To determine whether the mouse immune system is capable of adapting and mounting a cytoprotective response to repeated cardiac injury, 10 week old male and female mice were injected with isoproterenol (ISO), a drug used to treat bradycardia conditions that causes increased heart rate and contractility, peripheral vasodilation, and relaxation of the bronchial, gastrointestinal, and uterine smooth muscle (4); control mice received vehicle injections. All mice were allowed to recover for 7 days after injection, before receiving a second dose of either ISO or the vehicle solution. Additionally, to determine whether this cytoprotective response was maintained, they reinjected the ISO-pretreated mice with a second ISO injection 21 and 42 days after the initial injection (3).
To assess the severity of cardiac injury, Evans blue dye uptake and serum troponin I levels were monitored. Troponin, as well as other biomolecules, is released when the heart muscle has been damaged, making it an excellent indicator to determine whether ISO-induced cardiac injury is lessened after pre-exposure. Additionally, 2D echocardiographic studies were performed to determine left ventricular (LV) regional wall motion, and LV contractility by Langendorff perfusion (3).