Pelvic Nerve Stimulation Evokes Nitric Oxide Mediated Distal Rectal Relaxation in Pigs

Purpose  Pelvic nerve stimulation evokes a complex motility response in the pig rectum with a proximal decrease and a distal increase in cross-sectional area. This study investigated whether the distal increase in the cross-sectional area is because of smooth muscle relaxation mediated by nitric oxide. Methods  The pelvic nerves were stimulated with cuff electrodes in ten chloralose-anesthetized minipigs. Pressure, volume, and cross-sectional areas at five positions in the rectum were obtained during stimulation to examine the effect of N^G-nitro-L-arginine (an inhibitor of nitric oxide synthase) injection. Results  Stimulation evoked a median pressure decrease of 13 cm H₂O (range, 0–27; P < 0.05; n = 10) in the anal canal, a pressure increase of 6 cm H₂O (range,-15 to 30; P < 0.05; n = 10) in the rectum and a decrease of 39 mL (range, 30–63; P < 0.05; n = 6) in rectal volume. Rectal cross-sectional areas decreased 33 percent (range, 5–56; P < 0.02; n = 7) in the proximal part and increased 32 percent (range, 9–67; P < 0.02; n = 8) in the distal part. N^G-nitro-L-arginine eliminated the increase in the distal rectal cross-sectional area (n = 5) and the decrease in anal canal pressure (n = 9) in all tested animals. Conclusion  Pelvic nerve stimulation evokes distal rectal relaxation in pigs, sensitive to N^G-nitro-L-arginine, which suggests that this smooth muscle response is mediated by nitric oxide. This work was supported by grants from the Institute of Experimental Clinical Research, Aarhus University Hospital, Aarhus, Denmark Reprints are not available.