INFLUENCE OF PLASMA-PROTEINS ON HUMAN PLATELET METABOLISM

This study, which focuses on certain essential parameters of platelet metabolic activity-oxygen consumption, lactate production and cyclic AMP (cAMP) content-indicates that platelet metabolism is significantly influenced by the plasma protein environment. Thus, platelet oxygen consumption in platelet-rich plasma was 88 per cent higher than oxygen consumption of washed platelets. Oxygen consumption of washed platelets could be restored to values comparable to those obtained for platelet-rich plasma by the addition to the washed platelet suspensions of either autologous plasma, purified albumin or purified IgG immunoglobulin. In contrast, the addition of fibrinogen and purified IgA myeloma protein from a patient with bleeding diathesis and platelet dysfunction had no effect on oxygen consumption of washed platelets. Platelet lactate production was identical in platelet-rich plasma and washed platelet suspensions. The addition to washed platelets of autologous plasma, albumin or gamma globulin did not affect lactate production; however, when either fibrinogen or the purified IgA myeloma protein were added to suspensions of washed platelets, lactate production increased significantly over the values observed in either platelet-rich plasma or washed platelets. cAMP levels were considerably lower in washed platelets than in platelets in platelet-rich plasma. When gamma globulin and albumin were added to suspensions of washed platelets, cAMP levels further decreased; and this reduction in cAMP content was progressive with time. In contrast, the addition of fibrinogen to suspensions of washed platelets caused no change in platelet cAMP content. Thus, different plasma proteins affected different parameters of platelet metabolism in different ways. Although an understanding of the mechanisms whereby plasma proteins affect platelet membrane function and metabolic activity is lacking, our experiments underscore the need for a concise definition of the plasma protein environment in the assessment of human platelet metabolism. © 1979.