DECREASED GLUCOSE-TRANSPORTER (GLUT-4) CONTENT IN INSULIN-SENSITIVE TISSUES OF OBESE AUROTHIOGLUCOSE-TREATED AND MONOSODIUM GLUTAMATE-TREATED MICE

We assessed the content of two isoforms of glucose transporter (GLUT 1 and GLUT 4) in insulin-sensitive tissues of hypothalamic obese mice treated with either aurothioglucose (AuTG) or monosodium glutamate (MSG). The animals were studied when obesity had reached a plateau, and they were clearly insulin resistant. We studied different membrane fractions from white adipose tissue (WAT), such as fat-free extract (FFE), plasma membrane (PM) and microsomal (M) fractions. GLUT 4 expressed per protein content displayed a decrease of 50% (p<0.001) in all membrane fractions of AuTG- and MSG-treated mice. The PM GLUT 4 content, expressed per cell surface area, was reduced by 70% (p<0.01) in obese mice, and the total FFE GLUT 4, expressed per total fat mass, was 5 times reduced in obese mice. Compared to control mice, obese mice showed a reduction (p<0.01) of the GLUT 4 amount by 30% (AuTG) and by 40% (MSG) in total membrane fraction (TM) of skeletal and cardiac muscles. Similarly, a reduction of die GLUT 4 amount by 40% (AuTG) and by 45% (MSG) in FFE of brown adipose tissue was observed. The GLUT 1 content in FFE of WAT and TM of skeletal muscle showed no significant difference among the different animal groups. These results confirm a decreased expression of GLUT 4, but not of GLUT 1, in insulin-sensitive tissues, which may contribute to the impaired glucose utilization in these obese animals.