Chem. Pharm. Bull. 55(3) 372—375 (2007)

lar AMPc in respiratory tissue were initially attributed to other mechanisms, it is currently accepted that the changes are due to the competitive antagonism of these bases with receptors of the neurotransmitter adenosine. Adenosine exerts a depressor effect with important repercussions in the functioning of the cardiovascular, renal, immune and central nervous systems. In recent years the search for series of adenosine analogues that show agonistic or antagonistic properties against adenosine receptors has intensified. These receptors belong to a superfamily of rhodopsin-like, G protein-coupled receptors (GPCRs), of which four subtypes are known and designated as A1, A2A, A2B and A3. The receptors modulate the activity of adenylate cyclase either by stimulation (A2A and A2B) or inhibition (A1 and A3) of the activity. 3)