Effect of neuropeptide Y on adrenergic and non‐adrenergic, non‐cholinergic responses in the rat anococcygeus muscle

The effects of neuropeptide Y (NPY) were examined on adrenergic and non‐adrenergic, non‐cholinergic (NANC) neurotransmission in the rat anococcygeus muscle. NPY (0.1–0.3 μm) greatly potentiated the contractile responses induced by field stimulation. Prazosin (0.1 μm) completely abolished the stimulation‐induced responses either in the absence or presence of NPY. NPY (0.1–0.3 μm) enhanced only the contractile responses to low doses of noradrenaline (NA, 0.003–0.01 μm). Responses to tyramine were unaffected by the same concentrations of NPY. In superfused anococcygeus, previously loaded with [3H]‐NA, NPY (0.1–0.3 μm) failed to modify the basal, as well as the stimulation‐evoked, release of tritium at 2 and 4 Hz. NANC relaxations induced by electrical stimulation were significantly reduced, in a concentration‐related manner, by 0.1–0.3 μm NPY. 6 l‐NG‐nitro‐arginine (l‐NOARG, 30 μm) enhanced the stimulation (0.25–1 Hz)‐induced motor responses. In the presence of l‐NOARG (30 μm), NPY (0.1 μm) did not modify the motor responses induced by field stimulation (0.25–0.5 Hz). l‐Arginine did not reverse the NPY‐induced potentiation of stimulation‐induced motor responses. 7 The relaxations of anococcygeus muscle induced by sodium nitroprusside (SNP, 0.01–0.3 μm) were diminished by NPY (0.1–0.3 μm). 8 Our study suggests that NPY, at concentrations devoid of contractile effect, potentiates the motor responses of rat anococcygeus muscle as a consequence, at least in part, of the inhibition of NANC relaxing responses by a different mechanism from l‐NOARG. 1992 British Pharmacological Society