MYOCARDIAL GLUT-4 GLUCOSE-TRANSPORTER PROTEIN-LEVELS OF RATS DECLINE WITH ADVANCING AGE

Age-related changes in glucose metabolism and glucose transporter protein content have been described in adipose tissue and skeletal muscle, two tissues that express the GLUT-4 isoform of the glucose transporter protein. I studied the effect of age on the levels of GLUT-4 protein in a third insulin-sensitive tissue: the heart. Cardiac ventricles were sampled from male Fischer 344/Brown Norway F1 hybrid (F344/BNNia) rats. The total protein concentration of the left ventricle did not change with age. GLUT-4 levels per mg of protein declined by 15% between 3.5 and 13 months of age, and by another 12% during adulthood (between 13 and 25 months of age); when expressed per g wet weight, the decreases were 13% and 17%, respectively. Linear regression analysis revealed a significant (p < .0001) relationship (r2 = .634) between age and myocardial GLUT-4. These results demonstrate that the GLUT-4 levels in the left ventricle decrease in an age-related fashion and suggest that the capacity for glucose transport might also be reduced.