Proximal and distal segments of the possum sphincter of Oddi respond differently to neural and cholecystokinin octapeptide stimulation in vitro

Background/Aims: Previous studies have demonstrated separate pancreatic duc t (PD) and bile duct (BD) components of the sphincter of Oddi (SO) and sugg ested distinct proximal and distal functional segments. This study was desi gned to determine if proximal and distal segments of the BD component of th e SO (BD-SO) and PD component of the SO (PD-SO) responded equally to (1) ac tivation of SO-duodenal neural pathways, and (2) exogenous cholecystokinin octapeptide (CCK-8). Methods: Intact SO-duodenum preparations from Australi an brush-tailed possums (n = 6) were mounted in organ baths. SO activity wa s recorded from the proximal and distal segments of BD-SO and PD-SO +/- ele ctrical activation of duodenal nerves at two separate sites. Full thickness muscle strips from the proximal and distal segments of the BD-SO and PD-SO were prepared (n = 8), mounted in organ baths, and exposed to CCK-8 (10(-9 )-10(-6) M), +/- tetrodotoxin. Results: Activation of duodenal nerves evoke d different responses in some segments of the BD-SO and PD-SO, depending on the site of duodenal electrical stimulation. CCK-8 induced a concentration -dependent, tetrodotoxin-insensitive decrease in the contraction amplitude of SO muscle strips from the proximal but not the distal SO. BD-SO and PD-S O strips were not different. Conclusions: The SO is composed of BD and PD c omponents each of which contains proximal and distal segments that can resp ond independently to appropriate stimuli. Copyright (C) 2000 S. Karger AG, Basel.