrial pressure in patients with right ventricular dysfunction (p < .01). These beneficial effects lasted the whole period of prolonged inhaled nitric oxide therapy up to 6.5 days. However, when inhaled nitric oxide was withdrawn, pulmonary vasodilator effects rapidly disappeared, and Pao2/Fio2 ratio markedly deteriorated in all studied patients to return to pre-inhaled nitric oxide levels. Changes in plasma cyclic guanosine monophosphate and nitrate and nitrite paralleled those of pulmonary vasodilatory effects. An immediate increase in plasma cyclic guanosine monophosphate with a slightly delayed increase in plasma nitrate and nitrite was observed at inhaled nitric oxide start with no attenuation during the prolonged inhaled nitric oxide therapy. A marked decrease toward pre-inhaled nitric oxide levels was seen within hours of inhaled nitric oxide withdrawal. In addition, no alteration of plasma endothelin-1 or renin-angiotensin mediators was observed during or after inhaled nitric oxide therapy.

CONCLUSIONS

Our study showed a lack of attenuation in the beneficial effects of inhaled nitric oxide and a lack of alteration of endogenous nitric oxide, endothelin-1, and renin-angiotensin pathways during prolonged nitric oxide inhalation.

Attenuation of biologic compensatory action of cardiac natriuretic peptide system with aging

Although plasma B-type natriuretic peptide (BNP) levels increase with age, the mechanisms responsible for this increase are unknown. We investigated the predictors of elevated BNP in older subjects without cardiac systolic dysfunction and overt renal dysfunction. Furthermore, we analyzed the relations between BNP and its second messenger, cyclic guanosine monophosphate (cGMP), to aging. In 252 subjects (mean age 69 +/- 12 years) with left ventricular ejection fraction >/=50% and creatinine levels <==1.5 mg/dl, plasma levels of BNP, cGMP, blood urea nitrogen, creatinine, and beta2-microglobulin (an endogenous marker of renal function), estimated glomerular filtration rate, and echocardiographic data were prospectively evaluated. Plasma BNP levels increased with age (r = 0.4, p <0.0001). With use of multivariate analysis, predictors of elevated BNP levels were age, use of beta blockers, and serum beta2-microglobulin levels. The molar ratio of cGMP to BNP significantly decreased with aging (r = 0.55, p <0.0001). Elevated BNP in older subjects with normal cardiac systolic function may be due in part to renal impairment. With aging, biologic compensation of the cardiac natriuretic peptide system may be attenuated.

A new approach for extracellular spin trapping of nitroglycerin-induced superoxide radicals both in vitro and in vivo

Anti-ischemic therapy with nitrates is complicated by the induction of tolerance that potentially results from an unwanted coproduction of superoxide radicals. Therefore, we analyzed the localization of in vitro and in vivo, glyceryl trinitrate (GTN)-induced formation of superoxide radicals and the effect of the antioxidant vitamin C and of superoxide dismutase (SOD). Sterically hindered hydroxylamines 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine (CP-H) and 1-hydroxy-4-phosphonooxy-2,2,6,6-tetramethylpiperidin (PP-H) can be used for in vitro and in vivo quantification of superoxide radical formation. The penetration/incorporation of CP-H or PP-H and of their corresponding nitroxyl radicals was examined by fractionation of the blood and blood cells during a 1-h incubation. For monitoring in vivo, GTN-induced (130 microg/kg) O2*- formation CP-H or PP-H were continuously infused (actual concentration, 800 microM) for 90 to 120 min into rabbits. Formation of superoxide was determined by SOD- or vitamin C-inhibited contents of nitroxide radicals in the blood from A. carotis. The incubation of whole blood with CP-H, PP-H, or corresponding nitroxyl radicals clearly shows that during a 1-h incubation, as much as 8.3% of CP-H but only 0.9% of PP-H is incorporated in cytoplasm. Acute GTN treatment of whole blood and in vivo bolus infusion significantly increased superoxide radical formation as much as 4-fold. Pretreatment with 20 mg/kg vitamin C or 15,000 U/kg superoxide dismutase prevented GTN-induced nitroxide formation. The decrease of trapped radicals after treatment with extracellularly added superoxide dismutase or vitamin C leads to the conclusion that GTN increases the amount of extracellular superoxide radicals both in vitro and in vivo.

Comparison of glyceryl trinitrate-induced with pentaerythrityl tetranitrate-induced in vivo formation of superoxide radicals: effect of vitamin C

Glyceryl trinitrate (GTN) and pentaerythrityl tetranitrate (PETN) are among the most known organic nitrates that are used in cardiovascular therapy as vasodilators. However, anti-ischemic therapy with organic nitrates is complicated by the induction of nitrate tolerance. When nitrates are metabolized to release nitric oxide (NO), there is considerable coproduction of superoxide radicals in vessels leading to inactivation of NO. However, nitrate-induced increase of superoxide radical formation in vivo has not been reported. In this work, the authors studied the in vivo formation of superoxide radicals induced by treatment with PETN or GTN and determined the antioxidant effect of vitamin C. The formation of superoxide radicals was determined by the oxidation of 1-hydroxy-3-carboxy-pyrrolidine (CP-H) to paramagnetic 3-carboxy-proxyl (CP) using electron spin resonance spectroscopy. CP-H (9 mg/kg intravenous bolus and 0.225 mg/kg per minute continuous intravenous GTN or PETN 130 microg/kg) were infused into anesthetized rabbits. Every 5 min, blood samples were obtained from Arteria carotis to measure the CP formation. Both PETN and GTN showed similar vasodilator effects. Formation of CP in blood after infusions of GTN and PETN were 2.0+/-0.4 microM and 0.98+/-0.23 microM, respectively. Pretreatment with 30 mg/kg vitamin C led to a significant decrease in CP formation: 0.27+/-0.14 microM (vitamin C plus GTN) and 0.34+/-0.15 microM (vitamin C plus PETN). Pretreatment of animals with superoxide dismutase (15,000 units/kg) significantly inhibited nitrate-induced nitroxide formation. Therefore, in vivo infusion of GTN or PETN in rabbits increased the formation of superoxide radicals in the vasculature. PETN provoked a minimal stimulation of superoxide radical formation without simultaneous development of nitrate tolerance. The data suggest that the formation of superoxide radicals induced by organic nitrate correlates with the development of nitrate tolerance. The effect of vitamin C on CP formation leads to the conclusion that vitamin C can be used as an effective antioxidant for protection against nitrate-induced superoxide radical formation in vivo.

Digitalis increases brain natriuretic peptide in patients with severe congestive heart failure

Ouabain can cause increased secretion of atrial natriuretic peptide (ANP) from atrial cardiocyte culture, but the effects of digitalis in a therapeutic range on the secretion of cardiac natriuretic peptide including ANP and brain natriuretic peptide (BNP), mainly from the ventricle, in patients with congestive heart failure remain to be investigated. Therefore we studied the acute effects of intravenous infusion of a relatively low dose of digitalis or placebo on hemodynamics and neurohumoral factors including the plasma levels of ANP and BNP and cyclic guanosine monophosphate, a second messenger of cardiac natriuretic peptide, in 13 patients with severe congestive heart failure. No significant change in the hemodynamic parameters or neurohumoral factors was observed with placebo. After 1 hour of intravenous administration of deslanoside (0.01 mg/kg), there was a significant decrease of plasma renin activity and angiotensin II, aldosterone, and norepinephrine levels but no significant change of plasma levels of vasopressin and a significant decrease of the pulmonary capillary wedge pressure but no significant change in cardiac index. In addition, plasma levels of ANP (217 +/- 47 vs 281 +/- 70 pg/ml, p < 0.05), BNP (628 +/- 116 vs 689 +/- 132 pg/ml, p < 0.05), and cyclic guanosine monophosphate (9.7 +/- 1.1 vs 10.9 +/- 1.5 pmol/ml, p < 0.05) increased despite the decrease of pulmonary capillary wedge pressure (19.7 +/- 2.3 vs 16.8 +/- 2.3 mm Hg, p < 0.05). These results indicate the acute intravenous low dose of digitalis resulted in a significant increase in plasma levels of ANP, BNP, and cyclic guanosine monophosphate concomitant with the significant decrease of pulmonary capillary wedge pressure, suggesting the acute direct action of digitalis on the cardiac natriuretic peptides released from the heart in patients with severe congestive heart failure.

A positron emission tomography study of cerebral blood flow and oxygen metabolism in healthy male volunteers anaesthetized with eltanolone

BACKGROUND

The effects of eltanolone anaesthesia in humans on regional cerebral blood flow, regional cerebral metabolic rate of oxygen and oxygen extraction ratio were to be evaluated using positron emission tomography (PET).

METHODS

Six healthy male volunteers were studied. Series of PET-measurements with 15O and H2(15)O were carried out in the awake state (baseline)(n = 6), during eltanolone anaesthesia (n = 5) and during early recovery (n = 5), when the subjects were oriented with respect to person, place and time. Eltanolone was given as a programmed infusion.

RESULTS

Cerebral blood flow (rCBF) was reduced in almost all cortex regions studied by 31 +/- 16% (mean +/- SD, P < 0.01). During recovery rCBF increased to 109 +/- 26% of pre-anaesthetic baseline levels (P < 0.01). Eltanolone in the doses administered lowered oxygen metabolism (rCMRO2) by 52 +/- 8% (P < 0.01) in cortex regions. During recovery rCMRO2 increased to 90 +/- 13% of baseline (P < 0.01). The oxygen extraction (OER) in cortical regions decreased by 32 +/- 23% (P < 0.01) during anaesthesia and returned to 82 +/- 10% of baseline (P < 0.01) during recovery. Less reduction in cortical blood flow during eltanolone anaesthesia was seen in the uncus (P < 0.01), though no differences in the depression of oxygen metabolism were seen. Oxygen extraction remained homogeneous throughout the brain.

CONCLUSION

Eltanolone anaesthesia was shown to reduce cerebral oxygen metabolism and cerebral blood flow in healthy volunteers. There were no signs of ischaemic effects.

Sustained antiplatelet properties of nitroglycerin during hemodynamic tolerance in rats

Organic nitrates possess important antiplatelet actions that are useful in the treatment of unstable angina and myocardial infarction, but the susceptibility of platelets to nitrate tolerance has not been extensively studied. In normal conscious rats, we showed that continuous infusion of nitroglycerin (NTG) at 10 micrograms/min had no significant effect on mean arterial pressure (MAP) as compared with control, but hemodynamic tolerance could be demonstrated by MAP response to a bolus intravenous (i.v.) NTG challenge. By this criterion, continuous 8-h NTG infusion produced hemodynamic tolerance (a decrease in MAP response of 45.7 +/- 19.9%, p < 0.05), whereas D5W control and S-nitroso-N-acetylpenicillamine (SNAP) infusions did not. During NTG infusion, platelet-rich plasma (PRP) cyclic GMP was increased by 41.4 +/- 13.6% as compared with control and remained increased throughout the infusion (p < 0.05). Bleeding time during a 2-h infusion of NTG was 8.9 +/- 1.2 min as compared to 3.8 +/- 0.4 min in controls (p < 0.05). After 8-h of NTG infusion, the bleeding time was 10.2 +/- 1.4 min versus 4.4 +/- 0.4 min in controls (p < 0.05). NTG also decreased the PRP platelet concentration by 30% in 8 h, whereas D5W had no effect. In vitro experiments showed that platelets in themselves do not produce significant amounts of cyclic GMP. These data indicate that the biochemical and antiaggregation effects of NTG on platelets are not diminished during hemodynamic tolerance and that these effects may be dependent on extraplatelet production of nitric oxide (NO).

Comparison of hemodynamic effects and plasma cyclic guanosine monophosphate of nicorandil and nitroglycerin in patients with congestive heart failure

Hemodynamic tolerance has been observed within several hours of continuous infusion of nitroglycerin (NTG). We examined the hemodynamic parameters as well as femoral arterial and venous cyclic guanosine monophosphate (cGMP) concentrations during intravenous infusion of NTG or nicorandil, a nitrate and potassium channel opener, in patients with congestive heart failure. Doses of NTG or nicorandil were titrated to achieve a > or = 25% reduction in pulmonary capillary wedge pressure (PCWP) within 1 hour, and the infusion was maintained at a constant rate for 24 hours. The reduction in PCWP and mean arterial blood pressure was identical after a 1-hour infusion of either NTG or nicorandil. In the NTG group, PCWP and mean blood pressure were not significantly different from the baseline value at 12 hours, but in the nicorandil group PCWP and mean blood pressure remained significantly lower than the preinfusion value for 24 hours. The cGMP production with NTG (assessed by the difference between the plasma arterial and venous cGMP level) paralleled the changes in PCWP, suggesting that the plasma arteriovenous cGMP difference is a biochemical indicator of nitrate tolerance. Although the sustained decrease in PCWP was observed in the nicorandil group, cGMP production with nicorandil was also attenuated at 24 hours of continuous infusion. These findings suggest that the absence of the hemodynamic tolerance of nicorandil, a nitrate and potassium channel opener, is likely due to its action as a potassium channel opener, and not to its nitrate activity.