CENTRAL NEUROPEPTIDE-Y ENHANCES BILE SECRETION THROUGH VAGAL AND MUSCARINIC BUT NOT NITRIC-OXIDE PATHWAYS IN RATS

Neuropeptide Y (NPY) acts in the central nervous system to regulate ga strointestinal functions in rats and dogs. The effects of intracistern al injection of NPY on bile secretion and biliary components were inve stigated in urethane-anesthetized rats with bile duct cannula. Intraci sternal NPY (0.02-0.12 nmol) dose-dependently increased bile secretion by 9.2-19.5%. The secretory response occurred within the first 20-40 min and lasted for the 120-min observation period. Intravenous injecti on of NPY (0.12 nmol) did not modify bile secretion under identical co nditions. Biliary bile acid, phospholipid, and cholesterol secretion w ere not modified by intracisternal injection of NPY (0.12 nmol), where as bicarbonate was increased by 19.0 +/- 1.7% from 40 to 120 min after NPY injection. Cervical cord transection at the C6 level, acute bilat eral adrenalectomy (-120 min), or injection of NG-nitro-L-arginine met hyl ester (10 mg/kg, IV, -15 min), an inhibitor of nitric oxide biosyn thesis, did not alter intracisternal NPY (0.12 nmol)-induced stimulati on of bile secretion. Atropine (2.0 mg/kg, IP, -30 min) and bilateral cervical vagotomy (-120 min) completely abolished the stimulatory effe ct of intracisternal NPY (0.12 nmol) on bile secretion. These findings indicate that NPY acts in the brain to stimulate bicarbonate-dependen t bile secretion through vagal and muscarinic pathways and suggest tha t peptides in the central nervous system may be involved in the vagal regulation of bile secretion.