PLATELET IMIPRAMINE BINDING IS INCREASED IN ESSENTIAL THROMBOCYTHEMIA

A decrease in platelet serotonin content is well recognized in myeloproliferative disorders, although the basis for this is unclear. The relationship between decreased platelet serotonin and the number of serotonin transport channels in the platelet membrane was explored indirectly by measuring the number of the closely associated imipramine binding sites. Imipramine binding parameters were determined in 12 patients suffering from either essential thrombocythaemia or polycythaemia rubra vera and in 10 healthy controls. The maximal number of imipramine binding sites (B(max)) was increased in both patient groups, significantly so in those suffering from essential thrombocythaemia. This increase contrasts with a decrease in binding in other conditions known to be associated with decreased platelet serotonin. This study thus demonstrates a discrepancy in terms of reduced platelet serotonin content and increased imipramine binding on platelets from patients suffering from essential thrombocythaemia. It is suggested that further investigation of the imipramine binding site in these disorders, in parallel with measures of platelet serotonin content and uptake, is warranted.