THE IN-VITRO PRODUCTION OF THROMBOXANE-B(2) BY PLATELETS OF DIABETIC-PATIENTS IS NORMAL AT PHYSIOLOGICAL CONCENTRATIONS OF IONIZED CALCIUM

Platelets of patients with diabetes and no evidence of macroangiopathy produce normal amounts of thromboxane (Tx) B2 in vivo, whereas they u sually show increased production in vitro. Since in vitro studies have been usually performed in citrated PRP, we tested the hypothesis that the discrepancy between in vivo and in vitro studies is due to the lo w concentration of plasma ionized calcium ([Ca2+]o) that is present in citrated PRP. In fact, low [Ca2+]o artifactually potentiates the plat elet TxB2 production in vitro. Forty patients with diabetes mellitus a nd 37 matched controls were studied. Blood was anticoagulated with cit rate, the thrombin inhibitor D-phenylalanyl-1-prolyl-1-chloromethylket one (PPACK) or both anticoagulants. Platelet aggregation, release of C -14-serotonin and TxB2 production were induced in platelet rich plasma (PRP) by several agonists. The following results were obtained: i) Ci trated PRP: Arachidonic acid induced aggregation (p<0.01) and TxB2 pro duction (p<0.02) were significantly greater in patients than in contro ls. No statistically significant differences were found with other ago nists. ii) PPACK PRP: No statistically significant difference was foun d between diabetic platelets and controls. iii) PPACK plus citrate PRP : The results were not different from those obtained with citrate alon e. Therefore, our results show that diabetic platelets produce normal amounts of TxB2 in vitro when the [Ca2+]o is physiological.