Inhibition of rat pancreatic exocrine secretion by neuropeptide Y: studies in vivo and in vitro.

Neuropeptide Y (NPY) is a unique 36 amino acid peptide with strong sequence homology to pancreatic polypeptide and peptide YY. In the rat pancreas, NPY-positive fibers have been demonstrated in close association with exocrine structures, suggesting a regulatory role for the peptide. In conscious rats with pancreatic ductal cannulas, amylase output stimulated by cholecystokinin octapeptide (CCK-8: 0.2 microgram kg - 1 h -1) was dose-dependently inhibited by intravenous NPY infusion (20, 40, and 80 micrograms kg-1 h-1). Inhibitory effects were rapid in onset but reversed with cessation of NPY infusion. With continuous NPY infusion (40 microgram kg-1 h-1), prolonged inhibition of amylase output by the vagal stimulant 2-deoxyglucose (100 mg kg-1) was observed (greater than 50% inhibition in each of none consecutive 10-min periods). In contrast, NPY infusion in doses of 20, 40, or 80 micrograms kg-1 h-1 produced no alteration in immunoreactive somatostatin levels. In vitro, NPY incubation (10(-13)-10(-8) M) produced no change in basal amylase release from dispersed, purified acinar cells. In addition, co-incubation of NPY (10(-8)-10(-6) M) with CCK-8 (10(-13)-10(-8) M) produced no inhibition of CCK-stimulated amylase release from dispersed acini. In contrast, NPY (10(-6) M) produced significant inhibition of amylase release from pancreatic lobules that had been stimulated by 75 mM potassium (135 +/- 11% versus 177 +/- 18% of basal level) or by 25 microM veratridine (196 +/- 19% versus 398 +/- 152%).(ABSTRACT TRUNCATED AT 250 WORDS)