EFFECT OF TRIIODOTHYRONINE ON GLUCOSE-TRANSPORT IN RAT ADIPOCYTES

The in vine effect of thyroid hormones on glucose transport in insulin -stimulated muscle cells or adipocytes is still unclear. The objective of the present study was to assess the direct effect of 3,3',5-triiod othyronine (T3) on glucose transport and on the translocation of insul in-regulatable glucose transporter (GLUT4) in insulin-stimulated rat a dipocytes. This evaluation was performed using an in vitro assay to av oid the well-known systemic effects of this hormone ( e.g.: hyperinsul inemia). Adipocytes were isolated from epididymal adipose tissue of Sp rague-Dawley rats. Glucose transport assay and immunoblot analysis of GLUT4 were carried out in insulin-stimulated and unstimulated adipocyt es after treating with or without T3. The results were as follows; 1) T3 inhibited the glucose transport in insulin-stimulated and unstimula ted adipocytes in a dose-dependent manner. 2) T3 decreased the maximal response level (Vmax) but did not alter the sensitivity (Km) of gluco se transport to insulin. 3) T3 did not affect the translocation of GLU T4 from the intracellular pool to the plasma membrane. We concluded th at T3 inhibits the glucose transport in insulin-stimulated adipocytes in a post-receptor level without affecting the translocation of GLUT4 from the intracellular pool to the plasma membrane. This suggests that T3 acts by decreasing the intrinsic activity or the accessibility of GLUT4 in the plasma membrane.