Increased sensitivity of rabbit ear artery to noradrenaline following perivascular nerve stimulation may be a response to neuropeptide Y released as cotransmitter.

Neuropeptide Y (NPY 10(-10)-10(-7) mol/l) had little or no effect on the perfusion pressure of rabbit isolated ear arteries but potentiated the brief contractile responses to injections of noradrenaline, histamine or brief periods of electrical stimulation (2-20 Hz for 5 s). This effect was slowly reversible. Similar potentiation was seen following long periods of electrical stimulation (2-40 Hz for 1-5 min) which produced well sustained increases in perfusion pressure. Following even longer periods of electrical stimulation (10-30 min) during which the perfusion pressure was not maintained, responses to noradrenaline and histamine were potentiated but the responses to electrical stimulation for 5 s were greatly reduced. The increase in sensitivity following prolonged electrical stimulation may be due to NPY released as a cotransmitter.