Zucchella M

Effect of mental stress on platelet function in normal subjects and in patients with coronary artery disease

We studied the effect of emotional stress (mental arithmetic for 10 min) in 10 postinfarction patients and in 10 age-matched apparently healthy subjects as controls. Blood samples for platelet function studies and for the determination of epinephrine levels in serum were taken in basal conditions, at the end of mental stress and after 30 min of recovery. Patients were studied twice, in washout of medications and after oral administration of dipyridamole, 200 mg twice a day for 6 consecutive days. Mental stress induced in patients significant increments in different hemodynamic parameters (heart rate, systolic blood pressure and diastolic blood pressure) and in serum epinephrine levels. Concomitantly, the test produced a significant increase in platelet aggregation (induced by 3 microM ADP or 1 microgram/ml collagen), the formation of circulating platelet aggregates and an increase in plasma thromboxane B2 levels. Hemodynamic parameters and platelet function tests returned to baseline values after 30 min. Similar activation of hemodynamic parameters, similar increase in epinephrine levels and lower increase in platelet function by emotional stress were observed in control subjects. Treatment of patients with dipyridamole had no effect on stress-induced increase in hemodynamic parameters and epinephrine levels, but decreased stress-related platelet activation. These data can contribute to a better understanding of the complex relationships between psychosocial factors, the hemostatic system and vascular disease.

Tumor Cells Induce Platelet Aggregation and Intraplatelet Calcium Ion Movements

We studied platelet aggregation and changes in cytosolic Ca(++) concentrations induced by cells isolated from 5 human tumor tissues (2 hepatocellular carcinomas, 1 colon carcinoma, 1 gastric carcinoma and 1 pancreatic carcinoma). A Platelet Ionized Calcium Aggregometer was used and washed, aequorin loaded platelets were employed. Tumor cells were able to induce aggregation and an increase in cytoplasmic Ca(++) concentrations in the presence of trace amounts (10 µl) of PPP, while no aggregating response was found after addition of fibrinogen alone to washed platelets. The platelet aggregating activity of tumor cells was maintained in the presence of factor VII deficient plasma or of factor VIII deficient plasma, and disappeared completely when factor X deficient plasma was added to washed platelets. Furthermore, tumor cell induced platelet aggregation and Ca (++) movements were inhibited by hirudin (100 U/ml), a specific thrombin inhibitor, while concanavalin A (100 µg/ml), a tissue factor inhibitor, had no effect. Finally, preincubation of neoplastic cells with HgCl(2) (0.5 mM), a cysteine protease inhibitor, markedly decreased their ability to induce aggregation and Ca(++) movements; on the contrary, incubation of cells with soybean trypsin inhibitor (10 µg/ml), a serine protease inhibitor, or with concanavalin A (100 µg/ml) had no effect. These data suggest that cells isolated from human tumor tissues activate platelet function through the generation of thrombin, due to a cysteine protease which directly activates factor X.

Platelet Activation by Cells Isolated from Human Tumor Tissues: Effect of Cyclooxygenase Blockade

We have studied in a homologous system the effect on different platelet functions of cells isolated from 26 human tumor tissues (11 breast carcinomas, 11 colon carcinomas, 2 pancreatic carcinomas, 1 gastric carcinoma and 1 esophageal carcinoma). Tumor cells (10(5)/ml) significantly increased platelet adhesion to glass beads; they were also found to possess a potent platelet aggregating activity and aggregation was accompanied by significant release of ATP and platelet derived growth factor (PDGF) and by production of TXB(2). Preincubation of platelets with a low concentration (1 µM) of indobufen, a cyclooxygenase inhibitor, significantly reduced tumor cell induced TXB(2) production and ATP release, while the other platelet functions were not modified. Higher concentrations of the drug (10 or 100 µM) were also able to inhibit tumor cell-induced platelet aggregation and PDGF release, while platelet adhesion to glass beads was unchanged even at these doses. Finally, preincubation of neoplastic cells with indobufen (400µM) had no effect on their ability to induce platelet aggregation, TXB(2) production and ATP release. These data demonstrate that cyclooxygenase blockade in platelets has different effects on several platelet functions activated by the tumor cells that were investigated.