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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 µMADP or 1 µg/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.

Human 253J urinary carcinoma cells and the F1 (low-metastatic) and F10 (high-metastatic) variants of the B16 murine melanoma cell line have been shown to activate heparinized human platelets by an adenosine diphosphate (ADP)-dependent mechanism based on inhibition by creatine phosphate/creatine phosphokinase and the identification of aggregating concentrations (1 to 2 μmol/L)of ADP in cell-free culture supernatants by high-performance liquid chromatography. Aggregation did not occur in citrated samples, and hirudin was without effect. Studies were carried out to determine whether extracellular ADP arose from nonspecific cell damage during cell isolation and manipulation or was a specific process under control of the tumor cells themselves. Tumor cell damage during harvesting was shown not to be a factor because the amounts of ADP produced by the three cell lines (a)were inversely related to the appearance of lactic dehydrogenase in the culture supernatants and (b)were similar when measured in confluent monolayers, either in tumor cells after detach- ment and resuspension or after crossover studies involving culture in, alternatively. Hanks’ balanced salt solution and minimal essential medium. Metabolic control of ADP production was indicated by the fact that (a) it was not dependent on cell number, which suggests feedback inhibition; (b) it was reduced 60% when tumor cells were treated with p-chloromercuribenzene sulfonate; and (c) it was completely abolished in those treated with iodoacetic acid, which might be expected to increase nonspecific leakage. These studies indicate that ADP production by these three lines does not arise due to leakage induced by nonspecific membrane damage during cell harvesting and manipulation but is a discrete process under metabolic control of the tumor cells. Moreover, in B16 murine melanoma cells the ability to produce ADP and to support platelet aggregation appears to be unrelated to metastatic potential insofar as identical results were obtained with the F1 and F10 variants.