Cardiotonic Agents/pharmacology; Glucagon-Like Peptide 1/pharmacology; Immunoconjugates/pharmacology; Myocardial Infarction/prevention & control; Myocardial Reperfusion Injury/prevention & control; Peptide Fragments/pharmacology; Serum Albumin/immunology; Single-Domain Antibodies/pharmacology; Animals; Cardiotonic Agents/administration & dosage; Cardiotonic Agents/blood; Cardiotonic Agents/pharmacokinetics; Disease Models, Animal; Exenatide; Glucagon-Like Peptide 1/administration & dosage; Glucagon-Like Peptide 1/blood; Glucagon-Like Peptide 1/pharmacokinetics; Glucagon-Like Peptide-1 Receptor; Immunoconjugates/administration & dosage; Immunoconjugates/blood; Immunoconjugates/pharmacokinetics; Injections, Subcutaneous; Male; Myocardial Contraction/drug effects; Myocardial Infarction/metabolism; Myocardial Infarction/pathology; Myocardial Infarction/physiopathology; Myocardial Reperfusion Injury/metabolism; Myocardial Reperfusion Injury/pathology; Myocardial Reperfusion Injury/physiopathology; Myocardium/metabolism; Myocardium/pathology; Peptide Fragments/administration & dosage; Peptide Fragments/blood; Peptide Fragments/pharmacokinetics; Peptides/pharmacology; Rats; Rats, Sprague-Dawley; Receptors, Glucagon/agonists; Receptors, Glucagon/genetics; Single-Domain Antibodies/administration & dosage; Single-Domain Antibodies/blood; Venoms/pharmacology; Ventricular Function, Left/drug effects