RESUMO
Hemorrhagic tendency is frequent in uremic patients and is often associated with prolonged bleeding time and decreased platelet functions in vitro. Similarly, in multiple myeloma, platelet functions are affected, mainly by the inhibitory effect of paraprotein. We have studied patients with renal insufficiency and multiple myeloma to investigate the possible relation of oxidative stress to platelet functions, adhesion and aggregation activity. We observed diminished platelet aggregation response to collagen, ADP and thrombin receptor-activating peptide (TRAP) in both groups of patients as compared with normals. The adhesion of platelets to fibrin dimers was also diminished. Malondialdehyde concentration as a criterion of oxidative stress was significantly enhanced in both groups of patients together with increased concentrations of vitamins A and E. It seems to be possible that oxidative stress contributes to modification of adhesion proteins and fibrinogen and, thus, augments the observed inhibitory influence of vitamin E on platelet aggregation and adhesion. In conclusion, the concerted influence of both malondialdehyde and vitamins A and E can contribute to diminished platelet functions in renal insufficiency and augment the inhibitory influence of paraprotein on platelet functions in multiple myeloma.
