these include an exceptionally rapid onset of action , a ceiling effect at 50 % of maximal relaxation , and minimal retardation by concentrations of procaine that block or markedly retard relaxant responses to all other agonists.4 this distinctive pharmacological profile can not be reproduced by addition of exogenous catecholamines , 5-hydroxytryptamine , adenosine triphosphate ( atp ) or adenosine , or by addition of atp or adenosine following pretreatment with indomethacin .
C0001480
atp
C0001443
adenosine