Platelets in myeloproliferative disorders. II. Serotonin uptake and storage: correlations with mepacrine labelled dense bodies and with platelet density.

Platelet serotonin (5-HT) uptake and storage in the presence and absence of reserpine were studied simultaneously with platelet volume, density and dense bodies content (mepacrine test) in 33 patients affected with myeloproliferative disorders (MD): 12 chronic myeloid leukaemia (CML), 9 polycythaemia vera (PV), 6 essential thrombocythaemia (ET) and 9 agnogenic myeloid metaplasia (AMM). Observations were (1) a dramatic reduction of the initial velocity (Vi) uptake and of the granular pool of 5-HT; (2) a slight reduction of the number of platelet dense bodies which, in many cases, were less fluorescent than in controls; (3) an increase of the percentage of light platelets while platelet volume was mostly normal; (4) a significant correlation between the number of dense bodies per platelet volume unit and either the percentage of light platelets (r = 0.76) or the size of the granular pool of 5-HT (r = 0.81). These results support evidence of a quantitative and qualitative acquired storage pool syndrome in these patients. In addition, the Vi studies demonstrate that the serotonin uptake across the plasmatic membrane is abnormal.