Summary.Platelet adhesiveness tests using glass bead columns were performed in 54 normal subjects. Native blood was forced through the columns by a syringe pump at a flow rate of 6 ml/min, and effluent blood was collected in four aliquots of 2 ml each. The first two aliquots demonstrated a progressive increase in per cent platelet adhesiveness with maximum adhesiveness achieved in the second aliquot. The third and fourth aliquots showed decreased adhesiveness with a progressive broadening of the range of normal. In 11 of the 54 normal subjects the fourth aliquot of effluent blood contained more platelets than the original whole blood and indicated that platelets previously retained by the column were being returned to the effluent. The per cent platelet adhesiveness in the first aliquot did not vary with the platelet count. However, the absolute number of platelets retained by the column increased as the platelet count increased. Moreover, the number of platelets retained from a given aliquot was directly proportional to the number of platelets retained from previous aliquots. The return of platelets to the effluent in the fourth aliquot was associated with the smallest number of platelets retained from the first three aliquots. Adenosine inhibited the retention of platelets by glass bead columns. Retention of platelets by glass bead columns appears to be determined by platelet adhesion to glass surfaces, platelet to platelet aggregation due to released ADP, and spontaneous platelet disaggregation which becomes evident when the initial number of retained platelets provides an insufficient amount of ADP to sustain aggregation.
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