Resistance of the aged myocardium to exercise-induced chronic changes in glucose transport related protein content

The effects of acute exercise on myocardial content of glut-1 and glut-4 tr ansporters, insulin and IGF-1 receptors were assessed in control and chroni cally exercised 24-month-old C57Bl/6 mice. Myocardial glut-1, glut-4, insul in receptor (Ins R) and insulin like growth factor-1 receptor (IGF-1 R) pro tein levels were unaffected by 36 weeks of chronic exercise. However, myoca rdial protein content of glut-1, but not glut-4, was increased 12 h followi ng an acute exercise bout in control (46%) and chronically exercised (83%) aged animals. This increased glut-1 response following acute exercise occur red despite the finding that the chronic exercise failed to increase cardia c or skeletal muscle oxidative capacity as indicated by no change in citrat e synthase activity. Myocardial IGF-1 R content was unaffected by acute exe rcise whereas Ins R protein content was decreased 12 h following the acute exercise bout in the chronically exercised (-52%) and control (-28%) animal s. The effect of acute exercise on the protein content of glut-1 and Ins R was 80 and 84% greater respectively, in the chronically exercised animals. This suggests that the amplitude of the expression of these two proteins ma y be increased by chronic exercise, thus constituting a form of adaptation. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.