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Platelets of different densities are probably produced from megakaryocytes of different ploidy. Thromboxane B2 (TxB2) production was studied in density dependent subfractions of the total platelet population.  Platelets were isolated by a new technique using velocity sedimentation into a polyvinylpyrrolidone-coated colloidal silica (Percoll) gradient followed by equilibrium centrifugation through a continuous linear Percoll gradient. Fractionation of the second gradient yielded density-dependent platelet subpopulations which were functionally competent and showed minimal leukocyte and plasma protein contamination. By pooling fractions and adding buffer, suspensions containing similar concentrations of platelets representative of low, intermediate and high density subpopulations were prepared, each containing 20–30% of the total population. Aliquots of each suspension were stirred in an aggregometer and thrombin or arachidonic acid (AA) were added to induce aggregation. After three minutes the reaction was arrested by addition of ice cold ethanol and TxB2 measured by radioimmunoassay.  When 0.5 mM AA (final concentration) was the aggregating agent, for every 108 platelet the least dense subpopulations produced 10.2 ng TxB2, and the most dense subpopulations 22.4 ng TxB2,(means of four experiments), whilst the intermediate density subpopulations gave intermediate values. However, thrombin at 0.5 or 1.0 units/ml produced similar amounts of TxB2 in all subpopulations. In a second series of experiments, AA-stimulated serotonin secretion in density dependent platelet subpopulations correlated closely with platelet number.  These observations imply functional differences between platelet subpopulations.

Production Of Thromboxane B2 By Platelets Is Related To Their Density