Stimulation of insulin release by repaglinide and glibenclamide involves both common and distinct processes.
Fuhlendorff J., Rorsman P., Kofod H., Brand CL., Rolin B., MacKay P., Shymko R., Carr RD.
The action of repaglinide, a novel insulin secretagogue, was compared with the sulfonylurea glibenclamide with regard to the hypoglycemic action in vivo, binding to betaTC-3 cells, insulin secretion from perifused mouse islets, and capacity to stimulate exocytosis by direct interaction with the secretory machinery in single voltage-clamped mouse beta-cells. Two binding sites were identified: a high-affinity repaglinide (KD = 3.6 nmol/l) site having lower affinity for glibenclamide (14.4 nmol/l) and one high-affinity glibenclamide (25 nmol/l) site having lower affinity for repaglinide (550 nmol/l). In contrast to glibenclamide, repaglinide (in concentrations as high as 5 micromol/l) lacked the ability to enhance exocytosis in voltage-clamped beta-cells. Repaglinide was more potent than glibenclamide in stimulating insulin release from perifused mouse islets (EC50 29 vs. 80 nmol/l). The greater potency of repaglinide in vitro was paralleled by similar actions in vivo. The ED50 values for the hypoglycemic action were determined to be 10.4 and 15.6 microg/kg after intravenous and oral administration, respectively. The corresponding values for glibenclamide were 70.3 microg/kg (intravenous) and 203.2 microg/kg (oral). Further, repaglinide (1 mg/kg p.o.) was effective (P < 0.001) as an insulin-releasing agent in a rat model (low-dose streptozotocin) of type 2 diabetes. These observations suggest that the insulinotropic actions of repaglinide and glibenclamide in vitro and in vivo are secondary to their binding to the high-affinity repaglinide site and that the insulinotropic action of repaglinide involves both distinct and common cellular mechanisms.