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Measurement of platelet aggregation in ovine blood using a new impedance aggregometer.

BACKGROUND
Whole blood platelet aggregometry (impedance) is an important method to investigate platelet function disorders. Examination of hemostatic function in sheep is important with respect to their role as an animal model of human disease.


OBJECTIVE
The aim of this study was to evaluate and optimize selected methodological aspects (anticoagulant, agonist concentration) of impedance aggregometry in ovine blood using the new Multiplate 5.0 analyzer.


METHODS
Blood samples were collected in hirudin anticoagulant from 40 clinically healthy sheep. Samples from selected sheep were collected in citrate, with or without the addition of calcium chloride. The agonists adenosine diphosphate (ADP), collagen, ristocetin, arachidonic acid, and thrombin receptor-activating peptide (TRAP) were added in several concentrations to induce aggregation.


RESULTS
Based on maximum aggregation values and internal precision, no significant difference was found between ADP concentrations of 3-10 micromol/L and collagen concentrations of 3-5 microg/mL (P>.05). The lowest interindividual variation of approximately 3-4-fold was seen with 4 and 5 micromol/L ADP and 4 and 5 microg/mL collagen. Ristocetin, arachidonic acid, and TRAP did not induce significant aggregation at any concentration. Aggregation results were significantly lower when measured in citrate- vs hirudin-anticoagulated blood, regardless of the presence of calcium chloride.


CONCLUSIONS
Our results indicate that the multiplate impedance aggregometer is suitable for the measurement of platelet aggregation in sheep using optimal agonist concentrations of 4-5 micromol/L ADP and 4-5 microg/mL collagen. Hirudin-anticoagulated blood is the preferred sample material.