PURPOSE This experiment was performed to study the pharmacology of transmitters mediating the response, and the characteristics of the hypogastric nerve (HGN) of female rats, because electrical stimulation of the HGN was found to unexpectedly reduce urethral pressure in female rats. MATERIALS AND METHODS Male and female Wistar rats (weighing about 250 gm.), 10 weeks and 6 months old, respectively, were used under anesthesia. Fluid was infused from the bladder neck into the urethral lumen at a constant rate (0.5 ml./10 minutes), and infusion pressure signals were measured. Bilateral HGNs were electrically stimulated at 5 and 10 Hz for 30 s. RESULTS Electrical stimulation of the HGN reduced urethral infusion pressure in about 80% of the female rats, and the introduction of N(omega)-nitro-L-arginine methylester (L-NAME, 30 mg./rat, i.v.) elevated the urethral pressure response from a reduced state. Prazosin (0.1 mg./kg., i.v.) and hexamethonium (10 mg./kg., i.v.), which inhibited elevation of urethral pressure in male rats, also reversed and inhibited the elevation of urethral pressure in the female rats treated with L-NAME. CONCLUSION The HGN in female rats contained nerve endings that released nitric oxide (NO) and norepinephrine (NE). NO released during HGN stimulation inhibited the release of (NE) and reduced urethral infusion pressure in female rats. Nerves with synapses in the pelvic ganglia released NE in both male and female rats, but nerves that released NO did not have synapses in the ganglia. Only NE was released from the HGN nerve endings in male rats.