Neuropeptide Y potentiates purinergic as well as adrenergic responses of the rabbit ear artery.

The localisation of neuropeptide Y in the rabbit central ear artery and its pharmacological action on this preparation were investigated. Immunohistochemical studies demonstrated the presence of neuropeptide Y-like immunoreactivity in the perivascular nerves supplying the rabbit ear artery. Forty-eight hours after treatment with reserpine (5 mg/kg i.p. 48 h and 3 mg/kg i.p. 24 h prior to the experiment) catecholamine fluorescence in the rabbit central ear artery was abolished and the neuropeptide Y-like immunoreactivity was substantially reduced, suggesting that noradrenaline and neuropeptide Y were colocalised in sympathetic nerves. Contractile responses to exogenous noradrenaline (1 microM) and alpha,beta-methylene ATP (1 microM) were both significantly potentiated following incubation with neuropeptide Y (0.3 microM); the degree of potentiation being similar for both agonists. Electrical field stimulation of the rabbit central ear artery (16 and 64 Hz) produced frequency-dependent contractile responses which were abolished by tetrodotoxin (1 microM) and which were significantly potentiated in the presence of neuropeptide Y (0.3 microM). The responses to stimulation at 16 Hz were enhanced to a greater extent than the responses at 64 Hz. After blocking the noradrenergic component of the neurogenic response with prazosin (1 microM), the residual purinergic component, at both 16 and 64 Hz, was significantly enhanced in the presence of neuropeptide Y. However, following desensitisation of the P2-purinoceptor with alpha,beta-methylene ATP, neuropeptide Y had no significant effect on the residual noradrenergic component.(ABSTRACT TRUNCATED AT 250 WORDS)