2-[(Cyclohexylmethylene)hydrazino]adenosine (MRE-0470) is an A2A-adenosine receptor agonist that is a potent and selective coronary vasodilator.As part of a preclin. program, the pharmacol. and toxicol. of MRE-0470 have been studied in the rat.In isolated vas deferens, MRE-0470 activated A2B receptors (EC50 = 6.3 nM) and at higher concentrations activated A2B receptors (EC50 = 13 μM).In atrial tissues, MRE-0470 produced neg. inotropic and chronotropic actions through activation of A1 receptors (EC50 ∼ 9 μM).MRE-0470 produced no pos. inotropic or chronotropic actions in atrial or ventricular tissues.In anesthetized, reflex-blocked rats, MRE-0470 produced a decrease in hindquarter perfusion pressure (A2: ED50 = 0.31 μg) and a decrease in heart rate (A1: ED50 = 620 μg).In conscious rats, MRE-0470 (0.04-117 μ/kg bolus or 0.03-150 μ/kg/min infusion) produced dose-dependent hypotension and reflex tachycardia.MRE-0470 was rapidly eliminated from rat plasma with an elimination half-life of 10 min.In toxicol. studies, once per day 10-min i.v. infusions of 3, 30, or 150 μg/kg/min MRE-0470 for 14 consecutive days resulted in no deaths and no changes in blood chem., but resulted in decreased motor activity and dose-related cardiomyopathy.Cardiomyopathy did not occur following single doses of MRE-0470.The incidence of this lesion is related to the duration of the repeated reflex tachycardia.These studies show that MRE-0470 is a potent and selective A2A receptor agonist in the rat.The observed toxicol. of MRE-0470 is consistent with the exaggerated pharmacol. due to high-dose drug administration.