Effects of adrenaline on human blood platelets

Study on the Mechanism of the Adrenaline-Evoked Procoagulant Response in Human Platelets

Adrenaline has recently been found to trigger phosphatidylserine (PS) exposure on blood platelets, resulting in amplification of the coagulation process, but the mechanism is only fragmentarily established. Using a panel of platelet receptors' antagonists and modulators of signaling pathways, we evaluated the importance of these in adrenaline-evoked PS exposure by flow cytometry. Calcium and sodium ion influx into platelet cytosol, after adrenaline treatment, was examined by fluorimetric measurements. We found a strong reduction in PS exposure after blocking of sodium and calcium ion influx via Na+/H+ exchanger (NHE) and Na+/Ca2+ exchanger (NCX), respectively. ADP receptor antagonists produced a moderate inhibitory effect. Substantial limitation of PS exposure was observed in the presence of GPIIb/IIIa antagonist, phosphoinositide-3 kinase (PI3-K) inhibitors, or prostaglandin E1, a cyclic adenosine monophosphate (cAMP)-elevating agent. We demonstrated that adrenaline may develop a procoagulant response in human platelets with the substantial role of ion exchangers (NHE and NCX), secreted ADP, GPIIb/IIIa-dependent outside-in signaling, and PI3-K. Inhibition of the above mechanisms and increasing cytosolic cAMP seem to be the most efficient procedures to control adrenaline-evoked PS exposure in human platelets.

Resuscitation with epinephrine worsens cerebral capillary no-reflow after experimental pediatric cardiac arrest: An in vivo multiphoton microscopy evaluation

Epinephrine is the principal resuscitation therapy for pediatric cardiac arrest (CA). Clinical data suggest that although epinephrine increases the rate of resuscitation, it fails to improve neurological outcome, possibly secondary to reductions in microvascular flow. We characterized the effect of epinephrine vs. placebo administered at resuscitation from pediatric asphyxial CA on microvascular and macrovascular cortical perfusion assessed using in vivo multiphoton microscopy and laser speckle flowmetry, respectively, and on brain tissue oxygenation (PbO₂), behavioral outcomes, and neuropathology in 16-18-day-old rats. Epinephrine-treated rats had a more rapid return of spontaneous circulation and brisk immediate cortical reperfusion during 1-3 min post-CA vs. placebo. However, at the microvascular level, epinephrine-treated rats had penetrating arteriole constriction and increases in both capillary stalling (no-reflow) and cortical capillary transit time 30-60 min post-CA vs. placebo. Placebo-treated rats had increased capillary diameters post-CA. The cortex was hypoxic post-CA in both groups. Epinephrine treatment worsened reference memory performance vs. shams. Hippocampal neuron counts did not differ between groups. Resuscitation with epinephrine enhanced immediate reperfusion but produced microvascular alterations during the first hour post-resuscitation, characterized by vasoconstriction, capillary stasis, prolonged cortical transit time, and absence of compensatory cortical vasodilation. Targeted therapies mitigating the deleterious microvascular effects of epinephrine are needed.

Stress and the "extended" autonomic system

This review updates three key concepts of autonomic neuroscience-stress, the autonomic nervous system (ANS), and homeostasis. Hans Selye popularized stress as a scientific idea. He defined stress variously as a stereotyped response pattern, a state that evokes this pattern, or a stimulus that evokes the state. According to the "homeostat" theory stress is a condition where a comparator senses a discrepancy between sensed afferent input and a response algorithm, the integrated error signal eliciting specific patterns of altered effector outflows. Scientific advances since Langley's definition of the ANS have incited the proposal here of the "extended autonomic system," or EAS, for three reasons. (1) Several neuroendocrine systems are bound inextricably to Langley's ANS. The first to be described, by Cannon in the early 1900s, involves the hormone adrenaline, the main effector chemical of the sympathetic adrenergic system. Other neuroendocrine systems are the hypothalamic-pituitary-adrenocortical system, the arginine vasopressin system, and the renin-angiotensin-aldosterone system. (2) An evolving body of research links the ANS complexly with inflammatory/immune systems, including vagal anti-inflammatory and catecholamine-related inflammasomal components. (3) A hierarchical network of brain centers (the central autonomic network, CAN) regulates ANS outflows. Embedded within the CAN is the central stress system conceptualized by Chrousos and Gold. According to the allostasis concept, homeostatic input-output curves can be altered in an anticipatory, feed-forward manner; and prolonged or inappropriate allostatic adjustments increase wear-and-tear (allostatic load), resulting in chronic, stress-related, multi-system disorders. This review concludes with sections on clinical and therapeutic implications of the updated concepts offered here.

European Journal of Pharmacology - Regular article the antiplatelet effect of mirtazapine is mediated by co-blocking 5-HT2A and α2-adrenergic receptors on platelets: An in vitro human plasma-based study

Mirtazapine (MTZ) is a noradrenergic and specific serotonergic antidepressant that has been associated with an increased risk of bleeding. However, there is insufficient evidence confirming this association. We hypothesised that 5-HT_2A and α₂ receptor-mediated inhibitory effects of MTZ on platelets suppress platelet aggregation and increase the risk of bleeding. In this study, we examined the antiplatelet effect of MTZ on human platelets to test our hypothesis. Blood samples for platelet aggregation tests were obtained from 14 healthy volunteers. The antiplatelet effect of MTZ was evaluated using light transmission aggregometry. MTZ significantly suppressed platelet aggregation mediated both by the synergistic interaction of serotonin (5-HT) and adrenaline and the synergistic interaction of ADP and 5-HT or adrenaline. In conclusion, MTZ exerts its antiplatelet effects by co-blocking the 5-HT_2A and α₂-adrenergic receptors on platelets and also suppresses platelet aggregation induced by ADP and 5-HT or adrenaline. Therefore, when MTZ is used, especially for patients with a high risk of bleeding, the significance of its use must be considered carefully. In addition, the platelet aggregation pattern by adrenaline + 5-HT, ADP + adrenaline, and ADP + 5-HT was similar between humans and mice; however, this study did not directly compare the effects of MTZ on human and murine platelets. Therefore, under the conditions for inducing platelet aggregation using adrenaline + 5-HT, ADP + adrenaline, and ADP + 5-HT, mouse platelets can be used in the evaluation of the efficacy of antiplatelet drugs in humans.

Adrenaline May Contribute to Prothrombotic Condition via Augmentation of Platelet Procoagulant Response, Enhancement of Fibrin Formation, and Attenuation of Fibrinolysis

Background: Adrenaline is believed to play a role in thrombosis and hemostasis. The complex effect of its clinically relevant concentrations on thrombus formation, coagulation and fibrinolysis in human blood has never been specifically studied. Methods: Confocal microscopy was used to study thrombus formation under flow, exposure of phosphatidylserine (PS) in adhered platelets, to evaluate clots density, and to measure kinetics of fibrin formation and external fibrinolysis under flow. Flow cytometry was utilized to assess PS exposure in non-adhered platelets. Kinetics of clot formation and internal fibrinolysis was evaluated by thromboelastometry. Platelet aggregation was measured by optical aggremometry. Kinetics of clot retraction was assessed by using digital camera. Results: We found that adrenaline (1-10 nM) is able to enhance platelet activation evoked by subthreshold collagen (150 ng/ml), resulting in augmentation of platelet aggregation, thrombus formation under arterial flow conditions, platelet PS exposure, and formation of platelet-fibrin clots. The development of platelet procoagulant response evoked by adrenaline + low collagen was associated with the formation of denser platelet-fibrin clots and the decrease in rate of fibrinolysis despite whether lysis was initiated inside (internal fibrinolysis) or outside the clot (external fibrinolysis). The above phenomena were abolished by the α₂-adrenergic receptor antagonist, rauwolscine. Adrenaline-collagen synergism, expressed as PS exposure, was significantly reduced by cyclooxygenase inhibitor (acetylsalicic acid), GPIIb/IIIa receptor blocker (tirofiban), and P2Y₁₂ receptor antagonist (PSB 0739). Conclusion: Clinically relevant concentrations of adrenaline may significantly augment responses of human platelets in the presence of subthreshold concentrations of collagen, which should be considered during therapies involving adrenaline infusion. Routinely used antiplatelet drugs may reduce the prothrombotic state evoked by adrenaline-collagen synergism.

Depression and Cardiovascular Disease: The Viewpoint of Platelets

Depression is a major cause of morbidity and low quality of life among patients with cardiovascular disease (CVD), and it is now considered as an independent risk factor for major adverse cardiovascular events. Increasing evidence indicates not only that depression worsens the prognosis of cardiac events, but also that a cross-vulnerability between the two conditions occurs. Among the several mechanisms proposed to explain this interplay, platelet activation is the more attractive, seeing platelets as potential mirror of the brain function. In this review, we dissected the mechanisms linking depression and CVD highlighting the critical role of platelet behavior during depression as trigger of cardiovascular complication. In particular, we will discuss the relationship between depression and molecules involved in the CVD (e.g., catecholamines, adipokines, lipids, reactive oxygen species, and chemokines), emphasizing their impact on platelet activation and related mechanisms.

The extended autonomic system, dyshomeostasis, and COVID-19

The pandemic viral illness COVID-19 is especially life-threatening in the elderly and in those with any of a variety of chronic medical conditions. This essay explores the possibility that the heightened risk may involve activation of the “extended autonomic system” (EAS). Traditionally, the autonomic nervous system has been viewed as consisting of the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system. Over the past century, however, neuroendocrine and neuroimmune systems have come to the fore, justifying expansion of the meaning of “autonomic.” Additional facets include the sympathetic adrenergic system, for which adrenaline is the key effector; the hypothalamic-pituitary-adrenocortical axis; arginine vasopressin (synonymous with anti-diuretic hormone); the renin-angiotensin-aldosterone system, with angiotensin II and aldosterone the main effectors; and cholinergic anti-inflammatory and sympathetic inflammasomal pathways. A hierarchical brain network—the “central autonomic network”—regulates these systems; embedded within it are components of the Chrousos/Gold “stress system.” Acute, coordinated alterations in homeostatic settings (allostasis) can be crucial for surviving stressors such as traumatic hemorrhage, asphyxiation, and sepsis, which throughout human evolution have threatened homeostasis; however, intense or long-term EAS activation may cause harm. While required for appropriate responses in emergencies, EAS activation in the setting of chronically decreased homeostatic efficiencies (dyshomeostasis) may reduce thresholds for induction of destabilizing, lethal vicious cycles. Testable hypotheses derived from these concepts are that biomarkers of EAS activation correlate with clinical and pathophysiologic data and predict outcome in COVID-19 and that treatments targeting specific abnormalities identified in individual patients may be beneficial.

Epinephrine restores platelet functions inhibited by ticagrelor: A mechanistic approach

Ticagrelor, an antagonist of the platelet adenosine diphosphate (ADP)-P2Y₁₂ receptor is recommended for patients with acute coronary syndromes. However, ticagrelor exposes to a risk of bleeding, the management of which is challenging because platelet transfusion is ineffective, and no antidote is yet available. We hypothesized that the vasopressor drug epinephrine could counter the antiplatelet effects of ticagrelor and restore platelet functions. We assessed in vitro the efficiency of epinephrine in restoring platelet aggregation inhibited by ticagrelor and investigated the underlying mechanisms. Washed platelet aggregation and secretion were measured upon stimulation by epinephrine alone or in combination with ADP, in the presence or absence of ticagrelor. Mechanistic investigations used P2Y₁ and phosphoinositide 3-kinase (PI3K) inhibitors and included vasodilator-stimulated phosphoprotein (VASP) and Akt phosphorylation assays as well as measurement of Ca²⁺ mobilisation. We found that epinephrine restored ADP-induced platelet aggregation, but not dense granule release. Epinephrine alone failed to induce aggregation whereas it fully induced VASP dephosphorylation and Akt phosphorylation regardless of the presence of ticagrelor. In the presence of ticagrelor, blockage of the P2Y₁ receptor prevented restoration of platelet aggregation by the combination of epinephrine and ADP, as well as intracellular Ca²⁺ mobilisation. In combination with ADP, epinephrine induced platelet aggregation of ticagrelor-treated platelets through inhibition of the cAMP pathway and activation of the PI3K pathway, thus enabling the P2Y₁ receptor signalling and subsequent Ca²⁺ mobilisation. This proof-of-concept study needs to be challenged in vivo for the management of bleeding in ticagrelor-treated patients.

Intraoperative infusion of noradrenaline improves platelet aggregation in patients undergoing coronary artery bypass grafting: a randomized controlled trial

Essentials Strategies to improve platelet function may reduce excessive bleeding during cardiac surgery. Patients were randomized to standard care or standard care + noradrenaline infusion. Low-dose noradrenaline improved intraoperative platelet aggregation and clot formation. Noradrenaline may be considered to improve intraoperative hemostasis during cardiac surgery. SUMMARY: Background New approaches to prevent bleeding complications during cardiac surgery are needed. Objective To investigate if noradrenaline (NA) enhances platelet aggregation in patients undergoing coronary artery bypass grafting (CABG). Patients/Methods Twenty-four patients undergoing coronary artery bypass grafting (CABG) were included in a prospective parallel-group randomized study. All patients but one were treated with acetylsalicylic acid (ASA). In the treatment group (n = 12), mean arterial blood pressure (MAP) was maintained at pre-induction levels by NA infusion. In the control group (n = 12), NA was administered only if MAP decreased below 60 mmHg. Platelet aggregation (impedance aggregometry with ADP, arachidonic acid [AA] and thrombin-receptor activating peptide [TRAP] as initiators) and clot formation (clotting time, clot formation time and maximum clot firmness by EXTEM, INTEM and FIBTEM tests with thromboelastometry) were assessed before and 50 min after anesthesia induction (before cardiopulmonary bypass was initiated). Results All patients in the treatment group received NA (median dose after 50 min 0.09 (range 0-0.26) μg kg-1  min-1 ). Four patients in the control group also received NA (0.03-0.12 μg kg-1  min-1 ). There were differences between the treatment group and the control group in ADP- and AA-induced aggregation changes (ADP, +16 [25th-75th percentiles, 5-26] vs. -7 [-19 to -1] U; AA, +12 [-4 to 16] vs. -9 [-13 to 1] U). INTEM maximum clot firmness increased in the treatment group but not in the control group. Conclusion Infusion of clinically relevant doses of NA enhanced platelet aggregation and clot firmness in ASA-treated CABG patients. NA infusion is hence a potential new method to acutely improve platelet reactivity in patients on antiplatelet therapy undergoing surgery.

Adrenaline enhances in vitro platelet activation and aggregation in blood samples from ticagrelor-treated patients

BACKGROUND

Temporarily improved platelet reactivity may reduce the bleeding in patients on antiplatelet therapy who have ongoing bleeding or who are in need of acute surgery. Adrenaline can bind to adrenergic α2A-receptors on platelets and potentially enhance platelet reactivity.

OBJECTIVE

To assess if adrenaline can improve adenosine diphosphate (ADP)-induced platelet aggregation and activation in blood samples from patients on dual antiplatelet therapy with acetylsalicylic acid (ASA) and the ADP-receptor antagonist ticagrelor.

METHODS

Blood samples were collected from a total of forty acute coronary syndrome patients on dual antiplatelet therapy with ASA and ticagrelor. ADP-induced platelet aggregation (by impedance aggregometry) and activation (by flow cytometry) were assessed before and after supplementation with adrenaline and/or platelet concentrate.

RESULTS

Adrenaline supplementation (770 nmol L-1) increased median ADP-induced aggregation from 15 (25-75th percentiles: 10-20) to 26 (18-38) aggregation units. The effect was independent of concomitant platelet supplementation. Adrenaline also increased ADP-induced platelet activation: from 40% (36-54%) to 83% (74-88%) platelets with active fibrinogen receptor (binding PAC-1) and from 13% (7-21%) to 35% (18-50%) P-selectin-expressing platelets.

CONCLUSIONS

Adrenaline potentiated ADP-induced platelet aggregation and activation in blood samples from ticagrelor-treated patients. Adrenaline infusion may be a new method to enhance platelet function in ticagrelor-treated patients who are in need of acute surgery or have ongoing bleeding. In vivo studies are needed to confirm the present results.

The receptor EP3 to PGE2: A rational target to prevent atherothrombosis without inducing bleeding

The prostanoid E2 (PGE2) is known to modulate the aggregative response of platelets to their conventional agonists such as ADP, TXA2, thrombin or collagen. Through the activation of its receptor EP3, PGE2 sensitizes platelets to their agonists but also inhibits them through its two other receptors, EP2 and EP4. In mice, the net result of these opposed actions is the EP3-mediated potentiation of platelet aggregation and the in vivo aggravation of murine atherothrombosis. Since the pathway PGE2/EP3 is not involved in murine hemostasis, we propose a "platelet EP3 paradigm" to describe this apparently paradoxical association between the facilitating impact on atherothrombosis and the unaltered hemostasis. Consistent with this paradigm, a drug blocking EP3 dramatically decreased atherothrombosis without inducing bleeding in mice. In humans, several studies did not agree on the effect of PGE2 on platelets. Reinterpreting these data with the notion of "potentiation window" and taking the platelet initial cAMP level into account reconciled these inconsistent results. Thereby, the in vitro potentiating effect of PGE2 on human platelets becomes clear. In addition, the EP3 blocking drug DG-041 abrogated the potentiating effect of PGE2 in whole human blood but did not prolong bleeding times in volunteers. Thus, the murine "platelet EP3 paradigm" would apply to humans if the aggravating role of PGE2 on atherothrombosis is shown in patients. Therefore, testing an EP3 blocker in a phase III trial would be of high interest to fulfill the unmet medical need which is to control atherothrombosis without impacting hemostasis and thus to improve the prevention of myocardial infarction.

Circulating primers enhance platelet function and induce resistance to antiplatelet therapy

BACKGROUND

Aspirin and P2Y12 antagonists are antiplatelet compounds that are used clinically in patients with thrombosis. However, some patients are 'resistant' to antiplatelet therapy, which increases their risk of developing acute coronary syndromes. These patients often present with an underlying condition that is associated with altered levels of circulating platelet primers and platelet hyperactivity. Platelet primers cannot stimulate platelet activation, but, in combination with physiologic stimuli, significantly enhance platelet function.

OBJECTIVES

To explore the role of platelet primers in resistance to antiplatelet therapy, and to evaluate whether phosphoinositide 3-kinase (PI3K) contributes to this process.

METHODS AND RESULTS

We used platelet aggregation, thromboxane A2 production and ex vivo thrombus formation as functional readouts of platelet activity. Platelets were treated with the potent P2Y12 inhibitor AR-C66096, aspirin, or a combination of both, in the presence or absence of the platelet primers insulin-like growth factor-1 (IGF-1) and thrombopoietin (TPO), or the Gz-coupled receptor ligand epinephrine. We found that platelet primers largely overcame the inhibitory effects of antiplatelet compounds on platelet functional responses. IGF-1-mediated and TPO-mediated, but not epinephrine-mediated, enhancements in the presence of antiplatelet drugs were blocked by the PI3K inhibitors wortmannin and LY294002.

CONCLUSIONS

These results demonstrate that platelet primers can contribute to antiplatelet resistance. Furthermore, our data demonstrate that there are PI3K-dependent and PI3K-independent mechanisms driving primer-mediated resistance to antiplatelet therapy.

Hemoconcentration and hemostasis during acute stress: interacting and independent effects

BACKGROUND

Acute psychological stress can produce significant hemoconcentration as well as prothrombotic changes in blood, both of which may have potentially harmful effects on the cardiovascular system. It is unclear whether these effects are independent or have influence on each other.

PURPOSE

This review discusses research investigating the effects of acute psychological stress on hemoconcentration and hemostasis and explores future directions for psychohematology research. Physiology, associations with cardiovascular disease, and relationships between acute psychological stress are discussed independently for hemoconcentration and hemostasis, followed by an examination of the effects of stress-hemoconcentration on hemostasis.

CONCLUSIONS

Traditional methods of adjusting for stress-hemoconcentration effects (e.g., calculated plasma volume or hematocrit level corrections) may not be appropriate when examining stress-induced changes in hemostasis. The effects of acute stress on hemostasis should be examined in conjunction with hemoconcentration.

Influence of Bordetella pertussis on Adenosine Diphosphate-Induced Aggregation of Mouse Platelets

Several lines of evidence support the concept that Bordetella pertussis-induced histamine hypersensitivity in mice represents a malfunction in beta-adrenergic receptors of the autonomic nervous system. In this study mouse platelets were used as an in vitro test for such receptor dysfunction. It was found, to our knowledge for the first time, that platelets of normal mice were subject to the aggregative action of adenosine diphosphate (ADP) with the response pattern resembling that reported for cells of certain other species. These "normal" platelets were not aggregated by epinephrine, norepinephrine, or isoproterenol (isuprel). However, pretreatment with these catecholamines potentiated the platelet response to ADP. Potentiation by norepinephrine was suppressed in the presence of dibenzyline (an alpha-receptor antagonist); blockade of beta-type receptors with propranolol reduced isuprel enhancement. An extract of B. pertussis influenced aggregation initiated by a combination of ADP and isuprel in a way quite similar to propranolol pretreatment. These observations suggested the possible role of adrenergic receptors in at least the enchancement phenomena and, moreover, pointed to those types of experiments which might distinguish a receptor disturbance. Platelets derived from pertussis-vaccinated mice were more responsive to ADP than were those from normal animals. This alteration appeared to be a property of the cells and not of the suspending medium. ADP-initiated aggregation was also enhanced in the presence of epinephrine and norepinephrine. However, pretreatment with isuprel did not have the same effect as noted for normal donor platelets. These results point to a disturbance at the beta-adrenergic receptor level and lend support to the concept of beta-blockade in pertussis-treated mice.

Dipyridamole and low doses of heparin as a new successful physiopathologic and therapeutic approach in 2 cases of disseminated intravascular coagulation

OPERATIVE: We report 2 cases of disseminated intravascular coagulation (DIC) successfully treated with the combination of the platelet adhesiveness blocker dipyridamole and low doses of intravenous heparin.

METHODS

The first patient was a 17-year-old boy with septic arthritis; the second patient was a 12-year-old boy with a liver abscess. Both had hemocultures positive for Staphylococcus aureus. The diagnosis of DIC was defined by clinical signs of septicemia with fever, tachypnea, peripheral vasoconstriction, and low platelet counts (67,000/mm3 and 47,000/mm3, respectively). The second patient also presented with acute ischemia of the fingers and toes. General care was provided in the intensive care unit, and high doses of antibiotics were provided continuously (metronidazole and oxacillin or ceftriaxone). A 5% glucose solution containing dipyridamole (Persantine; Istituto De Angeli/Boheringer Ingelheim, Reggello, Italy) was administered by continuous intravenous infusion (20 mg/24 hours). In addition, regular heparin (Liquemin; Roche, Indianapolis, IN, USA) was administered at a dosage of 250 microg/kg per hour or 25 IU/kg per hour (6 mg/kg per 24 hours). These heparin doses are not able to promote complete blood anticoagulation. Treatment with heparin and dipyridamole was maintained for 10 days in the first patient and for 18 days in the second.

RESULTS

By 48 hours after treatment with dipyridamole and low-dose heparin, both patients recovered and presented with a good clinical condition and increased numbers of circulating platelets. Both patients were discharged in a safe clinical condition in the second month after hospital admission.

CONCLUSION

Successful clinical recovery of 2 young patients with DIC with an unfavorable clinical evolution and a prognosis for a lethal outcome was achieved with the combination of a continuous infusion of dipyridamole and low doses of heparin.

Increased beta-thromboglobulin in essential hypertension: interactions between arterial plasma adrenaline, platelet function and blood lipids

Twenty-three 50-year-old men with untreated, essential hypertension had elevated plasma concentrations of the platelet release product beta-thromboglobulin (BTG) compared to 14 age-matched control men (p less than 0.01). BTG correlated with arterial plasma adrenaline concentrations in the hypertensive (r = 0.44, p less than 0.05), normotensive (r = 0.73, p less than 0.01) and combined group (r = 0.51, p less than 0.01). Significant correlations (p less than 0.05) between BTG and cholesterol (LDL + VLDL fraction) were observed both in the hypertensive and the normotensive group. In the hypertensive group arterial adrenaline correlated with cholesterol (LDL + VLDL) (p less than 0.05). These findings are consistent with increased platelet activity in middle-aged men with essential hypertension, and may indicate that plasma adrenaline influence platelet function. The risk factors for coronary artery disease (blood pressure, lipid status, stress as evidenced by catecholamine release and platelet function) were positively related. Measurement of arterial instead of venous adrenaline is essential for the demonstration of the associations presented.

Association between mean platelet volume and autonomic nervous system functions: Increased mean platelet volume reflects sympathetic overactivity

BACKGROUND

Increased mean platelet volume (MPV) may reflect increased platelet activation or increased numbers of large, hyperaggregable platelets, and is accepted as an independent coronary risk factor. The adrenergic system has effects on platelet activation and thrombocytopoiesis.

OBJECTIVE

To assess the effects of autonomic nervous system activity on MPV in patients with acute myocardial infarction (MI).

METHODS AND RESULTS

Forty-seven patients with acute anterior MI were compared with 32 patients with healthy coronary arteries. All patients underwent heart rate (HR) variability analysis using 24 h Holter monitoring. Blood samples were taken for MPV measurements twice a day (day- and nighttime) during Holter monitoring. Mean HR, low frequency band of HR variability power spectrum to high frequency band of HR variability power spectrum (LF:HF) ratio, LF and MPV were higher in patients with anterior MI than in the control group. SD of all NN (RR) intervals, root mean square of successive differences, number of NN intervals that differed by more than 50 ms from the adjacent interval divided by the total number of all NN intervals, HF bands and platelet counts were lower in the patients with anterior MI than in the control group. Daytime LF bands, LF:HF ratio and MPV were significantly higher, and HF bands were significantly lower than the nighttime values for both groups. The differences in daytime and nighttime measurements were more significant in the patients with acute MI than in the control group. Pearson's correlation analysis showed that MPV was positively correlated with ventricle score, degree of left anterior descending artery stenosis, mean HR, LF bands and LF:HF ratio; and negatively correlated with the SD of all NN intervals, HF bands and platelet count. Multivariate analysis revealed that MPV was significantly affected by ventricle score and the LF:HF ratio.

CONCLUSIONS

MPV was significantly higher in the patients with acute MI. In both groups, MPV showed great daytime and nighttime variation, which can be attributed to alterations in the autonomic nervous system. The authors suggest that the prognostic role of increased MPV in patients with acute MI is closely associated with increased sympathetic activity and decreased HR variability.

Regulation of platelet function by catecholamines in the cerebral vasculature of the rabbit

1. 111In-labelled platelets were monitored continuously in the cerebral and pulmonary vascular beds of anaesthetized rabbits. Dopamine can, depending upon the concentration, either potentiate or inhibit thrombin-induced platelet accumulation in the cerebral vasculature of rabbits by unknown mechanisms. The effects of specific adrenergic and dopaminergic receptor antagonists were tested upon dopamine's actions on intracarotid (i.c.) thrombin-induced (80 u kg-1) platelet accumulation in the cerebral vasculature. The effect of adrenaline on the response to thrombin in this vascular bed was also investigated. 2. Thrombin-induced platelet accumulation was significantly (P<0.01) potentiated by dopamine (100 microgkg-1 min-1, i.c.) and this effect was significantly inhibited by infusion of the alpha-adrenoceptor antagonist, phentolamine. 3 A higher dose of dopamine (2 mg kg-1 min-1, i.c.) inhibited thrombin-induced platelet accumulation. The beta-adrenoceptor antagonist, propranolol, did not significantly alter this inhibitory effect whereas it was abolished by the dopamine D1 selective antagonist, SCH23390. 4 Adrenaline (when administered i.c. by bolus injection or infusion) had no significant effect on thrombin-induced accumulation at any of the doses tested. 5 Potentiation of in vivo platelet accumulation by dopamine therefore seems to occur via alpha-adrenergic receptors. However, the inhibitory effect of dopamine appears to be exerted via the activation of dopamine D1 receptors and not via beta-adrenergic receptors. Our findings confirm that dopamine, but not adrenaline, can modify platelet function in the cerebral vasculature and these observations may have implications for current and potential therapeutic uses of dopamine and selective dopaminergic compounds.

Modulation of human platelet function by L-canavanine: differential effects of low and high concentrations

L-Canavanine is a naturally occurring L-amino acid that interferes with L-arginine-utilizing enzymes owing to its structural analogy with this L-amino acid. In macrophages and polymorphonuclear leukocytes, which express inducible nitric oxide synthase (iNOS), L-canavanine is able to prevent the L-arginine-derived synthesis of nitric oxide (NO). Its effects on constitutive NOS (cNOS) are far less clear. Because human platelets synthesize NO from L-arginine through a cNOS and because intracellular NO levels modulate platelet function, we have investigated the effects of L-canavanine on parameters potentially influenced by NO, such as platelet levels of 3',5'-cyclic guanosine monophosphate (cGMP) and responses to different aggregating agents. In our experimental conditions, L-canavanine was able to influence the response of human platelets to different aggregating agents such as catecholamines, 5-hydroxytryptamine, and ADP. Low L-canavanine concentrations (10-100 micromol/l) decreased platelet responses, whereas a high concentration (1 mmol/l) was unable to exert antiaggregating effects. In resting platelets, L-canavanine reduced the levels of cGMP, starting from a concentration of 1 mmol/l; furthermore, at the same concentrations, it was able to reduce cGMP levels at the end of the aggregation induced by collagen. In conclusion, L-canavanine exerts differential effects on human platelets in relation to the concentrations: at low levels, it exerts antiaggregating effects by actions independent of NOS inhibition, whereas, at high levels, it inhibits NO synthesis and does not exert antiaggregating effects.

Active platelet 5-ht uptake in depressives treated with impramine and ect

Several studies have reported decreased platelet 5-HT uptake in patients of major depression. The present study was undertaken with the aim to study the active platelet 5-HT uptake in depressed patients and effect of treatment with imipramine/ECT on platelet 5-HT uptake in these patients. 30 patients of major depression and equal number of age and sex-matched controls were included in the study. The depressives received imipramine (N=15) or ECT (N=15). Pretreatment active platelet 5-HT uptake was lower in depressives. Treatment with imipramine resulted in significant decrease in 5-HT uptake while with ECT there was significant increase. The serotonergic mechanisms are discussed.

Ect and platelet 5ht uptake in major depression

Several studies have reported decreased platelet 5-HT uptake in patients of major depression. The mechanism of antidepressant action of ECT is not clear. The present work was undertaken with the aim to study the active platelet 5-HT uptake and the effect of ECT on it in patients of major depression. 15 patients of major depression (DSM-lll-R) and equal number of age and sex-matched controls were included in the study. Active platelet 5-HT uptake was determined before ECT, after a course of ECT and 7 days after last ECT. Platelet 5-HT uptake was. significantly lower in der essives than normal controls. After ECT treatment there was significant increase in 5-HT uptake which came down to pretreatment level after 1 week of last ECT. The effect of ECT on serotonergic system is discussed.

Effect of low concentration of epinephrine on human platelet aggregation analyzed by particle counting method and confocal microscopy

The effect of a physiologic concentration of epinephrine (Ep) on platelet activation was studied by using a novel method that simultaneously measures platelet aggregation by changes in light transmission and counts particles of various sizes by using light scattering. Detailed morphologic changes associated with activation process were studied by using confocal laser scanning microscopy (CLSM). A low concentration of Ep (20 nmol/L) corresponding to a high physiologic concentration triggered the formation of small platelet aggregates (diameter 7 to 30 microm) without any change in light transmission. The redistribution of filamentous actin (F-actin) and the expression of activated glycoprotein IIb-IIIa complex (GPIIb-IIIa), detected by PAC-1 binding, were also observed in the platelets comprising the small aggregates. Attempts were then made to detect changes in cytoplasmic ionized Ca2+ ((Ca2+)i) in individual platelets involved in the aggregate formation by CLSM with fluo-3, a Ca2+-indicating dye. Ep caused a weak (Ca2+)i increase in some individual platelets involved in the formation of small aggregates. This (Ca2+)i increase was associated with platelet aggregation, because no (Ca2+)i rise was detected in single platelets. Furthermore, platelets stimulated by Ep in the presence of RGDS or Ro 44-9883, a GPIIb-IIIa antagonist, did not form small aggregates or trigger a (Ca2+)i rise. Prior incubation with low concentrations of Ep (20, 100 nmol/L) enhanced the initial formation of small (diameter 7 to 30 microm), medium (diameter 30 to 50 microm), or large (diameter 50 to 70 microm) aggregates induced by a subthreshold concentration of adenosine diphosphate (0.25 micromol/L) as determined by the particle counting method. However, no apparent synergistic (Ca2+)i increase was observed in platelets involved in aggregate formation. From these observations the following conclusions have been reached. (1) A high physiologic concentration of Ep (20 nmol/L) is capable of triggering the formation of small aggregates, resulting in the redistribution of F-actin and the expression of activated GPIIb-IIIa complex. (2) An increase in (Ca2+)i is observed in platelets comprising the small aggregates. This increase is not related to the binding of Ep to its receptor but most likely is triggered by platelet-platelet association. (3) The characteristic potentiating effect of Ep is not due to the synergistic increase in (Ca2+)i.

Signal transduction system in epinephrine stimulated platelets; comparison between epinephrine sensitive and insensitive platelets

We recently reported the high prevalence of impaired platelet responsiveness only to epinephrine in healthy Japanese. This abnormality was associated with a 50% decrease in the number of alpha 2-adrenergic receptors. Platelets from non-responders (NR) do not undergo secondary platelet aggregation even after exposure to 100 microM epinephrine, but they can potentiate the effect of ADP to provoke platelet aggregation. To further define the nature of the defect and to delineate controversial steps of epinephrine stimulated signal transduction, a signaling pathway of epinephrine was investigated in platelets from NR and R(normal responder to epinephrine). In a unique particle counting apparatus, epinephrine initially triggered the formation of small platelet aggregates composing of 10-1000 cells from both R and NR, but the aggregates became larger (4600 > cells) only in platelets from R. Thus, platelets from NR lack the ability to form larger aggregates. A similar defect was reproduced by treating normal platelets with aspirin. In the presence of fibrinogen, platelets from NR lacked phospholipase A2 activation, determined by arachidonic acid liberation in the presence of inhibitors to cyclooxygenase and lipoxygenase. In the absence of fibrinogen, aggregation and phospholipase A2 activation were not evident in R and NR. The surface expression of GPIIb/IIIa was markedly decreased in platelets from NR after stimulation by epinephrine, in comparison with those from R. The resting level and epinephrine stimulated increase in cAMP were not significantly different between NR and R. Incubating R platelets with a half saturating dose of yohimbine rendered them insensitive to epinephrine. These results indicated that the impaired platelet aggregation induced by epinephrine was due to the impaired surface exposure of glycoproteins GPIIbIIIa integral to the activation of phospholipase A2, which requires the full and normal occupancy of the alpha 2-adrenergic receptor by epinephrine.

Factors that affect the size of platelet aggregates in epinephrine-induced activation: a study using the particle counting method based upon light scattering

Platelet aggregate size was determined with a newly-developed platelet aggregometer, PA-100 (KOWA), which can quantitatively evaluate the size and number of platelet aggregates by means of the particle counting method based upon light scattering. Epinephrine-induced platelet aggregation consists of two phases, the former characterized by the formation of small-sized aggregates (less than 100 cells), which is followed by the phase of large aggregate formation with concomitant decrease in the number of small aggregates. These findings suggest that small aggregates fuse to form large aggregates. Effects of various inhibitors and antibodies directed against platelet membrane glycoproteins were evaluated on the size of platelet aggregates induced by epinephrine. Cyclooxygenase inhibitors, thromboxane A2 receptor antagonists, and a Na+/H+ exchanger inhibitor (ethylisopropylamiloride) inhibited the formation of large aggregates (more than 100 cells) but not that of small aggregates. Cytochalasin B, which interferes with microfilaments, suppressed large aggregate formation, whereas taxol, which reacts with microtubules, had no effects. Anti-GPIIb/IIIa monoclonal antibody (MoAb) inhibited both the formation of small and large platelet aggregates, while antibodies directed against GPIb, thrombospondin, P-selectin, or PECAM-1 had no effects on platelet aggregate formation. These findings, taken together, suggest that intracellular alkalinization, thromboxane A2 formation and microfilament rearrangement are prerequisites for large platelet aggregate formation. GPIIb/IIIa is involved in the formation of small as well as large aggregates, but a membrane glycoprotein(s) responsible for the transition of small aggregates into large aggregates awaits to be determined.

Prevalence of impaired responsiveness to epinephrine in platelets among Japanese

The responsiveness of platelets only to epinephrine was markedly impaired in 23/140 (16%) healthy Japanese. The impaired responsiveness was not altered by changes in time and environment. Circulating level of catecholamines did not affect the responsiveness of platelets to epinephrine. A pilot family study indicated a possible familial nature of the defect. 3H methyl-yohimbine binding studies indicated that this defect was due to the decreased number of alpha 2 adrenergic receptor. Despite the defect, the potentiating effect of epinephrine on platelet aggregation stimulated by a low dose of ADP was normal. This abnormality is not apparently associated with any bleeding disorders and the clinical implication is unknown at present. It is, however, essential to acknowledge the prevalence of such defect in pursuing research on platelets stimulated by epinephrine.

Effects of exercise training and deconditioning on platelet function in men

Platelets play an important role in the pathogenesis of cardiovascular disease. It has also been noticed that regular exercise can reduce the risk of cardiovascular disease. This is the first study to demonstrate that endurance exercise training may suppress platelet adhesiveness and aggregation and that deconditioning may reverse the training effects. Healthy male sedentary subjects were randomly divided into control and training groups. The trained men were trained on a bicycle ergometer at about 60% of maximal oxygen consumption for 30 minutes per day, 5 days per week for 8 weeks, then deconditioned for 12 weeks. During the experimental period, blood samples of the trained subjects were collected before and immediately after a progressive exercise test every 4 weeks. The same experiments were applied to the controls at the beginning of this study and 8 weeks thereafter. A tapered parallel-plate chamber was used to assess platelet adhesiveness. Platelet aggregation induced by ADP was evaluated by the percentage of reduction in single platelet count. Our results showed that (1) platelet adhesiveness and aggregability were increased by short-term strenuous exercise in both control and trained groups, but the enhancement of platelet aggregability was decreased after exercise training in the trained subjects; (2) at rest and immediately after strenuous exercise, platelet adhesiveness and aggregability were decreased by training, whereas they were unchanged in the control group; and (3) deconditioning reversed the training effects on resting and postexercise platelet adhesiveness and aggregability back to the pretraining state. These results suggest that platelet adhesiveness and aggregability may be depressed by exercise training but be reversed back to the pretraining state after deconditioning.

Calcium supplementation attenuates an enhanced platelet function in salt-loaded mildly hypertensive patients

We designed this study to evaluate the effect of low versus high calcium intake on platelet function in salt-loaded patients with mild hypertension. After a 7-day period of dietary salt restriction, 19 patients were placed on a high salt (300 mmol/d), low calcium (6.25 mmol/d) diet for 7 days; 10 of these patients were given 54 mmol/d of supplementary calcium, and 9 patients were given placebo. At the end of the low and high salt regimens, we evaluated changes in blood pressure, platelet aggregation, and the platelet release reaction measured as plasma beta-thromboglobulin and platelet factor 4 levels. With high salt intake, significant increases in mean blood pressure (P < .02), red blood cell sodium (P < .01), and platelet aggregation induced by 3 mumol/L ADP (P < .01) and by 3.0 mg/L epinephrine (P < .05) were observed in the placebo-treated patients but not in the calcium-supplemented ones. Compared with the placebo-treated patients, calcium-supplemented patients had a smaller weight gain (P < .05) but excreted more sodium and calcium (P < .01) at the end of the high salt regimen. Calcium supplementation resulted in decreases in beta-thromboglobulin (P < .05), platelet factor 4 (P < .01), and plasma and urinary excretions of norepinephrine (P < .02) during the high salt, low calcium regimen. The decrease in plasma norepinephrine correlated positively with the decreases in beta-thromboglobulin (r = .72, P < .02) and platelet factor 4 (r = .85, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of adrenoceptor stimulation on aggregation of platelets from diabetic and control rats

1. Studies of cardiac and vascular responses have previously demonstrated that diabetes influences the sensitivity of these tissues to adrenoceptor stimulation. Adrenoceptors are also present on platelets where they modulate aggregatory responses. The present study investigates the influence of diabetes on these platelet adrenoceptor-mediated responses. 2. Rats were made diabetic with streptozotocin and platelet aggregatory responses to ADP were examined 2 or 12 weeks later. Aggregation to ADP of platelets from 2-week-diabetic rats was similar to that of platelets from age-matched controls, but platelets from 12-week-diabetic animals exhibited an enhanced aggregation to ADP. 3. In all groups studied, beta-adrenoceptor stimulation with isoprenaline caused a concentration-dependent inhibition of aggregation to ADP, whilst alpha-adrenoceptor stimulation with adrenaline was found to potentiate aggregation to ADP. The degree of inhibition or potentiation was found to remain unchanged by diabetes of either 2 or 12 weeks duration. 4. Previously reported increases in cardiac beta-adrenoceptor sensitivity and aortic alpha-adrenoceptor sensitivity were confirmed 2-week-diabetic animals, but these sensitivity changes were not observed in 12-week-diabetic rats. 5. The results indicate that, unlike the heart and vasculature, the influences of adrenoceptor stimulation on platelet aggregation are not altered by diabetes, even when aggregation to ADP is enhanced.

Platelet function defects associated with hemorrhage or thrombosis

Platelet dysfunction, especially acquired forms, is a common cause of hemorrhage, especially when associated with trauma or surgery. Although the hereditary platelet function defects are generally quite rare, hereditary storage pool disease is common enough to be suspected in an individual, usually a child, with characteristic historical and clinical findings. The acquired platelet function defects, especially those resulting from drugs, are common and should promptly be suspected in patients developing easy and spontaneous bruising, mild-to-moderate mucosal membrane hemorrhage, or unexplained bleeding associated with trauma or surgery. The template bleeding time is generally useful as a screening test of platelet function, but a normal template bleeding time, in the face of a suggestive history, suggestive clinical findings, or in a patient frankly bleeding, is not reliable, and platelet aggregation or lumiaggregation should be done in appropriate clinical situations. Also, prolongation of the template bleeding time is an unreliable predictor of clinical bleeding propensity. The mainstay of therapy for almost all these defects, if bleeding is significant, is the liberal infusion of appropriate numbers of platelet concentrates. The acquired platelet function defects should also be managed by attempts to treat or control the underlying disease, if possible, and offending drugs or potentially offending drugs should immediately be stopped.

Alpha-adrenoceptors

Major advances have been made in our understanding of the molecular structure and function of the alpha-adrenoceptors. Many new subtypes of the alpha-adrenoceptor have been identified recently through biochemical and pharmacological techniques and several of these receptors have been cloned and expressed in a variety of vector systems. Currently, at least seven subtypes of the alpha-adrenoceptor have been identified and the molecular structure and biochemical functions of these subtypes are beginning to be understood. The alpha-adrenoceptors belong to the super family of receptors that are coupled to guanine nucleotide regulatory proteins (G-proteins). A variety of G-proteins are involved in the coupling of the various alpha-adrenoceptor subtypes to intracellular second messenger systems, which ultimately produce the end-organ response. The mechanisms by which the alpha-adrenoceptor subtypes recognize different G-proteins, as well as the molecular interactions between receptors and G-proteins, are the topics of current research. Furthermore, the physiological and pathophysiological role that alpha-adrenoceptors play in homeostasis and in a variety of disease states is also being elucidated. These major advances made in alpha-adrenoceptor classification, molecular structure, physiologic function, second messenger systems and therapeutic relevance are the subject of this review.

Epinephrine augments von Willebrand factor-dependent shear-induced platelet aggregation

BACKGROUND

Shear-induced platelet aggregation (SIPA) is an important mechanism in thrombogenesis. von Willebrand factor (vWF) binding to platelet glycoprotein Ib (GP Ib) has been found to be crucial for platelet aggregation under the high shear force probably generated in stenosed coronary artery. The physiological significance of vWF-dependent SIPA has not been clarified.

METHODS AND RESULTS

Blood samples were collected from 23 normal volunteers. SIPA was continuously monitored using a modified cone-plate viscometer adapted for measuring the transmitted light intensity of the material. The effects of low concentrations of epinephrine, ADP, and collagen on SIPA under both low shear (12 dyne/cm2) and high shear (108 dyne/cm2) force were investigated. All agonists tested enhanced SIPA under low shear force, whereas only epinephrine augmented SIPA under high shear force. The maximum extents of SIPA under high shear force in the absence and presence of epinephrine (10 ng/ml) were 37.9 +/- 11.5% and 59.7 +/- 13.9%, respectively. The antagonist of the alpha 2-adrenergic receptor yohimbine (1 microgram/ml) antagonized the effects of epinephrine. The monoclonal antibody NMC-4 against vWF, which was shown to inhibit its binding to GP Ib, completely abolished SIPA under high shear force, even in the presence of epinephrine. However, this antibody only partially inhibited SIPA under low shear force.

CONCLUSIONS

Our findings suggest that epinephrine is the agonist that enhances SIPA mediated by vWF through its specific receptor. This may be clinically important because occlusion of the coronary artery often occurs in stenosed atherosclerotic vessels under sympathetic stimulation.

Hemostatic effects of ephedrine

The effects of ephedrine on coagulation and on fibrinolysis were studied in six healthy volunteers. Six volunteers, matched by age and sex, served as untreated controls. Ephedrine was found to significantly prolong mean bleeding time by 2 minutes. Ephedrine has been proposed to activate fibrinolysis, but we found no increased tPA activity. The platelet count, APTT, factor VIII and von Willebrand factor remained constant. In an in vitro study ephedrine was found to inhibit platelet aggregation induced by adrenaline and, to some extent, also by ADP. The inhibition was competitive and not mediated via beta 2 adrenoceptor stimulation. It is concluded that there are hemostatic effects of ephedrine and that these may be of clinical relevance, the drug being very commonly used in connection with procedures where blood loss as well as venous thromboembolism are considerable problems.

Studies on the effect of dopamine on the human platelet response

1. The present study investigated the in vitro effect of dopamine on platelet responses in healthy subjects. 2. Dopamine concentrations over 5 mumol/L induced a primary aggregating response and a slight release of alpha-granule proteins, beta-thromboglobulin and platelet factor-4 in all subjects. In 25% of investigated subjects a delayed secondary aggregation was observed with dopamine concentrations over 100 mumol/L. 3. Low dopamine concentrations (5-7.5 nmol/L) increased the platelet sensitivity to other aggregating agents (adenosine diphosphate, collagen and sodium arachidonate). The effect of subaggregating concentrations of serotonin was potentiated by dopamine. 4. The effect of dopamine on platelet responses was prevented by low concentrations of alpha-adrenoceptor antagonists (phentolamine and yohimbine); antagonists of dopamine receptors (haloperidol and domperidone) were able to decrease the extent of the dopamine-induced secondary aggregating wave in the responders, but they failed to prevent the primary aggregation and the effects on platelet response to other aggregating agents. 5. The present data demonstrated that the effects of dopamine on human platelets are mainly mediated by interactions with alpha-adrenoceptors.

Potentiation of ADP-induced aggregation in human platelet-rich plasma by 5-hydroxytryptamine and adrenaline

1. We have used dose-response curves to quantitate the potentiation of adenosine 5'-diphosphate (ADP)-induced aggregation and thromboxane (TXA2) generation by 5-hydroxytryptamine (5-HT) and adrenaline in human citrated platelet-rich plasma. We have also quantitated the inhibition of these responses by aspirin, ketanserin and yohimbine, singly and in pairs. 2. Ketanserin (5 microM) inhibited TXA2 production and the second wave of platelet aggregation induced by a range of concentrations of ADP alone. This indicates that endogenous 5-HT, released from the platelet dense granules, contributes significantly to responses induced by ADP. 3. When 5-HT (10 microM) was added before ADP, a lower concentration of ADP was required to cause 50% aggregation and TXA2 generation. The ratio of ADP concentrations (CR) to cause 50% aggregation in the presence and absence of 5-HT was 2.1 when only added 5-HT was considered, and 5.0 when endogenous 5-HT was also taken into account. 4. Potentiation of ADP-induced aggregation by 5-HT also occurred in the presence of aspirin, resulting in a CR of 2.3. As expected, ketanserin inhibited potentiation by 5-HT in the presence and absence of aspirin. Although aspirin caused substantial inhibition of aggregation induced by ADP and 5-HT (CR 3.4), further inhibition occurred when ketanserin was also present (CR 6.5). 5. A subthreshold concentration of adrenaline (0.25 microM) caused substantial potentiation of ADP-induced aggregation in the absence (CR 4.0) and presence (CR 2.0) of aspirin. As expected, yohimbine (9 microM) inhibited this potentiation.Maximum TXA2 generation induced by ADP increased from 32.5 to 59.4 pg per 106 platelets when adrenaline was present. Aggregation induced by ADP and adrenaline was markedly inhibited by aspirin (CR 5.1) but was further inhibited when yohimbine (9 microM) was also present (CR 10.0).6. Results from this in vitro study show ketanserin and yohimbine have the potential to be used in combination with aspirin as antithrombotic agents in vivo.

Therapeutic lidocaine concentrations have no effect on blood platelet function and plasma catecholamine levels

The effects of therapeutic plasma concentrations of lidocaine on blood platelet function and plasma catecholamine levels were assessed in 9 healthy subjects. There were no significant effects on plasma levels of beta-thromboglobulin, collagen and adenosine diphosphate-stimulated platelet aggregation, thromboxane-B2-concentration in plasma after collagen and ADP stimulated platelet aggregation, or on plasma nor-adrenaline and adrenaline. No significant correlation could be demonstrated between any of the variables tested. Thus, it appeared that lidocaine had no effect on platelets that could be of benefit in acute myocardial infarction. It should be possible to use lidocaine, in combination with thrombolytic therapies without increasing the risk of bleeding complications.

Different patterns of inhibition of adrenaline-induced platelet aggregation and kinetics in vivo by acetylsalicylic acid and indobufen

The inhibitory effect of 50 mg/kg lysyl acetylsalicylic acid (ASA) intravenously injected 24 and 4 h before 80 micrograms/kg adrenaline, 40 mg/kg indobufen injected 15 min before, or a combination of ASA plus indobufen on the platelet aggregation and kinetics was evaluated in anaesthetized dogs previously injected with 111indium- (111In-) labelled platelets using gamma-camera dynamics studies. The highest degree of inhibition, indicated by the lowest platelet aggregation ratio decrease and the most significant 111In-labelled platelet mobilization from hepatic and splenic stores with a corresponding increase of labelled and unlabelled platelet counts in blood, was obtained in ASA-treated dogs. Such changes were less marked when ASA plus indobufen was injected. In indobufen-treated dogs a similar mobilization of 111In-labelled platelets with an increase in circulating platelet numbers was evident only after the second adrenaline injection. It is concluded that platelet mobilization is mainly dependent on the production of an ASA-sensitive substance.