Interaction between secretin and a cholecystokinin-like peptide on pancreatic protein secretion and synthesis in the rat.

The effects of secretin and a cholecystokinin-like peptide alone and in combination on pancreatic protein secretion and synthesis were examined in anesthetized rats. L-[75Se]selenomethionine was given as an i.v. shot (5 microCi) followed by a continuous infusion (1 microCi/h). Pancreatic juice was collected basally for 1 h and then during a 4-h i.v. infusion of 0.5, 2.5, and 12.5 micrograms/kg/h of Thr28Nle31CCK25-33 (CCK-LP) alone or combined with 5 micrograms/kg/h of secretin, as well as during an infusion of secretin alone. The protein-bound radioactivity in pancreatic juice was taken to indicate secretion of newly synthesized proteins. The free and protein-bound radioactivity remaining in the gland after 2 h of stimulation was also investigated. Secretin alone slightly increased both protein secretion and secretion of newly synthesized proteins. Considerably greater effects were found with CCK-LP. The two lowest doses behaved similarly, whereas the volume and protein responses to 12.5 micrograms/kg/h were significantly lower and associated with large amounts of free radioactivity in pancreatic juice, suggesting leakage and cell damage. The addition of secretin transiently potentiated protein discharge and secretion of newly synthesized proteins and permanently increased the amount of protein-bound radioactivity per milligram of protein in response to all doses of CCK-LP. Secretin markedly increased volume and reduced the amount of free radioactivity in pancreatic juice with the largest dose of CCK-LP. The peptides were not found to influence amino acid uptake or incorporation of radioactivity into tissue proteins. This study demonstrates an interaction between the effects of secretin and those of CCK-LP on pancreatic protein secretion and synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)