SummaryPlatelet MAO activity and the aggregation response to epinephrine, ADP, and collagen were measured in normal subjects. There was a direct correlation between the amount of platelet MAO activity and the per cent aggregation induced by 1 and 2 μM epinephrine. There were lesser correlations between platelet MAO and ADP or collagen-induced aggregation. These findings suggest that platelet MAO may play a role in determining the response of human platelets to epinephrine.

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SummaryRat platelets were incubated in either balanced salt solution (BSS) buffered with imidazole, in plasma or in a third medium composed of BSS and plasma in a volume to volume mixture. Platelets incubated in imidazole BSS showed a more rapid decline in platelet count, earlier appearance of platelet clumping, greater consumption of glucose, greater production of lactic acid and CO2, and more rapid turnover of 32Pi. Platelets incubated in plasma showed less pronounced changes in these parameters while platelets incubated in imidazole BSS: plasma showed effects that were intermediate in degree to those observed with imidazole BSS or plasma alone. The possibility that these effects are related to the depletion of platelet ATP by imidazole is discussed.