In vitro activity: CGS 21680 HCl is an adenosine A2 receptor agonist with IC50 of 22 nM, exhibits 140-fold over A1 receptor. In an isolated perfused working rat heart model, CGS 21680C effectively increases coronary flow with an ED25 value of 1.8 NM. CGS 21680 binds adenosine A2 receptor with high affinity (Kd = 15.5 nM) and limited capacity (apparent Bmax = 375 fmol/mg of protein) to a single dass of recognition sites. In hippocampal slices, CGS 21680 apis weak agonist on pre- and postsynaptic measures of electrophysiologicaJ activity (putative Al receptor mediated events) and is ineffective at stimulating the formation of cAMP (a putative A2 mediated response). In striatal slices, CGS 21680 potently stimulates the formation of cAMP with an EC50 of 110 nM but is ineffective at inhibiting electrically stimulated dopamine release. CGS 21680A is the hydrochloride salt, while CGS 21680C is the sodium salt of CGS 21680.

Cell Assay: In rat striatal membranes, CGS 21680 potently prevents ligands from binding to A2 adenosine receptors with IC50 value of 22nM. In the binding assay, CGS 21680 shows no effect to other putative neurotransmitter/neuromodulator sites in brain membranes such as adrenergic, dopamine and serotonin. In the rat heart model, CGS 21680 is effective in increasing coronary flow with EC25 value of 2nM.