The role of the hypogastric nerve in bladder and urethral activity of the dog.

1. Stimulation of the hypogastric nerves increased the pressure in both the bladder and urethra of anaesthetized female dogs. 2. The responses were reduced but not abolished by the alpha-adrenoceptor antagonist phentolamine, whereas the beta-adrenoceptor antagonist propranolol was either without effect or increased the responses. Atropine, methysergide and hexamethonium were without effect. 3. Close arterial injection of phenylephrine increased and isoprenaline decreased urethral pressure but both produced only a slight increase in bladder pressure. 4. Hypogastric nerve stimulation reduced subsequent responses of the bladder and urethra to pelvic nerve stimulation or to close arterial injection of acetylcholine. Isoprenaline, but not phenylephrine, also had an inhibitory action and 5-hydroxytryptamine enhanced the responses. 5. In the presence of hexamethonium the inhibitory action of isoprenaline still occurred but 5-hydroxytryptamine no longer enhanced the responses, suggesting that 5-hydroxytryptamine acts on the ganglia and isoprenaline acts, at least partially, on smooth muscle. 6. These results suggest that the role of the hypogastric nerves may be to modify inputs to the bladder and urethra as well as to act directly on the smooth muscle.