Lobe-specific responses of cultured islet cells of canine pancreas to carbamylcholine, glucose, and pancreatic polypeptide

Using cultured islet cells from both splenic lobe (SL) and uncinate process (UP) of the dog pancreas, we have measured responses of insulin, glucagon, and pancreatic polypeptide (PP) to glucose, carbamylcholine (carbachol), and exogenous PP. The results show that both insulin and PP cells of the two developmentally distinct lobes of the pancreas respond differentially to secretagogues. The results suggest that PP may play a role in regulation of islet cell secretion. Secretion of insulin by SL and UP cultures in response to 28 mM glucose in a 2h incubation was significantly greater, 2.9- (p less than 0.01) and 1.5-fold (p less than 0.01), respectively, than secretion by respective control cultures at 2.8 mM glucose. The difference in degree of stimulation between SL and UP was also significant (p less than 0.02). At 2.8 mM glucose, SL and UP cultures secreted 10% and 8.8%, respectively, of immunoreactive insulin (IRI) contents of the cultured cells (NS). Dose-response curves showed that for up to 8.5 mM glucose the degree of stimulation of SL was no greater than UP, but the UP response had nearly plateaued; whereas, the SL response continued to increase, such that SL was greater than UP at 16.7 mM glucose (p less than 0.01). Secretion of PP by SL and UP cultures in response to 5 microM carbachol and 2.8 mM glucose in a 2-h incubation was significantly greater, 2.2- (p less than 0.002) and 3.9-fold (p less than 0.002), respectively, than secretion by respective control cultures without carbachol. The difference in degree of stimulation between SL and UP was also significant (p less than 0.01).