PRE‐AND POSTJUNCTIONAL EFFECTS OF NEUROPEPTIDE Y ON THE RABBIT ISOLATED EAR ARTERY

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Abstract
1. In the isolated perfused and superfused rabbit ear artery, neuropeptide Y (NPY, 0.3-100 nmol/l) had no direct vasoconstrictor action, but produced a concentration-dependent and reversible enhancement of vasoconstrictor responses to both sympathetic nerve stimulation and exogenous noradrenaline. 2. In arteries in which the noradrenergic transmitter stores had been radiolabelled with [3H]-noradrenaline, 100 nmol/l NPY inhibited the stimulation-induced (1 Hz for 30 s) release of radioactivity, but the lower concentrations tested (10 and 30 nmol/l) had no effect. NPY (10, 30 and 100 nmol/l) had no effect on the resting release of radioactivity. 3. Thus, NPY in low concentrations enhances vasoconstrictor responses in the rabbit ear artery by a postjunctional action; prejunctionally, NPY inhibits stimulation-induced transmitter release when it is present in high concentrations.

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