The inhibitory response of the rabbit anococcygeus muscle.

1. Strips of rabbit anococcygeus muscle were submaximally contracted by the addition of phenylephrine to the bath fluid. 2. Acetylcholine, dimethylphenylpiperazinium and electrical field stimulation caused relaxation. Relaxation induced by acetylcholine and field stimulation was blocked by tetrodotoxin but only the acetylcholine-induced response was inhibited by lignocaine, tetraethylammonium and hexamethonium. The responses to both acetylcholine and field stimulation were resistant to atropine, practolol, and sotalol. 3. Relatively high concentrations of ATP caused relaxation. 4. Histological investigation did not show any cells resembling autonomic ganglion cells. 5. It is suggested that both acetylcholine and field stimulation release an inhibitory transmitter from nerve endings and that the release by acetylcholine is mediated through nicotinic receptor stimulation.