Effect of dopamine on the cyclic adenosine monophosphate generating system in the rabbit internal carotid and middle cerebral artery.
The effect of in vitro addition of dopamine on the 3'-5'-cyclic adenosine monophosphate (cAMP) generating system of rabbit internal carotid and middle cerebral artery was studied. Dopamine increased cAMP levels in a dose-dependent manner in both arteries. The DA1-receptor antagonist SCH 23390 decreased the dopamine-elicited cAMP increase. On the contrary, the DA2-receptor antagonist L-sulpiride caused an increase in dopamine-dependent cAMP levels. The simultaneous addition of SCH 23390 and of L-sulpiride abolished any effect of dopamine on cAMP content. The DA2-receptor agonists bromocriptine and co-dergocrine decreased cAMP levels. The above findings indicate the existence in the rabbit internal carotid and middle cerebral artery of 2 types of dopamine receptors mediating respectively, the increase (DA1-effect) and the decrease (DA2-effect) of cAMP levels.