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AIM: To investigate the effects of oxytocin (OT) on isolatedrabbit proximal colon and its mechanism.METHODS: Both longitudinal muscle (LM) and circularmuscle (CM) were suspended in a tissue chamber containing5 mL Krebs solution (37 ℃), bubbled continuously with950 mL@L-1 O2 and 50 mL@L-1 CO2. Isometric spontaneouscontractile responses to oxytocin or other drugs wererecorded in circular and longitudinal muscle strips.RESULTS: OT (0.1 U@L-1) f ailed to elicit significant effectson the contractile activity of proximal colonic smooth musclestrips (P＞0.05). OT (1 to 10 U@L-1) decreased the meancontractile amplitude and the contractile frequency of CMand LM. Hexamethonium (10 μmol@L-1) partly blocked theinhibition of oxytocin (1 U@L-1) on the contractile frenquencyof CM. Nω-nitro-L-arginine-methylester (L-NAME, 1 μmol@L-1),progesterone (32 μmol@L-1) and estrogen (2.6 μmol@L-1) hadno effects on OT-induced responses.CONCLUSION: OT inhibits the motility of proximal colon inrabbits. The action is partly relevant with N receptor, butirrelevant with that of NO, progesterone or estrogen.