Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Finally, to confirm that our protocol of ischemic preconditioning is, as previously described [3, 9, 27], dependent on RISK and/or SAFE activation, we tested the effectiveness of both drugs to attenuate protection in hearts from Cx43 mice treated with vehicle (n = 4/group).
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