The In Vitro Production of Thromboxane B2 by Platelets of Diabetic Patients Is Normal at Physiological Concentrations of lonized Calcium

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Abstract
Platelets of patients with diabetes and no evidence of macroangiopathy produce normal amounts of thromboxane (Tx) B2 in vivo, whereas they usually 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 low concentration of plasma ionized calcium ([Ca 2+ ]o) that is present in citrated PRP. In fact, low [Ca 2+ ]o artifactually potentiates the platelet TxB2 production in vitro. Forty patients with diabetes mellitus and 37 matched Controls were studied. Blood was anticoagulated with citrate, the thrombin inhibitor D-phenylalanyl-l-prolyl-l-chloromethylketone (PPACK) or both anticoagulants. Platelet aggregation, release of 14C-serotonin and TxB2 production were induced in platelet rieh plasma (PRP) by several agonists. The following results were obtained: i) Citrated PRP: Arachidonic acid induced aggregation (p 2 production (p 2 in vitro when the [Ca2+]o is physiological.