bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Hypothesis for the Molecular Mechanism of Surface-Dependent Activation of Hageman Factor (Factor XII)
Authors: Griffin John H. 
Published: May 2019

The surface-dependent mechanism of activation of highly purified human Hageman factor (HF) was studied using 3H-DFP uptake as a quantitative active site titrant. HF was treated in various ways and the reaction mixture was exposed to 3 mM 3H-DFP for 5 min at 37°. Following addition of SDS and removal of free DFP by dialysis, the reaction products were analyzed on SDS gels. In solution, the HF zymogen at 80,000 MW took up 0.015 mol DFP per mol HF. HF bound to kaolin, celite, or ellagic acid with or without high MW kininogen took up the same 0.015 mol DFP per mol HF. However, HF bound to celite or kaolin with high MW kininogen and kallikrein took up 0.9 mol DFP per mol HF into a 28,000 MW fragment of HF. In approximately half of these activated HF molecules, this 28,000 MW fragment was linked by disulfide bonds to a 52,000 MW fragment in a surface-bound 80,000 MW form of activated HF. In clotting assays, DFP did not inhibit kaolin-bound HF unless the surface-bound HF first had been proteolytically activated by kallikrein.Kinetic studies of the cleavage of 125I-HF by kallikrein or by plasmin in the presence of high MW kininogen showed that kaolin-bound HF was cleaved more than 20 times faster than HF in solution.These results suggest that binding to kaolin or celite or ellagic acid, classically known as “activating surfaces”, does not convert a detectable fraction (< 1%) of the bound HF molecules to active enzymes. Rather, surface-binding makes HF molecules much more susceptible to proteolytic activation in the presence of high MW kininogen, and the reciprocal proteolytic activations of HF and prekallikrein are thus greatly stimulated by “activating surfaces”.
Heterogeneity of the Factor VIII/Von Willebrand Factor Protein in Von Willebrand’s Disease
Authors: Gralnick H. R. , Sultan Y. , Coller B. S. 
Published: May 2019

The recent advent of techniques to purify the factor VIII/von Willebrand factor (f.VIII/vWf) protein from plasma to quantitate the f.VIII/vWf protein and to measure the vWf (plasma ristocetin cofactor) have greatly added to our understanding of von Willebrand’s disease (vWd). The initial studies of antigen, procoagulant and vWf levels revealed a parallel reduction in all three activities in vWd suggesting a quantitative deficiency of the f. VIII/vWf protein and its biologic activities.Recent studies, however, have suggested three major forms of vWd. The first group of patients have a quantitative defect with a parallel reduction of the f.VIII/vWf protein and of the antigen, vWf and procoagulant activities. The second group of patients appear to have a qualitative defect of the f.VIII/vWf protein. These individuals have normal levels of the antigen and procoagulant activity; however, the vWf activity is reduced or absent. The third group of patients have a combination of a qualitative and quantitative deficiency. These variants resemble both previous groups in that there are reduced levels of the antigen, procoagulant and vWf activities but usually greater reduction of the vWf activity.Three major defects of the f.VIII/vWf protein have been recognized in vWd: 1) decreased plasma concentration of the f. VIII/vWf protein, 2) the apparent molecular weight of the protein is reduced and/or the largest molecular weight polymers are absent, and 3) there is a partial or total carbohydrate deficiency. For the f.VIII/vWf protein to express vWf activity, it must be of a minimal molecular size and have a specific carbohydrate content and/or sequence.
Immunological Arterial Injury in Atherogenesis
Authors: Minick C. R. , Williams L. R. , Alonso D. R. 
Published: May 2019

Our experiments indicate that the synergy of immunological arterial injury resulting from either immune complex disease or graft rejection and hypercholesterolemia will lead to atherosclerosis. Repeated or protracted immunological arterial injury in synergy with more modest hypercholesterolemia, like that in Western man, leads to arterial lesions which closely resemble chronic human atherosclerosis. Sites of immunological arterial injury retain their increased propensity to accumulate lipid for weeks and months following the injury.Indirect evidence from experiments of others suggests that increased endothelial permeability may be the primary event in some immunologically induced arterial injury. Results of our experiments indicate that endothelial damage and/or loss and platelet interaction with the arterial wall may be an early event in the pathogenesis of immunologically induced atherosclerosis. Moreover, our results indicate that at least in the instance of graft rejection, endothelial injury and platelet interaction may not only be an early event, but that continued injury and platelet interaction may contribute to progression of atherosclerosis.
Pharmacological Evaluation of Ticlopidine, A Novel Inhibitor of Platelet Function
Authors: Johnson M. , Walton P. L. , Cotton R. C. , Strachau C. J. L. 
Published: May 2019

Ticlopidine (T), 5-(2-chlorobenzyl)-4,5,6,7-tetrahydrothieno(3,2-C)pyridine hydrochloride (a product of Parcor Research) has been evaluated as an antiplatelet agent in various animal species and in human volunteers. T was inactive in vitro, but inhibited platelet aggregation induced by ADP, collagen, thrombin, arachidonic acid and prostaglandin (PG) endoperoxide, when administered orally to mice, rats, rabbits, guinea pigs, pigs, dogs and baboons. Platelet adhesiveness was reduced but platelet survival time was normal in treated animals. Basal PG synthesis and platelet ultra-structure were unaffected by T.T protected against acute thrombocytopenia and death from pulmonary embolism induced by i. v. injection of ADP or collagen. Thrombus formation in experimental models of extra-corporeal circulation and deep venous thrombosis was also impaired.In man, a single oral dose of 500mg was shown to be a potent inhibitor of ADP, collagen, adrenaline, ristocetin, bovine fibrinogen and 5HT-induced aggregation. A dose-effect relationship was apparent, 250 and 500mg resulting in ~47 and 75% inhibition of ADP-induced aggregation respectively. Inhibition was sustained by chronic daily dosing.There was a delay in the onset of action of T in vivo, but which then persisted after withdrawal for at least 48 hours, with no evidence of rebound hyperactivity. The duration of action of T correlated with platelet survival time, suggesting an irreversible modification of platelet function. T is a potent platelet inhibitor, exhibiting a novel mode of action and lack of agonist specificity, which may be of value in the treatment of thrombotic conditions.
Effect of Diazepam on Platelet Function
Authors: Carvalho A. C. , Colman R. W. , Vaillancourt R. , Cabrai R. , Anaya R. 
Published: May 2019

Diazepam (Valium) is one of the most prescribed medications in the world. Patients on Diazepam may need platelet function evaluation. Therefore, a study of its effect on both in vivo and in vitro platelet function was undertaken in 8 normal volunteers. Diazepam (10–40μg/ml) was incubated in vitro with platelet rich plasma (250,000/μl) at intervals of 15, 30, 60, 120, and 240 minutes followed by determination of platelet aggregation and 14C-serotonin release. Fifty percent inhibition of platelet aggregation and release by Diazepam was obtained at 1 hr with epinephrine (p<0.01) and at 2 hrs with ADP (p<0.01), but no significant effect was noted with collagen. The Diazepam inhibitory effect on platelet aggregation and release was overcome by high concentrations of aggregating agents, suggesting that its primary effect is not mediated by inhibition of prostaglandin synthesis.Following oral ingestion of 5mg of Diazepam, platelet aggregation and 14C-serotonin release were determined serially (2, 4, 8, 12, 24, and 48 hours) in the 8 normal subjects. After 8 hours, Diazepam inhibited ADP-induced aggregation and release by 39% (p<0.01) and epinephrine by 50% (p<0.01). No significant inhibition of collagen was observed. Forty-eight hours after Diazepam intake, platelet function returned to normal in all subjects.Our data show that Diazepam impairs both platelet aggregation and release in vitro and in vivo. Although the effect of Diazepam on in vivo hemostasis is still uncertain, our results suggest caution in the interpretation of platelet function testing in patients on this drug.
Cross Linking of Human Platelet Membrane Aminophospholipids:Changes Induced by Thrombin
Authors: Schick P. K. , Arosteguy P. 
Published: May 2019

The proximity of the aminophospholipids, phosphatidylethanolamine (PE) and phosphatidyl-serine (PS), in platelet membranes was probed with difluorodinitrobenzene (D) which reacts with and cross-links aminophospholipids when they are less than 5 A° apart. D can penetrate intact cells and labels lipids on either side of the membrane bilayer. The incubation of mixtures of pure PE and PS can result in the formation of the following derivatives: PE-D-PE, PE-D-PS, PE-D, PS-D-PS, PS-D. Following incubation of washed platelets with D, lipids and derivatives were extracted, separated by thin-layer chromatography, and quantitated by lipid phosphorus. The incubation of platelets with D (125μM) for 2 hours resulted in derivatization of 49% PE and 34.6%PS. When platelets were treated with thrombin (0.1U/ml) for 5 minutes prior to incubation with D, 71.4% PE and 53.8% PS reacted. Results are shown in Table; %PE(PS)=% total platelet PE(PS).In controls significant amounts of only PE-D-PE and PE-D-PS were detected and thus are intimately associated within platelet membranes. In thrombin-treated platelets significant amounts of PS-D-PS were formed which did not occur in controls. However, there was no increase in PE-D-PE and PE-D-PS. Also, in thrombin-treated platelets additional PE and PS reacted but were not close enough to be cross-linked. The study indicates that incubation of platelets with thrombin results in the unmasking or rearrangement of specific compartments of PE and PS within platelet membranes which may be critical for platelet hemostatic activities.
Adhesion of Platelets to Collagen
Authors: Meyer F. A. , Weisman Z. 
Published: May 2019

Platelets adhere to collagen fibers, undergo the release reaction and aggregate, soluble collagen, however, does not cause release or aggregation. Platelets, however, recognize soluble collagen since adhesion (but not aggregation) occurs when a soluble collagen coated surface is exposed to washed rabbit platelets in Tyrode and in competitive experiments preincubation of platelets with soluble collagen reduces the number adhering to a collagen surface. The latter effect is concentration dependent; preincubation with 100 μg/ml of soluble collagen reduces platelet adhesion by 70%.Similar competitive experiments were performed to examine the features on collagen responsible for platelet adhesion. Preincubation of platelets with a variety of soluble collagens, denatured soluble collagen, pepsin- and periodate-treated soluble collagen and cyanogen bromide peptides all decrease the ability of platelets to bind to a collagen surface. Similar effects arise moreover with the synthetic copolypeptides (Gly-Pro-Ala-Gly-Pro-Pro)n,(Gly-Pro-Pro)n and (Pro2Gly)n. In fact, the homopolymers, polyproline and polyhydroxyproline (but not proline or hydroxyproline) as well give effects similar to those of the collagen materials. The effect is rather specific since preincubation with plasma proteins and synthetic polypeptides based on other major amino acids present in collagen, viz. polyalanine, polyglutamic acid, polyaspartic acid, polyarginine and polylysine do not inhibit the binding of platelets. It would therefore appear that proline and hydroxyproline sequences incorporated in a macromolecular chain are the important, if perhaps not the only determinants involved in platelet recognition of collagen.Soluble collagen coated surfaces were used in this study, however, similar effects of the test material on platelet adhesion to collagen fibers could be demonstrated.
Deposition of Platelets on Collagen as Evaluated by 51Cr-Label or Morphometry: Effects of Aspirin
Authors: Tschopp Th.B. 
Published: May 2019

Whether aspirin inhibits platelet deposition on thrombogenic surfaces by its effect on adhesion-induced aggregation only or whether it also affects adhesion per se, is still controversial. This study compares platelet deposition determined from the deposited radioactivity using 51Cr-labeled platelets with platelet surface interaction as measured’by morphometry. Collagen fibrils of α-chymotrypsin-digested segments of rabbit aorta were exposed to citrated rabbit blood for 10 min in a perfusion chamber at 830 s-1 blood shear rate. The number (L) of deposited platelets as calculated from the 51cr-label amounted to 687±87x103/mm2 (mean ± SE of 35 control perfusions). The surface area covered with platelets (D) as determined by morphometry amounted to 31±2 % and that covered by platelet thrombi (T) (aggregates higher than 5 um) to 19±2 %. The deposited platelet mass (M) as measured by the sum of platelet cross section area multiplied by section thickness amounted to 564±66 μm3/mm2. Linear regression analysis showed platelet mass as determined by L and M to be highly correlated (R = 0.9509, 2p (0. 001). Thus platelet deposition on thrombogenic surfaces may be adequately measured by adding a small proportion (l3±1 %) of 51Cr -labeled homologous platelets to citrated blood.Aspirin (100 μM) significantly inhibited platelet deposition as shown by decreased values of L, M and T but did not decrease the surface area covered with platelets (D) as evaluated morpho-metrically. Thus the inhibition of platelet deposition on thrombogenic surfaces exerted by aspirin appears to be due to inhibition of a platelet reaction subsequent to adhesion.
Interaction of Human Platelets with the 2′, 3′-Dialdehyde Derivatives of ADP (o-ADP) and ATP (o-ATP) as Potential Affinity Labels for the ADP Receptor
Authors: Pearce P. H. , Scrutton M. C. 
Published: May 2019

In order to characterise the receptor responsible for mediating platelet aggregation and secretion induced by ADP we have synthesised oADP and oATP by periodate oxidation of ADP and ATP. oADP induces platelet shape change but inhibits aggregation competitively with respect to ADP. The properties of inhibition of aggregation induced by adrenaline, collagen or thrombin are also consistent with the conclusion that the effects of oADP result from interaction with the ADP receptor(s). The effects of oATP generally resemble those of oADP except that oATP inhibits, rather than induces, shape change and causes this effect at a concentration in excess of that required for inhibition of aggregation. ,Brief exposure of intact platelets to [3H]-oADP or oATP causes stable incorporation of [3H] into the membrane proteins. Analysis of [3H] distribution by SDS gel electrophoresis after prolonged dialysis against SDS/mercaptoethanol shows predominant incorporation of [3H]-OATP into a fraction at 28000 dal tons over a concentration range consistent with that required for inhibition of aggregation. When [3H]-OADP is used, incorporation occurs predominantly into 4 fractions at 28000, 45000 (probably actin), 65000 and 220000 daltons. The [3H] incorporation/ [oADP] relationship and the time course of incorporation suggest that the 28000 and 65000 dalton fractions are likely candidates for identification as ADP receptors. Our data suggest a tentative identification of the 28000 dalton fraction as the receptor responsible for mediating aggregation induced by ADP and also indicate the possibility that different receptors may be involved in induction of shape change and aggregation by this agonist.
Effect of Sulfinpyrazone and Aspirin on Platelet Loss Induced In Vitro by Activated Charcoal Hemoperfusion
Authors: Winchester James F. , Forbes Charles D. , Courtney James M. , Prentice Colin R.M. 
Published: May 2019

Activated charcoal hemoperfusion is used for drug overdosage and is potentially useful in acute hepatic failure and chronic uremia. While hemocompatibility of early devices has improved, platelet loss still occurs, and may be associated with hemorrhage.We have developed an in vitro circuit consisting of hemoperfusion column and lines with a total blood volume of 60 ml for use with human blood. Citrated whole blood hemoperfusion is associated with platelet depletion of similar magnitude for coated or uncoated charcoal (20%) whereas polymer coating of charcoal improved the profound platelet loss (90%) noted with perfusion of heparinized whole blood (3 U/ml) over uncoated charcoal.At 14 day intervals, in a double blind cross over study, we compared the effects of 2 days treatment with aspirin (ASA)(600 mg/day) or sulfinpyrazone (SP)(800 mg/day) alone or in combination against placebo, on platelet adsorption on 2% hydrogel coated or uncoated charcoal, and platelet retention on cuprophan membranes PT150 and PT250 in a test cell system, in 8 healthy male volunteers. Bleeding time was also measured before and after treatment using a spring loaded device.In a heparinized system, ASA, SP, and combination reduced mean platelet adsorption on coated charcoal from 53% to 41%, and mean platelet retention to membranes from 20% to 10%, whereas ASA alone reduced platelet adsorption on uncoated charcoal. Bleeding time,was prolonged by ASA but not by SP. These agents are capable of modifying platelet loss in vitro and may do so in vivo.
Mild Depression of Platelet Count and Altered Platelet Function in Acute Plasmodium Falciparum Infection
Authors: Essien E. M. , Ebhota M. I. 
Published: May 2019

We recently examined a possible role and extent of involvement of Plasmodium falciparum para-sitaemia in our earlier report of significantly lower circulating platelet numbers in healthy adult Nigerians (100 – 300x 103/ul) compared with matched Caucasians (150 – 140 χ 103/ml) ; (P<. 0.001), and in view of recently reported association of Plasmodium parasitaemia with thrombocytopaenia, consumptive coagulopathy (DIC) and other haemorrhagic syndromes. Ninety-eight febrile children aged between 8 months and 10 years whose fever was attributed to malaria parasitaemia only were admitted into the study. Platelet count, platelet aggregation, Factor VIII and FDP were determined on each blood sample which was collected before treatment was started. Tests were repeated 10-Hdays later. It was found that the mean platelet count of 132,000+61, 620/ul (1SD) during illness and immediately after treatment was significantly lower than the count of 234, 400+98, 480/ul, 10–14 days later, (t = 6.496 ; P<c 0.001 ). Significant thrombo cy topa emia (Platelets 70,000/ul) was observed only in Gfo of the subjects and none had any haemorrhagic symptoms. The effect was independent of age or degree of parasitaemia. Pre- and post-treatment leucocyte counts were similarly different (7952+2043 vs. 9221+3071 t = −2.81; P<0.05). Haematocrit values did not change significantly. However, in the response to platelet aggregating agents, it was found that the second wave of ADP-induced aggregation was regularly abolished during the parasitaemia.It is concluded that in hyperendemic Plasmodium falciparum environment, the malaria may often lead to mild depression of platelet count but that severe thrombocytopaenia is uncommon. The platelets may not be optionally functional.
Plasma ADPase Activity in Myocardial Ischemia
Authors: Heyns A. duP. , Badenhorst C. J. , Retief F. P. , KIeynhans P. H. T. , Potgieter G. M. 
Published: May 2019

Adenine nucleotides play a key role in platelet aggregation and in the autoregulation of myocardial perfusion. Low Km ADPase activity in plasma and accumulation of ADP catabolic products were investigated in patients with myocardial ischaemia and necrosis.ADPase activity was assayed by incubation of 2μM 14C-ADP in plasma at 37°C. Enzymatic reactions were terminated by heat, radio-active nucleotides separated by high voltage electrophoresis and quantitated. ADPase activity was expressed as pmol 14C-ADP catabolized per minute as assayed by two point substrate concentration analysis.
14C-ADP was catabolized in a single exponential manner. The breakdown products AMP, adenosine, inosine and hypoxanthine were detected. Mean ADPase activity, of 25 normal males was 102+ SD 15 and 15 normal females 85+SD 13. In the immediate postinfarction period 25 patients had a significantly (P<0,01) increased plasma ADPase : 127 + 40. ADPase was also significantly increased in the patients with crescendo angina (mean 131 + SD 42) (P<0,01). ADPase levels were higher in the coronary sinus than in peripheral blood of the same subject. In the rat heart >80% of total ADPase activity was located in the cytosol fraction after differential centrifugation of whole heart homogenate.Low Km ADPase activity is increased in myocardial ischaemia. The enzyme is released in anoxia. It thus may be a measurement of the well known metabolic pathway leading to adenosine accumulation in ischaemic heart muscle.
Selective Inhibition of Platelet Agglutination and Aggregation by Aromatic Amidino Compounds
Authors: Geratz J. D. , Tidwell R. R. , Brinkhous K. M. , Mohammad S. F. 
Published: May 2019

A series of aromatic amidino compounds were investigated for their inhibitory effect on platelet agglutination and platelet aggregation. Agglutination of fresh or fixed human platelets was produced by bovine plasma or by human plasma in combination with ristocetin, while aggregation of fresh platelets was induced by ADP, thrombin or collagen. Highly effective inhibitors were found for both types of platelet clumping, but there was no parallelism between the inhibitory activities in the two test systems.5-(5-Amidino-2-benzimidazolyl)-2-(4-hydroxybenzene)benzimidazole suppressed agglutination exclusively. Pentamidine, on the other hand, strongly blocked the aggregation reactions, but did not interfere with agglutination, even at high concentrations. Compounds which inhibited aggregation also prevented the liberation of serotonin from the platelets.This investigation has led to the identification of new specific inhibitors of platelet agglutination and aggregation which can serve an important role in future studies of the two processes. The exact mode of interaction between ami dines and platelets is still being explored.. In the case of agglutination, inhibition most likely occurred at the level of binding of ristocetin cofactor to the platelet membrane. In the case of aggregation, however, interference could have taken place at the membranes or in the cytoplasm and could have been enzymatic or non-enzymatic in nature.
Platelet Coagulant Activities in Metrizamide Gradient Platelets : Application to Bernard-Soulier and Thrombotic Disorders
Authors: Levy-Toledano S. , Dmoszynska A. , Baume H. de La , Dupuy E. , Caen J. 
Published: May 2019

A new technique for platelet isolation from five ml of total blood on metrizamide gradients has been applied to the study of platelet coagulant activities.” Assay methods have been described : contact product forming activity (CPFA), collagen induced coagulant activity (CICA) and platelet factor three (PF3) have been measured in the metrizamide gradient platelets (MGP) and found similar to that of platelets in platelet richplasma (PRP).Platelet coagulant activities of the MGP have been measured in patients with hemorragie tendencies like Bernard-Soulier (B-S) patients or those with thrombotic tendencies including diabetics with or without vascular complications or patients with transient ischemic attacks (TIA). CICA was not found in. all the 3 patients with B-S syndrome. 3 of the 10 diabetics showed an increased CPFA activity while 5 showed an increased CICA activity contrasting with the normal activities found in diabetics without vascular complications ; PF3 activity is increased in the two groups of diabetics. 3 patients of the 7 with TIA had an increased CPFA as well CICA.The results suggest that these activities may play some role in diabetics with vascular complications and in some cases with TIA.