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

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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. 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. Stimulation evoked a median pressure decrease of 13 cm H(2)O (range, 0-27; P < 0.05; n = 10) in the anal canal, a pressure increase of 6 cm H(2)O (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. 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.