Purinergic and non-purinergic innervation in the cerebral arteries of the dog.

1 Possible involvement of sympathetic purinergic transmission in the neurogenic response of dog cerebral and basilar arteries was examined with the use of alpha, beta-methylene ATP and adrenoceptor, cholinoceptor blocking agents. 2 In the isolated basilar arteries, electrical transmural stimulation produced a transient contraction which was frequently followed by a relaxation. This transient contraction was abolished after desensitization of P2-purinoceptors with alpha, beta-methylene ATP or by treatment with guanethidine. The relaxant response induced by electrical stimulation was also attenuated but was not abolished by such treatments. Prazosin, propranolol and atropine had no significant effect on the responses to electrical stimulation. Yohimbine augmented both the contractile and relaxant responses. 3 In most preparations of the dog middle cerebral arteries, electrical transmural stimulation produced only a relaxation. This relaxation was little affected after treatment with alpha, beta-methylene ATP or guanethidine, and was not inhibited by the other adrenoceptor and cholinoceptor blocking agents. 4 Tetrodotoxin abolished the responses induced by electrical transmural stimulation in both the basilar and middle cerebral arteries. 5 Exogenous ATP (10(-6) and 10(-5)M) produced a transient contraction followed by a relaxation of the basilar arteries and a relaxation of the middle cerebral arteries. Desensitization of P2-purinoceptors abolished the contractile response to ATP without affecting the amplitude of relaxation. 6. In the basilar and middle cerebral arteries preincubated with [3H]-noradrenaline, electrical transmural stimulation evoked an increase in 3H-efflux and this response was markedly inhibited by guanethidine or tetrodotoxin but was not affected by alpha, beta-methylene ATP. Yohimbine increased the evoked 3H-efflux. 7. These findings indicate that cerebral arteries of the dog are innervated by sympathetic purinergic nerves and non-sympathetic nerves which liberate unknown vasodilator substance(s), and that the former nerves are more dominant in the neurogenic response to electrical stimulation of the dog basilar artery than in the middle cerebral artery.