SYNERGISTIC EFFECT OF GLUCOSE AND PROLACTIN ON GLUT2 EXPRESSION IN CULTURED NEONATAL RAT ISLETS

We studied the synergistic effect of glucose and prolactin (PRL) on in sulin secretion and GLUT2 expression in cultured neonatal rat islets. After 7 days in culture, basal insulin secretion (2.3 mM glucose) was similar in control and PRL-treated islets (1.84 +/- 0.06% and 2.08 +/- 0.07% of the islet insulin content, respectively). At 5.6 and 22 mM g lucose, insulin secretion was significantly higher in PRL-treated than in control islets, achieving 1.38 +/- 0.15% and 3.09 +/- 0.21% of the islet insulin content in control and 2.43 +/- 0.16% and 4.31 +/- 0.24 % of the islet insulin content in PRL-treated islets, respectively. Th e expression of the glucose transporter GLUT2 in B-cell membranes was dose-dependently increased by exposure of the islet to increasing gluc ose concentrations. This effect was potentiated in islets cultured for 7 days in the presence of 2 mu g/ml PRL. At 5.6 and 10 mM glucose, th e increase in GLUT2 expression in PRL-treated islets was 75% and 150% higher than that registered in the respective control. The data presen ted here indicate that insulin secretion, induced by different concent rations of glucose, correlates well with the expression of the B-cell- specific glucose transporter GLUT2 in pancreatic islets.