Aspirin, Platelet Aggregation, and the Circadian Variation of Acute Thrombotic Events

The onset of several acute cardiovascular diseases occurs in a circadian pattern, with a peak incidence in the hours soon after awakening. This finding, coupled with laboratory data that confirm a surge in platelet activation during the early morning hours, suggests that acute changes in platelet aggregability may be an important trigger of thrombosis. Therefore, the efficacy of antiplatelet agents, such as aspirin, in reducing risks of vascular occlusion may result, at least in part, from a blunting of these short-term changes in platelet aggregability. In this review, clinical and laboratory evidence describing these cyclical changes is discussed, as is current evidence of the effects of aspirin on platelet function and the circadian variation of acute thrombosis.     

Flow Cytometric Analysis of Circadian Changes in Platelet Activation Using Anti-Gmp-140 Monoclonal Antibody

The hemostatic activity of blood shows a circadian variation with a higher frequency of acute coronary events in the morning. The thrombotic tendency of blood is influenced by many factors, including platelets. Diurnal changes of in vivo platelet activation were investigated by whole blood flow cytometry in 10 young healthy male volunteers using anti-GMP-140 (anti-α-granule membrane protein 140 kD) monoclonal antibody at 3h intervals from 06:00 to 24:00. We also studied circulating platelet aggregates to investigate whether there exists a similarity between the results of these methods. Results of flow cytometric analysis indicate that there is an increase in platelet activation during the period from 06:00 to 09:00. Platelet activation then decreases gradually during the period from noon to midnight. These changes are accompanied by a similar trend in circulating platelet aggregates. This suggests that GMP-140 expression on platelets is synchronized with or followed by platelet aggregate formation in vivo, and increased platelet activation may predispose individuals to thrombosis at this time.     

Circadian and weekly variation and the influence of environmental variables in acute myocardial infarction

Objectives

The aim of our study was to investigate the circadian and weekly variation and assess the influence of environmental variables on the occurrence of acute myocardial infarction (AMI).

Methods

Our study population consisted of 2983 consecutive patients admitted with AMI between January 2006 and May 2008. Data were abstracted from hospital records and partially from an electronic database. In patients with a known time of onset of AMI, circadian variation was analysed. In all patients, weekly variation of onset of AMI was analysed. Information on daily mean temperature, sunny hours, rainy hours, maximal humidity and mean atmospheric pressure was obtained from the KNMI database and the influence of these environmental variables on the incidence of AMI was analysed.

Results and conclusion

Incidence of AMI shows a circadian pattern with an increase in occurrence during daylight. AMI occurs equally on each day of the week and no relation was found between environmental variables and the occurrence of AMI.     

Circadian Variation of Cyclic AMP in the Rat Pineal Gland

Abstract: This study was carried out to investigate circadian variation of cyclic AMP contents in the rat pineal glands, using the high-energy microwave radiation technique. The pattern of cyclic AMP concentration in the pineal gland showed a distinct circadian variation, with the maximum level at 0200 and the lowest at 1400. The administration of propranolol completely blocked the dark-induced increase in the pineal cyclic AMP level at 0200, and the administration of isoproterenol induced a threefold, rapid increase in the cyclic AMP level at 1400, although it did not change the level at 0200.     

应用血栓弹力图评价替罗非班对行急诊介入的ACS患者血小板聚集功能及活性的影响

目的:应用血栓弹力图评估(TEG)替罗非班对急性冠脉综合症(ACS)患者血小板聚集功能及活性情况,探讨对于ACS患者行急诊介入时,早期应用替罗非班对介入治疗效果的影响.方法:入选100例拟行急诊介入治疗的ACS患者,于冠状动脉造影前随机分为干预组(在3分钟内推注替罗非班组10 μg/kg,以0.15 μg/kg/min速度静脉维持泵入36小时,共50例)和对照组(不应用替罗非班,共50例),分别于入选后即刻、替罗非班应用后24小时、停用后24小时抽血,采用血栓弹力图记录血小板聚集功能的抑制率(IPA)及活性.结果:两组之间的入选后即刻IPA差异无统计学意义(P＞0.05),替罗非班应用后24小时血小板聚集抑制水平达到高峰,IPA为(92.6±8.6)％,显著高于对照组[(33.3±9.8)％,P＜0.01],停用替罗非班后24小时,两组之间的IPA差异无统计学意义(P＞0.05).替罗非班应用24小时后,血小板活性显著低于对照组[(46.7+ 10.2) mm比(59.7+ 7.8) mm,P＜0.01].结论:TEG能动态监测凝血功能全过程,全面评估血小板功能及凝血情况,指导ACS患者抗血小板药物方案选择.在进行介入治疗的ACS患者中早期应用替罗非班较常规口服药物能更好地达到血小板聚集抑制作用,可以获得更好的即刻造影结果,减少术后缺血性事件发生,提高临床顸后情况.     

生物节律影响巨核细胞发育和血小板产生的研究进展

自然界中生物体的生命活动、生活习性都存在着一定的周期性变化。生物昼夜节律的产生是以内源性的生物钟系统为基础的。生物钟不仅易受到外界环境的影响,而且可以通过调控一系列特定的下游基因的表达,影响生物体的生理生化过程。巨核细胞是生成血小板的前体细胞,经过分化、增殖、成熟和裂解,最终生成血小板。血小板是一种没有细胞核的特殊细胞,在生理性止血和器官修复上发挥着重要作用,同时参与血栓等多种疾病的发生。近几年借助现代分子生物学和细胞生物学手段。证实了哺乳动物的巨核细胞和血小板的生成呈现明显的周期性的变化,利用生物钟基因缺失模型进一步发现了生物钟基因对巨核细胞和血小板的影响。本文概述了生物节律对巨核细胞和血小板的影响,为进一步研究巨核细胞的发育和血小板生成机制提供了参考。     

An Investigation of Natural Genetic Variation in the Circadian System of Drosophila melanogaster: Rhythm Characteristics and Methods of Quantification

Variation in four characteristics of the circadian locomotor activity rhythm was investigated in 24 true-breeding strains of Drosophila melanogaster with a view to establishing methods of phenotypic measurement sufficiently robust to allow subsequent biometric analysis. Between them, these strains formed a representative sample of the genetic variability of a natural population. Period, phase, definition (the degree to which a rhythmic signal was obscured by noise), and rhythm waveform were all found to vary continuously among the strains, although within each strain the rhythm phenotype was remarkably consistent. Each characteristic was found to be sufficiently robust to permit objective measurement using several different methods of quantification, which were then compared.     

An Investigation of Natural Genetic Variation in the Circadian System of Drosophila melanogaster: Rhythm Characteristics and Methods of Quantification

Variation in four characteristics of the circadian locomotor activity rhythm was investigated in 24 true-breeding strains of Drosophila melanogaster with a view to establishing methods of phenotypic measurement sufficiently robust to allow subsequent biometric analysis. Between them, these strains formed a representative sample of the genetic variability of a natural population. Period, phase, definition (the degree to which a rhythmic signal was obscured by noise), and rhythm waveform were all found to vary continuously among the strains, although within each strain the rhythm phenotype was remarkably consistent. Each characteristic was found to be sufficiently robust to permit objective measurement using several different methods of quantification, which were then compared.     

Effects of DK-002, a synthesized (6aS,cis)-9,10-Dimethoxy-7,11b-dihydro-indeno[2,1-c]chromene-3,6a-diol, on platelet activity

In the present study, the mechanism of antiplatelet activity of DK-002, a synthesized (6aS,cis)-9,10-Dimethoxy-7,11b-dihydro-indeno[2,1-c]chromene-3,6a-diol, was investigated. DK-002 inhibited the thrombin, collagen, and ADP-induced rat platelet aggregation in a concentration-dependent manner, with IC₅₀ values of 120, 27, and 47 μM, respectively. DK-002 also inhibited thrombin-induced dense granule secretion, thromboxane A₂ synthesis, and [Ca²⁺]_i elevation in platelets. DK-002 did not show any significant effect on ADP-induced inhibition of cyclic AMP elevation by prostaglandin E₁, but DK-002 was confirmed to inhibit ADP-induced [Ca²⁺]_i elevation and shape change. DK-002 inhibited 4-bromo-A23187-induced [Ca²⁺]_i elevation in the presence of creatine phosphate/creatine phosphokinase (CP/CPK, a ADP scavenging system) and indomethacin (a specific inhibitor of cyclooxygenase). DK-002 also inhibited Ca²⁺ mobilization in thrombin- or 4-bromo-A23187-stimulated platelets through its inhibitory effects on both Ca²⁺ release from intracellular stores and Ca²⁺ influx, in the presence of CP/CPK and indomethacin. Taken together, the present study shows that DK-002 has inhibitory effects on stimulation of platelets, and suggests that its antiplatelet activity might be related to the inhibitory mechanism on Ca²⁺ mobilization in stimulated platelets.     

Syntaxin 8 Regulates Platelet Dense Granule Secretion,Aggregation, and Thrombus Stability

Platelet secretion not only drives thrombosis and hemostasis, but also mediates a variety of other physiological and pathological processes. The ubiquitous SNARE machinery and a number of accessory proteins have been implicated in regulating secretion in platelet. Although several platelet SNAREs have been identified, further members of the SNARE family may be needed to fine-tune platelet secretion. In this study we identified expression of the t-SNARE syntaxin 8 (STX8) (Qc SNARE) in mouse and human platelets. In mouse studies, whereas STX8 was not essential for α-granule or lysosome secretion, Stx8^−/− platelets showed a significant defect in dense granule secretion in response to thrombin and CRP. This was most pronounced at intermediate concentrations of agonists. They also showed an aggregation defect that could be rescued with exogenous ADP and increased embolization in Stx8^−/− mice in vivo consistent with an important autocrine and paracrine role for ADP in aggregation and thrombus stabilization. STX8 therefore specifically contributes to dense granule secretion and represents another member of a growing family of genes that play distinct roles in regulating granule release from platelets and thus platelet function in thrombosis and hemostasis.     

Circadian Rhythm of Acute Phase Proteins under the Influence of Bright/Dim Light during the Daytime

We investigated the influence of two different light intensities, dim (100 lx) and bright (5,000 lx), during the daytime on the circadian rhythms of selected acute phase proteins of C‐reactive protein (CRP), α1‐acid glycoprotein (AGP), α1‐antichymotrypsin (ACT), transfferin (TF), α2‐macroglobulin (α2‐m), haptoglobin (HP), and ceruloplasmin (CP). Serum samples were collected from 7 healthy volunteers at 4 h intervals during two separate single 24 h spans during which they were exposed to the respective light intensity conditions. A circadian rhythm was detected only in ACT concentration in the bright light condition. The concentration of ACT, a positive acute phase protein (APP), increased (significantly significant differences in the ACT concentration were detected at 14:00 and 22:00 h) and AGP showed a tendency to be higher under the daytime bright compared to dim light conditions. There were no significant differences between the time point means under daytime dim and bright light conditions for α2‐M, AGP, Tf, Cp, or Hp. The findings suggest that some, but not all, APP may be influenced by the environmental light intensity.     

Circadian Rhythms in the Efficacy of Intravenous Alteplase in Patients With Acute Ischemic Stroke and Middle Cerebral Artery Occlusion

Circadian rhythm interactions of hemostatic factors can modify tissue plasminogen activator (tPA) effects. We assess the relationship of the time frame of intravenous tPA administration with the outcome of patients with acute ischemic stroke (AIS). We studied 135 consecutive patients with AIS and transcranial duplex documented middle cerebral artery (MCA) occlusion treated with intravenous tPA. Complete recanalization was defined as total improvement on thrombolysis in brain ischemia (TIBI) grades 2?h after tPA infusion. Clinical response was evaluated by the modified Rankin scale at 90 days. We determined plasminogen activator inhibitor-1 (PAI-1) levels in 33 patients with available plasma samples before treatment. Our results are follows: 92 (68.1%) patients were treated in the diurnal (9:00–21:00) and 43 (31.8%) in the nocturnal period (21:00–9:00). Complete recanalization was recorded in 52/135 (38.5%) patients. Both the rate of complete recanalization (45.6% vs. 23.2%; p?=?.01) and good clinical outcome (64.1% vs. 44.2%; p?=?.02) were significantly higher in the group of diurnal tPA administration compared with those treated in the nocturnal period. The adjusted odds ratio (OR) of diurnal tPA treatment for complete MCA recanalization was 2.37 (95% confidence interval [CI], 1.02–5.52; p?=?.045). Diurnal tPA infusion significantly improved the overall distribution of scores on the modified Rankin scale, as compared with nocturnal treatment (OR, 2.07; 95% CI, 1.16–4.64 by ordinal regression analysis). Low PAI-1 levels were associated with complete recanalization but did not significantly differ between the two time frames. In conclusion, diurnal administration of tPA is associated with complete MCA recanalization and better functional outcome at 90 days in patients with AIS. (Author correspondence: mgomis.germanstrias@gencat.cat, meritxellgomis@gmail.com)     

Circadian Variation of Myocardial Ischemia in Patients with Stable Coronary Artery Disease

The circadian variation of myocardial ischemia detected during 24-h ambulatory electrocardiographic monitoring (AEM) was analyzed in 123 patients with stable angina pectoris, positive exercise test, and angiographically proven coronary artery disease. A total of 437 ischemic episodes (ST-segment depression ≥ 1 mm and duration ≥ 1 min) were observed; 333 (76%) episodes remained asymptomatic, and only 104 (24%) episodes were accompanied by anginal pain. Ischemic episodes predominantly occurred during the morning hours, between 6 a.m. and noon, and another smaller peak was observed in the afternoon, between 4 and 5 p.m.; this diurnal pattern was influenced neither by the extent of coronary artery disease nor the degree of left ventricular dysfunction. The circadian variation was restricted to the 345 (78%) ischemic episodes preceded by increases in heart rate; the 92 (22%) episodes without prior heart rate changes occurred randomly throughout the day. The morning peak in ischemic episodes was not associated with less myocardial oxygen supply; in contrast, heart rate profile showed parallel increases during the morning and afternoon hours, indicating elevated myocardial demand during these periods. Ischemia-related ventricular arrhythmias were concentrated during the morning hours, but their overall prevalence was low–28 (6%) of 437 ischemic episodes. These findings may provide further insight into the pathomechanisms of acute clinical events in patients with coronary artery disease, since the circadian variation of myocardial ischemia is very similar to that observed for the onset of myocardial infarction and sudden cardiac death.     

Circadian Variation of Myocardial Ischemia in Patients with Stable Coronary Artery Disease

The circadian variation of myocardial ischemia detected during 24-h ambulatory electrocardiographic monitoring (AEM) was analyzed in 123 patients with stable angina pectoris, positive exercise test, and angiographically proven coronary artery disease. A total of 437 ischemic episodes (ST-segment depression ≥ 1 mm and duration ≥ 1 min) were observed; 333 (76%) episodes remained asymptomatic, and only 104 (24%) episodes were accompanied by anginal pain. Ischemic episodes predominantly occurred during the morning hours, between 6 a.m. and noon, and another smaller peak was observed in the afternoon, between 4 and 5 p.m.; this diurnal pattern was influenced neither by the extent of coronary artery disease nor the degree of left ventricular dysfunction. The circadian variation was restricted to the 345 (78%) ischemic episodes preceded by increases in heart rate; the 92 (22%) episodes without prior heart rate changes occurred randomly throughout the day. The morning peak in ischemic episodes was not associated with less myocardial oxygen supply; in contrast, heart rate profile showed parallel increases during the morning and afternoon hours, indicating elevated myocardial demand during these periods. Ischemia-related ventricular arrhythmias were concentrated during the morning hours, but their overall prevalence was low-28 (6%) of 437 ischemic episodes. These findings may provide further insight into the pathomechanisms of acute clinical events in patients with coronary artery disease, since the circadian variation of myocardial ischemia is very similar to that observed for the onset of myocardial infarction and sudden cardiac death.     

Circadian Variation in the Onset of Acute Cerebral Ischemia: Ethiopathogenetic Correlates in 80 Patients Given Angiography

In a continuous series of 80 acute ischemic hemispheric strokes, the onset of symptoms was between 6:01 a.m. and noon in 45% of cases, between noon and 6:00 p.m. in 22.5%, between 6:Ol p.m. and midnight in 31.25%, and between midnight and 6:00 a.m. in 1.25% (p < 0.0001). By means ofangiography and computerized tomography, and by detection of arterial and cardiac sources of emboli, four stroke subtypes were identified. Embolic and thrombotic strokes had their most frequent onset between 6:01 a.m. and noon (45% and 71%, respectively), whereas strokes of unknown origin and lacunar strokes were randomly distributed between 6:01 p.m. and midnight. The morning activation of the catecholaminergic system can account for this pattern of circadian onset of ischemic stroke.     

Circadian Variations in Blood Coagulation Parameters, Alpha-Antitrypsin Antigen and Platelet Aggregation and Retention in Clinically Healthy Subjects

Ten clinically healthy subjects (5 men and 5 women), 31 11 yrs of age, were studied at six timepoints (0800, 1200, 1600, 2000, 0000, 0400) distributed over a 1-week span. Circadian rhythms in platelet aggregation in response to adenosine diphosphate (ADP) and adrenalin (A), platelet adhesiveness measured as retention in a glass bead column, prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), fibrinogen, Factor VIII activity and alpha-1-antitrypsin antigen showed circadian rhythms. The plasma concentrations of plasminogen, alpha-2-macroglobulin, and antithrombin III (AT III) antigen, Factor V and fibrinogen degradation products showed no circadian rhythm by ANOVA or cosinor analysis. The phase relations of the rhythms of different coagulation parameters are of interest in the physiology and pathobiology of the coagulation-fibrinolytic system. The extent of the circadian rhythm (range of change) described is not of a magnitude to lead to diagnostic problems in the clinical laboratory. The timing of these rhythms, however, may determine transient risk states for thromboembolic phenomena, including myocardial infarction and stroke. Several but not all coagulation parameters suggest a transient state of hypercoagulability during the morning hours. The recognition of these rhythmic, and thus in the time of the occurrence predictable temporary risk states for thromboembolic phenomena, may lead to timed treatment and/or effective prevention.     

Circadian Variation in the Intracortical Accumulation Kinetics of Tobramycin in Conscious Rats

The time-dependent variation in the renal accumulation of aminoglycosides has not been extensively investigated. The aim of the present study was to better characterize the temporal variation in the intracortical accumulation kinetics of tobramycin. Female Sprague-Dawley rats weighing 210–254 g were maintained in a 14 h light/10 h dark cycle (light on 06h00–20h00). They were infused for 6 h with tobramycin to achieve individual steady-state serum levels of 0.5–15 μg/ml over four different periods of the day (02h00–08h00; 08h00–14h00; 14h00–20h00; and 20h00–02h00). As previously reported, the steady-state elevation of serum tobramycin concentrations was associated with a linear increase of the cortical concentration in all groups. The tobramycin accumulation rate was significantly lower in animals infused at 20h00–02h00 compared to rats infused at 08h00–14h00 (p < 0.001). The data suggest that the lower rate of tobramycin accumulation during the dark period might be responsible for the lower toxicity observed during this time.     

天麻醒脑胶囊对家兔血小板聚集和花生四烯酸诱导大鼠脑血栓形成的影响

采用比浊方法测定天麻醒脑胶囊在体内和体外对腺苷二磷酸（ADP）、花生四烯酸（arachidonic acid,AA）和血小板活化因子（platelet activating factor,PAF）诱导家兔血小板活化聚集的影响。采用从经大鼠颈内动脉注射诱发同侧大脑半球脑血栓形成方法评价天麻醒脑胶囊的抗脑血栓形成作用。天麻醒脑胶囊在体外呈浓度依赖性明显抑制从和ADP引起的血小板聚集,其半数抑制浓度（50％of inhibitory concentration,IC50）分别为1．83和3．25g/L。0．5和1g/kg的天麻醒脑胶囊于灌胃后明显抑制从诱导的家兔血小板聚集,本品1g/kg时显著阻抑ADP引起的血小板聚集。天麻醒脑胶囊在体内外对PAF诱导的血小板聚集均无明显影响。1、2g/kg天麻醒脑胶囊组的右侧与左侧脑重差值均显著减小,显著降低右脑伊文思蓝吸光度与右脑重的比值。结果提示,天麻醒脑胶囊具有较强的抗血小板和减轻脑血栓形成作用,有利于血小板聚集性增高的血栓栓塞性疾病的防治。     

Circadian Variation in the Occurrence of Paroxysmal Supraventricular Tachycardia in Clinically Healthy Subjects

The purpose of this study was to assess prospectively the circadian distribution of spontaneous paroxysmal Supraventricular tachycardia (PSVT) in drug-free subjects with no previous history or symptoms and signs of concomitant heart or lung disease. Of 112,424 presumably diurnally active patients admitted to the Emergency Department of a city hospital during a 2-year period (1990-1991), a total of 185 patients were screened with these characteristics. Time of symptom onset was exactly recordable in 177 (75 men and 102 women). Analysis of variance documented a higher incidence in the morning-afternoon hours. Cosinor analysis, although not a perfect method for the time series analysis, verified circadian rhythmicity with afternoon peak times. Our findings suggest that a circadian pattern in intrinsic electrical instability of the heart conduction system exists irrespective of the circadian fluctuations in the pathophysiologic mechanisms of the cardiovascular or lung diseases most frequently associated with PSVT itself.     

Feeding-Related Circadian Variation in tele-Methylhistamine Levels of Mouse and Rat Brains

Circadian changes in the brain histamine (HA) and tele-methylhistamine (t-MH) levels were studied in mice and rats after adaptation to an alternating 12-h light/dark cycle (lights on at 0600). Although there was no significant circadian fluctuation of the brain HA levels, the levels of t-MH, a major metabolite of brain HA, showed a marked circadian variation. In mice, the t-MH levels were about 80 ng/g from 1200 to 1800 but about two times higher values were obtained from 2400 to 0600 of the next morning. In rats, the t-MH levels ranged from 24 to 28 ng/g at 0600 and 1200, slightly increased at 1800, and reached at 2400 a peak twice as high as the levels seen during the light period. The t-MH levels again rapidly decreased during the subsequent 3 h. In mice fasted from 1200, the t-MH levels did not increase during the period of darkness. When mice were fed at 1200 after a 24-h fast, a significant increase in the t-MH levels was observed at 1800. There was no significant circadian variation of the HA and t-MH levels in the plasma of mice and rats. These results suggest that circadian variation in brain t-MH levels is related to feeding and possible subsequent changes in elimination of t-MH from the brain and/or turnover of HA in the brain. This phenomenon should be given due attention when HA dynamics in the brain are being assessed.