Effect of Tetrodotoxin on the Bladder Response to Pelvic Nerve Stimulation and Intra-arterial 1, 1-Dimethyl-4-phenylpiperazinium and Acetylcholine in the Dog

In dogs anesthetized with pentobarbital, responses of the urinary bladder with the hypogastric nerves intact and the pelvic nerves cut acutely were recorded as changes in intravesical pressure. In order to administer drugs selectively to the bladder, the vesical vascular bed was perfused with arterial blood via the caudal vesical arteries at a constant rate, and drug solutions were injected into the perfusion circuit at a point close to the bladder. Stimulation with a short train of electric pulses of the distal end of the cut pelvic nerve on either side and administration of 1, 1-dimethyl-4-phenylpiperazinium (DMPP) elicited a prompt monophasic contraction of the bladder. The responses to the nerve stimulation and to DMPP were readily abolished by tetrodotoxin. However, contractions in response to 10 and 30μg of acetylcholine were unchanged with that dose of tetrodotoxin which was sufficient to abolish the response to supramaximal stimulation of the pelvic nerve. From these results it was concluded that the contraction elicited by DMPP was mediated predominantly through excitation of the parasympathetic postganglionic neurons in the bladder wall, while that produced by acetylcholine was exclusively due to excitation of the smooth muscle.