Platelet Aggregation Threshold Research Articles

In vitro hemocompatibility investigation for the development of low-flow centrifugal blood pumps with less platelet clogging.

Low-flow blood pumps rated under 1 L/min are emerging for new medical applications, such as hemofiltration in acute use. In those pumps, platelet adhesion and aggregation have to be carefully considered because of clogging risk in the filter part. To find an acceptable hemocompatibility that can be applied to low-flow centrifugal blood pump design, the platelet aggregation index, clogging on a micromesh filter, and the hemolysis index were investigated using a low-flow blood pump designed for hemofiltration use. We conducted circulation testing in vitro using fresh porcine blood and two centrifugal pumps with different impeller inlet shapes. The Negative Log Platelet Aggregation Threshold Index (NL-PATI), which reflects the ability of residual platelets to aggregate, and flow rate were measured during reflux for 60 min, and the Normalized Index of Hemolysis (NIH (g/20 min)) was calculated. In addition, blood cell clogging after reflux was observed on the micromesh filter by SEM, and the adhesion rate was calculated. Our results showed that the platelet clogging on the micromesh filter occurred when the average NL-PATI was greater than 0.28 and the average NIH (g/20 min) was greater than 0.01. In contrast, platelet clogging on the micromesh was suppressed when NL-PATI was less than 0.17 and the NIH (g/20 min) was less than 0.003. These values might be used as acceptable hemocompatibility of low-flow centrifugal blood pumps with suppressed platelet clogging for hemofiltration pumps.

Influence of nonsteroidal anti-inflammatory drugs on aspirin\u2019s antiplatelet effects and suggestion of the most suitable time for administration of both agents without resulting in interaction

BackgroundLow-dose aspirin irreversibly inhibits platelet cyclooxygenase-1 (COX-1) and suppresses platelet aggregation. It is effective for secondary prevention of cardiovascular events. Because nonsteroidal anti-inflammatory drugs (NSAIDs) reversibly bind with COX-1, the antiplatelet effects of aspirin may be suppressed when NSAIDs are co-administered. This interaction could be avoided by avoiding simultaneous administration; however, the minimum interval that should separate the administration of aspirin and loxoprofen is not well known. In this study, we investigated how to avoid the influence of NSAIDs on the antiplatelet effects of aspirin. An in vitro experiment was performed to investigate the influence of ibuprofen and loxoprofen at various concentrations on aspirin’s antiplatelet action.MethodsPlatelet aggregation and thromboxane B2 (TXB2) levels were measured after addition of aspirin only and NSAIDs plus aspirin to platelet-rich plasma. NSAIDs were used at their maximum plasma concentrations, the assumed concentration after 6 h (for loxoprofen only), and the assumed concentration after 12 h of taking one clinical dose. Platelet aggregation threshold index (PATI), defined as the putative stimulus concentration giving 50% aggregation, was calculated as an index of aggregation activity.ResultsPATI decreased in ibuprofen plus aspirin group compared to that in the aspirin only group, regardless of ibuprofen concentration. Furthermore, PATI significantly decreased when aspirin was added after loxoprofen-trans-OH addition at the maximum concentration (4.1 ± 0.1 μg/mL), compared to that in aspirin only group (5.9 ± 0.1 μg/mL). PATI showed no significant difference after addition of loxoprofen at the assumed concentration after 6 h (aspirin only group, 5.0 ± 0.5 μg/mL; loxoprofen-trans-OH plus aspirin group, 4.9 ± 0.4 μg/mL).In addition, TXB2 concentration tended to decrease with increasing PATI.ConclusionsIt is desirable to avoid ibuprofen co-administration with the usual once-daily low-dose aspirin therapy; however, a 6-h interval between loxoprofen and aspirin could avoid this potential interaction when loxoprofen is taken before aspirin.

Quantification of Local Hemodynamic Alterations Caused by Virtual Implantation of Three Commercially Available Stents for the Treatment of Aortic Coarctation

Patients with coarctation of the aorta (CoA) are prone to morbidity including atherosclerotic plaque that has been shown to correlate with altered wall shear stress (WSS) in the descending thoracic aorta (dAo). We created the first patient-specific computational fluid dynamics (CFD) model of a CoA patient treated by Palmaz stenting to date, and compared resulting WSS distributions to those from virtual implantation of Genesis XD and modified NuMED CP stents, also commonly used for CoA. CFD models were created from magnetic resonance imaging, fluoroscopy and blood pressure data. Simulations incorporated vessel deformation, downstream vascular resistance and compliance to match measured data and generate blood flow velocity and time-averaged WSS (TAWSS) results. TAWSS was quantified longitudinally and circumferentially in the stented region and dAo. While modest differences were seen in the distal portion of the stented region, marked differences were observed downstream along the posterior dAo and depended on stent type. The Genesis XD model had the least area of TAWSS values exceeding the threshold for platelet aggregation in vitro, followed by the Palmaz and NuMED CP stents. Alterations in local blood flow patterns and WSS imparted on the dAo appear to depend on the type of stent implanted for CoA. Following confirmation in larger studies, these findings may aid pediatric interventional cardiologists in selecting the most appropriate stent for each patient, and ultimately reduce long-term morbidity following treatment for CoA by stenting.

Utility of whole‐blood aggregometry for evaluating anti‐platelet therapy for Kawasaki disease

Anti-platelet therapy for Kawasaki disease (KD) is often done without monitoring drug efficacy. The aim of this study was to investigate the utility of whole-blood aggregometry to evaluate the efficacy of anti-platelet therapy for KD. Of 37 late-phase KD patients included in the present study, 20 were prescribed anti-platelet drugs. Platelet-rich plasma (PRP) aggregation with collagen as the stimulus was measured using an optical aggregometer. The area under the curve of small and large size aggregations was calculated, and categorized into five classes: -2, -1, 0, 1, and 2. Whole-blood aggregation with collagen or adenosine 5'-diphosphate (ADP) as stimulus was evaluated using the platelet aggregation threshold index (PATI), which is the concentration of stimulus that induces a whole-blood aggregation rate of 50%. In both collagen- and ADP-induced aggregation, there was a negative correlation between PATI and class determination using the PRP technique (collagen, rs = -0.870, P < 0.0001; ADP, rs = -0.620, P < 0.0001). Moreover, the PATI in collagen- and ADP-induced aggregation was significantly higher in the anti-platelet drug therapy group than in the untreated group (collagen, P < 0.0001; ADP, P = 0.0002). The serum thromboxane B2 level in the anti-platelet drug therapy group was also significantly lower than that in the untreated group (P < 0.0001). PATI was significantly higher in those treated with thienopyridine drug combinations than those without drug therapy (P = 0.0036). Whole-blood aggregometry is useful for monitoring the efficacy of anti-platelet therapy for KD.

Tibetan Medicine: An Effective Botanical Supplement for Peripheral Vascular Circulation

This review provides an instructive example of how a botanical and mineral formula known in the tradition of Tibetan medicine as Gabyr-Nirynga (camphor combination), denoted as formula No. 28, has evolved into a contemporary application through scientific research. This developmental pathway has led to a standardized nutraceutical with clinically proven efficacy in alleviation of a form of atherosclerosis-peripheral arterial disease (PAD). The systematic scientific research began in Switzerland in 1970s and resulted in five, double-blind clinical studies conducted in various European countries on cardiovascular use of the formula. The formula’s mechanism of action has been described in Tibetan tradition based on its three groups of botanical and mineral ingredients: (1) main active ingredients, (2) auxiliary ingredients, and (3) components that offset the action of the first two groups and facilitate gastrointestinal absorption of the formula. Based on preclinical and clinical studies, several mechanisms of action relevant to alleviation of the PAD have been discussed, such as an increase in the threshold for platelet aggregation, lower total blood cholesterol and low-density lipoproteins (LDL), and prevention of blood lipid peroxidation. A study in an animal model of CNS inflammation, i.e. Experimental Allergic Encephalomyelitis (EAE), has shown that No. 28 can exert action as a biological response modifier improving response of the organism to chronic inflammation. This latter mechanism may be particularly relevant to the clinical benefits with No. 28 in patients with PAD, in view of cardiovascular disease increasingly considered as an outcome of a chronic inflammatory process. The integration of traditional knowledge of a botanical formula with science-derived pharmacology is referred in this paper as the Interactive Nutrients process.

Impact of proton pump inhibitors or famotidine on the antiplatelet actions during dual-antiplatelet therapy in Japanese patients

It has been reported that the antiplatelet action becomes attenuated when a proton pump inhibitor is used in combination with clopidogrel. The effect of an antacid causing platelet aggregation during the administration of clopidogrel was investigated. The subjects consisted of 265 patients with coronary artery disease. Platelet aggregation function testing (light transmittance aggregometry) was conducted while aspirin and clopidogrel 75mg were taken orally and the minimum concentration of aggregation induction platelet aggregation threshold index was measured. The ADP-PATI, measured with ADP as the inducing substance, was compared and investigated according to the type of concomitantly used antacid. The results of the ADP-PATI were: control group: 3.47±0.95μM (N=67), famotidine group: 3.80±0.52μM (N=32), rabeprazole group: 3.43±0.93μM (N=87), lansoprazole group: 3.28±1.04μM (N=63) and omeprazole group: 3.33±0.81μM (N=16). No statistically significant difference was observed regarding the ADP-PATI of respective groups compared to the control group. The concomitant use of famotidine, rabeprazole, lansoprazole, and omeprazole did not affect the antiplatelet action of clopidogrel in Japanese patients.

Impact of Platelet Reactivity to Adenosine Diphosphate Before Implantation of Drug-Eluting Stents on Subsequent Adverse Cardiac Events in Patients With Stable Angina

Diverse pharmacological effects of anti-platelet thienopyridines due to individual differences in metabolism have been reported. However, an association between on-treatment platelet reactivity and adverse ischemic events after drug-eluting stent (DES) implantation in Japanese patients has not been fully elucidated. A total of 450 consecutive patients on dual anti-platelet therapy (aspirin and ticlopidine) with stable angina who underwent DES implantation were enrolled. Adenosine diphosphate (ADP)-induced platelet aggregation was measured before DES implantation using the screen filtration pressure method. The ADP concentration necessary for 50% aggregation was designated as the platelet aggregation threshold index (PATI). A composite primary endpoint of cardiac death, myocardial infarction, target lesion revascularization (TLR), and stent thrombosis occurring within 1 year after stenting, was evaluated. A PATI value <4.8 µmol/L was defined as high on-treatment reactivity to ADP. The composite primary endpoint occurred in 55 patients (12.2%) in the 1-year-period after DES implantation, and the prevalence was 19.0% and 5.1% in groups with high and low on-treatment reactivity to ADP, respectively, showing a significantly higher prevalence in the high reactivity group (P<0.001). The main event was TLR (18.1% vs. 5.1%, P<0.001). These data suggested that high on-treatment platelet reactivity to ADP and subsequent occurrence of adverse ischemic events (particularly TLR) were correlated in patients with stable angina who underwent DES implantation.

Measuring Platelet Aggregation in Dialysis Patients With a Whole Blood Aggregometer by the Screen Filtration Pressure Method

A semi-automatic, whole-blood aggregometer based on the screen filtration pressure (SFP) method is now widely used clinically and in research, but has not been used with hemodialysis (HD) patients. We measured whole-blood platelet aggregation in HD patients by the SFP method. This retrospective cross-sectional study included 62 HD patients, of whom 47 were non-diabetic and 15 were diabetic; we also included a control group of healthy, non-uremic subjects. With the t-test, we examined differences in the platelet aggregation threshold index (PATI) in meaningful sub-groupings of the HD patients, depending on whether or not they had diabetes, and whether or not they had been given antiplatelet agents. Considering the non-diabetic HD patients first, their PATI values were significantly higher than those values in the control subjects (3.1 [1.0-5.2] vs. 1.8 [1.3-2.3] µM, P<0.001). The non-diabetic HD patients taking antiplatelet agents showed significantly (1.9 times) higher PATI values than the non-diabetic HD patients without antiplatelet agents (4.4 [1.8-7.0] vs. 2.3 [1.3-3.3] µM, P=0.003). We observed similar trends among diabetic HD patients. Whole-blood analysis by the SPF method seems to be a promising way of monitoring platelet function for HD patients.

Enhanced platelet activation following coronary stent implantation in patients on hemodialysis

Hemodialysis ("HD") has been suggested as a risk factor for stent thrombosis. However, platelet function in HD patients after coronary stent implantation remains unclear. The aim of this study was to evaluate platelet function following coronary stent implantation in HD patients. A total of 10 HD and 31 non-HD patients who underwent a first coronary stent implantation were studied. All patients received 100 or 200mg of asprin and thienopiridine (either ticlopidine 200mg or clopidogel 75mg) daily. Platelet function was assessed 2-6weeks (21±8days) after stent implantation by: (1) platelet maximal aggregation, using light transmittance aggregometry; (2) platelet aggregation threshold index, which was defined as putative concentration of agonist giving 50% maximum aggregation using whole-blood aggregometry; and (3) platelet activation markers (PAC-1 and CD62p), using whole blood flow cytometry. There were no differences between the two groups in baseline and procedure characteristics, except for a greater prevalence of hypertension and calcification in the HD group. Early stent thrombosis and bleeding did not occur in either group. Although no differences in platelet maximal aggregation or whole-blood aggregation were observed, expression of PAC-1 (39.6±9.1 vs 24.2±13.2%) and CD62p (10.4±5.5 vs 5.4±2.3%) were significantly increased in the HD group compared with the non-HD group. HD patients exhibited enhanced platelet activation after coronary stent implantation, but suppression of platelet aggregation was achieved by the current dual antiplatelet therapy.

Action of Aspirin on Whole Blood-Aggregation Evaluated by the Screen Filtration Pressure Method

There are few monitoring systems widely used in clinical practice for evaluating the effectiveness of aspirin therapy, so in the present study aspirin's antiplatelet effects we investigated with a whole blood aggregometer using a screen filtration pressure (SFP) method. Thirty-five healthy male volunteers took 100 mg/day aspirin for 14 days. Whole-blood aggregation was analyzed at baseline and on days 7 and 14, using collagen and adenosine diphosphate as the stimuli, and compared with the platelet-rich plasma (PRP) aggregation measured by optical aggregometer. The platelet-aggregation threshold index (PATI) for both methods, which was defined as the putative agonist-concentration giving half-maximal aggregation, and the PRP-maximal aggregation rate were analyzed. The maximal aggregation rate induced by 1.6 mg/L collagen decreased from 85.5% (80.8-92.8) [median (interquartile range)] at baseline to 51.5% (39-63.8) on day 14 (p<0.0001). The PRP-PATI and whole-blood PATI for collagen increased from 0.32 (0.28-0.70) to 1.82 mg/L (1.25-2.89) (p<0.0001) and from 0.28 (0.22-0.3) to 1.06 mg/L (1.01-1.29) (p<0.0001) respectively. The whole-blood PATI and PRP-PATI for collagen, as well as the maximal PRP aggregation rate, clearly distinguish platelet aggregability before and after aspirin intake. However, whole-blood analysis by the SFP-method is easier to perform, and is a promising method of monitoring aspirin's effects.

Abstract 2174: Increased Platelet Aggregability In Obstructive Sleep Apnea Syndrome Patients Is Improved By Nasal Continuous Positive Airway Pressure Treatment

Background and aim: Obstructive sleep apnea (OSA) is a risk factor for cerebrovascular diseases. One cause for them is an occlusive arterial thrombus triggered by local platelet activation. Whether OSA is an independent risk factor for increased platelet aggregability is unclear. Methods: We enrolled 124 patients with snoring or daytime sleepiness in whom 3% oxygen desaturation index (3%ODI), a principal marker of the severity of intermittent hypoxia and reoxygenation (IHR), was measured. We studied ex vivo ADP- and collagen-induced aggregation of platelet-rich plasma using an optical aggregometer. The agonist concentration giving half maximal aggregation was defined as the platelet-aggregation threshold index (PATI) value. Therefore, the lower PATI value implicates the higher aggregability. In 23 patients who underwent nasal CPAP, platelet aggregability was followed until 90 days. Results: There was a significant difference in the PATI value for ADP-induced aggregation between 66 patients with non-to-mild OSA (3%ODI≤15) (1.04±0.07 μM, mean±SE) and 58 patients with moderate-to-severe OSA(3%ODI&gt;15) (0.78±0.09 μM)(p=0.029). Multiple linear model revealed that 3%ODI strongly significantly contributed to the PATI values for ADP (p&lt;0.001) and collagen (p=0.0026) among the 59 subjects with a cardiovascular risk factor such as smoking, hypertension, diabetes mellitus or hyperlipidemia. However, the percentage of time of arterial O2 saturation&lt;90% during sleep did not significantly contribute to the PATI values for ADP (p=0.21) and collagen (p=0.20). After initiation of nasal CPAP therapy, the PATI values for ADP-induced aggregation significantly worsened transiently on day 30 (p=0.035), and then it recovered and improved at day 90 and the PATI for collagen-induced aggregation improved at day 90 without the transient exacerbation. Conclusions: OSA patients had increased platelet aggregability. Severity of IHR more significantly contributed to platelet aggregation than total hypoxic time. Among OSA patients with conventional cardiovascular risk factors, the effects of IHR on the platelet aggregability was prominent. Nasal CPAP initially induced a transient hyperaggregable state of platelets, after which it continued to improve.

Genetic strain differences in platelet aggregation of laboratory mice

To investigate the physiological role of novel genes and proteins in platelet activation, various knockout mice have been produced. A number of standard inbred mouse strains each possessing genetically unique characters such as high tumor generation, hyperglycemia or hyperlipidemia, have been bred. In breeding knockout mice for investigation of specific physiological functions, appropriate selection of parental or backcross strains is necessary. Thus, examination of strain-specific platelet characteristics is important. In the present study, platelet aggregation responses of 13 laboratory mouse strains, 129/Sv, A, AKR, BALB/c, C3H/He, C57BL/6J, CBA, DBA/1, DBA/2, ddY, FVB, ICR, and NZW, and the diabetic strain C57BL/KsJ db/db, were compared. Marked strain differences were observed in ADP- and collagen-induced platelet aggregation. The highest responses with both were seen in AKR/J and NZW/N, whereas the lowest were seen in DBA/2 and DBA/1. There was a 5-fold difference in the platelet aggregation threshold index (PATI) for ADP-induced PRP aggregation between AKR/J (0.6 microM) and DBA/2 (3.0 microM). With whole blood aggregation, the highest response was seen in AKR, whereas the lowest was seen in DBA/2 and DBA/1. The present study demonstrated that there is considerable strain difference in platelet aggregation among laboratory mice, which should be taken into account in backcrossing knockout strains.

Changes in platelet aggregation during cardiopulmonary bypass: comparison of poly-2-methoxyethylacrylate and heparin as a circuit coating material

At present, there are various biomaterials that have high biocompatibility. In particular, there are many types of coated circuits in cardiopulmonary bypass (CPB) systems. However, only a few clinical studies have investigated platelet aggregation caused by these coated circuits. In this study, a CPB system coated with poly-2-methoxyethylacrylate (X coating) was used to ascertain whether platelet aggregation could be suppressed during CPB, and a comparison was made between X coating and ordinary (covalently bonded) heparin coating. The subjects were 19 adult patients who were scheduled to undergo valve replacement or valvuloplasty. They were divided into two groups: group X (X coating) and group H (heparin coating). The platelet aggregation threshold index (PATI, grading curve) and beta-thromboglobulin and plalelet factor IV levels were assessed preoperatively (control), 5 min after heparin administration, 10 and 60 min after the start of CPB, and 0 and 2 h after the end of CPB. The results indicated that platelet aggregation was reduced during CPB and that platelets were activated. The changes in platelet aggregation associated with the X coating were shown to be similar to those associated with heparin coating.

The relation between cavitation and platelet aggregation during exposure to high-intensity focused ultrasound

Our previous study showed that high-intensity focused ultrasound (HIFU) is capable of producing “primary acoustic hemostasis” in the form of ultrasound (US)-induced platelet activation, aggregation and adhesion to a collagen-coated surface. In the current study, 1.1 MHz continuous-wave HIFU was used to investigate the role of cavitation as a mechanism for platelet aggregation in samples of platelet-rich plasma. A 5 MHz passive cavitation detector was used to monitor cavitation activity and laser aggregometry was used to measure platelet aggregation. Using spatial average intensities from 0 to 3350 W/cm 2, the effects of HIFU-induced cavitation on platelet aggregation were investigated by enhancing cavitation activity through use of US contrast agents and by limiting cavitation activity through use of an overpressure system. Our results show that increased cavitation activity lowers the intensity threshold to produce platelet aggregation and decreased cavitation activity in the overpressure system raises the intensity threshold for platelet aggregation. (E-mail: poliachi@u.washington.edu)

Characterization of platelet aggregation in whole blood of laboratory animals by a screen filtration pressure method

The characteristics of platelet aggregation of laboratory animals were investigated with whole blood and platelet-rich plasma (PRP). We measured the platelet aggregation threshold index (PATI) of whole blood and PRP aggregations induced by ADP or collagen, using a novel whole blood aggregometer, the WBA analyzer, with a screen filtration pressure (SFP) method. At 60 min after blood collection, PATI values of guinea pig, mouse, rat, dog and rabbit were 0.83, 1.78, 46.48, 49.85 and 53.42 μM for ADP-induced whole blood aggregation, respectively, whereas their PATI values for ADP-induced PRP aggregation were 1.16, 2.77, 2.65, 10.81 and 18.77 μM, respectively. These suggest that ADP-induced platelet aggregations of rat, dog and rabbit are suppressed in whole blood. PATI values of guinea pig, mouse, rat, dog and rabbit were 1.84, 0.62, 11.90, 2.34, 12.32 μg/ml for the collagen-induced whole blood aggregation, respectively, whereas their PATI values for the collagen-induced PRP aggregation were 4.21, 1.50, 5.36, 11.31, 13.30 μg/ml, respectively. Collagen-induced aggregation activity of the guinea pig, mouse and dog was significantly higher in whole blood than in the PRP. These results demonstrated that species differences in laboratory animals exist for whole blood aggregation, and that the SFP aggregometer may be useful to evaluate platelet function in various animal species.

Estimation of anti-platelet drugs on human platelet aggregation with a novel whole blood aggregometer by a screen filtration pressure method.

1. The effects of anti-platelet drugs on human whole blood aggregation were evaluated using a novel whole blood aggregometer by a screen filtration pressure (SFP) method. 2. The SFP whole blood aggregometer was found to successfully detect whole blood aggregation induced by ADP, collagen and TRAP by measuring the SFP of blood samples. The platelet aggregation threshold index (PATI), the concentration of agonist required with an inducing pressure rate of 50%, varied time-dependently after collection of blood. High values for ADP and collagen were noted immediately after blood collection, suggesting low aggregation activity of platelets, and gradually increase thereafter. 3. Cilostazol (phosphodiesterase 3 inhibitor), dipyridamole, aspirin and tirofiban all inhibited whole blood aggregation in vitro. Inhibitory effects of cilostazol and dipyridamole, but not tirofiban, were markedly enhanced 6 or 7 fold by long pre-incubation (60 min), compared with short pre-incubation (2 min). Such enhancement was only observed with ADP- and not collagen-induced whole blood aggregation. A similar phenomenon was also observed for aggregation with platelet rich plasma (PRP). Cilostazol inhibition of ADP-induced platelet aggregation was more potent with PRP than whole blood (PATI(200)=3.80+/-0.95 microM for whole blood; 2.04+/-0.61 microM for PRP). Inhibitory effects of dipyridamole were attenuated in PRP without erythrocytes. 4. These results demonstrate that the SFP aggregometer can sensitively detect anti-platelet aggregatory effects of various kinds of drugs. So that it is a useful tool for evaluation of anti-platelet drugs.

Combination of fosinopril and pravastatin decreases platelet response to thrombin receptor agonist in monkeys.

Both angiotensin-converting enzyme (ACE) inhibitors and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been shown to decrease cardiovascular morbidity and mortality. Results from clinical trials have suggested that HMG-CoA reductase inhibition might exert a beneficial effect independent of its lipid-lowering effect, and ACE inhibition may exert a benefit independent of blood-pressure lowering. To test the hypothesis that such an effect might be mediated by alteration in platelet reactivity, we studied 55 monkeys receiving both, 1, or neither of the ACE inhibitor fosinopril and the HMG-CoA reductase inhibitor pravastatin. Platelet responsiveness to collagen and to the thrombin receptor agonist (TRA) SFLRRN-NH2 was determined by aggregometry. For each agonist, the maximum rate and extent of aggregation were measured for each dose, and the concentration required for half-maximal response (C50) was determined. Each drug, when given alone, slightly decreased the dose of agonist required to produce 50% response in the rate and extent of platelet aggregation relative to control. The combination of the 2 drugs, however, produced a significant increase in the dose of TRA required to produce 50% response in the rate and extent of aggregation relative to either drug alone or the control group. This was not true for collagen. The magnitude of the change relative to the control group, 47% for rate and 30% for extent of aggregation, could confer considerable protection by changing the threshold for thrombin-induced platelet aggregation and, thus, decrease thrombosis.

Smoking further increases platelet activity in patients with mild hypertension.

In this study the authors examine whether smoking further heightens platelet activity and reduces fibrinolysis above that already present in mild hypertension. Ten smokers and 11 non-smokers, all with mild hypertension (defined as a diastolic pressure between 90 and 110 mm Hg) were compared for their platelet activity in vitro and in vivo and for their fibrinolytic activity. Successive measurements were made with the patients lying at rest after they had assumed the erect posture for 10 min and at the end of a 5-min moderately strenuous exercise test. The threshold for platelet aggregation by ADP in vitro was significantly lower in samples taken from the smokers at rest (1.4 +/- 0.9 mumol L(-1)) than in the non-smokers (3.5 +/- 2.5 mumol L(-1)), and the difference persisted both in the upright posture and after exercise. The level of platelet release of beta-thromboglobulin was, likewise, higher in the smokers in the upright posture. Neither standing up nor physical exercise had any significant influence on either of these two indices of platelet activity. The euglobulin clot lysis time was slightly longer in the smokers than in the non-smokers in all three experimental situations, but the differences were not significant. Inhibitor of tissue plasminogen activator was not materially different in the two groups (Table 2). The results indicate that smoking adds a further element of heightened platelet activity to that inherently present in hypertension.

Limited Proteolysis of Human α-Thrombin by Urokinase Yields a Non-Clotting Enzyme

Limited proteolysis of human alpha-thrombin by various proteases has been efficiently used to demonstrate the importance of two insertion loops located on the surface of this molecule. In the present study, we demonstrate that two-chain urokinase (tcu-PA) specifically cleaves the B chain of alpha-thrombin giving rise to a transient derivative, consisting of two non-covalently linked subunits. Although the thrombin derivative conserves its activity towards the synthetic substrate S-2238 (Km = 8.4 microM and kcat = 145 s-1 versus respectively 4.5 microM and 149 s-1 for alpha-thrombin), most of its coagulant activity is lost (140 NIH u/mg versus 3000 NIH u/mg) and its ability to activate platelets is considerably reduced (threshold for full platelet aggregation 2.5 nM versus 0.25 nM). The thrombin fragments were separated by HPLC and after reduction and S-carboxyamidemethylation were digested with a lysylendopeptidase; the resulting peptides were separated by HPLC and sequenced. One fragment corresponded to B chain fragment 1-73 and the second to B chain fragment 74-259 covalently linked to the A chain, indicating that tcu-PA cleaves selectively the peptide bond Arg 73-Asn 74 in the B chain. The proteolytic derivative obtained, designated beta u-thrombin, is therefore identical to the transient proteolytic derivative, beta 1-thrombin, produced by trypsin. Prolonged incubation with tcu-PA resulted in further conversion in a derivative analogous to gamma t-thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)

The Effect of Erythropoietin on Platelet Function and Fibrinolysis in Chronic Renal Failure

The influence of erythropoietin therapy on platelet function and fibrinolysis was evaluated in 12 anemic hemodialysis patients. Six months of therapy with human erythropoietin (50 to 80 IU/kg initially) raised the hemoglobin level to 10.8 g/dl but did not increase platelet activity in vivo as measured by beta-thromboglobulin or platelet factor 4. There was no change in the platelet aggregation thresholds in vitro for ADP, adrenaline, thrombin or collagen during treatment. Platelet number and volume were also unaffected. Fibrinolytic activity intensified as erythropoietin treatment proceeded, with a fall of euglobulin clot lysis time and rise in the activity of t-PA. PAI-1 levels also showed a downward trend, without reaching significance. Thus erythropoietin treatment in modest doses does not seem to adversely influence the hemostatic system in patients on hemodialysis.