Summary
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 <0.01) and TxB2 production (p <0.02) were significantly greater in patients than in Controls. No statistically
significant differences were found with other agonists. ii) PPACK PRP: No statistically significant difference was found between diabetic platelets and
Controls, iii) PPACK plus citrate PRP: The results were not different from those obtained with citrate alone. Therefore,
our results show that diabetic platelets produce normal amounts of TxB2 in vitro when the [Ca2+]o is physiological.
