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 duct (PD) and bile duct (BD) components of the sphincter of Oddi (SO) and suggested distinct proximal and distal functional segments. This study was designed to determine if proximal and distal segments of the BD component of the SO (BD-SO) and PD component of the SO (PD-SO) responded equally to (1) activation of SO-duodenal neural pathways, and (2) exogenous cholecystokinin octapeptide (CCK-8). Methods: Intact SO-duodenum preparations from Australian brush-tailed possums (n = 6) were mounted in organ baths. SO activity was recorded from the proximal and distal segments of BD-SO and PD-SO ± electrical 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 evoked 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-SO strips were not different. Conclusions: The SO is composed of BD and PD components each of which contains proximal and distal segments that can respond independently to appropriate stimuli. Copyright (C) 2000 S. Karger AG, Basel.