Action of pirenzepine on the human urinary bladder in vitro

The novel compound pirenzepine was tested for its antimuscarinic effect on the human urinary bladder "in vitro." Its behavior towards the contractions induced by acetylcholine or bethanechol and towards electrically induced contractions was identical to that of atropine. However, its potency was 100 to 300 times lower than that of atropine. Results obtained with ganglion blocking agents, tetrodotoxin and cooled preparations of urinary bladder seem to indicate the virtually total absence of ganglionic cells. On the other hand they point out the fundamental role of post-synaptic muscarinic M2 receptors as the most important component of the cholinergic system in the bladder. Of course the existence of other transmitters released at the cholinergic nerve endings after electrical field stimulation cannot be excluded on the basis of our experiments.