Blood pressure control by the renin-angiotensin system in normotensive subjects. Assessment by angiotensin converting enzyme and renin inhibition

Impaired angiotensin II signaling in septic shock

Recent years have seen a resurgence of interest for the renin-angiotensin-aldosterone system in critically ill patients. Emerging data suggest that this vital homeostatic system, which plays a crucial role in maintaining systemic and renal hemodynamics during stressful conditions, is altered in septic shock, ultimately leading to impaired angiotensin II-angiotensin II type 1 receptor signaling. Indeed, available evidence from both experimental models and human studies indicates that alterations in the renin-angiotensin-aldosterone system during septic shock can occur at three distinct levels: 1. Impaired generation of angiotensin II, possibly attributable to defects in angiotensin-converting enzyme activity; 2. Enhanced degradation of angiotensin II by peptidases; and/or 3. Unavailability of angiotensin II type 1 receptor due to internalization or reduced synthesis. These alterations can occur either independently or in combination, ultimately leading to an uncoupling between the renin-angiotensin-aldosterone system input and downstream angiotensin II type 1 receptor signaling. It remains unclear whether exogenous angiotensin II infusion can adequately address all these mechanisms, and additional interventions may be required. These observations open a new avenue of research and offer the potential for novel therapeutic strategies to improve patient prognosis. In the near future, a deeper understanding of renin-angiotensin-aldosterone system alterations in septic shock should help to decipher patients' phenotypes and to implement targeted interventions.

Influence of Angiotensin Converting Enzyme I/D Polymorphism on Hemodynamic and Antioxidant Response to Long-Term Intradialytic Resistance Training in Patients With Chronic Kidney Disease: A Randomized Controlled Trial

ABSTRACT

Corrêa, HdL, Deus, LA, Neves, RVP, Reis, AL, de Freitas, GS, de Araújo, TB, da Silva Barbosa, JM, Prestes, J, Simões, HG, Amorim, CE, dos Santos, MAP, Haro, A, de Melo, GF, Gadelha, AB, Neto, LS, and Rosa, TdS. Influence of angiotensin converting enzyme I/D polymorphism on hemodynamic and antioxidant response to long-term intradialytic resistance training in patients with chronic kidney disease: a randomized controlled trial. J Strength Cond Res 35(10): 2902-2909, 2021-The aim of the study was to verify the influence of Angiotensin-converting enzyme (ACE) I/D genotype on blood pressure, muscle mass, and redox balance response to long-term resistance training (RT) in end-stage renal disease patients. Three hundred and twenty subjects were randomized into 4 groups: II + ID control (II + ID CTL, n = 80), II + ID RT (II + ID RT, n = 79), DD control (DD CTL n = 83), and DD RT (DD RT, n = 78). The RT lasted 24 weeks with a frequency of 3 times per week, on alternative days. Each section consisted of 3 sets of 8-12 repetitions in 11 exercises, with training loads at 6 point (somewhat hard) to 8 point (hard) based on OMNI-RES scale and was prescribed during dialysis (intradialytic). Statistical significance was accepted with p < 0.05. The most relevant benefits in blood pressure were found for DD homozygotes (p < 0.0001), whereas allele I carriers displayed a higher increase in muscle mass (p < 0.0001). Hemodialysis clinics that already use RT for their patients could include the genotyping of ACE to identify the predisposal of the patients to respond to RT and to counteract kidney disease-related comorbidities.

Bradykinin analysis revived--a validated method for determination of its stable metabolite in whole blood by LC-MS/MS

Investigation of bradykinin involvement in diseases like hereditary angioedema has been greatly hindered by its rapid metabolism and generation, induced by sampling. Because of this, reliable measurements of bradykinin have yet to be introduced in clinical practice. Prevention of bradykinin generation during sampling, and determination of the in vivo generated stable metabolite BK1-5, should allow a reliable indirect measure of bradykinin involvement. An LC-MS/MS method has been developed to determine BK1-5 in human whole blood. The method inactivates metabolizing enzymes with ethanol, followed by solid phase extraction (C18), separation (C8) and detection (linear ion trap) through the transitions 287.25→320.20 (y3, quantifier), 408.20 (b4, qualifier) for BK1-5, and 292.17→330.20 (y3, quantifier), 408.20 (b4, qualifier) for the heavy labelled internal standard. The method showed acceptable linearity (n=3, r(2)=0.994), intra-run precision (CV<15%), inter-run precision (CV<15%) and accuracy (CV<14%), without matrix effects. LLOQ was 265.5 pmol L(-1) and LOD was 35.4 pmol L(-1). The method was used on blood samples from patients with hereditary angioedema, where BK1-5 was measured during attacks and in remision. The samples showed elevated concentrations (up to 1.7 nmol L(-1) during attacks and 265.5 pmol L(-1) in remission) compared to healthy volunteers (<35.4 pmol L(-1)). This is the first time BK1-5 in hereditary angioedema patients has been measured.

Effects of peroxisome proliferator-activated receptor-gamma activation with pioglitazone on plasma adipokines in nondiabetic patients with either hypercholesterolemia or hypertension

Adipokines are substances produced by the adipose tissue that may play significant roles in the mechanisms contributing to the development of atherosclerosis. Thiazolidinediones have been shown to improve endothelium-dependent vasodilation and to exert multiple antiatherosclerotic effects. This study tested the hypotheses that nondiabetic patients with cardiovascular risk factors have altered levels of adipokines that can be modified by pioglitazone treatment. Eighty patients with hypertension or hypercholesterolemia were in a double-blinded, placebo-controlled, crossover study. In each treatment phase, patients received pioglitazone 45 mg/day or placebo for 8 weeks. Endothelial function studies and biochemical assays were performed at the end of each 8-week treatment period. Twenty-two normal volunteers, matched with patients for age, gender, and body mass index, were recruited as a control group. Compared with controls, placebo-treated patients had lower adiponectin levels (11,160 +/- 763 vs 6,078 +/- 385 ng/ml, p <0.001) and similar plasma leptin levels (21.5 +/- 3.8 vs 16.2 +/- 1.5 ng/ml, p = 0.128) and resistin levels (5.1 +/- 0.4 vs 4.4 +/- 0.2 ng/ml, p = 0.250). In patients, pioglitazone treatment markedly increased adiponectin (+121%, p <0.001) and decreased resistin (-10.5%, p = 0.03). Leptin was not significantly decreased (-7.1%, p = 0.10). In multivariate analysis, pioglitazone-induced changes in endothelial reactivity to acetylcholine were the only significant predictor of increases in adiponectin. In conclusion, in nondiabetic patients with major cardiovascular risk factors, pioglitazone treatment beneficially influences circulating adipokine levels. The relation between the increase in adiponectin levels and the improvement in endothelial vasodilator activity suggests a mechanistic link between vascular effects and adiponectinemia.

Renin Inhibition: What Are the Therapeutic Opportunities?

Blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers has become a crucial element in cardiovascular and renal medicine. This review evaluates the potential of renin inhibition as an adjunct to therapies that depend on renin system interruption.

Hypovolaemia-induced vasodilatation during angiotensin AT1 receptor blockade: role of the AT2 receptor

AT(1) receptor antagonists may interfere with the haemodynamic determinants of arterial pressure either directly or indirectly through the stimulation of AT(2) receptor provided Ang II is available to interact with them. In order to evaluate the counteracting haemodynamic effect of AT(2) receptor, a prospective, randomized, controlled experimental study was carried out in anaesthetised juvenile pigs. Pigs were randomly assigned to receive placebo (n = 6), valsartan, an AT(1) receptor antagonist (a-AT(1) group; n = 6), or valsartan and PD 123319, an AT(2) receptor antagonist (a-AT(1-2) group; n = 6) after anaesthesia and before hypovolaemia by 20% of the total estimated blood volume. Thirty minutes after bleeding, the mean arterial pressure decreased significantly and similarly in the three groups (25-30%). The placebo group had a significant decrease in cardiac output (CO) without significant change in systemic vascular resistance (SVR). Conversely, in the a-AT(1) group, SVR decreased significantly with a moderate change in CO and addition of the AT(2) antagonist to the AT(1) antagonist (a-AT(1-2) group) did not abolish the lowering in SVR. The results suggest that AT(2) receptor has only a small if any contribution in the vasodilatation observed in the AT(1)-blockade group.

Hypotension Due to Interaction Between Lisinopril and Tizanidine

OBJECTIVE

To report a case in which significant hypotension occurred after initiation of tizanidine in a patient using the antihypertensive agent lisinopril.

CASE SUMMARY

A 48-year-old woman was admitted due to cerebral hemorrhage at the midbrain and pons, with extension to the fourth ventricle. Consciousness disturbance (Glasgow coma scale 4) with a decerebrate posture improved 5 days after stroke onset. As the BP was fairly high, antihypertensive agents, including lisinopril, were initiated. Three weeks later, the decerebrate rigidity and high BP remained, and tizanidine was initiated to see whether the decrease in muscle tone could facilitate hypertension control and motor recovery. However, the BP dropped dramatically within 2 hours after the first dose of tizanidine. The tizanidine and all of the antihypertensive medications were withdrawn. Tizanidine was used again after her BP had stabilized, but did not produce similar problems.

DISCUSSION

A similar event was reported in 2000. The reaction in our patient appeared after tizanidine initiation and improved after both lisinopril and tizanidine were discontinued. According to the Naranjo probability scale, this was classified as a possible drug interaction. This kind of reaction is seldom mentioned as occurring during co-administration with tizanidine. With its characteristics, tizanidine has the potential to compromise hemodynamic stability during concomitant angiotensin-converting enzyme inhibitor use.

CONCLUSIONS

Based upon the literature review, the hypotension in this patient was possibly due to the interaction between tizanidine and lisinopril.

Haemodynamic effects of an angiotensin-converting enzyme inhibitor and angiotensin receptor antagonist during hypovolaemia in the anaesthetized pig

BACKGROUND

Renin-angiotensin system antagonists, either angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor (AT(1)) antagonists, may interfere with regulation of arterial pressure during anaesthesia. This study aimed to compare the haemodynamic profile of anaesthetized pigs, which were subjected to haemorrhage in the presence of the ACE inhibitor enalaprilat or the AT(1) antagonist valsartan.

METHODS

Thirty-six pigs were assigned randomly to placebo, enalaprilat or valsartan groups. After a 30-min period of stabilization following anaesthesia and injection of the study drug, the animals were bled in two equal steps of 20% of their estimated blood volume (20% BV and 40% BV).

RESULTS

After bleeding of 20% BV, the mean arterial pressure (MAP) decreased significantly but similarly in each group (20-25%) but the placebo and the enalaprilat groups had a significant decrease in cardiac index (CI, 22% and 16%, respectively) without significant change in systemic vascular resistance (SVR). Conversely, in the valsartan group, SVR decreased significantly (23%, P<0.02 vs other groups) without significant change in CI (-4%). After bleeding of 40% BV, the CI decreased significantly compared with 20% BV in the three groups (19% in the placebo and enalaprilat groups, 14% in the valsartan group) but the MAP decreased significantly in the enalaprilat group only (23%). The SVR increased significantly in the placebo group (P<0.01 vs each of the other groups), but there were no differences in the change in SVR between the other groups.

CONCLUSION

Blockade of the renin-angiotensin system by either enalaprilat or valsartan leads to a similar decrease in arterial pressure during anaesthesia and haemorrhage but the haemodynamic profiles are quite different.

Enalapril acts through release of nitric oxide in patients with essential hypertension

BACKGROUND

Endothelial dysfunction has been proposed as an etiological agent in the pathogenesis of essential hypertension. Amongst the various antihypertensive drugs, angiotensin converting enzyme inhibitors (ACEI) have been implicated in modifying the vascular endothelium by the release of mediators that include bradykinin, nitric oxide, prostaglandins and thromboxane A2.

MATERIALS AND METHODS

To study the mechanism of action of enalapril, an ACEI, serum reactive nitrite intermediates (RNI) and citrulline, by products of nitric oxide metabolism were measured before and after treatment with enalapril in 25 consecutive patients of essential hypertension.

RESULTS

Following treatment serum RNI intermediate increased from a pretreatment value of 164.5 +/- 20.2 nmol/mL to a post treatment value of 266.9 +/- 47.3 nmol/mL (p < 0.05), however there was no significant change in the levels of citrulline (p > 0.1). There was no significant correlation between the severity of hypertension and serum RNI. Serum RNI levels were lower in the postmenopausal women but did not reach statistical significance.

CONCLUSIONS

It is postulated that enalapril exhibits its antihypertensive property through release of nitric oxide.

Pharmacokinetic-pharmacodynamic model for perindoprilat regional haemodynamic effects in healthy volunteers and in congestive heart failure patients

AIMS

We compared the relationships between the plasma concentrations (C) of perindoprilat, active metabolite of the angiotensin I-converting enzyme inhibitor (ACEI) perindopril, and the effects (E) induced on plasma converting enzyme activity (PCEA) and brachial vascular resistance (BVR) in healthy volunteers (HV) and in congestive heart failure (CHF) patients after single oral doses of perindopril.

METHODS

Six HV received three doses of perindopril (4, 8, 16 mg) in a placebo-controlled, randomized, double-blind, crossover study whereas 10 CHF patients received one dose (4 mg) in an open study. Each variable was determined before and 6-12 times after drug intake. E (% variations from baseline) were individually related to C (ng ml(-1)) by the Hill model E=Emax x Cgamma/(CE50gamma + Cgamma). When data showed a hysteresis loop, an effect compartment was used.

RESULTS

(means+/-s.d.) In HV, relationships between C and E were direct whereas in CHF patients, they showed hysteresis loops with optimal k(e0) values of 0.13 +/- 0.16 and 0.13 +/- 0.07 h(-1) for PCEA and BVR, respectively. For PCEA, with Emax set to -100%, CE50 = 1.87 +/- 0.60 and 1.36 +/- 1.33 ng ml(-1) (P = 0.34) and gamma = 0.90 +/- 0.13 and 1.11 +/- 0.47 (P = 0.23) in HV and CHF patients, respectively. For BVR, Emax= -41 +/- 14% and -60 +/- 7% (P = 0.02), CE50 = 4.95 +/- 2.62 and 1.38 +/- 0.85 ng ml(-1) (P = 0.02), and gamma = 2.25 +/- 1.54 and 3.06 +/- 1.37 (P = 0.32) in HV and CHF patients, respectively.

CONCLUSIONS

Whereas concentration-effect relationships were similar in HV and CHF patients for PCEA blockade, they strongly differed for regional haemodynamics. This result probably expresses the different involvements, in HV and CHF patients, of angiotensinergic and nonangiotensinergic mechanisms in the haemodynamic effects of ACEIs.

Is there a future for renin inhibitors?

Pharmacological interruption of the renin-angiotensin system is possible at three major sites, the angiotensin-converting enzyme (ACE), the AT1 receptor and at the interaction of renin with its substrate, angiotensinogen. Skeggs and his associates in 1957 argued logically but without prognostic accuracy that 'since renin is the initial and rate-limiting substance in the renin-angiotensin system, it would seem that the renin inhibition approach would be the most likely to succeed'. In fact, the development of agents that act at all three levels has enjoyed substantial success, yet renin inhibition, which showed early progress in studies in humans, has languished. Our task in this essay is to review the reasons for the slow evolution of renin inhibition and to discuss the potential of such agents in modern pharmacotherapy. All of the structure-action relationships have involved variation on the original peptide structure. The possibility that alternative approaches based on x-ray crystallography and reconstruction of the structure of the active site would lead to novel agents, appears not to have been explored systematically. This opportunity is all the more attractive because renin is one of the few targets that is actually soluble and amenable to x-ray crystallographic studies. At the moment, it appears that all renin inhibitor development programs have been closed, although hints periodically reappear to indicate that one company or another is pursuing a novel agent. The decision to close programs seems to have reflected not the therapeutic potential of renin inhibitors, but rather the cost of their synthesis, continuing problems with bioavailability and the remarkable success of the competitor class--the AngII antagonists. We believe that the potential of renin inhibition in human therapy has been under estimated and still shows substantial promise.

Comparison of arrhythmias among different left ventricular geometric patterns in essential hypertension

The differences of arrhythmias among distinct left ventricular geometric patterns in the patients with essential hypertension were studied. 179 patients with essential hypertension received 24 h dynamic ECG recording, ambulatory blood pressure monitoring, echocardiography examination, etc. According to the examinations, left ventricular geometric patterns and arrhythmias were identified. The comparison of morbidity of arrhythmias between the left ventricular remodeling group and the normal geometric pattern group was performed. The multiple stepwise regression analysis was carried out to identify the independent determinants of arrhythmias. After these predictors were controlled or adjusted, the severity of arrhythmias among different left ventricular geometric patterns was compared. It was found that the morbidity of atrial arrhythmia, ventricular arrhythmia and complex ventricular arrhythmias in the left ventricular remodeling group was significantly higher than in the normal geometric pattern group respectively. There were many independent factors influencing on arrhythmias in essential hypertension. Of all these factors, some indices of left ventricular anatomic structure, grade of hypertension, left atrial inner dimension, E/A, diastolic blood pressure load value at night and day average heart rate and so on were very important. After the above-mentioned factors were adjusted, the differences of the orders of arrhythmias between partial geometric patterns were reserved, which resulted from the differences of the geometric patterns. Many factors contributed to arrhythmias of essential hypertension, such as grade of hypertension, LVMI, LA, PWT and so on. The severity of arrhythmias was different in different left ventricular geometric patterns.

Heart rate variability and baroreflex sensitivity in idiopathic dilated cardiomyopathy

OBJECTIVE

To examine the relation between cardiac autonomic tone, assessed by baroreflex sensitivity and heart rate variability, and left ventricular function, arrhythmias on Holter monitoring, and clinical variables in patients with idiopathic dilated cardiomyopathy.

DESIGN

A prospective observational study.

PATIENTS

160 patients with idiopathic dilated cardiomyopathy and preserved sinus rhythm in the absence of antiarrhythmic drug treatment. Measures of heart rate variability obtained by digital 24 hour Holter recordings included the mean of all coupling intervals between normal beats (RRm), the standard deviation of the mean of normal RR intervals (SDNN), and the square root of the mean of the squared differences between adjacent normal RR intervals (rMSSD). Baroreflex sensitivity testing was performed using the phenylephrine method.

RESULTS

Mean SDNN (SEM) was 112 (46) ms, and baroreflex sensitivity was 7.5 (5.0) ms/mm Hg. SDNN showed a weak correlation with baroreflex sensitivity (r = 0.19, p < 0.05) and with left ventricular ejection fraction (r = 0.29, p < 0.05). SDNN showed no significant correlation with age (r = -0.07), the presence of non-sustained ventricular tachycardia (r = -0.13), or left ventricular end diastolic diameter (r = -0.07). In addition, baroreflex sensitivity showed no significant correlation with age (r = -0.13), non-sustained ventricular tachycardia (r = -0.08), left ventricular end diastolic diameter (r = 0.09), or ejection fraction (r = 0.14).

CONCLUSIONS

The weak correlation between baroreflex sensitivity and heart rate variability suggests that these two indices explore different aspects of cardiac autonomic control in patients with idiopathic dilated cardiomyopathy. The weak or absent correlation between baroreflex sensitivity, heart rate variability, and other potential non-invasive risk predictors, including left ventricular ejection fraction, left ventricular end diastolic diameter, and non-sustained ventricular tachycardia on Holter monitoring, indicate that these variables may have independent prognostic value in idiopathic dilated cardiomyopathy.

Impact of concurrent amiodarone treatment on the tolerability and efficacy of carvedilol in patients with chronic heart failure

OBJECTIVE

To assess the safety and efficacy of carvedilol when administered to heart failure patients already receiving amiodarone.

DESIGN

Retrospective analysis of the clinical outcome of 230 patients treated with carvedilol for chronic heart failure, stratified according to whether they were already receiving amiodarone (amiodarone group, 80 patients) or not (non-amiodarone group, 130 patients) at baseline.

SETTING

Heart failure clinic at a university affiliated public teaching hospital.

MAIN OUTCOME MEASURES

Incidence of adverse events; changes in functional status and echocardiographic dimensions at three months.

RESULTS

Adverse reactions to carvedilol occurred in 33 (41%) of the amiodarone group and 43 (29%) of the non-amiodarone group (p = 0.049). Carvedilol was discontinued in 21 (26%) of the amiodarone group and 37 (25%) of the non-amiodarone group (NS). The clinical outcome at three months did not differ significantly between the two groups; 31 (39%) of the amiodarone group improved their New York Heart Association status, 28 (35%) were unchanged, and 21 (26%) deteriorated compared with 67 (45%), 51 (34%), and 32 (21%), respectively, for the non-amiodarone group (NS). Both groups had highly significant decreases in heart rate and left ventricular end systolic dimension, and a significant increase in left ventricular ejection fraction after three months of carvedilol treatment, with no significant differences between the groups.

CONCLUSIONS

The beneficial effects of carvedilol on left ventricular remodelling, systolic function, and symptomatic status are not affected by concurrent treatment with amiodarone. Adverse reactions necessitating cessation of carvedilol are no more frequent in patients receiving amiodarone.

Increased bradykinin levels accompany the hemodynamic response to acute inhibition of angiotensin-converting enzyme in dogs with heart failure

To determine the short-term effects of angiotensin-converting enzyme (ACE) inhibition on hemodynamics and circulating levels of norepinephrine, angiotensin, and bradykinin, responses to enalaprilat and perindoprilat were examined at doses of 0.03, 0.3, and 1 mg/kg in permanently instrumented conscious dogs with pacing-induced heart failure (right ventricular pacing, 240-250 beats/min, 3 weeks). All doses of the two inhibitors produced similar decrease in mean aortic pressure and increase in cardiac output. Neither inhibitor affected plasma norepinephrine level. Both compounds induced a similar 60-80% decrease in blood angiotensin II level, a similar two- to eightfold increase in blood angiotensin I level, and a 80-95% decrease in the angiotensin II/angiotensin I ratio. There were also a fourfold to 10-fold increase in blood bradykinin-(1-9) level, a twofold increase in blood bradykinin-(1-7) level, and a 70-85% decrease in bradykinin-(1-7)/bradykinin-(1-9) ratio. In addition, the changes in total peripheral resistance induced by the two ACE inhibitors were weakly but significantly correlated with the changes in blood angiotensin II or blood bradykinin-(1-9). Thus whatever the specificity of enalaprilat and perindoprilat, both inhibitors produced similar acute hemodynamic effects in dogs with heart failure, which was associated with marked decrease in circulating angiotensin II level and increase in bradykinin-(1-9) level. This study, which measures for the first time in heart failure the blood bradykinin level after ACE inhibitors, indicates, in concert with angiotensin II reduction, a role for increased bradykinin-(1-9) level in mediating short-term hemodynamic effects of ACE inhibition in this model of heart failure.

Resuscitation from out-of-hospital cardiac arrest: is survival dependent on who is available at the scene?

OBJECTIVE

To determine whether survival from out-of-hospital cardiac arrest is influenced by the on-scene availability of different grades of ambulance personnel and other health professionals.

DESIGN

Population based, retrospective, observational study.

SETTING

County of Nottinghamshire with a population of one million.

SUBJECTS

All 2094 patients who had resuscitation attempted by Nottinghamshire Ambulance Service crew from 1991 to 1994; study of 1547 patients whose arrest were of cardiac aetiology.

MAIN OUTCOME MEASURES

Survival to hospital admission and survival to hospital discharge.

RESULTS

Overall survival from out-of-hospital cardiac arrest remains poor: 221 patients (14.3%) survived to reach hospital alive and only 94 (6.1%) survived to be discharged from hospital. Multivariate logistic regression analysis showed that the chances of those resuscitated by technician crew reaching hospital alive were poor but were greater when paramedic crew were either called to assist technicians or dealt with the arrest themselves (odds ratio 6.9 (95% confidence interval 3.92 to 26.61)). Compared to technician crew, survival to hospital discharge was only significantly improved with paramedic crew (3.55 (1.62 to 7.79)) and further improved when paramedics were assisted by either a health professional (9.91 (3.12 to 26.61)) or a medical practitioner (20.88 (6.72 to 64.94)).

CONCLUSIONS

Survival from out-of-hospital cardiac arrest remains poor despite attendance at the scene of the arrest by ambulance crew and other health professionals. Patients resuscitated by a paramedic from out-of-hospital cardiac arrest caused by cardiac disease were more likely to survive to hospital discharge than when resuscitation was provided by an ambulance technician. Resuscitation by a paramedic assisted by a medical practitioner offers a patient the best chances of surviving the event.

Circumstances and causes of out-of-hospital cardiac arrest in sudden death survivors

OBJECTIVE

To study the circumstances and medical profile of out-of-hospital sudden cardiac arrest (SCA) patients in whom resuscitation was attempted by the ambulance service, and to identify causes of SCA in survivors and factors that influence resuscitation success rate.

METHODS

During a five year period (1991-95) all cases of out-of-hospital SCA between the ages of 20 and 75 years and living in the Maastricht area in the Netherlands were studied. Information was gathered about the circumstances of SCA, as well as medical history for all patients in whom resuscitation was attempted by the ambulance personnel. Causes of SCA in survivors were studied and logistic regression analysis was performed to identify factors associated with survival.

RESULTS

Of 288 SCA patients in whom cardiopulmonary resuscitation (CPR) and advanced life support were applied, 47 (16%) were discharged alive from the hospital. Their mean (SD) age was 58 (11) years, 37 (79%) were men, and 24 (51%) had a history of cardiac disease. Acute myocardial infarction was diagnosed in 24 (51%) of the survivors; seven with and 17 without a history of cardiac disease. Ventricular fibrillation (VF) or ventricular tachycardia (VT) as the first documented rhythm was significantly positively associated with survival (odds ratio (OR) 5.7, 95% confidence interval (CI) 2.1 to 15.9). A time interval of less than four minutes between the moment of collapse and the start of resuscitation, and an ambulance delay time of less than eight minutes were significantly positively associated with survival (OR 3.3, 95% CI 1.3 to 8.6, and OR, 3.6, 95% CI 1.3 to 10.5, respectively). A history of cardiac disease was negatively associated with survival (OR 0.46, 95% CI 0.21 to 0.98).

CONCLUSIONS

Acute myocardial infarction was the underlying mechanism of SCA in most of the survivors, especially in those without a history of cardiac disease. CPR within four minutes, an ambulance delay time less than eight minutes, and VT or VF diagnosed by the paramedics were positively associated with success.

Delapril slows the progression of atherosclerosis and maintains endothelial function in cholesterol-fed rabbits

The renin-angiotensin system is an important modulator of arterial blood pressure and inhibitors of the angiotensin-converting enzyme (ACE-Is) and are currently used in the treatment of hypertension. The pleiotropic actions exerted by angiotensin II (AngII) on the functionality of the vessel wall may have pro-atherosclerotic outcomes; evidence for an anti-atherosclerotic effect of ACE-Is has been presented and an antioxidant effect has been attributed to thiol-containing ACE-Is, like Captopril. The present study has been undertaken to investigate the effect of Delapril, a lipophilic ACE-I, on the development of atherosclerosis in cholesterol-fed rabbits. While it did not correct hyperlipidemia, Delapril dose dependently inhibited the development of atherosclerosis, expressed as aortic area covered by lesions (23.3+/-4.1, 21.3+/-2.4 and 18.5+/-3.3% with Delapril at the daily dose of 5, 10 and 20 mg/kg, respectively, versus 38.2%+/-6.4 for control animals) and its effect was similar to that of Captopril (14.5+/-5.1% at the daily dose of 25 mg/kg). Furthermore, Delapril partially and dose dependently restored endothelium-dependent relaxation, which is impaired in vessels from hypercholesterolemic animals (51.80+/-12.18, 59.74+/-5.16, 69.13+/-8.70 maximal percent relaxation versus 48.26+/-3.05% for the untreated control and 67.67+/-6.72% for Captopril-treated animals). An antioxidant mechanism is unlikely to explain this data, since Delapril does not contain thiol groups. These observations suggest that Delapril may represent an effective pharmacological approach for the treatment of atherosclerosis during its early phases.

Acute renal effects of AT1-receptor blockade after exogenous angiotensin II infusion in healthy subjects

In 10 healthy normotensive volunteers on a normal sodium diet, we evaluated the renal effects of a single oral dose of 50 mg of irbesartan (SR 47436, BMS 186295), an angiotensin II AT1-receptor antagonist, in baseline conditions and during an exogenous angiotensin II infusion (2.5 ng/kg/min). We used a double-blind, placebo-controlled, crossover design. Hormones, blood pressure, renal hemodynamics, and urinary electrolytes were measured during each phase. To examine further the determinants of glomerular filtration at the microcirculation level, fractional clearance of neutral dextran was performed, and sieving curves were applied on a hydrodynamic model of ultrafiltration. Irbesartan administration was followed by an increase in active renin and plasma angiotensin II concentrations and renal plasma flow without change of systemic blood pressure, glomerular filtration rate, or plasma aldosterone concentration. Irbesartan did not affect either sieving curves or glomerular ultrafiltration determinants. Angiotensin II infusion at 2.5 ng/kg/min elicited a slight pressor response accompanied by a decrease in glomerular filtration rate and renal plasma flow and an enhancement of fractional dextran clearance over the radius range explored (3.4-5.4 nm). The transcapillary glomerular pressure gradient deltaP and the ultrafiltration coefficient kf were computed to increase by 9% and to decrease by 23%, respectively, without change in intrinsic membrane properties. Pretreatment with irbesartan prevented all these effects of angiotensin II.

The sympathetic nervous system and the renin-angiotensin-aldosterone system in cardiovascular disease

Both the sympathetic nervous system and the renin-angiotensin-aldosterone system (RAAS) have central roles in vascular adaptive processes. Stimulation of the 2 systems has been demonstrated in a range of cardiovascular disorders, including congestive heart failure and hypertension. However, elucidation regarding the interactions of the many factors involved in these 2 systems is lacking. Angiotensin-converting enzyme inhibitors have been used to reveal the contribution of some elements in the RAAS. Until relatively recently, little was known about the specific disturbances of the sympathetic nervous system in cardiovascular disease. Plasma norepinephrine levels, an indicator of sympathetic activity, have limited value because they are affected by various physiologic processes in addition to sympathetic activation. Newer approaches to the assessment of neurohormonal activity include the determination of the power content of heart-rate variability. More specific probes may lead to a better comprehension of neurohormonal physiology in health and disease and underlie future therapeutic advances targeted to prevention and treatment of specific syndromes.

Protective effect of captopril on ischemic myocardium

The protective effect and mechanism of action of the angiotensin-converting enzyme inhibitor (ACE-I) captopril was investigated in organelles from ischemic myocardial cells in a canine coronary ligation model. Sarcoplasmic reticulum (SR) and mitochondrial fractions were extracted from ischemic and nonischemic myocardial cells from captopril- and saline-treated (control) hearts. Heart rate, cardiac output, and right ventricular systolic blood pressure were similar in the captopril-treated and control groups. Left ventricular systolic blood pressure (LVPs) decreased gradually to 89% of the baseline value after captopril administration, and to 78% of the baseline value after ligation. Ca-ATPase activity in the SR, the respiratory control ratio (RCR) in the mitochondria, and dinitrophenol (DNP)-stimulated ATPase activity were significantly higher in ischemic myocardium from the captopril-treated group than from the saline-treated (control) group. The SH group content of both organelles was higher in the captopril-treated group. Our results suggest that, in addition to their hemodynamic effects, ACE-I agents containing SH groups protect the myocardium from ischemic damage by preventing enzyme oxidation.

An animal model of spontaneous arrhythmic death

Ventricular arrhythmias and the proclivity for sudden death have been identified in German shepherd dogs. This disorder is inherited, and affected animals can be consistently produced from an established colony. The arrhythmias are most prevalent in young dogs between 22 and 26 weeks of age, with death most frequent at this same age. Death occurs most frequently during presumed sleep or at rest after exercise or excitement. The QT interval is not prolonged; however, more frequent notching of the T wave exists in affected dogs compared to control dogs. Polymorphic rapid nonsustained ventricular tachycardia occurs most frequently following long RR intervals. Accordingly, perturbations that decrease the heart rate or enhance sinus arrhythmia increase the incidence of ventricular arrhythmias. Because the arrhythmias are age, behavior, and heart rate dependent, the autonomic nervous system may play a role in their generation. As determined by metaiodobenzyl-guanidine scintigraphy and immunocytochemical staining of tyrosine hydroxylase, cardiac sympathetic innervation is regionally deficient in affected dogs. Evidence suggests that initiation of the ventricular arrhythmias is caused by early afterdepolarization (EAD)-induced triggered activity originating from left ventricular Purkinje fibers. Alpha 1-adrenergic stimulation provokes EADs in the Purkinje fibers and ventricular arrhythmias in the dogs. The development of EADs may be related to heterogeneity of repolarizing currents (Ito in particular) in affected dogs. From this canine model of spontaneous ventricular arrhythmias, the opportunity exists to investigate the interplay between abnormal development of cardiac innervation and the genesis of lethal ventricular arrhythmias.

Altered patterns of cardiac intercellular junction distribution in hypertrophic cardiomyopathy

OBJECTIVE

To examine the distribution pattern of intercellular junctions (the mechanically coupling desmosomes and the electrically coupling gap junctions) in hypertrophic cardiomyopathy (HCM) hearts showing myofibre disarray.

DESIGN

Samples from six necropsied hearts were studied, representing the interventricular septum and the free walls of the left and right ventricles. Immunohistochemical labelling of desmoplakin was used as a marker for desmosomes, and of connexin43 as a marker for gap junctions, in single and double stainings. The slides were examined by confocal laser scanning microscopy.

RESULTS

Marked disorganisation of intercalated discs was observed in areas featuring myofibre disarray. Besides overall derangement, localised abnormalities in desmosome organisation were evident, which included: (1) the formation of abnormally enlarged megadiscs; (2) the presence of intersecting disc structures; and (3) aberrant side to side desmosomal connections. Gap junctional abnormalities included: (1) random distribution of gap junctions over the surface of myocytes, rather than localisation to intercalated discs; (2) abundant side to side gap junction connections between adjacent myocytes; and (3) formation of abnormally shaped gap junctions. Circles of myocytes continuously interconnected by gap junctions were also observed. Regions of the diseased hearts lacking myofibre disarray, and control hearts of normal patients and patients with other cardiac diseases, did not show these alterations.

CONCLUSIONS

The disorganisation of the intercellular junctions associated with myofibre disarray in HCM may play an important role in the pathophysiological manifestations of the disease. The remodelling of gap junction distribution may underlie the formation of an arrhythmogenic substrate, thereby contributing to the generation and maintenance of cardiac arrhythmias associated with HCM.

The role of endogenous bradykinin in blood pressure homeostasis in spontaneously hypertensive rats

1. The role of endogenous bradykinin in mean arterial blood pressure (BP) homeostasis was studied in spontaneously hypertensive (SHR) and normotensive (WKY) rats by the use of a bradykinin B2-receptor antagonist (BKant; Hoe 140, 11.6 micrograms kg-1) and converting enzyme (kininase II) inhibitor (captopril, 10 mg). To obtain a response to captopril that was induced through inhibition of kinin-degradation only and not through inhibition of angiotensin II-formation, the studies were performed on binephrectomized male rats to eliminate the renin-angiotensin system. 2. The role of the nitric oxide (NO) and the adrenergic systems were evaluated by the use of NO-synthase inhibitor (L-NAME, 0.3 g kg-1) and phentolamine (2 mg kg-1), respectively. 3. The rats were anaesthetized and pretreated with two injections of vehicle (PBS) or drugs spaced 5 min apart: PBS + PBS; BKant + PBS; PBS + L-NAME; BKant + L-NAME; or phentolamine + L-NAME. All rats were given captopril 15 min later. Time-control groups were treated with L-NAME but not captopril. 4. In WKY rats, captopril did not significantly alter BP in any of the groups. In the SHR-PBS + PBS group, on the other hand, captopril induced an immediate fall in BP (delta BP = -23 +/- 4 mmHg, P < 0.0017) which was completely blocked by BKant (delta BP = 2 +/- 2 mmHg) (P < 0.0011). L-NAME did not significantly alter the immediate hypotensive response to captopril but disclosed a later hypertensive reaction. In L-NAME + BKant-treated rats, both the hypotensive response and the late hypertension was abolished. In rats treated with phentolamine + L-NAME, the immediate fall in BP was not different from the controls whereas the late hypertension was absent. 5. BKant itself had no effect on basal BP in either WKY or SHR even when a 10 times higher dose was tested in a separate set of experiments. This was true also for conscious, nonnephrectomized SHR rats. 6. It was concluded that endogenous production of bradykinin was demonstrable through kininase II-inhibition in hypertensive but not in normotensive rats. However, this endogenous bradykinin did not play a role in basal BP homeostasis. The captopril-induced hypotension depended on kinin but, under the present conditions, not on NO as a mediator. The fall in BP induced a compensatory adrenergic hypertensive response which was revealed when the continuous NO-synthesis was blocked by L-NAME.

Chronic memory impairment after cardiac arrest outside hospital

OBJECTIVES

To evaluate the nature, prevalence, and severity of chronic memory deficit in patients resuscitated after cardiac arrest outside hospital and to determine whether such deficits are related to duration of cardiac arrest.

DESIGN

Case-control study.

SUBJECTS

35 survivors of cardiac arrest outside hospital and 35 controls matched for age and sex who had had acute myocardial infarction without cardiac arrest.

MAIN OUTCOME MEASURES

Subjects assessed at least two months after index event for affective state (hospital anxiety and depression scale), premorbid intelligence (national adult reading test), short term recall (digit recall test), and episodic long term memory (Rivermead behavioural memory test).

RESULTS

Cases and controls showed no difference in short term recall. Cases scored lower on Rivermead test than controls (mean (SD) score out of 24 points: 17.4 (5.4) v 21.8 (2.0), P < 0.001), particularly in subtests relating to verbal and spatial memory. Moderate or severe impairment was found in 37% of cases and in no controls. Severity of impairment of memory correlated significantly with measures of duration of cardiac arrest. This deficit was not significantly associated with subjects' age, interval from index event to assessment, occupation, measures of comorbidity, social deprivation, anxiety or depression scores, or estimated premorbid intelligence.

CONCLUSIONS

Clinically important impairment of memory was common after cardiac arrest outside hospital. Improvement in response times of emergency services could reduce the severity of such deficits. With an increasing numbers of people expected to survive cardiac arrest outside hospital, rehabilitation of those with memory deficit merits specific attention.

Effect of angiotensin converting enzyme inhibitors on quality of life in hypertensive patients. Pharmacodynamic basis

The aim of this review is to comment the results described in the literature concerning the possible pharmacodynamic mechanisms involved in the improvement of quality of life of angiotensin converting enzyme inhibitors that is just a working hypothesis. These drugs, widely used in the treatment of hypertension, prevent the formation of angiotensin II and the generation of free radicals, as well as the hydrolysis of bradykinin, enkephalins and endorphins. Different mechanisms have been implicated on quality of life: 1) increase of bradykinin levels in the central nervous system that would trigger the release of nitric oxide (NO), noradrenaline, acetylcholine, excitatory amino acids and vasopressin which are involved in memory and cognition; 2) increase of brain blood supply by enhanced NO synthesis; 3) interference with cholinergic mechanisms in the central nervous system by angiotensin II inhibition of acetylcholine release; 4) decrease of endorphin metabolism; and 5) interaction with hypothalamic-pituitary-adrenal axis that releases ACTH and vasopressin.

Renin inhibitors: cardiovascular drugs of the future?

This review explores whether the therapeutic attractiveness of renin inhibitors compared with angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor antagonists, is sufficient to warrant continued interest in their development for the treatment of cardiovascular disease. Clinical and experimental data available to date indicate that patients with hypertension and congestive heart failure will benefit from renin inhibition. However, clinical experience is very limited, and extra benefits of renin inhibitors compared with the other blockers of the renin-angiotensin system (RAS) have yet to be demonstrated. Some experimental data in animals and humans point to a greater effect of acute renin inhibition on renal blood flow than other modes of interference with the RAS. Again, the clinical benefits of such an effect, and particularly after long-term treatment, in hypertension and renal disease need to be determined. In today's cost-conscious health setting, only new drugs that bring additional clinical benefits have a good chance of being commercially viable. It remains to be seen whether renin inhibitors will fulfill these criteria.

Losartan: first of a new class of angiotensin antagonists for the management of hypertension

Angiotensin receptor antagonists represent a new class of drugs for the treatment of patients with hypertension. Reduction of blood pressure in patients with essential hypertension requires increased activity of the renin-angiotensin system. Losartan, the first orally active, nonpeptide angiotensin antagonist, specifically competes with angiotensin II (Ang II) for the AT1 receptor and reversibly alters the receptor. Maximum blood pressure reductions occur after doses of approximately 50 mg, although some patients will require 100 mg; the parent compound and a metabolite are responsible for a smooth 24-hour effect on blood pressure. Once-daily dosing with losartan has been documented to be safe. The drug's safety has been evaluated in 4,058 patients; of these patients, more than 1,200 were treated for longer than 6 months and more than 800 were treated for longer than 1 year with doses of 10 mg to 150 mg. Overall, no hypertensive patients were withdrawn from treatment because of elevated serum creatinine or potassium levels, and there were no reports of angioedema. In addition, some reductions in plasma uric acid levels were noted. Cough occurred significantly less often in patients treated with losartan than in those treated with hydrochlorothiazide or lisinopril. In contrast to angiotensin-converting enzyme (ACE) inhibitors, losartan does not activate bradykinin-nitric oxide-prostanoid vasodilation.

Clinical benefit of angiotensin-converting enzyme inhibitors in chronic heart failure

The ideal therapy for patients with chronic heart failure should reduce symptoms related to pulmonary congestion or low perfusion, prevent the progression of left ventricular dysfunction and, ultimately, should reduce mortality. Extensive studies in humans have investigated the effects of angiotensin-converting enzyme (ACE) inhibitors on these goals of therapy. As an example, the ACE inhibitor cilazapril significantly improved exercise tolerance, as borne out by a meta-analysis of six placebo-controlled, randomized 3-month trials. Comparison of the effects of cilazapril and captopril vs. placebo in one of the trials documented similar improvement in exercise tolerance (14 vs. 17%). Results from other randomized comparative trials suggest that the improvement in symptoms represents a class effect of ACE inhibitors. A beneficial effect of ACE inhibition on the progression of left ventricular dysfunction has also been demonstrated in the SOLVD trial, and a reduction of mortality has been amply documented in several mortality trials (CONSENSUS I, SOLVD, V-HeFT-II, SAVE, AIRE, SMILE) in patients with or without preceding myocardial infarction. Reports that ACE inhibitors also reduce the incidence of reinfarction after myocardial infarction have not been confirmed in all studies but raise the interesting concept that ACE inhibition may interact, in a beneficial but thus far not well-understood way, with key processes in the development of atherosclerosis, thereby preventing plaque rupture, thrombus formation, and myocardial infarction. Taken together, a large database convincingly demonstrates that ACE inhibitors are effective not only in improving symptoms but also in the prevention of progression of left ventricular dysfunction, in the reduction of mortality, and possibly in stabilizing the atherosclerotic disease process.

Angiotensin converting enzyme (ACE) inhibitors and kinin metabolism: evidence that ACE inhibitors may inhibit a kininase other than ACE

1. Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II, and also metabolizes bradykinin-(1-9) to bradykinin-(1-7) and bradykinin-(1-7) to bradykinin-(1-5). Increases in endogenous kinin levels may contribute to the therapeutic effects of ACE inhibitors. 2. ACE inhibitors increase vascular levels of both bradykinin-(1-9) and its ACE cleavage product bradykinin-(1-7), at doses below the threshold for ACE inhibition, leading to the proposal that ACE inhibitors may also inhibit a non-ACE kininase which cleaves both kinin peptides; this non-ACE kininase may be the major pathway of kinin metabolism in the vasculature and some other tissues. 3. In support of this proposal, ACE inhibitors potentiate bradykinin-(1-9) effects at doses which have little or no effect on ACE activity, as indicated by angiotensin I conversion to angiotensin II. ACE inhibitors also potentiate the actions of ACE-resistant kinin analogues, which may be susceptible to metabolism by a non-ACE kininase. 4. Identification and characterization of the putative non-ACE kininase which is inhibited by ACE inhibitors may reveal novel approaches to the tissue-specific modulation of kinin levels.

Favourable outcome in idiopathic ventricular fibrillation with treatment aimed at prevention of high sympathetic tone and suppression of inducible arrhythmias

OBJECTIVE

In the absence of an obvious cause for cardiac arrest, patients with idiopathic ventricular fibrillation are difficult to manage. A subset of patients has inducible arrhythmias. In others sympathetic excitation plays a role in the onset of the cardiac arrest. This study evaluates a prospective stepped care approach in the management of idiopathic ventricular fibrillation, with therapy first directed at induced arrhythmias and secondly at adrenergic trigger events.

SETTING

University Hospital.

PATIENTS

10 consecutive patients successfully resuscitated from idiopathic ventricular fibrillation.

INTERVENTIONS

Programmed electrical stimulation to determine inducibility, followed by serial drug treatment. Assessment of pre-arrest physical activity and mental stress status by interview, followed by beta blockade. Cardioverter-defibrillator implantation in non-inducible patients not showing significant arrest related sympathetic excitation.

MAIN OUTCOME MEASURE

Recurrent cardiac arrest or ventricular tachycardia.

RESULTS

Five patients were managed with serial drug treatment and four with beta blockade. In one patient a defibrillator was implanted. During a median follow up of 2.8 years (range 6 to 112 months) no patient died or experienced defibrillator shocks. One patient had a recurrence of a well tolerated ventricular tachycardia on disopyramide.

CONCLUSIONS

Idiopathic ventricular fibrillation may be related to enhanced sympathetic activation. Prognosis may be favourable irrespective of the method of treatment. Whether the present approach enhances prognosis of idiopathic ventricular fibrillation remains to be determined. However, it may help to avoid potentially hazardous antiarrhythmic drugs or obviate the need for implantation of cardioverter-defibrillators.

Role of the renin-angiotensin system in systemic and regional vascular responses to orthostatic stress in healthy volunteers

The effects of a single oral dose (5 mg) of the angiotensin-converting enzyme (ACE) inhibitor, ramipril, on the systemic and regional vascular responses to simulated orthostatic stress by the lower body negative pressure (LBNP) technique were investigated in eight healthy volunteers, in a double-blind, placebo-controlled crossover study. Arterial blood pressure remained unchanged throughout the study. Ramipril increased significantly forearm (venous occlusion plethysmography, + 37% +/- 4% from 1.98 ml.min-1.100 ml-1) and renal (PAH clearance, + 6 +/- 2% from 1.20 1.min-1) blood flows and decreased corresponding vascular resistances, 150 minutes after its administration and before LBNP. It also significantly reduced calculated filtration fraction and inhibited by approximately 86% plasma ACE activity. Lower body negative pressure at -10 and -20 mmHg induced a progressive and significant decrease in central venous pressure and significant increases in forearm, splanchnic (indocyanine green clearance) and total peripheral vascular resistances which were of the same magnitude after ramipril and placebo administrations. Ramipril blunted the LBNP-induced increase in renal vascular resistance observed at -20 mmHg after placebo but a similar increase in glomerular filtration rate (inulin clearance) was observed at LBNP-10 and -20 mmHg after ramipril and placebo. Calculated filtration fraction increased after placebo (LBNP-10 mmHg) and ramipril (LBNP-20 mmHg). Finally, LBNP-induced changes in biological parameters were similar after ramipril and placebo at all levels of LBNP. Thus, ramipril does not interfere with the adaptive forearm and splanchnic vascular responses and preserves renal hemodynamics during orthostatic stress simulated by LBNP in healthy volunteers.

Baroreflex sensitivity and neurohormonal activation in patients with acute myocardial infarction

OBJECTIVE

To examine the relationship between baroreflex sensitivity and neurohormonal activation in patients with an acute myocardial infarction.

METHODS

Baroreflex sensitivity, plasma noradrenaline, atrial natriuretic factor, endothelin-1, and plasma renin activity were measured in 37 male patients about 10 days after their first myocardial infarction, and in 15 healthy controls. Baroreflex sensitivity was assessed from the regression line relating the change in RR interval to the change in systolic blood pressure following an intravenous bolus injection of phenylephrine. The measurements were repeated after a follow up of three months.

RESULTS

There was a significant inverse correlation between baroreflex sensitivity and plasma noradrenaline measured before hospital discharge (r = -0.43, P < 0.01). Patients with increased plasma noradrenaline (> or = 2SD above the mean of the age matched control group) had significantly lower baroreflex sensitivity than patients with normal plasma noradrenaline (8.7 (SD 4.6) v 12.1 (6.1) ms/mm Hg, P < 0.05). The change in baroreflex sensitivity during the follow up showed a significant inverse correlation with the change of plasma noradrenaline (r = -0.450, P < 0.01). Furthermore, when patients with increased plasma noradrenaline before hospital discharge were analysed separately, baroreflex sensitivity at three months in patients in whom plasma noradrenaline had decreased to normal values was significantly higher than in patients in whom plasma noradrenaline had remained increased (14.6 (5.7) v 8.1 (8.1) ms/mm Hg, P < 0.05). On the other hand, baroreflex sensitivity was not related to the levels of plasma atrial natriuretic factor, plasma endothelin-1, or plasma renin activity. Neither was any relationship found between change in baroreflex sensitivity and change in plasma atrial natriuretic factor, endothelin-1, or plasma renin activity during the follow up.

CONCLUSIONS

The impairment baroreflex sensitivity after myocardial infarction was associated with increased concentration of plasma noradrenaline, that is, sympathetic activation, but not with plasma atrial natriuretic factor, endothelin-1, or plasma renin activity. Baroreflex sensitivity provides information about cardiac vagal control as well as about the balance of cardiac sympathetic-parasympathetic regulation.

Origin and pathophysiological role of increased plasma endothelin-1 in patients with acute myocardial infarction

To investigate the origin and pathophysiological role of increased plasma endothelin-1 (endothelin-1) concentration in patients with acute myocardial infarction (AMI), the authors measured plasma endothelin-1 sequentially after the onset of AMI and analyzed the origin by the simultaneously obtained blood samples from the radial artery, right atrium, and pulmonary artery in 28 patients with AMI. The data were correlated with cardiovascular hemodynamics, infarct size, and coronary arteriographic findings. Arterial endothelin-1 at twenty-four and seventy-two hours significantly correlated with mean pulmonary arterial pressure (r = 0.48, r = 0.46, P < 0.05, respectively), central venous pressure (r = 0.42 and 0.51, P < 0.05, respectively), and pulmonary vascular resistance (r = 0.42, r = 0.42, P < 0.05), and endothelin-1 at one hundred twenty hour significantly correlated with peak creatine kinase (r = 0.53, P < 0.05) and creatine kinase isozyme MB (r = 0.58, P < 0.01). Simultaneous blood samples showed no significant difference in endothelin-1 concentrations among them. However, a subgroup of patients with endothelin-1 concenration higher in the radial artery than that in the right atrium showed a significantly higher mean pulmonary arterial pressure (25.2 +/- 6.5 vs 17.0 +/- 1.6 mmHg, P < 0.05), peak creatine kinase (3594 +/- 1597 vs 865 +/- 495 IU/L, P < 0.05), and peak creatine kinase MB (214 +/- 91 vs 69 +/- 22 IU/L, P < 0.05) as compared with those in patients in whom endothelin-1 was higher in the right atrium than in the radial artery. Increased plasma endothelin-1 concentration in the early stage of AMI reflects higher pulmonary artery pressure and elevated pulmonary vascular resistance, while that in the later stage is related to the infarct size. The production of endothelin-1 in patients with severe pump failure may be accerelated in the pulmonary vascular bed, left ventricle, or systemic arterial trees, and the main origin in the later stage is possibly coronary vasculature in the infarcted area.

Nitric oxide-based possibilities for pharmacotherapy

The goal of nitric oxide (NO) based pharmacotherapy is to reach proper homeostasis of NO metabolism in the target tissue where endogenous production of NO is either too weak or excessively increased. In addition to the classic NO-based therapy of cardiovascular conditions with nitrates, a variety of new therapeutic possibilities have emerged including sexual disorders, gastrointestinal system, immunology, tumour growth regulation and respiratory disorders. NO levels of target tissues can be affected directly by NO donors, or indirectly by increasing the level of L-arginine, a substrate of nitric oxide synthase (NOS). While increased production of NO by induceable NO (iNOS) by, for example, cytokines does not at present seem therapeutically meaningful, increased NO production by constitutive NOS (cNOS) may be involved in the beneficial effects of ACE inhibitors or oestrogens. NO production may be pharmacologically decreased by inhibition of expression of iNOS by glucocorticoids while both cNOS and iNOS derived NO production is inhibited by administration of false substrates, for example L-NAME. Additionally, the respiratory system and related vessels can be reached directly and more selectively by inhalation of pure NO gas. Possible problems in administering NO and perhaps some NO-donors include the toxic nature of the compound itself whereby vital enzyme systems may be inhibited and tissue damaging radicals formed. Future prospects of NO-based pharmacotherapy may feature selective ligands to different NOS isoforms and tissue selective donors that release NO in a controlled fashion.

NASPE/ACC/AHA/ESC medical/scientific statement special report--clinical investigation of antiarrhythmic devices: a statement for healthcare professionals from a Joint Task Force of the North American Society of Pacing and Electrophysiology, the American College of Cardiology, the American Heart Association, and the Working Groups on Arrhythmias and Cardiac Pacing of the European Society of Cardiology

The goal of radiofrequency catheter ablation and the criterion for efficacy is the elimination of arrhythmogenic myocardium. The application of radiofrequency current in the heart clearly results in lower morbidity and mortality rates than thoracic and cardiac surgical procedures in general, and comparisons of therapy with radiofrequency catheter ablation and therapy with thoracic and cardiac surgical procedures in randomized clinical trials are unwarranted. Trials of radiofrequency catheter ablation versus medical or implantable cardioverter defibrillator therapy may be indicated in certain conditions, such as ventricular tachycardia associated with coronary artery disease. Randomized trials are recommended for new and radical departures in technology that aim to accomplish the same goals as radiofrequency catheter ablation. Surveillance using registries and/or databases is necessary in the assessment of long-term safety and efficacy.

Kinin-mediated activation of endothelial no formation: possible role during myocardial ischemia

Endothelial cells produce a variety of factors involved in the control of vascular tone, platelet activation and cell growth, one of the most important being nitric oxide (NO). Although continuously produced in response to fluid shear stress, the release of NO from these cells can be enhanced further by humoral stimuli, such as bradykinin. This is the result of a chain of complex intracellular events involving changes in Ca2+, pH and protein phosphorylation. Endothelial cells are also capable of synthesizing bradykinin from an endogenous source, the release of which is markedly enhanced under hypoxic conditions. The finding that ACE inhibitors promote the local accumulation of the peptide and increase its efficacy at the receptor level may partly explain the potent anti-ischemic and cardioprotective effects of these drugs.

The role of nitric oxide, adrenergic activation and kinin-degradation in blood pressure homeostasis following an acute kinin-induced hypotension

1. Nitric oxide (NO) has been suggested as the mediator of the vascular response to bradykinin. In the present study, we found that NO did not mediate the hypotensive response to bradykinin. In addition, the significance of kininase II in terminating a kinin-induced hypotension and the role of the adrenergic system in compensating for the acute fall in blood pressure (BP) was established. 2. In normal rats, the NO-synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) induced a rise in basal BP (delta BP = 40 +/- 6 mmHg, P < 0.0014) which was not altered by pretreatment with phentolamine (delta BP = 50 +/- 6 mmHg, NS). L-NAME did not attenuate the acute fall in BP in response to bradykinin (3-30 micrograms kg-1) or kallikrein (6-300 micrograms kg-1). However, a significant decrease was observed in the duration of the hypotensive response (P < 0.027). This shorter duration was not observed after pretreatment with phenotolamine in addition to L-NAME. Phentolamine alone prolonged the hypotensive response to bradykinin (P < 0.04). These experiments confirm the role of NO-formation as a hypotensive component in BP homeostasis but not the role of NO as a mediator in kinin-induced hypotension. It further shows that the continuous NO-release also impedes the compensatory adrenergic hypertensive response following the acute fall in BP induced by bradykinin. 3. The hypertensive response to intravenously administered phenylephrine was found to be unchanged by preadministration of L-NAME (NS) thus showing that L-NAME did not change the sensitivity to the adrenergic response. In a separate protocol on L-NAME-treated rats we found no difference in heart rate (NS) during the recovery period following bradykinin before as compared to after administration of phentolamine. It was therefore concluded that the observed alterations in the duration of the hypotensive response were most probably due to changes in peripheral vascular resistance.4. To confirm further that NO is not a mediator in kinin-induced hypotension, we used an experimental model where the response to bradykinin was prolonged by preventing kinin degradation by kininase II-converting enzyme inhibitor (CEI). To produce a hypotensive response purely dependent on kinin, the studies were performed after removal of the renin-angiotensin system by nephrectomy (Nx). In this model, bradykinin (6 microg kg-1, i.v.) induced a prolonged hypotensive response. Pretreatment with LNAME did not alter the magnitude or the progression of the hypotensive response to bradykinin, thus confirming that NO was not a mediator in BK-induced hypotension.5. To study the mechanisms involved in terminating the hypotensive response to bradykinin, the results from the Nx CEI-treated rats were compared with Nx animals not treated with CEL. In the latter group,bradykinin induced a short hypotensive response, i.e. 0.5 +/- 0.1 min as compared to the 17 +/- 1 min after CEI (P<0.003). After kininase II-inhibition (and L-NAME), BP recovery was totally dependent on the adrenergic system, since phentolamine prevented a recovery in BP during the experimental period(P<0.01, compared to the CEI/L-NAME group). These results demonstrate the importance of kininase II as the major agent in terminating a bradykinin-induced hypotension, whereas the adrenergic system plays a small, although significant role in compensating for the fall in BP. The continuous release of NO therefore not only lowers basal BP but also impedes the compensatory adrenergic response.