Reactivity of isolated canine cerebral arteries to adenine nucleotides and adenosine.

ATP (10(-8)-10(-5) M) produced phasic contraction in the canine basilar artery and relaxation in the middle cerebral artery. At high concentrations (10(-5) and 10(-4) M) a contractile response in the middle cerebral artery occasionally preceded relaxation. ADP, AMP, c-AMP and adenosine (10(-8)-10(-4) M) caused relaxation in all preparations except that ADP produced contraction in both cerebral arteries at high concentrations (10(-5) and 10(-4) M). These effects were observed in the absence or presence of active tension induced by 5-HT. The potency of ADP in producing vasodilation in the middle cerebral artery was greater than in the basilar artery, whereas that of the other agents was reversed. c-AMP showed the lowest potency among the agents tested on both arteries. The relaxing responses, but not contractile responses, to agents used were partially inhibited by theophylline. Phentolamine, propranolol, atropine, tetrodotoxin, ouabain or quinidine had little effect on both the contractile and relaxing responses. From these results, it is concluded that the canine cerebral arteries respond well to adenine nucleotides and adenosine and that the relaxing response is in part caused through theophylline-sensitive receptors.