<unk>  used as a second messenger can be the result of de novo purine biosynthesis via<unk>  monophosphate (AMP), though it is possible other pathways exist. When<unk>  enters the circulation, it is broken down by<unk>  deaminase, which is present in red blood cells and the vessel wall. Dipyridamole, an inhibitor of<unk>  nucleoside transporter, allows<unk>  to accumulate in the blood stream. This causes an increase in coronary vasodilatation.<unk>  deaminase deficiency is a known cause of immunodeficiency.
Adenosine
Dobutamine
Adrenaline
Nortilidine
Norepinephrine 
Norepinephrine
Iofetamine 
Epinephrine 