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

Abstract

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 mmol/L and collagen concentrations of 3-5 mg/mL (P 4.05). The lowest interindividual variation of approximately 3-4-fold was seen with 4 and 5 mmol/L ADP and 4 and 5 mg/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 mmol/L ADP and 4-5 mg/mL collagen. Hirudin-anticoagulated blood is the preferred sample material.

Assessment of platelet function in healthy sedated cats using three whole blood platelet function tests

“…26 The lower aggregation responses using citrated blood, in comparison to hirudinized blood, is consistent with findings in sheep, dogs, and humans. 3,13,23,27,32 Citrate was used in our study to facilitate blood collection for, and comparison between, the 3 platelet function tests.…”

“…Use of this device in animals has been evaluated in dogs, sheep, and in cats. 3,12,26 In the feline study, blood from 10 healthy cats was combined with eptifibatide or abciximab in vitro, and reduced platelet function was demonstrated for the former drug but not the latter. 26 The PF analyzer is a point-of-care platelet function test that has been evaluated more extensively in animals.…”

“…11,28 Platelet function has been variably evaluated with these tests in dogs, pigs, sheep, and horses. 3,20,29 Studies have also used these tests to evaluate platelet function in cats; however, the literature is limited. 17,22,26 584994V DIXXX10.1177/1040638715584994Whole blood platelet function testing in healthy catsHo et al…”

Validation of acute traumatic coagulopathy in an ovine model of trauma and haemorrhage

“…Sheep also demonstrate significant differences in platelet response to induced aggregation testing. Ovine platelets have proven unresponsive to TRAP-6, arachidonic acid and risocetin agonists and show less than 50% of the human response to ADP and collagen agonists (59,62) (table 5), which may make it difficult to accurately assess the contribution of platelet dysfunction to coagulopathy in this model. (54) ATC develops within 30 minutes of injury in human patients (22,37,89).…”

“…Animal models provide an alternative option as they facilitate the controlled and systematic evaluation of isolated insults in vivo, which may enhance mechanistic understanding and identify novel therapeutic targets. However animals are genetically distinct from humans, and demonstrate differences in coagulation assay parameters, coagulation factor concentrations and platelet function that may alter the susceptibility to ATC (58)(59)(60)(61)(62). For an animal model to be clinically relevant there needs to be more similarities than differences between the human coagulation system and that of the chosen animal species.…”