Anti-platelet activity of beta-adrenergic antagonists: inhibition of thromboxane synthesis and platelet aggregation in patients receiving long-term propranolol treatment

Potential Protective Role of Blood Pressure-Lowering Drugs on the Balance between Hemostasis and Fibrinolysis in Hypertensive Patients at Rest and During Exercise

In patients with hypertension, the triad represented by endothelial dysfunction, platelet hyperactivity, and altered fibrinolytic function disturbs the equilibrium between hemostasis and fibrinolysis and translates into a hypercoagulable state, which underlies the risk of thrombotic complications. This article reviews the scientific evidence regarding some biological effects of antihypertensive drugs, which can protect patients from the adverse consequences of hypertensive disease, improving endothelial function, enhancing antioxidant activity, and restoring equilibrium between hemostatic and fibrinolytic factors. These protective effects appear not to be mediated through blood pressure reduction and are not shared by all molecules of the same pharmacological class.

Effect of β-blockers on platelet aggregation: a systematic review and meta-analysis

AIMS

Platelets play an important role in cardiovascular disease, and β-blockers are often prescribed for cardiovascular disease prevention. β-Blockers may directly affect platelet aggregation, because β-adrenergic receptors are present on platelets. There is uncertainty about the existence and magnitude of an effect of β-blockers on platelet aggregation. The aim of this study was to perform a systematic review and meta-analysis of the effect of β-blockers on platelet aggregation.

METHODS

MEDLINE and EMBASE were searched until April 2014. Two reviewers independently performed data extraction and risk of bias assessment. Type of β-blocker, population, treatment duration and platelet aggregation were extracted. Standardized mean differences were calculated for each study and pooled in a random-effects meta-analysis.

RESULTS

We retrieved 31 studies (28 clinical trials and three observational studies). β-Blockers decreased platelet aggregation (standardized mean difference -0.54, 95% confidence interval -0.85 to -0.24, P < 0.0001). This corresponds to a reduction of 13% (95% confidence interval 8-17%). Nonselective lipophilic β-blockers decreased platelet aggregation more than selective nonlipophilic β-blockers.

CONCLUSIONS

Clinically used β-blockers significantly reduce platelet aggregation. Nonselective lipophilic β-blockers seem to reduce platelet aggregation more effectively than selective nonlipophilic β-blockers. These findings may help to explain why some β-blockers are more effective than others in preventing cardiovascular disease.

Influence of Different β-Blockers on Platelet Aggregation in Patients With Coronary Artery Disease on Dual Antiplatelet Therapy

INTRODUCTION

The use of β-blockers in the treatment of patients with coronary heart disease is associated with a decrease in the frequency of angina pectoris and mortality of patients. Due to the severity of the disease and previous cardiovascular interventions, many patients with coronary artery disease (CAD) use dual antiplatelet therapy to achieve greater inhibition of platelet aggregation. The influence of β-blockers on platelet aggregation in patients using antiplatelet therapy is not well understood.

OBJECTIVE

To examine the effect of different β-blockers on platelet aggregation in patients on dual antiplatelet therapy.

METHODOLOGY

The study included 331 patients who were treated at the Department of Cardiology, Clinical Center Kragujevac during 2011. Patients were divided into 4 groups depending on the type of β-blockers that were used (bisoprolol, nebivolol, metoprolol, and carvedilol). Platelet aggregation was measured using the multiplate analyzer and expressed through the value of adenosine diphosphate (ADP) test (to assess the effect of clopidogrel), ASPI test (to assess the effect of acetyl salicylic acid), TRAP test (to assess baseline platelet aggregation), and the ratio of ADP/TRAP and ASPI/TRAP ASPI/TRAP (ASPI - aranchidonic acid induced aggregation, TRAP - thrombin receptor activating peptide) representing the degree of inhibition of platelet aggregation compared to the basal value. In consideration were taken the representation of demographic, clinical characteristics, laboratory parameters, and cardiovascular medications between the groups.

RESULTS

Patients who used nebivolol had a significantly lower value of the ratio of ADP/TRAP (0.39 ± 0.30) compared to patients who used bisoprolol (0.48 ± 0.26; P = .038), and trend toward the lower values of ADP test (328.0 ± 197.3 vs 403.7 ± 213.2; P = .059), while there was no statistically significant difference in values of other laboratory parameters of platelet function between other groups.

CONCLUSION

Patients with CAD on dual antiplatelet therapy who used nebivolol had significantly lower levels of residual ADP-induced platelet aggregation compared to baseline than patients who used bisoprolol.

The influence of bisoprolol dose on ADP-induced platelet aggregability in patients on dual antiplatelet therapy

PURPOSE

Dual antiplatelet therapy is recommended after acute coronary syndrome or after percutaneous coronary intervention with coronary stent implantation. Many of the patients on dual antiplatelet therapy receive β-blockers; some of them could have antiaggregatory effect. Bisoprolol is a highly selective adrenoceptor-blocker, which is often used in the settings of percutaneous coronary intervention or acute coronary syndrome in patients on dual antiplatelet therapy. Its antiaggregative effect has not been extensively studied. Therefore, the aim of this study is to investigate the effect of bisoprolol on ADP-induced platelet aggregation in patients on dual antiplatelet therapy.

METHODS

Platelet aggregability has been measured in 100 patients on dual antiplatelet therapy with multiplate analyzer using ADP test in blood samples anticoagulated with heparin. ADP test values have been expressed by arbitrary units/minute. In univariate and multivariate regression analyses, we have investigated the influence of bisoprolol and its dose and also different factors, such as risk factors, concomitant drugs and their dosage, laboratory findings, on ADP test values.

RESULTS

Univariate regression analysis showed significant correlation between the bisoprolol dose and the ADP test value (P=0.046, B=52.55, 95% confidence interval 0.87-104.23), which was also shown in the multivariate regression analysis (P=0.018; B=57.011; 95% confidence interval 10.455-103.567).

CONCLUSION

We have identified a positive correlation between bisoprolol dose and ADP-induced platelet aggregability in patients on dual antiplatelet therapy.

The role of central noradrenergic dysregulation in anxiety disorders: evidence from clinical studies

The nature of the noradrenergic dysregulation in clinical anxiety disorders remains unclear. In panic disorder, the predominant view has been that central noradrenergic neuronal networks and/or the sympathetic nervous system was normal in patients at rest, but hyper-reactive to specific stimuli, for example carbon dioxide. These ideas have been extended to other anxiety disorders, which share with panic disorder characteristic subjective anxiety and physiological symptoms of excess sympathetic activity. For example, Generalized Anxiety Disorder is characterized by chronic free-floating anxiety, muscle tension, palpitation and insomnia. It has been proposed that there is chronic central hypersecretion of noradrenaline in Generalized Anxiety Disorder, with consequent hyporesponsiveness of central post-synaptic receptors. With regards to other disorders, it has been suggested that there is noradrenergic involvement or derangement, but a more specific hypothesis has not been enunciated. This paper reviews the evidence for noradrenergic dysfunction in anxiety disorders, derived from indirect measures of noradrenergic function in clinical populations.

ADP-induced platelet aggregation and metoprolol treatment of myocardial infarction patients. A controlled study

The effect of metoprolol on platelet aggregation was investigated in a group of postmyocardial infarction (MI) patients. The study was double-blind and included 63 subjects; 30 patients were maintained on metoprolol and 33 received placebo treatment. Adenosine diphosphate (ADP)-induced platelet aggregation was carried out in each subject close to 4 weeks after the acute MI. It was demonstrated that metoprolol as compared to placebo did not influence ADP-induced platelet aggregation in the present clinical setting.

Reduction of nonfatal reinfarctions in patients with a history of hypertension by chronic postinfarction treatment with metoprolol

The Stockholm Metoprolol Trial is a prospective double-blind placebo-controlled postmyocardial infarction study of 301 patients treated with metoprolol, 100 mg b.i.d., or matching placebo for three years. From this study we have retrospectively evaluated the outcome in patients with a history of treatment for hypertension prior to the index infarction. There were 41 such patients in the placebo group and 35 in the metoprolol group. Blood pressures during follow-up were nearly identical in the two groups. During the three years 11 patients died in the placebo group and 7 in the metoprolol group. Corresponding figures for nonfatal events such as reinfarction, coronary artery bypass surgery, cerebrovascular events and lower limb amputation were 12 vs. 1 (p less than 0.005), 3 vs. 0, 4 vs. 0 and 1 vs. 0, respectively. The numbers of patients with fatal and nonfatal events were 24 vs. 8 (p less than 0.01). In a retrospective subgroup analysis the results must always be interpreted with caution. The present results may, however, imply that postinfarction treatment with metoprolol reduces nonfatal atherosclerotic complications, especially nonfatal reinfarctions, in patients with a history of hypertension.

Infarct-related coronary artery patency and medication use prior to ST-segment elevation myocardial infarction

In patients who have ST-segment elevation myocardial infarction (STEMI), a patent infarct-related artery on the initial angiogram is associated with improved clinical outcomes, including decreased mortality. The present study assessed the influence of administering aspirin, beta blockers, statins, and angiotensin-converting enzyme inhibitors before STEMI on infarct-related artery patency. Our data demonstrate that patients who have STEMI and receive these medications on an outpatient basis before the event have a higher likelihood of having a patent infarct-related artery compared with patients who do not receive these medications. Further, our data demonstrate a graded association according to the number of such medications being administered: the likelihood of a patent infarct-related artery increased to >50% as the number of these medications increased.

Transregulation of the alpha2-adrenergic signal transduction pathway by chronic beta-blockade: a novel mechanism for decreased platelet aggregation in patients

Platelets play a pivotal role in the pathophysiology of acute coronary syndromes. Chronic beta-blockade has been shown to improve the long-term clinical outcome in coronary heart disease. Because platelets play a central role in thrombus formation, the aim of the present study was to investigate if chronic beta-blockade may transregulate the expression of alpha2-adrenergic receptors on human platelets and via this mechanism may modulate platelet activation. The densities of alpha2-adrenergic receptors of platelets were determined in healthy volunteers under chronic beta-blockade and as alpha2-adrenergic receptor-mediated function in catecholamine-induced platelet aggregation was determined. Chronic beta-blockade induced a time-dependent reduction of alpha2-adrenergic receptors. This reduction was accompanied by a decrease of the alpha-subunit of Gi proteins as demonstrated by Western blot analysis. This transregulation at both the receptor level and the G-protein level resulted in an almost complete loss of the alpha2-adrenergic receptor-mediated inhibition of adenylyl cyclase. The impairment of the alpha2-adrenergic receptor system correlated with a reduction of the catecholamine-induced activation and aggregation of human platelets. The functional transregulation of alpha2-adrenergic receptors by chronic beta-blockade in platelets and the consequent impairment of platelet activation may contribute to the therapeutic success of beta-blocker therapy.

Is the effect of antihypertensive drugs on platelet aggregability and fibrinolysis clinically relevant?

Hypertension is associated with decreased fibrinolytic potential, mainly expressed as elevated plasma plasminogen activator inhibitor type 1 (PAI-1) levels, and increased platelet aggregability, which may account in part for the increased risk of atherosclerosis and its clinical complications in hypertensive patients. The effects of antihypertensive drugs on this prothrombotic state have been investigated and controversial findings have been reported, possibly because of differences in study designs, patients selected, and methodology used. Scarce and conflicting data exist about the effects of diuretics and beta-adrenoceptor antagonists on the fibrinolytic system, whereas ACE inhibitors have generally been reported to improve the fibrinolytic balance by decreasing plasma PAI-1 levels, calcium channel antagonists have been shown to increase tissue plasminogen activator (tPA) activity, and angiotensin II type 1 (AT(1)) receptor antagonists seem to exert neutral effects. beta-Adrenoceptor antagonists, calcium channel antagonists, and AT(1)-receptor antagonists have been reported to exert anti-aggregatory effects on platelets, while contrasting data exist about the influence of ACE inhibitors. Clinical implications of the changes induced by antihypertensive drugs on the fibrinolytic balance and platelet function are still debated. In particular, the question of whether these changes may translate into different degrees of cardiovascular protection in hypertensive patients remains unanswered. While awaiting more information from clinical trials, the choice of antihypertensive drugs, particularly in high-risk patients, should take into account effects beyond their BP-lowering efficacy. Selected agents should have a favorable, or at least neutral, impact on fibrinolytic function and platelet activity.

Beta-blockers reduce the incidence of clinical restenosis: prospective study of 4840 patients undergoing percutaneous coronary revascularization

BACKGROUND

Restenosis after percutaneous transluminal coronary intervention (PCI) remains a serious complication in the treatment of coronary artery disease. Although beta-adrenergic receptor blockers (BBs) effectively reduce many cardiac events, no large prospective studies have examined the association of BBs with restenosis.

METHODS

We prospectively evaluated the association of BBs (prescribed at hospital discharge) with clinical restenosis in 4840 patients who underwent stent placement (60%), balloon angioplasty (32%), or rotational atherectomy (8%). Clinical restenosis was defined as repeat target lesion revascularization or coronary artery bypass grafting within 6 months of PCI. Other end points included 9-month clinical restenosis, repeat target lesion PCI (only), long-term (5-year) target lesion repeat-PCI, and major adverse cardiac events (MACE). Multivariable regression adjusted the effect of BBs on clinical restenosis for 15 covariables.

RESULTS

The average patient age was 63 years, 75% were men, and 37% received a BB prescription. The incidence of clinical restenosis was 12% overall and was lower among those prescribed a BB (10.0% for BB, 13.5% for none, adjusted odds ratio [OR] 0.76, P =.004). Other predictors of decreased restenosis included stent use, age, and smoking; predictors of increased restenosis included diabetes, atherectomy, and number of treated vessels. BBs also reduced 9-month clinical restenosis (10.3% vs 13.5%, OR 0.75, P =.004), MACE (16.5% vs 20.9%, OR 0.75, P <.001), 6-month target lesion restenosis (7.8% vs 10.2%, OR 0.75, P =.006), and 5-year target lesion restenosis (12.0% vs 14.0%, OR 0.83, P =.046).

CONCLUSIONS

beta-Adrenergic receptor blockers prescribed after PCI reduced the risk of clinical restenosis, target lesion restenosis, and MACE in this cohort of 4840 patients. The mechanism by which beta-blockers conferred a protective effect against restenosis remains to be determined.

Effects of prior beta-blocker therapy on clinical outcomes after primary coronary angioplasty for acute myocardial infarction

We hypothesized that pretreatment with beta blockers may improve clinical outcomes after primary angioplasty for acute myocardial infarction. We pooled clinical, angiographic, and outcomes data on 2,537 patients enrolled in the Primary Angioplasty in Myocardial Infarction (PAMI), PAMI-2, and Stent PAMI trials. We classified patients into a beta group (n = 1,132) if they received beta-blocker therapy before primary angioplasty or a no-beta group (n = 1,405) if they did not. We evaluated procedural complications and in-hospital and 1-year outcomes (death and major adverse cardiac events [death, reinfarction, target vessel revascularization, or stroke]) between groups. Beta patients were younger, had higher systolic blood pressure and heart rate, and were more likely to be in Killip class I at admission. They had lower left ventricular ejection fraction, greater door-to-balloon time, greater likelihood of having a left anterior descending artery culprit lesion, but a similar incidence of Thrombolysis In Myocardial Infarction 3 flow after angioplasty (92.6% vs 92.7%, p = 0.91). The beta group had less procedural complications (23% vs 34%, p <0.0001) and a lower incidence of death (1.8% vs 3.7%, p = 0.0035) and major adverse cardiac events (5.5% vs 7.8%, p = 0.027) during hospitalization. At 1 year, mortality remained lower in beta patients (4.9% vs 6.7%, log-rank p = 0.055). After adjustment for baseline differences, beta patients had significantly lower in-hospital mortality (odds ratio 0.41; 95% confidence interval 0.20 to 0.84; p <0.0148) and nonsignificantly lower 1-year mortality (odds ratio 0.72; 95% confidence interval 0.47 to 1.08; p = 0.11). Thus, pretreatment with beta blockers has an independent beneficial effect on short-term clinical outcomes in patients undergoing primary angioplasty for acute myocardial infarction.

Stress and the inflammatory response: a review of neurogenic inflammation

The subject of neuroinflammation is reviewed. In response to psychological stress or certain physical stressors, an inflammatory process may occur by release of neuropeptides, especially Substance P (SP), or other inflammatory mediators, from sensory nerves and the activation of mast cells or other inflammatory cells. Central neuropeptides, particularly corticosteroid releasing factor (CRF), and perhaps SP as well, initiate a systemic stress response by activation of neuroendocrinological pathways such as the sympathetic nervous system, hypothalamic pituitary axis, and the renin angiotensin system, with the release of the stress hormones (i.e., catecholamines, corticosteroids, growth hormone, glucagons, and renin). These, together with cytokines induced by stress, initiate the acute phase response (APR) and the induction of acute phase proteins, essential mediators of inflammation. Central nervous system norepinephrine may also induce the APR perhaps by macrophage activation and cytokine release. The increase in lipids with stress may also be a factor in macrophage activation, as may lipopolysaccharide which, I postulate, induces cytokines from hepatic Kupffer cells, subsequent to an enhanced absorption from the gastrointestinal tract during psychologic stress. The brain may initiate or inhibit the inflammatory process. The inflammatory response is contained within the psychological stress response which evolved later. Moreover, the same neuropeptides (i.e., CRF and possibly SP as well) mediate both stress and inflammation. Cytokines evoked by either a stress or inflammatory response may utilize similar somatosensory pathways to signal the brain. Other instances whereby stress may induce inflammatory changes are reviewed. I postulate that repeated episodes of acute or chronic psychogenic stress may produce chronic inflammatory changes which may result in atherosclerosis in the arteries or chronic inflammatory changes in other organs as well.

Modulation of beta-adrenergic receptor subtype activities in perioperative medicine: mechanisms and sites of action

This review focuses on the mechanisms and sites of action underlying beta-adrenergic antagonism in perioperative medicine. A large body of knowledge has recently emerged from basic and clinical research concerning the mechanisms of the life-saving effects of beta-adrenergic antagonists (beta-AAs) in high-risk cardiac patients. This article re-emphasizes the mechanisms underlying beta-adrenergic antagonism and also illuminates novel rationales behind the use of perioperative beta-AAs from a biological point of view. Particularly, it delineates new concepts of beta-adrenergic signal transduction emerging from transgenic animal models. The role of the different characteristics of various beta-AAs is discussed, and evidence will be presented for the selection of one specific agent over another on the basis of individual drug profiles in defined clinical situations. The salutary effects of beta-AAs on the cardiovascular system will be described at the cellular and molecular levels. Beta-AAs exhibit many effects beyond a reduction in heart rate, which are less known by perioperative physicians but equally desirable in the perioperative care of high-risk cardiac patients. These include effects on core components of an anaesthetic regimen, such as analgesia, hypnosis, and memory function. Despite overwhelming evidence of benefit, beta-AAs are currently under-utilized in the perioperative period because of concerns of potential adverse effects and toxicity. The effects of acute administration of beta-AAs on cardiac function in the compromised patient and strategies to counteract potential adverse effects will be discussed in detail. This may help to overcome barriers to the initiation of perioperative treatment with beta-AAs in a larger number of high-risk cardiac patients undergoing surgery.

Stress, inflammation and cardiovascular disease

Various psychosocial factors have been implicated in the etiology and pathogenesis of certain cardiovascular diseases such as atherosclerosis, now considered to be the result of a chronic inflammatory process. In this article, we review the evidence that repeated episodes of acute psychological stress, or chronic psychologic stress, may induce a chronic inflammatory process culminating in atherosclerosis. These inflammatory events, caused by stress, may account for the approximately 40% of atherosclerotic patients with no other known risk factors. Stress, by activating the sympathetic nervous system, the hypothalamic-pituitary axis, and the renin-angiotensin system, causes the release of various stress hormones such as catecholamines, corticosteroids, glucagon, growth hormone, and renin, and elevated levels of homocysteine, which induce a heightened state of cardiovascular activity, injured endothelium, and induction of adhesion molecules on endothelial cells to which recruited inflammatory cells adhere and translocate to the arterial wall. An acute phase response (APR), similar to that associated with inflammation, is also engendered, which is characterized by macrophage activation, the production of cytokines, other inflammatory mediators, acute phase proteins (APPs), and mast cell activation, all of which promote the inflammatory process. Stress also induces an atherosclerotic lipid profile with oxidation of lipids and, if chronic, a hypercoagulable state that may result in arterial thromboses. Shedding of adhesion molecules and the appearance of cytokines, and APPs in the blood are early indicators of a stress-induced APR, may appear in the blood of asymptomatic people, and be predictors of future cardiovascular disease. The inflammatory response is contained within the stress response, which evolved later and is adaptive in that an animal may be better able to react to an organism introduced during combat. The argument is made that humans reacting to stressors, which are not life-threatening but are "perceived" as such, mount similar stress/inflammatory responses in the arteries, and which, if repetitive or chronic, may culminate in atherosclerosis.

Modification of high blood pressure after myocardial infarction

The treatment of high blood pressure (BP) after myocardial infarction is extremely important to decrease reinfarction and mortality. BP should be controlled more strictly in this high-risk hypertensive population. Recently, many clinical trials have demonstrated the benefits of lifestyle modification and antihypertensive agents, particularly beta-blockers and angiotensin-converting-enzyme inhibitors for the treatment of acute myocardial infarction. Treatment with these agents that modify BP may benefit even normotensive patients after a myocardial infarction, although the benefit is greater in hypertensives.

Effect of propranolol on platelet signal transduction

Propranolol inhibits platelet secondary aggregation and secretion by mechanisms unrelated to its beta-adrenergic-blocking activity. We previously reported that a major effect of the drug is perturbation of the physical microenvironment of the human platelet membrane. To explore further the molecular mechanisms underlying propranolol-mediated platelet inhibition, we studied protein kinase C activity, estimated from the phosphorylation of the substrate protein pleckstrin, in propranolol-treated human platelets. The drug inhibited activation of the enzyme in thrombin-stimulated platelets but not in platelets stimulated with phorbol esters, indicating that its site of action might be upstream of protein kinase C. It also inhibited the activity of phospholipase C, determined from the extent of generation of inositol phosphates and phosphatidic acid, in platelets stimulated with thrombin as well as the non-hydrolysable GTP analogue guanosine 5'-[beta, gamma-imido]triphosphate in a dose-dependent manner. These data suggest that propranolol inhibits signal transduction in thrombin-stimulated platelets by interacting at the level of phospholipase C and exclude interaction of the drug with the downstream effector enzyme protein kinase C.

Contraction of isolated porcine coronary arteries is inhibited by high concentrations of propranolol

Isometric tension responses of isolated porcine coronary artery rings were studied in the presence of concentrations of propranolol higher than those necessary to block effects mediated by beta-adrenergic receptors. Propranolol (50-300 microM) inhibited contractions induced by 30 mM KCl and by histamine, norepinephrine, and acetylcholine in a concentration-dependent, noncompetitive fashion. The (+) propranolol isomer and the racemic mixture were equipotent inhibitors of contraction. Propranolol inhibition was partly reversed by increased extracellular Ca++. These effects of propranolol thus appeared to be independent of beta-blockade and could be relevant to some of the drug's observed but still unexplained in vivo actions.

Antiatherogenic effects of beta-adrenergic blocking agents: theoretical, experimental, and epidemiologic considerations

Theoretical considerations and results from experimental studies in animal models suggest that long-term beta-adrenergic blockade should be antiatherogenic. Some of these experimental results indicate that beta-blockers could inhibit atherogenesis and thus prevent clinical events independently of any effects on blood pressure through concomitant reductions in heart rate, blood velocity and energy, endothelial permeability to lipoproteins, and the likelihood of plaque rupture. Any such independent inhibition of atherogenesis implies, in turn, that beta-blockers might be more desirable than alternative antihypertensive therapies in persons at high risk for atherosclerotic diseases. Results of the three major trials directly comparing beta-blockers to diuretics in the primary prevention of coronary heart disease among patients with hypertension were largely inconclusive. However, ancillary data from these and other trials are consistent in demonstrating that beta-adrenergic blockade is associated with anti-coronary heart disease effects and, thus, is perhaps antiatherogenic. A definitive evaluation of the antiatherogenic effects of beta-blockers is not forthcoming because no large clinical trials directly assessing the effect of these drugs on atherosclerosis have been done or are planned.

On the relationship between the inhibition of thrombin stimulated aggregation and thromboxane formation in isolated platelets treated with betaadrenoceptor blocking drugs

Thromboxane B2 (TXB2) formation in isolated, thrombin-stimulated rat platelets was time dependent and appeared after 5 s of incubation. Beta-adrenoceptor blocking (BAB) drugs inhibited thrombin-stimulated TXB2 formation in the following rank order of potency: metipranolol approximately alprenolol approximately propranolol > oxprenolol > practolol. Atenolol was ineffective in inhibiting TXB2 production in stimulated platelets. The inhibition of thrombin-stimulated TXB2 formation by BAB drugs correlated with their inhibitory effect on thrombin-stimulated platelet aggregation, arachidonic acid liberation from membrane phospholipids and with their membrane fluidization. The higher was the liposolubility of the beta-adrenoceptor blocking drugs investigated, the higher was their inhibition of stimulated TXB2 formation. Hydrophilic, selective atenolol and practolol revealed slight or no inhibitory effect on stimulated thromboxane production.

Inhibition of platelet accumulation by beta 1-adrenoceptor blockade in the thoracic aorta of rabbits subjected to experimental sympathetic activation

Arterial platelet adhesion is an initiating event in the thrombo-embolic complications of atherosclerosis and may also accelerate the development rate of atherosclerotic lesions. Psychosocial stress has been shown to accelerate atherogenesis in animals, an effect probably mediated via beta-adrenoceptor activation. In view of the postulated roles of platelets and beta-adrenoceptor activation in atherosclerosis development, we decided to test whether beta blockade affects arterial platelet accumulation. We studied the accumulation of radioactivity from 111In-labelled platelets on the wall of the thoracic aorta of rabbits as a measure of platelet accumulation. During the exposure to the labelled platelets, the animals were also exposed to 3 hours of chloralose anesthesia. This is a reproducible model of experimental sympathetic activation, including beta-adrenoceptor activation, which we used to amplify possible effects of beta-blockade on platelet-vessel wall interaction. The effectiveness of the anesthesia in increasing sympathetic activity was verified by significant rises in mean arterial blood pressure (from 77 to 88 mmHg), heart rate (190 to 290 bpm), and plasma levels of norepinephrine (1.0 to 3.3 nM) and epinephrine (0.13 to 0.83 nM). In chloralose anesthetized rabbits, approximately 30 x 10(-9)% of the injected 111In accumulated in each square millimeter of intima at unbranched thoracic aorta. Platelet accumulation was significantly higher at arterial branching points, 70% higher at intercostal artery bifurcations, and 150% higher at coronary artery bifurcations than in unbranched aortic intima. Pretreatment with metoprolol in a dose resulting in "therapeutic" plasma levels significantly reduced platelet accumulation by 48% in unbranched aorta, 65% at intercostal, and 53% at coronary artery bifurcations.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of anaesthetic agents on platelet function

This paper reviews studies which have investigated the effect of anaesthetic agents on platelet function. The results of these studies suggest that halothane is the only agent in current use which inhibits platelet function in concentrations used clinically. Nitrous oxide appears to cause only a modest inhibition, while enflurane and isoflurane appear to have minimal or negligible effects. There is no current evidence that intravenous induction agents, opiates, or muscle relaxants affect platelet function. Reports indicate that local anaesthetic agents inhibit platelet aggregation, but only at concentrations far greater than peak plasma concentrations found during clinical use. Epidural anaesthesia may be associated with a reduction in platelet aggregation through a mechanism unrelated to direct local anaesthetic inhibition. The clinical significance of the effect of halothane on platelet function is not known. However, it is possible that halothane may affect bleeding or thrombotic complications in a similar manner to other 'anti-platelet' drugs.

Effect of the ultrashort-acting beta-blocker Brevibloc on free-radical-mediated injuries during the early reperfusion state

The left descending coronary artery (LAD) was ligated for 45 min or 90 min followed by 1-h reperfusion. During experiments the animals in Group I (15 dogs) received saline infusion, in Group II (20 dogs) they received the ultrashort-acting beta-blocker Brevibloc (esmolol HCl). The marker of lipid peroxidation the malondialdehyde (MDH) as well as endogen scavengers, the glutathione (GSH), and superoxide dismutase (SOD) were measured in the heart tissue homogenates. In blood and heart tissue samples the 6-keto-prostaglandin F1 alpha (PGF1 alpha) and thromboxane B2 (TXB2) were determined. Biochemical measurements revealed that esmolol HCl has beneficial effect on the free-radical-meduated-damage reducing the MDA content in the ischemic area. In Group I the value of MDA after 90 min of LAD ligature was 138 +/- 5.6%, in Group II the elevation was only 107.4 +/- 3.2%. After treatment with Brevibloc the GSH content of ischemic-reperfused areas decreased slightly (81.75 +/- 3.5% of the normal value), moreover, in Group I the depletion of GSH was considerable (64.5 +/- 4.2%). Coronary reperfusion caused the release of eicosanoids in both groups, mainly in the first 10 min. The highest value of thromboxane in blood samples could be measured in Group I after 90 min of LAD ligature (24.8 +/- 3.6 pmol/ml; the normal value 8-12 pmol/ml). In Group II during the same period of experiments the TXB2 in the blood was 14 +/- 3.7 pmol/ml. In heart tissue samples the amount of endoperoxides increased in ischemic and non-ischemic areas of Group I and II. Nevertheless, the calculated ratio of PGF1 alpha and TXB2 was near to the normal after Brevibloc treatment (0.85-0.9; the normal values were 1-1.2). These results indicate that esmolol HCl can modulate both the free-radical-mediated reaction and arachidonic acid metabolism.

Fish oil amplifies the effect of propranolol in mild essential hypertension

Forty-seven male patients with mild essential hypertension were randomly allocated to three subgroups. After a run-in period of 4 weeks, the first subgroup (n = 16) received propranolol (80 mg/day) for 36 weeks followed by a placebo period of 4 weeks. The second subgroup (n = 15), after a run-in period of 4 weeks, was given a supplement of encapsulated fish oil (9 g/day) for 36 weeks with a subsequent period of 4 weeks in which fish oil placebo was given. The third subgroup (n = 16), after a run-in period of 4 weeks, was given propranolol (80 mg/day) for 12 weeks, propranolol (80 mg/day) plus fish oil capsules (9 g/day equivalent to 1.8 g/day of eicosapentaenoic acid and 1.1 g/day of docosahexaenoic acid) for 12 weeks, propranolol plus fish oil placebo (same doses for 12 weeks) with a subsequent period of 4 weeks when propranolol placebo was administered. The results indicate a blood pressure-lowering effect of fish oil, which was comparable with that of propranolol. The simultaneous intake of fish oil plus propranolol was more effective than propranolol or fish oil alone. Propranolol treatment resulted in a decrease of plasma norepinephrine, plasma renin activity, and thromboxane B2 formation. After fish oil supplementation, plasma norepinephrine and thromboxane B2 formation were likewise reduced, whereas plasma renin activity appeared increased. The decrease of serum triglycerides, total and low density lipoprotein cholesterol as well as the rise of high density lipoprotein cholesterol are concomitant beneficial effects, which justify the consideration of fish oil alone or in combination with antihypertensive drugs for the treatment of mild hypertension.

Endothelial, platelet and leukocyte interactions in ischemic heart disease: insights into potential mechanisms and their clinical relevance

Recent investigations of the complex interactions among vascular endothelium, platelets and leukocytes have relevance to the pathogenesis of atherosclerosis and ischemic heart disease. Perturbations in the hemodynamic equilibrium maintained by these cellular elements may lead to vasospasm, in vivo thrombosis and a reduction in blood flow. Recent advances in the understanding of these interactions in health and disease states are summarized. The effect of pharmacologic agents on these cell-cell interactions are discussed to provide the reader with a general understanding of the relevance of these interactions in cardiovascular disease.

Effects of bopindolol on platelet function in hypertension at rest and during exercise

The effects of bopindolol, a new nonselective beta-blocking agent, on platelet function have been studied in 10 male hypertensive patients given the drug (1 mg/day) in turn for eight weeks. Bopindolol significantly (p less than 0.01) decreased the bicycle exercise- (1.5 W/kg body weight for 6 minutes) induced increase in platelet aggregation. During bopindolol-treatment both the slope and the height of the platelet aggregation response curve were moderately decreased at rest before exercise and significantly (p less than 0.05) decreased at rest after exercise. During exercise the slope amounted to 75.4 +/- 44 degrees before and to 70.8 +/- 5.3 degrees after therapy (p less than 0.01), the height to 64.0 +/- 11.9% before and to 58.1 +/- 14.7% (p less than 0.05) after therapy. Furthermore, bopindolol significantly increased the exercise-induced decrease in platelet sensitivity to PGI2 (p less than 0.05; IC-50-value: 2.10 +/- 0.47 vs 1.88 +/- 0.31 ng/ml) and PGD2 (p less than 0.05; IC-50-value: (19.88 +/- 2.10 vs 18.57 +/- 1.63 ng/ml). Bopindolol also significantly (p less than 0.05) decreased the exercise-induced elevation in serum-TXB2 (244.9 +/- 35.2 vs 237.3 +/- 27.2 ng/ml) and plasma-TXB2 (15.7 +/- 6.3 vs 13.1 +/- 3.7 pg/ml). The platelet count, the plasma levels of 6-oxo-PGF1 alpha, beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) were not affected by bopindolol. It is concluded that bopindolol favourably affects platelet function, in that it lowers exercise-induced platelet aggregation and TXB2-formation in therapeutical doses and increases platelet sensitivity to antiaggregatory prostaglandins.(ABSTRACT TRUNCATED AT 250 WORDS)

Synergistic inhibitory effects of adrenoceptor antagonists and prostacyclin, and umbilical artery-derived prostacyclin-like activity on platelet aggregation

Adrenoceptor antagonists are being used increasingly for the treatment of pregnancy-induced hypertension (PIH). Previous studies have shown that these drugs can inhibit platelet aggregation and thromboxane production. The aims of this study were to determine (i) whether adrenoceptor antagonists had any effect on vascular prostacyclin (PGI2) production and (ii) whether these drugs acted synergistically with PGI2 and the PGI2-like activity derived from umbilical artery to inhibit platelet aggregation in vitro. The adrenoceptor antagonists labetalol, pindolol and propranolol were found to have no effect on PGI2 production from the umbilical artery at low drug concentrations. These agents were also found to act synergistically with both pure PGI2 and PGI2-like activity derived from umbilical artery to inhibit platelet aggregation. This synergistic effect may be beneficial in the treatment of disorders which are associated with reduced PGI2 production, such as PIH where such synergy may help compensate for PGI2 deficiency.

Characterization of the effects of propranolol on the physical state of platelet membrane

The direct membrane effect of propranolol was studied in vitro on washed platelet preparations. Propranolol has been reported to inhibit platelet aggregation by mechanisms unrelated to its beta-blocking activity. In the present study, the drug was found to enhance 1-anilino-8-naphthalene sulfonate binding to platelet membrane by increasing the number of binding sites. Steady-state anisotropy was studied by labeling the platelets with the hydrophobic fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Propranolol was observed to decrease the equivalent microviscosity of the membrane. When the infinitely slow decaying component of fluorescence anisotropy (r infinity), which is proportional to the square of lipid order parameter, was calculated from the anisotropy data, a decrease in these parameters was also indicated. A higher fusion activation energy for viscosity in the propranolol-treated platelets reflected a lesser degree of order of the hydrocarbon chains in the lipid bilayer.

Influence of propranolol on platelet aggregation and thromboxane B2 production from platelet-rich plasma and whole blood

The beta-adrenoceptor antagonist propranolol is used in the therapy of hypertension and ischemic heart disease. The aim of our study was to evaluate the effects of this drug on platelet aggregation and on synthesis of thromboxane B2 (the stable metabolite of Thromboxane A2) from platelet rich plasma (PRP), whole blood samples and during spontaneous clotting. The results indicate that propranolol at concentrations near the therapeutic range, significantly inhibit collagen and thrombin-induced platelet aggregation and TxB2 synthesis from PRP. Furthermore the drug demonstrates inhibitory activity on B-TG release and TxB2 production from whole blood samples and on spontaneous clotting. The results suggest that some benefits of propranolol in the treatment of patients with coronary artery disease or cardiovascular conditions associated with platelet hyperaggregability may also be related to interference with platelet activation "in vivo" and with TxA2 generation.

Suppression of silent ischemia by metoprolol without alteration of morning increase of platelet aggregability in patients with stable coronary artery disease

To determine the effect of metoprolol on silent ischemia and platelet aggregability, 10 patients with coronary artery disease were studied with a randomized, double-blind, placebo-controlled, crossover trial. Patients were treated with metoprolol (200 mg b.i.d.) or placebo for 1 week and then received the alternate therapy. Two days before the end of each treatment period, platelet aggregability was studied for 24 hours, and a 48-hour ambulatory electrocardiogram was obtained. Compared with placebo, metoprolol significantly decreased the total number (from 26 to 4, p less than 0.1) and duration (from 735 to 84 minutes, p less than 0.01) of silent ischemic episodes. This decrease was accompanied by a decrease in the mean blood pressure (from 127/81 to 118/71 mm Hg, p less than 0.01) and the mean heart rate (from 70 to 54 beats/min, p less than 0.01). The incidence of silent ischemic episodes in the morning was significantly higher in untreated patients than in treated patients. The few episodes observed during metoprolol treatment occurred at the same time as the peak incidence observed during placebo treatment. During placebo treatment, platelet aggregability increased from 6:00 to 9:00 AM as reflected by a decrease in the threshold concentrations of ADP and epinephrine required to induce biphasic platelet aggregation (from 4.8 +/- 0.8 to 2.6 +/- 0.4 microM, p less than 0.02; and from 7.3 +/- 2.3 to 1.8 +/- 0.9 microM, respectively, p less than 0.02). Metoprolol did not alter the basal level nor blunt the morning increase of platelet aggregability.(ABSTRACT TRUNCATED AT 250 WORDS)

Atherosclerosis in rabbits identified as high and low responders to an atherogenic diet and the effect of treatment with a beta 1-blocker

In order to investigate whether initial plasma lipid concentrations could be used to distinguish between high and low responders to an atherogenic diet, rabbits were divided into 3 groups according to their plasma concentrations of cholesterol and phospholipids after 4 weeks on a standard rabbit diet. Plasma cholesterol and phospholipid levels were less than 0.5 mM, less than 1.1 mM, respectively, in group 1 (n = 17), greater than 0.5 mM, less than 1.1 mM, in group 2 (n = 13), and greater than 0.5 mM, greater than or equal to 1.1 mM, in group 3 (n = 14). After 7 weeks on a diet containing 0.25% cholesterol and 3% coconut oil, animals in groups 1 and 2 had a lower increase in their plasma lipid levels compared with group 3. Half of each group was then treated with the beta 1-adrenoceptor antagonist metoprolol during the next 14 weeks on the atherogenic diet. At the end of the study, the extent of atherosclerosis both in the aortas and in the coronary arteries of the control animals showed a positive correlation to plasma cholesterol and to plasma phospholipid concentrations integrated over time. The metoprolol-treated animals in groups 1 and 2 had a reduction of atherosclerosis compared with their respective controls. We conclude that subpopulations of rabbits that react differently on an atherogenic diet can be identified by their initial plasma lipid levels, and that metoprolol treatment of low responders to an atherogenic diet significantly reduces atherosclerotic lesions of the aorta.

Platelet activity and selective beta-blockade in migraine prophylaxis

Migraine is associated with increased platelet activity and an incidence of cerebrovascular ischemic events. Because cerebrovascular events might result from platelet aggregation, enhancing platelet activity further in the treatment of migraine is not desirable. beta-Adrenoceptor blockers effective in migraine prophylaxis include propranolol (nonselective) and metoprolol (beta 1-selective), but it is uncertain how beta-receptor subtype selectivity might influence platelet behavior in migraine. In 29 patients, comparable clinical responses were obtained with therapeutic doses during 1 month of treatment with propranolol, metoprolol, and the beta 2-selective Li 32-468. Propranolol increased and metoprolol decreased platelet aggregation and ATP release, and the effect of Li 32-468 could be related to that of propranolol. These actions can be largely explained in terms of what is known of platelet beta-receptors and therefore can be generalized to other effective beta-blockers. Since altered platelet activity does not account for the efficacy of these agents in migraine, the actions of beta-blockers on platelets should be considered as side effects. Those beta-blockers inhibiting platelet activity should be preferred in migraine treatment, assuming equal efficacy, which implies the use of beta 1-selective blockers.

Effect of labetalol on human platelet function

1. The effects of the alpha-beta-adrenergic antagonist labetalol on the activation of human platelets by adrenaline and other aggregating stimuli have been investigated. 2. Labetalol inhibited platelet aggregation and secretion induced by collagen and the second phase of aggregation caused by ADP, platelet activating factor, adrenaline and ionophore A23187. Adrenaline-induced platelet activation was inhibited by the lowest labetalol concentration. The response to Na arachidonate was minimally affected and the arachidonate-induced thromboxane B2 generation was only partially prevented. 3. The pre-incubation with low concentration of ionophore A23187 overcame labetalol's inhibition of collagen-induced platelet aggregation. 4. Labetalol did not influence intraplatelet cyclic AMP levels. 5. The present investigation provided evidences that the modulation of human platelet function by labetalol could be related also to a decreased Ca2+ availability.

Effects of three beta-blockers with different pharmacodynamic properties on platelet aggregation and platelet and plasma cyclic AMP

The effects of three different types of beta-adrenoceptor blocking agents on platelet aggregation and on platelet and plasma cyclic AMP content have been studied in 14 patients with mild hypertension given each drug in turn for two weeks. The drugs were a non-selective blocking agent with high intrinsic sympathomimetic activity, pindolol, the nonspecific blocking agent propranolol, and the beta 1-selective metoprolol. The threshold values of ADP and adrenaline for irreversible platelet aggregation were significantly higher for pindolol and metoprolol than for propranolol. The cyclic AMP content of platelets was higher during pindolol and metoprolol than during propranolol treatment. Pindolol produced a substantial increase in plasma cyclic AMP relative to the other two drugs. Thus, platelet aggregation and cyclic AMP formation are influenced by beta-adrenoceptor blockade in proportion to intrinsic sympathomimetic activity and affinity for different beta-adrenoceptor subtypes.

Platelets and antiplatelet therapy in ischemic heart disease

Blood platelets have been shown to play an important role not only in thrombosis, but also in the pathogenesis of coronary artery disease and its complications. Drugs that affect platelets have been shown to reduce mortality in survivors of acute myocardial infarction, to reduce the risk of myocardial infarction in patients with unstable angina, and to preserve the potency of saphenous venous grafts used to bypass obstructed coronary arteries. The drugs may also play a role in the primary prevention of arteriosclerosis and in preventing thrombotic complications following coronary angioplasty.

Effect of metoprolol on diet-induced atherosclerosis in rabbits

The effect of metoprolol, a beta 1-blocker, on atherogenesis was evaluated in rabbits fed a diet supplemented with 0.25% cholesterol and 3% coconut oil for 21 weeks. After 7 weeks on the diet, the rabbits were randomly divided into treated (n = 22) and untreated (n = 22) groups. Treated animals received metoprolol subcutaneously by an osmotic pump for 14 weeks, resulting in a plasma level of 774 +/- 69 nM during the investigation. Plasma concentrations of cholesterol, triglycerides, and phospholipids did not differ between the two groups. Nor were there any significant differences between the two groups in plasma concentrations of apolipoprotein A-I, apolipoprotein B, apolipoprotein C-III, and apolipoprotein E measured by electroimmunoassay. At the end of the study, the aortas were cut into three portions and the extent of atherosclerosis was determined by morphometry. The group that had received metoprolol had significantly (p less than 0.015) less atherosclerosis in the aorta (ascending plus arch 37.8 +/- 6.8%, thoracic 32.9 +/- 6.1%, abdominal 19.8 +/- 6.1% of total intimal area; mean +/- SEM) than the controls (ascending plus arch 54.9 +/- 7.1%, thoracic 48.0 +/- 6.2%, abdominal 25.9 +/- 5.5%).

Differential effects of timolol and metoprolol on platelet function at rest and during exercise

Ten male patients suffering from stable angina pectoris were studied at rest and immediately after exercise during treatment either with timolol (a non-selective beta-blocker) or with metoprolol (a beta 1-selective blocker). Timolol induced a significant increase in platelet aggregation and a reduction in platelet cyclic AMP, and it also raised the plasma adrenaline at rest and during exercise as compared to the pre-treatment level. Metoprolol had none of these effects. Prior to medication and during metoprolol treatment, exercise led to an increase in the peripheral platelet count, whereas timolol was associated with a reduction of platelets during physical effort. Neither drug affected platelet thromboxane B2 at rest. During exercise, its level was not affected in the pre-treatment period or during metoprolol treatment but it was sharply increased by timolol therapy.

Antiplatelet effects of oral diltiazem, propranolol, and their combination

1. The antiplatelet effects of a single oral dose of the calcium entry blocker diltiazem (60 mg), the beta-adrenoceptor blocker propranolol (40 mg), and their combination were studied in five healthy subjects. 2. Platelet aggregation and ATP release induced by adrenaline and ADP and ADP induced platelet thromboxane A2 generation were significantly inhibited (P less than 0.05) by either diltiazem or propranolol, although propranolol tended to have greater inhibitory effects on platelet function than diltiazem that did not reach statistical significance. 3. Combination therapy resulted in additive antiplatelet effects that were significantly (P less than 0.05) greater than either drug alone. 4. These data indicate that combined administration of a calcium entry blocker and a beta-adrenoceptor blocker results in additive inhibitory effects on platelet function. These effects may mediate part of the therapeutic efficacy of combination therapy in patients with coronary artery disease.

Influence of some beta blockers (pindolol, atenolol, timolol and metoprolol) on aggregation and arachidonic acid metabolism in human platelets

The effects of four beta-adrenoceptor blocking agents on platelet aggregation, formation of thromboxane from exogenous arachidonic acid (AA) in platelets, on AA incorporation in platelet phospholipids, and on platelet phospholipase activity were studied. Of the four drugs pindolol inhibited thromboxane formation in a dose-related (0.25-1.0 mM) manner apparently by exerting its influence at the cyclooxygenase (CO) level. This drug also inhibited aggregation induced by AA, collagen, epinephrine and ADP. Atenolol and metoprolol though not showing inhibition of AA-induced aggregation did inhibit collagen- and ADP-induced aggregation; metoprolol reversed ADP-induced aggregation, and abolished second phase of epinephrine-induced aggregation. Timolol did not inhibit aggregation induced by all the aggregating agents. Atenolol inhibited (by ca. 10%) TxB2 formation in platelets from exogenous as well as endogenous AA at rather high concentrations (1.0 mM). Metoprolol and timolol did not do so. The observations reported here can be best explained by taking into account the membrane stabilizing effects and lipophilic properties of the drugs.

Platelet function in patients admitted with a diagnosis of myocardial infarction

Platelet function and thromboxane A2 release were measured in 71 patients admitted to a coronary care unit with a provisional diagnosis of acute myocardial infarction (AMI). All measurements were carried out within twenty-four hours of admission. Of these, 35 patients had the diagnosis of AMI confirmed. The remainder (n = 36), who did not have AMI (NMI), were divided into two groups: those (n = 18) with an unequivocal history of previous vascular disease and those without vascular disease (n = 18). Platelet aggregation and thromboxane A2 (TXA2) release were significantly increased in the AMI group when compared with those in the NMI without vascular disease group or a healthy control group with similar age and sex distribution. Aggregation and TXA2 release in the NMI patients with vascular disease were greater than those in controls and did not differ significantly from those in the AMI group. Patients in the AMI or NMI with vascular disease groups who were taking beta-blockers or calcium channel antagonists at the time of admission showed significantly less platelet aggregation than those who were not taking these drugs. Heparin, added in vitro at therapeutic concentrations, induced significantly more aggregation in patients in the AMI and NMI with vascular disease groups than in the NMI without vascular disease group. We conclude that: platelets obtained from patients with AMI are hyperaggregable and release more TXA2; platelets from patients with significant vascular disease are hyperaggregable, even in the absence of AMI, although they are not as hyperaggregable as those from AMI; treatment with nifedipine and beta-blockers protects these patients from platelet hyperaggregability; heparin induces significant aggregation of platelets from patients with AMI and NMI with vascular disease. These observations are of importance in considering the pathogenesis and treatment of AMI and ischemic heart disease.

Adrenaline infusion evokes increased thromboxane B2 production by platelets in healthy men: the effect of beta-adrenoceptor blockade

The effects of direct adrenergic stimulation, achieved by 60-min adrenaline infusion (0.1-0.2 microgram kg-1 min-1), on thromboxane B2 (TxB2) production by platelets in whole blood ex vivo and on ADP-induced platelet aggregation were studied in seven healthy male volunteers. The effects of two beta-adrenergic blocking agents, pindolol and practolol, on the adrenaline-induced changes were furthermore analyzed. Adrenaline administration resulted in an about ten-fold elevation in plasma adrenaline, and an about three-fold increase in TxB2 production by platelets at 30 min of infusion. The increased TxB2 production persisted throughout the entire adrenaline infusion, and up to 30 min of postinfusion period (recovery). Pindolol blunted markedly the effects of adrenaline on platelet TxB2 production, whereas practolol seemed to have only a weak effect. The sensitivity of platelets to ADP-induced aggregation did not change during the 60 min of adrenaline infusion. However, at 60 min of recovery the platelets showed a significantly increased sensitivity to ADP. Correspondingly, pindolol treatment did not affect platelet sensitivity during the infusion period, but at 60 min of recovery it had caused a significantly decreased sensitivity of platelets to ADP-stimulation. Plasma-free fatty acids increased markedly during the adrenaline infusion. This increase was totally blocked by pindolol, but only partly by practolol. The present results demonstrate that adrenaline, at plasma levels seen for example, in complicated myocardial infarction, stimulates platelet TxB2 production and increases the sensitivity of platelets to ADP after the infusion. Pindolol, but not practolol, inhibits these adrenaline-induced changes in platelet behaviour.

Effects of bevantolol and atenolol on symptoms, exercise tolerance and metabolic risk factors in angina pectoris

To assess the effects of bevantolol on stable angina pectoris of effort and its impact on metabolic risk factors, a comparison study of this beta 1-blocking agent and atenolol was undertaken in 40 subjects (mean age 51 years). After a 4-week, single-blind, placebo washout period, 12 men and 8 women were randomized to receive 150 mg of bevantolol twice daily and 12 men and 8 women to treatment with 100 mg of atenolol once daily in a parallel, double-blind, 12-week treatment phase. Patients were assessed at weeks 2, 6 and 12 after bicycle exercise until angina or ST-segment depression greater than or equal to 0.15 mV appeared. Concentrations of cholesterol lipoproteins and 3 prostaglandin metabolites were determined. One patient receiving bevantolol was withdrawn from the study because of insufficient efficacy and 2 receiving atenolol were withdrawn because of side effects. After 2 weeks of therapy, significant decreases were seen in both groups in the number of angina attacks, mean sitting heart rate, systolic and diastolic blood pressure, mean maximum heart rate during exercise and mean double-product of systolic blood pressure and heart rate at the end of exercise. There was a trend toward significance in the increase of mean duration of exercise and total work performed with both agents, although these values were not statistically significant. Both high density lipoproteins and the ratio of high density lipoproteins to low density lipoproteins increased in the bevantolol group and decreased in the atenolol group. These changes were statistically significant at week 6.(ABSTRACT TRUNCATED AT 250 WORDS)