Tissue-specific expression of functional platelet factor XI is independent of plasma factor XI expression

Platelet factor XI is an alternatively spliced product of the factor XI gene expressed specifically within megakaryocytes and platelets as an approximately 1.9-kb mRNA transcript (compared with approximately 2.1 kb in liver cells) lacking exon V. Flow cytometry with an affinity-purified factor XI antibody, with PAC1 antibody (to the GPIIb/IIIa complex on activated platelets), and with S12 antibody (to P-selectin, an alpha-granule membrane protein expressed on the platelet surface during secretion) on platelets activated with ADP, thrombin, thrombin receptor peptide (SFLLRN amide), or collagen at various concentrations exposed platelet factor XI and PAC1 antibody binding in parallel. Unactivated platelets expressed approximately 40% of total platelet factor XI but no PAC1 binding sites. Enhanced membrane exposure of platelet factor XI is independent of alpha-granule secretion, because ADP and collagen exposed platelet factor XI but no S12 binding sites. Platelets from four patients with plasma factor XI deficiency (<0.04 U/mL) had normal constitutive and activation-dependent expression of platelet factor XI. Well-washed platelets from normal and from factor XI-deficient donors incubated with low concentrations of thrombin (0. 05 to 0.1 U/mL) corrected the clotting defect observed with factor XI-deficient plasma. Thus, functionally active platelet factor XI is differentially expressed on platelet membranes in a tissue-specific manner both constitutively and in a concentration-dependent fashion by various agonists in the absence of detectable plasma factor XI.

Training for dental screening using clinical photographs

OBJECTIVE

To determine how the referral pattern from school screening of a group of dentists changed following a training programme.

DESIGN

Eighty clinical photographs of teeth were shown to a group of dentists both before and after a training programme. The photographs were of teeth in various stages of the carious process from children aged between three and 15 years. The dentists were shown each of the 80 photographs and were asked to categorise each slide according to the decision they were most likely to make during school screening.

CLINICAL SETTING

An NHS Community Trust in Merseyside, UK.

PARTICIPANTS

A group of 12 community dental officers.

OUTCOME MEASURES

Evaluation was carried out in relation to consensus refer/not refer decisions. Consensus was defined as the majority decision provided that no more than two dentists disagreed with the majority.

RESULTS

As a consequence of training there was a change from no consensus to consensus in 21.5 per cent of the slides, whereas only 2.5 per cent changed from consensus to no consensus. However, after training there was still no consensus on 30 per cent of the slides.

CONCLUSIONS

This study demonstrates a means by which referral decisions from school screening can be audited.

Characterization of extracellular nucleotide-induced Mac-1 (alphaM beta2 integrin) surface expression on peripheral blood leukocytes

Extracellular nucleotides, released during vascular injury, stimulate hematopoietic cells resulting in various physiological responses. We have determined that nucleotides can stimulate the expression of Mac-1 on peripheral blood leukocytes. ATP stimulated the expression of Mac-1 in a time- and dose-dependent manner with maximum expression occurring in 5 min at 10 microM ATP. This increase in surface expression was observed in monocytes and granulocytes was dose-dependent and was comparable in extent to the increase induced by the chemotactic peptide, formyl-Met-Leu-Phe. Other nucleotides including 2-MeSADP, ADP, UTP, and 2MeSATP had similar effect. Nucleotide-mediated stimulation of Mac-1 expression in granulocytes was completely inhibited by Ro-31-8220, a specific inhibitor of protein kinase C, while variable inhibition was observed in monocytes. These results demonstrate the stimulation of peripheral blood leukocytes by nucleotides causing an increased surface expression of Mac-1 which may be mediated by the activation of protein kinase C.

Characterization of P2 purinergic receptors on human erythro leukemia cells

We have investigated the nature of the nucleotide receptors on human erythro leukemia (HEL) cells, a cell line with some megakaryocytic properties, using a combination of pharmacological, photoaffinity labeling, and molecular biological techniques. Fura-2 loaded HEL cells responded to 2-methylthio ATP, ATP, 2-methylthio ADP, ADP and UTP with an increase in intracellular calcium. 2 Methylthio ADP was the most potent agonist. When external calcium was chelated with EDTA, calcium responses were observed indicating the mobilization of intracellular stores. These responses showed evidence of both homologous and heterologous receptor desensitization. In photoaffinity labeling experiments, beta-[32P]-AzPET-ADP was incorporated into three protein species with mobilities corresponding to M(r) approximately 55 kDa (doublet) and approximately 43 kDa. Labeling of approximately 55 kDa proteins was specifically inhibited by ADP, while that of the approximately 43 kDa was inhibited specifically by UTP. Nucleotide sequence analysis of the positive clones obtained by screening the HEL cell cDNA library with mouse P2U cDNA revealed that the P2U receptor from HEL cells is identical to the previously cloned human P2U receptor. These experiments suggest that the HEL cells contain a P2Y purinoceptor responding to ADP, in addition to a P2U receptor and possibly also a third P2 purinoceptor with a unique agonist profile.

Mapping of the P2U purinergic receptor gene to human chromosome 11q 13.5-14.1

We mapped a human P2U purinergic receptor gene to chromosome 11q13.5-14.1. Oligonucleotide primers complementary to a part of the human P2U purinergic receptor cDNA were used to amplify a region from genomic DNAs from a panel of mouse/human somatic cell hybrid cell lines, each containing a single human chromosome. A PCR product of the expected size (378 bp) resulted from a single hybrid cell line containing human chromosome 11. The gene was further localized to a region of chromosome 11 using a sub-chromosomal hybrid panel containing different segments of chromosome 11. Based on the specific PCR product obtained and its Southern hybridization to the P2U receptor cDNA, the human P2U receptor gene was localized to chromosome 11q13.5-14.1.

The effect of using a pre-brushing mouthwash (Plax) on removal of tooth stain in vivo and in vitro

The aim of this study was to determine whether the use of a pre-brushing mouthwash Plax reduced extrinsic tooth-staining in vivo and in vitro. Firstly, in a double-blind placebo controlled cross-over study, 20 subjects with tooth staining used Plax or a placebo for 14-day periods separated by a 1-month wash-out period. The area of stain was assessed before and after each mouthwash had been used from clinical photographs. Secondly, extracted 3rd molar teeth were stained with tea and chlorhexidine. After exposure to either Plax or placebo, the teeth were brushed in a standardized manner. The area and intensity of stain were assessed before and after rinsing and brushing. Results of the study in vivo showed that the mean % stained area for any of the surfaces studied changed very little throughout the study. No statistically significant changes were detected (Student t-test, p > 0.05). Results of the study in vitro showed that the mean area of stain fell by 19% after exposure to Plax and by 17% after exposure to placebo. No statistically significant changes were detected (Student t-test, p > 0.05). There were also no significant changes in intensity (Wilcoxon signed rank sum test p > 0.1).

Identification of a receptor for ADP on blood platelets by photoaffinity labelling

The synthesis of a new analogue of ADP, 2-(p-azidophenyl)-ethythioadenosine 5'-diphosphate (AzPET-ADP), is described. This compound contains a photolabile phenylazide group attached to the ADP molecule by a thioether link at the purine 2 position. It has been prepared in radioactive form with 32P in the beta-phosphate at a specific radioactivity of 100 mCi/mumol. The reagent activated platelets, causing shape change and aggregation, with somewhat lower affinity than ADP. On photolysis the affinity was increased. The reagent also inhibited platelet adenylate cyclase stimulation by prostaglandin E1, with considerably higher affinity than ADP. On photolysis the affinity was decreased. AzPET-ADP competitively inhibited the binding of 2-methylthio[beta-32P]ADP, a ligand for the receptor by which ADP causes inhibition of adenylate cyclase. In the dark, AzPET-[beta-32P]ADP bound reversibly and with high affinity to a single population of sites similar in number to the sites that bind 2-methylthio[beta-32P]ADP. Binding was inhibited by ADP and by ATP and by p-chloromercuribenzenesulphonic acid (pCMBS). On exposure to u.v. light in the presence of platelets, AzPET-[beta-32P]ADP was incorporated covalently but non-specifically into several platelet proteins, although prominent intracellular proteins were not labelled. Specific labelling was confined to a single region of SDS/polyacrylamide gels, overlying but not comigrating with actin. Incorporation of radioactivity into this region was inhibited by ADP and by ATP as well as by ADP beta S, ATP alpha S and pCMBS, but not by adenosine, GDP or AMP. Inhibition of AzPET-[beta-32P]ADP incorporation was closely correlated with inhibition of equilibrium binding of 2-methylthio[beta-32P]ADP. These results suggests that the labelled protein, which migrates with an apparent molecular mass of 43 kDa in reduced gels, is the receptor through which ADP inhibits adenylate cyclase.

Clopidogrel inhibits the binding of ADP analogues to the receptor mediating inhibition of platelet adenylate cyclase

Clopidogrel, like the homologous thienopyridine derivative ticlopidine, selectively inhibits platelet aggregation induced by ADP. We have previously described two nucleotide-binding sites on platelets related to ADP-mediated platelet responses. The first is a high-affinity binding site for 2-methylthio-ADP (2-MeSADP) that is linked to the inhibition of stimulated adenylate cyclase. The second is the 100-kd exofacial membrane protein aggregin, which is labeled by the reactive ADP analogue 5'-p-fluorosulfonylbenzoyl adenosine (FSBA) that is related to shape change and aggregation. We set out to determine if either of these sites is blocked in vivo by clopidogrel or its active metabolite. Six subjects were given clopidogrel (75 mg/day for 10 days) in a double-blind crossover experiment. All of the subjects developed prolonged bleeding times while taking the drug. The rate of onset of the effect on bleeding time varied among subjects. Platelet aggregation induced by ADP or thrombin was significantly impaired by the drug treatment, but no effect was detected on shape change. The incorporation of [3H]FSBA into aggregin was also unaffected. Inhibition of adenylate cyclase by ADP or by 2-MeSADP was greatly reduced in all subjects, and in the case of 2-MeSADP, there was evidence for a noncompetitive effect. Inhibition of adenylate cyclase by epinephrine was unaffected. In the three subjects for whom binding measurements were made, the number of binding sites for [32P]2-MeSADP was reduced from 534 +/- 44 molecules per platelet during control and placebo periods (11 determinations) to 199 +/- 78 molecules per platelet during drug treatment (three determinations). There was no consistent change in the binding affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Propofol for repeated burns dressings in a child: a case report

The use of propofol for repeated burns dressings in a severely psychologically disturbed child is described. The benefits of using this method rather than the traditionally used ketamine are discussed. The lack of adverse side-effects and rapid restarting of feeding were found to be advantageous.

P47 phosphoprotein of blood platelets (pleckstrin) is a major target for phorbol ester-induced protein phosphorylation in intact platelets, granulocytes, lymphocytes, monocytes and cultured leukaemic cells: absence of P47 in non-haematopoietic cells

Aggregating agents including phorbol esters which activate protein kinase C induce the rapid phosphorylation of a Mr = 47,000 cytosolic protein in blood platelets (P47 or pleckstrin). This protein is well resolved by analytical 16-BAC----SDS two-dimensional PAGE and was purified from platelets by preparative 16-BAC----SDS PAGE. Polyclonal antibodies were raised to the protein in mice and rabbits. These antisera detected a single protein with the migration of P47 on Western blots of platelet extracts, and the rabbit antisera immunoprecipitated 32P-labelled P47 from platelet cytosol. The presence of P47 in other haematopoietic cells was determined by prelabelling them with 32P and observing increased 32P incorporation into the location of P47 on autoradiographs of 16-BAC----SDS analytical PAGE of cells exposed to phorbol ester. The identity of the phosphoprotein found in this location was further established by probing Western blots of SDS PAGE gels of cultured cell lines with the P47 antisera. P47 was detected in peripheral blood lymphocytes, monocytes and granulocytes (including the granulocytes of two unrelated patients with X-linked chronic granulomatous disease). P47 was also found in HL-60 promyelocytes (especially after differentiation with retinoic acid), U937 histiocytes, HEL leukaemia cells, and Raji 'B' lymphoblasts. It was not detected in normal erythrocytes, K562 leukaemic cells, MOLT-3 'T' lymphoblasts, or in wide range of non-haematopoietic cell lines. We conclude that P47 is a major target for the action of phorbol ester induced phosphorylation in platelets, normal leucocytes and some haematopoietic cell lines. These cells have as their common feature the ability when stimulated to develop adhesive functions on their plasma membranes.

Effect of platelet activation on the agglutination of platelets by von Willebrand factor

Agglutination of human platelets by bovine von Willebrand factor (vWF) or by human vWF in the presence of ristocetin is inhibited by ADP and by several other platelet agonists but not by epinephrine. Vincristine, which causes a shape change by disrupting microtubules, neither inhibited agglutination nor blocked the effect of ADP. The action of ADP was blocked by ATP, by p-fluorosulfonylbenzoyladenosine, and by the thiol-reactive regents cytochalasin A and p-chloromercuribenzenesulfonate. In contrast to its effects on vWF, ADP enhanced agglutination induced by wheat germ lectin. ADP caused a small decrease in the number and affinity of binding sites for vWF on platelets, too small to explain the inhibition of agglutination. The ability of ADP and other agonists to inhibit agglutination appears to be related neither to inhibition of adenylate cyclase nor to the loss of their discoid shape but rather to the membrane changes that accompany the shape change.

The in vitro buffering capacity of soluble paracetamol

The capacity to neutralise gastric acid was investigated in three over-the-counter paracetamol preparations. Panadol (Winthrop Laboratories) showed a buffering capacity equal to that of existing antacids because of the agents used to make it dissolve. This property, together with its mild analgesic action, widespread availability and palatability, may make it a useful agent for acid aspiration prophylaxis.

Suppurative chondritis: its incidence, prevention, and treatment in burn patients

A retrospective study of 317 cases of suppurative otochondritis occurring in a population of 4794 burned patients successively admitted to one institution between 1967 and 1984 is presented. During the study interval, the incidence of the disease decreased from 20 percent to less than 3 percent in patients with burns of one or both ears. The bacterial species associated with chondritis, principally Pseudomonas aeruginosa and Staphylococcus species, did not change. Patients admitted later than the second postburn day exhibited a significantly greater incidence of chondritis. The crucial factors in prevention of this complication appear to be avoidance of pressure on burned ears and topical chemotherapeutic control of local Pseudomonas infection. Systemic antibiotic prophylaxis did not appear to influence the incidence in the studied population. Several approaches to clinical management of suppurative chondritis are reviewed.

Evaluation of the Minitek system for characterization of Bacillus species

Minitek (BBL Microbiology Systems, Cockeysville, Md.) substrate disks were evaluated as alternatives to conventional tests for the characterization of Bacillus species. Results were compared for 10 reference isolates and 87 isolates from food sources. The overall agreement of results between the Minitek and conventional tests was 92% for reference strains and 86% for food isolates.

Improved selective medium for the isolation of lipase-positive Clostridium botulinum from feces of human infants

Isolation of lipase-positive Clostridium botulinum from fecal specimens establishes the diagnosis of infant botulism, contributes to the diagnosis of food-borne botulism, and is most easily accomplished by use of selective media. Modification of an available selective medium, C. botulinum inhibitory medium (CBI), enabled more rapid isolation of C. botulinum. The modified medium (botulinum selective medium [BSM] contained (per liter) 25 g of dehydrated heart infusion broth, 20 g of agar, 30 ml of egg yolk suspension, 250 mg of cycloserine, 76 mg of sulfamethoxazole, 4 mg of trimethoprim, and 100 IU of thymidine phosphorylase at pH 7.4. The two media were compared by using 15 fresh fecal specimens from infant botulism patients (10 type A and 5 type B) and a C. botulinum isolate that had been obtained from an infant botulism patient and that was mixed into a fresh stool specimen from a healthy human infant. In comparison to CBI, BSM always provided better suppression of the nonbotulinum fecal flora and earlier emergence of lipase-positive colonies. Diagnosis of infant botulism was accomplished sooner with BSM than with CBI because isolation of lipase-positive C. botulinum was easier.

Rapid death of infant rhesus monkeys injected with Clostridium difficile toxins A and B: physiologic and pathologic basis

Clostridium botulinum can colonize and produce botulinal toxin in the human infant intestine, which the toxin then permeates to cause generalized flaccid paralysis, and occasionally, sudden death. This study was undertaken to test the hypothesis that toxins produced by other intestinal clostridia, e.g., C. difficile, might also cause systemic illness and sometimes death in infants (J Pediatr 100:568, 1982). Because this hypothesis could not be evaluated clinically until the systemic manifestations of C. difficile toxins in primates were known, infant rhesus monkeys were given 6 to 11 micrograms/kg of the recently purified C. difficile toxins A or B, either intravenously or intraperitoneally. The animals showed no abnormalities for several hours, but then developed lethargy, hypotonia, hypothermia, and, shortly before death, sudden elevation of serum concentrations of potassium, magnesium, and phosphorus and of enzymes that derived mainly from skeletal muscle, heart and brain. Five of six animals died quietly 3.5 to 8.0 hours after onset of symptoms. Death appeared to result from cessation of breathing, after which the sinus tachycardia then deteriorated to a flat ECG. Necropsy findings were insufficient to explain the cause of death. It appears that in infant monkeys microgram amounts of C. difficile toxins A and B can produce a rapid quiet death, the cause of which is undetectable at necropsy, a situation pathologically reminiscent of crib death in human infants, although the possible clinical identity of these two conditions has yet to be established.

2-Methylthioadenosine[beta-32P]diphosphate. An agonist and radioligand for the receptor that inhibits the accumulation of cyclic AMP in intact blood platelets

2-Methylthio-ADP and its radioactive analogue [beta-32P]2-methylthio-ADP were synthesized and used to investigate platelet receptors for ADP. 2-Methylthio-ADP induced platelet aggregation and shape change, and inhibited cyclic AMP accumulation in platelets exposed to prostaglandin E1. Compared with ADP, 2-methylthio-ADP was 3-5 times as active as an aggregating agent and 150-200 times as active as an inhibitor of cyclic AMP accumulation. Binding of [beta-32P]2-methylthio-ADP to platelets was measured after centrifuging them through silicone oil to separate platelets from their suspension medium. Binding was reversible, saturable, and specific, with between 400 and 1,200 sites/cell in different platelet preparations. There was no evidence for a second class of binding sites with different affinity. The second order association rate constant was approximately 3.5 X 10(6) M-1 S-1, and the first order dissociation rate was 0.024 s-1, both measured at 23 degrees C. The dissociation equilibrium constant (approximately 15 nM) was about three times higher than the concentration giving half-maximal inhibition of prostaglandin E1-stimulated cyclic AMP accumulation in platelet-rich plasma. Binding was inhibited by ADP (Ki = 3.5 microM), ATP (7 microM), 2-azido-ADP (0.12 microM), inosine diphosphate (IDP, 150 microM), guanosine diphosphate (GDP, 350 microM), and AMP (800 microM). Binding of 2-methylthio-ADP was also blocked by the non-cell-penetrating thiol reagent, p-mercuribenzene sulphonate, a reagent that blocks the inhibition of adenylate cyclase by ADP, but which does not block the ability of ADP to induce aggregation or platelet shape change. The amount of 2-methylthio-ADP bound at saturation was independent of pH in the range 6-8, but the affinity was reduced at pH 6 compared with pH 6.5-8.0. The dissociation constant was not temperature dependent in the range 32 degrees -40 degrees C, whereas the rate of dissociation of 2-methylthio-ADP from platelets after the addition of an excess of ADP approximately doubled over this range. The activation energy for dissociation was approximately 15 kcal/mol. Our results support the conclusion that platelets have a receptor for ADP, which inhibits cyclic AMP accumulation, and which has a sulphydryl group in the binding pocket.

Factor VIII-induced superaggregation of human platelets

High concentrations of bovine factor VIII cause clumping of platelets into a few very large aggregates. This response is termed superaggregation. It is distinct from factor-VIII-induced agglutination but is also independent of both extracellular calcium ions and platelet energy metabolism. Neither agglutinating lectins nor aggregating agents, including thrombin, ADP, the ionophore A23187, and U46619, a prostaglandin analog, can induce superaggregation, even at very high concentrations. Washed platelets undergo superaggregation, and superaggregation does not increase the amounts of fibrinogen or albumin trapped by agglutinated platelets. It is not inhibited by membrane-stabilizing drugs or by colchicine or cytochalasin-B. Formaldehyde and glutaraldehyde prevent superaggregation without affecting the binding of radiolabeled factor VIII to the platelets. Superaggregated platelets are separated by approximately 50 nm and are not shape-changed or degranulated. In adenosine diphosphate (ADP) induced aggregation, the platelets are distorted and only 30 nm apart. Superaggregation is reversed by dextran sulfate, and the dispersed platelets are still able to respond to ADP. Our observations are consistent with the binding of high molecular weight multimers of bovine factor VIII to more than one receptor on each platelet, with superaggregation occurring through recruitment of additional receptors. This process may be interrupted by protein crosslinking reagents, such as formaldehyde and glutaraldehyde.

Distribution of phosphatidylethanolamine arachidonic acid in platelet membranes

Arachidonic acid (20 : 4) and other fatty acids and aldehydes in phosphatidylethanolamine (PE) present on the platelet surface was determined. Surface-exposed PE was isolated by using 2,4,6-trinitrobenzenesulfonate, a non-penetrating probe (Schick, P.K., Kurica, K.B. and Chacko, G.K. (1976) J. Clin. Invest. 57, 1221--1226). PE contains 50% total platelet arachidonic acid. Approx. 16% platelet PE is present on the platelet surface. The study showed that the fatty acid and aldehyde composition of PE on the platelet surface is virtually identical to that in PE present inside the platelet. Therefore, 8 nmol arachidonic acid are present in PE in the outer layer of the plasma membrane in 10(9) platelets.

Intraintestinal toxin in infant mice challenged intragastrically with Clostridium botulinum spores

Conventionally raised suckling mice were injected intragastrically with 10(5) spores of a Clostridium botulinum type A culture. Botulism was not observed, but 80% or more of mice challenged when 8 to 11 days old had botulinum toxin in the large intestine 3 days later. Mice younger than 7 days or older than 15 days were resistant to the challenge. When in vivo toxin production was started by spores given to 9-day-old mice, toxin was present in the intestine at 1 through 7 days postchallenge but with greatest consistency between 1 and 4 days. Total toxin in an intestine ranged up to 1,920 50% lethal doses as titrated intraperitoneally in adult mice. The dose infecting 50% of a group of 9-day-old mice was 700 (95% confidence limits of 170 to 3,000) spores per animal. Toxin was formed in the lumen of the large intestine; it was not associated with the ileum. Injection of 10(5) spores intraperitoneally into 9-day-old mice resulted in toxin production in the large intestines of 30% of the test animals.

Depletion of platelet amine storage granules by the antithrombotic agent, suloctidil

Suloctidil, a compound with antithrombotic properties in animal models, causes depletion of human platelet serotonin stores during 1-5 hr incubation with platelet-rich plasma in vitro. This effect is not attended by leakage of cytoplasmic nucleotides or by alterations in cyclic AMP metabolism, malondialdehyde production or energy balance. 5HT uptake was also inhibited but uptake of adenine was not. 5HT released by suloctidil appeared in the supernatant as oxidation products, though the amine also accumulated when re-uptake was blocked by imipramine.

Malondialdehyde production by platelets during secondary aggregation

A method is described for increasing the sensitivity of the thiobarbiturate assay for malondialdehyde by concentrating the coloured reaction product. The basal level of malondialdehyde-like material in plasma was found to be about 0.03 micrometer. Platelets synthesized malondialdehyde when stimulated by collagen or thrombin and also during the second phase of aggregation induced by ADP or adrenaline.

Metabolism and function of human platelets washed by albumin density gradient separation

A method for washing platelets by albumin density gradient separation, originally designed for the study of platelet coagulant activities, has been modified for platelet aggregation and metabolic studies. Platelets are sedimented into a continuous density gradient of isosmolar albumin containing apyrase to protect them from clumping and physical injury and are resuspended in calcium-free Tyrode's solution. The mean recovery of platelets after two separations relative to platelet-rich plasma (PRP) was 90.3%. When small amounts of plasma were added to washed platelet suspensions, aggregation and release of [14C]5-hydroxytryptamine (5HT) in response to adenosine diphosphate (adp) or 5HT were similar to results obtained with PRP. When fibrinogen was substituted for plasma, ADP-induced aggregation occurred but was feeble. Without added plasma or fibrinogen, platelets were refractory to ADP and insensitive to the cyclic endoperoxide analogue U44619. When both ADP and U44619 were added simultaneously, in low concentrations, to washed platelets without added plasma or fibrinogen, aggregation occurred immediately. Washed platelets were not aggregated by adrenaline, which potentiated ADP-induced aggregation. Several biochemical measurements which are sensitive indicators of cellular damage were normal in washed platelets, including [14C]adenine uptake, adenylate energy charge, hypoxanthine formation and the response of adenylate cyclase to stimulation by PGE1 or PGD2. Platelet coagulant activities were not made available and heparin-neutralizing activity (HNA) was not spontaneously released by the washing procedure, but the washed platelets responded normally to appropriate agents by developing coagulant activities and releasing HNA. The ultrastructure of washed platelets was similar to those in control PRP. Inclusion of apyrase in the first albumin gradient had a beneficial effect on platelet morphology, aggregation and metabolism, but washing at 37degreesC compared with 25degreesC did not. Albumin density gradient separation is a useful method for isolating platelets for aggregation and metabolic studies.

The effects of ATP on platelets: evidence against the central role of released ADP in primary aggregation

The influence of freshly purified ATP on the effects of aggregating agents on human platelets was studied. ATP inhibited aggregation induced by ADP competitively (Ki = 20 muM) and immediately without need for prior incubation. ATP had no effect on primary aggregation induced by adrenaline, thrombin, vasopressin, or 5-hydroxytryptamine (5HT). ATP inhibited the shape change and the consumption of metabolic ATP induced by ADP but did not inhibit these effects when induced by thrombin, vasopressin, or 5HT. ATP counteracted the inhibition by ADP of PGE1-stimulated cyclic AMP production in platelets but did not reduce inhibition by adrenaline. It is concluded that adrenaline, thrombin, 5HT, and vasopressin each can induce primary aggregation of human platelets by a mechanism independent of extracellular ADP.

The interaction of bovine factor VIII with human platelets

Treatment of human platelets with purified bovine Factor VIII caused three types of aggregation: (a) primary agglutination; (b) secondary aggregation involving the platelet release reaction; and (c) super-aggregation, in which the platelets were gathered into only a few large clumps. Removal of calcium ions or treatment with p-hydroxymercuiriphenyl sulfonate blocked the release reaction, but not primary agglutination or super-aggregation. Platelets treated with formalin were not aggregated by ADP, thrombin, or collagen, but were agglutinated by bovine Factor VIII, although they did not show super-aggregation. For malin-treated platelets were agglutinated by phytohemagglutinin P less extensively and less rapidly than by bovine Factor VIII. Treatment of platelets and Factor VIII with neuraminidase released 60 and 53%, respectively, of the sialic acid residues without affecting the agglutination reaction or the procoagulant activity of the Factor VIII. Agglutination was inhibited by high salt concentrations, dextran sulfate, and heparin. During agglutination, both the procoagulant and platelet-agglutinating activities of Factor VIII became bound to the platelet surface.

The role of thrombin in ADP-induced platelet aggregation and release: a critical evaluation

The role of thrombin in ADP-induced aggregation and release in vitro was critically examined. The addition of heparin or hirudin to citrated platelet rich plasma did not prevent aggregation or release. The addition of citrate to heparinized plasma restored secondary aggregation and release. Hirudin did not prevent irreversible aggregation. These results are incompatible with the hypothesis that thrombin is a primary and necessary mediator of platelet aggregation (Ardlie & Han, 1974; Han & Ardlie, 1974a, b, c). This hypothesis is based in part on the assumption that EDTA enhances the elution of clotting factors from platelets; we found no enhanced elution of factors II, V, X, VIII, IX or XI when platelets were washed in EDTA.

Hereditary giant platelet syndrome. Absence of collagen-induced coagulant activity and deficiency of factor-XI binding to platelets

The platelets from two related patients with the hereditary giant platelet syndrome were examined. They were larger than normal but otherwise ultrastructurally normal; they contained increased storage pools of adenine nucleotides and heparin-neutralizing activity and took up serotonin at an increased rate. They aggregated normally with ADP and collagen but failed to aggregate with bovine factor VIII and Ristocetin. Some change in shape occurred with ADP, and the reduction in adenylate energy change after addition of ADP to platelet-rich plasma was smaller than normal. Platelet coagulant activities including contact product forming activity, intrinsic factor-Xa forming activity and platelet factor 3 activity were normal or increased, but collagen-induced coagulant activity was absent whether tested in washed platelet suspensions or platelet-rich plasma. Platelet washing experiments showed decreased binding of factors V and VIII to hereditary giant platelets and no detectable factor XI in washed platelet suspensions. It is concluded that (1) the hereditary giant platelets studied lacked a binding mechanism for factors, V, VIII and XI; (2) the normal development of collagen-induced coagulant activity apparently depends upon the binding of factor XI to the platelet membrane; and (3) the defective prothrombin consumption observed in these patients may have resulted from the failure of their platelets to bind factor XI.

The influence on platelet aggregation of drugs that affect the accumulation of adenosine 3':5'-cyclic monophosphate in platelets

1. The involvement of intracellular 3':5'-cyclic AMP in the inhibition of platelet aggregation by prostaglandin E(1), isoprenaline and adenosine has been examined by a radiochemical technique. Platelet-rich plasma was incubated with radioactive adenine to incorporate (14)C radioactivity into platelet nucleotides. Pairs of identically treated samples were taken, one for the photometric measurement of platelet aggregation induced by ADP, the other for estimation of the radioactivity of 3':5'-cyclic AMP. 2. Theophylline, papaverine, dipyridamole and 2,6-bis-(diethanolamino)-4-piperidinopyrimido[5,4d]pyrimidine (compound RA233) were found to inhibit 3':5'-cyclic AMP phosphodiesterase from platelets. At concentrations of 3':5'-cyclic AMP greater than 50mum the most active inhibitor was dipyridamole; at 3':5'-cyclic AMP concentrations less than 19mum, papaverine and compound RA233 were more active than dipyridamole. 3. In the presence of compound RA233 (50mum), the effectiveness of prostaglandin E(1) as an inhibitor of platelet aggregation was increased tenfold. Compound RA233 also increased the stimulation by prostaglandin E(1) of the incorporation of radioactivity into 3':5'-cyclic AMP. 4. Compound RA233 (50mum) increased the effectiveness of both adenosine and 2-chloroadenosine as inhibitors of aggregation by 70-100-fold, and in the presence of compound RA233 both adenosine and 2-chloroadenosine stimulated the incorporation of radioactivity into 3':5'-cyclic AMP; the extent of the stimulation was proportional to the logarithm of the nucleoside concentration. 5. Compound RA233 (100-500mum) inhibited platelet aggregation by itself and caused small increases in the radioactivity of 3':5'-cyclic AMP. Partial positive correlations were found between the radioactivity of 3':5'-cyclic AMP in platelets measured at the time of addition of the aggregating agent (ADP) and the extent to which the aggregation was inhibited. 6. The results are interpreted as indicating that adenosine, 2-chloroadenosine, isoprenaline, prostaglandin E(1) and drugs that inhibit platelet 3':5'-cyclic AMP phosphodiesterase all inhibit aggregation by a common mechanism involving intracellular 3':5'-cyclic AMP.

The release of nucleotides, 5-hydroxytryptamine and enzymes from human blood platelets during aggregation

1. Adenosine diphosphate (ADP) and adrenaline caused the aggregation of human platelets suspended in plasma containing citrate anticoagulant and stirred at 37 degrees C. The aggregation occurred in two phases and the second phase was associated with the appearance in the plasma of up to 30% of the ATP and 55% of the ADP present in the platelets. The concentration of ADP appearing in the plasma was up to 7 times the concentration added.2. Radioactivity was released by ADP and by adrenaline from platelets labelled with radioactive 5-hydroxytryptamine; this release was closely correlated with the second phase of aggregation and with the release of nucleotides.3. Acid phosphatase, beta-glucuronidase and adenylate kinase were released to a small extent during second phase aggregation by ADP or adrenaline; thrombin and collagen particles caused significantly greater release of beta-glucuronidase than of either acid phosphatase or of adenylate kinase.4. Morphological changes indicating degranulation of the platelets were observed during the second phase of aggregation produced by adrenaline and by ADP.5. The second phase of aggregation, degranulation of platelets, and the release of nucleotides, of labelled 5-hydroxytryptamine and of enzymes, were all inhibited by concentrations of amitriptyline which did not inhibit aggregation.

Effects of adrenaline on human blood platelets

1. Adrenaline at concentrations too low to cause aggregation of human platelets potentiates the aggregation by adenosine diphosphate. Noradrenaline has the same effect but is less active than adrenaline; isopropylnoradrenaline is inactive or inhibitory.2. The potentiation of adenosine diphosphate by catecholamines is blocked by the adrenergic alpha-receptor antagonists phentolamine and dihydroergotamine but not by 2-halogenoethylamines or by adrenergic beta-receptor antagonists.3. Both the first and second phases of adenosine diphosphate aggregation are potentiated by catecholamines but the second phase more than the first.4. The release from the platelets of adenine nucleotides which is associated with the second phase of aggregation is also increased by adrenaline.

The adenylate kinase of human plasma, erythrocytes and platelets in relation to the degradation of adenosine diphosphate in plasma

1. Adenylate kinase (EC 2.7.4.3) has been shown to be present in human plasma obtained by conventional means and the adenylate-kinase activities of plasma and of lysed and intact human platelets and erythrocytes have been measured at 37 degrees by sensitive spectrophotometric methods. 2. The activities found in plasma ranged from 2.7 to 22.9mumoles of ADP formed/min./l. and in lysed platelets and lysed erythrocytes mean values of 0.79 and 12.0mumoles of ADP formed/min./10(9) cells respectively were found. Intact platelets and erythrocytes showed little or no activity. 3. The apparent K(m) of plasma adenylate kinase for ADP was found to be 1.4-1.6mm. 4. The adenylate-kinase activity of plasma was correlated with the free haemoglobin present and the larger part of the activity could be accounted for by haemolysis occurring either during the withdrawal of the blood or in vivo. 5. Aggregation of platelets by ADP, collagen fibres or thrombin released up to 16% of the platelet adenylate kinase into the suspending medium. 6. Measurement of the rate of breakdown of 1.6mum-ADP in plasma gave values of about 0.1mmu-mole/min./ml. This was not increased by addition of sufficient erythrocyte lysate to increase the activity of plasma adenylate kinase five to ten times. 7. It was concluded that the activity of adenylate kinase found in plasma, even after aggregation of the platelets, is insufficient to account for the rate of breakdown of low concentrations of ADP usually observed, and that another enzyme is responsible for this process.