DEXAMETHASONE INDUCES THE GLUT4 GLUCOSE-TRANSPORTER, AND RESPONSES OF GLUCOSE-TRANSPORT TO NOREPINEPHRINE AND INSULIN IN PRIMARY CULTURES OF BROWN ADIPOCYTES

Glucose uptake into brown adipose tissue is enhanced directly by norepinephrine released from the sympathetic nerves. In the present study, we tried to establish culture conditions for brown adipocytes which are favorable for investigation of this unique glucose transport. Stromal-vascular cells isolated from the interscapular brown adipose tissue of newborn rats differentiated into brown adipocytes expressing the uncoupling protein, when the cells were maintained on collagen-coated dishes. These cells, however, did not show an increase in 2-[H-3] deoxyglucose transport in response to insulin or norepinephrine, nor did they exhibit expression of the GLUT4 glucose transporter, whereas GLUT1 was present, as judged on Western blotting. Pre-treatment of confluent cells with dexamethasone induced a response of glucose transport to either insulin or norepinephrine, and the expression of GLUT4, together with notable accumulation of lipid droplets. The induction of GLUT4 expression by dexamethasone was dose-dependent and potentiated by insulin. These results indicate that treatment of cultured brown adipocytes with dexamethasone makes it feasible to analyze the mechanism underlying the enhancement of glucose transport induced by norepinephrine.