[Altered circadian rhythm of platelet aggregation in patients on longterm hemodialysis]

Chronic uremia is associated with a bleeding tendency, and paradoxically with propensity for thrombotic complications. Several physiological systems are subject to circadian rhythm, including among others hemostasis, platelet aggregability and fibrinolysis. Alterations in these rhythms were suggested to be involved in the pathogenesis of sudden cardiac and cardiovascular complications of diabetes mellitus. As cardiovascular events are the most frequent cause of death in dialyzed patients, we studied circadian rhythm of platelet function in chronically hemodialyzed patients in relation to blood and plasma serotonin. We investigated 16 patients (mean age 49.7 +/- 12.2 years, 10 females, 6 males) who had been maintained on chronic hemodialysis. Control group consisted of 8 age matched healthy volunteers. Blood was collected after 15 min. rest at 8:00, 11:00, 17:30, and 23:00 from antecubital veins. Platelet aggregation was measured according to the method of Born. Following concentrations of aggregating agents were used: ADP 5 microM; collagen, 2 micrograms/ml; arachidonic acid 0.75 microM, serotonin 1 microM; and ristocetin 1.5 micrograms/ml. Serotonin was measured in whole blood and plasma by HPLC method. In PRP from healthy subjects aggregatory responses to ADP and arachidonic acid were significantly higher at 17:30 than at 8:00. In uremic patients aggregatory response to ADP and ristocetin was more intensive at 11:30 and 23:00 in comparison to 8:00. Whole blood 5-HT did not change during the day, while plasma 5-HT concentration increased significantly in uremics at 11:30 in comparison to initial value. In conclusion, our study demonstrates that in chronically dialyzed patients circadian changes in platelet aggregation are different from normal persons.