Effects of the non-selective beta-adrenoceptor blocking agent, carteolol, on platelet function, blood coagulation and viscosity

Moderate-intensity aerobic exercise vs desmopressin in adolescent males with mild hemophilia A: a randomized trial

Persons with mild hemophilia A (HA) may use intranasal desmopressin prior to sports participation. Desmopressin is expensive and can cause vomiting, headache, palpitation, and occasionally seizures. Our group has previously documented a 2.3-fold increase in factor VIII activity (FVIII:C) in adolescents with mild HA after moderate-intensity aerobic exercise. Herein, we report principal findings of a randomized trial of intranasal desmopressin vs a standardized, moderate-intensity aerobic exercise regimen in adolescents with mild HA. Our primary objective was to compare the change in FVIII:C associated with these 2 interventions. We also examined changes in hemostatic parameters arising from their sequential administration. The study was conducted simultaneously at the Hospital for Sick Children, Canada, and Nationwide Children's Hospital, USA. Thirty-two eligible male adolescents (mean age ± standard deviation: 16.1 ± 2.6 years) with mild HA (mean baseline FVIII:C: 27.9% ± 18.4%) were randomized to 1 of 4 study arms (desmopressin followed by exercise, desmopressin alone, exercise followed by desmopressin, and exercise alone). Blood work was obtained at baseline and at 3 subsequent time-points. Participants randomized to exercise cycled on an ergometer for approximately 12 minutes, with the final 3 minutes at 85% of their predicted maximum heart rate. Standard weight-based dosing of desmopressin was used. Mean immediate increase in FVIII:C was 1.7-fold with exercise compared with 1.9-fold with desmopressin (noninferiority, P = .04). Exercise-induced improvement in hemostatic parameters including FVIII:C was brief compared with more sustained improvements seen with desmopressin. More than 60% of participants randomized to receive both exercise and desmopressin achieved normal (>50%) FVIII:C, 75 and 135 minutes into the study protocol.

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.

Vasodilating beta-adrenoceptor blockers as cardiovascular therapeutics

beta-Adrenoceptor blocking agents (beta-blockers) have been established as therapeutics for treatment of patients with hypertension, ischemic heart diseases, chronic heart failure, arrhythmias, and glaucoma. However, their clinical use is limited because some patients are adversely affected by their side effects. The discovery of cardioselective (beta(1)-selective) blockers has overcome some of the problems. Current retrospective studies have revealed that vasodilating beta-blockers (so-called beta-blockers of the third generation) have advantages over the conventional type of beta-blockers in terms of minimizing the adverse effects and improving the disease-derived dysfunction, thus enhancing the quality of life variables. Some of the possible advantages include improvement of insulin resistance, decrease in low-density lipoprotein cholesterol in association with increase in high-density lipoprotein cholesterol, attenuation of bronchial asthma attack and respiratory dysfunction, alleviation of coronary vasospasm provocation, peripheral circulatory disturbances, and erectile dysfunction, and better patient compliance. Release of nitric oxide, antioxidant action, beta(2)-adrenoceptor activation, Ca(2+) entry blockade, and other mechanisms underlying the vasodilating action may be responsible for the beneficial therapeutic effects of these agents.

Unheralded sudden cardiac death: do autonomic tone and thrombosis interact as key factors in aetiology?

Unheralded sudden cardiac death is a personal and family tragedy that continues to elude research-based progress on aetiology or prevention. Instinctive links between autonomic imbalance, sympathetic activation and serious arrhythmia are longstanding and backed by many observational reports. However the role of the more familiar mechanisms of coronary occlusion and thrombus formation are underplayed. Sympathetic overactivity may also mediate sudden death through precipitation of vasospasm; platelet activation and inhibition of endogenous fibrinolysis as well as the propagation of arrhythmia. The integration of autonomic, thrombotic and vascular tone may be the key to better understanding of the individual process of unheralded sudden cardiac death. In this review we analyse the evidence for this hypothesis.

Lack of significant effect of therapeutic propranolol on measurable platelet function in healthy subjects

Propranolol, a non-selective beta blocker, was administered orally in therapeutic doses. The effects of a single dose (160 mg) and one week's treatment (80 mg twice a day) on platelet function were compared in healthy young subjects. There were no significant changes in circulating platelet aggregates, template bleeding time, platelet factor 3 availability and thromboxane beta 2 (TX beta 2) generation. Platelet aggregation responses as assessed by angle of slope and maximal percentage aggregation (all agonists) and lag phase (collagen) showed no changes of biological importance, although minor changes reaching significance were observed with some agonists. These findings suggest that propranolol does not significantly affect platelet function when taken at doses commonly encountered in clinical practice.

Plasma levels of platelet secretory proteins

Platelets contain three types of secretory organelles: the dense granules, the alpha granules, and the lysosomes. Most of the proteins secreted from platelets are stored in the alpha granules, whereas the dense granules contain substances such as adenine nucleotides, serotonin, Ca++, and inorganic pyrophosphate types as well as a heparatinase. Three of the secreted alpha granule proteins have been measured by radioimmunoassay and it has been suggested that levels of these proteins in patient plasmas provide an index of in vivo platelet activation and secretion. These three are beta-thromboglobulin, platelet factor 4, and thrombospondin. In this chapter the chemistry of these proteins will be considered briefly, as will their clearance from the circulation, and then the clinical studies will be reviewed critically. Since radioimmunoassays were developed for these proteins (the first was reported in 1975), there has been a profusion of reports on levels of one or another of these proteins in a wide range of disease states, and these reports have indicated secreted platelet protein levels ranging from normal to grossly elevated in a given disease state. Possible reasons for such variability will be discussed.

Inhibition of thromboxane and prostacyclin production in whole blood by adrenoceptor antagonists

There is increasing evidence implicating thromboxane A2 (TxA2) in vascular disease. Adrenergic blocking agents have been used with success in the secondary prevention of myocardial infarction. The aim of this study was to determine whether adrenergic blocking agents had any effect on the production of TxA2 and prostacyclin (PGI2) from whole blood in vitro. Fresh whole blood without anticoagulant was placed in glass tubes containing either drug or vehicle, the latter acting as control, and allowed to clot at 37 degrees C for 30 minutes. The serum PGI2 metabolites (PGI2M) and TxB2 (the stable hydration product of TxA2) were determined by radioimmunoassay. Labetalol, pindolol and propranolol all inhibited both PGI2M and TxB2 production in a dose dependent manner, while atenolol had no effect. Labetalol was the most potent significantly inhibiting TxB2 production at a drug concentration compatible with that found in-vivo. This inhibitory effect on TxB2 production may be of benefit in the treatment of vascular disease.

Beta-adrenoceptor antagonists and human platelets: relationship of effects to lipid solubility

Six beta-adrenoceptor antagonists (propranolol (+ and - isomers); ICI-118,551; oxprenolol; timolol; metoprolol; and practolol (+ and - isomers), chosen to represent a spectrum of physicochemical and pharmacological properties, inhibited the response of human platelets to all aggregating agents tested. For any given aggregating agent the extent of inhibition correlated with the lipid solubility of the beta-adrenoceptor antagonist and showed no relation to other properties of these compounds. Inhibition of aggregation by the beta-adrenoceptor antagonists was manifested as a parallel shift to the right in the dose-response curve. Analysis of these data according to Arunlakshana and Schild (Br. J. Pharmac. 14, 48-58 (1969] showed a dependence of the apparent pA2 on the agonist employed and gave a slope approximating unity when ADP, 9,11-epoxymethanoprostaglandin H2 (U-46619), adrenaline, 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (PAF) or arachidonate were used as agonists. Slopes significantly greater than unity, and approaching a value of 2, were obtained when this analysis was applied to data obtained using collagen in the presence or absence of aspirin, 12-O-tetradecanoylphorbol-13-acetate (TPA), or a divalent cation ionophore (A-23187) as agonists. Inhibition by (+/-) propranolol of secretion induced by collagen was manifested as a parallel shift to the right in the dose-response curve for collagen. The Schild plot of these data has a slope of unity. (+/-)-Propranolol inhibited thromboxane B2 production induced by collagen but over a similar concentration range had little effect on conversion of arachidonate to thromboxane B2. (+/-)Propranolol had no significant effect on the level of cyclic-3',5'-AMP (cAMP) in unstimulated platelets or on the increase in the level caused by addition of forskolin, but caused partial inhibition of the increase in platelet cAMP induced by prostaglandin E1. It also completely abolished inhibition by ADP of the increase in [cyclic-3',5'-AMP] induced by prostaglandin E1. These data are interpreted on the basis of a model in which interaction of propranolol with phosphatidylserine and phosphatidylinositol causes inhibition of phospholipases C and A2, inhibition of protein kinase C and alteration of membrane receptor properties as a consequence of distortion of their microenvironment.

Increased platelet adhesion and aggregation in hypertensive patients: effect of atenolol

Fourteen patients with established hypertension followed a double-blind crossover-styled trial to study the effects of 100 mg/day atenolol compared to placebo. Atenolol was found to be an effective antihypertensive agent, reducing both systolic and diastolic blood pressure. Hypertensive patients appear to have increased in vitro platelet adhesion and aggregation. Atenolol significantly reduced platelet adhesion, but had little effect on aggregation. This may be important in contributing towards the now-recognised cardio-protective effect of the beta-adrenoceptor blocking agents. Blood chemistry and haematological parameters were unchanged; but whereas plasma cholesterol and plasma triglyceride levels remained normal, there was a significant fall in plasma high-density lipoprotein cholesterol levels. Side effects were very few.