Comments on the atropine resistance of the neurogenic contractile response of the rat detrusor muscle.

The resistance to atropine or scopolamine of the neurogenic contractile response to field stimulation of intramural nerves of the rat detrusor was studied during the early phase of Wallerian degeneration in vitro and in vivo. The neurogenic contractile response to low frequency stimulation of control bladders was completely resistant to atropine or scopolamine in vitro. As a matter of fact the response was enchanced by the drugs. In vivo a transient shortening of the response could be seen. 26-34 h after bilateral extirpation of the pelvic ganglia there was prominent degeneration activity in the bladders in vitro as well as in vivo. Atropine or scopolamine inhibited this activity in vivo but enhanced it in vitro. The neurogenic contractile response to field stimulation of the bladder nerves was blocked in vivo but not in vitro by the antimuscarinic drugs 26-34 h after neurectomy. The results support the concept that the excitatory neurotransmission in the detrusor is essentially cholinergic. An explanation of the difference between the in vivo and the in vitro results based on differences in degree of blockade of pre- and post-junctional muscarinic receptors and diffusion of the antimuscarinics in the tissue is proposed.