Fibrinogen: a possible link between social class and coronary heart disease.

Mortality from coronary heart disease in civil servants in the lowest grade of employment has been found to be about three times that of men in the highest grade of employment. As part of an investigation of this finding several haemostatic variables were measured in a sample of 29 men in lower grades of employment and 45 men in higher grades. There was a significant difference in plasma fibrinogen concentrations between men in lower grades of employment and those in higher grades (mean 3.39 g/l v 2.95 g/l, respectively; p less than 0.01) but not in other haemostatic variables. Multiple regression analyses showed significant independent associations of fibrinogen concentration with smoking (p less than 0.05) and grade of employment (p less than 0.05). The size of the observed difference between the grades of employment was similar to that between those dying of coronary heart disease or surviving during longitudinal study; it may therefore be an important part of the mechanism underlying social class differences in coronary heart disease. The statistical relation between fibrinogen concentrations and other characteristics that may be concerned in the aetiology of coronary heart disease was examined. A summary measure of job stress was significantly related to fibrinogen concentration (p less than 0.01) and made a substantial contribution to explaining the differences between grades of employment. Behaviour type and a score of physical activity were not significantly related to fibrinogen concentration.     

Postprandial hyperlipemia inhibits platelet aggregation without affecting prostanoid metabolism

The objective of this work was to characterize changes in platelet aggregability during postprandial hypertriglyceridemia with special emphasis on arachidonic acid metabolism. Ten healthy young men consumed 100 g fat after a fasting period of 12 hr. In-vitro platelet aggregation induced by ADP and collagen was measured at 0, 3, 5, and 9 hours after the fat intake. The major arachidonic acid metabolites, 12-hydroxyeicosatetraenoic acid (12-HETE), thromboxane A2 (TXA2), prostaglandin F2 alpha (PGF2a), and prostaglandin E2 (PGE2) produced during collagen-induced platelet activation were quantified by gas chromatography/mass spectrometry. A significant decrease in platelet aggregability induced by both ADP and collagen was detected during the postprandial hyperlipemia. No significant changes could be found in the prostanoid pattern of collagen activated platelets. There was no correlation between the degree of the inhibition of platelet aggregation and the relative or absolute increase of triglyceride-levels in the plasma during the postprandial hyperlipemia.     

Relation between extent of coronary artery disease and blood viscosity.

Blood viscosity (shear rate 100/s) and its major determinants (packed cell volume, plasma fibrinogen concentration, and plasma viscosity) were measured before coronary angiography in 50 men aged 30-55 and related to the extent of coronary artery disease. Twenty-six men had extensive disease (stenosis of two or three major coronary vessels), and 24 had either stenosis of one vessel or no stenosis. The 26 men with extensive disease had significantly higher mean blood viscosity than those with mild or no disease and 25 healthy controls (p less than 0.001). The increased viscosity was due partly to a higher packed cell volume and partly to a higher fibrinogen concentration; plasma viscosity was not significantly increased. These differences could not be explained by smoking history. These results suggest an association between increased blood viscosity and extensive coronary artery disease in men, which merits further investigation.     

The Effect of Exercise on Platelet Aggregability and Lipid Peroxidation

The effects of single bicycle ergometric exercises of a moderate or high intensity on platelet ADP-dependent aggregation, content of malonic dialdehyde (MDA), and activity of catalase were studied in young men with relatively high working capacities. Platelet aggregability either increased or decreased in response to the exercise. Hyperaggregation was recorded in about two-thirds of the subjects and hypoaggregation, in one-third. Changes in the aggregation parameters correlated with their basal values at rest. Muscular activity raised the aggregability of platelets when it was initially low and lowered it when it was initially high. An increased intensity of exercise made these correlations stronger. The exercise-caused changes in the MDA content in platelets also correlated with its basal level. A low MDA content at rest increased, and an initially high MDA content decreased. The response of hypoaggregation was associated with moderate and strong correlations between the basal content of MDA and catalase activity in platelets and the exercise-induced changes in the MDA content and platelet aggregability. It was concluded that a high basal level of MDA in platelets is a factor decreasing platelet aggregability during muscular activity.     

Activation of the fibrinogen receptor on human platelets exposed to alpha chymotrypsin. Relationship with a major proteolytic cleavage at the carboxyterminus of the membrane glycoprotein IIb heavy chain

The serine proteinase alpha chymotrypsin from bovine pancreas (CT) is known to expose fibrinogen binding sites on the surface of human platelets in the absence of cell activation and granular secretion. This is accompanied by the appearance of membrane-bound chymotryptic fragments of both glycoprotein (GP) IIb and GPIIIa, the two subunits of the platelet fibrinogen receptor, the GPIIb-IIIa complex. However, no clear relationship between discrete proteolytic event(s) within GPIIb-IIIa and fibrinogen-binding-site expression has yet been established. We have now evaluated the proteolysis of GPIIb-IIIa by CT by Western blot analyses using a panel of polyclonal and monoclonal antibodies against GPIIb or GPIIIa. The different proteolytic events were then correlated with the kinetics of the expression of active fibrinogen binding sites on platelets, as measured through the binding of 125I-labelled purified fibrinogen and to the capacity of CT-treated platelets to aggregate. Treatment of platelets with CT at 22 degrees C resulted in the expression of fibrinogen binding sites prior to cleavage of GPIIIa (Mr approximately 90,000) into a previously described, major membrane-bound fragment with Mr 60,000. In contrast, fibrinogen receptor expression closely paralleled a proteolytic cleavage at the carboxy terminus of the GPIIb heavy chain (Mr approximately 120,000), which was converted into a faster migrating species with Mr approximately 115,000). This proteolysis resulted in the release of a soluble peptide with an expected molecular mass of less than 3.7 kDa. Quantitation of this peptide using a competitive immunoenzymatic assay, confirmed that its release from the platelet surface correlated with the expression of fibrinogen binding sites and aggregability. When platelets were exposed to CT at 37 degrees C, a prompt increase in fibrinogen binding sites and platelet aggregability was observed, whereas the GPIIb heavy chain was rapidly converted into the carboxy-terminal-cleaved form. However, incubation at 37 degrees C for longer than 10 min resulted in extensive and simultaneous degradation of both the GPIIb heavy and light chains and of GPIIIa, with the latter being converted into the 60-kDa fragment. These later events were associated with a sharp decline of platelet aggregability and a reduction in the number of fibrinogen binding sites. These data allow us to propose that an early and limited proteolytic processing of the GPIIb component of the platelet fibrinogen receptor is associated with a shift of this receptor complex into a state which expresses specific binding sites for fibrinogen. Further cleavage of GPIIIa to generate the 60-kDa fragment results in loss of receptor activity.     

Relation of fetal and infant growth to plasma fibrinogen and factor VII concentrations in adult life.

OBJECTIVE--To determine whether reduced fetal and infant growth are associated with higher plasma fibrinogen and factor VII concentrations in adult life. DESIGN--Follow up study of men born during 1920-30 whose weights at birth and at 1 year had been recorded by health visitors, and men born during 1935-43 whose size at birth had been measured in detail. SETTING--Hertfordshire and Preston, England. SUBJECTS--591 men born in east Hertfordshire who still lived there and 148 men born in Preston who still lived in or close to the city. MAIN OUTCOME MEASURES--Plasma fibrinogen and factor VII concentrations. RESULTS--Among men in Hertfordshire mean plasma fibrinogen and factor VII concentrations fell with increasing weight at 1 year (from 3.21 g/l in men of less than or equal to 18 lb to 2.93 g/l in men greater than or equal to 27 lb and from 122% of standard to 103%; p less than 0.001, p less than 0.005 respectively). The trends were independent of cigarette smoking, alcohol consumption, body mass index, and social class. Neither plasma fibrinogen nor factor VII concentration was related to birth weight. In men in Preston, however, fibrinogen concentration fell progressively as the ratio of placental weight to birth weight decreased (p = 0.01). CONCLUSIONS--Reduced growth in fetal life and infancy is strongly related to high plasma concentrations of the haemostatic factors fibrinogen and factor VII. This may be a persisting response to impaired liver development during a critical early period.     

Characteristics affecting fibrinolytic activity and plasma fibrinogen concentrations.

As part of a study to determine the extent to which the haemostatic system is implicated in the onset of clinically manifest ischaemic heart disease, characteristics influencing fibrinolytic activity (FA) and plasma fibrinogen concentrations were examined in 1601 men aged 18-64 and 707 women aged 18-59 in several occupational groups in North-west London. In men FA noticeably decreased till the age of about 58, when there was a small rise. In women a small increase in FA between 18 and about 40 was followed by a slightly larger fall between 40 and 59. There was a pronounced negative association of FA with obesity. FA was significantly less in smokers than non-smokers, though the effect was not large. FA increased with alcohol consumption. FA in men appeared to be greatest in the lower social classes, and men on night shift had poorer FA than those on day work. FA was greater in women using oral contraceptives than in those not using these preparations. In both sexes FA increased with exercise, but there were no associations between any of the characteristics studied and the increase. Plasma fibrinogen concentrations increase with age and obesity, are higher in smokers than non-smokers, and fall with alcohol consumption. In women the concentrations are higher in those using oral contraceptives. The general epidemiology of FA and plasma fibrinogen concentrations suggests that they may well be implicated in the pathogenesis of ischaemic heart disease.     

Human blood plasma advanced oxidation protein products (AOPP) correlates with fibrinogen levels

In 1996 a novel oxidative stress biomarker, referred to as advanced oxidation protein products (AOPP) was detected in the plasma of chronic uremic patients. The aim of the present studies was to find out that which plasma fraction(s) is responsible for AOPP reactivity. Thermal treatment of pooled samples of human citrate-plasma or EDTA-plasma at 50 degrees C resulted in a rapid and parallel loss of fibrinogen concentration and AOPP reactivity. On the basis of time course and t1/2 values following thermal treatment, AOPP was indistinguishable from fibrinogen. There was a statistically significant (p < 0.0001) correlation between levels of blood plasma fibrinogen and AOPP in patients (n = 61) with various peripheral vascular or cardiovascular diseases. There was also a significant (p < 0.0001) relationship between plasma levels of fibrinogen and molar AOPP/fibrinogen ratio indicating that higher fibrinogen concentrations were associated with more oxidatively transformed groups on the molecule. Results of the present studies suggest that post-translationally modified fibrinogen is a key molecule responsible for human plasma AOPP reactivity. It remains to be elucidated what is the pathophysiological significance of the post-translationally modified fibrinogen in the inflammation-associated events of atherosclerosis, in platelet aggregation, and as a cardiovascular risk biomarker.     

Role of chronic exercise in decreasing oxidized LDL-potentiated platelet activation by enhancing platelet-derived no release and bioactivity in rats

This study investigates how chronic exercise affects Ox-LDL mediated-platelet activation. Five-week-old male Wistar rats were assigned to either control or trained groups. Trained rats were treadmill-trained for 10 weeks after familiarization. The following measurements were taken in both control and trained groups: plasma lipid profile, oxidation of LDL, platelet adhesiveness, aggregability, cGMP contents, plasma and platelet-NO metabolite (nitrite plus nitrate) levels, and urinary 8-iso-prostaglandin F2alpha (8-iso-PG F2alpha) levels. Based on those measurements, major findings in this study can be summarized as follows: 1) the trained group prolonged the lag time of isolated LDL subjected to copper-induced in vitro oxidation significantly longer than the control group; 2) although having higher plasma and platelet derived-NO metabolite levels, the trained group had lower urinary excretion of 8-iso-PGF2alpha than the control group; 3) the trained group had a lower platelet adhesiveness and aggregability and higher platelet derived-NO metabolite and cGMP productions than the control group; 4) the trained group had a lower Ox-LDL-potentiated platelet adhesiveness and aggregability and Ox-LDL-attenuated NO metabolite and cGMP productions in platelet than the control group; and 5) treating the platelet with L-arginine inhibited Ox-LDL-potentiated platelet activation in both control and trained groups. Results in this study demonstrate that amounts of preformed lipid peroxides decrease while NO production (which acts as an antioxidant) is significantly increased after chronic exercise. Moreover, exercise training decreases Ox-LDL-potentiated platelet activation most likely by enhancing platelet-derived NO release and bioactivity.     

Presence of factors that activate platelet aggregation in mitral stenotic patients' plasma

BACKGROUND: Although the association between mitral stenosis (MS) and increased coagulation activity is well recognized, it is unclear whether enhanced coagulation remains localized in the left atrium or whether this represents a systemic problem. To assess systemic coagulation parameters and changes in platelet aggregation, we measured fibrinogen levels and performed in vitro platelet function tests in plasma obtained from mitral stenotic patients' and from healthy control subjects' peripheral venous blood. METHODS: Sixteen newly diagnosed patients with rheumatic MS (Group P) and 16 healthy subjects (Group N) were enrolled in the study. Platelet-equalized plasma samples were evaluated to determine in vitro platelet function, using adenosine diphosphate (ADP), collagen and epinephrine in an automated aggregometer. In vitro platelet function tests in group N were performed twice, with and without plasma obtained from group P. RESULTS: There were no significant differences between the groups with respect to demographic variables. Peripheral venous fibrinogen levels in Group P were not significantly different from those in Group N. Adenosine diphosphate, epinephrine and collagen-induced platelet aggregation ratios were significantly higher in Group P than in Group N. When plasma obtained from Group P was added to Group N subjects' platelets, ADP and collagen-induced, but not epinephrine-induced, aggregation ratios were significantly increased compared to baseline levels in Group N. CONCLUSION: Platelet aggregation is increased in patients with MS, while fibrinogen levels remain similar to controls. We conclude that mitral stenotic patients exhibit increased systemic coagulation activity and that plasma extracted from these patients may contain some transferable factors that activate platelet aggregation.     

Human blood plasma advanced oxidation protein products (AOPP) correlates with fibrinogen levels

In 1996 a novel oxidative stress biomarker, referred to as advanced oxidation protein products (AOPP) was detected in the plasma of chronic uremic patients. The aim of the present studies was to find out that which plasma fraction(s) is responsible for AOPP reactivity. Thermal treatment of pooled samples of human citrate-plasma or EDTA-plasma at 50°C resulted in a rapid and parallel loss of fibrinogen concentration and AOPP reactivity. On the basis of time course and t_1/2 values following thermal treatment, AOPP was indistinguishable from fibrinogen. There was a statistically significant (p < 0.0001) correlation between levels of blood plasma fibrinogen and AOPP in patients (n = 61) with various peripheral vascular or cardiovascular diseases. There was also a significant (p < 0.0001) relationship between plasma levels of fibrinogen and molar AOPP/fibrinogen ratio indicating that higher fibrinogen concentrations were associated with more oxidatively transformed groups on the molecule. Results of the present studies suggest that post-translationally modified fibrinogen is a key molecule responsible for human plasma AOPP reactivity. It remains to be elucidated what is the pathophysiological significance of the post-translationally modified fibrinogen in the inflammation-associated events of atherosclerosis, in platelet aggregation, and as a cardiovascular risk biomarker.     

Fibrinogen binding to human platelet plasma membranes. Identification of two steps requiring divalent cations

Fibrinogen binding to platelet plasma membranes, which is a prerequisite for platelet aggregation, was determined by incubating 125I-labeled fibrinogen with isolated membranes and measuring the amount of radioactivity sedimenting with the membranes through 15% sucrose. Fibrinogen binding was optimal at 10(-3) M Ca2+. Scatchard analyses of the fibrinogen binding showed that the membrane capacity for fibrinogen was 1.6 X 10(-12) mol/mg of membrane protein, with a dissociation constant (Kd) = 1.2 X 10(-8) M. When Ca2+ levels were manipulated by the addition of varying amounts of EGTA at a fixed Mg2+ concentration of 3 X 10(-3) M, specific binding of fibrinogen to platelet membranes occurred only at Ca2+ concentrations greater than or equal to 10(-6) M. Membranes isolated from platelets of an individual with Glanzmann's thrombasthenia bound only 12% as much fibrinogen as control platelets. The data in the present study suggest that there are two divalent cation binding sites that must be occupied for fibrinogen to bind: one site is specific for calcium and is saturated at 10(-6) M Ca2+; the other site is less specific and is saturated at a 10(-3) M concentration of either Ca2+ or Mg2+. Fibrinogen binding to intact platelets and, consequently, platelet aggregation only required 10(-3) M extracellular divalent cation and was not specific for Ca2+. These data indicate that the cytoplasm is a potential source for the requirement of 10(-6) M Ca2+, and that changes in the intracellular concentration of Ca2+ may cause the expression of fibrinogen receptors during ADP-induced platelet activation.     

蝮蛇抗栓酶治疗银屑病产生耐受性原因探讨

目的通过治疗银屑病５０例临床观察,探讨部分病例未能治愈与机体对蝮蛇抗栓酶产生耐受性原因分析。方法用蝮蛇杭栓酶０．７５ＩＵ加入生理盐水中静滴,治疗前、后及各疗程间监测血小板计数与血浆纤维蛋白原变化。结果药效消失后,血小板计数与血浆纤维蛋白原增高超过治疗前水平。结论该类药物治疗其他血栓性疾病可将血小板计数与血浆纤维蛋白原增高作为药效消失及耐受性产生的一项指标。     

Secretory dysfunction of vascular endothelium limits the effect of angiotensin converting enzyme inhibitor quinapril on aggregation of erythrocytes in experimental hypertension.

Using automatic erythrocyte aggregometer type MA-1 (Myrenne gmbh, Germany), we investigated the hypothesis that therapeutic effectiveness of quinapril--angiotensin converting enzyme inhibitor (ACEI)--in the treatment of hypertension would correlate with improvement of red blood cell (RBC) aggregability. Experiments were performed on commercially available inbred strain of spontaneously hypertensive male rats (SHR) aged 19-21 weeks. Age-matched normotensive Wistar-Kyoto (WKY) rats genetically related to SHR were used as a control. Aggregability of RBC in hypertensive rats was significantly higher than in control WKY animals. Quinapril (100 microg/kg) administered i.p. for 8 days improved RBC aggregability in normotensive rats but surprisingly not in SHR animals. Beneficial effect of quinapril on RBC aggregation observed in normotensive animals did not occur when this drug was injected in combination with aspirin (1 or 50 mg/kg) or with indomethacin (20 mg/kg) or with L-NAME (10 mg/kg). However, much the same damaging effects on RBC aggregability were observed when aspirin, indomethacin or L-NAME were each administered into normotensive animals without quinapril. In contrast with normotensive rats, aggregability of RBC in SHR was not affected either by quinapril or by indomethacin and by L-NAME, given separately or in combination. The only compound significantly worsening RBC aggregability in SHR was aspirin but this effect was not dose-dependent. Quinapril-induced improvement of RBC aggregability in normotensive rats (but not in SHR) was completely abolished by simultaneous administration of B2 receptor antagonist icatibant and successfully mimicked by 8 days of treatment with bradykinin. In vitro aggregability of RBC isolated from WKY was not affected by previous incubation (30 min at 37 degrees C) with quinapril, indomethacin or L-NAME. Only aspirin (3 mM) significantly increased RBC aggregability as compared to placebo. It is concluded that under physiological conditions quinapril efficiently inhibits RBC aggregability and this effect is modulated by secretion of endothelial mediators, mainly prostacyclin and nitric oxide. In hypertension quinapril, in spite of lowering of arterial blood pressure, is unable to display its beneficial effects on RBC aggregability possibly due to the hypertension-induced/accompanied dysfunction of vascular endothelium. Aspirin revealed unique erythrocyte damaging properties, presumably independent of inhibition of cyclooxygenase but related to a direct membrane protein acetylation.     

Aggregin: a platelet ADP receptor that mediates activation

ADP is known to induce platelet shape change, aggregation, and exposure of fibrinogen binding sites as well as inhibit stimulated adenylate cyclase. The platelet is unique in that its purinergic receptor prefers ADP over ATP, which functions as a competitive antagonist. The affinity reagent, 5'-p-fluorosulfonylbenzoyl adenosine (FSBA), has been used to covalently label a single membrane protein, aggregin, on the external platelet surface with mol wt of 100 kDa. Concomitant with incorporation of FSBA, ADP-induced shape change, aggregation, and fibrinogen binding is inhibited. FSBA is also a weak agonist at short times and high concentration, which suggests that prior noncovalent binding to aggregin takes place before covalent modification. Aggregin differs from platelet glycoprotein IIIa in its physical and immunochemical properties. Aggregin is distinct from the receptor coupled to adenylate cyclase. Using FSBA as a probe, platelet aggregation by thromboxane A2 analogs and collagen was shown to be dependent on ADP but not the shape change induced by these agonists. Binding to aggregin is required for epinephrine-induced aggregation. In turn, epinephrine increases the affinity of ADP for its receptor. Thrombin at concentrations greater than 2 nM (0.2 units/ml) stimulates platelet aggregation independent of ADP, but by raising cytoplasmic Ca2+ it activates platelet calpain, which in turn cleaves aggregin. Thus aggregin, in addition to serving as the ADP receptor linked to shape change and aggregation, plays a role in fibrinogen receptor latency that is relieved entirely by ADP binding to or proteolysis of aggregin.     

Dynamics of platelet glycoprotein IIb-IIIa receptor expression and fibrinogen binding. II. Quantal activation parallels platelet capture in stir-associated microaggregation.

There is broad agreement that platelet aggregation is generally dependent on fibrinogen (Fg) binding to the glycoprotein (GP) IIb-IIIa receptor expressed on the activated platelet surface. We therefore compared rates and extents of aggregation and of fibrinogen receptor expression and specific Fg binding to activated platelets, as a function of ADP concentration. Human citrated platelet-rich plasma (diluted 10-fold) was stirred with adenosine diphosphate (ADP) for 10 s or 2 min to measure rates and extent of aggregation, respectively, determined from the decrease in the total number of particles. The number of fibrinogen receptors and bound Fg were measured from mean fluorescence values obtained with FITC-labeled IgM monoclonal antibody PAC1 and the IgG monoclonal antibody, 9F9, respectively, using flow cytometry as presented in part I (Frojmovic et al., 1994). Because flow cytometric and aggregation measurements were routinely determined at room temperature and 37 degrees C, respectively, we also compared and found temperature-independent initial rates of aggregation. The fraction of platelets with fluorescence values above one critical threshold value, corresponding to maximally "activated" platelets (P*), increased with increasing activator concentration and correlated linearly with the fraction of platelets recruited into aggregates for ADP (r > 0.9). Aggregation was not rate-limited by fibrinogen receptor expression or by Fg binding. It appears that each platelet expresses its maximal Fg receptors at a critical ADP concentration, i.e., occupancy of ADP receptors. This, in turn, leads to rapid Fg occupancy and capture of such "quantally activated" platelets into aggregates.     

Glycerol stress and platelet integrity

Platelet response to glycerol gradient was studied using a few in vitro parameters. These were platelet count, mean platelet size, platelet response to hypotonic stress (PHRS), and collagen-induced platelet aggregation. An equal volume of 1-10% (w/v) glycerol in plasma was added at once to the platelet concentrate resulting in 0.5-5% (w/v) final glycerol concentration. The concentrate was kept at 22 degrees C for 60 min. Platelets were then separated by one centrifugation and resuspended in glycerol-free plasma. A loss in platelet count was observed when the gradient of glycerol was more than 3%. This was associated with an increase in mean cell size and a reduction in aggregability. With 5% glycerol stress, a loss of 30% in cell count, an increase in 18% in cell size, and a 78% loss in aggregability was observed. Declining of PRHS was shown already with a 1% glycerol gradient and 69% of this function was suppressed by 5% glycerol stress. In other experiments, 5% glycerol was first added, them removed in 5 steps with a gradient of 1% each. When time interval between each step was less than 0.5 min, platelet loss and PRHS reduction were 17 and 47% respectively. These values were gradually improved to 4% and 11-20%, respectively, as increasing time interval up to 15 min. It was concluded that a gradient of 1% glycerol and a 15-min interval for each step minimizes the detrimental osmotic stress on platelets while glycerol is added or removed. Our findings may lead up to devising an improved protocol for platelet cryopreservation with glycerol.     

Inhibition of platelet aggregation by a fibrinogenase from Naja nigricollis venom is independent of fibrinogen degradation

Fibrinogenases, proteinases which release peptides from the carboxy-terminal end of fibrinogen, are classified as alpha-fibrinogenases or beta-fibrinogenases, based on their ability to preferentially attack the A alpha or B beta chain, respectively, of fibrinogen. alpha-Fibrinogenases have been shown to inhibit platelet aggregation whereas beta-fibrinogenases do not. We have studied the inhibition of platelet aggregation by proteinase F1, an alpha-fibrinogenase from Naja nigricollis venom. This proteinase inhibits whole blood aggregation in a dose-dependent manner, with an IC50 value of 145 micrograms. However, the proteinase fails to inhibit aggregation in washed platelet suspensions. Thus, proteinase F1 appears to require a plasma factor to cause inhibition. Since fibrinogen acts as an adhesive protein which links platelets during aggregation, and since proteinase F1 cleaves fibrinogen, we investigated the role of fibrinogen in the inhibition of platelet aggregation by proteinase F1. The degradation products of fibrinogen formed by the proteinase did not cause significant inhibition. Thus, the inhibition of platelet aggregation appears to be independent of the formation of fibrinogen degradation products. We also studied the effect of proteinase F1 on aggregation of platelets that were reconstituted with defibrinogenated plasma. The proteinase inhibited aggregation of platelets even in the absence of plasma fibrinogen. Proteinase F1 was about 4-fold more potent in inhibiting platelet aggregation in defibrinogenated blood. From these results, we conclude that the inhibition of platelet aggregation by proteinase F1 from N. nigricollis venom is independent of its action on fibrinogen.     

Platelet fibrinogen. Identity and initial observations on the mode of its degradation by plasmin.

Fibrinogen has been purified from human platelets. Platelet fibrinogen exhibits a characteristic pattern in agar gel immunoelectrophoresis different from that of plasma fibrinogen. Stepwise plasmin degradation has been used in further elucidation of the molecular properties of the platelet protein. Examination of comparative digests by immunologic and gel electrophoretic methods has revealed that (1) the platelet protein is more resistant to plasmin degradation, (2) the plasmin-produced fragments of platelet fibrinogen differ consistently from those of its plasma counterpart, and (3) platelet fibrinogen is different from fragment X of plasma fibrinogen. It is suggested that platelet fibrinogen may contribute to the stability of the thrombus.