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Biomedical subjects

G Escolar

Publications and source records attributed to G Escolar.

At least 181 records · Page 10Linked to original sources
PubMed1986

Epinephrine reverses the inhibitory influence of aspirin on platelet-vessel wall interactions.

The effect of in vitro aspirin treatment and alpha adrenergic receptor stimulation on the interaction of platelets with the subendothelium was studied using citrated human blood obtained from normal control donors. Reconstituted blood following drug treatment was circulated through a chamber which housed everted segments of deendothelialized rabbit aorta. The wall shear rate was 800 sec-1. Surface coverage of platelets were morphometrically evaluated. Aspirin treatment significantly reduced platelet thrombi on exposed subendothelium. However, platelet spreading was increased. There was no significant difference in the total percent coverage of platelets in the vascular surface between the aspirin treated group and normal controls. Epinephrine exposure of aspirin treated platelets completely reversed the effect of alterations induced in platelet behavior by aspirin. Epinephrine exposed aspirin treated platelets had as many platelet thrombi on exposed subendothelium as normal control platelets. In addition, epinephrine treatment decreased the spreading of aspirin treated platelets on the vascular surface. Results of the present study and our earlier findings suggest that the epinephrine induced membrane modulation may be a major mechanism for protecting the hemostatic role of platelets after their function is compromised in vivo and in vitro. The failure of aspirin to offer significant protection in many clinical trials may be due to the presence of a salvage pathway in platelets provided by the mechanism of membrane modulation.

Aspirin↗
PubMed1986

Platelet activation induced by a human neuroblastoma tumor cell line is reduced by prior administration of ticlopidine.

Ticlopidine (250 mg twice daily) was administered to human volunteers for seven days and the response of their heparinized platelet-rich plasma to SKNMC (ADP-dependent) human neuroblastoma cells was examined. The first wave of platelet aggregation, characteristic of ADP-dependent human tumor cell lines, was completely abolished but was replaced by a lag period prior to the onset of aggregation. In the Baumgartner perfusion apparatus there was a marked inhibition in the thrombus generated by the presence of SKNMC cells with a concomitant increase in the percentage of surface coverage. These results suggest that the administration of ticlopidine could be useful to prevent some of the steps of metastatic dissemination in which activated platelets may play a role.

Adenosine Diphosphate↗
PubMed1986

Development of a computer program to analyze the parameters of platelet-vessel wall interaction.

The use of the Baumgartner perfusion system allows the morphometric quantification of platelets interacting with vessel wall, however it presents the basic difficulties of morphometrical measurements. In order to facilitate the procedure of evaluation we developed a semiautomated method to avoid the complexity of the classical evaluation. Our system consists on an optical picture analysis system connected with a specially developed computer program which allows fast quantification. Simultaneously to the outlining of interacting platelets the computer program recognizes, corrects, selects and stores the information, in order to perform the final calculations as previously established. This system has been demonstrated to be as effective as the classical morphometric evaluation in the measure of platelets interacting with subendothelium. Potential sources of error such as subjectivity of the observers in selecting the class of interacting platelets are avoided. The use of this combined method opens the possibility to adapt the Baumgartner perfusion system to clinical routine and to the screening of drugs that modify platelet adherence.

Animals↗
PubMed1986

Organization of the actin cytoskeleton of resting and activated platelets in suspension.

The present study has employed lysine, phalloidin, and a low concentration of osmic acid to protect the actin cytoskeleton of resting and thrombin-activated platelets during detergent extraction and fixation in suspension. Thin sections of resting platelets revealed a fine amorphous layer containing a few short actin filaments mimicking discoid shape and a randomly dispersed network of actin polymers in the cytoplasm. Following thrombin activation, the cytoskeleton consisted of a peripheral layer of submembrane actin filaments following the contour of shape change, a variable number of filaments in peripheral cytoplasm and extending into pseudopods, and a concentric mass of actin filaments with constricted microtubule rings in cell centers. Prior treatment with cytochalasin B (CB) appeared to reduce the number of actin filaments in resting platelets. Thrombin activation of CB-treated cells resulted in separation of actin filaments, which became concentrated in cell centers, from microtubule coils remaining at the cell periphery. The appearance of detergent-extracted cytoskeletons of platelet actin protected during fixation in suspension by lysine and phalloidin was remarkably similar to that of resting or CB-treated platelets before and after thrombin activation when viewed in conventionally prepared thin sections without exposure to detergent during fixation. The advantage of the new procedure is revelation of the actin filament organization in suspended platelets, which is obscured by the usual glutaraldehyde-osmic acid fixation technique.

Actins↗
PubMed1986

Defective platelet adhesion on vessel subendothelium in uremic patients.

Bleeding time, platelet retention on glass beads, and ristocetin-induced platelet agglutination (RIPA) in platelet-rich plasma were simultaneously determined for 20 patients with chronic renal failure and previous hemorrhagic history. In seven patients chosen at random out of a group of 16 in whom the three tests were abnormal, RIPA of uremic-isolated platelets in presence of normal platelet-poor plasma (PPP) and of normal platelets in presence of patient PPP were performed. In all cases, the first assay showed diminished agglutination, suggesting a platelet defect; however, uremic PPP did not inhibit the agglutination of normal platelets. In the same patients, the interaction of platelets with subendothelium was evaluated using Baumgartner's perfusion method. The subendothelial surface covered by platelets was significantly decreased in experiments with uremic whole blood when compared to normal controls. The interaction of platelets with subendothelium was also decreased when perfusions were carried out with platelet-plasma mixtures containing either normal washed platelets and uremic PPP or uremic washed platelets and normal PPP. These results show an impaired platelet adhesion caused both by a platelet and a plasmatic abnormality. Since uremic PPP decreased the adhesion of normal platelets to subendothelium but did not inhibit RIPA, it seems probable that the plasmatic defect could result in a defective binding between vWF and subendothelium. The influence of the red cell count on the platelet adhesion to subendothelium was reconfirmed by comparing perfusions of reconstituted blood with hematocrit values of 20% to 23% and 40% to 45%. In summary, a defective platelet adhesion to subendothelium has been postulated in uremic patients, caused by platelet and plasmatic alterations that are influenced by a low hematocrit.

Adult↗
PubMed1986

Morphometric evaluation of thrombogenesis by microvesicles from human tumor cell lines with thrombin-dependent (U87MG) and adenosine diphosphate-dependent (SKNMC) platelet-activating mechanisms.

The Baumgartner perfusion apparatus has been used for quantitative comparison of the interaction of platelets with subendothelium in the presence of microvesicles derived from SKNMC (human neuroblastoma) cells, which aggregate platelets by an adenosine diphosphate (ADP)-dependent mechanism, and U87MG (human glioblastoma) cells, which function by a thrombin-dependent mechanism. The derived microvesicles from each line were as effective as the intact cells in inducing thrombogenesis on both undigested and alpha-chymotrypsin-digested subendothelium. Thrombus size on digested vessels was greater than on undigested vessels by fivefold for SKNMC cells and microvesicles and by 20-fold for U87MG cells and sevenfold for U87MG microvesicles. The results show that microvesicles from both cell lines initiate interactions between platelets and subendothelium identical to those caused by intact tumor cells. The results also demonstrate that intact tumor cells in the circulation may not be necessary for the thromboembolic complications of malignancy.

Adenosine Diphosphate↗
PubMed1985

Effects of zinc acexamate on gastric mucosal resistance factors.

The effects of zinc acexamate on gastric defensive systems were evaluated in the rat. Gastric ulcers induced by oral administration of three necrotic agents (0.6 N HCl, 25% NaCl, 100% ethanol) were markedly reduced by different pretreatments with zinc acexamate. This cytoprotective effect was not modified by previous treatment with indomethacin (30 mg/kg orally). Zinc acexamate pretreatment also prevents the disruption of the gastric mucosal barrier induced by aspirin (40 mM) and increases mucus production in the gastric glands and tracheal walls. These observations suggest that the antiulcer effects described for zinc salts could be the result, at least partly, of an action increasing gastric mucosal defensive systems.

Aminocaproates↗
PubMed1985

Effects of divalent cations on the interaction of platelets with tumor cells: aggregation and perfusion studies with two homologous human systems.

The effects of chelation of divalent cations in the interaction of platelets and tumor cells has been studied in a homologous human system using human platelet-rich plasma and two tumor cell lines of human origin: SKNMC (neuroblastoma) cells, which cause platelet aggregation by an adenosine diphosphate-dependent mechanism, and U87MG (glioblastoma) cells, which function by a thrombin-dependent mechanism. When added at zero time, citrate 14 mmol/L completely abolished aggregation in heparinized (5 U/ml) platelet-rich plasma by either cell line, but the degree of inhibition was reduced by later addition of the chelating agent. Calcium citrate 8 mmol/L reduced by only 10%, indicating that citrate anion was not responsible for the inhibition. Addition of Ca++ or Mg++ alone or in combination at concentrations up to 1.5 mmol/L did not reverse the inhibition. Addition of higher concentrations of Ca++ (2 mmol/L) caused immediate clotting, whereas concentrations of Mg++ up to 6 mmol/L were without effect. Inhibition could be reversed by washing the platelets free of citrate and resuspending in heparinized platelet-rich plasma. Aggregation by either cell line was inhibited by EDTA and EGTA. In the Baumgartner perfusion apparatus, platelet interaction with subendothelium was increased about 50-fold in the presence of SKNMC cells, but this effect was also abolished after addition of citrate. After addition of U87MG cells to heparinized PRP, there was a 400-fold increase in platelet interaction with subendothelium, and complex thrombi containing red cells, white cells, and fibrin were formed. This stimulation was reduced to control levels by addition of citrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Platelets↗
PubMed1984

Tissue factor in microvesicles shed from U87MG human glioblastoma cells induces coagulation, platelet aggregation, and thrombogenesis.

Microvesicles (diameter ca 200 nm) from the cell-free supernatant of U87MG human glioblastoma cell caused platelet aggregation and coagulation in a manner identical with that previously shown for the intact cells. Both activities were inhibited by dansylarginine -N-(3-ethyl-1,5-pentanediyl) amide (DAPA), confirming the thrombin-dependent nature of both activities. The specific activities per microgram of protein were 2-10 times greater in the microvesicles than in the plasma membrane fraction, suggesting localization in specific membrane domains. Sucrose density centrifugation gave a single protein peak (density 1.14) with congruent procoagulant and platelet aggregating activities. Both activities required the extrinsic pathway, as shown by studies with factor-deficient plasmas, and both were inhibited by heating (60 min/100 degrees C), by reduction and alkylation, and by incubation of the microvesicles with rabbit anti-bovine brain tissue factor antibody. These observations were confirmed using microvesicles from the HL-60 human promyelocytic leukemia cells, which are known to contain tissue factor activity. The results suggest that both procoagulant and proaggregating activities are causally related through the presence of tissue factor in the microvesicles. Studies with the Baumgartner perfusion apparatus showed that U87MG microvesicles increased the size of adherent thrombi nearly tenfold and that these thrombi were associated with nucleated cells from the blood. The increase in adherent thrombi did not occur if perfusion was carried out in the presence of DAPA, confirming the role of thrombin in their formation.

Antibodies↗
PubMedDate not supplied

Experimental basis for the use of red cell transfusion in the management of anemic-thrombocytopenic patients.

The Baumgartner perfusion technique was used as an experimental model to study the combined influence of red cell (RBC) and platelet counts on the interaction of platelets with the subendothelium. At normal hematocrit and a platelet count of 100,000 per microliter, platelet adhesion and platelet aggregate (PAG) formation on subendothelium were statistically decreased. At lower platelet counts (50,000/microliter), there was an even more marked reduction in the formation of PAGs. The critical role of RBCs was demonstrated in experiments at low hematocrit; the formation of PAGs was impaired in perfusions at 20 percent hematocrit at any platelet count tested. Platelet deposition on subendothelium was almost absent at 50,000 platelets per microliter, suggesting a negative synergistic effect for the association of low hematocrit (20%) with a low platelet count. Perfusion experiments carried out with nonanticoagulated blood drawn directly from anemic patients with mild thrombocytopenia (43,000-58,000 platelets/microliter) before and after RBC transfusion were in agreement with previous experiments that indicated that normalization of both platelet count and hematocrit is required to achieve optimum hemostasis. Our data give experimental support for the transfusional management of patients with anemia and thrombocytopenia.

Anemia↗