Use of reserpine and 6-hydroxydopamine supports evidence for purinergic cotransmission in the rabbit ear artery.

The relative roles of noradrenaline and ATP in the contractile response of the rabbit central ear artery following electrical stimulation of the sympathetic perivascular nerves were investigated after treatment with reserpine and 6-hydroxydopamine. In control tissues, electrical stimulation produced frequency-dependent contractile responses that were reduced, but not abolished, following incubation with the alpha 1-adrenoceptor antagonist prazosin (10(-6) M). Desensitisation of the P2X-purinoceptor by alpha,beta-methylene ATP (10(-6) M) abolished the prazosin-resistant component of the response. Tissues removed from reserpine-pretreated animals responded to electrical stimulation with small, frequency-dependent contractions, despite a dramatically reduced tissue noradrenaline content. Prazosin (10(-6) M) had no significant effect on these contractile responses. Following P2X-purinoceptor desensitisation, the neurogenic responses were virtually abolished. Tissues that had been incubated with 6-hydroxydopamine failed to respond to electrical stimulation at the parameters used in the control and reserpine-pretreated vessels. This study provides supporting evidence for the involvement of noradrenaline and ATP in sympathetic cotransmission in the rabbit central ear artery.