Effects of gastrointestinal hormones and carbamylcholine on cAMP accumulation in isolated pancreatic duct fragments from the rat.

A modification of a technique to isolate kidney tubule fragments and pancreatic acinar cells has been used to prepare a suspension of pancreatic duct fragments from rats with pancreatic lipomatosis due to pretreatment with penicillamine and a copper-free diet. This suspension is 90-95% pure almost without any acinar cell contamination. The accumulation of 3',5'-cyclic adenosine monophosphate (cAMP) in response to various gastrointestinal hormones, hormone-like substances and theophylline was studied in these isolated pancreatic duct fragments. In the absence of theophylline, secretin increased the level of cAMP in a dose-dependent manner with a maximum at 10(-6) M. With supramaximal doses the concentration of cAMP decreased. During maximal stimulation with secretin the level of cAMP was dependent on the concentration of fragments in the incubation mixture. Vasoactive intestinal peptide (VIP) also increased the formation of cAMP. However, VIP was 10 times less effective than secretin on a molar basis. The addition of various concentrations of VIP to a submaximal dose of secretin did not alter cAMP levels as compared to the levels observed with the same concentration of secretin alone. Theophylline (5 x 10(-3) and 10(-2) M) stimulated cAMP accumulation and 5 x 10(-3) M theophylline potentiated the response to secretin and VIP. Pancreozymin (20 and 99% pure), glucagon bovine pancreatic polypeptide and carbamylcholine did not effect the level of cAMP when given alone or in combination with secretin. These data lend support to the hypothesis that cAMP is the intracellular mediator of the action of secretin and VIP on the pancreatic duct cells.