Inhibitory Effects of Oxytocin on Jejunal Migrating Myoelectric Complex Activity in Fasted Rats: Role of Oxytocin and...

The migrating myoelectric complex (MMC) is the electrical basis of fasting small intestinal motility. Although oxytocin (OT) regulates gastrointestinal functions through oxytocin receptors (OTRs), its effect on jejunal MMC activity during fasting remains unclear. This study investigated the effects of OT on jejunal MMC activity in fasted rats and evaluated the involvement of OTRs, glucagon-like peptide-1 receptors (GLP-1Rs), and nitric oxide (NO) pathways. Bipolar electrodes were implanted at three jejunal sites in adult male Sprague Dawley rats for MMC recordings. After recovery and 18 h fasting, OT was administered intraperitoneally (4-32 µg/kg) following one hour of basal recording. To assess mechanisms, rats were pretreated with the OTR antagonist atosiban (2 mg/kg), the GLP-1R antagonist exendin (9-39) (200 µg/kg), or the nitric oxide synthase inhibitor NG-nitro-L-arginine (L-NNA; 5 mg/kg) before OT (16 µg/kg). Oxytocin dose-dependently reduced spike frequency and MMC cycle number (p < 0.05-0.001 vs. vehicle). Atosiban completely reversed these effects (p < 0.001 vs. OT), while exendin (9-39) partially attenuated them (p < 0.01-0.001 vs. OT). L-NNA showed no significant effect. These findings indicate that OT inhibits jejunal MMC activity via OTR-dependent mechanisms with partial involvement of GLP-1R signaling but not NO pathways.