Small bowel gastrointestinal stromal tumor presenting with gastrointestinal bleeding in patient with type 1 Neurofibromatosis: Management and laparoscopic treatment. Case report and review of the literature.

INTRODUCTION AND IMPORTANCE: Gastrointestinal stromal tumor (GIST) is the most common mesenchymal neoplasm of the gastrointestinal tract. It may be asymptomatic; nevertheless, gastrointestinal bleeding is the most frequent symptom, due to mucosal erosion. Its poor lymph node metastatic spread makes GIST often suitable of minimally invasive surgical approach. The importance of this study is to increase the awareness among physicians about this condition in particular scenarios as in our case and to stress the role of laparoscopic surgery. CASE PRESENTATION: A 74-year-old female patient presented to the emergency department with hematemesis, followed by haematochezia and melena. The patient had a medical history of type 1 Neurofibromatosis (NF1). She underwent, after CT scan, esophagogastroduodenoscopy, and endoscopic haemostasis. Finally, we performed a laparoscopic resection of a mass of the first jejunal loop. The postoperative period was predominantly uneventful. Pathological examination confirmed a low-risk GIST. CLINICAL DISCUSSION: Proximal jejunal GIST may cause an upper and lower gastrointestinal bleeding. A multidisciplinary team approach is mandatory for the correct management of this disease and its complications (bleeding). GISTs are indicated as the most commonly gastrointestinal NF1 associated tumours. In case of localised and resectable GIST surgical treatment is the mainstay and laparoscopic surgery is a valid alternative. CONCLUSION: In case of abdominal bleeding mass in a NF1 patient, it is important to keep in mind the well-known association between NF1 and GIST to facilitate the diagnosis and to quickly perform the appropriate treatment. Laparoscopic approach is safe and effective if the oncological radicality is respected.

Aggregation-related association of lipid with the cytoskeleton of rabbit and human platelets prelabeled with [3H]palmitic acid. Similar effects of adenosine diphosphate- and thrombin-induced aggregation.

To investigate the association of lipid with the cytoskeleton of platelets during aggregation, rabbit and human platelets were isolated and labeled with [3H]palmitic acid; lipid extraction showed approximately 80% in phospholipid. Limited aggregation was induced with ADP or thrombin, and the cytoskeleton was isolated after lysis with 1% Triton X-100, 5 mM EGTA. Cytoskeleton from unactivated platelets had approximately 0.03% of the total label in the platelets, but after aggregation with ADP (2 microM) or thrombin (0.1 U/ml) for 20-30 s, 1.5-8% of the label was with the cytoskeleton. Fibrinogen enhanced aggregation and the association of label with the cytoskeleton; incorporation of label increased exponentially as aggregation proceeded, decreased exponentially during deaggregation, and appeared to be related to the number of sites of contact. Inhibitors that increase cyclic AMP inhibited aggregation and cytoskeletal labeling, but aspirin had no effect. Some experiments were done with DNase I and Ca2+ in the Triton X-100 lysis medium to cause actin depolymerization, under conditions in which the Ca2+-dependent protease activity was inhibited. This greatly reduced the association of label with the cytoskeleton at early time points, but when aggregation had proceeded further, a large proportion of the label was not dissociated by this treatment. These findings, electron microscopy, and the enrichment of the cytoskeleton of aggregated platelets with only some of the membrane proteins that were labeled by the 125I-lactoperoxidase method, indicated that with limited aggregation, the 3H-labeled lipid was mainly associated with the cytoskeleton and not with trapped membrane fragments resulting from incomplete lysis. Since the pattern of cytoskeleton labeling ([3H]palmitate) and the selective association of some membrane proteins with the cytoskeleton/lipid complex was the same with ADP and thrombin, the reactions must be dependent on aggregation and not on events associated with the release of granule contents.

Changes in depressive symptoms as AIDS develops. The Multicenter AIDS Cohort Study.

OBJECTIVE: The authors sought to determine whether rates of depressive symptoms change from early- to late-stage HIV-1 infection and to determine the predictors of depressive symptoms as AIDS develops. METHOD: The data for this study were from 911 HIV-seropositive men-community volunteers from four U.S. cities-who entered the 10-year Multicenter AIDS Cohort Study without a diagnosis of AIDS and subsequently developed AIDS. The subjects underwent semiannual follow-ups during the study period. The outcome measures-overall depressive symptoms, nonsomatic depressive symptoms, syndromal depression, and severe depression-were assessed over the 5 years before and the 2 years after AIDS diagnosis from responses on the Center for Epidemiologic Studies Depression Scale (CES-D Scale). RESULTS: Depressive symptoms were stable over time from month 60 to month 18 before AIDS developed. However, beginning 12-18 months before AIDS diagnosis, there was a significant rise in all measures of depression, which reached a plateau within 6 months before AIDS developed. At this plateau, there was a 45% increase in mean CES-D Scale scores above baseline. An elevated CES-D Scale score in the earlier stages of infection, a self-report of AIDS-related symptoms (such as rash and lymphadenopathy), concurrent unemployment, cigarette smoking, and limited social supports were consistent predictors of higher rates of depression as AIDS developed. CONCLUSIONS: There is a dramatic, sustained rise in depressive symptoms as AIDS develops, beginning as early as 18 months before clinical AIDS is diagnosed. Prior depression, HIV-disease-related factors, and psychological stressors contribute to this rise. This robust phenomenon invites further characterization.

Agglutination of rabbit platelets in plasma by the thrombin inhibitor D-phenylalanyl-L-prolyl-L-arginyl chloromethyl ketone.

The specific thrombin inhibitor D-phenylalanyl-L-prolyl-L-arginyl chloromethyl ketone (FPRCH2Cl, PPACK) has been used as an anticoagulant with human blood to permit the preparation of platelet-rich plasma in which the physiological concentration of Ca2+ is maintained. When we attempted to use FPRCH2Cl (40 microM) as an anticoagulant for rabbit blood, clotting was prevented for at least 6 h at room temperature, but nearly all the platelets agglutinated. Thromboxane B2 was not formed and indomethacin and prostaglandin E1 were not inhibitory. The presence of citrate delayed this agglutination, but only EDTA (not EGTA) prevented it, indicating a dependence on Mg2+. Addition of FPRCH2Cl to suspensions of rabbit platelets in Tyrode-albumin solution had no effect on responses to ADP or collagen, but completely blocked all responses to human or rabbit thrombin. Thus plasma is required for the agglutination. Intravenous injection of FPRCH2Cl (5 mg/3 kg rabbit) reduced the platelet count to less than 50% by 15 to 25 min. Thus FPRCH2Cl cannot be used as an anticoagulant for rabbit blood when platelets are to be examined, and has a profound effect on the platelet count in vivo in rabbits. These effects should be considered when FPRCH2Cl is used as an antithrombotic agent for in vivo experiments with rabbits.

Effect of the concentration of Ca2+ in the suspending medium on the responses of human and rabbit platelets to aggregating agents.

The effect of the concentration of Ca2+ in the suspending medium of human and rabbit platelets on aggregation, release of 14C-serotonin, and TXB2 formation in response to ADP, thrombin, 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (PAF), collagen and arachidonic acid was studied in either platelet-rich plasma anticoagulated with D-phenylalanyl-prolyl-arginyl chloromethylketone (PPACK) or citrate, or suspensions of washed platelets in modified Tyrode-albumin solutions containing 1 mM Mg2+ and concentrations of added Ca2+ ranging from 0 to 5 mM. In response to ADP, thrombin, or PAF, human platelets were stimulated to form TXA2 by close platelet contact in a low-Ca2+ medium; at physiological concentrations of Ca2+, TXB2 formation was much less and declined progressively as the concentration of Ca2+ was raised. When the formation of TXA2 was blocked with aspirin or indomethacin, aggregation and release by human platelets were strongest at physiological concentrations of Ca2+. Rabbit platelet responses differed markedly from those of human platelets because close contact of rabbit platelets in a low-Ca2+ medium did not promote TXA2 formation. Rabbit platelet responses were more strongly inhibited by the lack of added Ca2+ in the medium than the responses of human platelets, possibly because rabbit platelets do not contain releasable Ca2+. In all studies of human platelets in media with low concentrations of Ca2+, the additional contribution to platelet responses of TXA2 formed because of close platelet contact should be considered because TXA2 formation is not usually stimulated in this way at physiological concentrations of Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of tris on responses of human and rabbit platelets to aggregating agents.

Despite reports that Tris [tris (hydroxymethyl)aminomethane] affects platelets, it is often used to buffer suspending media. Human or rabbit platelets were washed and resuspended in Tyrode solution containing apyrase and 0.35% albumin. Addition of 15 mM Tris partially inhibited primary aggregation induced by 10 microM ADP and inhibited aggregation and release of 14C-serotonin from prelabelled platelets stimulated with low concentrations of thrombin (0.05-0.2 U/mL), or collagen. Platelets resuspended in 15 mM Tris, 0.15 M NaCl, 0.35% albumin, pH 7.5, did not aggregate in response to 10 microM ADP whereas platelets in Tyrode-albumin aggregated extensively. Ca2+ (5 mM) did not overcome the inhibition of thrombin-induced aggregation. Tris (15 or 1.5 mM) potentiated aggregation and release induced by sodium arachidonate (20-50 microM) or the ionophore A23187 (0.6-1 microM). Pretreatment of platelets with aspirin did not prevent potentiation by A23187, indicating that it is not mediated through activation of the arachidonate pathway. The inhibitory and potentiating effects of Tris are similar to those of amino sugars, lysine, arginine and primary amines such as methylamine and cadaverine, and may represent general effects of amines on platelets. Potentiation of the effects of some aggregating agents and inhibition of others re-emphasizes the concept that there are several different mechanisms through which aggregation can occur. Tris-based buffers are unsuitable for platelet suspending media and their use as solvents for aggregating agents or inhibitors should be limited.

Effect of cAMP phosphodiesterase inhibitors on ADP-induced shape change, cAMP and nucleoside diphosphokinase activity of rabbit platelets.

The effects of cAMP phosphodiesterase inhibitors on ADP-induced shape change and cAMP concentrations have been studied. Caffeine (10 mM), theophylline (8 mM), dipyridamole (0.2 mM), or papaverine (0,05 mM) prevented the shape change of washed rabbit platelets induced by 0.4 microM ADP. At these concentrations, none of these cAMP phosphodiesterase inhibitors increased 14C-cAMP in platelets in which the cytoplasmic adenine nucleotides had been labelled with 14C-adenine. By a protein binding assay, only papaverine by itself increased platelet cAMP above its basal level. These results indicate that two pools of cAMP may exist in platelets. Both methods showed that stimulation of platelet adenylate cyclase with PGE1 (1 microM) resulted in an increase in platelet cAMP and all these cAMP phosphodiesterase inhibitors potentiated this increase caused by PGE1. By themselves, some of these compounds may act through mechanisms that do not involve platelet cAMP. The effects of these cAMP phosphodiesterase inhibitors on platelet nucleoside diphosphokinase (NDK) activity were also investigated. At concentrations that prevented ADP-induced shape change, papaverine and dipyridamole had no effect on the formation of 14C-ATP from 14C-ADP by washed rabbit platelets. The methylxanthines partially inhibited NDK activity of washed rabbit platelets and of isolated platelet membranes, probably due to the structural similarity between the adenine ring of ADP and these substances. However, adenine (8 mM) inhibited ADP-induced shape change and platelet NDK activity but was a less effective inhibitor of ADP-induced platelet aggregation. Thus it seems unlikely that interference with platelet NDK or the ADP receptor is the major mechanism by which the methylxanthines inhibit platelet functions.

Degranulation of human platelets by the thrombin receptor peptide SFLLRN: comparison with degranulation by thrombin.

A new, simplified method of degranulating human platelets using the thrombin receptor peptide SFLLRN (20 microM) is described; released fibrinogen cannot be converted to fibrin, and the platelets are not exposed to a proteolytic enzyme, as they are when thrombin is used for degranulation. The peptide-degranulated platelets regain their disc shape and are recovered as single platelets which have released approximately 90% of the contents of their dense granules. Their procoagulant activity is greater than that of control platelets, but somewhat less than that of thrombin-degranulated platelets. Without added fibrinogen, the peptide-degranulated platelets aggregate slightly in response to 50 microM SFLLRN, and to collagen, arachidonic acid, the thromboxane A2 mimetic U46619, platelet activating factor, ADP, and the divalent cation ionophore A23187; added fibrinogen enhances aggregation caused by these agonists. Extensive aggregation of peptide-degranulated platelets is caused by thrombin in the absence of added fibrinogen; it may be that the alternative thrombin receptor that is not activated by SFLLRN is responsible for the strong response to thrombin. Aggregation responses to most of the agonists are greater than those observed previously with thrombin-degranulated platelets. By this method, platelets are obtained that have been degranulated in a way that is similar to in vivo degranulation. They are useful for studies of platelet responses without the complicating effects of released granule contents, and for investigation of the characteristics and functions of platelets that have come in contact with release-inducing agents in vivo.

Reactions of polylysine with human platelets in plasma and in suspensions of washed platelets.

The effects of polylysine on human platelets have been examined in citrated platelet-rich plasma (PRP) and in suspensions of washed platelets in various media. In PRP, polylysine caused aggregation after a lag phase. Heparin inhibited this completely. At certain concentrations of polylysine, two phases of aggregation occurred, the second being associated with release of 14C-serotonin from prelabelled platelets; this phase was inhibitable with prostaglandin E1, acetylsalicylic acid, sulphinpyrazone, adenosine, apyrase, or creatine phosphate/creatine phosphokinase. Polylysine-induced release also occurred in PRP with EDTA or hirudin as anticoagulant. In suspensions of washed platelets in Tyrode solution containing 0.35% or 4% albumin, or 1% gelatin, polylysine caused immediate platelet-to-platelet adherence and very little release of 14C-serotonin or platelet lysis. Heparin inhibited aggregation, but acetylsalicylic acid, prostaglandin E1, adenosine, apyrase, creatine phosphate/creatine phosphokinase or EDTA did not. In a modified Tyrode-albumin medium containing 1 mM magnesium but no calcium, polylysine-induced aggregation was associated with the release of 14C-serotonin which could be inhibited by acetylsalicylic acid or indomethacin; this is similar to the effect of ADP in this medium. In Tyrode solution without albumin or gelatin, polylysine-induced platelet aggregation was associated with release of a large percentage of 14C-serotonin, together with as much as 18% lysis; indomethacin inhibited this release reaction.

Effects of plasmin on rabbit platelets.

The effects of plasmin have been examined because platelets may be exposed to plasmin in vivo and treatment of platelets with plasmin shortens platelet survival. Rabbit plasmin was prepared by urokinase activation of plasminogen immobilized on lysine-Sepharose. Plasmin caused rabbit platelets to aggregate and release the contents of their amine storage granules, but aggregation was slower than in response to ADP or thrombin. EDTA, prostaglandin E1, or creatine phosphate/creatine phosphokinase were inhibitory, but indomethacin was not. Deaggregation did not occur when platelets had been aggregated by a concentration of plasmin that caused extensive release of granule contents. EDTA or prostaglandin E1 caused deaggregation. Low concentrations of ADP and plasmin acted synergistically in causing platelet aggregation. Plasmin decreased the amounts of platelet membrane glycoproteins that stained with periodic acid-Schiff reagent; glycoprotein I was more susceptible than glycoprotein II and III. Concentrations of plasmin that induced the release of amine storage granule contents also released PAS-staining granule glycoproteins. Platelets incubated with plasmin, washed and resuspended, were not aggregated by ADP, but were aggregated strongly by the combination of fibrinogen and ADP, and bound 125I-fibrinogen to a greater extent than untreated platelets. Platelets preincubated with a high concentration of plasmin were unresponsive to thrombin, but were sometimes aggregated by fibrinogen. Plasmin decreased the buoyant density and increased the median size of platelets. Thus plasmin, as well as ADP and thrombin, may contribute to the density shift observed in platelets from rabbits in which thrombosis and continuous vessel injury have been induced.

Characteristics of thrombin-degranulated human platelets: development of a method that does not use proteolytic enzymes for deaggregation.

A method has been developed for preparing suspensions of washed human platelets that have lost as much as 90% of their dense granule and alpha granule contents as a result of stimulation by thrombin (0.9 U/ml for 3 min at 37 degrees C), and recovering the platelets without using a proteolytic enzyme. Glycyl-L-prolyl-L-arginyl-L-proline (GPRP) was used to prevent polymerization of released fibrinogen and arginyl-glycyl-aspartyl-serine (RGDS) to block the interaction of released fibrinogen, vWf or fibronectin with the glycoprotein IIb/IIIa complex. The thrombin used to degranulate the platelets was neutralized with D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (FPRCH2Cl) and prostaglandin E1 was added to return the platelets towards a disc shape. The degranulated platelets aggregated in response to ADP, platelet activating factor, arachidonate and the thromboxane A2 mimetic, U46619 in the presence of added fibrinogen; the platelets changed shape but did not aggregate in response to collagen. Thrombin and the calcium ionophore, A23187, caused aggregation without added fibrinogen. Synergism between pairs of aggregating agents at low concentrations was observed. Little TXB2 was formed when the platelets were reaggregated by thrombin. RGDS and F(ab')2 fragments of an antibody to fibrinogen inhibited reaggregation induced by thrombin and A23187 indicating that small amounts of fibrinogen at the platelet surface may support aggregation by strong agonists. Adherence of thrombin-degranulated platelets to a collagen-coated surface was less than for controls, but spreading was more extensive. Electron-microscopic immunogold cytochemistry with anti-human fibrinogen IgG showed numerous gold particles in platelet vacuoles.(ABSTRACT TRUNCATED AT 250 WORDS)

Palmitic acid-labeled lipids selectively incorporated into platelet cytoskeleton during aggregation.

Previous experiments showed that during the early stages (20-30 seconds) of aggregation induced by adenosine diphosphate (ADP, 2 microM) or thrombin (0.1 U/mL) of rabbit or human platelets prelabeled with [3H]palmitic acid, labeled lipid became associated with the cytoskeleton isolated after lysis with 1% Triton X-100, 5 mM EGTA [ethylene glycol-bis-(beta-aminoethyl ether)]-N,N,N',N'-tetra-acetic acid. The association appeared to be related to the number of sites of contact and was independent of the release of granule contents. We have now investigated the nature of the labeled lipids by thin-layer and column chromatography and found differences between the distribution of the label in intact platelets (both stimulated and unstimulated) and the isolated cytoskeletons. In both species, and with either ADP or thrombin as aggregating agent, 70-85% of the label in both intact platelets and in the cytoskeletons was in phospholipids. The distribution of label among the phospholipids in the cytoskeletons was similar to that in intact platelets except that the percentage of label in phosphatidylcholine was significantly higher in the cytoskeletons of human platelets than in the intact platelets, and the percentage of label in phosphatidylserine/phosphatidylinositol was significantly lower in the cytoskeletons of rabbit platelets and thrombin-aggregated human platelets than in intact platelets. The cytoskeletons contained a lower percentage of label in triacylglycerol, diacylglycerol, and cholesterol ester than the intact platelets. Contrary to a report in the literature, we found no evidence for the incorporation of diacylglycerol and palmitic acid into the cytoskeleton.(ABSTRACT TRUNCATED AT 250 WORDS)

Incorporation of lipids labeled with various fatty acids into the cytoskeleton of aggregating platelets.

Earlier studies showed that during the first 20 to 25 seconds of aggregation induced by thrombin (0.1 U/mL) or adenosine diphosphate (ADP) (2 microM) of rabbit or human platelets prelabeled with [3H]palmitic acid, labeled lipid became associated with the cytoskeleton (isolated after lysis with 1% Triton X-100, 5 mM EGTA [ethylene glycolbis-(beta-aminoethyl ether(N,N,N',N'-tetraacetic acid] in the presence of 0.5 mM leupeptin and 50 mM benzamidine). In comparison with labeled lipid in intact platelets, the labeled lipid that was associated with the cytoskeleton was enriched in phospholipids and ceramide. To determine whether these effects were specific for lipids labeled with palmitic acid, we studied rabbit platelets in which lipids had been labeled by incubation of the platelets with pairs of 14C- or 3H-labeled palmitic, stearic, arachidonic, and linoleic acids. Examination of the distribution of label among the lipid classes of intact platelets showed that phospholipids contained most of the label. Under the conditions of limited, thrombin-induced aggregation used, labeled lipids were not lost from the platelets and the distribution of label among the lipid classes was essentially unchanged. There were major differences in the incorporation of labeled lipids into the cytoskeleton. The greatest incorporation (2.1 to 2.8% of the label in the platelets) was observed with palmitic acid-labeled lipids; by direct comparison, only 44% as much of the label of stearic acid-labeled lipids, 21% as much of the label of linoleic acid-labeled lipids, and only 6% as much of the label of arachidonic acid-labeled lipids was incorporated into the cytoskeleton.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cephalothin and penicillin G on platelet function in vitro.

High concentrations of cephalothin or penicillin G inhibit a number of the functions of human or rabbit platelets in citrated platelet-rich plasma (PRP) and in suspensions of washed platelets. The reactions shown to be inhibited are: ADP-induced shape change and the primary and secondary phases of aggregation and release induced by ADP or adrenaline in human cirtated PRP; release and aggregation of washed human platelets exposed to collagen, thrombin, vasopressin, or the ionophore A 23,187; aggregation of washed human platelets exposed to phytohaemagglutinin from Phaseolus vulgaris (PHA) or polylysine; release induced by concanavalin A or PHA in suspensions of washed platelets from rabbits; platelet adherence to a collagen-coated surface or to the damaged intimal surface of the rabbit aorta; platelet factor 3 availability; lysis of rabbit platelets by an antiserum directed against them; and clot retraction. Neither antibiotic affected serotonin-induced aggregation; a high concentration of cephalothin slightly inhibited the initial rate of serotonin uptake. Penicilloic acid showed about half the inhibitory effect of penicillin G on ADP-induced aggregation. In citrated human platelet-rich plasma, ampicillin and oxacillin inhibited ADP-induced aggregation to the same extent as similar concentrations of penicillin G; in suspensions of washed platelets, however, ampicillin was less inhibitory than penicillin G or oxacillin. Platelet ultrastructure, assessed by transmission electron microscopy, was not visibly altered. Evidence that the antibiotics become bound to platelets is the finding that platelets incubated with the antibiotics ans resuspended in fresh media showed less response to aggregating agents compared with control platelets. Penicillin G and related antibiotics may be inhibitory because they coat the platelet surface. Their effects on platelet functions are probably responsible for excessive bleeding and increased bleeding times observed in patients and volunteers receiving high doses of these antibiotics.

Duration of the effect of aspirin on the synthesis of thromboxane by density subpopulations of rabbit platelets stimulated with thrombin.

The controversy concerning the relationship between platelet buoyant density and platelet age is unresolved. Our earlier results with rabbit platelets indicate that the most-dense subpopulations are enriched in young platelets and that some platelets become less dense as they age. Other investigators have concluded that platelets either do not change in density upon aging or become more dense. In the present experiments, rabbit platelets were separated on discontinuous gradients of Stractan. Most-dense platelets synthesized significantly more thromboxane B2 (TXB2) (1.27 ng per 10(6) platelets) in response to thrombin (0.75 U/mL) than did least-dense platelets (0.70 ng per 10(6) platelets), indicating that the arachidonate pathway in most-dense platelets is more active than in least-dense platelets. After aspirin administration to rabbits, most-dense platelets recovered their ability to synthesize thromboxane B2 significantly more quickly than did least-dense platelets. Because the platelet cyclooxygenase that is responsible for TXB2 formation is permanently inhibited by aspirin, it is only the new platelets entering the circulation that will be able to form TXB2. These results indicate that, at least in rabbits, the most-dense platelets are enriched in young platelets, and that platelets decrease in density as they age in the circulation.

Platelet sialic acid and platelet survival after aggregation by ADP.

Some investigators have reported recently that platelet surface sialic acid is decreased during ADP-induced aggregation, whereas others have reported an increase. Since removal of sialic acid from the platelet surface shortens platelet survival, we have determined the survival of platelets that have been aggregatad by ADP. We have also measured the amount of sialic acid in the suspending fluid of platelets after ADP-induced aggregation. ADP-induced aggregation did not cause the loss of sialic acid from rabbit platelets (which do not undergo a release reaction in response to ADP) nor from washed human platelets in a medium containing physiologic concentrations of calcium in which granule contents are not released. In a medium without added calcium, ADP caused the release of 14C-serotonin (42.5% +/- 3%) from human platelets, but less than 4% of the sialic-acid-containing material was released. It seems likely that little of the releasable sialic acid of platelets is in the dense granules or the alpha-granules. Thrombin (5 U/ml) released 90.0% +/- 3.4% of the serotonin from human platelets but only 20.6% +/- 7.4% of the total sialic-acid-containing material. Neuraminidase removed 42.3% of the total sialic acid, presumably from the platelet surface. Rabbit platelets that had been aggregated by ADP and deaggregated survived normally when returned to the circulation. This observation also provides evidence that they had not lost membrane sialic acid during aggregation and deaggregation.

The use of the synthetic peptide, Gly-Pro-Arg-Pro, in the preparation of thrombin-degranulated rabbit platelets.

The method for preparing thrombin-degranulated platelets has been modified to avoid the use of plasmin or successive treatments with small amounts of thrombin, while still achieving more than 90% release of platelet amine storage granule contents. It was necessary to prevent the fibrinogen released from the platelets during thrombin treatment from forming an insoluble fibrin mesh that could trap the platelets and hinder their deaggregation. To accomplish this we have treated rabbit platelets with 0.73 U/ml of thrombin for 1 min in the presence of the synthetic peptide, Gly-Pro-Arg-Pro, which prevents the polymerization of fibrin molecules. We have demonstrated that it also prevents 125I, initially added as 125I-fibrinogen, from associating with the platelets in a form that was not removed by centrifuging and washing during the preparation of thrombin-degranulated platelets, and we infer that products formed from the fibrinogen released from the platelets would also be prevented from associating with them. Thrombin-degranulated platelets prepared by this method have lost 92% of their granule contents and they can be washed and resuspended. These platelets aggregate normally upon stimulation with thrombin, adenosine diphosphate (ADP), or arachidonate. Thus, Gly-Pro-Arg-Pro is useful in preparing thrombin-degranulated platelets for studying platelet reactions without the complicating effects of released materials such a ADP and fibrinogen.

Changes in serum lipoprotein(a) in hyperlipidemic subjects undergoing long-term treatment with lipid-lowering drugs.

Though the exact physiology and pathology of lipoprotein(a) [Lp(a)] remains unknown, it has been demonstrated that increased serum Lp(a) levels are correlated with an increased risk of atherosclerotic vascular disease. The effects of lipid-lowering drugs on Lp(a) levels is unclear because of inconsistencies between study designs. This study analyzes the effects of the commonly used lipid-lowering drugs pravastatin (PRAV), lovastatin (LOV), and cholestyramine (CHOL) on serum Lp(a) and other serum lipid levels in a parallel study design. Hyperlipidemic men (n = 32) were enrolled from three centers and treated for 48 weeks in a multicenter clinical trial using PRAV, LOV, CHOL, or a placebo (for the first 16 weeks only). Baseline serum low-density lipoproteins (LDL-C), high-density lipoproteins (HDL-C), and triglycerides were 199 +/- 38, 40 +/- 9, and 160 +/- 70 mg/dl, respectively. At the end of 48 weeks, serum plasma LDL-C declined in patients randomized to PRAV, LOV, and CHOL, respectively, by 31%, 29%, and 23% (all p < 0.001); HDL increased by 4%, 11%, and 11% (all p < 0.001); and TG changed by -16%, -28%, and +43% (all p < 0.001). Subjects in PRAV and LOV changed Lp(a) by 9% and 3%, respectively. Although there was an initial Lp(a) decline in the first 8 weeks of CHOL therapy (p < 0.05, ANOVA), this returned to baseline after 48 weeks. In this parallel study design PRAV, LOV, and CHOL are effective LDL-lowering medications with minimal effects on plasma Lp(a).