An Underlying Mechanism for the Altered Hypoglycemic Effects of Nateglinide in Rats with Acute Peripheral Inflammation

The hypoglycemic effects of nateglinide (NTG) were examined in rats with acute peripheral inflammation (API) induced by carrageenan treatment, and the mechanisms accounting for altered hypoglycemic effects were investigated. NTG was administered through the femoral vein in control and API rats, and its plasma concentration profile was characterized. The time courses of the changes in plasma glucose and insulin levels were also examined. Although the plasma concentration profile of NTG in API rats was marginally distinguishable from that in control rats, the hypoglycemic effect of NTG was more persistent in API rats than in control rats. In addition, NTG elevated the plasma level of insulin more intensely in API rats than in control rats. Then, the islets of Langerhans were procured by perfusing the pancreas with collagenase solution in control and API rats, and the pancreatic mRNA expression of preproinsulin (Ins1), as well as that of sulfonylurea receptor ABCC8 (Abcc8), were examined. As a result, the expression of preproinsulin and ABCC8 mRNA increased in API rats. These findings suggest that the hypoglycemic effect of NTG was potentiated in API rats due to increased insulin secretion in the pancreas, which was caused by enhanced preproinsulin synthesis and expression of the sulfonylurea receptor.