Pancreatic beta-cell function and islet-cell proliferation: Effect of hyperinsulinaemia

Pancreatic beta-cell function was studied in adult female rats, in which endogenous insulin demand was fully met by SC infusion of human insulin (4.8 IU/24 h) for 6 days, resulting in hyperinsulinaemia and severe hypoglycaemia. The amount of pancreatic endocrine tissue declined by 40%, (pro)insulin mRNA, as determined by in situ hybridisation by 95%, and the amount of stored insulin by 90%. Islet-cell proliferation as determined by 24 h of BrdU infusion declined by 60%. Basal glucose levels normalized within 2 days after the insulin treatment was ended, whereas about 1 week was needed to restore the amount of pancreatic insulin, glucose-induced insulin release, and glucose tolerance to normal values. The amount of endocrine tissue recovered within 48 h and mRNA abundance within 96 h after discontinuation of the insulin infusion, whereas at that time islet-cell proliferation still showed a sixfold increase, before returning to control levels after 1 week. These results show that after a period of suppression of beta-cell function, recovery of insulin synthetic capacity does not immediately result in normalization of insulin stores and insulin release. Under these conditions, episodes of hyperglycaemia may occur, which may act as a stimulus for islet-cell proliferation.