Parasympathetic denervation abolishes acetylcholine-induced relaxation in the rat iris dilator.

An anomalous change in response to exogenously applied acetylcholine (ACh) was found in the rat iris dilator muscle after surgical parasympathetic denervation. The relaxation induced by nerve stimulation in the normal dilator muscles disappeared after the denervation. ACh elicited relaxation and contraction at low (less than 3 X 10(-6) M) and higher doses, respectively, in the normal muscles. The relaxing response to ACh was almost abolished after the denervation, while the maximum contractile response to ACh was not affected significantly.