Abstract

BACKGROUND
Glucocorticoids play important roles in the regulation of glucose homeostasis. It is well known that glucocorticoids reduce hepatic and peripheral tissue sensitivity to insulin, but the roles of glucocorticoids on insulin secretion and synthesis in pancreatic beta cells are still unclear. We have investigated the direct effects of glucocorticoids on insulin secretion and synthesis in rat insulinoma (INS-1) cells. METHODS: Insulin content and 11.2 mM glucose-stimulated insulin secretion (GSIS) were measured in INS-1 cells after culture with or without 1 micrometer dexamethasone (DEX). Preproinsulin mRNA levels were analyzed by real-time RT-PCR and normalized to the internal control. Effect of RU486 on DEX-induced inhibition of GSIS and preproinsulin mRNA synthesis was evaluated. RESULTS: Insulin content of INS-1 cells cultured in RPMI containing 11.2 mM glucose in the presence of DEX was not different from that of control cells. After 1-h preincubation in 2.8 mM glucose, basal insulin secretion from cells treated with DEX did not differ from that of controls, but GSIS was significantly reduced in the cells treated with DEX in comparison to control cells. The expression of preproinsulin mRNA relative to beta-actin mRNA was also lower in the cells treated with DEX. Glucocorticoid receptor antagonist improved DEX-induced inhibition of GSIS and preproinsulin mRNA synthesis. CONCLUSION: DEX inhibited GSIS and preproinsulin mRNA synthesis in INS-1 cells. Glucocorticoid receptor antagonist ameliorated the reduced GSIS and preproinsulin mRNA synthesis induced by DEX.

• Keywords: Beta cell;Dexamethasone;Glucocorticoids;Glucocorticoid receptor antagonists;Insulin Secretion;Insulin Synthesis;RU486;