Neuropeptide Y: a candidate neurotransmitter for biliary motility

Neuropeptide Y (NPY) is a recently discovered polypeptide found in neurons throughout the gastrointestinal tract and in especially high concentrations in the biliary tree. This study was designed to test the functional significance of these high concentrations in the biliary tree by determining the effect of intravenous NPY on sphincter of Oddi and gallbladder motility. In adult male prairie dogs a side-hole, pressure-monitored perfusion catheter was placed through a choledochotomy into the duodenum and positioned in the sphincter of Oddi. A perfusion catheter was also placed in the gallbladder fundus. Sphincter of Oddi and gallbladder pressures were recorded before and during intravenous infusions of NPY at doses of 10, 100, and 500 ng/kg/min. Each dose was administered to seven separate animals. No effects were seen at the 10 or 100 ng/kg/min doses. NPY at the 500 ng/kg/min dose significantly increased sphincter of Oddi phasic wave frequency, amplitude, and motility index (MI = F X A). In addition, gallbladder pressure was significantly increased after 20 min of intravenous infusion of NPY at the 500 ng/kg/min dose. No significant changes in blood pressure were noted. These data suggest that in the prairie dog, systemic intravenous infusion of NPY significantly increases sphincter of Oddi phasic wave activity and gallbladder pressure. These findings are similar to those observed with intravenous cholecystokinin but opposite of those seen with peptide YY in this species. We hypothesize that neuropeptide Y may be an important neurotransmitter or neuromodulator regulating bile flow.